Numerical methods for seakeeping problems

Abstract

It is my pleasure to present you a review of the recently published book of Springer Nature on ‘Numerical Methods for Seakeeping Problems’. The three co-authors of the book are internationally renowned experts in the development of numerical methods/software tools and their use in solving practical problems of seakeeping of ships and floating structures. The material of the book is to a large extent based on lectures held at the Technical University Hamburg-Harburg and the University of Duisburg-Essen, as well as on cited publications of the authors. Even more, all three authors have many years of experience with the service work of a major classification society (Germanischer Lloyd), when they supported the needs of the international maritime industry. Whereas in the past the knowledge of ship’s seakeeping was considered of prime importance only for special types of ships (e.g. naval ships), when compared to ship’s calm water performance and stability, it is not so nowadays in view of enhanced requirements for ship’s operation in realistic sea conditions and the safety of ships, of people onboard and cargo related to ship’s dynamic (intact and damage) stability. Even more, the recently introduced international regulations for the reduction of Green House Gas emissions, affecting both ship’s design and operation, call for methods and tools to assess ship’s performance in realistic sea conditions. The gained knowledge from the longstanding development of efficient numerical methods and software tools, along with their practical use, are presented in this book by a renowned team of experts and will be briefly commented in the following. The book consists of 17 chapters. After a brief introduction into the subject of the book in chapter 1, while considering marine accidents that were affected by adverse weather conditions, the theory of seakeeping is gradually introduced by first presenting the governing fundamental equations of fluid flow (incompressible viscous and ideal fluids) and the rigid body motions (nonlinear and linearized equations of motion) in chapter 2. In chapter 3, fundamental numerical methods for the incompressible potential flows (with and without lift) are presented, along with a demonstration software tool for the two-dimensional flow around a smooth body without lift. In chapter 4 the basic theory of regular and irregular water waves is introduced, while considering the linear superposition principle and spectral analysis techniques for the simulation of linear and nonlinear natural seaways and their ensuing statistics of important parameters. In chapter 5, quasi two-dimensional strip theory seakeeping methods are elaborated, starting with a brief history of developments after the fundamental work of F. Ursell in 1949. Strip theory methods became very popular over the years due to their low computational effort and the wide dissemination of the ensuing theory and numerical implementation. The linear and nonlinear computation of added mass, hydrodynamic damping and of the wave exciting forces on 2D sectional forms is herein presented, as well as the determination of the ship motions and wave induced forces in regular waves by a strip theory method originally developed by H. Söding (code PDStrip). Finally, the effect of hull interaction of multi-hull vessels on the radiated and diffracted waves is discussed. In chapter 6, an efficient three-dimensional Green Function/Panel seakeeping method is presented, and discussed, in which the forward speed effect is accounted for in a simplified way by exploiting basic assumptions of slender body theory. Examples of application by use of the code GL Panel are presented and discussed (T. E. Schellin). In chapter 7, a linear three-dimensional Rankine source method is presented, and discussed. It is first applied to the steady flow problem of a ship with forward speed (wave resistance problem) and then extended to the unsteady, time harmonic flow problem of a ship moving with forward speed in a regular wave train. Special attention is paid to the numerical treatment of the free surface boundary condition and of a transom stern, if applicable. Results of the implemented method are presented in a series of publications of H. Söding and his associates. In chapter 8, a new, fully nonlinear Rankine source method developed by H. Söding is presented, and typical results of its application in comparison with model experiments and RANS methods are discussed. The method allows the computation of large (nonlinear) ship motions and of wave-induced loads, as encountered in severe sea conditions. In difference to the previously presented frequency-domain methods, this is a timedomain method simulating the ensuing physical problem in the time-domain, while accounting for nonlinearities of the above still waterplane hull form and of the ensuing kinematic body and free surface boundary conditions. In chapter 9, viscous flow field methods are presented and discussed. After a brief introduction and presentation of the Reynolds-Averaged Navier Stokes (RANS) Equations, the basic field flow methods are introduced, namely Large Eddy Simulation (LES) and Hybrid Model methods. Issues of grid generation, including