Note: Descriptions are shown in the official language in which they were submitted.
t
SYSTEM AND METHOD OF DAMPING VIBRATIONS OF TOWER STRUCTURES
FIELD OF THE INVENTION
[0001] The present invention is a system and a method of damping
vibration of a tower
structure at one or more natural frequencies thereof.
BACKGROUND OF THE INVENTION
[0002] Relatively lightweight structures such as poles and towers
(e.g., communication
towers used for radio or cell phone communications purposes or lighting masts)
may be subject
to cross-wind vibrations. These vibrations have a detrimental impact on the
fatigue life of the
structures. As is well known in the art, vibration of the tower structure at
one or more natural
frequencies thereof are of particular concern.
[0003] The tower structures have relatively small masses, and may
be, for example,
approximately 50 feet to 2,000 feet high. Tower structures that are either
circular, semi-circular
or triangular in cross-section are considered susceptible to these types of
vibrations.
[0004] In general, the communications or other devices supported by
the tower structure
are located at the top of the tower, or near the top of the tower. Recently,
it has become common
for the tower structure to include a shroud or housing formed and positioned
to enclose the
communications or other devices, e.g., at the top of the tower. However, it
has been found that
the shrouded towers tend to be somewhat more susceptible to vibrations, and
consequently metal
fatigue. Accordingly, the problem of addressing metal fatigue in poles and
towers appears to be
generally becoming a more pressing issue.
[0005] Tower structures of the prior art are identified by
reference character 10 in Figs.
1A-2. As can be seen in Fig. 1A, the tower structure 10 includes a shroud 12
at, or proximal to,
a top end 14 of the tower structure.
[0006] Another prior art tower structure 10 is illustrated in Fig.
1B. In Fig. 1B, a base 16
of the tower structure 10 is also shown. The tower structure has a length "L"
extending between
the base 16 and the top end 14 (Fig. 1B).
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[0007] The prior art tower structure 10 that is illustrated in Fig. 2 is
three-sided, rather than
circular in cross-section. The tower structure 10 of Fig. 2 includes a shroud
12 at, or proximal to,
the top end 14 of the tower structure. (As will be described, embodiments of
the invention are
illustrated in the balance of the attached drawings.)
[0008] Referring to Fig. 1 B, it can be seen that the top end 14 of the
tower structure 10 is
free, and the base 16 is secured in the ground. Accordingly, when the tower
structure 10 vibrates,
the greatest amplitudes thereof typically are at or near the top end. As is
well known in the art,
the metal fatigue tends to be most pronounced at or near the base 16, because
the portion of the
tower structure at or in the ground is fixed, and unable to move, although the
balance of the tower
structure is able to move.
[0009] In general, the metal fatigue is most serious at or near the base.
If not addressed,
the tower ultimately will fail.
SUMMARY OF THE INVENTION
[0010] There is a need for a system and a method for damping vibration of
a tower
structure at one or more natural frequencies thereof that overcomes or
mitigates one or more of
the disadvantages or defects of the prior art. Such disadvantages or defects
are not necessarily
included in those listed above.
[0011] In its broad aspect, the invention provides a system for damping
vibration of a
tower structure at one or more natural frequencies of the tower structure. The
system includes
one or more tank assemblies with one or more tanks having a floor and one or
more walls, and a
fluid positioned in the tank to a preselected depth above the floor, the fluid
in the tank occupying
a tank volume. The wall is formed to define one or more average travelling
distances of a wave
through the fluid initiated by the vibration of the tower structure at the
natural frequency. The
system also includes one or more inserts located on the floor in the tank for
damping movement
of the fluid. The insert has a top edge thereof at a preselected height above
the floor. The
preselected depth of the fluid is greater than the preselected height of the
insert, to enable the
wave to move through the fluid located in the tank along the average
travelling distance. The
preselected depth and the average travelling distance are selected so that the
fluid is movable at
the one or more selected ones of the natural frequencies and out of phase with
the vibration of
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the tower structure at the one or more selected ones of the natural
frequencies, to dampen the
vibration of the tower structure.
[0012] In another of its aspects, the invention provides a system for
damping vibration of
a tower structure at one or more natural frequencies of the tower structure,
the tower structure
having three sides. The system includes one or more tank assemblies with one
or more tanks
having a floor and one or more tank walls, and a fluid positioned in the tank
to a preselected depth
above the floor, the fluid in the tank occupying a tank volume. The system
also includes one or
more inserts located on the floor in the tank, the insert having a top edge
thereof at a preselected
height above the floor. The tank wall is formed to define an average tank
travelling distance of a
tank wave through the fluid in the tank. The preselected depth is greater than
the preselected
height of the insert, to enable the tank wave to move through the fluid
located in the tank along
the average tank travelling distance. The preselected depth and the average
tank travelling
distance are selected so that the fluid in the tank is movable at a selected
frequency that is the
same as a selected one of the natural frequencies at which the tower structure
vibrates, wherein
the fluid in the tank is movable at the selected natural frequency and out of
phase with the vibration
of the tower structure at the selected natural frequency, to dampen the
vibration of the tower
structure at the selected natural frequency.
[0013] In another of its aspects, the invention provides a tower system
including a tower
structure extending between a base and a top end, the tower structure being
subject to vibration
at one or more natural frequencies and a system for damping the vibration, the
system being
located on the tower structure. The system includes one or more tank
assemblies with one or
more tanks having a floor and one or more walls. The system also includes a
fluid positioned in
the tank to a preselected depth above the floor, the fluid in the tank
occupying a tank volume, and
one or more inserts located on the floor in the tank for damping movement of
the fluid, the insert
having a top edge thereof at a preselected height above the floor. The tank is
formed to define
an average travelling distance of a tank wave through the fluid in the tank.
The preselected depth
is greater than the preselected height, to enable the tank wave to move
through the fluid located
in the tank along the average travelling distance. The preselected depth and
the average
travelling distance are selected so that the fluid in the tank volume is
movable at a selected
frequency that is the same as a selected one of the one or more natural
frequencies and out of
phase with the vibration of the tower structure at the selected one of the
natural frequencies, to
dampen the vibration of the tower structure.
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ir
[0014] In another of its aspects, the invention provides a method
of determining one or
more natural frequencies of a tower structure and structural damping thereof,
the tower structure
extending above ground level between a base at the ground level and a top end.
The method
includes securing one or more accelerometers to the tower structure at one or
more locations
thereon proximal to the top end, and causing the tower structure to vibrate at
the one or more
natural frequencies. With the accelerometer, acceleration data resulting from
vibration of the
tower structure at the natural frequencies is obtained. The acceleration data
is transmitted from
the accelerometer to a processor. With the processor, the acceleration data is
processed to
determine the one or more natural frequencies, and the structural damping
thereof.
[0015] In yet another of its aspects, the invention provides a
method of determining one
or more natural frequencies of a tower structure and structural damping
thereof, the tower
structure extending above ground level between a base at the ground level and
a top end. The
method includes securing a first accelerometer to the tower structure at a
first location proximal
to the top end, and securing a second accelerometer to the tower structure at
a second location
at a preselected distance below the top end. The tower structure is caused to
vibrate at the one
or more natural frequencies. With the first accelerometer, first location
acceleration data at the
first location resulting from vibration of the tower structure at the one or
more natural frequencies
is obtained. With the second accelerometer, second location acceleration data
at the second
location resulting from vibration of the tower structure at the one or more
natural frequencies is
obtained. The first and second location acceleration data is transmitted from
the first
accelerometer and the second accelerometer respectively to a processor. With
the processor,
the first and second location acceleration data is processed to determine the
natural frequencies
and the structural damping.
[0016] In another of its aspects, the invention provides a method
of assessing a system
for damping vibration of a tower structure at one or more actual natural
frequencies of the tower
structure and actual structural damping thereof, the tower structure extending
between a base
and a top end, the system being located proximal to the top end, and an
initial structural damping
prior to the installation of the system on the tower structure being known.
The method includes
determining one or more theoretical natural frequencies of the tower structure
with the system
installed thereon, and securing one or more accelerometers to the tower
structure at a first
location thereon. The tower structure is caused to vibrate at the one or more
actual natural
frequencies. With the accelerometer, acceleration data resulting from
vibration of the tower
structure at the one or more actual natural frequencies is obtained. The
acceleration data is
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1,
transmitted from the accelerometer to a processor. With the processor, the
acceleration data is
processed to determine the one or more actual natural frequencies of vibration
of the tower
structure with the system installed thereon, and the actual structural damping
thereof. With the
processor, the one or more actual natural frequencies is compared to the one
or more theoretical
frequencies, and the actual structural damping is compared to the initial
structural damping.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will be better understood with reference to
the attached drawings, in
which:
[0018] Fig. 1A (also described previously) is an isometric view of
a shrouded tower of the
prior art;
[0019] Fig. 1B (also described previously) is an isometric view of
another shrouded tower
of the prior art;
[0020] Fig. 2 (also described previously) is an isometric view of
another shrouded tower
of the prior art;
[0021] Fig. 3A is a top view of an embodiment of a system of the
invention, drawn at a
larger scale;
[0022] Fig. 3B is a cross-section of the system of Fig. 3A;
[0023] Fig. 3C is a side view of the system of Figs. 3A and 3B
mounted proximal to a top
end of a tower structure, drawn at a smaller scale;
[0024] Fig. 3D is another top view of the system of Fig. 3A, drawn
at a smaller scale;
[0025] Fig. 4A is a top view of an alternative embodiment of the
system of the invention,
drawn at a larger scale;
[0026] Fig. 4B is a cross-section of the system of Fig. 4A;
[0027] Fig. 4C is a side view of the system of Figs. 4A and 4B
mounted proximal to a top
end of a tower structure, drawn at a smaller scale;
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V
[0028] Fig. 4D is another top view of the system of Fig. 4A, drawn
at a larger scale;
[0029] Fig. 5A is a top view of another alternative embodiment of
the system of the
invention;
[0030] Fig. 5B is a cross-section of the system of Fig. 5A;
[0031] Fig. 5C is a side view of the system of Figs. 5A and 5B
mounted proximal to a top
end of a tower structure, drawn at a smaller scale;
[0032] Fig. 5D is another top view of the system of Fig. 5A, drawn
at a larger scale;
[0033] Fig. 6A is a top view of another alternative embodiment of
the system of the
invention, drawn at a larger scale;
[0034] Fig. 6B is a cross-section of the system of Fig. 6A;
[0035] Fig. 6C is a portion of the top view of the system of Fig.
