A Frequency Domain-Based Sensitivity Study of a Submarine Manoeuvring Model

Abstract

A frequency domain-based analysis of a submarine maneuvering model has been completed and used to study the effects of parameter uncertainty. The maneuvering model of the BB1-X submarine has been analyzed for the purpose of understanding the consequences of reduced input fidelity. Inputs were varied individually and ranked based on the resulting deviation from the original model. The model was also reduced to include fewer degrees of freedom or dynamic effects and compared with the original fully detailed model. The intention of this study is to determine which data are most crucial to the accurate maneuvering simulation of a submarine. Depending on the application of such a model, certain accuracies may be sacrificed to reduce resource requirements and save cost. The results of this study give some guidance as to which types of parametric data need to be the most detailed. Although the results will not give exact sensitivities for all submarine maneuvering models, it will give an indication of which areas should be focused on. 1. Introduction Producing a maneuvering model of a submarine must always be a balance between desired model fidelity and available resource and time. Depending on the purpose of a particular model, fidelity may be sacrificed in certain areas in the interests of reducing computational time or data input requirements. Before making this reduction, however, it is important to understand how various simplifications will affect the overall dynamic characteristics. If this is well understood, the process of creating models that are fit for purpose can be streamlined. The parametric data for a maneuvering model are often produced through experimental work or computational fluid dynamics (CFD) simulations. A certain amount of force and moment data can provide sufficient information to calculate a set of hydrodynamic coefficients which are used to populate a maneuvering model. The higher the data requirements, the longer these processes take. When reducing the extent of parametric data required, it is desirable to reduce detail in a manner which has minimal effect on the maneuvering model, and therefore, it is important to know which of the hydrodynamic coefficients are the most significant. For submarines, there is very little documented information about this in the open literature. An effort to describe the significance of some coefficients was first attempted by Ray et al. (2010). Ray provides an analysis of the hydrodynamic coefficients and their effect on a longitudinal zigzag maneuver. The analysis, however, focuses on eight coefficients and vertical plane motion only. The analysis in this report is significantly more comprehensive.