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The Isaacs wave-energy pump: Field tests off the coast of Kaneohe Bay, Hawaii
Ocean Engng. Vol. 5, pp. 235-242. © Pergamon Press Ltd., 1978. Printed in Great Britain.
THE FIELD
TESTS
ISAACS
OFF
WAVE-ENERGY
0029-8018/78/0801-0235
$02.00/0
PUMP:
THE COAST OF KANEOHE NOVEMBER 1976 MARCH 1977
BAY,
HAWAII
GERALD L. WICK and DAVID CAS]TEL Scripps Institution of Oceanography, Institute ot" Marine Resources, University of California, [~ Jolla 92093, U.S.A. and Foundation for Ocean Research, San Diego, California 92121, U.S.A. Abstract---Field tests conducted on a wave-power pump showed that this simple design conceived by Professor John D. lsaacs is suitable for wave-energy extraction around the Hawaiian Islands. In the small model tested, over 200 W of mechanical power were produced. Larger models could extract several orders of magnitude more power. Further research needs to be done with prototype models. The transmission of the power to the shore still needs to be examined. A by-product of the operation of the pump is nutrient rich water pumped from the bottom of the pipe. In our test, the water was pumped from 300 ft. It is feasible with a similar design that the water can be pumped from 1000 ft where the water is richer in nutrients. This water could then be used to stimulate the growth of marine plants. l~ A S S E S S M E N T
OF
EXTENT
AND DISTRIBUTION IN T H E O C E A N S
OF
WIND-WAVE
ENERGY
THE ENERGY and power in ocean wind waves can be considerable. A typical average sea state has approximately 1,5 m waves at an 8 sec period. These waves correspond to a mean flux of wave power across a section of the ocean of the order of 10 kW/m. Summed over the entire ice-free ocean, the total power available would be 2.7 x 1012 W. Locally this flux varies from 103 kW/m in gales, to low values of 10 3 kW/m or less. Our estimate of the total power of 2.7 × 10a2 W is about 1 0 ~ of the total projected power needs of man in 2000 A.D. ([saacs; Wick and Schmitt, 1977). The power is, of course, transmitted locally and at great distance by water motion from the effects of wind acting on the ocean surface. The water surface acts as a great transmission belt delivering integrated wind power from distant disturbances. Thus, both in the short and long term, waves and wave power are more persistent than wind and wind power. There is an optimal length of fetch for the most efficient transfer of power from wind to wave. At that point, wave height and period are usually shorter than those of a fully developed sea. Where winds persist over long distances, as in the tradewind belt, the wave could therefore be cropped repeatedly; the shorter period associated with cropping is generally advantageous to conversion systems, thus utilization makes wave power not only greater, but also more readily available. In this way, as much as 35 x 10is W of mechanical power might be extractable from wind waves (Isaacs, Wick and Schmitl, 1976). Waves vary in several ways. In the short term, their period and wave length fluctuate, necessitating a non-resonant non-synchronous system to extract their power, and their height varies, requiring some short-term power reservoir. This is of fundamental importance to the design of wave-power devices and has been discussed in a previous paper (Isaacs, Castel and Wick, 1976). 235
236
GERALDL. WICKand DAVIDCASTEL
The waves' long-term persistency depends primarily on location. Wave charts of oceans of the northern hemisphere generally indicate two maxima roughly corresponding to the latitudes of the easterly trade winds, such as those at Hawaii, and of the westerlies. The primary maximum is centered at about 55°N. The charts also show that the waves are most energetic in winter over the entire ocean. At all seasons, the sea-states usually diminish near continental coastlines and near the ice cover. For the two spatial maxima t,f the North Atlantic, the percentage frequency of waves greater than 5 ft is 80 and 50~/o for the winter months, 50 and 2 0 ~ for the lowest three months (summer). In the North Pacific the c~,responding frequencies are 70 and 40 o,/, for winter, and 30 and 20 ~ for summer, wl~ere the secondary spatial maxima apply only to the eastern tropical Pacific; in the western tropical Pacific there seem to be no secondary spatial maxima as the frequencies drop to 10 and 2 " for the winter and summer season respectively. The Pacific