6A, drawn at a larger scale;
[0036] Fig. 6D is a portion of the cross-section of the system of
Fig. 6B, drawn at a larger
scale;
[0037] Fig. 6E is a side view of the system of Figs. 6A-6C mounted
proximal to the top
end of a tower structure, drawn at a smaller scale;
[0038] ' Fig. 6F is another top view of the system of Fig. 6A, drawn
at a larger scale;
[0039] Fig. 6G is a portion of the top view of the system of Fig.
6F, drawn at a larger scale;
[0040] Fig. 7A is a top view of a subassembly of another
alternative embodiment of the
system of the invention, drawn at a smaller scale;
[0041] Fig. 7B is a cross-section of the subassembly of Fig. 7A;
[0042] Fig. 7C is a top view of an embodiment of the system of the
invention including the
subassembly of Fig. 7A mounted on a three-sided tower structure, drawn at a
smaller scale;
[0043] Fig. 7D is another top view of the system of Fig. 7C;
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IP
[0044] Fig. 8 is a schematic illustration of a prior art tower
structure with an accelerometer
mounted thereon, drawn at a smaller scale;
[0045] Fig. 9 is a schematic illustration of a prior art tower
structure with two
accelerometers mounted thereon; and
[0046] Fig. 10 is a schematic illustration of the tower structure
including the system
installed thereon, and an accelerometer secured to the tower structure.
DETAILED DESCRIPTION
[0047] In the attached drawings, like reference numerals designate
corresponding
elements throughout. In particular, to simplify the description, the reference
numerals previously
used in Figs. 1A-2 are used again in connection with the description of the
invention hereinafter,
except that each such reference numeral is raised by 100 (or whole multiples
thereof, as the case
may be) where the elements correspond to one or more of the elements
illustrated in Figs. 1A-2.
[0048] Reference is first made to Figs. 3A-3D to describe an
embodiment of the system
of the invention indicated generally by the numeral 120. As will be described,
the system 120 is
for damping vibration of a tower structure 110 (Fig. 3C) at one or more
natural frequencies of the
tower structure 110. In one embodiment, the system 120 preferably includes one
or more tank
assemblies 122. The tank assembly 122 includes one or more tanks 124. The tank
124 has one
or more floors 126 and one or more walls 128, as will be described. The
embodiment of the tank
assembly 122 illustrated in Figs. 3A and 3B includes only the outer perimeter
wall 128. As can
be seen in Fig. 3B, the system 120 includes a fluid 130 positioned in the tank
124 to a preselected
depth "D" above the floor 126. The fluid 130 in the tank 124 occupies a tank
volume "VT" (Fig.
3B). The wall 128 is formed to define one or more average travelling distances
"TD" (Fig. 3D) of
a wave "W" through the fluid 130 initiated by the vibration of the tower
structure 110 at the one or
more natural frequencies.
[0049] As shown in Figs. 3A and 3B, the system 120 also includes
one or more inserts
132 located on the floor 126 in the tank 124, for damping movement of the
fluid 130. The insert
132 preferably has a top edge 134 thereof at a preselected height "H" above
the floor 126 (Fig.
3B).
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SP
[0050] Those skilled in the art would appreciate that the tower
structure 110 may be
subject to vibration at more than one natural frequency thereof. Such
vibration may be, for
example, due to the wind acting upon the tower structure. However, as will be
described, the
system 120 is designed for suppression or attenuation of vibration of the
tower structure 110 at a
selected natural frequency thereof.
[0051] It is preferred that the preselected depth "D" of the fluid
130 is greater than the
preselected height "H" of the insert 132, to enable the wave "W" to move
through the fluid 130
along the travelling distance "TD". As will also be discussed, the preselected
depth "D" and the
travelling distance "TD" preferably are selected so that the fluid 130 is
movable at a frequency
that will interfere with the selected natural frequency when the structure is
vibrating, to dampen
the vibration of the tower structure 110 at that natural frequency.
Preferably, the tank assembly
122 is configured so that the fluid moves at the selected natural frequency of
the structure that is
to be suppressed, however, the fluid's movement is out of phase relative to
the movement of the
structure, so that the fluid's movement dampens the vibration of the structure
at the selected
natural frequency.
[0052] It is also preferred that the tank assembly 122 includes a
cover portion 141,
covering the tank 124 (Fig. 3B). As can be seen in Fig. 3B, the cover portion
141 preferably is
secured to, and supported by, the wall 128. In one embodiment, the cover
portion 141 preferably
includes an opening therein (not shown) through which the fluid 130 may be
introduced into the
tank 124. It will be understood that, for clarity of illustration, the cover
portion 141 and the fluid
130 are omitted from Fig. 3A.
[0053] As can be seen in Figs. 3A-3C, in one embodiment, the wall
128 of the tank 124
preferably is an outer perimeter wall that is defined by an outer perimeter
radius 140 thereof
centered on a center point "C" of the tank assembly 122.
[0054] As can be seen in Fig. 3A, the insert 132 preferably is
centrally located on the floor
126, i.e., centrally located relative to the wall 128 that partially defines
the tank 124. It is also
preferred that the insert 132 is a circular ring.
[0055] Those skilled in the art would appreciate that the system
120 may be located on
the tower structure 110 at any suitable location. As can be seen in Fig. 3C,
in one embodiment,
it is preferred that the tank assembly 122 is configured to be located on the
tower structure 110
proximal to a top end 114 of the tower structure 110. Locating the system 120
at the top end 114,
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or proximal thereto, permits the system 120 to have the greatest damping
effect on the vibration
of the tower structure 110, i.e., as compared to locating the system 120
elsewhere (lower) on the
tower structure 110. This is because, when the tower structure 110 vibrates,
the amplitude of
such vibration is the greatest at the top end 114 (i.e., the free end) of the
tower structure 110.
[0056] It will be understood that, when the system 120 is mounted on the
tower structure
110, the tank assembly 122 is secured to the tower structure 110, by any
suitable means. For
the purposes hereof, the tower structure 110, and the tank assembly 122
secured to it, are
collectively referred to as a structure "S" (Fig. 3C).
[0057] Where it is intended to suppress or attenuate more than one
natural frequency of
the structure, then the system preferably is configured accordingly, as
described further below.
However, if only one natural frequency of the structure "S" is selected to be
suppressed or
attenuated, then the system 120 preferably is configured accordingly as
illustrated in Figs. 3A-
3D, i.e., to dampen vibrations at only one natural frequency of the structure.
The system 120
illustrated in Figs. 3A-3D is for damping vibrations of the tower structure
110 at one selected
natural frequency thereof.
[0058] For instance, if the structure "S" is initially moved in a first
direction indicated by
arrow "A" in Fig. 3D, then the fluid 130 moves in a direction opposite to the
first direction. As will
be described, after moving as far as possible in the first direction, the
structure moves in an
opposite second direction, i.e., the structure vibrates. However, due to the
travelling distance
"TD" in the tank 124 and the depth "D" of the fluid 130, the fluid 130 moves
in the direction opposite
to the direction of travel of the structure at a frequency that is the same as
(or substantially the
same as) the natural frequency of the structure that is to be suppressed. The
wave action of the
fluid interferes with the movement of the tower structure 110 at the natural
frequency, thereby
dampening movement of the tower structure 110 at the natural frequency.
[0059] The travelling distance "TD" is the distance that the wave "W"
travels across the
tank 124. It will be understood that, to simplify the description, only one
wave is described and
illustrated, although a succession of waves would be generated in practice by
vibration of the
structure "S". The direction of movement by the structure "S" may be any
direction. For example,
in Fig. 3D, when the structure "S" is pushed in the direction indicated by
arrow "A1", the wave
travels across the tank 124, from one location "I" at the wall 128 to a
radially opposed location
"K", on the other side of the tank 124.
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[0060] In Fig. 3D, other exemplary directions of travel initiated by
winds or other forces
are indicated by arrows "A" and "J".
[0061] It will be understood that the tank assembly 122, being secured
to the tower
structure 110, moves with the tower structure 110. It is believed that the
fluid 130 commences
moving in the direction opposite to the direction in which the structure "S"
moves at the same time
as the structure "S" moves. The sloshing motion of the fluid 130 moves in the
opposite direction,
so that its movement is out of phase relative to the movement of the tower
structure in such
direction, e.g., the direction indicated by arrow "A". Part of the damping
effect of the system 120
may be attributed to the out of phase motion with respect to the structure "S"
(i.e., the tower
structure, and the tank assembly secured to it).
[0062] It will be understood that the movement of the structure "S" may,
for example, be
due to wind pushing on the structure "S". An initial movement of the structure
"S" in the direction
indicated by arrow "Al" generates the wave "W" in the fluid 130, travelling
the travelling distance
"TD" in the direction indicated by the arrow "Al".
[0063] In this example, after the structure "S" is initially moved in
one direction (for
example, as indicated by arrow "A" in Fig. 3D), the structure "S" then moves
subsequently in a
second (opposite) direction indicated by arrow "B" in Fig. 3D, i.e., the tower
structure 110 is
vibrating, at a natural frequency thereof. However, when the tower structure
110 moves in the
second direction, then the fluid 130 also moves, in a direction opposite to
the second direction.
Accordingly, the movement of the fluid 130 in the direction opposite to the
second direction also
tends to dampen the vibration of the tower structure at the natural frequency.
[0064] When the structure "S" (i.e., the tower structure 110, and the
tank assembly 122
secured to it) changes its direction of travel (i.e., from the first direction
to the second direction),
the fluid 130 changes its direction of travel, opposite to the direction of
travel of the structure "S".
There is an out of phase difference between the structure's change in
direction, and the fluid's
change in direction, and it is believed that this out of phase motion
contributes to the damping
effect of the system 120.
[0065] Those skilled in the art would also appreciate that, when the
tower structure
vibrates, the shift between movement of the structure "S" in the first
direction to movement thereof
in the second direction is relatively rapid. As noted above, that corresponds
to a change in
direction of travel of the fluid 130 (i.e., from the first direction to the
second direction). The initial
CA 3053057 2019-08-26
amplitude of the vibration at the top end 114 may be relatively small. Also,
the vibration of the
tower structure 110 may persist for some time, with the dampening of such
vibration by the system
120 causing a gradual decrease in the amplitude of the vibration until the
vibration ceases.
[0066] In summary, while the tower structure vibrates, it is frequently
changing its direction
of travel. As described above, the fluid moves at the same frequency as the
structure, but in a
direction opposite to the structure's direction, and because of this, the
fluid is out of phase relative
to the structure's movement. From the foregoing, it can be seen that the
movement of the fluid,
which is caused by movement of the structure, is a sloshing motion, i.e., the
fluid's direction of
travel changes when the structure's direction of travel changes. It is
believed that the sloshing
motion of the fluid also changes its direction of travel with changes in the
direction of movement
of the structure "S" over time. This also enhances the damping effect of the
system 120.
