Session: 06-03-01 Fluid-Structure, Multi-body and Wave-body Interaction I

Paper Number: 122596

122596 - Fully Nonlinear Interaction of Water Waves and a Submerged Cylinder With Wave Breaking Detection and Suppression 

In this paper, interactions between a fixed submerged circular cylinder and free surface waves in near breaking conditions are numerically simulated in time-domain using two-dimensional (2D) fully nonlinear potential flow (FNPF) models, and comparisons are made to published experimental and theoretical results. To achieve accurate and efficient simulation results, the newly proposed immersed-boundary adaptive harmonic polynomial cell (IB-AHPC) method is adopted to solve the boundary value problem governed by the Laplace equation. The incoming waves experience strong nonlinear deformations when passing through the submerged cylinder. In addition to being diffracted, the energy of the incident waves is transferred to shorter superharmonic free waves. At the submerged cylinder’s lee side, higher-order harmonic components of these free waves are significant, even can be comparable to the incoming wave amplitude. Then the wave profile becomes asymmetric and skewed and may eventually reaches the point of physical wave breaking. Hence, it is of practical interest to investigate the hydrodynamic forces exerting on the cylinder while the waves are near breaking. Though the fully nonlinear wave model is valid up to wave breaking, a numerical breakdown can occur precedingly the commencement of the actual wave breaking. Despite flow models based on Navier-Stokes equations representing more complete physics, their applications to engineering involving strongly nonlinear and breaking waves are still limited due to computational costs. Therefore, it is desirable to extend the FNPF model to be more stable when waves are approaching their breaking limits without actually modelling the overturning waves. The wave breaking can be suppressed in a pragmatic manner by artificially specifying the wave energy dissipation related to the breaking process or replacing the waves with a smoothed profile. In this study, the implementation of such a method is mainly composed of two steps. Firstly, the wave breaking onset is detected by a criterion related to the Lagrangian downward vertical accelerations of free surface wave particles. This criterion allows identify when and where the breaking suppression should be started. Secondly, localized smoothing is applied to the free surface profile where the criteria are exceeded. This smoothing procedure is implemented by a classic three 3-point filter in a 10-point region. Once the numerical simulation is stable, the hydrodynamic forces exerting on the submerged circular cylinder in severe cases approaching wave breaking are studied in detail. Because the real physics of wave breaking process is complex and not yet fully understood, the effects of the implemented wave breaking model on the hydrodynamic forces are also discussed. The obtained results can be applied to designs of related ocean engineering structures such as a submerged floating tunnel.

Presenting Author: Qihao Wu Ocean University of China

Presenting Author Biography: Qihao Wu received the B.S. degree in Naval Architecture and Ocean Engineering from Ocean University of China, Qingdao, China, in 2018. He is currently working toward the Ph.D. degree in Harbor, Coastal and Offshore Engineering with the College of Engineering, Ocean University of China, Qingdao, China. His research interests include numerical simulation, marine hydrodynamics, and wave-body interaction.

Authors:

Qihao Wu Ocean University of China
Yujing Chen Ocean University of China
Min Zhang Ocean University of China
Yanlin Shao Technical University of Denmark