Ki-Sup Kim

Study on the Three Dimensional Flow Characteristics of the Propeller Wake Using PIV Techniques

A stereo-PIV (particle image velocimetry) technique is used to investigate the vortical structure of the wake behind a rotating propeller in the present study. A four bladed propeller is tested in a cavitaion tunnel without any wake screen. Hundreds of instantaneous velocity fields are phase-averaged to reveal the three dimensional spatial evolution of the flow behind the propeller. The results of conventional 2-D PIV are also compared with those of the stereo-PIV to understand the vortical structure of propeller wake deeply. The variations of radial and axial velocities in the 2-D PIV results seem to be affected by the out-of-plane motion. generating a little perspective error in the in-plane velocity components of the slipstream. The strong out-of-plane motion around the hub vortex also causes the perspective error to vary the axial velocity component a little at the near wake region. The out-of-plane velocity component had the maximum value of about 0.3U0 in the tip vortices and continued its magnitude in the wake region.

Development of automotive engine cradle by hydroforming process

The hydroforming technology may bring many advantages to automotive applications in terms of better structural integrity of the parts, lower cost from fewer part count, material saving, weight reduction, lower springback, improved strength and durability and design flexibility. In this study, the whole process of front sub-frame parts development by tube hydroforming using steel material having tensile strength of 440 MPa grade is presented. At the part design stage, it requires feasibility study and process design aided by CAE (Computer Aided Design) to confirm hydroformability in details. Effects of parameters such as internal pressure, axial feeding and geometry shape in automotive engine cradle by the hydroforming process were carefully investigated. Overall possibility of hydroformable engine cradle parts could be examined by cross sectional analyses. Moreover, it is essential to ensure the formability of tube material on every forming step such as pre-bending, preforming and hydroforming. At the die design stage, all the components of prototyping tool are designed and interference with the press is examined from the point of deformed geometry and local thinning.

PIV Aanalysis of Vortical Flow behind a Rotating Propeller in a Cavitation Tunnel

A two-frame PIV (Particle Image Velocimetry) technique is used to investigate the wake characteristics behind a marine propeller with 4 blades at high Reynolds number. For each of 9 different blade phases from to , one hundred and fifty instantaneous velocity fields are measured. They are ensemble averaged to study the spatial evolution of the propeller wake in the region ranging from the trailing edge to one propeller diameter (D) downstream location. The phase-averaged mean velocity shows that the trailing vorticity is related to radial velocity jump, and the viscous wake is affected by boundary layers developed on the blade surfaces and centrifugal force. Both Galilean decomposition method and vortex identification method using swirling strength calculation are very useful for the study of vortex behaviors En the propeller wake legion. The slipstream contraction occurs in the near-wake region up to about X/D : 0.53 downstream. Thereafter, unstable oscillation occurs because of the reduction of interaction between the tip vortex and the wake sheet behind the maximum contraction point

Development of Design Technology for Safety Enhancement of Damaged Ship

AbstractLoss of human lives and properties including environmental dama ge due to large scale accidents requires change of our perception to marine saf ety. IMO is trying to re-establish overall marine safety system through long term plan such as GBS. Along this line, current regulation based safety evaluation is in pro cess of changing into performance based methods, and for this transition, simulation based safety evaluation during design stage considering damage is highly necessary. In this paper, first, damage scenario is developed from IMO regulations and accident case studies. Then an integrated and simulation based safety evaluation prototype system considering both damage stability and structural safety is developed for the use during ship design process. ※Keywords: Marine accident(해양사고), Damaged ship(손상선박), Safety as sessment(안전성평가), Design technology(설계기술), Compartment modification(구획변경) 1. 서론 해양사고를 방지하고 해양사고로부터 인명과 재산 및 환경보호를 위한 각종 노력이 국제해사기구 접수일: 2008년 2월 25일, 승인일: 2009년 1월 13일✝교신저자: dklee@moeri.re.kr, 042-868-7222

Study on the Drag Reduction of 2-D Dimpled-Plates

The main objective of the present study is to investigate the roles of the micro-dimpled surface on the drag reduction. To investigate the effectiveness of the micro-dimpled surface, the flat plates are prepared. The micro-size dimples are directly carved on the metal surface by ultrasonic nano-crystal surface modification (UNSM) method. Momentum of the main flow is increased by the dimple patterns within the turbulent boundary layer (TBL), however, there is no significant change in the turbulence intensity in the TBL. The influence of dimple patterns is examined through the flow field survey near the flat plate trailing edge in terms of the profile drag. The wake flow velocities in the flat plate are measured by PIV technique. The maximum drag reduction rate is 4.6% at the Reynolds number of . The dimples tend to increase the drag reduction rate consistently even at high Reynolds number range.