[0067] The movement of the structure may be in any direction. As
examples, in Fig. 3D,
arrow "A" indicates one direction in which motion of the structure may be
initiated, and arrow "J"
indicates another direction in which motion of the structure may be initiated.
The sloshing motion
of the fluid 130, in response to the movement of the structure initiated in
the direction indicated
by arrow "A", is generally indicated by the arrow "Ao" (Fig. 3D). The sloshing
motion of the fluid
130, in response to movement of the structure initiated in the direction
indicated by arrow "J", is
generally indicated by the arrow "Jo". The arrows "Ao" and "Jo" are two-headed
arrows, to indicate
that the fluid is subjected to the sloshing motion, due to the vibrating
motion of the structure.
[0068] It will be understood that the vibration of the tower structure
may be initiated, for
example, by winds acting upon the tower structure. It will also be understood
that the foregoing
description of the movement of the wave "W" through the fluid 130 is
simplified, for clarity of
illustration. Those skilled in the art would appreciate that, in practice, the
structure "S" may be
subjected to a number of vibrations, at a number of frequencies, causing
numerous movements
of the fluid 130.
[0069] From Figs. 3A and 3B, it can be seen that, advantageously, the
system 120 is
configured to respond in the same way to vibration of the tower structure that
is initiated in any
direction, due to the outer perimeter wall 128 and the insert 132 being
circular in plan view. In
particular, because the wall 128 is circular in the system 120 illustrated in
Figs. 3A-3D, the
travelling distance "TD" of the wave "W" is the same in any direction.
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t
s
[0070] The fluid 130 may be any suitable fluid. In one
embodiment, the fluid 130
preferably includes a mixture of water and an anti-freeze liquid. For example,
the anti-freeze
liquid may be glycol.
[0071] The water and the anti-freeze liquid may be mixed
together in any suitable
proportions. For instance, in one embodiment, the fluid 130 preferably
includes approximately 40
percent water by mass and approximately 60 percent anti-freeze liquid by mass.
[0072] As a practical matter, it is preferred that the level of
the fluid 130 in the tank 124 is
checked from time to time, e.g., once every four or five years. It is believed
that, overtime, some
water vapor may escape, so that there may be a small loss of fluid volume due
to evaporation.
[0073] Those skilled in the art would appreciate that the
preselected height "H" of the
insert 132 and the preselected depth "D" of the fluid 130 may be any suitable
dimensions
respectively, as needed to dampen the vibration of the tower structure 110 at
the natural
frequency thereof that is to be suppressed or attenuated. The preselected
depth "D" of the fluid
130 preferably is greater than the preselected height "H" of the insert 132.
It is believed that,
where the preselected height "H" is between about 40 percent and about 60
percent of the
preselected depth "D", improved damping results are achieved. For instance, in
one embodiment,
the preselected height "H" of the insert 132 preferably is approximately 50
percent of the
preselected depth "D" of the fluid 130.
[0074] The insert 132 appears to provide a surprisingly
effective improvement on the
damping effect that may be provided in the absence of the insert. Based on
testing done to date,
it appears that including the insert causes the system to be 2.5 to three
times more effective at
damping the vibrations.
[0075] As described above, the system 120 illustrated in Figs.
3A-3D is for damping
vibration of the tower structure 110 at one natural frequency thereof.
However, as noted above,
depending on the circumstances, the tower structure may be subject to
vibration at more than
one natural frequency.
[0076] An alternative embodiment of the system 220 that is
illustrated in Figs. 5A-5D is
for damping vibration of a tower structure 210 (Fig. 5C) at two natural
frequencies, i.e., a first
natural frequency, and a second natural frequency. It will be understood that
the first and second
natural frequencies differ substantially, the first natural frequency being a
relatively lower
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=
,
frequency, and the second natural frequency being a relatively higher
frequency. The system
220 is designed to suppress or attenuate vibration of the tower structure 210
at the two selected
natural frequencies of the structure.
[0077] As can be seen in Fig. 5A, in one embodiment, the system
220 preferably includes
a tank assembly 222 having a floor 226 and a circular intermediate wall 242
having an
intermediate wall radius 244 centered on a center point "2C" of the tank
assembly 222 thereof.
The tank assembly 222 preferably also includes one or more tanks. In one
embodiment, the tank
assembly 222 preferably includes an outer tank subassembly 246 that is
positioned between the
intermediate wall 242 and an outer perimeter wall 238, and an inner tank 224,
defined by the
intermediate wall 242. Preferably, the outer tank subassembly 246 includes a
number of outer
tank compartments 248. It is also preferred that each of the outer tank
compartments 248 is
defined by first and second walls 250, 252 between the intermediate wall and
the outer perimeter
wall that are radially aligned with the center point and spaced apart by a
predetermined radial
distance 254 at the intermediate wall 242 (Fig. 5A).
[0078] Accordingly, the tanks included in the tank assembly 222
are the inner tank 224
and the outer tank compartments 248. It is preferred that inserts are
positioned in each of the
inner tank and in the outer tank compartments 248.
[0079] Preferably, the system 220 includes an inner insert 256
centered on the center
point "20", the inner insert 256 having an inner insert top edge 258 at a
preselected inner insert
height 259 above the floor 226. The inner insert 256 preferably is centrally
located in the inner
tank 224 (Figs. 5A, 5B).
[0080] As can be seen in Fig. 5A, the system 220 preferably
also includes a number of
outer inserts 260. The outer inserts 260 preferably are centrally located in
each of the outer tank
compartments 248 respectively, on outer portions 262 of the floor 226. Each of
the outer inserts
260 preferably has an outer insert top edge 264 located at a preselected outer
insert height 266
above the outer portion 262 of the floor 226 (Fig. 56).
[0081] The system 220 preferably also includes a fluid 230 that
is located in the inner tank
224 to a preselected first depth 268 above the floor 226. The fluid 230 in the
inner tank 224
occupies an inner tank volume "MT".
13
CA 3053057 2019-08-26
=
,
[0082] Preferably, the fluid 230 is also located in the outer
tank compartments 248 to a
preselected second depth 270 therein above the outer portion 262 of the floor
226 (Fig. 5B). The
fluid 230 in each of the outer tank compartments 248 occupies an outer tank
compartment volume
"V "
vol.
[0083] The intermediate wall 242 preferably is formed to define
an average travelling
distance "TD," (Fig. 5D) of an inner tank wave "Wl" (Fig. 5B) through the
fluid 230 in the inner
tank 224. Also, each of the outer tank compartments 248 is formed to define an
average travelling
distance "TD2" (Fig. 5D) of an outer tank wave "W2" (Fig. 5B) through the
fluid 230 in each of the
outer tank compartments 248.
[0084] The preselected first depth 268 of the fluid 230 is
greater than the preselected
inner insert height 259, to enable the inner wave "Wl" to move through the
fluid located in the
inner tank 224 along the travelling distance "TD," (Fig. 5B).
[0085] The preselected second depth 270 is greater than the
preselected outer insert
height 266, to enable the outer tank wave "W2" to move through the fluid 230
located in each of
the outer tank compartments 248 along the travelling distance "TD2" in each
compartment (Fig.
5B).
[0086] The preselected first depth 268 and the average inner
travelling distance "TD,"
preferably are selected so that the fluid 130 in the inner tank is movable at
the first natural
frequency, so that the movement of the fluid out of phase with the structure's
vibration at the
second natural frequency dampens vibration of the tower structure 210 at the
first natural
frequency.
[0087] Also, the preselected second depth 270 of the fluid 230
and the average travelling
distance "TD2" preferably are selected so that all the fluid 230 that
collectively constitutes all of
the outer tank compartment volumes "Vor" is movable at the second natural
frequency, so that
movement of the fluid out of phase with the structure's vibration at the
second natural frequency
dampens vibration of the tower structure at the second natural frequency.
[0088] It is also preferred that the tank assembly 222 includes
a cover portion 241,
covering the inner tank 224 and also covering the outer tank subassembly 246
(Fig. 5B). As can
be seen in Fig. 5B, the cover portion 241 preferably is secured to, and at
least partially supported
by the outer perimeter wall 238 and the intermediate wall 242. In one
embodiment, the cover
14
CA 3053057 2019-08-26
portion 241 preferably includes one or more openings therein (not shown)
through which the fluid
230 may be introduced into the inner tank 224 and also into the outer tank
compartments 248.
[0089] It will be understood that the cover portion 241 and the fluid
230 are omitted from
Fig. 5A, for clarity of illustration.
[0090] The first natural frequency is a first mode (i.e., a relatively
lower frequency), and
the second natural frequency is a second mode (i.e., a relatively higher
frequency). It will be
understood that the inner tank 224 is formed to receive the fluid 230 to the
first depth 268, to
dampen vibration of the tower structure 210 at the first natural frequency,
which is the lower
natural frequency. Similarly, the outer tank subassembly 246 is formed to
receive the fluid 230 to
the second depth 270, to dampen vibration of the tower structure 210 at the
second natural
frequency, which is the higher natural frequency.
[0091] For the purposes hereof, the tower structure 210, and the tank
assembly 222
secured to it, are collectively referred to as a structure "2S" (Fig. 5C). As
can be seen in Fig. 5D,
when the structure "2S" is pushed in the direction indicated by arrow "2A",
the fluid 230 in the
inner tank 224 moves correspondingly, as represented by the arrow "2A1".
Similarly, when the
structure "2S" is pushed in the direction indicated by arrow "2J", the fluid
230 in the inner tank
224 moves accordingly, as indicated by arrow "2J11. In Fig. 5D, it can be seen
that the average
travelling distance "Tal" of the fluid 230 in the inner tank 224 is the same,
regardless of the
direction in which the structure "2S" is pushed.
[0092] However, because the tank compartments 248 are not circular in
plan view, the
travelling distance of the outer tank wave "W2" in each respective outer tank
compartment is
approximately the same and may differ slightly, depending on the direction of
movement of the
fluid. For example, the movement of the fluid 230 in the outer tank
compartment in response to
the force applied to the structure "2S" in the direction indicated by arrow
"2A" is represented by
arrows "2A0". The corresponding movement of the fluid 230 in the outer tank
compartments 248
resulting from the force applied to the structure "2S" in the direction
indicated by arrow "2J" is
illustrated by arrows "2.10". It can be seen in Fig. 5D that, depending on the
radial position of a
selected outer tank compartment relative to the direction of the force applied
to the structure, the
travelling distance of the fluid in the selected outer tank compartment is
approximately the same
and may vary slightly. For this reason, the average travelling distance "TD2"
is determined, to
provide a travelling distance value for the outer tank compartment, for every
direction of
CA 3053057 2019-08-26
movement of the fluid, is approximately the travelling distance thereof. For
exemplary purposes,
"TD2" is illustrated in Fig. 5D.
