• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.57 no.4
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• pp.283-291
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• 2021

The Korean stow net is a fishing method that utilizes the changing direction of the net entrance with the tidal current. This study attempted to obtain basic data from the recent offshore stow net fisheries to improve the gear by analyzing the dynamic behavior of the nets affected by current speed and direction using computer simulations. A numerical calculation was performed at a current speed of 0.5 knot between 2.5 knot at each 0.5 knot. The time taken for the gear opening was the longest from 0.5 knot at 1,500 seconds and the shortest from 2.5 knot at 450 seconds in the simulations. In all cases, the net width and tension at net deployment gradually decreased as the current speed decreased. However, the net height tended to increase inversely proportional to the current speed. During the net rotation, the net height was maintained at all cases. The net width and tension fluctuated, but the regularity was very low. In this study, the calculated simulation data showed that the opening efficiency decreased proportional to the current speed. The opening efficiency is related to the catching efficiency; therefore, it is necessary to improve the gear to enhance its opening efficiency.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.7
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• pp.930-936
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• 2003

A new method of direct current motor drive, which requires neither shaft encoder nor speed estimator, is presented. The proposed scheme is based on decreasing current gap between a numerical model and an actual motor. By supplying the identical instantaneous voltage to both model and motor in the direction of reducing the current difference, the rotor approaches to the model speed, that is, reference value. The performance of direct current motor drives without speed sensor is generally poor at very low speed. However, in this system, it is possible to obtain good speed performance in the low speed range.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.57 no.3
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• pp.236-245
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• 2021

In this study, a drifting test using a experimental vessel (2,966 tons) in the northern waters of Jeju was carried out for the first time in order to obtain the fundamental data for drift. During the test, it was shown that the average leeway speed and direction by GPS position were 0.362 m/s and 155.54° respectively and the leeway rate for wind speed was 8.80%. The analysis of linear regression modes about leeway speed and direction of the experimental vessel indicated that wind or current (i.e. explanatory variable) had a greater influence upon response variable (e.g. leeway speed or direction) with the speed of the wind and current rather than their directions. On the other hand, the result of multiple regression model analysis was able to predict that the direction was negative, and it was demonstrated that predicted values of leeway speed and direction using an experimental vessel is to be more influential by current than wind while the leeway speed through variance and covariance was positive. In terms of the leeway direction of the experimental vessel, the same result of the leeway speed appeared except for a possibility of the existence of multi-collinearity. Then, it can be interpreted that the explanatory variables were less descriptive in the predicted values of the leeway direction. As a result, the prediction of leeway speed and direction can be demonstrated as following equations. Ŷ₁= 0.4031-0.0032X₁+0.0631X₂-0.0010X₃+0.4110X₄ Ŷ₂= 0.4031-0.6662X₁+27.1955X₂-0.6787X₃-420.4833X₄ However, many drift tests using actual vessels and various drifting objects will provide reasonable estimations, so that they can help search and rescue fishing gears as well.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.4
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• pp.503-510
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• 2003

A new method of induction motor drive, which requires neither shaft encoder nor speed estimator, is presented. The proposed scheme is based on decreasing current gap between a numerical model and an actual motor. By supplying the identical instantaneous voltage to both model and motor in the direction of reducing the current difference. the rotor approaches to the model speed. that is. reference value. The indirect field orientation algorithm is employed for tracking the model currents. The performance of induction motor drives without speed sensor is generally characteristic of poorness at very low speed. However, in this system, it is possible to obtain good speed response in the extreme low speed range.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.3
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• pp.142-149
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• 1994

In order to investigate the environmental properties of set net grounds located in the coastal waters of Yeosu. The current in the vicinity of set net grounds was observed by drogue and current meter in 1990 and 1992. The results obtained are summarized as follows: The direction of tidal current at the north enterance of Yeosu bay was southerly in ebb and northwesterly in flood without the distiction of the neap tide and the spring tide. In spring tide the maximum Velocity of the tidal current was 68 cm/sec in ebb and 66 cm/sec in flood. In neap tide the maximum velocity of the tidal current was 37 cm/sec in ebb and 35 cm/sec in flood. And so the direction of residual current was the south ward mainly and 21 cm/sec. The direction of tidal current at set net fishing grounds was southwesterly in ebb and westerly or northwesterly in flood. Regardless of the distinction of neap and spring. The maximum velocity of the current in spring tide was 50 cm/sec in ebb and 40 cm/sec in flood and that in neap was 28 cm/sec in ebb and 25 cm/sec in flood. In spring tide the speed vector along the major axis of semidiurnal tide component was three times as large as diurnal tide. In neap tide, however, the speed vector was about 50% less then that in spring tide, and the semidiurnal tide and diurnal tide were equal in the size of current ellipse and the direction of major axis. The sea area had a southwesterly residual current. 11 cm/sec in spring tide and 7 cm/sec in neap tide. According to the result of drogue tracking, the vicinity of set net fishing ground had a southerly residual current which formed in Yeosu Bay and a weak westerly residual current toward Dolsando from Namhedo. Therefore, set net fishing ground in coastal water of Yeosu was distributed in boundary of inner water which formed from Seamjin river and offshore water supplied from the vicinity of Sorido and Yochido.

