• 대한의용생체공학회:의공학회지
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• 제18권2호
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• pp.147-156
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• 1997

Various prosthetic heart valves have been developed and used clinically, but they have problems, such as thrombogenecity, hemoltsis, high cost and low durability. New types of trileaflet polymer heart valves have been developed in order to use them as inlet and outlet valves in a ventricular assist device. The aim of this study is to determine the hydrodynamic effectiveness of the newly designed trileaflet polymer valves and their feasibility for temporary use in the blood pumps. Trileaflet polymer valves are made of polyurethane, because of its good blood compatibility, high tonsil strength and good resistance to fatigue. An in vitro experimental investigation was perf'ormed in order to ev91ua1e hydrodynamic performance of the trileaflet polymer valves having different design and fabrication tech- niques. The St. Jude Medical valve (SJMV) and floating-type monoleaflet polymer valve (MLPV) were also tested The pressure drop across the valve, leakage volume, and the flow patterns mere investigated for valves. The result of comparative tests showed that the trileaflet polymer valves had a better hydrodynamic performance than the others. TPV which has two stable membrane shape showed the lowest back flow. The pressure hops of TPVs were lower than that of MLPV, but slightly higher than SJMV. The hydrodynamic performance of valves under the pulastile flow showed the similar results as steady flow. The velocity profiles and turbulent intensities were measured at the distal sites of valves using a hot-film anemometer. Central flow was maintained in trileaflet polymer valves, and the maximum turbulent intensities were lower in TPVs comparing to MLPV.

• Corrosion Science and Technology
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• 제14권5호
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• pp.218-225
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• 2015

The electrochemical behaviors of various metals with and without diamond-like-carbon (DLC) coating in 3.5 wt% NaCl solution were investigated. The effect of hydrodynamic conditions was focused by employing a rotating disc electrode (RDE). The experimental results showed that each bare metal had a more positive corrosion potential and a higher corrosion rate due to enhanced oxygen transport at the higher rotating speed of the RDE. DLC coating caused a substantial increase in the corrosion resistance of all metals studied. However, localized corrosion was still found in the DLC-coated metal at sites where deposition defects existed. Surface morphology examination was performed after the electrochemical test to confirm the roles of hydrodynamic conditions and DLC coating.

• 수산해양기술연구
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• 제55권1호
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• pp.62-73
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• 2019

Recently, copper alloy netting has been proposed as a material for aquaculture facilities that can be set in harsh offshore environments. To design a cage made of copper alloy netting, it is necessary to calculate the flow of water through the netting and force of external sources on the netting. Therefore, this study measured and analyzed the current velocity reduction after passing through the netting and the hydrodynamic forces acting on the netting using copper alloy netting with nine solidity ratios. As a result of the reduction rate of the flow velocity through the netting, the flow reduction rate was increased as the solidity ratio of netting was increased. The flow reduction rate was also increased as the attack angle on the netting was decreased. In analyzing the resistance on the netting, we also discovered that resistance was increased with increase in the flow velocity and solidity ratio. An analysis of the hydrodynamic coefficient acting on the netting is shown that the drag coefficient tends to increase as the attack angle increases. We also analyzed the hydrodynamic coefficient according to the variation of the Reynolds number. When the drag coefficients acting on the netting were analyzed with the different Reynolds numbers, the Reynolds number increased from over 0.3 m/s to a relative constant. Finally, the copper alloy nettings had a smaller velocity reduction rate when comparing the flow velocity reduction rate between copper alloy nettings and nylon nettings.

• 대한조선학회논문집
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• 제51권5호
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• pp.369-379
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• 2014

Planing hull forms have significant influences on those hydrodynamic performances in calm water and in waves. Therefore, the hydrodynamic performance of a planing vessel should be predicted by model tests or theoretical calculations, and be confirmed whether it shows the performance requirements at the design stage. In this study, four planing hull forms are designed with the goal of the improvement of resistance and seakeeping performance, and 1/6.5 scale model tests are carried out in Seoul National University towing tank. The effects of design parameters such as length-to-beam ratio, deadrise angle and forebody shape on the hydrodynamic performance are investigated, based on model test results. Running attitude and resistance of model ships in calm water are also estimated by empirical formulae proposed by Savitsky (1964; 2007; 2012), and compared with the model test results. It is shown that calm water performance of non-prismatic planing hulls can be predicted well by Savitsky (2012)'s formula which improves the original Savitsky(1964/2007)'s formula by taking into account the variations of deadrise angles, and the actual angles between the hull bottom and the free surface.

