Experimental Study on the Motion of a Flexible Hose Net Used in Automated Net-Hauling System

In the set-net fishery, large amount of manpower is needed for hauling the box chamber to harvest fish. With aging problem and labor insufficiency, the labor-intensive net-hauling method faces the problems of lower production, lower efficiency and higher operational risk. An automated net-hauling system using the flexible hose net which is installed in the box chamber is being developed to solve such problems. With air injected from one edge of the hose net, the hoses are inflated and the buoyancy force increases, the net floats up gradually, cornering the fish in the other edge. To corner and harvest the fish efficiently and safely, the deformation and the motion parameters of the hose net are of significance. This paper presents the results of the water tank experiment using 1/6 scale model, which was conducted to analyze the deformation of the hose net with different volumes of air in, the time spent for floating up and sinking down and the average velocities of sinking and floating processes. The results showed that when the attached weight reached 42.5% of the maximum buoyancy force of the hose net, the net could float up gradually in an ideal form and sink down smoothly through natural exhaust and stretched on the bottom of the water tank. The time spent and average velocities in floating up and sinking down processes varied with air pressure and air flow rate, making it possible to control the motion of the hose net by adjusting the air flow in practical operation.

Motion Analysis of Flexible Hose Based on Water Tank Experiment

Set net fishery faces the problems of decrease in harvest, with lack of labor and aging of fishermen. These problems make it necessary to develop a new automatic harvesting way of set net fishery. An automatic net-hauling system is one of the promising ways, while the system using rubber tubes and polyethylene pipes are not prevailing because of the high maintenance cost and the difficulty in the operation. In the present study, the flexible hose net is proposed to harvest fish in the box chamber net of set net fishery. The flexible hose net is installed on the water bottom below the box chamber net. Compressed air is injected from one edge of the hose net to haul the box chamber net gradually, resulting in cornering fish in the other edge. In the preset study, the feasibility of the net-hauling system for set net fishery was examined by water tank experiment. The variation in the formation of the hose net and the time for sinking and floating were examined, changing the parameters such as air pressure and buoyancy balance. As a result, the hose net sank automatically if the weight attached to the hose net was 39% of the total buoyancy of the hose net with full of air. The time spent for sinking operation was about 160 s, which corresponds to about 10 min for actual hose net according to the similarity law. However, it should be noted that the similarity of water pressure could not be reproduced in the water tank experiment. To reduce the sinking time, the initial inner pressure of the hose net must be the atmospheric pressure before the beginning of the sinking operation. There is an inflection point between the flexible hoses with and without air. It is worried that air flow in the flexible hoses may be impeded. So the inside structure of the flexible hoses may have to be improved to secure the air flow in any condition. In relation to the difficulty in reproducing the water pressure condition in the water tank, the numerical analysis will be required to reproduce the motion of the hose net and its sinking time both for scaled and full-scale models. In the future, three-dimensional coupled model of fluid, structure, and air flow will be developed and validated by the experimental data, beginning with the simple two-dimensional modeling of the motion of the hose net.

Experimental Investigation of the Green Water Loads on a Wave-Piercing Tumblehome Ship

This paper presents the results of an experimental investigation of green water loads on a wave-piercing tumblehome ship. A water tank experiment was carried out in head regular waves by using a self-propelling segmented ship model. Wave probes and pressure sensors were arranged on the bow deck along the longitudinal and transverse directions. The height of water and the impact pressure on the deck were measured and their distributions in different wave conditions studied. The motion of the water flowing on the deck was recorded by a high-speed video system. Based on the experimental results, it was found that the green water is more serious with the increase of incident wave height and ship speed. The bow shape has little effects on the occurrence of green water, but it influences the green water loads to some extent. The distribution of green water pressure is different from that of green water height due to the strong nonlinearity of green water pressure.

A Fundamental Study on the Applicability of the Floating Large Size Tsunami Shelter

A floating large-size tsunami shelter (FLTS) has been proposed. The shelter can evacuate more than 1500 people to evacuate from run-up tsunami. The floating tsunami shelter can be lifted by buoyancy when tsunami hitting. In this study, First, Authors assumed Principal specifications of the FLTS from estimation of damage and second we evaluated the validity and safety of a floating large size tsunami shelter using the mooring dolphin by water tank experiment and numerical simulation that is moving particle semi-implicit method (MPS). As a result, enough performance was recognized. The mooring of dolphin was reduced the motion against 10m height tsunami than no moored. However it became clear about the numerical simulation that improvement was more necessary. In particular, the collision model was necessary improved by the existing model.

An Experimental Study on Performance Verification of the New Type High Performance Anchor

In order to prevent the accident of the ships under anchorage, an anchor is a very important tool. The anchor with various types and performances has been developed over the centuries. For example, JIS types and AC-14 types are mostly applied to Japanese ships at present. However, marine accidents by dredging anchor are eliminated even now. As for it, there is a problem in the shape of an anchor. The purpose of this research is to develop a higher performance anchor. In this paper, new type high performance anchor is developed. And, anchor water tank experiment for performance verification of new type high performance anchor is carried out. As a result, the usefulness of the new type high performance anchor was confirmed.