A FINITE ELEMENT MODEL FOR DYNAMIC ANALYSIS OF MOORING CABLES

A finite element model has been constructed for numerical analysis of the dynamic response of mooring cables. The model is non-linear, taking into account the velocity squared dependence of the drag force, large deviations away from equilibrium and the effect of tension variation in the equations of motion. The solution method is deterministic in the time domain and is intended for analyzing transient phenomena. The equations of motion are formulated in matrix form. Normal modes are defined for small amplitude oscillations about equilibrium, and the equations of motion are transformed to normal coordinates. A new (to our knowledge) method for integrating approximately the coupled equations of motion numerically was developed as a variation of New Mark's method. The coupled force terms are decoupled by assuming each as a function of time only over short intervals of time and a trial and error process is used to estimate the state at the end of the interval. The mode of excitation particularly studied here is that of a forced motion of one end of the cable (the upper point of fixation to the moored vehicle). Several examples are analyzed. Some of these are of a theoretical nature, allowing correlations with analytical solutions. Finally two examples of mooring lines are analyzed, under transient pull from rest in equilibrium and under harmonic forced motion of the upper end.

  • Corporate Authors:

    Massachusetts Institute of Technology

    Department of Ocean Engineering, 77 Massachusetts Avenue
    Cambridge, MA  USA  02139
  • Authors:
    • Johansson, P I
  • Publication Date: 1976-1

Subject/Index Terms

Filing Info

  • Accession Number: 00142341
  • Record Type: Publication
  • Source Agency: Massachusetts Institute of Technology
  • Report/Paper Numbers: PhD Thesis
  • Files: TRIS
  • Created Date: Nov 23 1976 12:00AM