View non-flash version
July 2013 www.sname.org/sname/mt (mt notes) industrial applications have all been proposed. erefore, in addition to a focus on accuracy and user friendliness in common with Tidal Bladed, the development of WaveDyn also focused on exibility and the ability to model a wide range of structures and WEC types. WaveDyn uses a exible, multi-body calculation code for use in time domain performance and loading simulations for single machines and small WEC arrays. e multi-body formulation enables a WEC simulation model to be built up by joining any number of self-con- tained bodies, each with a range of physical properties. e bodies that are linked together can have structural, hydrodynamic, PTO, and moorings components. All of the applicable loads and dynamic response of the system are then coupled in the time domain solver to produce the simulation results. A variable time step, adaptive order algorithm is employed by the solver, so that WaveDyn adjusts to the complexity of the built-up model. e active adjustment to the speed of the system dynamics facilitates rapid, desktop PC simulation times without compromising the accuracy of results. It also was important that the tool enabled a wide range of wave conditions as input, from measured sea states to parameterized spectral shapes (including directional spectra). e current version of the tool can incorporate nonlinear hydrostatic loads and rst-order hydrodynamic loads (diraction and radiation forces) by processing data output from an external potential ow solver. As such, at this stage of its development, the tool is primarily valid for simulation of WEC per- formance and operational loading, as the models may break down in extreme seas where the assumptions behind linear hydrodynamics may no longer hold. Commercial work undertaken by GL GH with spe- cic technology developers, such as Columbia Power Technologies Inc. in the United States and AW-Energy Oy in Finland, has provided validation data sets that cover very dierent machine types and subsystems. We also are leading the Performance Assessment of Wave and Tidal Array Systems (PerAWaT) project commissioned and funded by the ETI. is provided large-scale tank testing of high-precision physical models for two dis- tinctly dierent WEC concepts?Wavebob and Pelamis, in collaboration with Wavebob Ltd. and Pelamis Wave Power Ltd., as well as comparisons with high-delity, fully non-linear hydrodynamic models. The simulation of large-scale (approximately 1:20), high-specication, experimental models of the commercial WEC developed by Wavebob Ltd. dem- onstrates how the design tool can be used to support technology development. e Wavebob models were tested in the seakeeping and manoeuvring basin at MARIN, in the Netherlands, which is one of the largest facilities of its type in the world. Tests with single mod- els were conducted in November 2011, to gather data on the behavior of the device in isolation. To investigate the interactions between WECs operating in an array, subse- quent tests were conducted in March 2012 with a group of four models. Infrared motion capture equipment was used to track the motions of the WEC(s) in six degrees of freedom. e PTO joints contained computer-controlled servo motors in order to faithfully represent the proper- ties of the proposed full-scale design. Tests were carried out in a range of wave conditions, from sinusoidal regu- lar waves through to irregular, directionally spread waves that were representative of realistic sea conditions. is testing resulted in a comprehensive data set that could be compared to the numerical models developed with WaveDyn, validating the accuracy of the simulations for use in design development. Moving forward A primary goal behind the development of these tools was to establish a standard platform for the design of MHK technologies. Their development has signifi- cantly advanced the understanding of individual device loading and performance, and is also feeding in to an understanding of the interactions between devices that will be crucial for planning commercial-scale arrays of WECs and marine current turbines. Future tools being developed under the ETI commissioned and funded PerAWaT project, WaveFarmer and TidalFarmer, build upon this knowledge to provide wave and tidal farm planning and array performance calculation tools. Meanwhile, developing fully-coupled design tools sophisticated enough to simulate all of the applicable loads on MHK systems, while capturing the physics of the systems correctly, and still enabling those simulations to be run rapidly on desktop PCs, is an ongoing process. Further validation and improvement is being pursued, and as more full-scale prototypes are tested in relevant ocean conditions, the design tools that helped enable the deployment of those prototypes also will benet. MTJarett Goldsmith is an engineer and project manager in wave and tidal energy at GL Garrad Hassan. Developing Design Tools continued