EXPERIMENTAL INVESTIGATION INTO THE FLOW AROUND A MANOEUVRING LNG CARRIER ON SHALLOW WATER

The objective of this research project is to supply information on the hydrodynamical flow around a manoeuvring vessel on shallow water. The flow patterns and the resulting forces and moments acting on the LNG carrier with twin gondola aft-body as a consequence of a drifting motion are studied. Hydrodynamic forces and moments acting on a ship change remarkably depending on the water depth. Accurate prediction of the hydrodynamic derivatives of vessels on shallow water and the ability to quantify the effect of form variations is needed. Information from these experiments is used to better understand the effect of water depth. The flow observation, wave profile measurements and force' measurements contribute to the comprehension of the observed phenomena and can be used to validate and accelerate the development of potential flow, Reynolds Averaged Navier Stokes (RANS) and semi-empirical simulation codes. The experiments consist of towing a model of a 300 meter LNG carrier in the MARIN shallow water basin in water depth to draught ratios. State-of-the-art flow measurements with Particle Image Velocimetry (PIV) measurements were carried out up and down stream of the hull at several planes along the ship. Some representative flow fields are presented to demonstrate the influence of the water depth on the flow around the model. Besides the flow measurements the hydrodynamic forces and moments were measured. 1. BACKGROUND The aim of the project is to acquire a better understanding of the complex three-dimensional flow around and the hydrodynamic forces on a LNG-carrier under manoeuvring conditions for different water depths including shallow water. The tests were performed in the shallow water basin of MARIN. In the last years, the development of Computational Fluid Dynamics (CFD) for maritime purposes has made considerable progress. CFD is now a serious alternative for simple model tests. However, a powerful method to validate the results obtained with CFD was not available until the new non-intrusive technique of Particle Image Velocimetry (PIV) entered the maritime research market. In this project, PIV tests were performed to obtain detailed velocity fields around a manoeuvring ship. The results will be compared with the viscous flow solver Parnassos and the conclusions can be used for further development. 2. THE MARIN LNG CARRIER For the study a modern twin-gondola LNG-carrier design is selected, the MARIN LNG-carrier, see Figure 2.1 and Table 1. The model is tested bare hull, no rudders nor bilge keels are fitted. Black paint is used on the model hull to minimize the reflections from the laser. Figure 2.1 Body plan of the MARIN LNG-carrier. Table 1 Main dimensions of the investigated MARIN LNG-carrier. DESIGNATION Length between perpendiculars Length on the wateriine Breadth moulded on WL Draught moulded on FP Draught moulded on AP Wetted surface area bare hull LCB position forward of midship Block coefficient Midship section coefficient Prismatic coefficient Length-Breadth ratio Breadth-Draught ratio Length-Draught ratio SYMBOL UP Lm B TF TA S CB C„ cP Lpp/B B/T L*/T MAGNITUDE 300.00 308.40 50.00 11.70 11.7