[0093] It will be understood that the system 220 may be located on the
tower structure
210 at any suitable location. As can be seen in Fig. 5C, in one embodiment, it
is preferred that
the tank assembly 222 is configured to be located on the tower structure 210
proximal to the top
end 214 of the tower structure 210. Locating the system 220 at the top end
214, or proximal
thereto, permits the system 220 to have the greatest impact possible on the
vibration of the tower
structure 210. This is because, when the tower structure vibrates, the
amplitude of such vibration
is typically the greatest at the top end 214 of the tower structure 210.
[0094] It will also be understood that, when the system 220 is mounted on
the tower
structure 210, the tank assembly 222 is secured to the tower structure 210, by
any suitable means.
[0095] For instance, if the structure "2S" is initially moved in a first
direction indicated by
arrow "2A" in Fig. 5D, then the fluid 230 in the inner tank 224 and in the
outer tank compartments
248 moves in an opposite direction, opposite to the direction of travel of the
structure, as indicated
by the arrows "2A1", "2A0". As will be described, after moving as far as
possible in the first
direction, the structure moves in an opposite second direction, i.e., the
structure vibrates.
However, due to (i) the travelling distance "TDi" and the depth 268 of the
fluid 230 in the inner
tank 224, and (ii) the average travelling distance "TD2" and the second depth
270 of the fluid 230
in the outer tank compartments 248, the fluid 230 in the inner tank 224, and
also the fluid 230 in
all of the outer tank compartments 248, move at respective first and second
fluid frequencies that
are, respectively, the same as the first and second natural frequencies of the
structure "2S".
Accordingly, the sloshing movement of the fluid 230 in the inner tank 224
dampens the vibration
at the first mode and the sloshing movement in all the outer tank compartments
248 dampens the
second mode vibration of the tower structure 210.
[0096] It will be understood that the tank assembly 222, being secured to
the tower
structure 210, moves with the tower structure. However, it is believed that
the fluid 230 begins to
move in the opposite direction, so that its movement is out of phase relative
to the movement of
the structure "2S" in the first direction. Part of the damping effect of the
system 220 may be
attributed to the out of phase motion between the structure "2S" (i.e., the
tower structure, and the
tank assembly secured to it) and the fluid 230.
16
CA 3053057 2019-08-26
ir
,
[0097] Those skilled in the art would appreciate that wind may
cause a tower structure to
vibrate. It will be understood that Fig. 5D is simplified, for clarity of
illustration, and therefore does
not fully show the structure "2S" vibrating.
[0098] In this example, after the structure "2S" is initially
moved in a first direction
indicated by arrow "2A", it then moves subsequently in a second direction
indicated by arrow "26"
in Fig. 5D, i.e., the tower structure 210 is vibrating. However, when the
tower structure 210 moves
in the second direction and is oscillating in the first natural frequency,
then the fluid 230 also
moves in the inner tank 224, at the same frequency but in an opposite
direction. Accordingly, the
movement of the fluid 230 in the second direction also tends to dampen the
vibration of the tower
structure at the first natural frequency thereof.
[0099] Also, it is believed that, when the structure "2S" (i.e.,
the tower structure, and the
tank assembly secured to it) moves, for example, in the direction indicated by
arrow "2A" but
oscillates in the second natural frequency, then the fluid 230 in the outer
compartments 248 also
moves, in the outer compartments 248, at the same frequency but in an opposite
direction.
Accordingly, the sloshing movement of the fluid 230 in the outer compartments
248 tends to
dampen the vibration of the tower structure 210 at its second natural
frequency.
[0100] Those skilled in the art would also appreciate that, when
the structure "2S"
vibrates, the shift between movement of the structure "2S" in the first
direction to movement
thereof in the second direction is relatively rapid. As noted above, the out
of phase difference
between the motion of the structure and that of the fluid 230 provides
damping. Also, the vibration
of the structure "2S" may persist for some time, with the dampening of such
vibration causing a
gradual decrease in the amplitude of the vibration until the vibration ceases.
[0101] From the foregoing, it can be seen that, while the
structure "2S" vibrates, it is
frequently changing its direction of travel. It is believed that is
accompanied by the fluid changing
its direction of travel at the same frequency as the structure "2S" oscillates
over time, enhancing
the damping effect of the system 220.
[0102] As noted above, the vibration of the structure "2S" may
be initiated, for example,
by wind. From Figs. 5A and 5B, it can be seen that, advantageously, the inner
tank 224 and the
inner ring 256 are configured to respond generally in the same way to
vibration of the structure
"2S" that is initiated in any direction, due to the intermediate wall 242 and
the ring 256 being
circular in plan view.
17
CA 3053057 2019-08-26
[0103] It will be understood that the fluid depths 268, 270 may be any
suitable depths.
However, in one embodiment, the preselected inner ring height 259 is
approximately 50 percent
of the preselected first depth 268 of the fluid 230. It is also preferred that
the preselected outer
ring height 266 is approximately 50 percent of the preselected second depth
270 of the fluid 230
in each of the outer tank compartments 248.
[0104] It will be understood that the outer tank compartments 248 have
smaller
dimensions (i.e., as compared to the inner tank 224) to limit the distance the
fluid can travel in
each outer tank compartment 248 ("TD21), when the fluid oscillates due to
movement of the tower
structure 210. The size of each of the outer tank compartments is determined
by the frequency
(in this example, the second natural frequency) that is to be suppressed or
attenuated.
[0105] Similarly, the travel distance "TD1", i.e., the size of the inner
tank 224, is determined
by the frequency (in this case, the first natural frequency) that is to be
suppressed or attenuated.
[0106] As can be seen in Fig. 5B, in one embodiment, the preselected
second depth 270
of the fluid 230, and the preselected outer ring height 266 preferably are the
same, or substantially
the same, in each of the outer tank compartments 248 respectively.
[0107] The outer tank compartments 248 are the same size, and the
preselected second
depth 270 and the preselected outer ring height 266 are the same in each, so
that the fluid in all
of the outer tank compartments 248 collectively constitutes a relatively large
mass of the fluid 230
that is movable at the second selected frequency.
[0108] It will be understood that the fluid positioned in the outer tank
compartments 248
may not necessarily be the same as the fluid, which is located in the inner
tank 224. However,
as a practical matter, it is preferred that the same fluid 230 is located in
the inner tank 224 and in
the outer tank compartments 248. Those skilled in the art would appreciate
that utilizing different
fluids in the inner tank 224, on one hand, and in the outer tank compartments
248, on the other
hand, may complicate somewhat the installation of the system, and the
maintenance of the fluid
at the preselected depths in the system.
[0109] The fluid 230 may be any suitable fluid. In one embodiment, the
fluid 230
preferably includes a mixture of water and an anti-freeze liquid. For example,
the anti-freeze
liquid may be glycol.
18
CA 3053057 2019-08-26
[0110] The water and the anti-freeze liquid may be mixed together in any
suitable
proportions. For instance, in one embodiment, the fluid 230 preferably
includes approximately 40
percent water by mass and approximately 60 percent anti-freeze liquid by mass.
As noted above,
the level of the fluid preferably is checked from time to time, in case of
evaporation.
[0111] Those skilled in the art would appreciate that, depending on the
circumstances, a
tower structure may be subject to vibration at more than two natural
frequencies. Multiple systems
or combinations thereof can be used at different locations on the tower
structure to address each
of the susceptible (natural) frequencies.
[0112] Another alternative embodiment of the system 320 is illustrated
in Figs. 6A ¨ 6G.
The system 320 is designed to dampen vibration of a tower structure 310 (Fig.
6E) at first and
second natural frequencies thereof. It will be understood that the first
natural frequency is a first
mode (i.e., a relatively low frequency), the second natural frequency is a
second mode (i.e., at a
higher frequency, higher than the first natural frequency). The system 320 is
designed to
suppress or attenuate vibration of the structure at the two selected natural
frequencies of the
structure.
[0113] In one embodiment, the system 320 preferably includes a tank
assembly 322
having a floor 326 and a circular first intermediate wall 342 having a first
intermediate wall radius
344 centered on a center point "3C", and a circular second intermediate wall
372 having a second
intermediate wall radius 374 centered on the center point "3C" (Fig. 6C). As
can also be seen in
Fig. 6A, the system 320 preferably also includes an outer perimeter wall 338
that is circular in
plan view, and centered on the center point "3C".
[0114] In one embodiment, the tank assembly 322 preferably includes a
first outer tank
subassembly 346, positioned between the first intermediate wall 342 and the
second intermediate
wall 372, an inner tank 324 defined by the first intermediate wall 342, and a
second outer tank
subassembly 376, positioned between the second intermediate wall 372 and the
outer perimeter
wall 338.
[0115] As can be seen in Figs. 6A and 6C, the first outer tank
subassembly 346 preferably
includes a number of first outer tank compartments 378. As illustrated in Fig.
6C, each of the first
outer tank compartments 378 preferably is defined by first and second inner
walls 380, 382
between the first and second intermediate walls that are radially aligned with
the center point "3C"
and spaced apart by a predetermined first radial distance 384, at the first
intermediate wall.
19
CA 3053057 2019-08-26
[0116] It is also preferred that the second outer tank subassembly 376
includes a number
of second outer tank compartments 386. Preferably, each of the second outer
tank compartments
386 is defined by first and second outer walls 388, 390 between the second
intermediate wall and
the outer perimeter wall that are radially aligned with the center point "30"
and spaced apart by a
predetermined second radial distance 392, at the second intermediate wall
(Fig. 60). Each of the
second outer tank compartments 386 preferably is also defined by the outer
perimeter wall 338
(Fig. 6C).
[0117] In one embodiment, the system 320 preferably includes an inner
insert 356
centered on the center point "30" of the tank assembly 322. The inner insert
356 preferably has
an inner insert top edge 358 at a preselected inner insert height 359 above
the floor 326 (Fig.
6D).
[0118] The system 320 preferably also includes a number of first outer
inserts 360 and a
number of second outer inserts 394. Each of the first outer inserts 360
preferably is centrally
located in each of the first outer tank compartments 378 respectively on a
first outer portion 362
of the floor 326 (Fig. 6C). As can be seen in Fig. 6D, each of the first outer
inserts 360 preferably
has a first outer insert top edge 364 at a preselected first outer insert
height 366 above the first
outer portion 362 of the floor 326.
