Dynamic Behavior and Deformation Analysis of the Fish Cage System Using Mass-Spring Model

Fish cage systems are influenced by various oceanic conditions, and the movements and deformation of the system by the external forces can affect the safety of the system itself, as well as the species of fish being cultivated. Structural durability of the system against environmental factors has been major concern for the marine aquaculture system. In this research, a mathematical model and a simulation method were presented for analyzing the performance of the large-scale fish cage system influenced by current and waves. The cage system consisted of netting, mooring ropes, floats, sinkers and floating collar. All the elements were modeled by use of the mass-spring model. The structures were divided into finite elements and mass points were placed at the mid-point of each element, and mass points were connected by springs without mass. Each mass point was applied to external and internal forces, and total force was calculated in every integration step. The computation method was applied to the dynamic simulation of the actual fish cage systems rigged with synthetic fiber and copper wire simultaneously influenced by current and waves. Here, we also tried to find a relevant ratio between buoyancy and sinking force of the fish cages. The simulation results provide improved understanding of the behavior of the structure and valuable information concerning optimum ratio of the buoyancy to sinking force according to current speeds.

Energy Consumption and Greenhouse Gas Emission of Korean Offshore Fisheries

This paper presents the energy and greenhouse gas(GHG) emission assessments of Korean offshore fisheries. The consumption of energy by fisheries is a significant concern because of its attendant environmental effect, as well as the cost of the fuel consumed in fishing industry. With the global attention of reducing GHG emission and increasing energy efficiency of fuel, the seafood industry needs to further understand its energy use and reduce its GHG emission. In the present study, the amount of energy consumed and the GHG emission of Korean offshore fisheries in a period from 2009 to 2013 were examined. Offshore fisheries accounted for 24% of Korean production in 2013 and 60% of fuel consumption related GHG emission. Whereas the total GHG emission intensity of this sector improved slightly between 2009 and 2012; as such emission decreased by approximately 1.9%, which increased again in 2013. The average amount of total GHG emission in this five years period was 1.78 × 10~6 tons of carbon dioxide equivalent/year(tCO_2eq. y^(-1)). Active fishing gear was found to consume 20% more fuel than passive gear. However, the production from passive gear was 28%, lower than 72% from active gear. The reason for this is that less abundant stationary resources are harvested using passive gear. Furthermore, the consumption of fuel was significantly influenced by the fishing method. Implementation and development of new fishing technologies and methods are important for improving energy efficiency and reducing the climate impact on fisheries. To realize these purposes, the fishery management system needs to be established by centralizing on energy efficiency and climate effect.

Experimental Investigation and Numerical Analysis to Develop Low-Energy Large-Midwater Trawls

Fuel consumption in fisheries is a primary concern because of its effects on the environment and the costs incurred by fishermen. Many studies have been conducted to reduce the fuel consumption in fishing operations. Fuel consumption due to fishing gear during a fishing operation is generally related to the hydrodynamic resistance on the gear. This means that fuel consumption is proportional to the drag created by the towing speed. Based on numerical methods, this study suggests a new approach to reduce fuel consumption in fisheries. The results of the simulation are in good agreement with those of model experiments. The total as well as partial resistance forces on the gear are calculated by simulation. The simulation results suggest improved materials and gear structure for reducing the hydrodynamic forces on the gear while maintaining gear performance. The method for assessing the gear performance involves measuring the height and width of the net mouth. Furthermore, this study investigates the efficiency of a low-energy trawl from an economic point of view. The findings of this study will be useful in reducing greenhouse gas （GHG） emissions in fishing operations, and thereby contribute toward lowering fishing costs by saving fuel.

A comparison of two wave energy converters’power performance and mooring fatigue characteristics-One WEC vs many WECs in a wave park with interaction effects

The production of renewable energy is key to satisfying the increasing demand for energy without further increasing pollution.Harnessing ocean energy from waves has attracted attention due to its high energy density.This study compares two generations of floating heaving point absorber WEC,WaveEL 3.0 and WaveEL 4.0,regarding their power performance and mooring line fatigue characteristics,which are essen-tial in,e.g.,LCoE calculations.The main differences between the two WECs are the principal dimensions and minor differences in their geometries.The DNV software SESAM was used for simulations and anal-yses of these WECs in terms of buoy heave motion resonances for maximising energy harvesting,motion characteristics,mooring line forces,fatigue of mooring lines,and hydrodynamic power production.The first part of the study presents results from simulations of unit WEC in the frequency domain and in the time domain for regular wave and irregular sea state conditions.A verification of the two WECs’motion responses and axial mooring line forces is made against measurement data from a full-scale installation.In the second part of the study,the influence of interaction effects is investigated when the WECs are installed in wave parks.The wave park simulations used a fully-coupled non-linear method in SESAM that calculates the motions of the WECs and the mooring line forces simultaneously in the time domain.The amount of fatigue damage accumulated in the mooring lines was calculated using a relative tension-based fatigue analysis method and the rainflow counting method.Several factors that influence the power performance of the wave park and the accumulated fatigue damage of the mooring lines,for example,the WEC distance of the wave park,the sea state conditions,and the direction of incoming waves,are simulated and discussed.The study’s main conclusion is that WaveEL 4.0,which has a longer tube than WaveEL 3.0,absorbs more hydrodynamic energy due to larger heave motions and more efficient power production.At the same time,the accumulated fatigue damage in the moorings is lower compared to WaveEL 3.0 if the distance between the WECs in the wave park is not too short.Its motions in the hor-izontal plane are larger,which may require a larger distance between the WEC units in a wave park to avoid losing efficiency due to hydrodynamic interaction effects.