| Popis: |
The thesis begins by describing the experimental determination of the hydrodynamic coefficients of two test models; an Edinburgh duck and a semi-submerged, horizontal right circular cylinder. The impedance and wave force coefficient matrices are measured for these two models, and in the case of the cylinder are checked against exact analytical results. The radiation and scattering pattern matrices are also measured. Synthesis of optimal (complex-conjugate) control is achieved for the cylinder in one and two degrees-of-freedom, and for the duck in one, two and three degrees-of-freedom. Synthesis is defined as the pre-computation of drive signals to simulate control using prior knowledge of the incident wave and the device hydrodynamics. The concept of complex-conjugate control with amplitude constraint is introduced, and synthesised for the cylinder. This is compared with the results for control without constraint. A discrepancy is found between efficiency calculated at the duck axis and efficiency calculated from the wave amplitudes. This is traced to physical losses in the system. These losses are due to the scale of the test models, and may not be present at full-scale. Having accounted for these losses, the results for the synthesis runs agree well with predictions based on the model coefficients and hydrodynamics. This suggests that the linear model can be used to predict the effect of changes in shape on the forces, displacements and velocities of an optimally controlled device. Full-scale performance is predicted for a 10m diameter duck in unidirectional mixed seas. Two pseudo-optimal control strategies are defined which are based on the impedance measurements. Four different physical configurations are considered. It is found that changing the configuration will roughly determine the effectiveness of the device, and choosing the correct control strategy for that configuration fine tunes performance. The two pseudo-optimal strategies are simple to implement, but are nearly as effective as complex-conjugate control. |
