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HAVBRUK2-Stort program for havbruksforskning

High resolution numerical modelling of floating flexible fish cages

Alternative title: High resolution numerical modelling of floating flexible fish cages

Awarded: NOK 11.7 mill.

This project has aimed at developing a complete framework for resolving the hydrodynamics of a floating fish farm structure and analysing the structural response of the whole construction in a single high resolution CFD model. Several works in current literature have investigated the hydrodynamics and structural response of the various components of a fish cage independently. Due to the strong interaction between the different components of a fish cage structure, it is essential to evaluate the hydrodynamics and structural responses of the different components in a single framework. In this direction, the vision of this project was to incorporate an Finite Element Method (FEM) model to analyse the structural response to the environmental loading that is accurately represented by a Computational Fluid Dynamics (CFD) model. The open source hydrodynamics framework REEF3D, developed at the Department of Civil and Environmental Engineering (NTNU), has been widely used to investigate several problems in the field of coastal and marine engineering such as analysis of breaking waves, breaking wave forces on cylinders, hydrodynamics of an oscillating water column wave energy device and motion of floating structures on waves. Thus, the model was a perfect starting point and was extended during the course of the project to simulate special aspects of a floating fish cage. Strong collaboration with National partners SINTEF Ocean and International Partners Ludwig-Franzius-Institute, University of Hannover, Germany and Indian Institute of Technology-Bombay, India has provided a rich international research environment and the research results can be disseminated to the stakeholders in the aquaculture industry at an international level. At the current and final stage in the project, the numerical algorithms for mooring and nets for the fish cage have been implemented in the model. The 6DOF algorithm for calculating the motion and forces on the floating object has been successfully updated to provide more accurate results in three-dimensional simulations. Complete floating offshore aquaculture structures have been modeled and the journal paper describing the research have been published. The model development has been presented at several conference and several journal papers have been published. Five Masters theses and one PhD thesis have been carried out with the new model to verify the new 6DOF algorithm and the mooring model. Experiments have been conducted at Hannover to validate the model results for floating bodies in waves. One Phd thesis at IIT Bombay has been finished during the project, where the current numerical framework has been used. Collaboration with SINTEF Ocean has made the model an industry relevant tool by including features essential for practical use.

A complete framework for resolving the hydrodynamics of an open ocean floating fish farm structure is developed, validated and disseminated in the current project. Significant contributions to existing research were made: 1. Development of a rigid-body FSI solver for the rigid floating structure based on the fluid dynamics solver REEF3D. 2. Development of a numerical mooring model, that combines flexibility with efficiency in order to cope with the demands of OOA systems. 3. Development of a non-linear structural dynamics solver for the net, accounting for large motions and non-linear material. 4. Development of a coupling methodology for the interaction of deformed elastic porous structures and the fluid. 5. The new wave model REEF3D::FNPF is developed and validated to resolve the waves in Norway's coastal zone delivering realistic design wave conditions for OOA structures can be estimated.

This project aims at developing a complete framework for resolving the hydrodynamics of a floating fish farm structure and analysing the structural response of the whole construction in a single high resolution CFD model. Several works in current literature have investigated the hydrodynamics and structural response of the various components of a fish cage independently. Due to the strong interaction between the different components of a fish cage structure, it is essential to evaluate the hydrodynamics and structural responses of the different components in a single framework. In this direction, the vision of this project is to incorporate an Finite Element Method (FEM) model to analyse the structural response to the environmental loading that is accurately represented by a Computational Fluid Dynamics (CFD) model. The open source CFD model developed at the Department of Civil and Transport Engineering NTNU has been widely used to investigate several problems in the field of coastal and marine engineering such as analysis of breaking waves, breaking wave forces on cylinders, hydrodynamics of an oscillating water column wave energy device and motion of floating structures on waves. Thus, the model can be extended to simulate special aspects of a floating fish cage. This steadily growing industry in Norway requires focussed research to maintain its quality and growth with environmental and safety considerations in mind. The main challenge will lie in the implementation and coupling of the CFD model with the FEM model. Strong collaboration with National partners MARINTEK and International Partners Franzius Institute, University of Hannover, Germany and Indian Institute of Technology-Bombay, India will provide a rich international research environment and the research results can be disseminated to the stakeholders in the aquaculture industry at an international level.

Publications from Cristin

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Funding scheme:

HAVBRUK2-Stort program for havbruksforskning