[0119] Each of the second outer inserts 394 preferably is centrally
located in each of the
second outer tank compartments 386 respectively on second outer portions 396
of the floor 326
(Fig. 60). Preferably, each of the second outer inserts 394 has a second outer
insert top edge
398 at a preselected second outer insert height 399 above the second outer
portion 396 of the
floor 326 (Fig. 6D).
[0120] It will be understood that the respective dimensions of each of
the first outer tank
compartments 378, and the dimensions of the first outer rings 360 positioned
therein respectively,
preferably are substantially identical. The same fluid 330 preferably is
positioned in each of the
first outer tank compartments 378 to the same depth therein.
[0121] It will also be understood that the respective dimensions of the
second outer tank
compartments 386, and the dimensions of the second outer rings 394 positioned
in each of the
second outer tank compartments, preferably are substantially identical. Also,
the same fluid 330
preferably is positioned in each of the second outer tank compartments 386 to
the same depth
therein.
CA 3053057 2019-08-26
[0122] As can be seen in Figs. 6B and 6D, it is also preferred that the
fluid 330 is located
in the inner tank 324 to a preselected first depth 368 above the floor 326.
The fluid 330 in the
inner tank 324 occupies an inner tank volume identified in Figs. 6B and 6D by
reference character
"3VIT".
[0123] The first intermediate wall 342 preferably is formed to define an
average inner tank
travelling distance "TD3" (Fig. 6F) of an inner tank wave "W3" (Fig. 6B)
through the fluid 330 in the
inner tank 324. The preselected first depth 368 (Fig. 6D) preferably is
greater than the inner insert
height 359, to enable the inner tank wave 'W3" to move through the fluid 330
located in the inner
tank 324 along the travelling distance "TD31
.
[0124] The fluid 330 preferably is also located in the first outer tank
compartments 378,
to a preselected first outer depth 370 therein above the first outer portion
362 of the floor 326.
The fluid 330 in each of the first outer tank compartments 378 respectively
occupies a first outer
tank compartment volume "1-3V01-''.
[0125] Each of the first outer tank compartments 378 preferably is formed
to define a first
outer tank average travelling distance "TD4" (Fig. 6G) of a first outer tank
wave "W4" (Fig. 6D)
through the fluid 330 in each of the first outer tank compartments 378
respectively. The
preselected first outer depth 370 preferably is greater than the first outer
insert height 366, to
enable the first outer tank wave "W4" to move through the fluid 330
respectively located in the first
outer tank compartments 378 along the travelling distance "TD4" (Fig. 6D).
[0126] Preferably, the fluid 330 is also located in the second outer tank
compartments
386, to a preselected second outer depth 301 therein above the second outer
portion 396 of the
floor 326. The fluid 330 in each of the second outer tank compartments 386
respectively occupies
a second outer tank compartment volume "2-3V01-".
[0127] It is also preferred that each of the second outer tank
compartments 386 is formed
to define a second outer tank average travelling distance "TD5" (Fig. 6G) of a
second outer tank
wave "W5" (Fig. 6D) through the fluid 330 in each of the second outer tank
compartments 386
respectively. The preselected second outer depth 301 preferably is greater
than the second outer
insert height 399, to enable the second outer tank wave 'W5" to move through
the fluid 330
respectively located in the second outer tank compartments 386 along the
travelling distance
"TD5" (Fig. 6D).
21
CA 3053057 2019-08-26
[0128] Preferably, the preselected first depth 368 of the fluid 330 and
the average
travelling distance "TD3" are selected so that fluid in the inner tank volume
"3VIT" is movable at
the first natural frequency. The movement of the fluid in the inner tank 324
is out of phase with
the vibration of the tower structure 310 at the first natural frequency, to
dampen vibration of the
tower structure 310 at the first natural frequency.
[0129] It is also preferred that the preselected first outer depth 370 of
the fluid 330 and
the average travelling distance "Tat" are selected so that the fluid in all of
the first outer tank
compartments (i.e., the sum thereof) is movable at the second natural
frequency. The movement
of the fluid in the first outer tank compartments is out of phase with the
vibration of the tower
structure 310 at a second natural frequency, to dampen vibration of the tower
structure 310 at the
second natural frequency.
[0130] Preferably, the preselected second outer depth 301 of the fluid
330 and the
average travelling distance "TD5" are selected so that the fluid in all of the
second outer tank
compartments (i.e., the sum thereof) is movable at the second natural
frequency. The movement
of the fluid in the second outer tank compartments is out of phase with the
vibration of the tower
structure 310 at the second natural frequency, to dampen vibration of the
tower structure 310 at
the second natural frequency.
[0131] Preferably, the tank assembly 322 includes a cover portion 341
that covers the
inner tank 324, the first outer tank compartments 378, and the second outer
tank compartments
386 (Figs. 6B, 6D). As can be seen in Figs. 6B and 6D, the cover portion 341
preferably is secured
to, and supported by, the outer perimeter wall 338, the first intermediate
wall 342, and the second
intermediate wall 372. In one embodiment, the cover portion 341 preferably
includes one or more
openings (not shown) through which the fluid 330 may be introduced into the
inner tank 324, the
first outer tank compartments 378, and the second outer tank compartments 386.
It will be
understood that, for clarity of illustration, the cover portion 341 and the
fluid 330 are omitted from
Figs. 6A, 6C, 6F, and 6G.
[0132] The system 320 may be located on the tower structure 310 at any
suitable location.
It is preferred that the tank assembly 322 is configured to be located on the
tower structure 310
proximal to a top end 314 of the tower structure 310. Locating the system 320
at the top end 314,
or proximal thereto, permits the system 320 to have the greatest possible
impact on the vibration
of the tower structure 310.
22
CA 3053057 2019-08-26
r
,
[0133] It will be understood that, when the system 320 is
mounted on the tower structure
310, the tank assembly 322 is secured to the tower structure 310 by any
suitable means. For the
purposes hereof, the tower structure 310, and the tank assembly 322 secured to
it, are collectively
referred to as a structure "3S" for convenience (Fig. 6E).
[0134] The system 320 (Figs. 6A-6D) is an alternative
embodiment, similar to the system
220 (Figs. 5A-5D), except that the two outer tank subassemblies 346, 376 are
required to
suppress the second mode of vibration motion of the tower structure, unlike
the single outer tank
subassembly 246. In this way, the two outer rows of tank compartments (i.e.,
in subassemblies
346 and 378) could be said to functionally correspond to the single outer row
of tank
compartments in the system 220.
[0135] For instance, if the structure "3S" is initially moved in
a first direction indicated by
arrow "3A" in Fig. 6F, then the fluid 330 is moved in a direction opposite to
the first direction. The
structure also moves in an opposite second direction, i.e., the structure
vibrates. However, due
to the travelling distance "TD3" and the depth 368 of the fluid 330 in the
inner tank, the fluid 330
in the inner tank 324 moves in the direction opposite to the direction of
travel of the structure at a
frequency that is the same as (or substantially the same as) the first natural
frequency of the
structure.
[0136] Similarly, due to the average travelling distance "Tat"
and the depth 370 of the
average fluid 330 in the first outer compartments 378, and the average
travelling distance "TD5"
and the depth 301 of the fluid in the second outer tank compartments 386, the
fluid 330 in all of
the first outer tank compartments 378, and the fluid 330 in all of the second
outer tank
compartments 386, moves in the direction opposite to the direction of travel
of the structure at a
frequency that is the same as the second natural frequency of the structure.
[0137] Accordingly, the movement of the fluid 330 in the inner
tank 324 and in all the outer
tank compartments 378, and in all of the second outer tank compartments 386,
in response to
movement of the tower structure 310 dampens vibration of the structure "3S".
[0138] As can be seen in Fig. 6F, when the structure "3S" is
pushed in the direction
indicated by arrow "3A", the fluid 330 in the inner tank 324 moves
correspondingly, as represented
by the arrow "3A1". Similarly, when the structure 3S is pushed in the
direction indicated by arrow
"3J", the fluid in the inner tank 324 moves accordingly, as indicated by arrow
"1.11". In Fig. 6F, it
23
CA 3053057 2019-08-26
}
,
can be seen that the average travelling distance "TD3" of the fluid 330 in the
inner tank 324 is the
same, regardless of the direction in which the structure "3S" is pushed.
[0139] As can be seen in Fig. 6F, neither the first outer tank
compartments 378 nor the
second outer tank compartments 386 are circular in plan view. Accordingly, the
travelling distance
of the first inner tank wave "Wa" in each respective first outer tank
compartment 378 is
approximately the same but may differ slightly, depending on the direction of
movement of the
fluid. For example, the movement of the fluid in the first outer tank
compartment 378 in response
to the force represented by arrow "3A" is represented by arrows "1-3A0". The
corresponding
movement of the fluid in the first outer tank compartments 378 resulting from
the force represented
by arrow "3J" is illustrated by arrows "1-3,10". It can be seen in Fig. 6F
that, depending on the
radial position of a selected first outer tank compartment relative to the
direction of the force
applied to the structure "3S", the travelling distance of the fluid in the
selected first outer tank
compartment may vary.
[0140] The travelling distance of the first inner tank wave
"W5" in each respective second
outer tank compartment 386 is approximately the same but may differ slightly,
depending on the
direction of movement of the fluid. For example, the movement of the fluid in
the second outer
tank compartment in response to the force represented by arrow "3A" is
represented by arrows
"2-3A0". The corresponding movement of the fluid in the second outer tank
compartments 386
resulting from the force represented by arrow "3J" is illustrated by arrows "2-
3.10". It can be seen
in Fig. 6F that, depending on the radial position of a selected second outer
tank compartment 386
relative to the direction of the force applied to the structure, the
travelling distance of the fluid in
the selected second outer tank compartment 386 may vary.
[0141] Because neither the first outer tank compartments 378
nor the second outer tank
compartments 386 are circular, the respective travelling distances therein,
"Tat" and "TD5"
respectively, are average travelling distances. That is, each of the average
travelling distances
is an arithmetic average of the possible travelling distances in an outer tank
compartment.
[0142] It will be understood that the tank assembly 322, being
secured to the tower
structure 310, moves with the tower structure 310. However, it is believed
that the fluid 330
commences moving in the direction opposite to the direction in which the
structure "3S" moves at
the same time as the structure "3S" moves. The fluid 330 moves in the
direction opposite to the
first direction, so that its movement is out of phase relative to the movement
of the tower structure
24
CA 3053057 2019-08-26
310 in the first direction (indicated by arrow "3A"). Part of the damping
effect of the system 320
may be attributed to the out of phase motion with respect to the structure
"3S" (i.e., the tower
structure, and the tank assembly secured to it).
