Development and Application of a Potential Flow Computer Program: Determining First and Second Order Wave Forces at Zero and Forward Speed in Deep and Intermediate Water Depth

Abstract

A ship traveling in irregular sea with a steady forward speed is a classical hydrodynamics problem which still presents many challenges. An in-house computational code MDLHydroD based on potential theory has been developed to address this problem. A Green function based approach is followed in frequency domain to obtain the linear forces and motion of the vessel. A perturbation approach is then applied to extract the second order forces, and the added resistance on the ship is thus obtained.

The numerical method is then extended to consider finite water depth effects. A new finite depth Green function is developed and implemented in the 3D potential code. This allowed analysis of ship motion with forward speed in intermediate water depths.

An optimization framework is then developed to solve the inverse problem of ship hull optimization which is classified as a multi variable multi objective problem with nonlinear constraints. The three main problems encountered in the inverse design of ship hull are: automated geometry creation, prediction of forces due to fluid structure interaction and modifying the hull towards a better performing hull form. For this study, a parametric hull form based on typical ship parameters is developed which can be altered to obtain different ship hulls that can be analyzed using the developed hydrodynamic code MDLHydroD. A number of different optimization solvers are studied to understand and select appropriate solver for ship hull optimization. Solvers based on evolutionary algorithms were found to be adequate and used to demonstrate the capabilities of the hull optimization framework. Both single and multi-objective optimization algorithms are implemented. A selected optimized design from the Pareto front is then compared with initial design to show the effectiveness of the optimization method.

This study will provide a thorough analysis of hydrodynamic load prediction methodologies and its application in obtaining safer, fuel efficient and more stable hull forms.