Note: Descriptions are shown in the official language in which they were submitted.
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PNEUMATIC SURF WAVE PRODUCTION FOR POOLS
The present invention concerns a method and apparatus for erect-
in a water wave in a pool of sufficient amplitude and wave con-
tour to permit a person, with -the aid of a surf board, to practice
the sport of surfing on it.
The creation of waves with parallel wave fronts in swimming pools
has long been known. For example, apparatus capable of producing
such waves is disclosed in US Patent No. 375,684 to Bamag-
Mahogany AGO. accepted June 30, 1932 and in US. Patent No.
2,056,855 to F. K. Her issued October 6, 1936. These types of
waves are to be distinguished from the resonance type waves such
as are produced by the method and apparatus disclosed in US.
Patent No. 3,629,877 issued December 28, 1971 to the applicants
here. None of these cited patents discloses creation of a surf-
in wave which must have an amplitude of about two meters or
more above the undisturbed water level of the pool and have a
cross sectional contour suitable for surfing. US. Patent
3,473,334 to Dexter issued October 21, 1969, discloses a method
and apparatus for creating a surfing wave. There, water is
pumped from above into a reservoir located at one end of a pool
to create a hydraulic head. A gate beneath the water is then
raised to place the reservoir in communication with the pool.
The water driven from the reservoir by the hydraulic head flows
against a deflector which directs the flow upward to create a
surfing wave nearly two meters high. The placement of the gate
below the water level creates maintenance problems since moving
parts must be serviced under water or the pool drained of a very
large amount of water.
Summary of The Invention
The present invention provides apparatus and methods of producing
waves for surfing with maximum efficiency. The high efficiency
is obtained by concentrating the energy of a freely falling
hydraulic head of water along smooth inside walls of a reservoir
that is in submarine communication with a pool of water. The
wall more distant from the pool includes a continuously curving
surface that it tangentially joined to the adjacent, relatively
level portion of the pool floor. This smooth transition avoids
turbulence and other losses of energy that occur when the pool
floor is not aligned with the inside rear reservoir wall or con-
twins discontinuities. Preferably, the lower extremity of the
front reservoir wall, besides being smooth, also terminates
in a continuous curve curving only toward the pool to avoid the
creation of turbulence
A hydraulic head is created in the reservoir by sealing the
reservoir against the intrusion of air and evacuating air from
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the reservoir. The partial vacuum created causes water to
enter the reservoir above the normal, i.e., undisturbed
level of water in the pool and be stored. When a hydraulic
head of the desired height has been created by the
evacuation of air from the reservoir, the reservoir is
suddenly vented to the atmosphere so that the stored water
flows downward under the influence of gravity and transfers
energy to the water in the pool to create a surfing wave.
Preferably a vent having an area of at least one third the
LO horizontal cross sectional area of the reservoir is opened,
so that the stored water can flow without being restricted
by the rate at which air enters the reservoir. The
described reservoir characteristics permit the water to
reach a velocity as near its theoretical maximum as possible
pharaoh maximum energy efficiency and transfer.
According to an aspect of the invention, an apparatus
for producing a surfing wave above the undisturbed level of
water in a pool having a floor, said apparatus comprises:
a reservoir having an interior volume disposed
partial above and partially below the level of undisturbed
water in a pool, generally opposed front and rear walls, and
generally opposed side walls to form with said front and
rear walls, a first horizontal cross sectional area, each
said wall terminating in a lower extremity to define an
punning communicating between said reservoir and said pool
below said level of undisturbed water in said pool, the
floor of said pool being inclined upwardly from the
lowermost portion of said opening, said reservoir including
a first aperture for admitting air, said first aperture
avowing a second cross sectional area at least one third that
of said fist horizontal cross sectional area;
suction means in communication with said reservoir for
evacuating air from said reservoir; and
valve means for selectively sealing said reservoir
3Sagainst the intrusion of air and rapidly opening said first
aperture to ventilate said reservoir to the atmosphere.
