• Journal of the Korean Society for Marine Environment & Energy
• /
• v.17 no.3
• /
• pp.198-204
• /
• 2014

Ships sailing the seas encounter air resistance. The air resistance depends on the shape of the above-water hull, the ship speed, the wind speed and wind direction. The experimental or statistical methods which are used to predict the air resistance are one of the essential procedures of the calculation of the towing force of the disabled ships. This paper shows simplified air resistance prediction method using the variables of the projected area of the above-water hull, the speed of the ship, the wind speed and its direction. These methods have been applied to the existing computer program which had been set up to predict the towing force of the disabled ships.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.59 no.4
• /
• pp.344-353
• /
• 2023

In the actual sea, the additional resistance due to external force such as wind, current and wave is accompanied, and the required power is added in response to these resistance. Especially when the ship is sailing at low speed, the effects of wind and current have a great impact on the safe control of the ship. Likewise, it is thought that the effects of wind and current have a great impact on the trawl ship control since the towing speed of a bottom trawl ship is a low speed of 3 to 4 knots. If the reduce of ship speed and the increase of engine power due to the influence of wind and current can be identified, the safe towing power can be calculated based on a given engine output. Thus, the appropriate size of a fishing gear can be determined. In this study, a total of 20 trawl operations were conducted for seasonal maritime research in the same research area according to the operation mode of propeller. Based on navigation data, trawl fishing data, and engine performance data acquired during the towing fishing gear, and data of ship speed, hull resistance, fishing gear resistance, wind force and current force according to an incidence angle were estimated. The overall power for these loads was calculated and compared with the measured engine power, and the effects of wind force and current force on the engine power were investigated.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.17 no.1
• /
• pp.9-14
• /
• 1984

To study the correlation of the net drag force, net height, and towing speed, three kinds of similiar size model trawl nets were experimented in the still watertank ($60m{\times}4m{\times}3m$). The scale ratios of model nets, 2 seam, 4 seam, and 6 scam net were 1/31.3, 1/20.0, and 1/44.4 respectively, The maximum streched circumferences of the bag net were same length, i. e. 140cm. Net drags were propotional to the $1.75{\sim}1.98th$ order of towing speed and showed similar result as Koyama's net drag equation. Net heights were propotional to the $-0.85{\sim}-0.72th$ order of towing speed. It could observe that the towing nets showed normal shape in $3.0{\sim}3.5$ knot full scale towing speed but bad shape below $1.0{\sim}1.5$ knot. And it showed tendency to lift the bag net and codend with increasing speed.

• Structural Engineering and Mechanics
• /
• v.83 no.6
• /
• pp.835-851
• /
• 2022

This paper analyzes the variation law of the pipe lateral vibration characteristics, it was treated as a beam model, and was dispersed into several subunits based on the FEM. The corresponding stiffness and mass matrix of the pipe was deduced by using Hermite interpolation function, and the overall dynamic balance equation was established. The lateral vibration under different pipe lengths, thicknesses and towing speeds are solved by integral method. The results show that the pipe vibration trend decreases first and then increases, and the vibration value at the ore bin is larger than that at the pump set, and the value at the top is the largest, and the least value location can change with the length increase. Increasing length and thickness can reduce lateral vibration value, while increasing speed can increase the value. Neither the thickness nor the towing speed will change the location where the least value occurs. The vibration intensity will increase with the decrease of pipe length and thickness and the increase of towing speed.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.33 no.2
• /
• pp.118-131
• /
• 1997

An opening efficiency experiment of anchovy boat seine has been carried out using a half size of the ordinary seine to reduce the size of the seine net and to improve the fishing efficiency from field operation. The intervals of towing boats were set at 100, 200 and 300m, and the towing speed, at 0.6, 0.9, and 1.2k't by possible combinations of them. The vertical openings of wing net, inside wing net, bagnet and flapper as well as the spreads of the seine net and the towing tension of the warp were measured, to find out efficient fishing gear and method of the anchovy boat seine. The results obtained are as follows : 1. The vertical opening of the inside wing net ranged from 8.7m to 12.0m at the normal current and from 7.0m to 10.0m at the counter current, and that of the wing net, from 8.4m to 19.8m at the normal current and from 4.9m to 16.3m at the counter current. The vertical opening of the wing net and inside wing net decreased as the towing speed and intervals of the boats increase, from 66% to 16% and from 32% to 18% of the normal opening, respectively. 2. The vertical opening of the fore of bag net ranged from 7.9m to 12.8m at the normal current and from 7.4m to 9.7m at the counter current, and that of the flapper, from 3.4m to 5.1m at the normal current and from 4.4m to 5.1m at the counter current, and that of the flapper, from 3.4m to 5.1m at the normal current and from 4.4m to 5.1m at the counter current. The vertical opening of the bag net was from 98% to 57% of the normal opening and the flapper showed a circular shape and it rose up to the upper layer with a slower towing speed. 3. The vertical opening of the end of the bag net ranged from 7.1m to 9.3m at the normal current and from 7.4m to 8.8m at the counter current. The end of the bag net rose up to the upper layer, This phenomenon was more apparent as the towing speed and the interval of the boats increase. 4. The towing tension of the experimental nets increased from 648kg to 2,716kg at the normal current and from 1,050kg to 6,010kg at the counter current with increasing towing speed. 5. The net depth of the anchovy seine was stable with the higher towing speed and the wider interval of the boats, but it was unstable by rising up to the upper layer with the lower towing speed and the narrower interval of towing boats.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.57 no.4
• /
• pp.271-282
• /
• 2021