• 대한조선학회논문집
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• 제54권2호
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• pp.96-101
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• 2017

Amphibious assault vehicles have been used in the Marine Corps. In recent years, their ability to move faster is becoming one of the most important considerations. At high speeds, the vehicle tends to sink at the stern and sometimes the opposite occurs. Such dynamic trim plays a significant role in determining the vehicle's hydrodynamic performance. Furthermore, an excessive trim by stern upsets the viewing angle. We have thus considered a stern hydrofoil to reduce the dynamic trim of the amphibious assault vehicle. Laboratory-scale resistance tests were conducted in a towing tank at the Seoul National University (SNU). This study aims to make a preliminary assessment of the hydrodynamic performance of the vehicle with the stern hydrofoil and to investigate permissible speed range of the vehicle. The experimental results show that the stern hydrofoil can successfully achieve a reduction of both the dynamic trim and the hydrodynamic resistance at running speeds above 20 km/h.

• Journal of Advanced Marine Engineering and Technology
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• 제37권6호
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• pp.623-630
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• 2013

본 연구는 기 개발된 인플래터블 카약(RPO-2)과 새롭게 개발된 인플래터블 카약(RD-FK-11, RD-FK-12)의 유체역학적인 성능평가를 위하여 경사시험과 선회시험은 해양공학수조에서 저항시험은 축소된 모형선을 제작하여 회류수조에서 수행되었다. 결론적으로 각각의 카약에 대한 다양한 성능시험결과 복원성 측면에서는 KONA가 유리하고, 선회력과 무게중심 측면에서는 RD-FK-12가 우수하고, 저항성능 측면에서는 RD-FK-11이 KONA와 RPO-2에 비해 우수하였다.

• 한국해양공학회지
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• 제34권4호
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• pp.237-244
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• 2020

In this study, we investigate surge force, heave force, and pitch moment, which are vertical plane hydrodynamics acting on Manta-type unmanned underwater vehicles (UUVs), using a model test and computational fluid dynamics (CFD) simulation. Assessing the maneuvering hydrodynamic characteristic of an underwater glider in the initial design stage is crucial. Although a model test is the best approach for obtaining the maneuvering hydrodynamic derivatives for underwater vehicles, numerical methods, such as Reynolds averaged Navier-Stokes (RANS) equations, have been used owing to their efficiency in terms of time and cost. Therefore, we conducted an RANS-based CFD calculation and a model test for Manta-type UUVs. In addition, we conducted a validation study through a comparison with a model test conducted at a circular water channel (CWC) in Korea Maritime & Ocean University Furthermore, two RANS solvers (Star-CCM+ and OpenFOAM) were used and compared. Finally, the maneuvering hydrodynamic forces obtained from the static drift and resistance tests for a Manta-type UUV were presented.

• 수산해양기술연구
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• 제15권2호
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• pp.61-66
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• 1979

Skipjack, Katsuowonus vagans, yellow tail Seriola quinqueradiata and Scomberomorus sinensis are largely caught by trolling gear in the coastal waters of Jeju Island. The author determined the hydrodynamic resistance of the trolling gears uscd in the waters, estimated the pulling force of the fish species above mentioned by use of body weight, and then calculated the minimum diameter of the lines of trolling gears. The results obtained are as follows: 1. The hydrodynamic resistance of the trolling gears present linear relationship in accordance with the towing speed of the gears. 2. The diameter of seizing leader, leader gut and branch line used in the waters might be durable to catch skipjack and yellow tail, whereas the diameter of those must be weak in intensity for Scomberomorus zinensis.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권3호
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• pp.478-489
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• 2015

In the present study, a hydrodynamic hull-form optimization algorithm for a container ship was presented in terms of the minimum wave-making resistance. Bell-shaped modification functions were developed to modify the original hull-form and a sequential quadratic programming algorithm was used as an optimizer. The wave-making resistance as an objective function was obtained by the Rankine source panel method in which non-linear free surface conditions and the trim and sinkage of the ship were fully taken into account. Numerical computation was performed to investigate the validity and effectiveness of the proposed hull-form modification algorithm for the container carrier. The computational results were validated by comparing them with the experimental data.

• Journal of Advanced Marine Engineering and Technology
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• 제39권3호
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• pp.334-341
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• 2015

본 연구는 새로운 3종 인플래터블 카약(inflatable kayak)의 유체역학적인 성능을 평가하여 신제품 개발에 필요한 정보를 제공하는 것이다. 유체역학적 제계산 및 해양공학수조와 회류수조를 이용하여 유체역학적인 성능을 평가한 결과는 첫째, v-hull kayak의 복원팔이 132.4mm으로 가장 크고, 선회반경은 가장 작게 나타났다. 둘째, needle knife kayak의 저항은 71N으로 가장 작게, 무게중심은 0.128m 가장 낮게 나타났으나 전반적으로 밀림(draft)이 발생하였다. 결론적으로 v-hull kayak은 복원성과 선회성면에서 needle knife kayak은 무게중심과 저항성면에서 우수하다고 판단된다.