A preferred design for a-vent includes a relatively
large aperture having a lid that is held against an aperture
in the reservoir by atmospheric pressure when the pressure
pa
in the reservoir is reduced. spring or other biasing
force urges the cover away from the reservoir. A relatively
small aperture in the reservoir is connected to the
atmosphere through a valve such as a solenoid valve. After
the pressure has been reduced in the reservoir, the valve
is rapidly opened. A sudden rise in pressure inside the
reservoir releases the lid under the influence of the spring
so that the large vent is opened without the application of
a large force. The interval between the opening of the
vulva and release of the lid is too short to permit any
significant flow of water from the reservoir.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross sectional, schematic side view of a
preferred embodiment of surf wave producing apparatus
l5according to the invention.
fig. 2 is a cross section, schematic side view of an
embodiment of model surf wave producing apparatus according
to the invention upon which measurements have been made.
Fig. 3 is a schematic, cross sectional side view of a
proofread embodiment of a valve according to the invention.
Fig. is a schematic plan view of an embodiment of a
reservoir according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A cross sectional side view of a surfing pool 1 as
Sheehan in Figure 1. The pool includes a reservoir 3 having a
front wall 5 toward a pool 7 and rear wall Y away from pool
7. A to 11 of _ _
US
r
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reservoir 3 may be opened or closed by a bitterly type
valve having a vane 13 mounted on an axle 25. Pool 7 has a
floor 17 that is substantially level adjacent to reservoir 3
but which inclines upward in a sloped portion 19 at a
distance from the reservoir as is known in wave pools. A
sup 21 at the extreme end of pool 7 collects water that
overflows the pool end when a surfing wave propagates to the
end of the pool.
In order to produce efficiently a surfing wave, that is, a
wave having an amplitude of about two meters or more and a
contour suitable for surfing, it is necessary to transfer
energy to -the pool with maximum velocity and minimum losses
to turbulence and friction. It is known to produce waves ion
pools by creating a hydraulic head, that is, storing water
above the level of the quiet or undisturbed water in a pool,
and releasing the head. It is also known that the maximum
velocity for a wave having an amplitude h measured from the
bottom of the pool V that is ye-, where g is the
gravitational acceleration. Obviously this relation is
limited to relatively shallow depths for in deep water such
as the ocean there are no waves. However, this relationship
is useful in a design for creating a surfing wave having
maximum energy and the velocity necessary for surfing. For
a surfing wave of a desired height, the hydraulic head
necessary can be determined from the known relationship
between the height of a hydraulic head and the freely
falling velocity of flow from it. Namely,
VA = 2gH(l-Hv/H)
where VA = the velocity of flow
H - the height of the hydraulic head, and
g = gravitational acceleration
H = equivalent head height lost to flow
resistance
In order to achieve the maximum wavy velocity, v = v with
a particular head height, an assumption as to thy flow
losses must be made. generous assumption allowing a large
margin of safety is H = H/2, that is that half the
equivalent head height is wasted in the flow. Then to
achieve a discharge velocity from the reservoir equal to the
maximum theoretical wave velocity, H h. It is also
necessary to reduce the flow resistance and turbulence to a
minimum to achieve the desired energy transfer from the
downwardly flowing water into the pool. In reality, it is
more correct to refer to an energy transfer than water flow
since little change in the total volume of water results
prom release of water stored in the reservoir into the pool.
The quantities just mentioned are further identified in
Figure 1, where h is the level of water in the pool when it
is not disturbed my a surfing wave. (In addition, the far
lateral
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side of the pool edge 23 is shown to illustrate that the wave
crest preferably does not flow over the sides of the pool.
Were that overflow to occur the desired wave contour at the
ends of the parallel wave would be destroyed before the wave
reached sup 21.)
It is disclosed in US Patent No. 375,684 and US. Patent No.
2,056,855 to draw water into a reservoir by pneumatic means
and we prefer to use that technique here. Reservoir 3 is open
to pool 7 beneath the undisturbed water level 25. As shown in
Figure 1, front wall 5 -terminates in a lower extremity below
and, preferably just below water level 25. In addition, it is
preferred that the lower extremity of front wall 5 terminate
in a continuous curve bending toward pool 7 to improve the
flow of water from reservoir 3 and avoid turbulence. Likewise,
the interior surfaces of walls 5 and 9 are preferably smooth.
