Numerical simulation of planing hull in regular waves

Sayeed, Tanvir Mehedi (2010) Numerical simulation of planing hull in regular waves. Masters thesis, Memorial University of Newfoundland.

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Abstract

The problem of predicting the motions of planing craft is extremely difficult. The planing hull motions in waves lead to strong non-linearities that cannot be depicted well by linear analysis of motion. A non-linear mathematical model (3 degree of freedom program) has been developed for predicting the vertical motions of a planing hull in regular head waves. Since the model is nonlinear, the computations are made in the time domain. The model has its origins in the non-linear strip theory developed by Zarnick (1978). The model can input variable deadrise angles to account for hull geometry. It is assumed that the wavelengths are large in comparison to the boat length and the wave slopes are small. Wave input is restricted to monochromatic linear deep water waves. The thrust and the friction drag forces are assumed to act through the centre of gravity. The hull is divided into a series of two-dimensional wedges. The forces and moments acting on the craft are calculated by modelling wedge impact and integrating the result along the length of the hull. This model can also predict the vertical accelerations which are important design criteria for planing hulls. -- The numerical model is verified with the experimental model test results of Fridsma (1969), Chiu & Fujino (1989), and Katayama et al. (2000). The model has shown promising results in predicting the heave and pitch motions in semi-planing and planing regions of speed. For the very high speed vessels and to predict the vertical accelerations, the model still needs to include exact slamming forces. -- Experimental investigations have been carried out with a 10° deadrise wedge varying the drop heights and the mass of the wedge. These factors have been found to have negligible influence in predicting the maximum pressure coefficient. The analytical prediction method developed by Chuang (1973) is found to be an accurate tool for determining maximum slamming pressures. Follow up experiments could be performed varying the deadrise of the wedge and doing some oblique drop tests to further verify Chuang's (1973) prediction method. Then this method could be implemented in the numerical simulation of planing hulls.

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