A Numerical Approach for Hydrodynamic Performance Evaluation of Multi-Degree-Of-Freedom Floating Oscillating Water Column (Owc) Devices
A numerical approach has been developed in this study for hydrodynamic analysis of complex-shaped oscillating water column (OWC) converters. Physically, in the circumstance when the device is free to move or moored in waves, the airflow movement inside the chamber is coupled tightly with the changing of internal fluid surface and the hydrodynamic response of the device. By taking these coupling effects into account, appropriate boundary integral equations are formulated with supplemental theoretical relations. The boundary value problem is then solved using a higher-order boundary element method (HOBEM). After obtaining the wave force and dynamic air force, the coupled motions and hydrodynamic efficiency are evaluated by integration. In particular, unlike the conventional methods limited to fixed OWCs, the proposed method is proved applicable to those floating with coupled rigid body motions. An optimal turbine parameter is hence mathematically derived to maximise wave power absorption. Besides the linear quantities, nonlinear wave drift loads are evaluated via a newly derived formulation that accounts for the far-field contribution as well as the oscillating air pressure over the internal fluid surface. Based on the above methodology and the resulting tool, numerical studies are carried out for cylindrical devices. Different modes of body motion and typical free-surface oscillation modes in the chamber are analysed and discussed. It is found that, for an OWC with an attached arc-shaped plate or connected to a submerged caisson, its wave power absorption can be characterised by a series of apparent peaks. One is associated with resonant piston motion of the internal fluid, while the others are in close proximity to the resonance frequencies of body motions involving surge, heave, and pitch. Numerical results also indicate the benefits of floating OWCs from the coupled rigid-body motion modes and the OWC's resonance, expanding the frequency range of efficient conversion and improving the device's adaptability to variable oceanic environments
Year of publication: |
[2022]
|
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Authors: | Cong, Peiwen ; Teng, Bin ; Liu, Yingyi ; Ning, Dezhi |
Publisher: |
[S.l.] : SSRN |
Saved in:
freely available
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