Reservoir 3 may be constructed in a conventional way from
poured concrete. Rear wall 9 at its lower extremity has a
continuous curved portion bending toward pool 7. As emphasized
by the gap in Figure 1 between wall 9 and pool floor 17, a
gap which does not exist in an actual pool, floor 17 is sub-
staunchly level adjacent wall 9 and is tangentially joined
to it. Therefore water flowing from reservoir 3 does not
descend to a lower pool floor, as shown in US Patent No.
375,684 and US. patent No. 2,056,855. Thereby a substantial
loss of energy is avoided. Moreover, neither of those patents
discloses any ability to produce a surfing wave which may be
attributable to the energy lost in the falling water which
must rise again to produce the waves. See US. Patent No.
2,056,855 at page 3, left column, lines 10 to 17 where the
only producible wave patterns are slow rolling or rapid choppy
waves. Likewise, with our design, no deflector such as is
disclosed in US. Patent No. 3,473,334 is necessary to create
a surfing wave. The deflection of flow consumes energy and no-
dupes the efficiency of the apparatus, a problem avoided in
our design.
Reservoir 3 includes an outlet 27 above the highest water level
in the reservoir that is connected to conventional suction
means such as a fan or vacuum pump that is not illustrated.
The suction means extract air from the reservoir in the
direction indicated by arrow 29, preferably continuously as in
OK. Patent No. 375,684. Reservoir 3 may be sealed from in-
trusion of air from the atmosphere by the closing of the butter-
fly valve. Axle 15 is rotated to place vane 13 across the
opening in top 11 of reservoir 3 as indicated by the broken
lines of Figure 1. Then as air is extracted a partial vacuum
is created so that water is drawn into reservoir 3 to a height H
above the undisturbed water level ho. The water can flow into
the reservoir from pool 7 or it may be drawn through pipes from
sup 21. In either case, the level of the pool water is not
noticeably reduced.
04
When the hydraulic head reaches the desired height if, the
butterfly valve it suddenly opened to admit atmospheric air
into reservoir 3 so that -the stored water is released and the
energy of its downward flow is transformed into a surf wave.
We have had tests of the operation of our new surf pool design
conducted to determine if it would junction as desired. The
pool was built on a 1 : 10 scale, was 5 m in length, 50 cm
wide and the reservoir projected about 70 cm out of the water.
Suction was obtained from an industrial vacuum cleaner and
a flap closing the top of the reservoir was manually opened
when the desired head height was achieved. A cross sectional
sketch of -the pool is shown in Figure 2. The depth, LO, of
poolreservolr for these tests was 47 cm. It should be noted
that some of the symbols used in Figure 1 were used in report-
in these test results, but given different definitions in the
tests. In these tests, h is the depth of the undisturbed water
which was 25 cm. The test model included a shutter 31 that could
be vertically adjusted to different depths below the surface
of the water. In these tests, the shutter projected into the
water a distance s of 4 cm. In the tests the height H of the
hydraulic head was varied. The results were as follows:
H ho
(cm) (cm)
21 *
38 ~21
26 16
18
, 19 *
38 21 *
21
In the results marked with a star, the wave actually spilled
over the side walls of the pool. When these tests are scaled
up to a full size pool, then a surfing wave of 2.1 m should be
obtained. The contour of the waves observed in these tests was
satisfactory for surfing. A hydraulic head of 3. a to 5 m, plus
some margin for scaling-up losses, would be required to produce
a full scale surfing wave.
In operating embodiments of the inventive surf wave apparatus,
it is important that a sufficient rate of air flow into the
evacuated reservoir be provided to avoid additional energy
losses. If the air flows in too slowly when the valve is opened,
the rate at which water flows out of the reservoir will be no-
larded and the desired high efficiency energy transfer from the
hydraulic head to the surf wave will not be achieved. In order
to avoid these energy losses at least one third of the horizontal
cross sectional area of the reservoir should be opened to the
atmosphere at once. Referring to Figure I a plan view of a
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reservoir having a front wall I opposing rear wall I and
opposing side walls 45 and 47 joining the front and rear walls,
the horizontal cross sectional area is that area enclosed by
the broken lines which describe a horizontal perimeter of the
interior surfaces of those walls.
