Hydrodynamic Response of Multiple Fish Cages Under Wave Loads

2014 ◽  
Author(s):  
Ke Hu ◽  
Shixiao Fu ◽  
Yuwang Xu ◽  
Leixin Ma ◽  
Yifan Chen
Keyword(s):  
Element Model ◽  
Mooring Line ◽  
Wave Loads ◽  
Fish Farms ◽  
Mooring Lines ◽  
Marine Aquaculture ◽  
Wave Propagation Direction ◽  
Environmental Loads ◽  
Hydrodynamic Response ◽  
Fish Cages

Nowadays, marine aquaculture is playing an important role in meeting people’s ever increasing need for sea foods high in protein. The multiple fish cages are commonly used in large fish farms currently. Mooring systems in these fish cages should be strong enough to withstand extreme environmental loads. Thus, a reliable mooring system is required in designing safe structures. In this paper, a finite element model is built. The floating collar is simulated by the beam element, the twine of the net and the mooring lines are simulated by the truss elements. The geometric nonlinearity of the net model and the material nonlinearity of the mooring line are considered. In this analysis, the hydrodynamic forces estimated by Morison equations are applied to the model. The hydrodynamic response of multiple fish cages under the wave loads by considering the pretension of mooring line is carefully studied. The maximum tension in mooring lines under different wave propagation direction is also analyzed in this study.

Numerical Analysis of a Vessel-Shaped Offshore Fish Farm

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Andreas Vangdal Høiland ◽  
Muk Chen Ong
Keyword(s):  
Wind Waves ◽  
Single Point ◽  
Fish Farm ◽  
Mooring Line ◽  
Mooring System ◽  
Wave Loads ◽  
Fish Farms ◽  
Mooring Lines ◽  
Environmental Loads ◽  
Fish Cages

The aquaculture industry is aiming to move fish farms from nearshore areas to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves, and currents. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system, and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from the frequency-domain (FD) analysis. A mooring system with six mooring lines was designed to avoid possible interactions with the fish cages. Time-domain (TD) simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared under various wave and current conditions. The effects due to misalignment of wave and current directions on the responses were discussed. Finally, the responses using flexible and rigid net models were compared under steady current conditions.

A Preliminary Study of a Vessel-Shaped Offshore Fish Farm Concept

2017 ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Muk Chen Ong
Keyword(s):  
Wind Waves ◽  
Single Point ◽  
Open Water ◽  
Fish Farm ◽  
Mooring Line ◽  
Mooring System ◽  
Wave Loads ◽  
Fish Farms ◽  
Environmental Loads ◽  
Fish Cages

The aquaculture industry is aiming to move fish farms from near-shore area to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves and current. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from frequency domain analysis. A preliminary mooring system was designed to avoid possible interactions with the fish cages. Time domain simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared in various waves and current conditions. The effects due to misalignment of waves and current directions on the responses were also studied.

Simulation of Passing Vessel Effects on Moored Vessel Mooring Response due to Environmental Loads

2017 ◽  
Author(s):  
Nandhini Vasudevan ◽  
S. Nallayarasu
Keyword(s):  
Experimental Data ◽  
Critical Review ◽  
Separation Distance ◽  
Mooring Line ◽  
Review Of Literature ◽  
Limited Data ◽  
Mooring Lines ◽  
Comprehensive Review ◽  
Environmental Loads ◽  
Mooring Forces

A critical review of literature on the mooring forces on the berthed ship together with the passing vessel effects indicates limited data, thus requiring additional studies. Four methods have been found in the literature namely (a) Seelig’s, (b) Flory’s, (c) Kreibel’s, and (d) Modified Seelig’s methods. A comprehensive review and comparison of existing methods has been carried out to verify the applicability of each method to certain conditions and also to establish the parameters for study. It has been found that displacement of the vessels, separation distance between the vessels and velocity of the passing vessel greatly influence the passing vessel forces on moored ship. The software OPTIMOOR has been used to verify Flory’s and Seelig’s methods with the experimental data of Remery and also to study the combined effect of environmental loads and passing vessel effects on mooring lines. The results indicate that the interaction of waves and passing vessel effects are too onerous. Conclusions have been arrived based on the results that for separation distance of 100 m or less between vessels has a greater influence on mooring line forces, leading to breakage of lines.

