“Mighty Whale” is a floating Oscillating Water Column (OWC) type wave power device which has a ability absorbing the energy from ocean waves and dissipate the wave height behind the device. So, it can supply the electric energy and can produce the calm sea area for utilizing of coastal zone. Japan Marine Science and Technology Center (JAMSTEC) has put into the project for R&D on Mighty Whale since 1987, and is desighing of the prototype from 1995. So for, we could have a insight on basic behavior, characteristices, safety and economics of the Mighty Whale by theoretical, numerical estimation and evaluation, experimental studies in water tank using the scale models and foundamental discussion on the general design. The construction of the prototype of Mighty Whale will be finished by May 1999, and the open sea test will be carried out by the end of March 2001. This paper describes the project and the design of the prototype of Mighty Whale.
The most of governors for marine diesel engine is still designed based on the classical PID control theory. Various methods have been proposed for tuning PID parameters. One of the conventional methods often used in the gain tuning is the Ziegler Nichols ultimate method. There are some problems, however, when this conventional method is apllied to operating marine diesel engine as follows; 1) It is not always safe technique because a proportional gain in this method is gradually increased until the system reaches a critical state. 2) The success of the technique depends largely on operator's experience. To solve these problems, it is neccesary to adopt some automatic gain tuning technique, which does not give great influences on the system and can be easily implemented without danger. In this paper, a simple and a safe automatic gain tuning method using relay control is provided for diesel engine governor system with PID control law. In this method, a limit cycle with small amplitude is occurred, at the beginning, through a fuel oil pump rack, and then the amplitude and the period of the limit cycle are observed. Since the two quantities obtained under such limit cycle equivalently correspond to those by the Ziegler Nichols ultimate method, these are utilizable as the parameters for obtaining the optimal gains recommended by Ziegler Nichols. This technique is applied to the governor system of a small training ship, full scale experiments were carried out and the results of the experiments are discussed.
Recently the air pollution caused by marine diesel has become a more serious problem. For such engines heavy fuel, e. g. bunker fuel oil, is usually used. High residual portion and long ignition delay are the main disadvantage of heavy fuel. Their effects are especially severe at low load, which is the running condition of ships near the seashore where the pollution is a more serious problem. In this study the emission from a relatively high speed marine diesel engine using heavy fuel is examined. Because the effects caused by heavy fuel can be observed more clearly on a high speed diesel engine, such one was used for the experiments instead of a low speed engine. The experiments show clearly that heavy fuel causes higher smoke density than gas oil. The higher smoke density is caused by direct impingement of the unevaporated residual portion onto the piston. On the other hand the effect of heavy fuel on NOx emission can not be explained simply, because it is influenced by two counteracting effects : the higher pre-mixed combustion rate, which increases NOx formation, and the later ignition timing, which decreases it.