distributional pattern is somewhat unexpected, particularly the subdued sea-state in the western tropical Pacific. Although the strength of the easterly trade winds averages about one or two Beaufort numbers less than that of the westerlies, one would expect that the trade winds' directional and temporal coherence would cause high persistency of waves. Moreover, one would expect that high waves would be more persistent downwind in the trade wind belt than upwind. Perhaps this enigma exists only as a result of insufficient data. Sea-state and wind observations are fewer in the mid-regions of the Pacific They are fewer still in the southern oceans (including all of the Indian Ocean), for whi('b only old and sketchy wind-rose data exist and sea-state charts are not available. The foregoing analysis is based on wave- and wind-charts published in the Atlas for Mariners (U.S. Navy Hydrographic Office 1959, now U.S. Naval Oceanographic Office). Obviously a more adequate compilation of wave statistics is essential for assessing the wave-power resource. Better wave statistics would also serve the various needs and interests of many national and international agencies whose representatives have called for the creation of a Northern Hemisphere Wave Atlas. 2. THE WAVE PUMP AND ITS PERFORMANCE The Isaacs wave pump is illustrated in Fig. I. It consists of a vertical riser containing a flapper valve and a buoyant float at the surface; slack tethered, it responds directly to wave motion. During operation, the flapper valve closes for approximately half the wave cycle, forcing the entrained water column to follow the upward motion of the float. As the float starts to descend on the ocean surface, inertial forces maintain the entrained water on an upwards course, carrying it higher than the wave height. Subsequent cycles raise this water successively higher until pressure suitable for power generation is reached. The wave train maintains water flow under pressure. The pressure is limited by the length of" the pipe and by the prevailing sea-state. This water can be accumulated in a pressure chamber and bled off through a turbine. On a test cruise in 1973, a 200 ft long pump magnified ninefold the pressure head of 6 ft waves. A 300 ft model pump has magnified the pressure head over 20 times. Details of the pump's operation have been published elsewhere. (Isaacs. Castel and Wick, 1976). 3. RESULTS OF THE HAWAII TEST NOVEMBER 1976-MARCH t977 With support provided by the State of Hawaii to the Natural Energy Laboratory of Hawaii, personnel affiliated with Scripps Institution of Oceanography (SIO) and the
The Isaacs wave-energy pump
237
Reservoir TurbogenereforE
(- -~Valve
./\ FIG. 1. Foundation for Ocean Research (FOR), San Diego, designed, constructed, launched in Hawaiian waters and monitored a version of the [saacs wave pump. Engineer David Castei and Dr. Gerald Wick carded out the project with advice from Professor John Isaacs. The float wa,i enlarged and modified from an existing model that was tested off the coast of La Jolla in the spring of 1975 (Isaacs, Castel and Wick, 1976). The float was about 8ft diameter on the top and was shaped as a body of revolution having exponential sides. This shape enhances the pumping action. The float supported a cluster of three flexible polyethylene pipes each 300 ft long. Two of them had a 1.4 in. diameter and the third was 2 in. diameter. The one-way check valve was at the bottom of the pipes which were held taut by a 400 lb weight. On the deck the pipes led through separate valves into two accumulator tanks in series. The tanks smooth out the water flow so that it emerges from a nozzle in a steady stream. From the nozzle, the jet of water impacted upon a 12 in. Pelton wheel impulse turbine which was designed and constructed at FOR especially for this project. The turbine was linked through a water seal to a generator which was to provide electricity for a series of light globes. In laboratory tests, everything functioned as planned under the pressure and flows anticipated for the trade wind seas off Hawaii. As the generator was a standard automobile alternator, several modifications were required to adapt it to our use. In particular, pressureactivated switches connected the load onto the generator to insure that it did not overload and lug. Unfortunately, we were unable to adequately test the electrical part of the p u m p as it failed during the sea trial due to corrosion in the generator. The generator and electrical parts were placed in a water-tight compartment. But its integrity must have diminished over the six-week period while the float was in the water and the seas were unseasonally
