Impact loads and wave kinematics on a fixed truncated circular cylinder due to nonlinear waves in a 2-D tank

Abstract

This thesis presents a result of measurements and analyses of the wave kinematics and impact loads on a scaled ISSC-TLP column fixed in a 2-D wave tank. The objective is to find out the mechanics of impact loads varied with kinematics in both space and time, and develop a method to predict nonlinear wave kinematics and forces in time domain using the measured wave elevation. Three typical nonlinear waves were employed to develop and validate a new prediction model for nonlinear wave kinematics and forces in time domain. Both predicted and measured data agree very well. Validation of linear diffraction theory for surface piercing vertical truncated structures should be performed by extensive experiments and numerical wave tank technique. Simultaneous measurements of the particle velocities under the crest, the wave elevation at the energy concentrated location, the wave elevation on the cylinder surface, dynamic pressure distribution and impact force were performed to study the relationships between impact loads and kinematics using an asymmetric steep non-breaking wave. The strong nonlinear kinematics in front of the structure may cause forming air pocket. Both expansion and compression of air pocket at high frequency may produce high frequency dynamic pressure as well as high frequency impact force. Weak impact crest force is about two times that of Stokes 5th-order-like wave with an equivalent wave height, while asymmetric steep-front wave particle velocity at 12-cm above SWL is much higher than that of the equivalent Stokes 5th-order-like wave. Maximum runup reached about 1.34 times the maximum wave height. The rise time was much longer than drop time which is in contrast to the other results using plunging breakers.