This paper describes the hardware and software currently being used at Heriot-Watt University to generate short crested seas in a 9*9m square wave basin. In addition the paper describes the principles of the systems in use and what modifications are likely in the future.
Scale model testing is an established method for evaluating designs of offshore and coastal fixed and floating structures. Second order wave interaction effects for floating systems in multi-directional seas require particular attention as the numerical simulation of such systems is still in the early stages of development. Several methods for the simulations of multi-directional sea states in model wave facilities have been developed, each of which has Heriot-Watt tank wave signals are generated by the convolution of a two dimensional non-recursive digital filter with digitally generated pseudo white noise as described by Linfoot et al1.
The wave basin is 9m × 9m × 0.9m (deep) and is equipped with 18 independent bottom-hinged "absorbing" wavemakers positioned along one side of the basin. Beaches on the remaining three sides absorb waves and thus reduce phase-locked reflections to a minimum. The operation of wave makers of this design are described by Salter et al2. It is possible to produce regular waves and long-crested random seas as well as short-crested seas which closely match the power spectra and spreading specified within a frequency range of 0.3Hz to 3.0 Hz. A 32 bit microcomputer is used to generate the time series signals which are then amplified and applied to the motors driving the individual wave making flaps. Figure 1 shows a schematic outline of the generation system. Each wave generator servo motor is driven by a separate independent power amplifier with a local analog controller which includes force and velocity feedback signals from the wavemaker.