238
Gi~RALDL. Wick and DAVIDC~,S~L
calm. The diode rectifier was attacked by salty water vapour and developed an open circuit. The calm weather we experienced was symptomatic of the very unusual weather that occurred world-wide in the winter of 1976. We did, however, obtain useful data for the flow, pressure and acceleration of the float. The flow meter was designed and built at FOR. Other parameters we had hoped to measure were the position of the check valve at the bottom of the float (open or closed) and the electrical power output. The data were telemetered on command from the float which wa~ about three miles offshore to a shore station where the data were stored in analog and digital forms. The telemetry system was designed and built by Bob Lowe of STO. In addition to its capability to transmit data to shore on command, it also could store the data on a tape recorder on board. Although we experienced a lot of problems getting the bugs out of this system, we did get some good data on the mechanical aspects of the system. The assembly and launch took place at the Naval Undersea Center (NUC) located on the marine air base at Kaneohe Bay, Oahu. We acknowledge the full cooperation and support of Captain Jesse Burks and his staff at NUC. Without their competent help, the operation would have been much more difficult. The wave pump was assembled at N U C during the last part of October and the first of November. It was launched on November 12 with the aid of a Marines' helicopter (Fig. 2) We appreciate the interest and cooperation of the Heavy Helicopter Division. It was a unique launch with the helicopter picking up the p u m p from the bay at the fuel pier and depositing it about three miles out to sea where another crew attached it to the mooring line. Considering its complexity, the entire operation went very well. Sometime during the launch or shortly after, one of the pipes broke. It was not diagnosed for two days and then could not be repaired until the sea became calm. This is one of the ironies of extracting energy from waves. We need a high sea to generate power and a calm sea to make repairs During the protracted calm from the end of November through December, it was discovered that the generator had corroded. When several attempts to repair it failed, the pumped water was released vertically into the air through a nozzle (Fig. 3). On two to three foot seas, the water continuously flowed to a height of about 20 ft. During a storm, the pressure gauge on the tank registered 40 psi discharging through a ~in. orifice giving a power of 225 W. The sea state was 6 see waves at 3-4 ft height with a power density of about 4000 W/ft. The effective diameter of the float at the pipes is about 2.5 in. giving a potential power output of about 830 W. At no-flow conditions, the p u m p amplified the wave height by a factor of 30. The p u m p was converting about 25 % of the wave energy that it intercepted. As the waves are renewable, the crucial factor is the cost/kW compared to other energy sources. It is difficult to estimate this value, but capital costs will decrease with size of the p u m p and may be as low as $350/kW. This value is for power at the p u m p : transmission also needs to be considered. Nonetheless, this source of energy may become immediately competitive in some applications. ['he action of the float conformed to our theoretical model. During the period of the tests on moderate seas, the wave pump had an output of between 100 W and 300 W. Most of tile time the wave heights were two to four feet with occasional swells reaching six to eight feet. Figures 4 and 5 show spectra of buoy accelerations and power output. They were taken on different days. The units for acceleration are m/sec z, and for power, watts. In order to determine the total output, the power curve must be integrated. Subsequent
Fro. 2,
The Isaacs wave-energy pump Period,
IO000 8.000 I '
l
J
4,000 ['
241
sec
2000 I
r
~
I
I000 I
,
~
I
"'l
J
,
Wovepurnp
spct
Tape wove2 File 72 CH. I Power • CH, 3 Buoy occeleretior,
4-
N:I024 (data somples) (2= groups of 4 AT= 0.250 sec, ~ F = 00156 HZ,
~J
IST
,o-
t
I
COG2 0r25
l
I
L
,,
0250
,
I
l
J
~
I
,
,
0500 Frequency,
I/2
plot
, 2000
HZ
2 0
a.
o
i,
....
