Irregular Wave and Current Loads on a Fish Farm System

Accurate calculation of the design mooring loads on an aquaculture fish farm mooring system is often a difficult task. The fish farm system has a large horizontal extension with variable environmental conditions across the entire structure. In addition, the drag loads on the fish nets are thought to be the governing environmental force. This means that the mean position of the fish farm is a function of the mean of the fluid particle velocity squared, where the fluid particle velocity must be taken as the sum of current and wave induced fluid particle velocities. Additional offsets will be slowly varying, where the response time will depend on the total mooring stiffness. The magnitudes depend on the height and length on wave groups in the irregular sea state. The paper presents simulations of the response of such a system to a set of combined irregular waves and current conditions. The response evolution in time is discussed as well as parameters affecting the maximum responses in the systems (displacements and loads). Finally, the resulting loads on the fish farm in irregular waves are compared to loads obtained in equivalent regular waves, as this is an often used engineering practice when analyzing the response and mooring loads of a fish farm.

AMBEMAR-DSS: A Decision Support System for the Environmental Impact Assessment of Marine Renewable Energies

The high energy demand and the threat of climate change have led to a remarkable development of renewable energies, initially through technologies applied to the terrestrial environment and, recently, through the awakening of marine renewable energies. However, the development of these types of projects is often hampered by failure to pass the corresponding environmental impact assessment process. The complexity of working in the marine environment and the uncertainties associated with assessing the impacts of such projects make it difficult to carry out objective and precise environmental impact assessments. AMBEMAR-DSS seeks to establish a basis for understanding and agreement between the different stakeholders (project developers, public administrations, environmental organizations and the public in general), in order to find solutions that allow the development of marine renewable energies, minimizing their environmental cost. For this purpose, a DSS is proposed which, based on cartographic information and using objective and quantifiable criteria, allows comparative assessments and analyses between different project alternatives. The analytical procedures used by the system include, among others, hydrodynamic modeling tools and visual impact simulators. In addition, impacts on marine species are assessed taking into account intrinsic ecological and biological aspects. The magnitude of the impacts is quantified by means of fuzzy logic operations and the integration of all the elements is carried out by an interactive multi-criteria analysis. The results are shown in tables, graphs and figures of easy interpretation and can be also visualized geographically by means of a cartographic viewer. The system identifies the main impacts generated in the different phases of the project and allows establishing adequate mitigation measures in search of optimized solutions. The establishment of the assessment criteria has been based on the abundant, but dispersed, scientific literature on the various elements of the system and having the opinion of experts in the various fields. Nevertheless, the DSS developed constitutes a preliminary basis on which to build and improve a system with the input of researchers, promoters and experts from different disciplines.

Investigation on the Probabilistic Distribution of the Stress Range of Net Cage Floater of Fish Cage for Fatigue Life Prediction

The failure risk of fish cages has increased in the harsher environmental conditions as fish farms have moved into the open sea in recent years. Fatigue failure is an important limit state for the floating system of the fish cage under the long-term action of waves. This study is presented to investigate the applicable probability density function for estimating fatigue life of the high-density polyethylene (HDPE) floating collars. The stress response of the floating collars system in random wave is firstly analyzed based on the finite element analysis combined with a hydrodynamic model. The stress histories of floating collars under each sea state are counted using the rainflow method as a benchmark for fatigue frequency domain analysis. The distribution of stress range was fitted by various probability density functions including Rayleigh, Weibull, Gamma and generalized extreme value (GEV) distributions. Comparisons of the estimated fatigue life using different distributions with rainflow statistic results were performed. Results indicate fatigue estimation based on the GEV and Gamma distributions by removing the negligible low stress range give much more accurate fatigue damage results of the short-term stress range distribution. While Weibull distribution overestimates the fatigue lifetime of the floating collar based on the short-term distribution of stress ranges.

