Hydrodynamic Research on and Optimizing Dynamic Positioning System of a Deep Water Drilling Vessel
Authors: Wichers Johan , Bultema Stephen , Matten Richard 
Published: October 2008

Abstract
Computer simulations and model tests have been used to design and optimize the hydrodynamic performance of a Deep Water Drilling Vessel operating under full DP. The paper describes the procedure used to investigate the thruster-hull and thruster-thruster interaction and the automatic closed loop control system as used for the computer simulations and model tests. Results of the thruster interaction investigation will be shown. Results of the computer simulations on the DP heading capabilities in various design operating weather conditions will be presented and compared with the results of the model tests.

Introduction
The deep water drilling vessel is a fully dynamic positioned large displacement monohull. The vessel is designed for drilling operations in water depths up to 10,000 ft. Investigations were focussed on the design storm conditions in the Gulf of Mexico and potential operations West of Shetland. In the design stage of the vessel hydrodynamic research was applied to the vessel. Besides theoretical and experimental investigations on the dynamic positioning system also research was carried out on the prediction of the speed of the vessel. The total research program therefore can be split in the following parts. Tests in the Deep Water Towing Tank. The main reason for the tests was to predict the service speed of the vessel. For this purpose a model of the vessel provided with 6 azimuthing stock thrusters on a scale 1:26.81 as used and the following tests were carried out:propeller open water characteristics,resistance tests for the scantling draft (T = 13.00 m) with open moonpool,resistance tests for the transit draft (TF = 7.97 m; TA = 8.97 m) with open and closed moonpool,propulsion tests for the transit and scantling draft with open moonpool.
From the results with the represented model equipped with the appendages and fitted with 6 KaMeWa thrusters the following speeds were predicted for the ship in service condition with a sea margin of 15 per cent:transit draft more than 14 knots,scantling draft more than 12 knots.
In addition to these tests preparation tests for the DP system were carried out. The following tests were carried out:hull current loads with the ship in scantling draft;thruster-hull interaction in calm water;thruster-thruster interaction in calm water.

DP Computer Simulation Study.
Prior to the DP tests a DP computer simulation study was carried out. The study was carried out with the DPSIM computer program, Ref. 1. The objectives of the DP study was to identify and optimize the DP controller settings incl. the thruster allocation algorithm for the DP capability of the vessel in various design storm conditions. Besides the particulars of the vessel also the wind, current and wave drift data and thruster particulars were necessary as input for the computer simulation study. The wind coefficients were derived from windtunnel tests, see Ref. 2. The current coefficients were derived from the towing tests and the wave heading dependent quadratic transfer functions of the wave drift forces/moment were computed with a 3-D diffraction program, see Ref. 3.