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.
SUMMARYThe authors created a Web-based integrated education support system that unified the data in the administrative system and the education system in a university. The purpose of the system was to make the administrative system and education system data that had previously been separated seamless, and to implement seamless access from inside and outside the university while maintaining security. Moreover, the authors emphasized the development of a portal site as a point of contact for the system. As a result of using software packages and existing technology for the other servers and databases, and making a policy of not changing the administrative system at all, the authors were able to create the system in a short period of 5 months. After the system was operational, preparation and review for class could be done at home, and evaluations of reports and final determinations of grades could be done from outside the university. This confirmed that the education system was effective. Finally, the authors looked at the trouble and performance problems that occurred involving local rules in the business department during operation, as well as countermeasures for them.
Autonomous underwater vehicles (AUVs) have become promising tools for marine geological surveys to collect information such as the topography of the seafloor and the location of hydrothermal plumes. Visual surveys and sampling are mainly conducted using human-occupied vehicles or remotely operated vehicles. To obtain detailed visual data more efficiently, a hovering-type AUV (Hobalin), which has the novel ability to autonomously navigate within a vent field, was developed to explore hydrothermal deposits. This vehicle was deployed in an active hydrothermal vent field located in the western offshore of Kumejima Island at a depth of approximately 1,400 m. Visual observations were performed with submillimeter image resolution via low-altitude navigation using still cameras. Moreover, a height estimation method for chimney structures was proposed utilizing an obstacle avoidance system composed of a sheet laser and a forward-looking camera with hovering maneuver capability. It was determined that hovering-type AUVs can facilitate the effective survey of hydrothermal vents and the acquired data can be utilized for subsequent sampling by human-occupied vehicles and remotely operated vehicles.
This paper addresses experimental and numerical validation of power output efficiency about an approximate complex-conjugate control with considering the copper loss (ACL) method. A bottom-fixed point absorber type wave energy convertor (WEC) model was used for the experiments carried out at National Maritime Research Institute, Japan (NMRI). In order to model a power take-off (PTO) system constructed by a permanent magnet linear generator (PMLG), a liner shaft motor (LSM) was used for the model test. To investigate characteristics of the ACL method, the resistive load control (RLC) method and approximate complex-conjugate control (ACC) method were also tested by the WEC model. A simulation code based on WEC-Sim (Wave Energy Converter SIMulator) v2.0 written by MATLAB/Simulink, which is developed by collaboration works between the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (Sandia), was used for the validation. The simulated results in regular waves have good agreement with measured ones in terms of the float heave motion, the vertical force and the control input force. Through the experiments and numerical simulations in regular waves, the ACL method has advantages in high power production compared with the RLC and the ACC methods for the WEC model. In addition, the power output characteristics of the ACL method in irregular waves were checked experimentally and numerically.
There is an increasing need for utilization of ocean renewable energy (ORE) around Japanese coast because Japan is surrounded by ocean. Because technologies for harnessing ORE have not been mature enough, Japanese government selects some demonstration sites for ORE devices and some demonstration projects are going. As these projects are progressed, the operation and maintenance (O&M) activities will increase and become essential factors for the success of demonstration projects. Hence, weather window analysis is required to quantify the levels of access for ORE devices in the demonstration projects, and commercial projects in the future. In this paper, two new parameters are proposed in order to evaluate accessibility to ORE devices. One is the operational probability, and the other is the forecasted waiting time. The operational probability assesses weather duration with considering variability of wave condition. The forecasted waiting time is an expectation value of waiting time before O&M planners get next chance to arrange the O&M activities. In order to check the effectivity of the proposed 2 parameters, accessibility is evaluated for significant wave height in terms of the 2 proposed parameters, these are • Operational probability • Forecasted waiting time and 3 conventional parameters, these are • Excess probability • Persistence probability • Waiting time between windows The accessibility is evaluated at two locations along the Japanese coast. This study reveals that large differences are caused between persistence probability and operational probability when operational wave height limit occurs intermittently and required window length is long. The forecasted waiting time has the same variation tendency as the waiting time between windows.
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