FastFEM: Behaviour of fast ships in waves

Lead Research Organisation: University of Leeds
Department Name: Applied Mathematics

Abstract

The use of fast (10 to 60m) ships has become popular in maritime operations. They nowadays emerge in search and rescue operations, surveillance, Coast Guard activities, interceptor and security missions, anti drugs and piracy actions, in fast supply to offshore platforms, and for crew transport and wind farm maintenance. The main advantage is their speed, while the challenge is to maintain safe seakeeping at high speeds in mild to heavy seaway, while also keeping these ships affordable, reliable, fuel efficient and comfortable. We propose to develop new simulation tools for the dynamics of fast ships and surrounding waves in breaking seas, and to validate these simulations with advanced and novel towing tank laboratory experiments.

Classical calculations of waves are based on (non)linear potential flow wave theory. Such simulations are quite good provided accurate numerical methods are used, but can never deal with wave breaking due to the potential flow Ansatz. In addition, potential flow wave codes in three dimensions need to become computationally more efficient. This requires further scientific development (work package WP1 at the University of Twente, The Netherlands by Jaap van der Vegt with Onno Bokhove), especially when wave and ship dynamics are fully and nonlinearly coupled, as proposed. Another key issue in WP1 is preservation of the variational formulation of wave dynamics, to ensure numerical stability, within our partially existing discontinuous Galerkin finite element methodology (DGFEM). Our first innovation is to simulate wave breaking around the ships, as well as incoming breaking waves, with a new, advanced single-phase mixture theory for the water-air mixture (in WP2 at the University of Leeds). In contrast to other numerical methods that can deal with wave breaking (such as Volume of Fluid methods and Smoothed Particle Hydrodynamics), our method does not lead to (unwanted) numerical wave damping in areas with smooth waves. Our second innovation is that the new method is by design constructed to include our (variational) potential flow limit with nonlinear ship dynamics. Hence, this new methodology for fast ships in breaking seas does require that the DGFEM for the combined ship and potential flow wave dynamics is fully developed as well (in WP1). Essential is the anticipated validation of both (integrated) simulation tools against advanced and new towing tank experiments. Beyond the numerical validation, these towing tank experiments (in WP3 at Delft University of Technology, The Netherlands by Rene Huijsmans) provide direct and new data to the users in the form of the measured (nonlinear and breaking) wave environment around fast ships, pressures on their hulls as well as onboard accelerations. These laboratory measurements will be directly used by our users: Damen Shipyards, MARIN, Royal Netherlands Navy, Royal Netherlands Rescue Organisation (KNRM), Bureau Veritas, and Lloyds Register, while the proposed simulation tools supporting new hull designs will form a sustained investment.

Planned Impact

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Publications


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Gagarina E (2016) On variational and symplectic time integrators for Hamiltonian systems in Journal of Computational Physics