Hyochul Kim

Analysis of a jet-controlled high-lift hydrofoil with a flap

A jet-controlled high-lift hydrofoil with a flap is investigated using both experimental and computational methods. Experiments were carried out in a cavitation tunnel to measure forces and moment acting on the hydrofoil, and surface pressure distribution. The measured data show the feasibility of such a device for marine applications. Computational studies have also been carried out in parallel with the measurements. The computational results are analyzed in terms of global and local quantities using available experimental data. The present computational results compare well with the well-known experimental data for circulation control flows. The results for flow around a hydrofoil with a blown flap further validate the concept behind the proposed device. The results of the study demonstrate the applicability of the technology to the design of practical control surfaces.

Influence of Jet Nozzle Arrangement on the Performance of a Coanda Foil

The Coanda effects demonstrate that a jet stream applied tangential to a curved surface can generate lift force by increasing the circulation. Many experimental and numerical studies have been performed on the Coanda effect and it is found to be useful in various fields of aerodynamics. The Coanda effect may have practical application to marine hydrodynamics since various control surfaces are being used to control behaviors of ships and offshore structures. In the present study, numerical computations are performed to find the applicability of the Coanda effect to the marine control surfaces. For the purpose, changes in flow characteristics around a flapped foil due to the Coanda effect have been simulated by RANS equations discretized with a cell-centered finite volume method (FVM). In the process, special attention has been given to the influence of jet nozzle arrangement on the lift characteristics of the Coanda foil. It is found that the shape as well as the location of the jet intake and jet exit affects the lift performance of the foil significantly.

Numerical Study on the Gap Flow of a Rudder System with Bisymmetric Blocking Bar

AbstractIn recent practice a half round prismatic bar has fillet welded or formed through foundry work along the centerline on rear concave surface of the horn to mitigate gap flow between fixed and movable part of the rudder system. When the gap clear ance has been blocked with this practice, numerical simulations indicate that the pra ctices are not only effective in reducing the gap flow but also in mitigating the cavitation. Th e blocking effects are remarkably improved when a pair of blocking bar is bisymmetrica lly attached with respect to centerline on the opposite convex surface of the movable part. The blocking bar could be placed on the exposed surface under maximum rudder angle. This implies that the blocking bar could be easily adopted not only in a design stage but also in a maintenance stage for mitigating rudder cavitation. In addition, the numerical simulations imply that more improvements could be anticipated through the selection of sect ion shape of prismatic bar for gap flow blocking.

A Study on the Effect of the Heeled and Trimmed Conditions on Propulsive Performance of VLCC

In recent years, many environmentally disastrous maritime accidents resulted from oil or fuel spills from damaged vessels. The situation becomes worse especially when the early counter treatment is not prompt enough. To properly handle this type of accidents and prevent further disasters, the propulsive performance of damaged vessels must be better understood for salvage operations, as well as for containing oil spills while the vessels are being towed or self-propelled. Until now, many hydrodynamic studies have focused on the propulsive performance of undamaged vessels but only a few studies on that of damaged vessels. in this paper, both experimental and computational methods are used to study the propulsive performance of a VLCC in heeled and/or trimmed conditions. For experimental studies, measurement systems should be modified to adapt to the variations of attitude of a damaged vessel. For numerical studies, CFD programs should be also extended to be applied to asymmetrically floating conditions.

A Study on the Resistance Characteristics of a Stepped Planing Hull Using a High-Speed Towing System

With increasing demands of high speed transportation, recently a lot of high speed marine vehicles, such as SWATH, semi-planing craft, planing craft, hydrofoil craft, SES and so on, have been paid attention especially in high speed region over the Froude number 0.5. The resistance characteristics of the vehicles should be experimentally evaluated in the towing tank. At the Seoul National University, a light-weight cantilever type towing carriage was devised and installed in the towing tank. Wireless measurement devices were also provided for appropriate data acquisition during high-speed towing tests. With the new carriage system, a series of model tests were performed to investigate the hydrodynamic characteristics of a stepped planning hull in the towing tank and the resistance performances of the hull are introduced in this report.

Prediction of Propulsive Performance of VLCC at Heeled and Trimmed Conditions

In recent years, many environmentally disastrous oil spill accidents from damaged vessels become worse especially when the early treatment is not prompt enough. To properly handle this type of accidents and prevent further disasters, international organizations establish and impose various rules and regulations. In assessing the damages and providing salvage operations, the propulsive performance of damaged vessels is of great importance, as well as for containing oil spill while the vessels are being towed or self-propelled. Until now, many naval hydrodynamics researches have focused on the propulsive performance in normal operating conditions and only a few studies for damaged vessels are found in literature. In this paper experimental method is used to study the Propulsive performance of a very large crude-oil carrier (VLCC) in .heeled and/or trimmed conditions.

