The Use of Model Reduction via Balanced Realizations in the Description of Ship Motion

Abstract

The model reduction scheme via balanced state space realizations is discussed for an application example from the area of ship motion control. The reduction can be applied to a second order subsystem which represents the hydrodynamic core of the model. This model sometimes has been found ill conditioned with respect to identification. It can be demonstrated that the reduction process via balanced realizations provides a systematic insight into the system theoretic causes of identification problems and justyfies some ad hoc simplifications that are commonly used in ship modelling. Finally we briefly discuss the reduction of models estimated from experimental data. The Hankel singular values can be seen to give valuable information about the appropriate order of the model.