,ll,rl
'
,
l,,
(
F I G . 4.
analysis will optimize the pump parameters and determine a transfer function from sea state to power output. On March 23, 1977, during a storm, the float broke its moorings and washed up on a nearby island, Chinaman's Hat. Thus it survived for over four months with commendable performance considering the modest funds that were available. After December, the telemetry system started giving problems and restricted data collection. Also there was another break in the pipes, but that was repaired. As a result of this project, one of the few wave energy conversion devices tested in the open sea, we are encouraged that all the fundamental problems in extracting wave energy are solvable. With proper scaling and careful construction, the wave pumps could at short notice provide thousands of watts to the State of Hawaii, and even millions of watts at a later time.
_4_
rO~
GERALD L. W I C K a n d DAVID CASTEL
tO000 8.000 [ I
'
4000 I
Period, sec 2..000
,
'"T
i
I
"
'
tO0~; '
~
I
I
I ~ ' 'I
I
Wovepump
I 1
i0 ~
'
Tope wave2 File 53
Buoy
occeleration,
•~ iOc N , 4 0 9 6 (data ~mples)
~0-
Q- groups of, 16 A T - 02..50 sile, ,~ F=0,0156 HZ I IST I/2 plot 0062 0125
0250
0500
Frb"quency,
:000
HZ
FIt;. ~.
Acknowledgements --We acknowledge support 11ollt the State or' Hawaii Departnlertt o[ Planning and Economic Development and the Foundation for Ocean Research.
I~.EFER E N C ES ISAACS, J. b., CASrEL, D. and WI(:K, G. L. 1976. Utilization of the energy in ocean waves. Oceatl Engng 3,
175-187. lSAACS, J. D., WICK, G. L. and SCHMrrT, W. R. t976. "Utilization of the energy in ocean waves", Institute of Marine Resources, University of California, IMR reference No. 76-10, 37 pp. U.S. Navy Hydrographic Office. 1959. Atlas for Mariners, vols. I and II. WICK, G. L. and SCHMITr, W. R. 1977. Prospects for renewable energy from the sea. Mar. Tech. Soc. J, !1, 16-21.
THE FIELD
TESTS
ISAACS
OFF
WAVE-ENERGY
0029-8018/78/0801-0235
$02.00/0
PUMP:
THE COAST OF KANEOHE NOVEMBER 1976 MARCH 1977
BAY,
HAWAII
GERALD L. WICK and DAVID CAS]TEL Scripps Institution of Oceanography, Institute ot" Marine Resources, University of California, [~ Jolla 92093, U.S.A. and Foundation for Ocean Research, San Diego, California 92121, U.S.A. Abstract---Field tests conducted on a wave-power pump showed that this simple design conceived by Professor John D. lsaacs is suitable for wave-energy extraction around the Hawaiian Islands. In the small model tested, over 200 W of mechanical power were produced. Larger models could extract several orders of magnitude more power. Further research needs to be done with prototype models. The transmission of the power to the shore still needs to be examined. A by-product of the operation of the pump is nutrient rich water pumped from the bottom of the pipe. In our test, the water was pumped from 300 ft. It is feasible with a similar design that the water can be pumped from 1000 ft where the water is richer in nutrients. This water could then be used to stimulate the growth of marine plants. l~ A S S E S S M E N T
OF
EXTENT
AND DISTRIBUTION IN T H E O C E A N S
OF
WIND-WAVE
ENERGY
THE ENERGY and power in ocean wind waves can be considerable. A typical average sea state has approximately 1,5 m waves at an 8 sec period. These waves correspond to a mean flux of wave power across a section of the ocean of the order of 10 kW/m. Summed over the entire ice-free ocean, the total power available would be 2.7 x 1012 W. Locally this flux varies from 103 kW/m in gales, to low values of 10 3 kW/m or less. Our estimate of the total power of 2.7 × 10a2 W is about 1 0 ~ of the total projected power needs of man in 2000 A.D. ([saacs; Wick and Schmitt, 1977). The power is, of course, transmitted locally and at great distance by water motion from the effects of wind acting on the ocean surface. The water surface acts as a great transmission belt delivering integrated wind power from distant disturbances. Thus, both in the short and long term, waves and wave power are more persistent than wind and wind power. There is an optimal length of fetch for the most efficient transfer of power from wind to wave. At that point, wave height and period are usually shorter than those of a fully