Underwater welding techniques are recently used for the repair and maintenance of offshore structures. There are two types of underwater welding techniques such as“dry”and“wet”. They are identified in accordance with the existence of water in the welding environment.
Although dry welding seems to be more frequently used in practical applications, wet welding is simple and less expensive, and so it is more appropriate especially for the emergency repair. In this paper, mixed gas shield welding is executed to estimate fundamental characteristics of wet welding. Coefficients of heat transfer are used to evaluate how much heat energy is transferred from the plate surface to surrounding water. In addition, three dimensional FDM is applied to numerically analyze temperature distributions within the plate, where coefficients obtained above are incorporated.

View full abstract

Profiles of gas species concentration and temperature (T _max: K) near the tip in normal diffusion flames of various fuel structures are measured, paying special attention to the role of reaction zone on the formation mechanism of soot precursors in the blue-violet flame. The fuels chosen for study are 1-Butene, 2-Butene, 1, 3-Butadiene, Acetylene, Allene, Benzene, Toluene, and Ethene. The sooting tendency of employed fuel becomes much highter as the T_max is measured much lower.
Toluene>Benzene>Allene>Butadiene>Acetylene>Ethene.
It show that sooting tendency due to fuels is independent of the initial fuel concentration from the measured results of temperature.

View full abstract

This paper presents the influence of injection direction on the performance of a diesel engine driven by water-in-gas oil emulsified fuel.
The experiments were conducted on a small direct injection diesel engine equipped with a bowl in the piston, and the directions of fuel injection were changed from the bowl center (ψ=0°: normal condition) to the side wall of the combustion chamber (ψ= 50°), using a single hole nozzle with nozzle diameter of 0.6mm.
It was found that when water-in-gas oil emulsified fuel was used, the specific fuel consumption increased significantly compared with gas oil operation as the injection direction changed toward the side wall of the chamber, especially at ψ=50°, whereas the NOx concentration and smoke density were remarkably reduced.
The reason may be considered that the degree of constant volume of combustion ηglh and the cooling loss φw deteriorate respectively.

View full abstract

A study is made on a relatively simple system which can find the abnormal conditions of a diesel engine in a short time utilizing the sounds emitted from the engine. The 4-cycle diesel engine, whose rated power is 1100kW, is used in this experimental study. The experiments are carried on a voyage.
A statistical method can be used for detecting abnormalities. The basic sound pattern of normal operation in the engine is formed. Sample sound is compared with this basic sound pattern, and judge whether the engine turn abnormal condition.
In this system, authors cosider a series of process of the sounds sampling, data processing, judging whether the sounds are normal, as a sequential operation and examine algorithm which can quickly perform these processings by a personalcomputer. In conclusion, this paper shows the results of this system continuously performing a series of processing from sounds sampling to judgment on whether they are normal. The diagnose takes time of 28 seconds for a 4 stroke cycle, and its results can also be commented favorably.

View full abstract

This paper has two objects, one is to present a new computer control system for a digital control system (DDC) instead of a conventional governor for the main diesel engine and another is to discuss a control law based on the discrete type of the PID controller.
In general, in the case of operating the diesel engine, the governor is indespensable because of its unstable control characteristics, and has played very important roll so far. But, with year there have been a lot of requests to the engine governor, for example, how to overcome the propeller racing, how to decrease fuel oil consumption and so on. In particular, the propeller racing in the rough sea has been a very serious problem in the ocean going ship, because this phenomenon breaks down the propulsion system and then decrease its reliability. Consequently, for studying on such serious and difficult problems, we constructed a new DDC system for the marine systems at the same time when the training ship“SHIOJIMARU”was built up in 1988.
Next, we investigate the characteristics of on the discrete type of the PID theory from the viewpoint of practical techniques. More, we propose our new control method for the speed control of the diesel engine and then on the basis of our new method, we provide the outline of software used in our sea test.
Finally, the DDC based on the computer system is proved to be very useful system by illustrating our experimental results.

View full abstract