Modeling the Flow Around and the Hydrodynamic Drag on Net Meshes Using reef3d

Gang Wang,Tobias Martin,Hans Bihs,Liuyi Huang

doi:10.1115/1.4051408

Abstract

Abstract The hydrodynamics and flow around net meshes has recently drawn more and more attention because it is closely related to the expected forces on aquaculture. In terms of modeling the hydrodynamic forces on nets, Morison or screen force models are ordinarily. However, they mainly rely on empirical, experimental, or cylindrical hydrodynamic coefficients, neglecting the flow interactions between adjacent net twines. In this study, the open-source hydrodynamic toolbox reef3d is adopted to analyze the flow around net meshes and investigate the hydrodynamic drag on the structure. The simulation accuracy is in good agreement with flume experiments and previous research. The results demonstrate that 2 × 2 or 3 × 3 mesh cases are more reliable for studying the flow around net meshes including the flow interactions around adjacent twines. It is further shown that controlling the solidity of the net through changing net bar diameters has different effects on the flow around meshes than controlling it by the twine length. This article presents a first step in the aim to derive a new empirical formula for the drag coefficients depending on the solidity and fluid properties, which is more appropriate for the physics involved in offshore conditions.

Highlights

Due to the pollution and the increase of aquaculture in coastal areas, the fish farming industry tends to move to the offshore area
It is attributed to the formation of a vortices after flowing through the structures, which leads to the decrease of the flow velocity
It is concluded that the flow field around the center a 1 × 1 mesh shows significant different patterns than for other cases covering more crossed cylinders and intersections. 2 × 2 and 3 × 3 mesh cases are more reliable when studying the flow around net meshes and wake patterns because the flow interactions around the net bars and the effects from the surrounding meshes are considered

Summary

Introduction

Due to the pollution and the increase of aquaculture in coastal areas, the fish farming industry tends to move to the offshore area. Open ocean aquaculture facilities are typically more complicated and increased in size compared to traditional flexible floating cage. Since the sea environment loadings in deep water are more severe than in near-shore areas, fish farms experience large dynamic responses and deformations of the nets leading to fatigues or unpredictable damages [1]. The nets of fish farms in extreme wave-current loadings risk collision with fish which leads to the damage of the net meshes [2]. The hydrodynamics around the net meshes used in offshore fish farms are still not investigated with respect to flow interaction effects. It is crucial to study the flow around net meshes adopted in offshore fish farms

Methods

Results

Conclusion