In this study, in order to manufacture an underwater apparatus that can control the depth and posture itself in shallow sea, underwater depth-posture perceptive system had been developed. It had been examined experimentally as following ; the trial underwater apparatus, which was composed of the depth-posture sensing section, signal-processing section, actuator controlling section, power supply section, plastic body, and four actuators with a propeller, had been made. The pressure sensor and acceleration sensor were adopted as the device of sensing the depth and posture. The signal processing had been constructed based on an equation of motion conceming a body in underwater. The motion experiment of the trial apparatus had been conducted in the 3m-depth serene water pool. The experimental results indicated the depth-posture perceptive system was effective, because it had controlled the trail device based on detecting the physical quantity of the motion.

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本論文は油と水からなる二層流体の刃型堰越流に関する理論的研究である。これはまた,越流堰を備えた タンクで海面に流出した油を回収する際,堰を越流してタンクに流入する油と海水の流量を推算するための 基礎的研究である。ここでは,油と水が堰を越流する場合について,エネルギー式に基づく解析解を求め, 実験値と比較した。油と水が刃型堰を完全越流する場合,限界水深は堰のやや下流側で形成されることが示 唆された。

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'Japan Sea Proper Water' exists deeper than at the depth of 200m in Japan Sea. This water、is purity, lower in water temperature and richer in nutrients than upper water of Tsusima Current. Its upwelling to euphotic zone enables a sea area to improve primary production and forms productive fishery ground. We consider that the intemal waves between those two layers lift up the nutrients-rich water to euphotic zone and also have a close relation to fishes living on continental shelf. In this paper, we focus on off westem Hokkaido area and the characteristic of the intemal wave which exists in about 200m depth was investigated in hydraulic experiment for creating fishery ground. The results are as follows ; 1) One of the intemal waves off Westem Hokkaido is generated by the pulsation of the Tsusima warm current at the Tsugaru strait and transmitted along west coast of Hokkaido under the influence of Coriolis force. 2) The sea areas which have large intemal wave height are selected. The places are expected to use intemal wave easily for planning the fishery ground. 3) Experiments with three different scale models were carried out. These results shows reasonable agreement in terms of distribution Of the intemal wave height.

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In case of fishing training vessel, the engine room is much narrower and much noisier than that of merchant training ship, and it is hard to hear the voices of speaker partner. Therefore, it is difficult to educate the cadets by the orals. With a view to improve the education, a experiment was conducted to evaluate a radio communication system for training on noisy engine room. This system consists of a noise-canceling microphone and radio equipment, which was allowed the two-way conversation by clear voice between engineer and cadets. The results showed that this system was in a good, and the system also resulted clear voice to contribute to leveling up the training efficiency. This result suggests that this system could be utilized as a radio communication for education and training on engine room.

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We tried to prevent settlement and proliferation of marine fouling organisms by electric current using titanium wire. Experiments were carried out over two periods between June 1997 and January 1998. During the first period, We set polyvinyl chloride plates, which each had a titanium electrode around them and a weak electric current passed through them. We changed the distance between the two electrodes, that is the length of the plates, and examined the degree of fouling on the plates. During the second period, we extended the titanium electrode which was 6.4m long to increase the electric current. We also set ropes to examine the fouling on the ropes. We used solar panels and rechargeable batteries as the power supply and for the electrode, cords in which titanium thin wire was twisted. We could constantly supply about 8V. During the first period, 1 or 2mA of current was used. A lot of fouling organisms were observed on the plates regardless of the distance of electrodes or the use of electricity. During the second period, a current of more than 6mA was used. Minimal fouling was observed on the ropes. We estimated that the electric current more than 6mA was sufficient to prevent marine fouling organisms although further experimental confirmation is needed.

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Growth and survival rate were examined for adult Ruditapes philippinarum in Honjo Area of Lake Nakaumi. This area is a brackish lake enclosed by embankments built for reclamation. Two pipes for sea-water induction of 2.5m in diameter were constructed on March 1998, to investigate potential of fishery promotion. Containers carrying 50 individuals of Ruditapes each were set on lake bottom of 2 stations ; (1) Pipe-Front in Honjo and (2) Off-Eshima in Honjo Area. Growth, Survival rate and water quality (temperature, salinity, dissolved oxygen) were examined between 1.5m and 4m in water depth for these stations, from June 4 to November 5 in 1998. Shell growth is apparently higher among individuals set on 1.5m depth than on 4m depth, for both Pipe-Front and Off- Eshima stations. This low growth on 4m depth was supposed to be derived from combined factors such as lower dissolved oxygen, lower food supply, lower water current effect and so on. Mass mortality occurred around off Eshima Island in the end of July. This event was derived by concurrent death of sea algae, Cladofphora speciosa. The water current through the induction pipes appears to make better environment for animals enough to ayoid the influence of this mortal event. However the pipes could not avoid the low growth of Ruditapes on 4m depth.

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An experiment was conducted on the selection of artificial fish habitats by Silurus (parasilurus) asotus according to their materials, and the effects of such materials on their behavior. Four pipes each of bamboo, vinyl chloride, concrete and ceramic were placed on the tank bottom, The number of time Silurus asotus entered the pipes of each material, as well as the number, length of stay and behavior of fish in the pipes were observed. The percentage of pipes entered by Silurus asotus was 53.7%. The percentage of entry by material was hichest for bamboo, followed by concrete, vinyl chloride and ceramic, The percentage of entry by two fish at the same time was in the order of bamboo vinyl chloride, concrete and ceramic, and that of entry by three fish at the sane time was in the order of bamboo, concrete, vinyl chloride and ceramic, Bamboo, pipes ranked the highest in all cases. The good results with bamboo pipes both in terms of the number of fish entering and the length of their stay, were presumed to be caused not only by the taxis of Silurus asotus, but also by the unique attractiveness or the nature of bamboo, which hindets transmission of sound and vibration by absorbing vibrations, however, details could not be elucidated in this experiment.

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Behaviour and habitat of the red spotted grouper Epinephelus akaara was studied by underwater observation at Tajima Coast of Hyogo prefecture in Japan Sea. It was suggested that rocky reefs should be necessary for the fish as a habitat, especially for juvenile. The habitats in juvenile were shallower than 5m depth and deepened with growth. From the results of the observation, the release of artificial seedlings should be conducted to rocky shore with some crevice or piled rock in 5m depth.

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The intemal wave is closely related to the seawater quality and the behavior of fish in coastal sea area. Therefore, the characteristics of intemal wave have been used extensively to make some attempts for creation of fishing grounds and nurseries. The intemal wave is generated by meteorological change of wind or atmospheric pressure, ocean current,tide and so on. The paper presented the generation mechanisms, theoretical analysis and program coded with BASIC for the calculation of two-layered interfacia=ong wave generated by tide. And it also explained the numerical calculation of two-layered interfacial long wave that was generated by tide in the region of continental shelf, submarine ridge and bay. The Coriolis forde caused by the rotation of the earth was neglected here.

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