developed sea. Where winds persist over long distances, as in the tradewind belt, the wave could therefore be cropped repeatedly; the shorter period associated with cropping is generally advantageous to conversion systems, thus utilization makes wave power not only greater, but also more readily available. In this way, as much as 35 x 10is W of mechanical power might be extractable from wind waves (Isaacs, Wick and Schmitl, 1976). Waves vary in several ways. In the short term, their period and wave length fluctuate, necessitating a non-resonant non-synchronous system to extract their power, and their height varies, requiring some short-term power reservoir. This is of fundamental importance to the design of wave-power devices and has been discussed in a previous paper (Isaacs, Castel and Wick, 1976). 235
236
GERALDL. WICKand DAVIDCASTEL
The waves' long-term persistency depends primarily on location. Wave charts of oceans of the northern hemisphere generally indicate two maxima roughly corresponding to the latitudes of the easterly trade winds, such as those at Hawaii, and of the westerlies. The primary maximum is centered at about 55°N. The charts also show that the waves are most energetic in winter over the entire ocean. At all seasons, the sea-states usually diminish near continental coastlines and near the ice cover. For the two spatial maxima t,f the North Atlantic, the percentage frequency of waves greater than 5 ft is 80 and 50~/o for the winter months, 50 and 2 0 ~ for the lowest three months (summer). In the North Pacific the c~,responding frequencies are 70 and 40 o,/, for winter, and 30 and 20 ~ for summer, wl~ere the secondary spatial maxima apply only to the eastern tropical Pacific; in the western tropical Pacific there seem to be no secondary spatial maxima as the frequencies drop to 10 and 2 " for the winter and summer season respectively. The Pacific distributional pattern is somewhat unexpected, particularly the subdued sea-state in the western tropical Pacific. Although the strength of the easterly trade winds averages about one or two Beaufort numbers less than that of the westerlies, one would expect that the trade winds' directional and temporal coherence would cause high persistency of waves. Moreover, one would expect that high waves would be more persistent downwind in the trade wind belt than upwind. Perhaps this enigma exists only as a result of insufficient data. Sea-state and wind observations are fewer in the mid-regions of the Pacific They are fewer still in the southern oceans (including all of the Indian Ocean), for whi('b only old and sketchy wind-rose data exist and sea-state charts are not available. The foregoing analysis is based on wave- and wind-charts published in the Atlas for Mariners (U.S. Navy Hydrographic Office 1959, now U.S. Naval Oceanographic Office). Obviously a more adequate compilation of wave statistics is essential for assessing the wave-power resource. Better wave statistics would also serve the various needs and interests of many national and international agencies whose representatives have called for the creation of a Northern Hemisphere Wave Atlas. 2. THE WAVE PUMP AND ITS PERFORMANCE The Isaacs wave pump is illustrated in Fig. I. It consists of a vertical riser containing a flapper valve and a buoyant float at the surface; slack tethered, it responds directly to wave motion. During operation, the flapper valve closes for approximately half the wave cycle, forcing the entrained water column to follow the upward motion of the float. As the float starts to descend on the ocean surface, inertial forces maintain the entrained water on an upwards course, carrying it higher than the wave height. Subsequent cycles raise this water successively higher until pressure suitable for power generation is reached. The wave train maintains water flow under pressure. The pressure is limited by the length of" the pipe and by the prevailing sea-state. This water can be accumulated in a pressure chamber and bled off through a turbine. On a test cruise in 1973, a 200 ft long pump magnified ninefold the pressure head of 6 ft waves. A 300 ft model pump has magnified the pressure head over 20 times. Details of the pump's operation have been published elsewhere. (Isaacs. Castel and Wick, 1976). 3. RESULTS OF THE HAWAII TEST NOVEMBER 1976-MARCH t977 With support provided by the State of Hawaii to the Natural Energy Laboratory of Hawaii, personnel affiliated with Scripps Institution of Oceanography (SIO) and the