Design Idea of Suspension for Traction Wheel of Novel High Speed Towing Carriage

In the conventional towing tank, the ordinary towing carriage has a speed barrier which caused not only by the limitation of the length of towing tank but also the limitation of acceleration. Therefore the length of the towing tank should be decided carefully from the planning stage of the towing tank construction. Consequently the acceleration of the towing carriage should be taken less than 0.06g practically to avoid the slip of the wheel on rail. Due to the increasing demand of the high speed experiments on the development of special novel ship, the requirement of the high speed towing carriage is continuously increased recently. When the minimum measuring time of the towing experiment is prescribed as five seconds, the carriage should be accelerated with higher than 0.12 g to get the speed of 18 m/sec even in the towing tank having a length of 400m in length approximately. This means that the requirement of acceleration is bigger than twice of the ordinary practices of carriage acceleration. In such a condition the exerted total power of motor could not converted to traction force for the acceleration of the carriage without slip. To over come these difficulties a pair of horizontal traction wheels are reinforced to each of the ordinary vertical carrier wheel and appropriate suspension system has been devised for the towing tank of super high speed operation. It is believed that the design of novel suspension system adaptable for the high speed acceleration of towing carriage will play a important role as a reference for the remodeling of the towing tank for high speed experiment.

A Study on the High Lifting Device Equipped with the Trailing Edge Rotor for the Enhancement of Circulation Control

For a long times it has been believed that the Magnus effect of the rotating cylinder could be utilized for the lifting devices applicable to marine practices. It has been reported that the rotating cylinder installed on upper deck of commercial vessel could play a energy saving role however the idea might be applicable in a very rare case in ship building practices. In this study special high lift rudder system equipped with the trailing edge rotor has been suggested in correspondence with the increasing requirement of greater rudder force. Through the numerical simulation it is cleared that the trailing edge rotor could play a role in enhancement of circulation and refinement of boundary layer of the rudder system. At the same time it is found out that the lift force of the rudder system without rotation of trailing edge rotor could be doubled when the circumferential velocity of the trailing edge rotor is equal to twice of the inflow velocity.

NEW PRODUCTION SYSTEM FOR VESSELS OF COMPOSITE MATERIALS USING AN ADJUSTABLE MOULD

Publisher Summary This chapter proposes a new method for construction of a fiber-reinforced plastic (FRP) ship. In the method, hull shape is defined only by the line elements, and conventional molds for FRP construction method are not used. A 1/3 scale and a full scale mock-ups of a bow portion is manufactured on a proposed pin jig production system to identify and solve the difficulties for practical use. The plates are linked together to complete the hull shape and additional laminas are stacked inside until necessary thickness is obtained. To verify the proposed method and identify the possible flaws, a 1/3 scale model is constructed on the adjustable mold. The hull surface is divided into several pieces and developed onto a plane surface. Hull form of a typical planing boat can be easily modified into a set of developable surfaces with minor modification. It is found that the new production procedure can be successfully applied to the construction of planning vessels made of FRPs. The shape of a developable hull can be represented by line elements placed along the ruling lines and supported by pin jigs attached on the precision bed. It is possible that the system can be used as an adjustable mold for deformation of plane plate to form a hull shape, if the number and rigidity of the elements are enough.

Note on the Development of Ballast Water Shifting System for Solar Tracking of the Floating Photovoltaic Plant

지구온난화로 인하여 탄소배출을 줄이는 문제가 세계적 관심의 대상이 되면서 강력한 불변의 자원인 태양광을 이용하는 문제가 주요한 과제로 대두되고 있다. 태양광 발전시스템은 일조량 확보 가 일차적 조건이므로 사막이나 초지와 같은 지리적 조건을 활용 하는 것이 유리하다. 이에 대하여 호수나 하천과 같은 수면 상에 설치하는 경우에는 육상에 설치할 때 반드시 필요한 부지 조성과 기초공사 등과 같은 부대 공사가 줄어들며 임목벌채와 같은 환경 을 저해하는 공사가 불필요하게 된다. 또한, 태양광 발전 시스템을 수면 상에 설치하면 태양 전지판이 수면에서 일어나는 자연대류현 상으로 인한 냉각효과가 있어서 발전효율이 높아지는 이점이 있다. (Choi, et al., 2013; 2014; Trapani, 2013) 부유식 발전시스템 (Kim, 2011; Lee, 2011)의 규모는 시스템 생산과 설치수역으로의 운송 및 설치, 유지 보수를 운용상의 편 익을 고려하여 설계하여야 한다. 또한 수역의 수심변화나 흐름의 유무 등을 고려하여야 하며 태풍 등의 바람 영향을 함께 고려하 여 설계하여야 한다. 그리고 설계된 단위 시스템들은 집단화하여 경제성을 갖춘 대단위발전시스템으로 구축할 수 있어야 한다. 태 양광 발전 시스템은 효과적으로 계류 고정하는 기술이 필요하게 된다. 태양광 발전시스템은 고정위치에 계류된 상태에서 밸러스트 수의 적재만으로 태양 전지판이 항상 태양을 향하도록 제어하는 것이 가능하다. 이때 부유체는 강한 바람을 받더라도 충분한 복원 안정성을 가져야 하는 동시에 최소한의 밸러스트 수를 사용하여 밸러스트 수 이동으로 태양을 추적하는 부유식