A Study on Development of the Performance Analysis Method of the Floating OWC-WEC Using the MPS Method

When concrete examination towards utilization is needed, it is necessary to estimate the safety and the performance of a floating Oscillation Water Column (OWC)-type wave energy converter under abnormal oceanographic phenomenon such as large waves, wave impact force, deck wetness and complex motion of mooring system. Therefore, to choose a proper numerical method is important. This present paper describes a fundamental study about estimation of safety and performance of floating OWC-type wave energy converter using the two-phase flow MPS method. In this research, firstly, new algorithm is installed in order to solve problems of the two-phase flow MPS method. Secondly, applicability to an response analysis of a wharf installation type OWC-WEC of the improved MPS method is examined by wave pressure acting to the OWC-WEC and response in the air chamber of the OWC-WEC.

Hydrodynamic Evaluation of a Generic Sail Used in an Innovative Prawn-Trawl Otter Board

In prawn-trawling operations, otter boards provide the horizontal force required to maintain net openings, and are typically low aspect ratio (∼0.5) flat plates operating on the seabed at high angles of attack (AOA; 35–40°). Such characteristics cause otter boards to account for up to 30% of the total trawling resistance, including that from the vessel. A recent innovation is the batwing otter board, which is designed to spread trawls with substantially less towing resistance and benthic impacts. A key design feature is the use of a sail, instead of a flat plate, as the hydrodynamic foil. The superior drag and benthic performance of the batwing is achieved by (i) successful operation at an AOA of ∼20° and (ii) having the heavy sea floor contact shoe in line with the direction of tow. This study investigated the hydrodynamic characteristics of a generic sail by varying its twist and camber, to identify optimal settings for maximum spreading efficiency and stability. Loads in six degrees of freedom were measured at AOAs between 0 and 40° in a flume tank at a constant flow velocity, and with five combinations of twist and camber. The results showed that for the studied sail, the design AOA (20°) provides a suitable compromise between greater efficiency (occurring at lower AOAs) and greater effectiveness (occurring at higher AOAs). At optimum settings (20°, medium camber and twist), a lift-to-drag ratio >3 was achieved, which is ∼3 times more than that of contemporary prawn-trawling otter boards. Such a result implies relative drag reductions of 10–20% for trawling systems, depending on the rig configuration.

Power Generation Potential of a VLFS Equipped With OWC Type WECs and Damper Effects on Elastic Motion

This paper describes potential of PTO (Power Take-Off) and the damper effect of motion in a large scale pontoon type floating structure on which lots of oscillating water column (OWC) type wave energy convertors (WEC) are installed. It is enable to use upper space for utilizing marine renewable energy such as wind power, tidal power, wave power generation farm using large pontoon structure. Due to the concept, it should reduce cost of maintenance as well. For investigation of PTO and elastic motion behaviours of large floating structures, we calculated three types of models on which OWC devices were installed differently. We examined how much reduction was possible when including elastic motion effects and the fixed type which radiation wave was not taken into account. In this paper, a boundary condition in order to give effect of a free water surface with air pressure is theoretically modeled. We can directly consider influence of wave energy absorption to hydrodynamic forces and wave exciting forces on the floating structure with the Green’s function method based on the linear potential theory. In the modeling, a boundary condition on a free water surface and an equation of state within an air-chamber above OWC are mathematically and linearly formulated. Air-pressures and vertical displacement within OWC areas can be simultaneously and directly solved by setting both the variables and by solving the simultaneously equations of the air-pressure and the vertical displacement. As a result, performance of PTO and hydroelastic motion of the floating structure increased when including elastic motion effect. In addition, expected value of annual PTO was about 4.4MW with 146 OWCs.

On Optimal Method of Mooring Ship in Floating Tsunami Protection Wharf

On the vessels moored the quay, the situation such as drifting and runs on the quay due to the breaking of the mooring lines is generated by the tsunami. The authors are clarified for applicability of the proposed floating tsunami protection wharf (FTPW) and install more mooring tether. The effect of FTPW is most promising as disaster prevention and mitigation measures for the vessels moored quay, but exert a sufficient effect in the transverse tsunami incident, but the effect cannot be confirmed in the longitudinal tsunami incident. Therefore, it is necessary to go in combination in FTPW and tsunami countermeasures in consideration of the longitudinal tsunami incident, such as install more mooring tether and new mooring method. The objectives of present study are to consider valid mooring method for longitudinal tsunami incident and also to propose a tsunami most effective countermeasure of wharf mooring vessel.