• 전기의세계
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• v.16 no.1
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• pp.7-13
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• 1967

There are many kinds of motors operating by rated voltage which is constant. In this paper, the characteristics of separately excited direct current motor is analyzed when its terminal voltage is varied as its load current. As for this source, direct current generator of a series field is used, and it is driven at constant speed by a primemover. The induced voltage of the generator is propotional to its load current but it saturates as its load current is large. The charateristics of motor is studied by analog computer because of the nonlinearity of generator. The results are as follows: (1) The load current and the rotor speed of motor increase as the load of motor increases. But the speed of rotor decreases for the influence of the saturation of the iron of generator field when its load current is large. (2) Decreasing the inertia of motor and increasing the inductance of the armature circuit improve the stability of motor and the region of stable state. (3) By changing the field current of the motor, the speed and the direction of rotor can be controlled in wide range.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.58 no.4
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• pp.299-309
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• 2022

Among the fishing vessels operating in the coastal waters, jigging fishing vessels were considered representative vessels engaged only by wind, sea, tide, and external force. Then, a fishing vessel with a length of shorter than 10 m from July 1, 2018 to August 5, 2019 was studied to obtain a drift prediction model by multiple regression analysis. In the correlation analysis between variables for leeway of speed and direction, the speed and direction of tidal seem to be the most affected in coastal waters. Therefore, it should be considered an explanatory variable when conducting drift tests. As a result of multiple regression analysis on the predicted equations of leeway speed and direction due to the external force on the drift of the fishing vessel, p < 0.000 was considered significant in the F-test, but the coefficient of determination was 55.2% and 37.8%. The effect on the predicted leeway speed was in the order of the tidal speed and current speed. In addition, the impact on the predicted leeway direction was in the order of the tidal speed and current speed. ŷ(m/s) = - 0.0011(x1) + 0.9206(x2) + 0.0001(x3) + 0.0002(x4) + 0.0050(x5) + 0.0529(x6) + 0.2457 ŷ(degree) = 0.6672(x1) + 93.1699(x2) + 0.0585(x3) - 0.0244(x4) - 1.2217(x5) + 4.6378(x6) - 0.0837

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.37.1-37
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• 2001

Electric plating is used in various industry field. Specially, pulse plating is able to deposit material at high current density compared to conventional DC plating. For example, pulse plating can get more fine grain, can improve adhesion and metal distribution and current efficiency, can reduce internal stress and crack. Therefore, we developed bidirection pulse power supply(BPPS) which has high speed pulse current and high current density and improve deposition quality and increase plating speed in this paper. BPPS(Bidirection pulse power supply) needs high speed rising time, falling time and output current accuracy. BPPS consists of rectifier part, chopper part, invertor part, and control part. Rectifier part changes outprt current direction.

• The Journal of Korea Robotics Society
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• v.13 no.3
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• pp.182-189
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• 2018

The purpose of this paper is to suggest the methodology for the establishment of operational concept for speed-up of defense robot and improvement direction of the defense acquisition system for the defense robot. In order to achieve this goal, the current defense acquisition system was analyzed into long-term planning, mid-term programming, and project execution stages. And I suggest the methodology for the establishment of operational concept for speed-up of defense robot and direction of development of the defense robot acquisition system considering the characteristics of the robot in terms of core technologies of robot, robot ecosystem and effectiveness-based-robot-design, respectively. Based on the methodology for establishment of the operational concept of defense robot and development direction of the defense acquisition system presented in this study, it will be possible to design efficiently the defense robot in the future.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.1
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• pp.98-104
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• 1999

To investigate the relationships between ocean environmental characteristics, the time-series data of temperature and salinity observed at a station near at Hanlim set net in 1995 and 1996 are analyzed, and the results are as follow ; 1. In hanlim set net, the diurnal range of temperature and salinity variation in summer is very large and the amplitude of short-period fluctuation of temperature and salinity is very large. That is, not only the water of the middle and bottom layers (low temperature and high salinity) but also the coalstal water (high temperature and low salinity) appears alternatively depending on the current direction 2. from the result of mooring for 22 days in Hanlim set net, the mean speed and direction of tidal current in neap tide were 9.1 cm/sec and south westward in ebb time, and 11.6 cm/sec and north or northeastward in flood time, respectively. The highest speed of the current was 15cm/sec in ebb time, and 22.6 cm/sec in flood time. The mean speed and direction of tidal current in spring tide were 10.4 cm/sec, and southwestward in ebb time, and 12.3 cm/sec, and north or northestward in flood time, respectively. The highest speed of the current was 19.4 cm/sec in ebb time, and 20 cm/sec in flood time respectively. The mean speed of the current in flood time was larger than that in ebb time. The velocity vector along the major axis of semidiurnal tide ($M_2$) component was 1.5 times larger than that of diurnal tide ($K_1$), The major directions of two compornants were northwestward and east-southeastward and residiual current were 3.25 cm/sec and northwestward-directed. Result of TGPS Buoy tracer for 3 days between Biyang-Do and Chgui-Do showed that the mean speed was 1.6 knot in ebb time and 1.3 knot in flood time. Direction of tidal was southwestward in ebb time and northeastward in flood time respectively. The maximum current speed was 4.8 knot in ebb time and 3.7 knot in flood time respectively. The mean speed and direction of tidal in of offshore were 1.7 knot and northwestward in flood time. The residual current appeared 0.3 knot northeastward.