Effects of Axial Dampers And Elastic Joints On the 3-D Dynamic Responses of a Deep-Ocean Pipe With Torsional Coupling

Abstract

The 3-D nonlinear pipe code, 3DNLPIPE, is updated with the modeling of axial vibration dampers and elastic joints installed on a very long vertical pipe. During ocean mining operations in the deep ocean, the vertical pipe undergoes a large deflection (Chung, Cheng and Zheng, 1995), with coupled bending (xand yo), axial (z-) and torsional (8z-) displacements. For this case, the present analysis of the 3-D nonlinear coupled responses shows that proper arrangements of the axial vibration dampers at proper positions along the pipe without the elastic (or flexible) joints can effectively reduce the axial stress. The axial dampers can slightly decrease the mean bending deflection, while the elastic joints slightly increase it. The elastic joints can be arranged along the pipe to be effective in reducing the axial stress as well as bending moments. Furthermore, the best combination of the multiple elastic joints and the axial dampers along the pipe can be achieved to reduce static, as well as mean dynamic, deflections, axial stress, bending moments and torsional deformation. The elastic joints can make the biaxial and torsional vibrations reach steady state, while the axial dampers do not. The 5-s axial resonance period of the present example of an 18,OOO-ft pipe is a very commonly encountered wave period in the ocean, and it can excite axial pipe vibration.