This study aims to understand the opening efficiency of the finless porpoise escape guide net by the type of extension net that is the part to which the escape guide net is attached in stow net. To this end, extension nets were manufactured in full size and the net mouth area and towing tension were investigated according to the towing speed (0.2, 0.4, 0.6 and 0.8 m/s) and the type of extension net (25 mm net and raschel net) in the water tank. As a result, the net mouth area of the guide net was larger when the raschel net was used for the extension net than when the 25 mm net was used under all towing speeds. In addition, regardless of the type of extension net, the net mouth area reached about 80% of the maximum value at a towing speed of 0.4 m/s. In the field, fishing operation of stow net is performed only when the current speed is above 0.4 m/s. Therefore, the speed of 0.4 m/s was confirmed as a meaningful value to determine whether it is possible to operate. As a result of analyzing the relationship between the net mouth area of the guide net and the towing tension, it was confirmed that the difference in the net mouth area of the guide net according to the type of the extension net was due to the difference in the solidity ratio.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.36 no.4
• /
• pp.281-286
• /
• 2000

To analyze the shape of the net mouth of bottom trawl which is composed with 6 seams net, the field experiment was carried out on the sea near Kokunsan Is, Western sea of Korea. The distance of otter board, net height, trawl speed and resistance of the fishing gear were respectively measured according to the change of warp length and towing speed. The results obtained are summarized as follows : 1. The spreading distance of the otter board has been increased straightly according to the increment of towing speed and warp length. The rate of increase by the warp length has been greatly higher than the rate of increase by the towing speed. The total variation of the spreading distance was 57.0-82.8m, and it was occupied 43-62% of the hand rope, net pendent and the length of nets. 2. The height of net mouth has been decreased straightly according to the increment of towing speed and warp length. The rate of decrease by the towing speed has been greatly higher than the decrease rate of the warp length. The total variation of the net height was 3.1-4.0m. 3. When the distance of wing tip is increased, the height of net mouth is decreased, but the ratio of the decreasing rate of the height of net mouth for the increasing rate of the distance of wing tip was gradually low according to the increment of warp length. 4. The ratio of the distance of both wing tip for the height of net mouth has been increased gradually according to the increment of towing speed and warp length, and the total variation of the ratio was 4.17-7.81 times.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.51 no.3
• /
• pp.312-320
• /
• 2015

The 1/5 scale-down model of the Bycatch Reduction Device (BRD) from an Argentinean demersal trawl was tested in a circulating water channel. The BRD is designed to help small Hake (merluza, merluccius hubbsi) to escape from a trawl. It is settled in front of a trawl codend, and is equipped with selection grids that help small fish to escape from the gear and guiding panels that help fish to meet with the grids. Bars of the grids are wires covered by the PVC and other parts of the BRD are made of net. When the velocity was less than 0.65 m/sec (2.81 Kont when translated to real towing speed) which is slow speed compared with real towing speed, position between an upper guiding panel and an upper selection grid were good to help small fish to escape. When the velocity was more than 0.8 m/sec (3.41 Knot when translated to real towing speed) which is similar to and faster than real towing speed, it was considered that small fish may have difficulties in escaping because the gap was not enough between an upper guiding panel and an upper selection grid. The lower selection grid was sat on the bottom of the tank without an angle due to the weight that it carries. Improvements were proposed to position the panels and the grids better.

• New & Renewable Energy
• /
• v.7 no.4
• /
• pp.42-49
• /
• 2011

The objective of this paper is to suggest a new method of a wind turbine performance test. The performance test of a wind turbine is generally carried out in a wind tunnel. The test needs not only a high-accuracy measuring system but also durable structure to withstand high speed turbine rotation and wind flow. Therefore, we tried turbine performance test using a towing tank to improve stability and reliability. Because a turbine rotates more slowly and generates more torque in the water than in the wind tunnel under similarity conditions. In this study, we developed turbine performance test systems and verified the turbine test method using a towing tank through comparing results of the wind tunnel and the towing tank test.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.19 no.4
• /
• pp.259-265
• /
• 2016

The present study aims to design and utilize a model test system of a Caisson in wet towing condition, to assess towing stability of a 9,300 ton class caisson. The suggested towing system was designed to provide regular tension on the towline, whereas the previous model test system towed the model in constant speed. The new model test system was expected to reproduce the towing condition more realistically than the test system with constant speed condition, as the tugboat in actual towing condition tows the towline with constant power. Model tests were conducted in a towing tank with 1/30 scaled model. In the model tests, six-degrees-of-freedom motion of the caisson model and tension on the towline were measured and analyzed. By using the new system, fluctuation of the motion of model and tension on the towline decreased. The variation in the draft and initial trim was applied in the model tests. In the initial trim condition, the motion and towing force decreased.