Previous Research
"An Investigation Into the Hydrodynamic Efficiency of an Oscillating Water Column" in Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2007 - Michael T. Morris-Thomas, Rohan J. Irvin, Krish P. Thiagarajan.
This report describes an experimental study on the wave interaction with a 1:12.5 scale model of an oscillating water column to examine energy efficiencies for power take-off. With a wave environment comprised of plane progressive waves of steepnesses ranging from kA=0.01 to 0.22 and water depth ratios varying from kh=0.30 to 3.72 where k, A and h represent the wave number, wave amplitude and water depth, respectively. The focus of the report is on the influence of the front wall geometry on OWC's performance. Two-dimensional inviscid theory is compared to experimental results and is used to explain noted trends. It has revealed that the efficiency depends heavily on the natural frequency of the OWC and the geometry of the front wall. A peak hydrodynamic efficiency of ~70% was achieved by all front wall geometries but one which was the one with a rounded aperture which had a peak efficiency of over 80%. It is believed that this increase in efficiency was caused by a decrease in flow separation at the aperture. It is known that an increase in front wall sumbergence reduces the natural frequency of the system but it was noted that it also affected efficiency for large values Kh
This report describes an experimental study on the wave interaction with a 1:12.5 scale model of an oscillating water column to examine energy efficiencies for power take-off. With a wave environment comprised of plane progressive waves of steepnesses ranging from kA=0.01 to 0.22 and water depth ratios varying from kh=0.30 to 3.72 where k, A and h represent the wave number, wave amplitude and water depth, respectively. The focus of the report is on the influence of the front wall geometry on OWC's performance. Two-dimensional inviscid theory is compared to experimental results and is used to explain noted trends. It has revealed that the efficiency depends heavily on the natural frequency of the OWC and the geometry of the front wall. A peak hydrodynamic efficiency of ~70% was achieved by all front wall geometries but one which was the one with a rounded aperture which had a peak efficiency of over 80%. It is believed that this increase in efficiency was caused by a decrease in flow separation at the aperture. It is known that an increase in front wall sumbergence reduces the natural frequency of the system but it was noted that it also affected efficiency for large values Kh
"Model studies of Oscillating Water Column Wave-Energy Device" in Journal of Energy Engineering, Apr 1995, v 121, n 1, p 14-27 - Paul Mario Koola, M. Ravindran P. A
Paper highlighting the results of the scale model experiments carried out on a 1:100 scale prototype wave energy caisson. The performance of a harbour OWC device is influenced by the design period of the wave and the water depth at the site and the average site conditions were: A period of 10s, water depth of 12m and an average significant wave height of 1.52m. Monochromatic wave test were compared to an irregular sea and the effect of geometric parameters are discussed and compared with a possible theoretical maximum and optimized parameters selected for the prototype. 1s period chosen as the energy period of the model. Monochromatic wave-height was obtained by equating the power P in a random see to that in a regular sinusoidal wave. Various dimensions of the device were found to strongly influence the frequency response of the device such as Width, Length of device, harbour length etc. These parameters were varied until peak performance was achieved at 1 Hz wave frequency - the scaled-down frequency at the site. Thicker walls with rounded edges increased the efficiency by about 20% but this improvement would have to offset the additional cost of contruction. Very good performances of nearly 75% of theoretical estimates were achieved.
Paper highlighting the results of the scale model experiments carried out on a 1:100 scale prototype wave energy caisson. The performance of a harbour OWC device is influenced by the design period of the wave and the water depth at the site and the average site conditions were: A period of 10s, water depth of 12m and an average significant wave height of 1.52m. Monochromatic wave test were compared to an irregular sea and the effect of geometric parameters are discussed and compared with a possible theoretical maximum and optimized parameters selected for the prototype. 1s period chosen as the energy period of the model. Monochromatic wave-height was obtained by equating the power P in a random see to that in a regular sinusoidal wave. Various dimensions of the device were found to strongly influence the frequency response of the device such as Width, Length of device, harbour length etc. These parameters were varied until peak performance was achieved at 1 Hz wave frequency - the scaled-down frequency at the site. Thicker walls with rounded edges increased the efficiency by about 20% but this improvement would have to offset the additional cost of contruction. Very good performances of nearly 75% of theoretical estimates were achieved.
