• 수산해양기술연구
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• 제60권1호
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• pp.27-36
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• 2024

The towing distance, which is speed over the ground, and the water flow quantity, which is speed through the water, were used when estimating the amount of Metapenaeus joyneri resources that rose to the surface at night using the swept area method in order to compare and analyze the difference. It was conducted using a shrimp dredge, trial fishing gear for catching Metapenaeus joyneri. Catch during the entire survey period was 188.9 kg. Monthly catch ranged from 3.1 to 109.2 kg, highest in June and lowest in September. The swept volume calculated using the speed over the ground was about 13% higher than using the speed through the water. Metapenaeus joyneri resources estimated using the towing distance ranged from 320.1 to 14,649.8 kg. Resources estimated using the water flow quantity ranged from 278.5 to 12,886.3 kg. Therefore, the amount of Metapenaeus joyneri resources estimated using the speed over the ground was about 14% higher than the method using the speed through the water, indicating that the amount of resources was overestimated.

• 대한조선학회 특별논문집
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• 대한조선학회 2015년도 특별논문집
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• pp.28-33
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• 2015

Speed log measurement has always been of utmost importance to the mariners. To date the most accurate maritime speed measurement comes from Doppler measurement, where speed may be measured relative to either water(speed through water) or seabed(speed over ground). Recently, a clarification has been issued by the International Maritime Organization (IMO) regarding the speed measuring devices, which could ultimately impact the final arrangement of these devices for ships being constructed after July 1, 2014. This paper will discuss the clarification in depth and necessary action which shall be taken by the owners and operators of the ships impacted.

• Journal of Biosystems Engineering
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• 제8권1호
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• pp.38-46
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• 1983

This study was carried out to investigate the possibility of improving the performance of a kerosene engine with water addition. The engine used in this study was a single-cylinder, four-cycle kerosene engine with the compression ratio of 4.5. Water could be successfully added into the inlet manifold by an extra carburetor for the volumetric ratios of 5, 10, 20, and 30 percents. Variable speed tests at wide-open throttle were performed for five speed levels in the range of 1,000 to 2,200rpm for each fuel type. Volumetric efficiency and brake specific fuel consumption were determined, and brake thermal efficiency based on the lower heats of combustion of kerosene was calculated. To examine variation in fuel consumption, CO concentration, and cooling water temperature, part load tests were also performed. The results obtained are summarized as follow. (1) Brake torque increased almost in proportion to volumetric efficiency. But the ratio of increase in torque was greater than that of volumetric efficiency. Mean torque over the speed range of 1,000 to 2,200rpm increased 1, 3, 7, and 2 percents for 5, 10, 20, and 30 percents water addition, respectively. The increase in brake torque with water addition was greater at lower speeds. (2) Mean brake specific fuel consumption over the speed range of 1,000 to 2,200rpm decreased 1, 2, 3, and 3 percents for 5, 10, 20, and 30 percents water addition, respectively. (3) Mean temperature of cooling water over the speed range of 1,000 to 2,200rpm decreased 2, 4, 8, and 12 percents for 5, 10, 20, and 30 percents water addition, respectively. (4) The effects of decreasing CO concentration in the exhaust emissions with water addition were significant. At the speed range of 1,000 to 2,200rpm, CO concentration in the exhaust emissions decreased 2, 10, 23, percents for 5, 10, and 20 percents water addition, respectively. (5) Deposits were not discovered in the combustion chamber during the experiment. However, a little rust was formed in the water-supply carburetor.

• International Journal of Internet, Broadcasting and Communication
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• 제16권2호
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• pp.169-178
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• 2024

This study aimed to investigate the effects of water depth and speed on the activation of lower muscles during squat exercises, utilizing electromyography(EMG). It involved ten male participants in there. Participants performed 30 squats over a minute at a speed of 60bpm and maximum speed squats until exhaustion within a minute. The Integrated electromyography(iEMG) readings for the rectus femoris showed statistically significant differences due to water depth and speed, with a significant interaction effect between depth and speed during squat exercises. The iEMG readings for the biceps femoris also showed statistically significant differences, with a significant interaction effect between depth and speed during squat exercises. The iEMG readings for the gastrocnemius showed statistically significant differences according to water depth and speed. However, the interaction effect of water depth and speed during squat exercises did not show a statistically significant difference. In contrast, the iEMG readings for the tibialis anterior demonstrated statistically significant differences, with a statistically significant interaction effect during squats. These findings suggest that water depth and speed positively influence the activation patterns of lower muscles. Therefore, appropriately tailored aquatic exercises based on water depth for individuals with musculoskeletal discomfort, including the elderly or those with physical impairments, can effectively reduce physical strain and enhance balance, as well as physical and perceptual aspects. It is concluded that such exercises could provide a safer and more effective method of exercise compared to ground-based alternatives.

• Journal of Hydrospace Technology
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• 제2권1호
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• pp.10-17
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• 1996

If a point impulse travels over free surface of water of finite depth, surface waves consist of divergent waves. The crestlines of those divergent waves are short and end on the cusp line if the impulse travels at a subcritical speed. But the crestlines become infinitely long and there are no cusps if the impulse travels at a supercritical speed.