[0143] In this example, if the tower structure 310 is initially moved in
the first direction
(represented by arrow "3A"), then the structure moves subsequently in a second
direction
indicated by arrow "36" in Fig. 6F, i.e., the tower structure 310 vibrates.
However, when the tower
structure 310 moves in the second direction, then the fluid 330 also moves in
the second direction
(i.e., in the inner tank 324, in all of the first outer compartments 378, and
in all of the second outer
compartments 386), but at a frequency in each respectively that is the same as
the first and
second natural frequencies respectively. Accordingly, the movement of the
fluid 330 in the
second direction also tends to dampen the vibration of the tower structure 310
at the first and
second natural frequencies thereof.
[0144] Also, it is believed that, when the structure "3S" (i.e., the
tower structure, and the
tank assembly secured to it) moves, for example, in the direction indicated by
arrow "3A" but
oscillates in the second natural frequency, then the fluid 330 in the first
and second outer tank
compartments 378, 386 also moves, in such tank compartments, at the same
frequency but in an
opposite direction. Accordingly, the sloshing movement of the fluid 330 in the
outer compartments
378, 386 tends to dampen the vibration of the tower structure 310 at its
second natural frequency.
[0145] Those skilled in the art would also appreciate that, when the
tower structure
vibrates, the shift between movement of the structure "3S" in the first
direction to movement
thereof in the second direction is relatively rapid. As noted above, the out
of phase difference
between the motion of the structure "3S" and that of the fluid 330 provides
damping. Also, the
vibration of the structure "3S" may persist for some time, with the dampening
of such vibration
causing a gradual decrease in the amplitude of the vibration until the
vibration ceases.
[0146] From the foregoing, it can be seen that, while the structure "3S"
vibrates, it is
frequently changing its direction of travel. It is believed that is
accompanied by the fluid changing
its direction of travel at the same selected two frequencies as the structure
"3S" over time,
enhancing the damping effect of the system 320.
[0147] It will be understood that the fluid depths 368, 370, 301 may be
any suitable depths.
However, in one embodiment, the preselected inner ring height 359 is
approximately 50 percent
of the preselected first depth 368 of the fluid 330. As illustrated, the
preselected first outer ring
CA 3053057 2019-08-26
,
,
height 366 is somewhat less than approximately 50 percent of the preselected
first outer depth
370 of the fluid 330 in each of the first outer tank compartments 328.
Preferably, the preselected
second outer ring height 399 is approximately 50 percent of the preselected
second outer depth
301 of the fluid 330 in each of the second outer tank compartments 386.
[0148] It will be understood that the first and second outer
tank compartments 378, 386
have smaller dimensions (i.e., as compared to the inner tank 324) to limit the
distance the fluid
can travel in each compartment 378, 386, when the fluid 330 oscillates due to
movement of the
tower structure 310. The size of each of the first and second outer tank
compartments (i.e., the
average travelling distances "Tat", "TD5" is determined by the frequency (in
this example, the
second natural frequency) that is to be suppressed or attenuated.
[0149] Similarly, the size of the inner tank 324 (i.e., the
travelling distance "TD3") is
determined by the frequency (in this case, the first natural frequency) that
is to be suppressed or
attenuated.
[0150] As can be seen in Figs. 6B and 6D, in one embodiment, the
preselected first outer
depth 370 of the fluid 330 and the preselected first outer ring height 366
preferably are the same,
or substantially the same, in each of the first outer tank compartments 378.
[0151] The first outer tank compartments 378 preferably are each
the same size, and the
preselected first outer depth 370 and the preselected first outer ring height
366 preferably are the
same in each, so that the fluid in all the first outer compartments 378
may.collectively constitute
a relatively large mass of the fluid 330 that is movable at the second natural
frequency.
[0152] It is also preferred that the second outer depth 301 of
the fluid 330 and the
preselected second outer ring height 399 are the same, or substantially the
same, in each of the
second outer tank compartments 386.
[0153] As an example, the first outer depth 370 is shown as
being greater than the second
outer depth 301. It will be understood that the depths 370, 301 may be any
suitable depths.
[0154] The second outer compartments 386 preferably are each the
same size, and the
second outer depth 301 and the preselected second outer ring height 399
preferably are the same
in each, so that the fluid 330 in all the second outer compartments 386 may
collectively constitute
a relatively large mass of the fluid 330 that is also movable at the second
natural frequency.
26
CA 3053057 2019-08-26
,
,
[0155] It will be understood that the fluid positioned in the
first and second outer tank
compartments 378, 386 may not necessarily be the same as the fluid which is
located in the inner
tank 324. Similarly, different fluids (i.e., different from each other) may be
positioned in the first
and second outer compartments respectively. However, as a practical matter, it
is preferred that
the same fluid 330 is located in the inner tank 324 and in the first and
second outer tank
compartments 378, 386. Those skilled in the art would appreciate that
utilizing different fluids in
the inner tank 324 and in the first and second outer tank compartments 378,
386 may complicate
somewhat the design and installation of the system, and the maintenance of the
fluid at the
preselected depths in the system.
[0156] The fluid 330 may be any suitable fluid. In one
embodiment, the fluid 330
preferably includes a mixture of water and an anti-freeze liquid. For example,
the anti-freeze
liquid may be glycol.
[0157] The water and the anti-freeze liquid may be mixed
together in any suitable
proportions. For instance, in one embodiment, the fluid 330 preferably
includes approximately 40
percent water by mass and approximately 60 percent anti-freeze liquid by mass.
[0158] Another alternative embodiment of the system 420 of the
invention is illustrated in
Figs. 4A ¨ 4D. Preferably, the system 420 is designed to dampen vibration of a
tower structure
410 (Fig. 4C) that is subject to vibration at a single, relatively high
natural frequency. The system
420 is designed to suppress or attenuate vibration of the tower structure 410
at the selected
natural frequency of the structure.
[0159] In one embodiment, the system 420 preferably includes a
tank assembly 422
having a floor 426 and a circular intermediate wall 442 having an intermediate
wall radius 444
centered on a center point "4C". The system 420 preferably also includes an
outer tank
subassembly 446 positioned between the intermediate wall and an outer
perimeter wall 438. It is
also preferred that the outer tank subassembly 446 preferably includes a
number of outer tank
compartments 448.
[0160] As can be seen in Fig. 4A, each of the outer tank
compartments 448 preferably is
defined by first and second walls 450, 452 between the intermediate wall and
the outer perimeter
wall that are radially aligned with the center point spaced apart by a
predetermined radial distance
454 at the intermediate wall 442. Preferably, the system 420 also includes a
number of inserts
460, each of the inserts 460 being located in each of the outer tank
compartments 448
27
CA 3053057 2019-08-26
,
,
respectively. Each of the inserts 460 has a top edge 434 at a preselected
height 466 above the
floor 426 (Fig. 4B).
[0161] It is also preferred that the system 420 includes a
fluid 430 that is located in each
of the outer tank compartments 448 to a preselected outer tank depth 470. The
fluid 430 in each
outer tank compartment 448 occupies an outer tank compartment volume "4VoT".
[0162] As can be seen in Figs. 4A, 4B, and 4D, the intermediate
wall 442 defines a central
opening 471 in the tank assembly 422.
[0163] It is also preferred that the tank assembly 422 includes
a cover portion 441,
covering the outer tank subassembly 446 (Fig. 4B). As can be seen in Fig. 4B,
the cover portion
441 preferably is secured to, and at least partially supported by, the outer
perimeter wall 438 and
the intermediate wall 442. In one embodiment, the cover portion 441 preferably
includes one or
more openings therein (not shown) through which the fluid 430 may be
introduced into the outer
tank compartments 448.
[0164] It will be understood that the cover portion 441 and the
fluid 430 are omitted from
Fig. 4A, for clarity of illustration.
[0165] Preferably, each of the outer tank compartments 448 is
formed to define an
average outer tank travelling distance "TD6" of an outer tank compartment wave
"Ws" through the
fluid 430 in each of the outer tank compartments 448 respectively (Fig. 4D).
[0166] The preselected outer tank depth 470 preferably is
greater than the preselected
height 466, to enable the outer tank compartment wave "We" to move through the
fluid 430 located
in each of the outer tank compartments 448 respectively.
[0167] The preselected depth 470 of the fluid 430 and the
average travelling distance
"TD6" preferably are selected so that the fluid 430 constituting the total of
the outer tank
compartment volumes "4V0T" is movable at a frequency that is the same as a
natural frequency
of vibration of the tower structure that is to be suppressed or attenuated, to
dampen the vibration
of the tower structure.
[0168] The system 420 may be located on the tower structure 410
at any suitable location.
As can be seen in Fig. 4C, in one embodiment, it is preferred that the tank
assembly 422 is
configured to be located on the tower structure 410 proximal to a top end 414
of the tower
28
CA 3053057 2019-08-26
structure 410. Locating the system 420 at the top end 414, or proximal
thereto, permits the system
420 to have the greatest impact possible on the vibration of the tower
structure. This is because,
when the tower structure vibrates, the amplitude of such vibration is
typically the greatest at the
top end 414 of the tower structure 410.
[0169] It will be understood that, when the system 420 is mounted on the
tower structure
410, the tank assembly 422 is secured to the tower structure 410, by any
suitable means. For
the purposes hereof, the tower structure 410, and the tank assembly 422
secured to it, are
collectively referred to as a structure "4S", for convenience (Fig. 4C).
[0170] The travelling distance of the outer tank compartment wave "NA/6"
in each
respective outer tank compartment 448 is approximately the same and may differ
slightly,
depending on the direction of movement of the fluid. Because of this, the
travelling distance "TD6"
is an average of the travelling distances inside the outer tank compartment
448. For example,
the movement of the fluid in the outer tank compartment in response to the
force represented by
arrow "4A" is represented by arrows "4A0". The corresponding movement
resulting from the force
represented by arrow "4J" is illustrated by arrows "4,10". It can be seen in
Fig. 4D that, depending
on the radial position of a selected outer tank compartment relative to the
direction of the force
applied to the structure, the travelling distance of the fluid in the selected
first outer tank
compartment is approximately the same.
[0171] For instance, if the structure "4S" is initially moved in a first
direction indicated by
arrow "4A" in Fig. 4D, then the fluid 430 is moved in the same direction.
However, due to the
average travelling distance "TD6" and the outer tank depth 470 of the fluid
430, the fluid 430 in all
of the outer tank compartments 448, moves at respective a fluid frequency that
is slightly different
from the natural frequency. Accordingly, the movement of the fluid 430 in all
the outer tank
compartments 448, in response to movement of the tower structure 410 at the
natural frequency
thereof, dampens such vibration of the tower structure 410.
