Tadashi Nimura

Experimental Study for SPAR Type Floating Offshore Wind Turbine With Blade-Pitch Control

The experimental proof of the floating wind turbine has been started off Goto Islands in Japan. Furthermore, the project of floating wind farm is afoot off Fukushima Prof. in north eastern part of Japan.It is essential for realization of the floating wind farm to comprehend its safety, electric generating property and motion in waves and wind.The scale model experiments are effective to catch the characteristic of floating wind turbines.Authors have mainly carried out scale model experiments with wind turbine models on SPAR buoy type floaters. The wind turbine models have blade-pitch control mechanism and authors focused attention on the effect of blade-pitch control on both the motion of floater and fluctuation of rotor speed.In this paper, the results of scale model experiments are discussed from the aspect of motion of floater and the effect of blade-pitch control.Copyright

Model Experiments on the Motion of a SPAR Type Floating Wind Turbine in Wind and Waves

The study of floating offshore wind turbines has recently been attractive to many research groups in the renewable energy. Because the area of shallow water along Japanese coast is limited, the development of floating base for wind turbine is inevitable for making large scale wind farms. There are some problems to be solved for floating offshore wind turbines. Besides the mechanical problems of turbines, the influence of the motion of the floater in wind and waves to the electric generation properties, the safeties of floating structures such as the fatigue of machines and structures or criteria of electric facilities should be studied. Several types of floating structures have been proposed such as SPAR, TLP, pontoon, and semi submersibles. The authors have focused on SPAR type because its simpler shape seems to have economical advantages. In this paper, the authors performed experiments in a wind tunnel and a water basin from the viewpoint of “wind turbines on a SPAR type floating structure”. Firstly, forced pitching experiments were operated in a wind tunnel, and the difference in two types of wind turbines, upwind type and downwind type, is discussed. The former type is very popular and the latter type is thought to be suitable for floating structure. Secondly, experiments which thought to be more relevant for a floating wind turbine were carried out in a water basin. The relationship between the location of the attachment point of mooring lines and the motion of the SPAR in waves, and the influence of pitching angle of turbine blades to the motion of the SPAR in waves were inspected. In these experiments it was used a mechanism to control the pitch angle of the blades of the scale model of wind turbine.Copyright

VIM Model Test and Assessment on a Semi-Submersible Type Floater With Different Column Intervals

Semi-submersible type offshore floating structures are expected to be used in the Japanese coastal area and at sea off Japan for promoting resource exploitation and development in near future. As a moored offshore floating structure may be suffered from current, Vortex-induced Motion (VIM) effect should be assessed in an appropriate manner since the VIM may cause fatigue damage of the floating structure’s mooring lines. VIM phenomenon on semi-submersible type floating structures, however, is not clear, and its comprehension is insufficient since there are only small number of open research papers with lack specifications of the structures. Moreover, a standardized assessment method for the VIM on them has not ever been proposed.At first in this paper, the results of VIM measurement test using some large semi-submersible floating structure models in relatively high Reynolds number flow are presented, and afterwards simplified estimation method, that is useful in the design stage for a semi-submersible type offshore floating structure, is introduced as one trial.Copyright

Model experiment of a launcher of a Deep-Sea Monitoring Robot System

National Maritime Research Institute (NMRI), in cooperation with Underwater Technology Research Center, Institute of Industrial Science, University of Tokyo, is developing a Compact Deep-Sea Monitoring Robot System for investigation of sunken ships in deep sea. This system is consisted of a launcher and a small vehicle, and it has characteristics of both AUV and ROV. A launcher corresponds with its mother ship by using optical fiber cable. There is no umbilical cable between a launcher and a vehicle, and the communication is performed by acoustic communication. A launcher submerges holding a vehicle by gravity. It controls its rudders for approaching to a target point. Just before reach the sea bottom, a launcher releases an anchor, launches a vehicle to start mission. In order to pursue the best configuration for effective horizontal movement during descending motion, preliminary calculation and experiments were carried out for two types of configurations, a fuselage with fins and rudders and a fuselage with rudders but no fins. This paper describes the results of calculation and experiments at a deep-sea model basin. The basic mechanism of descend were confirmed.

PMM Test Analysis for Added Mass Coefficients of Asymmetric Bodies

Abstract PMM (Planar Motion Mechanism) test for an FPSO (Floating Production, Storage and Offloading) model of which form is asymmetric were carried out in order to obtain added mass coefficients of the model. Analysis procedure for calculating added mass coefficients of asymmetric bodies is presented. This procedure uses oblique motion test data. The procedure is applied to the PMM test data of the FPSO model. Added mass characteristics of the FPSO model confirm applicability of the procedure to analysis of PMM test data for calculating added mass coefficients of asymmetric bodies.