Optimal Design Methodology for Multi-Component Mooring Systems in Deep Water

2010 ◽  
Author(s):  
Long Yu ◽  
Jiahua Tan
Keyword(s):  
Optimal Design ◽  
Deep Water ◽  
Design Methodology ◽  
Element Model ◽  
Gas Production ◽  
Mooring Line ◽  
Mooring System ◽  
Offshore Platforms ◽  
Mooring Lines ◽  
Restoring Force

Multi-component mooring systems, one of the crucial equipments of offshore platforms, play an important role in deep water oil&gas production because of relative low cost and light weight. A single mooring line can be constructed by combination of wire ropes, chains, fiber ropes, buoys and connectors etc. and provide adequate restoring force at fairlead point of platforms. Although the static and dynamic analyzing approaches for a determined multi-component system have been studied already, it is still hard to design and predetermine an appropriate mooring system that can satisfy the codes with multi-component lines. Referred to the conventional mooring system design method, this paper brings out an optimal design methodology for multi-component mooring systems. According to quasi-static method, at extreme offset position of the platform, an optimization model for designing the multi-component mooring line with biggest tension in deep water has been provided. Then, with the aid of design wave method and morison equation, a finite element model has been used to calculate mooring line dynamics at each fairlead point in time domain. The nonlinear interaction of mooring lines and seabed has also been investigated. Heave and surge of the platform have also been considered. Both 2D and 3D mooring system models have been built to search the interference of the lines and directional influence of environment loads like current and wave. The paper applied this set of analyzing methods and processes into a deep water semisubmersible serving at South China Sea. Compared with the results calculated by other software, the methodology mentioned in the paper got similar result with less weight and bigger restoring force.

Numerical Study on Hydrodynamic Behavior of Deepwater Spar Platform with Different Mooring Configurations

2011 ◽  
Vol 137 ◽  
pp. 50-58
Author(s):  
Jin Wei Sun ◽  
Xiu Tao Fan ◽  
Xiao Zheng Wan ◽  
Shi Xuan Liu
Keyword(s):  
Static Analysis ◽  
Numerical Study ◽  
Coupled System ◽  
Element Model ◽  
System Structure ◽  
Mooring Line ◽  
Mooring System ◽  
Performance Study ◽  
Spar Platform ◽  
Mooring Lines

The motion performance of Spar platform and dynamic characteristics for the mooring lines under different mooring configurations have been studied both in static analysis and coupled dynamic analysis. First, 3D hydrodynamic finite element model is built and the effects of the mooring system are taken into account by giving the specified pre-tension, angle and stiffness of the mooring lines on the fairleads. And hydrodynamic analysis of Spar platform is performed by the way of utilizing potential flow theory in frequency domain in order to calculate the hydrodynamic coefficients. Then, static analysis is applied to obtain restoring stiffness curves for the mooring system, structure displacements and mooring line tensions etc.. At last, coupled time domain analysis of the motion response of Spar is conducted for the coupled system and the dynamic tensions of mooring lines are calculated. The research results can be served as a reference for the selection and the performance study for mooring systems during preliminary design.

scholarly journals A Study on the Effectiveness of the Heading Control on the Mooring Line Tension and Position Offset for an Arctic Floating Structure under Complex Environmental Loads

2021 ◽  
Vol 9 (2) ◽  
pp. 102
Author(s):  
Hyun Hwa Kang ◽  
Dae-Soo Lee ◽  
Ji-Su Lim ◽  
Seung Jae Lee ◽  
Jinho Jang ◽  
...  
Keyword(s):  
Standard Procedure ◽  
The Arctic ◽  
Mooring Line ◽  
Dynamic Positioning ◽  
Positioning System ◽  
Station Keeping ◽  
Mooring Lines ◽  
Environmental Loads ◽  
Dynamic Positioning System ◽  
Heading Control

Even though interest in developing the Arctic region is increasing continuously, the standard procedure to be used to analyze the station-keeping performance of a floater considering ice loads has not been established yet. In this paper, the effectiveness of heading control with a dynamic positioning system is analyzed to evaluate the improvement of the performance of the station-keeping system in the ice conditions. Complex environmental loads with ice-induced forces were generated and applied to a ship type floater with dynamic positioning and mooring systems. Three-hour time-domain simulations were conducted for the two different station-keeping systems with mooring only and mooring with a dynamic positioning system. Position offsets and mooring line tensions for the two scenarios were compared with maximum values and most probable maxima (MPM) values. The results of the simulation showed that the heading control can reduce 8.2% of MPM values for the mooring lines and improve the station-keeping performance by about 16.3%. The validity of the station-keeping system that was designed was confirmed, and it is expected that the specification of mooring lines can be relaxed with the heading control.