The Isaacs wave-energy pump
237
Reservoir TurbogenereforE
(- -~Valve
./\ FIG. 1. Foundation for Ocean Research (FOR), San Diego, designed, constructed, launched in Hawaiian waters and monitored a version of the [saacs wave pump. Engineer David Castei and Dr. Gerald Wick carded out the project with advice from Professor John Isaacs. The float wa,i enlarged and modified from an existing model that was tested off the coast of La Jolla in the spring of 1975 (Isaacs, Castel and Wick, 1976). The float was about 8ft diameter on the top and was shaped as a body of revolution having exponential sides. This shape enhances the pumping action. The float supported a cluster of three flexible polyethylene pipes each 300 ft long. Two of them had a 1.4 in. diameter and the third was 2 in. diameter. The one-way check valve was at the bottom of the pipes which were held taut by a 400 lb weight. On the deck the pipes led through separate valves into two accumulator tanks in series. The tanks smooth out the water flow so that it emerges from a nozzle in a steady stream. From the nozzle, the jet of water impacted upon a 12 in. Pelton wheel impulse turbine which was designed and constructed at FOR especially for this project. The turbine was linked through a water seal to a generator which was to provide electricity for a series of light globes. In laboratory tests, everything functioned as planned under the pressure and flows anticipated for the trade wind seas off Hawaii. As the generator was a standard automobile alternator, several modifications were required to adapt it to our use. In particular, pressureactivated switches connected the load onto the generator to insure that it did not overload and lug. Unfortunately, we were unable to adequately test the electrical part of the p u m p as it failed during the sea trial due to corrosion in the generator. The generator and electrical parts were placed in a water-tight compartment. But its integrity must have diminished over the six-week period while the float was in the water and the seas were unseasonally
238
Gi~RALDL. Wick and DAVIDC~,S~L
calm. The diode rectifier was attacked by salty water vapour and developed an open circuit. The calm weather we experienced was symptomatic of the very unusual weather that occurred world-wide in the winter of 1976. We did, however, obtain useful data for the flow, pressure and acceleration of the float. The flow meter was designed and built at FOR. Other parameters we had hoped to measure were the position of the check valve at the bottom of the float (open or closed) and the electrical power output. The data were telemetered on command from the float which wa~ about three miles offshore to a shore station where the data were stored in analog and digital forms. The telemetry system was designed and built by Bob Lowe of STO. In addition to its capability to transmit data to shore on command, it also could store the data on a tape recorder on board. Although we experienced a lot of problems getting the bugs out of this system, we did get some good data on the mechanical aspects of the system. The assembly and launch took place at the Naval Undersea Center (NUC) located on the marine air base at Kaneohe Bay, Oahu. We acknowledge the full cooperation and support of Captain Jesse Burks and his staff at NUC. Without their competent help, the operation would have been much more difficult. The wave pump was assembled at N U C during the last part of October and the first of November. It was launched on November 12 with the aid of a Marines' helicopter (Fig. 2) We appreciate the interest and cooperation of the Heavy Helicopter Division. It was a unique launch with the helicopter picking up the p u m p from the bay at the fuel pier and depositing it about three miles out to sea where another crew attached it to the mooring line. Considering its complexity, the entire operation went very well. Sometime during the launch or shortly