on Floating Offshore Wind Turbine (FOWT) Systems

　Marine renewable energy attracts as one of the solution of grobal warming and depletion of fossil fuels issue. It is often said that an offshore wind generation has a lot of energy potential among the marine renewable energy. Because the sea around Japan is deep, floating systems will be more important than the system of bottom mounted. But the floating system for operation is not fixed yet. We are investigating the floating offshore wind turbine system via both experimental approach and numerical approach for operating economically and managing safely.

Motion of a Semisubmersible type FOWT

The key point of a towarding realization of FOWT is recutction of a cost in construction and installation stage and high efficiency generation. The reduction of motions of FOWT must be need for the solution. We designed and proposed Semi-submersible type FOWT. In the design we considered hydrodynamic interaction among the legs and wave free shape effect to reduce the motion in waves. We carried out a tank test using a 1/100th model of 5MW-class and confirmed and investigated the hydrodynamic motion of FOWT.

SPAR+Vertical Axis type FOWT

It can be installed a main generetor and heavy equipments to the bottom/near water line area of Vertical Axis type FOWT. If it is true, this is a large advantage of a Vertical Axis type for acceissiblity and safty in maintenace work. Of course, low gravity design has an advantage in motion of the FOWT in waves and contributes a minimization of the FOWT system. In that motivation we started the investigation of adaptation of VA-FOWT to economics and safty.

on Floating Wave Energy Converter (WEC)

Wave Energy is one of the Marine renewable energy like offshore wind, current and tidal energy. Wave Energy Converter (WEC) is a device which can trans a wave energy to an electricity by its motion and so on. The point of wave energy is that it is vibrated unlike wind and current energy. So, there are numerous challenging points to achive the realization of floating WEC. Our view point is basically the optimization of the shape, mass distribution and arrangement of the bodies capturing the wave energy via the numerical and experimental approach.

Anti-symetric shape WEC system

There are two types in WEC one of which is to convert the wave energy via potential energy induced by relative wave displacement to a floating body and the other one is to convert the wave energy via a dynamic energy of a floating body. In this research we focused on the later one. The proposed model (see in picture) has an anti-symmetric shape which is easy to be oscillation in waves.

on Mooring line systems

There are many floating offshore structures in the world. Mooring lines are necessary equipments for keeping their position on site reasonably even in a harsh sea state. We developed a numerical code which can treat the interaction between a floating body motion and dynamic motion of catenary type mooring lines based on 3-D BEM and Lumped-Mass method.

Non-linear response of moored floating structure in waves

It must be need the floating structure for development the ocean space. And the structure must be connected to the sea bottom via mooring lines. Many of the researches and a dynamic equation treat the restoring force of mooring lines as like spring effect. This means the effect of the mooring lines' reaction force will act linearly to the floating structure via the spring coefficents. In this reseach we forcus the change of the spring coeffients due to the length of line, depth of the sea and so on.

Tool for optimization of the combination in the mooring system

There are various types of mooring systems each of which has a paticular response charactor. When we design a mooring system, we choose one system which satisfies the requierment from numerous vairous combination. In the research, weight of chain, distance from anchering point and tension of a mooring line are changed as the design parameter, then we examine the sensitivity of these parameters.

on Hydroelastic motion of VLFS

A Very Large Floating Structure (VLFS) is relatively thin plate like structure comparison with its horizontal width. So an elasticity of the VLFS is relatively smaller than ordinal ship and floating structure. The low elasticty induces its elastic deformation in waves. The inteeaction problem between the elastic deformation and the hydrodynamic force is called as hydroelastic problem. We analyze the hydroelastic problem of a VLFS.

Optimization of the horizontal shape of VLFS in 2 directional waves
It is often said that a VLFS consists of multi floating units. This means that there is a combination of the unit for reduceing the hydroelastic deformation of the VLFS. The figure shows the one of the example of hydrolastic deformation on a VLFS in 2-directional waves and wave field around the VLFS.

on Hydrodynamic motion of Riser in deep sea

When we pump an oil from a oil field at sea bottom, we must use a pipe. The pipe is called as riser. The riser is usually made by steel but often made by flexible materials. Of course, the flexibilty induce the deformation of the riser by various external force. We examined the deformation of the riser via the model experiment and numerical consideration.

on Impact of a human activity to an ecosystem of coastal zone

We investigate a number and a size distribution of short-neck-clam at Uminokoen in Yokohama city almost every month. The sea side park (Uminokoen) is well known as a leisure (=shiohigari & swiming ) spot. Do you know shiohigari? If you know the shiohigari event of Japan, you will have an interest of the impact of the shiohigari to the eco-system of Uminokoen.
Investigation @Tokyo Bay