Numerical Analysis of a Tip Vortex Flow for Propeller Tip Shapes

In order to control the tip vortex cavitation occurring around the tip of a rotating propeller blade, researches on the propeller cavitation and blade tip vortex flows have been increased. In this paper, the propeller tip vortex flow for a blunt and sharp tips was studied using an unsteady Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. In numerical open water test, torques, thrusts, pressure distributions and vortex flows were compared for various rotating speeds. To consider a hull wake, the nominal wake was specified in inlet boundary condition. Pressure distributions and vortex flows with the hull wake were investigated for various propeller rotating angles. From the results, it was confirmed that the blunt tip propeller delayed the tip vortex flow Ke ywords :P ropeller blade tip(추진기 날개 끝), Tip vortex flow(날개 끝 보오텍스 유동), Computational fluid dynamics(CFD, 전산유체역학)

Development of the Driving Pump for the Low Noise Large Cavitation Tunnel

AbstractIt is reported to develop the driving pump for the Low Noise La rge Cavitation Tunnel(LOCAT) which is under construction at Maritime & Ocean E ngineering Research Institute(MOERI). For low background noise condition of the LO CAT, it is crucial not only the best pump efficiency but also no cavity occurrence at any operating conditions. Design condition of the pump is determined by considering the required pump headrise, flow quantity, shaft rotation velocity and pump diameter. Performanc e analysis of the pump is conducted using commercial CFD codes (BladeGen + , CFX-10), and the predicted results are verified by a series of model tests. Cavity was not observe d at any operating condition in the model test, which were conducted at the midium cavitation tunnel of MOERI. The optimum pump for LOCAT, named as LP-11, was successfully developed through a series of pump design processes composed of blade design, perfo rmance analysis and model test. ※Keywords: Driving pump(구동펌프), Low noise(저소음), Cavitation(캐비테이션), Required headrise(요구양정)

PIV Measurements of Rudder Inflow Induced by Propeller Revolution in Hull Wake

In the present study, the flow fields in between the propeller and the semi-spade rudder are investigated by using PIV technique to find out the influences of both simulated hull wake and propeller wake on the incident flow to the rudder. The velocity fields are measured at the propeller rotation angle of and the rudder deflection angles of . Flow fields measured at each rudder deflection angle are analyzed in terms of angle-of-attack against the rudder leading edge. The hull wake increases the angle-of-attack more than that in the uniform inflow condition, forming the angle-of-attack of about at 0.7R(R

Construction of a Test Ship with Two Waterjet Propulsion System and Its Sea Trial Test

This paper describes the design and construction of a test ship with waterjet propulsion system for sea-triai test. Local flow characteristics around intake and nozzle of a operating waterjet propulsion system are measured at a sea trial to investigate between hull and waterjet propulsion. Flow rate is corrected by bollard pull test and shaft power is measured directly using a torque meter The measured results are compared with the predicted results on the basis of DB. Those experimental data will be useful for the future works to develope the model test method and method for powering performance prediction.

CFD Analysis of Marine Propeller-Hub Vortex Control Device Interaction

전 세계적인 온실가스 저감 노력에 따라 선박에 대한 온실가 스 배출 감축 규제가 강화됨에 따라 국제법에 의해 에너지 효율 설계지수(Energy Efficiency Design Index, EEDI)가 2013년부터 건조되는 신조선박에 적용되고 있다. 저속운항(slow-steaming) 을 통한 연비 향상의 노력과 함께 국제해사기구(IMO)에서 발표 한 EEDI는 선박의 설계단계부터 기술적으로 고려해야하는 중요 한 지표로 자리 잡으면서 다양한 형태의 친환경 선박이 개발되고 있다. 이에 대응하기 위해 많은 연구자들은 선박의 저항 및 추진 효율 향상을 목표로 하는 다양한 연구를 수행하고 있으며, 특히, 장치의 설치가 용이하고 기존선박에도 비교적 쉽게 적용할 수 있 는 에너지절감장치(Energy Saving Device, ESD)에 대한 연구가 증가하고 있는 추세이다 (Kang, et al., 2004; Park, et al., 2011; Lim, et al., 2013; Shin, et al., 2013). 가변피치 프로펠 러(Controllable Pitch Propeller, CPP)를 포함하여 추진효율을 향상시킬 수 있는 에너지절감장치에는 덕트(duct), 스테이터 (stator), 프로펠러 허브 보오텍스 조절장치(Propeller Hub Vortex Control, PHVC) 등을 예로 들 수 있다. 그 중에서도 프로펠러 캡 (cap)에 위치하는 PHVC는 허브 보오텍스 유동을 제어하여 회전 운동에너지(rotational kinetic energy) 손실을 줄이는 효과를 발 생시켜 프로펠러의 추력 증가와 함께 토오크 감소를 얻을 수 있 는 장치이다 (Hansen, et al., 2011). Kim, et al.(2015)은 균일 류 유동 및 모형선 반류 중에서 각각 PHVC 피치각 변화 및 프로 펠러와 PHVC 상대 설치각도 변화에 따른 프로펠러와 PHVC의 상호작용 특성 파악을 위하여 대형 캐비테이션터널(LCT)에서 체 계적인 시험적 연구를 수행하였으며 추력, 토오크, 효율 및 PHVC 하류에서 유속분포 특성변화를 보여주었다. 한편, 일반적으로 알려진 바와 같이 설계 단계에서 개발된 장 치들의 유체역학적 성능을 검증하는 것은 쉽지는 않다. 따라서 프로펠러와 허브 보오텍스 조절장치 상호작용