[0172] It will be understood that the tank assembly 422, being secured
to the tower
structure 410, moves with the tower structure. However, it is believed that
the fluid 430
commences moving in an opposite direction to the first direction at exactly
the same time as the
structure "4S" begins to move. Instead, the wave "W6" of the fluid 430 begins
to move in the
opposite direction, so that the fluid wave "W6" movement is out of phase
relative to the movement
of the tower structure in the first direction. Part of the damping effect of
the system 420 may be
29
CA 3053057 2019-08-26
,
,
attributed to the out of phase motion with respect to the structure "48"
(i.e., the tower structure,
and the tank assembly secured to it).
[0173] In this example, after the structure "4S" is initially
moved in the first direction "4A"
(Fig. 4D), it then moves subsequently (reversing its motion) in a second
direction indicated by
arrow "46" in Fig. 4D, i.e., the tower structure 410 is vibrating. However,
when the tower structure
410 moves in a direction opposite to the second direction, then the fluid 430
also moves in the
second direction, in all of the outer compartments 448. Accordingly, the
movement of the fluid
430 in the second direction also tends to dampen the vibration of the tower
structure at the natural
frequencies.
[0174] Also, it is believed that, when the structure "4S"
(i.e., the tower structure, and the
tank assembly secured to it) changes its direction of travel (i.e., from the
first direction to the
second direction), the fluid 430 is still moving in the first direction. Once
again, there is an out of
phase difference between the structure's movement in a direction of travel,
and the fluid's
movement in the opposite direction, and it is believed that this out of phase
motion contributes to
the damping effect of the system 420.
[0175] Those skilled in the art would also appreciate that,
when the tower structure
vibrates, the shift between movement of the structure "4S" in the first
direction to movement
thereof in the second direction is relatively rapid. As noted above, that
corresponds to a change
in direction of travel of the fluid 430 (i.e., from the first direction to the
second direction). Also, the
vibration of the tower structure 410 may persist for some time, with the
dampening of such
vibration causing a gradual decrease in the amplitude of the vibration until
the vibration ceases.
[0176] From the foregoing, it can be seen that, while the tower
structure vibrates, it is
frequently changing its direction of travel. It is believed that the sloshing
motion of the fluid
changes its direction of travel as quickly as the structure "48" over time.
This also enhances the
damping effect of the system 420.
[0177] As noted above, the vibration of the tower structure 410
may be initiated, for
example, by wind.
[0178] It will be understood that the outer tank depth 470 may
be any suitable depth.
However, in one embodiment, the preselected outer ring height 466 is
approximately 50 percent
of the preselected outer tank depth 470 of the fluid 430.
CA 3053057 2019-08-26
[0179] It will be understood that the size of each of the outer tank
compartments 448 is
determined by the natural frequency of the tower structure 410 that is desired
to be suppressed
or attenuated.
[0180] As can be seen in Fig. 4B, in one embodiment, the preselected
outer tank depth
470 of the fluid 430, and the preselected outer ring height 466 preferably are
the same, or
substantially the same, in each of the outer tank compartments 448.
[0181] The outer tank compartments 448 are the same size, and the
preselected outer
tank depth 470 and the preselected outer ring height 466 are the same in each,
so that the fluid
in all the outer tank compartments 448 collectively constitutes a relatively
large mass of the fluid
430 that is movable at the selected frequency.
[0182] The fluid 430 may be any suitable fluid. In one embodiment, the
fluid 430
preferably includes a mixture of water and an anti-freeze liquid. For example,
the anti-freeze
liquid may be glycol.
[0183] The water and the anti-freeze liquid may be mixed together in any
suitable
proportions. For instance, in one embodiment, the fluid 430 preferably
includes approximately 40
percent water by mass and approximately 60 percent anti-freeze liquid by mass.
[0184] As noted above, the tower structure may be generally round in
cross-section, or
triangular. In Figs. 7A ¨ 7D, an embodiment of the system 520 of the invention
(Fig. 7C) is
illustrated that is configured to be positioned on a tower structure 510 (Fig.
7C) that, in cross-
section, has the general outline of an equilateral triangle. The tower
structure 510 has three sides
503, 505, 507 (Fig. 7C). The system 520 is for damping vibration of the tower
structure 510 that
extends between a base (not shown) and a top end 514 thereof, at one or more
natural
frequencies of the tower structure 510.
[0185] As can be seen in Fig. 7C, the system 520 is configured to fit
onto the three-sided
tower structure 510.
[0186] In one embodiment, the system 520 preferably includes a tank
assembly 522.
Preferably, the tank assembly 522 includes one or more tanks 524 with one or
more floors 526
and one or more walls 509. As will be described, in one embodiment, each of
the tanks 524
preferably is square in plan view.
31
CA 3053057 2019-08-26
,
[0187] As illustrated in Fig. 7C, the tank assembly 522
preferably includes three groups
511A, 511B, 511C of tanks 524, as will be described. It will be understood
that the system is
designed to suppress or attenuate vibration of the tower structure 510 at a
selected natural
frequency thereof.
[0188] Preferably, the system 520 also includes a fluid 530
positioned in the tank(s) 524
to a preselected depth 568 above the floor 526 (Fig. 7B). The fluid in the
tank 524 occupies a
tank volume identified by reference character "5\4" (Fig. 7B). Preferably, the
system 520 also
includes one or more inserts 560, each of the inserts 560 being centrally
located in a selected
one of the tanks 524, on the floor 526. The insert 560 preferably has a top
edge 564 thereof at a
preselected height 566 above the floor 526 (Fig. 7B).
[0189] Preferably, the tank compartment wall 509 is formed to
define an average tank
compartment travelling distance "TD7" of a tank compartment wave "W7" through
the fluid 530 in
the tank 524.
[0190] The preselected depth 568 is greater than the preselected
height 566 of the insert
560, to enable the tank compartment wave "W7" to move through the fluid
located in the tank 524
above the preselected height 566 of the insert 560 at a selected frequency.
[0191] The preselected depth 568 and the average travelling
distance "TD7" preferably
are selected so that the fluid 530 constituting the tank volume "5Vo-r" is
movable at the frequency
that is the natural frequency of the tower structure that is to be suppressed.
The fluid's movement
is out of phase with the vibration of the tower structure at the natural
frequency that is to be
suppressed or attenuated, to dampen the vibration of the tower structure 510.
[0192] As can be seen in Fig. 7A, in one embodiment, the tank
assembly 522 preferably
includes a number of the square tanks 524. It will be understood that the
system 520 may include
tanks that have any suitable configuration, e.g., the tanks 524 may be square,
round, semi-
square, or semi-round in plan view. Preferably, the square tanks 524 are
arranged in a group
511 in the tank assembly 522 (Fig. 7A). As will be described, each of the
groups 511 preferably
is configured to fit on a selected one of the sides 503, 505, 507 of the tower
structure 510. The
fluid 530 in all of the square tanks 524 is movable at the same frequency as
the selected natural
frequency of the tower structure 510, but the fluid is moved at such frequency
out of phase with
the movement of the structure, to dampen the vibration of the tower structure
510.
32
CA 3053057 2019-08-26
,
,
[0193] For convenience, the three groups of tanks in the tank
assembly 522 are identified
in Fig. 7C by reference characters 511A, 511B, and 511C. The groups identified
by reference
characters 511A, 511B, and 511C are mounted on the sides 503, 505, and 507 of
the tower
structure 510 respectively (Fig. 7C). It will be understood that, for the
purposes hereof, the
structures of the groups 511, and the fluid 530 therein, are substantially
identical.
[0194] It is also preferred that the tank assembly 522 includes
one or more cover portions
541, covering the tanks 524 (Fig. 7B). As can be seen in Fig. 7B, the cover
portion 541 preferably
is secured to, and at least partially supported by, the walls 509 of each tank
524. In one
embodiment, the cover portion 541 preferably includes one or more openings
therein (not shown)
through which the fluid 530 may be introduced into the tanks 524.
[0195] It will be understood that the cover portions 541 and the
fluid 530 are omitted from
Figs. 7A, 7C, 7D, and 7E, for clarity of illustration.
[0196] The system 520 may be located on the tower structure 510
at any suitable location.
As can be seen in Fig. 7C, in one embodiment, it is preferred that the tank
assembly 522 is
configured to be located on the tower structure 510 proximal to the top end
514 of the tower
structure 510. Locating the system 520 at the top end 514, or proximal
thereto, permits the system
520 to have the greatest impact possible on the vibration of the tower
structure. This is because,
when the tower structure vibrates, the amplitude of such vibration is the
greatest at the top end
514 of the tower structure 510.
[0197] It will be understood that, when the system 520 is
mounted on the tower structure
510, the tank assembly 522 is secured to the tower structure 510, by any
suitable means. For
the purposes hereof, the tower structure 510, and the tank assembly 522
secured to it, are
collectively referred to as a structure "5S", for convenience (Fig. 70).
[0198] As noted above, the vibration of the tower structure 510
may be initiated, for
example, by wind.
[0199] For instance, if the structure "5S" is initially moved in
a first direction indicated by
arrow "5A" in Fig. 7D, then the fluid 530 is moved in a direction opposite to
the first direction.
However, due to the average travelling distance "TD7" and the depth 568 of the
fluid 530, the fluid
530 in all the tanks 524 moves at the fluid frequency that is the same as the
natural frequency of
the tower structure 510 that is to be controlled. Accordingly, the movement of
the fluid 530 in the
33
CA 3053057 2019-08-26
,
tank 524 in response to movement of the tower structure 510 at the natural
frequency, dampens
such vibration of the tower structure 510.
[0200] It will be understood that the tank assembly 522, being
secured to the tower
structure 510, moves with the tower structure. However, it is believed that
the fluid 530
commences moving in the opposite direction at the same time as the structure
"5S" begins to
move. The sloshing motion of the fluid 530 is in the opposite direction at
that point, so that its
movement is out of phase relative to the movement of the tower structure in
the first direction.
Part of the damping effect of the system 520 may be attributed to the out of
phase motion with
respect to the structure "5S" (i.e., the tower structure, and the tank
assembly secured to it).
[0201] The travelling distance of the outer tank compartment wave
"W," in each
respective tank 524 is approximately the same but may differ slightly,
depending on the direction
of movement of the fluid. Because of this, the travelling distance "TD," in
each of the tanks 524
is an average of the travelling distances inside the tank 524. For example,
the movement of the
fluid in the tank 524 in response to the force represented by arrow "5A" is
represented by arrows
"5A0". The corresponding movement resulting from the force represented by
arrow "5J" is
illustrated by arrows "5J0". It can be seen in Fig. 7D that, depending on the
position of a selected
tank 524 relative to the direction of the force applied to the structure, the
travelling distance of the
fluid in the selected tank 524 is approximately the same but may vary
slightly.
