Abstract

This study aims to investigate the influence of fishnet mesh size on a floating platform. A self-developed, time-domain numerical model was used for the evaluation. This model is based on potential flow theory, uses the boundary element method (BEM) to solve nonlinear wave-body interactions, and applies the Morison equation to calculate the hydrodynamic forces exerted on fishnets. The mooring system is treated as a linear and symmetric spring. The results near the resonant frequency of the platform indicate that the smaller the fishnet mesh size, the lower the heave, pitch, and sea-side tension response amplitude operators (RAOs), but the higher the reflection coefficient. The results in the lower frequency region reveal that the smaller the fishnet mesh size, the lower the surge and heave RAOs, but the higher the pitch and tension RAOs. Meanwhile, the time-domain results at the resonant frequency of heave motion are shown to indicate the influences of a platform with various fishnets mesh sizes on the rigid body motion, mooring line tension, and transmitted wave heights. In addition, a comparison of nonlinear effects indicates that, after reducing the fishnet mesh size, the second-order RAOs of heave, pitch, and sea-side tension decrease, but the changes are minor against the first-order results.

Highlights

  • In recent years, owing to environmental impacts and spatial conflicts with other industries, the development of marine cage aquaculture moved towards deep sea operations

  • Many researchers adopted the Morison-type numerical model to study the hydrodynamic characteristics of marine fish cages [3,4,5,6,7,8,9,10]

  • In order to evaluate the hydrodynamic forces on the floating body using Equation (13), both gradients of velocity potential (∇φ) and unsteady φt terms on the wetted body surface must be determined beforehand. ∇φ is evaluated by the regular boundary element method (BEM), while φt is determined by an acceleration potential method proposed by [28], taking the advantage of the feature that φt satisfies the Laplace equation:

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Summary

Introduction

In recent years, owing to environmental impacts and spatial conflicts with other industries, the development of marine cage aquaculture moved towards deep sea operations. Many researchers adopted the Morison-type numerical model to study the hydrodynamic characteristics of marine fish cages [3,4,5,6,7,8,9,10]. This net cage structure has been treated as a so-called small-body in order to ignore the wave–body interaction. HInistmhisodsteuldhya,swbeeecnonvtianluideattoedexbpyloprehythsiecaiml mpaocdt eolf tfeisshtsneatnmd esshhows gosiozde aognretheemheyndt.roTdhyenraemseicarcchhar[1ac6t]esrtisutdicisedofrealnataeqducaocunldtuitrieonpslastufocrhma,swnietht daepvitehw, noeft pwriodvtihd,inagnda the norenfleinreenacreityfoor fthdeydneavmeilcopremspenotnosef.aInnetth-tiyspsetuadqyu,awcuelctuornetifnlouaetitnogepxlpaltoforermth.e impact of fishnet mesh size on the hydrodynamic characteristics of an aquaculture platform, with a view of providing a reference fo2r. FiFgiugurere11. .(a(a))TThheeccoonncceepptt ddeessiiggnnaanndd((bb))ddeefifinnitiitoionnsksektecthchofotfhtehfeloflaotiantginpglaptlfaotrfmorwmitwh iathfisahfinseht ninetain a nunummereirciacal lwwaavveettaannkk

Governing Equation
Inflow Boundary Condition
Free Surface Boundary Condition
Body Surface Boundary Condition
Curvilinear Coordinate System
Corner Problem between the Free Surface and Body Surface
Acceleration Potential Method
2.10. Modal Decomposition Method
2.11. Mooring Force
2.12. Wave Forces on Fishnet
2.13. Consideration of Damping Effects
Numerical Model Test
Frequency-Domain Results
Time-Domain Results
Nonlinear Dynamic Properties
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