after, one of the pipes broke. It was not diagnosed for two days and then could not be repaired until the sea became calm. This is one of the ironies of extracting energy from waves. We need a high sea to generate power and a calm sea to make repairs During the protracted calm from the end of November through December, it was discovered that the generator had corroded. When several attempts to repair it failed, the pumped water was released vertically into the air through a nozzle (Fig. 3). On two to three foot seas, the water continuously flowed to a height of about 20 ft. During a storm, the pressure gauge on the tank registered 40 psi discharging through a ~in. orifice giving a power of 225 W. The sea state was 6 see waves at 3-4 ft height with a power density of about 4000 W/ft. The effective diameter of the float at the pipes is about 2.5 in. giving a potential power output of about 830 W. At no-flow conditions, the p u m p amplified the wave height by a factor of 30. The p u m p was converting about 25 % of the wave energy that it intercepted. As the waves are renewable, the crucial factor is the cost/kW compared to other energy sources. It is difficult to estimate this value, but capital costs will decrease with size of the p u m p and may be as low as $350/kW. This value is for power at the p u m p : transmission also needs to be considered. Nonetheless, this source of energy may become immediately competitive in some applications. ['he action of the float conformed to our theoretical model. During the period of the tests on moderate seas, the wave pump had an output of between 100 W and 300 W. Most of tile time the wave heights were two to four feet with occasional swells reaching six to eight feet. Figures 4 and 5 show spectra of buoy accelerations and power output. They were taken on different days. The units for acceleration are m/sec z, and for power, watts. In order to determine the total output, the power curve must be integrated. Subsequent
Fro. 2,
The Isaacs wave-energy pump Period,
IO000 8.000 I '
l
J
4,000 ['
241
sec
2000 I
r
~
I
I000 I
,
~
I
"'l
J
,
Wovepurnp
spct
Tape wove2 File 72 CH. I Power • CH, 3 Buoy occeleretior,
4-
N:I024 (data somples) (2= groups of 4 AT= 0.250 sec, ~ F = 00156 HZ,
~J
IST
,o-
t
I
COG2 0r25
l
I
L
,,
0250
,
I
l
J
~
I
,
,
0500 Frequency,
I/2
plot
, 2000
HZ
2 0
a.
o
i,
....
,ll,rl
'
,
l,,
(
F I G . 4.
analysis will optimize the pump parameters and determine a transfer function from sea state to power output. On March 23, 1977, during a storm, the float broke its moorings and washed up on a nearby island, Chinaman's Hat. Thus it survived for over four months with commendable performance considering the modest funds that were available. After December, the telemetry system started giving problems and restricted data collection. Also there was another break in the pipes, but that was repaired. As a result of this project, one of the few wave energy conversion devices tested in the open sea, we are encouraged that all the fundamental problems in extracting wave energy are solvable. With proper scaling and careful construction, the wave pumps could at short notice provide thousands of watts to the State of Hawaii, and even millions of watts at a later time.
_4_
rO~
GERALD L. W I C K a n d DAVID CASTEL
tO000 8.000 [ I
'
4000 I
Period, sec 2..000
,
'"T
i
I
"
'
tO0~; '
~
I
I
I ~ ' 'I
I
Wovepump
I 1
i0 ~
'
Tope wave2 File 53
Buoy
occeleration,
•~ iOc N , 4 0 9 6 (data ~mples)
~0-
Q- groups of, 16 A T - 02..50 sile, ,~ F=0,0156 HZ I IST I/2 plot 0062 0125
0250
0500
Frb"quency,
:000
HZ
FIt;. ~.
Acknowledgements --We acknowledge support 11ollt the State or' Hawaii Departnlertt o[ Planning and Economic Development and the Foundation for Ocean Research.
I~.EFER E N C ES ISAACS, J. b., CASrEL, D. and WI(:K, G. L. 1976. Utilization of the energy in ocean waves. Oceatl Engng 3,
175-187. lSAACS, J. D., WICK, G. L. and SCHMrrT, W. R. t976. "Utilization of the energy in ocean waves", Institute of Marine Resources, University of California, IMR reference No. 76-10, 37 pp. U.S. Navy Hydrographic Office. 1959. Atlas for Mariners, vols. I and II. WICK, G. L. and SCHMITr, W. R. 1977. Prospects for renewable energy from the sea. Mar. Tech. Soc. J, !1, 16-21.