Optimal Set-Point Chasing of Position Moored Vessel

2010 ◽  
Author(s):  
Shaoji Fang ◽  
Mogens Blanke ◽  
Bernt J. Leira
Keyword(s):  
Line Tension ◽  
Small Radius ◽  
Mooring Line ◽  
Mooring Lines ◽  
Environmental Loads ◽  
High Position ◽  
Fixed Weight ◽  
Surface Vessels ◽  
Critical Tension ◽  
Optimal Set

Dynamic positioning of surface vessels moored to the seabed via a spread mooring system are referred to as position mooring (PM), the main objective of which is to keep the vessel within a small radius from a given position while preventing mooring line breakage. When environmental loads become high, position mooring systems apply thruster forces to protect mooring lines and position accuracy may need be relaxed. This paper suggests a new position chasing algorithm that works entirely online, is optimal according to a criterion and can protect any number of mooring lines simultaneously. Tensions of all mooring lines are included in a cost function where the criticality for each mooring line determine individual weights. With this strategy, external environment effects are included directly by without needing predefined tabular settings of environmental loads as in earlier approaches. There is no limitation to the number of mooring lines that can be close to critical tension. A reliability index is used as weight to include the dynamic influence of mooring line tension. Detailed simulations illustrate the features and advantages of the new method and results are compared with those of a fixed weight algorithm.

scholarly journals Transient Responses Evaluation of FPSO with Different Failure Scenarios of Mooring Lines

2021 ◽  
Vol 9 (2) ◽  
pp. 103
Author(s):  
Dongsheng Qiao ◽  
Binbin Li ◽  
Jun Yan ◽  
Yu Qin ◽  
Haizhi Liang ◽  
...  
Keyword(s):  
Service Condition ◽  
Mooring Line ◽  
Mooring System ◽  
Transient Effects ◽  
Floating Platform ◽  
Transient Responses ◽  
Mooring Lines ◽  
Performance Deterioration ◽  
Steady State Responses ◽  
Influence Process

During the long-term service condition, the mooring line of the deep-water floating platform may fail due to various reasons, such as overloading caused by an accidental condition or performance deterioration. Therefore, the safety performance under the transient responses process should be evaluated in advance, during the design phase. A series of time-domain numerical simulations for evaluating the performance changes of a Floating Production Storage and Offloading (FPSO) with different broken modes of mooring lines was carried out. The broken conditions include the single mooring line or two mooring lines failure under ipsilateral, opposite, and adjacent sides. The resulting transient and following steady-state responses of the vessel and the mooring line tensions were analyzed, and the corresponding influence mechanism was investigated. The accidental failure of a single or two mooring lines changes the watch circle of the vessel and the tension redistribution of the remaining mooring lines. The results indicated that the failure of mooring lines mainly influences the responses of sway, surge, and yaw, and the change rule is closely related to the stiffness and symmetry of the mooring system. The simulation results could give a profound understanding of the transient-effects influence process of mooring line failure, and the suggestions are given to account for the transient effects in the design of the mooring system.

Experimental Investigation vs Numerical Simulation of the Dynamic Response of a Moored Floating Structure to Waves

2014 ◽  
Author(s):  
Daniele Dessi ◽  
Sara Siniscalchi Minna
Keyword(s):  
Dynamical Behavior ◽  
Irregular Waves ◽  
Mooring Line ◽  
Floating Structure ◽  
Mooring Lines ◽  
Wave Energy Converters ◽  
Time Histories ◽  
Actual Configuration ◽  
Proper Orthogonal ◽  
Dynamic Wave

A combined numerical/theoretical investigation of a moored floating structure response to incoming waves is presented. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used as a multipurpose platform for hosting wind-turbines, aquaculture farms or wave-energy converters. The dynamic wave response is investigated with numerical simulations in regular and irregular waves, showing a good agreement with experiments in terms of time histories of pitch, heave and surge motions as well as of the mooring line forces. To highlight the dynamical behavior of this complex configuration, the proper orthogonal decomposition is used for extracting the principal modes by which the moored structure oscillates in waves giving further insights about the way waves excites the structure.

Optimized Mooring Line Simulation Using a Hybrid Method Time Domain Scheme

2014 ◽  
Author(s):  
Niels Hørbye Christiansen ◽  
Per Erlend Torbergsen Voie ◽  
Jan Høgsberg ◽  
Nils Sødahl
Keyword(s):  
Hybrid Method ◽  
Time Domain ◽  
Computation Time ◽  
Mooring Line ◽  
Mooring Lines ◽  
Fem Model ◽  
Input Variables ◽  
The Time Domain ◽  
The Cost ◽  
Short Time

Dynamic analyses of slender marine structures are computationally expensive. Recently it has been shown how a hybrid method which combines FEM models and artificial neural networks (ANN) can be used to reduce the computation time spend on the time domain simulations associated with fatigue analysis of mooring lines by two orders of magnitude. The present study shows how an ANN trained to perform nonlinear dynamic response simulation can be optimized using a method known as optimal brain damage (OBD) and thereby be used to rank the importance of all analysis input. Both the training and the optimization of the ANN are based on one short time domain simulation sequence generated by a FEM model of the structure. This means that it is possible to evaluate the importance of input parameters based on this single simulation only. The method is tested on a numerical model of mooring lines on a floating off-shore installation. It is shown that it is possible to estimate the cost of ignoring one or more input variables in an analysis.

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