Simulating the Dynamics of a Chain Suspended Sub-sea Load Using Modified Components from the Modelica MultiBody Library

Abstract

In this paper, the philosophy of the lumped-mass approach is adopted in specifying components so as to enable the Modelica compiler to formulate equations governing the motion of a chain-suspended sub-sea load, subjected to waves and current. The discretized simulation model of the chain-suspended load is built up using the components available in the MultiBody library of OpenModelica, after making necessary modifications. The combined wave and current loads acting on the segments are determined using the Morison equation, and applied as discrete external forces on the lumped segmental masses. The component model is developed and implemented using the OMEdit GUI, and the simulation results are then compared with those for a similar system modelled in the popular commercial ocean-engineering time-domain simulation software, Orcaflex, to demonstrate satisfactory agreement. Conclusions are drawn, and the simulation files are made available for public access.