[0202] In this example, after the structure "5S" is initially moved
in the first direction, it
then moves subsequently in a second direction indicated by arrow "513" in Fig.
7D, i.e., the tower
structure 510 is vibrating. However, when the tower structure 510 moves in the
second direction,
then the fluid 530 also moves in a direction opposite to the second direction,
in the tank 524.
Accordingly, the movement of the fluid 530 in response to the movement of the
structure "5S" in
the second direction also tends to dampen the vibration of the tower structure
at the natural
frequencies.
[0203] Also, it is believed that, when the structure "5S" (i.e., the
tower structure, and the
tank assembly secured to it) changes its direction of travel (i.e., from the
first direction to the
second direction), the fluid 530 is still moving opposite to the first
direction. Once again, there is
out of phase difference between the structure's change in direction of travel,
and the fluid's change
in direction, and it is believed that this out of phase motion contributes to
the damping effect of
the system 520.
34
CA 3053057 2019-08-26
[0204] Those skilled in the art would also appreciate that, when the
tower structure
vibrates, the shift between movement of the structure "5S" in the first
direction to movement
thereof in the second direction is relatively rapid. As noted above, that
corresponds to a change
in direction of travel of the fluid 530 (i.e., from opposite to the first
direction, to opposite to the
second direction). Also, the vibration of the tower structure 510 may persist
for some time, with
the dampening of such vibration causing a gradual decrease in the amplitude of
the vibration until
the vibration ceases.
[0205] From the foregoing, it can be seen that, while the tower structure
vibrates, it is
frequently changing its direction of travel. It is believed that the sloshing
motion of the fluid also
changes its direction of travel at the same frequency as the structure "5S"
over time. That also
enhances the damping effect of the system 520.
[0206] It will be understood that the fluid depths 568 may be any
suitable depths.
However, in one embodiment, the preselected ring height 566 is approximately
50 percent of the
preselected depth 566 of the fluid 530. It will also be understood that the
dimensions of the tanks
524 are determined by the frequency (in this example, the natural frequency)
that is to be
suppressed or attenuated.
[0207] As can be seen in Fig. 7B, in one embodiment, the preselected
depth 568 of the
fluid 530, and the preselected ring height 566 preferably are the same, or
substantially the same,
in each of the tanks 524.
[0208] The fluid 530 may be any suitable fluid. In one embodiment, the
fluid 530 includes
a mixture of water and an anti-freeze liquid. For example, the anti-freeze
liquid may be glycol.
[0209] The water and the anti-freeze liquid may be mixed together in any
suitable
proportions. For instance, in one embodiment, the fluid 530 preferably
includes approximately 40
percent water by mass and approximately 60 percent anti-freeze liquid by mass.
[0210] The invention preferably also includes a tower system 508 (Fig.
7C), which
includes the system 520 and the tower structure 510.
[0211] Those skilled in the art would appreciate that, in order to
determine the one or
more natural frequencies of the tower structure, it is preferred that such
determination may be
made by measurements of the tower structure, when vibrating. Those skilled in
the art would also
CA 3053057 2019-08-26
.
,
appreciate that it is also necessary to assess the extent to which the
vibration of the tower
structure is affected by structural damping.
[0212] Preferably, the invention includes a method of
determining the one or more natural
frequencies of a tower structure 610 of the prior art, as well as a method of
measuring the
structural damping that is associated with one or more of the natural
frequencies. As can be seen
in Fig. 8, the tower structure 610 extends above ground level "G" between a
base 616 at the
ground level and a top end 614. In one embodiment, the method includes, first,
securing an
accelerometer 613 to the tower structure 610 at one or more locations at the
top end 614, or
proximal to the top end 614. The tower structure 610 is then vibrated, as will
be described.
[0213] With the accelerometer 613, acceleration data resulting
from vibration of the tower
structure 610 is obtained. The acceleration data is transmitted from the
accelerometer 613 to a
processor 615. With the processor 615, the acceleration data is processed to
determine the one
or more natural frequencies and the corresponding structural damping.
Preferably, in such
processing, digital filters are used to separate the measured data signal into
separate signals,
each such signal representing the attenuation of a signal under a different
natural frequency.
[0214] As noted above, the tower structure 610 is relatively
tall and slender. Preferably,
a first end 617 of flexible element 619 is attached to the top end 614 of the
tower structure 610.
A pulling device 621 is attached to a second end 623 of the flexible element
619 (Fig. 8). The
pulling device 621 pulls on the flexible element 619 in the direction
indicated by arrow "E" in Fig.
8, causing the top end 614 to be bent in the direction that the pulling device
621 pulls.
[0215] Preferably, once the top end 614 has been pulled in the
direction of arrow "E" to a
predetermined initial position, the flexible element 619 is quickly released
by the pulling device
621. Due to the sudden release of the top end 614, the tower structure 610
vibrates, in the
directions indicated by arrows "F" and "H" in Fig. 8.
[0216] Those skilled in the art would be aware of suitable
pulling devices 621, and also of
suitable flexible elements 619.
[0217] As noted above, the acceleration data, which indicates
the vibrating behavior of
the tower structure, is then processed by the processor 615 to determine the
one or more natural
frequencies of the tower structure 610. The acceleration data may be
transmitted to the processor
615 via any suitable means. Those skilled in the art would be aware of
suitable software for
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,
,
analyzing the acceleration data in the frequency domain in order to determine
the one or more
natural frequencies of the tower structure 610. Also, the acceleration data is
analyzed in the time
domain to determine a damping ratio of the tower structure 610, by using
digital filters to separate
the measured data signal into separate signals, each representing the
attenuation of the signal
under a different natural frequency.
[0218] In an alternative embodiment, schematically illustrated
in Fig. 9, two
accelerometers may be utilized. In this embodiment, a first accelerometer 713
is secured to a
tower structure 710 at a first location 725 proximal to a top end 714, and a
second accelerometer
727 is secured to the tower structure 710 at a second location 729 a
preselected distance 731
below the top end 714. Next, the tower structure 710 is vibrated.
[0219] With the first accelerometer 713, first location
acceleration data is obtained at the
first location 725 resulting from vibration of the tower structure 710. With
the second
accelerometer 727, second location acceleration data is obtained at the second
location 729
resulting from vibration of the tower structure 710. The first and second
location acceleration data
is transmitted from the first accelerometer 713 and the second accelerometer
727 respectively to
a processor 715. With the processor 715, the first and second location
acceleration data is
processed to determine the one or more natural frequencies and the associated
structural
damping of the tower structure 710. Preferably, in such processing, digital
filters are used to
separate the measured signals into separate signals, each representing the
attenuation of the
signal under a different natural frequency.
[0220] In one embodiment, in order to cause the tower structure
710 to vibrate at the one
or more natural frequencies, a first end 717 of a flexible element 719 is
attached to the top end
714, and a pulling device 721 is attached to a second end 723 of the flexible
element 719. The
pulling device 721 pulls on the flexible element 719 in the direction
indicated by arrow "E", to
move the top end 714 toward the pulling device 721, and then suddenly releases
the flexible
element 719, thereby causing the top end 714 to vibrate, as indicated by
arrows "F" and "H" in
Fig. 9.
[0221] The first and second acceleration data preferably is
transmitted to the processor
715 by any suitable means. Those skilled in the art would be aware of suitable
software for
analyzing the first and second acceleration data in order to determine the one
or more natural
frequencies of the tower structure 710.
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[0222] Those skilled in the art would appreciate that, once an embodiment
of the tank
assembly of the system of the invention has been secured to a tower structure
810, the natural
frequency (or natural frequencies) of the overall structure "8S" (Fig. 10)
differs slightly from the
natural frequency (or natural frequencies) of the tower structure 810 alone.
Also, the installation
of the damping system of the invention on the tower structure provides a
significant enhancement
or increase to the structural damping of the structure (i.e., the tower
structure, and the tank
assembly). It will be understood that a tank assembly 822 of the system 820 is
secured to the
tower structure 810 (Fig. 10). It will also be understood that the structure
"8S" includes the tower
structure 810 and the tank assembly 822 of the system 820.
[0223] Those skilled in the art would appreciate that the structure "8S",
once the fluid (not
shown) has been introduced into the tank assembly, the structural damping of
the overall structure
will be increased. The purpose of the assessment of the structure "8S" is to
determine, after the
system 820 has been installed, whether adjustments to the system 820 should be
made, so that
it may dampen vibration of the structure more effectively.
[0224] Accordingly, the invention includes a method of assessing the
system 820 for
damping vibration of the tower structure 810 at one or more natural
frequencies thereof. As can
be seen in Fig. 10, the system 820 preferably is mounted at a top end 814 of
the tower structure
810. The method includes securing an accelerometer 813 to the structure "8S"
at a location that
is proximal to the top end 814 of the tower structure 810. The structure 810,
with the system 820
installed thereon, is vibrated.
[0225] In one embodiment, in order to cause the structure 810 to vibrate,
a first end 817
of a flexible element 819 is attached to the top end 814, and a pulling device
821 is attached to a
second end 823 of the flexible element 819. The pulling device 821 pulls on
the flexible element
819 in the direction indicated by arrow "E", to bend the top end 814 toward
the pulling device 821,
and then suddenly releases the flexible element 819, thereby causing the top
end 814 to vibrate,
as indicated by arrows "F" and "H" in Fig. 10.
[0226] With the accelerometer 813, acceleration data is obtained
resulting from vibration
of the structure "8S". The acceleration data is transmitted from the first
accelerometer 813 to a
processor 815.
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[0227] With the processor 815, the acceleration data is processed to
determine the one
or more actual frequencies of vibration of the structure "8S" as well as the
corresponding structural
damping.
[0228] In addition, with the processor, the one or more actual measured
structural
damping and frequencies are compared to the one or more initial structural
damping and
theoretical frequencies. Based on such comparisons, suitable adjustments to
the system 820
may be determined. It is preferred that this process is repeated until the
damping that is effected
by the system 820 is satisfactory.
[0229] Alternatively, more than one accelerometer may be utilized.
[0230] It will be appreciated by those skilled in the art that the
invention can take many
forms, and that such forms are within the scope of the invention as claimed.
The scope of the
claims should not be limited by the preferred embodiments set forth in the
examples, but should
be given the broadest interpretation consistent with the description as a
whole.
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