Dynamic Positioning Capability Analysis for Marine Vessels Based on A DPCap Polar Plot Program

Lei Wang,Sheng-Wen Xu,Jian-Min Yang

doi:10.1007/s13344-018-0010-4

Abstract

Dynamic positioning capability (DPCap) analysis is essential in the selection of thrusters, in their configuration, and during preliminary investigation of the positioning ability of a newly designed vessel dynamic positioning system. DPCap analysis can help determine the maximum environmental forces, in which the DP system can counteract in given headings. The accuracy of the DPCap analysis is determined by the precise estimation of the environmental forces as well as the effectiveness of the thrust allocation logic. This paper is dedicated to developing an effective and efficient software program for the DPCap analysis for marine vessels. Estimation of the environmental forces can be obtained by model tests, hydrodynamic computation and empirical formulas. A quadratic programming method is adopted to allocate the total thrust on every thruster of the vessel. A detailed description of the thrust allocation logic of the software program is given. The effectiveness of the new program DPCap Polar Plot (DPCPP) was validated by a DPCap analysis for a supply vessel. The present study indicates that the developed program can be used in the DPCap analysis for marine vessels. Moreover, DPCap analysis considering the thruster failure mode might give guidance to the designers of vessels whose thrusters need to be safer.

Highlights

A dynamically positioned (DP) vessel is by the International Maritime Organization (IMO) and the certifying class societies (DNV, ABS, LR, etc.) defined as a vessel that automatically maintains its position and heading exclusively by means of active thrusters (Sørensen, 2011)
The software program is composed of two units: estimation of the environmental forces and moment and the thrust allocation logic
A thrust allocation logic was presented in detail, from the formulation of the problem, approximation of the thrust region to the handling of non-convex thrust regions

Summary

Introduction

A dynamically positioned (DP) vessel is by the International Maritime Organization (IMO) and the certifying class societies (DNV, ABS, LR, etc.) defined as a vessel that automatically maintains its position and heading (fixed position or pre-determined track) exclusively by means of active thrusters (Sørensen, 2011). 90–98 developed software program capable of conducting the DPCap analysis for marine vessels. The accuracy of the DPCap analysis is determined by the precise estimate of the environmental forces as well as the effectiveness of the thrust allocation logic. The newly developed software program consists of two main parts: one is the estimation of the environmental forces; the other is the thrust allocation logic. The quadratic programming method is adopted to allocate the total thrust on every thruster of the vessel, due to the high efficiency and robustness of this method (De Wit, 2009). Estimation of the environmental forces and moment is based on the model tests, hydrodynamic computation, and empirical formulas (Sørensen and Ronass, 2001). For azimuthal thrusters and main thrusters with a rudder, constraints are absolutely nonlinear

Tunnel thruster

Findings

Conclusion