A further complication may arise in opening the desired large
area of the reservoir to the atmosphere. Referring back to
Figure 1, when vane 13 is closed and reservoir 3 is evacuated,
atmospheric pressure tends to interfere with the operation of
the valve. The portion of vane 13 on one side of axle 15 will
be held closed by atmospheric pressure while the other portion
will be pushed open. As a result, an unsatisfactory seal
between the vanes and top 11 may be produced with unacceptable
air leakage into the reservoir. This leakage could interfere
with the achievement of, or require greater energy to achieve,
the desired hydraulic head H.
An alternative form of valve is shown schematically in Figure 3.
There the top wall or ceiling 51 of a reservoir is shown in
cross section having a relatively large opening Wylie 51 has
an upstanding portion 55 which may be circular as illustrated.
A lid 57 covers opening 53 and a gasket 59 of rubber or other
suitable compressible material forms an air-tight seal between
lid 57 and wall portion 55 when they are held together. A
frame 61 is mounted on top of wall 51 to support a helical spring
63 that is connected to lid 57. When lid 57 is in its closed
position as shown, spring 63 is in tension and urges the lid
toward its open position. Two solenoids 65 also are supported
on frame 61 and have their plungers disposed opposite lid 57.
When the plungers are extended they engage lid 57 to urge it
toward its closed position and place the lid in contact with
gasket 59. Solenoids 65 are connected through an electrical
switch 67 to an electrical source 69. A second aperture 71 in
wall 51 has a much smaller cross sectional area than opening 53.
A valve 73, preferably a solenoid valve, is connected through
piping to aperture 71 to the atmosphere. valve 73 is electrically
connected through a switch 75 to power source 69. In this valve
embodiment, aperture 71 is used to control the release of cover
57. At the beginning of a wave cycle, switch 67 is closed and
solenoids 65 depress lid 57 extending spring 63 to urge lid 57
upward. Valve 73 is closed/ as is normal. The evacuation of
air from the reservoir begins and atmospheric pressure seals
lid 57 to wall portions 55. Switch 67 is opened. When the de-
sired hydraulic head height H is reached, switch 75 is closed
so that valve 73 is opened to the atmosphere. Air rushes through
valve 73 in the direction indicated by -the arrow quickly raising
the pressure in the reservoir sufficiently to permit lid 57
to be opened by the force of spring 63. The opening of aperture
_ 7 _ I
53 exposes sufficient area for the inflow of air that water
flows down and out of the reservoir a-t a rate not restricted
by -the rate of airflow into the reservoir. In this embodiment
it is important that -the pressure within the reservoir rise
quickly so that lid 57 is moved to the open position before
a substantial amount of water flows out of the reservoir. If
the delay between the openings of -the aperture is less than
about one second, the inertia of the water in the reservoir
will aid in achieving the desired result. Without using a
construction such as that just described, very large forces
would be required to open lid 57 against atmospheric pressure
since it must have a relatively large area to permit a rapid
flow of a large volume of air into the reservoir. In practice,
a small aperture such as 71 need only have an area of about
1 my for a larger aperture total area of 70 my. If the areas
are in a ratio between the range of 1 to lCoand 1 to 200,
then the desired result is achieved. The same result might
also be achieved mechanically by using a crankshaft linked to
covers on the large and small apertures and arranged so that
a cam opens the small aperture just prior to the opening of
the large aperture by another cam.
Because the relatively large area that needs to be opened in
a reservoir for the admission of air, for example I m in 2
a reservoir having a horizontal cross sectional area of 200 m ,
it may be preferred to use a number of valves in parallel.
Such an arrangement is shown in Figure 4 where top wall or
ceiling 49 of a reservoir is shown. There, three large
apertures 81, 83 and 85 are contained in wall 49 and each
such aperture is accompanied by a smaller control aperture,
87, 89 and 91, respectively. Each of these aperture pairs
would be fitted by a valve assembly as previously described or
in a combined assembly in a form that would be obvious to one
skilled in the art. It may also be desirability use a single
small, control aperture to reduce the cost of the apparatus
and the possibility that the larger area covers might no
open simultaneously. In any event a total control aperture
area of 1 m should be adequate for the example of this pane-
graph.
The invention has been described with reference to certain pro-
furred embodiments. Various modifications and additions within
the spirit of the invention will occur to those of skill in
their art. Accordingly, the scope of the invention is limited
solely by the following claims.
