THE DISTRIBUTION OF THE HYDRODYNAMIC 



FORCES ON A HEAVING AND PITCHING 



SHIPMODEL IN STILL WATER 



J. Gerritsma and W. Beukelman 



Technological University 



Delft, Netherlands 



ABSTRACT 



Forced oscillation tests are carried out with a segmented shipmodel to 

 investigate the distribution of the hydrodynannic forces along the hull 

 for heaving and pitching motions. 



The vertical forces on each of the seven sections of the shipmodel are 

 measured as a function of forward speed and frequency. By using the 

 in-phase and quadrature components of these forces, an analysis is 

 made of their distribution along the length of the shipmodel. 



The experinnental results are compared with the results of a simple 

 strip theory, taking into account the effect of forward speed. 



The comparison shows a satisfactory agreement between theory and 

 experiment. 



INTRODUCTION 



The calculation of shipmotions in regular head waves by using a strip theory, 

 has been discussed in a number of papers. Recent contributions were given by 

 Korvin-Kroukovsky and Jacobs [1], Fay [2], Watanabe [3] and Fukuda [4]. 



In these papers the influence of forward speed on the hydrodynamic forces 

 is considered and dynamic cross-coupling terms are included in the equations 

 of motion, which are assumed to describe the heaving and pitching motions. 



In earlier work [5] it was shown that a relatively small influence of speed 

 exists on the damping coefficients, the added mass and the exciting forces, at 

 least for the case of head waves and for speeds which are of practical interest. 

 On the other hand, forward speed has an important effect on some of the dynamic 

 cross- coupling coefficients. Although, at a first glance these terms could be 

 regarded as second order quantities, it was pointed out by Korvin-Kroukovsky 

 [l] and also by Fay [2] that they can be very important for the amplitudes and 

 phases of the motions. This has been confirmed in [5] where the coupling terms 



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