Experimental Study on a Motion of “Underwater Platform” Including Hydro-Elastic Deformation in Waves

A new type of floater for floating offshore wind turbine (FOWT) was proposed. The floater, named an “underwater platform”, aims at high economic efficiency of energy generation of floating wind farm. The underwater platform is a large scale submerged structure which has small water plane area and can support several wind turbines. It is expected that the platform has small motion characteristics in waves because of its small water plane area, and it contributes for FOWT to generate energy safety. In this study, the feasibility and usefulness study about the platform was carried out through experiments and numerical simulations. The first experiment was conducted with partial rigid model of the platform to verify the feasibility. From the experiment, it was confirmed that the model has small motion characteristics in waves. The experimental results were compared with numerical simulations of potential theory and they were well matched. Besides, the coupling analysis with aero-hydro dynamics was also carried out and it was confirmed that the stability of the platform was enough in steady wind condition. The second experiment was conducted with elastic body model to study the elastic deformation of the platform in waves. From the experiment, it was confirmed that the deformation is small when the draft was 250mm (50m in the actual model).

Estimation of Risk of Progressive Drifts in a Wind Farm Caused by Collision of Drift Ship

In off-shore wind turbine, it is difficult to determine the risk of accident caused by the mooring destruction through experiment. In this paper, the authors discuss the risk, with the case of a drifting ship wanders into the wind farm. In the design of a floating offshore wind turbine (FOWT), drift of a FOWT is considered as a serious failure mode and the mooring system must be designed to avoid the failure. The failure of mooring line is not initiated just by extreme environmental load but can be initiated by collision with a drifting ship, which enters the wind farm. This phenomenon is difficult to investigate by a tank experiment. So far, little knowledge exists about the phenomenon. In this research, a simulator to reproduce the collision process of a FOWT and a drift ship and a progressive drift of FOWTs in a wind farm was developed. Using this simulator and statistics of drift incidents of a ship, a procedure to evaluate risk of progressive drifts in a wind farm was established. In that case, second accident that a wind turbine which has started drifting caused by the drifting ship collides with one another wind turbine is expected. As a result, the risk mainly depends on the risk of drifting caused by a large displaced ship. In addition, the risk partly depends on the arrangement of wind farm.

Numerical Study on the Deformation of a Net Panel in Steady and Oscillatory Flow

Based on the hydrodynamic coefficients obtained in a series of experiment on a full-scale net panel, numerical simulation is conducted to study the interaction between flow and the flexible net in waves and current. Finite element model was constructed and modified Morison Equation was adopted to estimate the deformation of the net sheet. The deformation of the net sheet was investigated quantitatively by estimating the minimum projected area and comparing the area reduction ratio under each test case. Furthermore, the relationship between the net’s area reduction ratio and the nondimensionalized parameters in the model testing, including the structure’s Reynolds number, KC number, frequency parameter and reduced velocity was discussed.

Evaluation of Wearing Pipe for Subsea Mining With Large Particles in Slurry Transportation

For a fundamental understanding of pipe wear under hydraulic transportation of deep-sea mining, a small scale test is conducted because there are many restrictions in conducting a full scale test. The small scale test apparatus are set up using the pipes of about 80mm in diameter and the rocks of which maximum particle diameters are about 20mm are used. In the test, the pipe materials and the pipe inclination are changed to evaluate the differential of the amount of pipe material loss. Furthermore, the amount of the pipe material loss in full scale is estimated based on the small scale test results.

Basic Plan of Medi-Float on Big Disaster Installed in the River

An innumerable number of buildings in the coastal part of the east side of Japan were devastated by the Great East Japan Earthquake and Tsunami. Medical institutions also suffered the damage caused by tsunami, and the function to carry out the medical act has been spoiled. And the disabled concentrated on the medical institution which avoided tsunami damage. Under such circumstances, assistance from the water area began three days after the earthquake disaster, and much support supplies reached the stricken area. It was revealed that the support from the water area including the river was extremely effective against the stricken area. And then, the Tokyo Inland Earthquake disaster was assumed, floating medical support system (hereafter, Medi-Float) installed in the quay of Arakawa River in Tokyo was proposed. Medi-Float is movable; furthermore, it is built in the structural system of having very high isolation characteristics. The float proposed in this study is a facility based on a completely new concept and hence it is difficult to get approval as simply a hardware structure or facility, even if it is safe. Our study considers the constraints with respect to installing the system on the river as the basic plan of the specific Medi-Float. It takes into account the floor planning and flow planning based on operational methods, considers scale planning and weight calculation and the structural strength of the float foundation. The study conducts basic plan of the feasibility of the first-of-its-kind medical float as a marine structure. As the next step, the research on dynamic behavior of Medi-Float will be started, and the validity of this design is verified, technical issues in the design of the Medi-Float should be clarified.