|Title: Dynamic Stability of Heavy Lift Vessels During Loss of Tandem Load|
|Written by: Hannes Hatecke|
|in: Promotion 2016|
Abstract: This study investigates the hazard of capsizing of crane ships after an accidental loss of the lifted load. If this load is lifted by two cranes in a so-called tandem lift, the load generally does not fall off both cranes simultaneously. In fact, both cranes fail rather subsequently and thus there exist a duration where the load and the ship act as a coupled multi-body system. In order to access the coupled dynamics, this study presents a simulation method which computes the motions of a loss of load during a tandem lift. Here, the load and the ship are modeled as two rigid bodies which are connected by a rigid rope. Thus, a fully non-linear multi-body system with 11 degrees-of-freedom is obtained for which the equations of motions are given in minimal coordinates. The hydrodynamic forces are considered by a superposition of non-linear hydrostatic forces, linear radiation forces, and viscous roll damping forces. The radiation forces are efficiently computed by a state-space model which is based on a newly developed time domain identification scheme for multiple degrees-of-freedom systems. Before the proposed simulation method is applied to assess the hazard of capsizing of crane ships after a loss of load during tandem lifts, it has successfully been validated against a series of model tests. It is found that the timing of the subsequently occuring loss of load and the crane configurations can have a large influence on the likelihood of a capsize. Furthermore, current stability criteria are reviewed against a realized direct assessment of the dynamic stability after a loss of load.