Advanced Numerical Modelling of Wave Structure Interactions

 Advanced Numerical Modelling of Wave Structure Interactions

Advanced Numerical Modelling of Wave Structure Interactions

A distinguishing characteristic of anthropogenically engineered coastal environments is the highly complex interaction that exists between solid structures and the waves that impinge upon them. Similar interchanges also occur between waves and natural structures, such as reefs or rock outcrops.

The interaction takes place because of the strong influence that the structure shape imposes on the hydrodynamics, which is often complex, necessarily fully three-dimensional and two-way, because of the dynamically induced movement of the structure that can result from the hydrodynamic forcing. In turn, structure motion simultaneously leads to changes in the hydrodynamics processes themselves.

The problem of modelling fluid structure interactions accurately has grown in importance over the last two decades with the increasing deployment of various types of marine devices, breakwaters protecting port terminals, land reclamations and biological or natural defense solutions; all of which lie within the coastal zone.

Throughout the 1990s and early 2000s the boundary integral element method (BIEM) was used extensively, and almost exclusively, to simulate non-linear water waves and the interaction between steep waves and structures. Whilst this method has proved to be efficient for the determination of fluid-structure interaction (especially in two spatial dimensions) it is based on potential flow
theory, which requires the flow to be both irrotational and inviscid. More recently, within the last 10- to 20-years, Computational Fluid Dynamics (CFD) approaches have been employed to solve the full fluid motion described by the Navier-Stokes, or Reynolds Averaged Navier-Stokes (RANS), equations incorporating a free surface (air-water interface).

This type of modelling includes viscous and rotational effects and, by employing sophisticated numerical techniques, surface effects such as wave breaking (with full overturning in plunging breakers) can be simulated. Therefore, when viscous/turbulent effects and/or air entrainment effects cannot be justifiably neglected, the use of CFD models is required for meaningful simulations. The current approach is to employ the CFD model only in the immediate surroundings of the structure due to two primary limiting factors.

First, the computational cost of simulating relatively large computational domains is prohibitive. Second, as a consequence of numerical (i.e., non-physical) diffusion, the majority of available CFD models cannot accurately model waves propagating over long distances (e.g., of the order of tens of kilometers).

The goal of this book is to bring together a comprehensive catalogue of state-of-the-art numerical modelling techniques for all key aspects of wave structure interaction within the coastal zone. Each of these approaches has its advantages and drawbacks, and consequently it has advocates and detractors; therefore, we aim to present an unbiased view and let each of the methods speak for themselves. A unitary approach is sought by evaluating different
coastal structures subjected to a range of coastal hydrodynamics in each chapter. These vary from wave generation and propagation to the violent wave structure interaction that leads to greenwater overtopping, as well as the key problems of impulsive wave loading on, and scour around, coastal structures.

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