On steady drifting motion of a ship in waves

Abstract Experiment is carried out to measure hydrodynamic forces and moment in oblique motion in calm water for a training ship model. Wave drift forces and moment for various wavelength and encounter angle for the ship in drifting motion is estimated by calculation of 3-D panel method based on an assumption that these can be approximated at zero forward speed. Equations of motion of steady drifting condition in long crested regular wave are solved by using experimental and calculated hydrodynamic forces and moment. Plural solutions obtained shows that steady drifting condition is not unique.

Evaluation of RTK-OTF positioning system for free running manoeuvrability test of a model ship

A free running model test using the real-time-kinematic on-the-fly (RTK-OTF) mode in GPS was carried out in a 80-by-80 meter square basin. This positioning system consists of three GPS receivers, one radio link and an onboard personal computer for data storage. One GPS receiver was located on the shore as a base station which transmits reference data every 1.0 second and two others were on the model ship as mobile stations which produce fore and aft position data every 0.2 seconds (5 Hz) or 1.0 seconds (1 Hz) selectively. An ultrasonic positioning system was also used for comparison to discuss the accuracy and reliability of the GPS data. Fixed point observations proved that GPS 1 Hz and 5 Hz data had an accuracy of about 0.4 cm and 4.0 cm horizontal RMS respectively. On the other hand, it was observed that error of constant length measurement between the fore and aft GPS antennas which is one of indices to measure accuracy under moving conditions did not exceed /spl plusmn/4 cm for GPS 5 Hz positioning and /spl plusmn/1 cm for GPS 1 Hz positioning. Manoeuvrability characteristics such as speed, yaw rate, drift angle and yaw angle during free running tests were also calculated using fore and aft position data and are confirmed to have sufficient accuracy. Noise sources in the GPS 5 Hz data and their properties are also discussed.

MEASUREMENT OF STERN FLOW FIELD OF A SHIP IN OBLIQUE TOWING MOTION

In this paper, we describe on the results of our investigation on a stern flow field of a ship in oblique towing motion. The purpose of this investigation is to get basic data necessary and available for developing, improving and verifying an estimation method of hydrodynamic forces acting on a ship in manoeuvring motion.We used three VLCC model ships. They have almost same principal dimensions but different stern shapes. One ship has a V shaped stern, another ship has an U shaped stern, and the other ship has a medium shape stern between the V and the U shaped stern.Kinds of experiments that we did are measurement of flow field by 5 hole Pitot tube, observation of flow field by tuft and measurement of hydrodynamic forces acting on a model ship. By these experiments, we investigated characteristics of flow field around a ship in oblique towing motion, and discussed relation among stern shape, flow field and hydrodynamic forces.There is no big difference qualitatively among stern flow field of these three model ships in oblique towing motion, characteristics of which are represented by two groups of separating vortices. However, there are clear differences in strength, concentration and range of distribution of wake and vorticity among three model ships.Concerning to hydrodynamic forces acting on a model ship in oblique towing motion, there is little difference in magnitude itself of hydrodynamic forces, but there is a clear difference in center of pressure that has a serious effect on a ship manoeuvrability.These results will be useful data for framing a flow model, developing, improving and verification of estimation method of flow field and hydrodynamic forces, and for examination of ship stern shape.

Optical Measurement of Model Ship motion Using a Tracking System by a Moving Carriage

Six-degree of freedom motion of a free-running model ship in waves was measured at a model ship basin equipped with a moving carriage by using an optical motion measurement system. The carriage can track a model ship automatically by using another system that measures the horizontal movement of a model ship. Measured optical ship motion data are compared with data obtained by a fiber optical gyro to evaluate the optical data validities. Discussion about applicability of the optical measurement system both to the motion measurement and carriage tracking is provided.

Basic Study of Advanced Sail-assisted Ships

Investigation in wind tunnel tests of the aerodynamic characteristics of a hybrid sail, consisting of a slat, a hard sail, and a soft sail was combined with experimental clarification of the interactive effects of plural hybrid sails on deck. We measured the hydrodynamic characteristics of underwater fins for advanced sail-assisted ships in tank tests, and analyzed their effectiveness on steady sailing performance, as well as investigating through wind tests the aerodynamic characteristics of a new hybrid sail that utilizes a deck crane as its boom. The weather routing system we developed for advanced sail-assisted ships showed in calculations for a North Pacific Ocean route that an advanced sail-assisted bulk carrier can cut emission of carbon dioxide by a total of 17.4 percent on the average, compared with a conventional bulk carrier.