Solomonidis, Christos; (1992) Parallel computation in the synthesis of random waves by digital filtering. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is concerned with the development of algorithmic tools for the simulation of multidirectional random wave kinematics. The digital filtering method is adopted since it affords the possibility of uninterrupted generation of random records of arbitrary duration. An implementation of the proposed method on parallel processors is presented and its performance discussed. A review of the methods used for wave simulation is first presented. A distinction is drawn between general random field simulations and the simulation of random wave fields obeying linear wave mechanics in a dispersive medium. In the former case the appropriate ARMA model is three dimensional. In the case of the medium obeying wave mechanics and admitting a dispersion relation, like the sea waves, the use of the directional spreading function and a one dimensional propagation law makes it possible to limit the ARMA model to a univariate case. In the filtering method proposed here, the surface elevation is generated at one gridpoint and transmitted to other gridpoints by further filtering operations. Recursive filters developed in previous work are adopted for the first part of the algorithm. For the transmission in the horizontal direction, recursive digital filters are designed here and proposed as more cost effective alternatives to the existing FIR filters. The errors committed by the two methods are compared. The results are also checked by examining the first to forth statistical moments. As a further application to the method, the modification of the wave field around a large body is studied by the linear diffraction theory. Digital filters that incorporate the contribution of the diffracted waves in the total motion are designed. The implementation of the proposed algorithm on a parallel computer is studied Various configurations on an eight transputer board hosted in a standard PC are examined and aspects of optimizing the performance of the parallel program are presented. The resulting high speed continuous generation of waves at the nodes of a large spatial grid can be used for real time visual display. It may also be fed into a dynamical analysis of an offshore structure, with the ultimate purpose of estimating the temporal statistics of the response.

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