Non-linear coupled transverse and axial vibration of a compliant structure, part 2: Forced vibration

Responses of a beam undergoing both axial and transverse vibration are stud ied when the beam is subjected to transverse forces. The beam is supported by a torsional spring at the base and has a point mass at the free end. Thi s is a simplified model of a complaint offshore structure. It is assumed th at the environmental forces are due to waves and current. The semi-empirica l Morison equation is used to model the fluid forces. Waves in this case ar e assumed to be random and their heights follow the Pierson-Moskowitz spect rum. Borgman's method is used to obtain the wave height from the Pierson-Mo skowitz spectrum, and the wave velocities and the accelerations are obtaine d from the wave height using the Airy linear wave theory. The wave velociti es and accelerations are then used in the Morison equation to form the flui d forcing function. As a preliminary study, the harmonic force is used to m odel the fluid force. When the deterministic harmonic force at various freq uencies is applied, subharmonic resonances of order 1/2 are observed. Param etric studies of random forcing are performed by varying current velocity a nd significant wave height. (C) 2000 Academic Press.