Survey Research on Legal System of Floating Residence and on Management of Water Utilization in the United States: Case Study on Seattle, Washington and Sausalito, California

Effective utilization of oceanic space in Japan is just recent compared to U.S. Since the end of 19th century, water utilization and management for residence constructed on lake was promoted in U.S. It is then the aim of this paper to comprehend the laws and regulations for floating residence as well as water utilization and management of United States. Through web survey, each State in United States will be searched if there are existing laws and regulation on floating residence. After searching and reading all conditions of the U.S. States regarding laws and regulation as well as legal positions on floating residence, two states in the west coast of U.S: Seattle in Washington and Sausalito, California are chosen for this study. Floating residence in U.S. are divided into two; the Floating Homes and Houseboats. Floating Homes are handled by law the same with homes built in land while Houseboats are treated as type of ship. The State managing the water will lease it to the private sector, then, building of Floating Home will be carried out. Furthermore, design and construction of Floating Homes follow the building standards of the counties and cities where it will be built.

Predicting the Heading Misalignment of a Vessel-Shaped Offshore Fish Farm Under Waves and Currents

A vessel-shaped fish farm concept for open sea applications has been proposed recently. The whole system consists of a vessel-shaped floater, fish cages positioned longitudinally along the floater, and a single-point mooring system. The whole system weathervanes; this feature increases the spread area for the fish waste. However, the downstream cages may experience reduced water exchange when the vessel is parallel to the currents. This situation may jeopardize the fish health. A dynamic positioning (DP) system may be necessary to improve the flow conditions. This paper investigates the misalignment angle between the heading of the vessel-shaped fish farm and the currents under combined wave and current conditions. The misalignment angle is critical for the estimation of the DP system consumption. A numerical model of the fish farm system with flexible nets is developed. Current reduction factors are included to account for the flow velocity reductions between the net panels. The heading of the system is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. An integrated method using metamodels is proposed and applied for the prediction of the misalignment angle for a reference site. The probability distribution of the misalignment angle between the vessel heading and the currents is calculated using the Kriging metamodel for the reference site. Based on the prediction, the requirement for the DP system to improve the flow condition in the fish cages is discussed.

A Towing Test of a Floating Type VAMT With Cycloidal Pitch-Controlled Blades

Sea areas around the Japanese Islands which is feasible for tidal current generation are not a lot because sea sites where tidal current velocity is above 2.0 m/s are a few. We can find such sea sites at a west side of the Kyushu Island especially. However, we would earn electrical energy to be generated if it is able to generate electricity long time using around 1.0 m/s in current velocity. A vertical axis turbine should be better than horizontal axis types because VATs can take relatively higher torque. It is very useful that we can set and control a marine turbine to be higher performance in various current velocity. The present study introduce variable pitch-control system to a vertical axis turbine for tidal current generation. The pitch-control system adapts a cycloidal mechanism so that to vary pitch angle of turbine blades is conducted mechanically. The study developed a vertical axis marine turbine with cycloidal pitch-controlled three blades which was based on previous studies and experimental data. The diameter of the turbine is 1.0 m, length of a blade is 1.3 m. The turbine was set on a floating structure in order to carry out towing tests at a sea. We obtained several kinds of data from the towing tests, which were turbine torque, the number of rotation of the turbine, output power from an electrical generator and acceleration of the floating structure. As a result, the turbine made 50 W power from the generator. Although the PTO was not so large, the pitch-control was effective very much. Some issues were found at the same time. We need to consider and develop more useful gears, assemble methods to be feasible of variable pitch system.

Basic Characteristics of the Primary Conversion of an OWC Type WEC Installed on a Wave Dissipating Double-Caisson

Several types of oscillating water column (OWC) type wave energy converters (WECs) are researched and developed in the world. They are floating types and fixed types. In case of a fixed type, wave dissipating caissons could be replaced to WECs of an OWC type. On OWC types, installation of the projecting-walls (PWs) is useful in order to improve PTO performance. In this study, it was considered that a double dissipating caisson was used as an OWC type WEC with PWs. A front caisson of the double caisson seems the area surrounded by PWs and a back caisson can be seen as an OWC. The paper studied basic property of the primary conversion from wave power to power of air from model tests in a wave tank. As a result, wave height strongly effects on behaviours of OWC motion as well as air pressure. Finally, the primary conversion was affected by wave height. Besides, the concept of use of a double caisson was useful from the primary conversion over 80 % evaluated using test data.

