Renewable Energy
pneumatic and hydraulic conversion steps and their associated losses. Te company believes that direct- drive systems are the future of wave power because they are more efficient and reliable as well as easier to maintain. Te number-one design challenge was to optimise the design of the buoy to maximise the proportion of wave power transferred to the buoy. Relative capture width is a dimensionless measure of the efficiency of the device in capturing the available energy of the wave. A relative capture width of 1 means that the buoy has captured 100 per cent of available wave energy.
As Columbia Power set out to determine the optimal shape for the buoy, engineers looked at five different hydrodynamic simulation software packages. Te company selected ANSYS AQWA software because of its ease of use, and tests showed that it provided a better match with physical experiments than did competitive software. Columbia Power also valued that ANSYS AQWA offers both frequency and time domain solutions. Frequency domain solutions are faster, which makes them ideal for quickly evaluating a large number of shapes, while time domain solutions provide the high level of accuracy needed to refine to the best shapes in the later stages of the design process. Columbia Power engineers developed an initial concept design in SolidWorks, built a prototype and tested it at 1/33 scale in the Tsunami Wave Basin at the Hinsdale Wave Laboratory at Oregon State University. Te team used high-resolution cameras to track light- emitting diodes on the buoy, measuring its motion in the waves. Engineers exported the concept design to ANSYS
AQWA software and performed a time domain simulation while using a wave climate with the same amplitude and frequency as that measured in the wave tank. Tere was a very good match between the measurements and predictions from ANSYS AQWA. Since then, engineers have used ANSYS AQWA as their primary design tool to optimise the shape of the fibre-reinforced plastic (FRP ) buoy. Columbia Power has since evaluated over 350
different geometries with ANSYS AQWA in an effort to maximise the relative capture width of the buoy. At the same time, the company worked closely with Ershigs Inc, its structural partner that produces the FRP floats, to explore the manufacturability of various shapes and to ensure that the final design can be produced at a low cost. Te company also looked at the survivability and environmental impact of proposed buoy designs. Columbia Power engineers used a sinusoidal wave shape and a suite of wave frequencies ranging from two seconds to 20 seconds for frequency domain simulations. Te response amplitude operators calculated by ANSYS AQWA software were used in a
post processing routine written by Columbia Power engineers that calculates the relative torque and speed of the buoy as well as the relative capture width. Once they felt that they were close to an optimal shape for the buoy, Columbia Power engineers moved to time domain modelling, which makes it possible to evaluate the nonlinear effects of the waves. Te team evaluated the shapes that had proven best in frequency domain modelling against a variety of wave climates, including those found at seven different coastal locations around the world. At the same time, engineers began optimising the power takeoff system that converts mechanical energy into electrical energy. ANSYS AQWA model results from frequency domain models were post processed in Matlab Simulink to incorporate the power takeoff reaction torque and to compute power output. Te ANSYS AQWA time domain models were coupled to a DLL that simulated both linear and nonlinear power takeoff operation. Te DLL for the power takeoff model was developed in Matlab Real Time. Engineers used the output from ANSYS AQWA to drive a numerical model developed in Simulink that simulates the power takeoff system and control strategy. Te control strategy tunes the power takeoff to the wave climate by changing the amount of current produced by the generator, which, in turn, changes the mechanical load placed on the system. Tis makes it possible to consider in a single model the effects of different buoy shapes, power takeoff system designs and control strategies; it also helps to determine the power that would be generated by each approach in a variety of different wave climates.
Electromagnetic simulation software Columbia Power recently began using Maxwell electromagnetic simulation software from ANSYS to optimise the design of the generator. Engineers evaluated three different electromagnetic simulation software packages and concluded that Maxwell was the easiest to use and the most stable. Maxwell is being used to analyse the electromagnetic performance of the generator while varying the air gaps between the rotor and stator, different magnet geometries, different magnet types, and different types of steel. Te overall goal is to maximise the generator’s energy output while minimising its cost. As a technology start-up with far-from unlimited funding, Columbia Power must be capital efficient. By focusing its development efforts on simulation and using physical testing judiciously as a verification tool, it is moving forward in the development process much faster than would be possible using traditional development methods. ANSYS AQWA and Maxwell simulation software enable the company to make its mistakes in the computer, where they are far less expensive than in the ocean. ●
Bradford S Lamb is President and Ken Rhinefrank is Vice President of Research and Development, Columbia Power Technologies, LLC, Corvalis, USA.
www.columbiapwr.com
52
www.engineerlive.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68