Parallel efficiency of a boundary integral equation method for nonlinear water waves

We describe the application of domain decomposition on a boundary integral method for the study of nonlinear surface waves on water in a test case for which the domain decomposition approach is an important tool to reduce the computational effort. An important aspect is the determination of the optimum number of domains for a given parallel architecture. Previous work on hetero- geneous clusters of workstations is extended to (dedicated) parallel platforms. For these systems a better indication of the parallel performance of the domain decomposition method is obtained because of the absence of varying speed of the processing elements

Resonant behaviour of an oscillating wave energy converter in a channel

A mathematical model is developed to study the behaviour of an oscillating wave energy converter in a channel. During recent laboratory tests in a wave tank, peaks in the hydrodynamic actions on the converter occurred at certain frequencies of the incident waves. This resonant mechanism is known to be generated by the transverse sloshing modes of the channel. Here the influence of the channel sloshing modes on the performance of the device is further investigated. Within the framework of a linear inviscid potential-flow theory, application of the Green theorem yields a hypersingular integral equation for the velocity potential in the fluid domain. The solution is found in terms of a fast-converging series of Chebyshev polynomials of the second kind. The physical behaviour of the system is then analysed, showing sensitivity of the resonant sloshing modes to the geometry of the device, that concurs in increasing the maximum efficiency. Analytical results are validated with available numerical and experimental data.Comment: Accepted for publicatio

Time domain prediction of first- and second-order wave forces on rigid and elastic floating bodies

The application and development of a transient three-dimensional numerical code ITU-WAVE which is based on panel method, potential theory and Neumann-Kelvin linearization is presented for the prediction of hydrodynamics characteristics of mono-hull and multi-hull floating bodies. The time histories of unsteady motions in ambient incident waves are directly presented with regards to impulse response functions (IRFs) in time. The first order steady forces of wave-resistance, sinkage force and trim moment are solved as the steady state limit of surge radiation IRFs. The numerical prediction of the second order mean force which can be computed from quadratic product of first-order quantities is presented using near-field method based on the direct pressure integration over floating body in time domain. The hydrodynamic and structural parts are fully coupled through modal analysis for the solution of hydroelastic problem in which Euler-Bernoulli beam is used for the structural analysis. A stiff structure is then studied assuming that contributions of rigid body modes are much bigger than elastic modes. A discrete control of latching is used to increase the bandwidth of the efficiency of Wave Energy Converters (WEC). ITU-WAVE numerical results for different floating

Wave-Slope Soaring of the Brown Pelican

We theoretically assess the energy savings associated with wave-slope soaring of the brown pelican over near-shoaling ocean surface waves. The steady, constant altitude flight of a pelican is analyzed as a control. The airflow induced by a passing wave, or the “wave-induced wind,” is theoretically analyzed for shallow water solitary waves. These waves are assumed to be well described by the KdV equation. We use potential flow theory to describe the wave- induced wind. Using a regular expansion of the Stokes stream function and the Green’s function for Laplace in 2D with Dirichlet boundary conditions, we obtain integral expressions for the horizontal and vertical components of the wave-induced wind in a frame of reference moving with the wave. The theory results in expressions wherein provided with the amplitude and period of an incoming swell, horizontal and vertical components of the wave-induced wind in a frame of reference moving with the wave are produced. Wave-slope soaring flight is analyzed over near-shoaling solitary waves on size scales corresponding to wind swell, with amplitude of 1m and period of 10s. We find an upper bound benefit of 57.6% decrease in required mechanical power output as compared with flight out of ground effect and 52.4% benefit as compared with standard ground effect flight. The theory in this work define sufficient evidence that wave- slope soaring could become a viable strategy for energy efficient flight of unmanned autonomous vehicles (UAVs)