A Fundamental Study on Collision of a Tsunami Drifting Objects Against Structures Using MPS Method and FEM

The large-scale tsunami generated by the Great East Japan Earthquake on March 11, 2011 caused a great deal of damage. In addition to tsunami hydrodynamic forces, loads generated by drifting objects such as ships and cars can cause destruction in coastal areas. As such, impact forces due to collisions of drifting objects are an important consideration in the design and planning of structures in coastal areas. Depending on the size of the drifting object, it is difficult to evaluate the effect of the impact force at the time of collision through tank experiments. Therefore, it is necessary to develop a numerical simulation method that can reasonably evaluate such effects. Such a method must consider the nonlinear interactions among drifting objects, a fluid, and fixed structures. In the present study, we used the moving particle semi-implicit (MPS) and finite element methods to calculate the effect of collisions between drifting objects and structures, and then verified the results experimentally. The MPS method was applied to calculate the loads and pressures due to the collisions. These results were then used to simulate the deformation of the structure using the finite element method. A tank experiment was then conducted in order to confirm the accuracy of the numerical calculations. The deformation of a rod-shaped steel structure was measured following collision with a floating acrylic plate. The experimental results confirmed the accuracy of the numerical calculations.

Research Regarding the Conceptual Change Observed in the Sea City Concept

From the 1960th to 1980th years in the second half of the 20th century, numerous “sea city concepts” were proposed as a new city image. Among these concepts, in Japan, the sea city concept reflecting the current urban development situation of that time, was drawn by the architects as an image of the ideal city. During that period, in Japan for the purpose of the further economic development, the landfilled industrial zones were created in the surroundings of large metropolitan areas of Tokyo, Osaka and Nagoya. It led to the concentration of the population due to the people fleeing to the big cities from the provinces for employment, which created various problems of big cities such as population overcrowding, land shortage, traffic jams, air pollution, etc., so the different tasks became apparent. As a way to solve such problems, a sea city plan has been proposed. The oldest initiative was the Tokyo Bay concept of 1958 which proposed the creation of a new city by creating a new land by landfilling Tokyo Bay. However, that initiative only covered the expansion of the existing land, and didn’t make any advantage of “ocean” resources. For that reason, the further proposals subsequently enabled taking advantage of the sea by creating the canals, artificial islands or pile-style structures which led to adoption of proposal to float up. After that, the sea city concepts basing on the floating type had increased, and the subjected water area transited from the shallow water to the offshore area. Furthermore, the authors are planning to arrange the process of transition of the concept of the sea city by taking into account the changes the way oceans are treated and the structures relative to time.

A Fundamental Study on Motion Characteristics and Cargo Handling Efficiency of the Large-Scale Floating Coal Transshipment Station

This paper describes the motion characteristics and cargo handling efficiency of the Large-Scale Floating Coal Transshipment Station (LFTS). Indonesia is a main country supplying coal in the Asia-Pacific region, it is important to ensure a stable coal supply to Japan. Because the topography of the seabed near East Kalimantan Island, Indonesia’s main coal production area, is shallow, it is difficult for bulk carriers to reach the coast. Therefore, LFTS is proposed, which will be used as a relay base between coal-barging barges from land and bulk carriers offshore. By installing LFTS, improvement of coal transport efficiency is expected. In considering feasibility of the LFTS system, it is important to know the cargo handling operation rate in the target area, LFTS can load 500,000 tons of coal and the draft will fluctuate greatly depending on the loading condition of coal. Therefore, when the draft is shallow, the freeboard becomes large and resonates with long-term component of the wind load and when the draft is deep, the wave force and fluid force including the slowly varying wave drift force affect the fluctuation. Also, LFTS and bulk carrier are large-scale structures, the fluid forces acting on both affect each other, so the influence of hydrodynamic mutual interference between two floating bodies cannot be ignored. In this study, fluid analysis in consideration of the hydrodynamic mutual interference of LFTS system is conducted. And, response analysis of LFTS and a bulk carrier in irregular wave which considered compound external forces such as wave load and slow varying wave drift force, wind load, tidal current was performed. As a result, it was confirmed that the motion response of LFTS was not upset because LFTS was large. Therefore, without considering the motion response of the LFTS, the cargo handling efficiency is calculated from the response analysis results of the bulk carrier and the oceanic condition of the setting sea area. As a result, the cargo handling efficiency is satisfied in the state where bulk carrier is installed leeward of LFTS, and it was confirmed that the LFTS system could be operated satisfactorily if the installation was appropriate.