Yukinari Fukumoto

Progressive Drifting of Floating Wind Turbines in a Wind Farm

A wide range of platform types have been investigated for a floating wind turbine. Most of the research projects on a floating wind turbine assume that a land based wind turbine is to be installed on a platform with minimum modification to reduce the overall cost. For this reason, allowable limit of a motion of wind turbine is limited to lower value, for example, five degrees for static inclination and one to two degrees for pitching motion. So far analysis and design of motion characteristics of the platform have been main research concern. One key research area less focused is floating platform related risk. If the wind energy would be one of the major sources of power supply, wind farms which are comprised of large number of floating wind turbines must be deployed in the ocean. Wind turbines will be closely spaced in a wind farm so that installation cost should be minimized. In such an arrangement, a wind turbine accidentally started drifting has some possibility to collide or contact with the moorings of neighboring wind turbines and might cause progressive drifting of wind turbines. This paper present investigation of scenario of progressive drifting of floating wind turbines and evaluate risk of the scenario. Quantitative risk of several arrangements of wind farms is estimated. Effect of arrangement of wind turbines in a wind farm and safety factor used in design moorings is discussed.Copyright

Collision of a Drifting Ship With Wind Turbines in a Wind Farm

A multiple collisions caused by a drifting ship which lost control and entered into a wind farm (WF) may cause relatively large risk for a WF comprised of bottom mounted type offshore wind turbines. A bottom mounted type wind turbine will be installed relatively close to shore in Japan and sometimes close to dense marine traffic area. Consideration of the risk will be necessary in planning a WF.This paper presented an estimation of a damage caused by collision with a drifting ship accidentally entered a wind farm. The WF is assumed comprised of bottom mounted type offshore wind turbines. The size of the drift ship considered in the analysis is 6788 GT. For smaller ships, damage to wind turbine considered to be small. Entry of ships from sides other than the one facing sea route was ignored because the number of ship entries from the sides was considered small. Under a number of limitations, risk of multiple collisions in WF by a drifting ship was formulated and quantitatively estimated.Copyright

Tsunami Wave Force Acting on Axisymmetric Caisson Foundations

Tsunami wave force acting on the axisymmetric caisson foundations was investigated through the hydraulic model tests. Water surface profile of tsunami caused by the 2011 off the Pacific coast of Tohoku Earthquake observed 11m deep and 3km offshore of Choshi city (Fukumoto et al. , 2012) was used as the incident wave. By using the pumptype tsunami wave maker the observed tsunami profile was well reproduced in the wave-basin. Tsunami wave pressure distribution and wave forces acting on the axisymmetric caisson foundations were measured. Based on these experiment data, a mathematical formula expressing peak wave pressure distribution with the parameter of the incident tsunami height was proposed.