"Analytical and experimental investigation on the hydrodynamic performance of onshore wave-power devices" in Ocean Engineering, Jul 2002, v 29, n 8, p 871-885 - D.J. Wang, M. Katory, Y.S. Li
A 1:12 scale model of an OWC is used to verify a numerical model for the hydrodynamic performance of an OWC. The effect of bottom slope on performance is also investigated analytically and experimentally. The models performance was "numerically studied within linear wave theory by using a boundary element method based on the Wehausen and Laitine 3D shallow water Green's function". In the model experiments, the wave periods ranged from 0.91 to 3.02 s which for the prototype corresponds to a frequency range of 0.6 to 2.0 rad/s. For one of the cases, several levels of damping were assumed in the numerical calculations and it was found that the calculated results all agreed with experimental data. Results agreed well for the pressure ratios and capture width except near resonant frequencies. As the slope of the bottom increases, the peaks of capture-width ratios will have lower frequencies. Changes in water depth at the shoreline also affect the hydrodynamic performance significantly.
A 1:12 scale model of an OWC is used to verify a numerical model for the hydrodynamic performance of an OWC. The effect of bottom slope on performance is also investigated analytically and experimentally. The models performance was "numerically studied within linear wave theory by using a boundary element method based on the Wehausen and Laitine 3D shallow water Green's function". In the model experiments, the wave periods ranged from 0.91 to 3.02 s which for the prototype corresponds to a frequency range of 0.6 to 2.0 rad/s. For one of the cases, several levels of damping were assumed in the numerical calculations and it was found that the calculated results all agreed with experimental data. Results agreed well for the pressure ratios and capture width except near resonant frequencies. As the slope of the bottom increases, the peaks of capture-width ratios will have lower frequencies. Changes in water depth at the shoreline also affect the hydrodynamic performance significantly.
"Scale 1:10 Wave Flume Experiments on ITT Oscillating Water Column Wave Energy Device" in Proceedings of International Scientific Committee of the International Symposium on Ocean Energy Development ODEC'93, 26-27 August 1993, Muroran, Hokkaido, Japan - Kai-Uwe Graw
Presentation of tests done on a 1:10 scale model of an oscillating water column for the Indian Institute of Technology (IIT) at the technical University of Berlin. Flow conditions around the chamber with orthogonal wave approach under 20 degrees were smooth and calm. flow separation, secondary waves and eddis were observed which did not affect OWC performance. No dangerous resonant motions between walls were detectable. Two series of tests with regular waves were performed: one varied the period and the other the height of the wave. Results showed large scattering of data which was attributed to the inertia of the OWC. it was concluded that the behaviour inside the chamber does not change significantly when the orifice diameter, the direction of wave approach or the water level is changed. For wave periods smaller than the design period, the second harmonic superimposed on the chamber pressure appeared. This is important as it gave pressure values linked to waves of much higher energies. measured values of the capture factor are less than for previous tests on a 1:100 scale model but show the same tendencies.
Presentation of tests done on a 1:10 scale model of an oscillating water column for the Indian Institute of Technology (IIT) at the technical University of Berlin. Flow conditions around the chamber with orthogonal wave approach under 20 degrees were smooth and calm. flow separation, secondary waves and eddis were observed which did not affect OWC performance. No dangerous resonant motions between walls were detectable. Two series of tests with regular waves were performed: one varied the period and the other the height of the wave. Results showed large scattering of data which was attributed to the inertia of the OWC. it was concluded that the behaviour inside the chamber does not change significantly when the orifice diameter, the direction of wave approach or the water level is changed. For wave periods smaller than the design period, the second harmonic superimposed on the chamber pressure appeared. This is important as it gave pressure values linked to waves of much higher energies. measured values of the capture factor are less than for previous tests on a 1:100 scale model but show the same tendencies.