Trim wedge optimization with viscous free surface computations

Today, varying fuel prices and high competition in the maritime transport sector cause that shipyards continuously have to improve the design of their ships. Stern wedges are nowadays frequently used to improve the fuel efficiency. In this paper, we use an (x; y; z)-co-ordinate system fixed to the ship, with x positive aft and z upwards, as is shown in Figure 1. The resistance is obtained by integrating the x-component of the force distribution over the hull. The forces consist of the sum of the friction forces and the pressure times a local area. As describedin ([1]) and illustrated in Figure 2, a trim wedge leads to an increased pressure at the aft part of the hull. As a result, the velocity will decrease, resulting in a reduced friction force at the aft part. Both the increased pressure and the reduced friction force contribute to a decrease of the resistance. The increased pressure will also affect the dynamic trim of the ship. Model testing can be used to design a hull/trim wedge combination but it suffers from several drawbacks. First, building and testing a model is a time-consuming and Figure 1. Coordinate systemFigure 2. Forces working on the aft part of the ship influencedby a trim wedge costly process.