• 해양환경안전학회지
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• 제28권2호
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• pp.254-261
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• 2022

모든 선박은 충돌을 피하기 위해 안전속력을 준수하여야 하고, 우리나라 영해 및 내수에서 속력의 제한규칙을 준수하여야 한다. 그리고 선박교통관제사는 선박이 안전속력과 속력의 제한규칙을 준수하도록 적절히 관제하여야 한다. 국제해상충돌예방규칙에서 안전속력은 선박이 명시적으로 몇 노트의 속력으로 항행하여야 하는지 규정하고 있지 않다. 반면에 국내법에서는 교통안전특정해역 등에서 제한속력을 지정하여 이를 준수하도록 하고 있다. 이 속력의 제한규칙은 주로 대지속력을 기준으로 하고 있으나, 대수속력을 기준으로 하는 곳도 있다. 이 논문은 최근 5년간 발생한 해양사고와 제한속력 위반율에 대해 분석하였고, 국제해상충돌예방규칙상 안전속력, 국내외법상 속력의 제한규칙 및 해양안전심판원 재결 중 안전속력을 준수하지 아니한 사례에 대해 살펴보았다. 그 결과, 이 논문에서는 국내법상 속력의 제한규칙이 선박에서 해양사고 예방을 위해 반드시 준수되어야 한다는 것과 선박이 이 규칙을 준수하기 쉽고, 선박교통관제사가 선박을 적절히 관제할 수 있도록 대수속력으로 규정된 속력의 제한규칙을 대지속력으로 개정할 필요가 있다는 것을 제시하였다.

• 한국환경과학회지
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• 제20권7호
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• pp.819-828
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• 2011

This research was done to clarify the cooling effect of water particles generated from a fountain. This effect is a one way to control the heat island effect of big cities. The result of this research was drawn by setting the jets of water in a certain height, and then studying the diffusion of water particles, which is affected by the size of the particles and the wind speed, and the cooling effect caused by the diffusion. 1) When a diameter of a water drop was 500 ${\mu}m$ and the wind speed was 2.0 to 6.0 m/sec, the water drop diffused 75 to 190m, and the water vapor spread over 175 to 440 m. As a result, there was more than $0.5^{\circ}C$ of cooling effect on the temperature in the atmosphere 130 to 330m around the water fountain. 2) When a diameter of a water drop was 750 ${\mu}m$ and the wind speed was 2.0 to 6.0 m/sec, the water drop diffused 65 to 150 m, and the water vapor spread over 160 to 405 m. Moreover, there was more than $0.5^{\circ}C$ of cooling effect on the temperature in the atmosphere 110 to 275 m around the water fountain. 3) After studying on the relationship between the diameter of water drop and the wind speed, and the diffusion of water particles and the range of the atmosphere that was cooled, a result could be drawn from the research that the smaller the diameter of the water vapor gets and the faster the wind speed becomes, the wider the water particles diffuse and the cooler the atmosphere around the fountain becomes. 4) This research further extrapolates that when the ordinary water(tap water, water from river and stream) is used in a fountain, the cooling effect of the air near the fountain can be approached similarly. If the seawater is used in a fountain, there is to be more to concern not only on cooling effect on the air, but also on other effects on surrounding environment generated by the salt in seawater.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.867-875
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• 2014

Planing crafts were specifically designed to achieve relatively high speeds on the water. When a planing craft is running at high speed, dynamic pressure on the bottom makes the boat rise on the surface of the water. This reduces the area of the sinking surface of the boat to increase air resistance. Air resistance means the resistance that occurs when the hull and deck house over the surface of the water come in contact with the air current. In this paper, we carried out a CFD numerical analysis to find optimal deck houses that decreased air-resistance on the water when planing crafts are running at high speed. We finally developed the deck house shape of high-speed planing crafts that optimally decreased air resistance.

• 해양환경안전학회지
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• 제20권2호
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• pp.193-201
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• 2014

본 연구는 강조류 해역을 통과하는 선박의 해양사고를 방지하기 위해 안전한 항행속력과 적절한 통과시기를 제시하였다. 이 자료의 해석을 위하여 2010년 7월 12일부터 15일까지 명량수도를 대상으로 통과선박의 AIS 데이터 수집과 2010년 9월 4일 현장조사를 실시하였고, 여기서 수집된 자료를 바탕으로 최소항행속력(minimum navigation speed)과 여유 제어력을 감안한 적정항행속력(optimum navigation speed), 조류속력별 대응타각(respond rudder angle)을 산출하였다. 또한 조위와 조류속력 데이터를 분석해 안전한 통과시기를 제시하였다. 이 연구를 통해 얻은 결과는 다음과 같다. (1) 조류의 유속이 4.4 kn 이상이 되면 선박의 타만으론 자력 조선이 불가능하다. (2) 강한 조류에 의해 발생되는 유압력과 회두모멘트에 대응하기 위해서는 최소항행속력은 조류의 2.3배, 적정항행속력은 조류의 4.0배 이상이어야 한다. (3)사리 기간 중 명량수도 적정 통과 시기는 고 저조시간 1시간 전부터 최소 30분 전까지이며 고 저조가 된 이후 5시간 동안은 4 kn 이상의 유속이 남아있는 시간으로 이 지역 항해를 자제해야 한다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권6호
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• pp.1007-1019
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• 2015

The determination of the required seawall height is usually based on the combination of wind speed (or wave height) and still water level according to a specified return period, e.g., 50-year return period wind speed and 50-year return period still water level. In reality, the two variables are be partially correlated. This may be lead to over-design (costs) of seawall structures. The above-mentioned return period for the design of a seawall depends on economy, society and natural environment in the region. This means a specified risk level of overtopping or damage of a seawall structure is usually allowed. The aim of this paper is to present a conditional risk probability-based seawall height design method which incorporates the correlation of the two variables. For purposes of demonstration, the wind speeds and water levels collected from Jiangsu of China are analyzed. The results show this method can improve seawall height design accuracy.