One fluid formulation for floating offshore renewable energy devices

One-fluid formulation for floating offshore renewable energy devices

Liang Yang(1), Dimitris Stagonas(2), Cranfield University

(1) Division of Energy and Power, Cranfield University, Bedford, UK

(2) Division of Energy and Power, Cranfield University, Bedford, UK

The overall scientific goal of this research is a step change in the numerical simulation of complex Multiphysics problem, involving multibody dynamics (MBD), solid mechanics and wave hydrodynamics, which lies well beyond the capacity of today's analytical solutions. From the modelling standpoint, the ideas pursued in this research will represent an original contribution in the numerical analysis of MBD and fluid mechanics coupling, with an efficient methodology to model connected structures as a continuum. In the ‘one-fluid’ formulation, e.g.

[1], the multiple connected rigid bodies aremodelled as a different phase of non-viscous fluid, and their motions are linked by aunified equation by Lagrange Multipliers. The whole system is solved in a continuum and unified manner, and there is no explicit imposing the coupling boundary or condition or usage of MBD governing equations. The key ingredients of this methodology are:

1) the solution of the underlying Navier-Stokes equations and

2) the consideration of distributed Lagrange multipliers to enforce rigid bodyconstraints. From the spatial discretisation point of view, we employ a Cartesian staggered Finite Volume scheme (Marker-and-Cell (MAC) grid) and a level set methodology to describe the evolution of the various interacting phases. Results suggest that the unified ‘one-fluid’ equation can predict the dynamic response of, e.g., WECs, and fixed and moving cylinders in the numerical wave tank [2] and [3].

[1] Yang, L. (2018). One-fluid formulation for fluid and structure interaction with free surface.Comput. Methods Appl. Mech. Eng., 332, 102-135.

[2] Yang, L., Yang, H., Yan, S., Ma, Q. and Bihnam, M. (2016). Comparative study on waterimpact problem. In Proc. 26th ISOPE.

[3] Yang, L., Stagonas, D., Chen, S. (2020). Comparative Study on Steep Focused WavesInteractions with Fixed and Moving Cylinder. ISOPE Shanghai, China, June 14 - June 19.Inreview.Page