Jungkeun Oh

A Proposal on Standard Rudder Device Design Procedure by Investigation of Rudder Design Process at Major Korean Shipyards

Recently, a very large vessels maneuvering performance, rudder performance and rudder designs importance are considered to be an important subject. However, there have been few studies on the design process of rudder device before. The aim of this paper is to investigate a design process of rudder device and to propose a generalized design process of rudder device. Firstly, we investigated the rudder device design process of Korean major shipyards. And the differences of a torque calculation method, rudder section design, maneuvering performance examination method, etc. were analyzed theoretically. Secondly, the design process of rudder device was divided into concept design, initial design and detail design, rudder profile and design method have been selected through rudder form determination process. And principal dimension and steering gear capacity were determined. Maneuvering performance was also examined by simulation tool. In detail design, design criteria which had been considered in rudder initial design was investigated thoroughly. Also a rudder torque, rudder cavitation performance and rudder structure analysis were estimated. And maneuvering performance was also examined by model test. Finally, based on the results of investigation, the design process of rudder device was generalized and proposed.

A Study for Improvement of Lift Performance of a Horn-type Rudder with the Coanda Effect

The Coanda effect is noticeable when a jet stream is applied tangential to a curved surface since then the jet stream remains attached to the surface beyond the point where flow separates otherwise and results in augmentation of circulation and lift. Numerous experimental and numerical studies have been performed in various fields of aerodynamics to exploit the Coanda effect and many of them found to be useful. It can be speculated that the Coanda effect may have practical application to the field of marine hydrodynamics as well since various control surfaces are being used to control behaviors of ships and offshore structures. In the present study, the Coanda effect has been applied to a horn type rudder and a series of numerical computations and model experiments are performed to find the practical applicability. The results indicate that the Coan da jet increases the lift coefficient of the rudder as much as 52% at the momentum coefficient Cj = 0.1 and the rudder angle α = 10°.

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.

Design of tactile device for medical application using magnetorheological fluid

For the tactile recognition of human organ in minimally invasive surgery (MIS), this paper presents a novel tactile device that incorporates with magnetorheological (MR fluid). The MR fluid is contained by diaphragm and several pins. The operator for MIS can feel different force (or stiffness) from the proposed tactile device by applying different magnetic field or current. In order to generate required force from the device, the repulsive force from the human body is measured as reference data and an appropriate size of tactile device is designed and manufactured. It has been demonstrated via experiment that the repulsive force corresponding to the human body can be achieved by applying proper control input current. In addition, it has been shown that we can control the repulsive force by dividing the tactile device by several sections.

Rudder Gap Cavitation and Its Suppression Devices

Development of rudder gap flow blocking device for lift augmentation and cavitation suppression is presented. In order to verify the performance of this device, cavitation visualization and surface pressure measurements were carried out in a cavitation tunnel. Numerical simulations were conducted using a computational fluid dynamics code for more rigorous verification. The new rudder system is equipped with cam devices, which effectively close the gap between the horn/pintle and movable wing parts. The experimental and computational results show that the proposed rudder system is superior to the conventional rudder systems in terms of the lift augmentation and cavitation suppression.© 2008 ASME

A Numerical Study on the Control of the Gap Flow Using a Fluid Supply Device

AbstractRecently, horn-type rudders are generally being used at high speed container ships and are frequently suffering from the cavitation occurs on the rudder surface in the vicinity of the gap between the horn and rudder plate. In the present study, a fluid supplying device is employed as to decrease the gap cavitation of the horn-type rudder. The device is devised to inject the water against the pressure side through the nozzle installed inside of the gap to control the gap flow. Numerical calculations are performed to investigate the effectiveness of the device and the results show that the device can noticeably reduce the gap cavitation. The rates of water injection for achievement of the maximum retardations of gap flow are also sought. ※Keywords: Horn-type rudder(혼타), Gap flow control(간극 유동제어), Cavitation(공동현상), Fluid supplying device(유체 공급 장치), Numerical Simulation(수치해석) 1. 서론 최근 선박의 대형화 및 고속화 추세에 따라 프로펠러, 타, 안정기용 핀 등에서 공동현상이 자주 발생하고 있다. 이러한 공동현상은 날개 주위로흐르는 물이 흡입면을 지날 때 증기압보다 낮은

Two-dimensional Model Tests for Rudder Gap Cavitation and Suppression Devices

The increasing size and speed of cargo ships result in high speed flow in propeller slipstream, and thereby cavitation is frequently observed on and around a rudder system. Rudder gap cavitation is the most difficult one to control and suppress among various types of the cavitation on a rudder system. In the present study, experiments of the incipient cavitation and pressure measurement were carried out for typical cargo ship rudder sections with and without the suppression devices, which were suggested by the authors. Fundamental understanding of the rudder gap cavitation inception was obtained along with its relevance to the surface pressure distribution. It is confirmed that the gap flow blocking devices effectively suppress the rudder gap cavitation and, at the same time, augment lift.

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.

Development of Algorithm for Stereoscopic PIV using Normalized Cross-correlation

Contrary to the conventional single-point measuring devices such as LDV, pitot-tube, hot-wire, etc., it would be possible to measure instantaneously 3-D flow fields with a stereoscopic PIV system. In this paper, we present an analysis algorithm for a stereoscopic PIV system using the normalized cross-correlation (NCC) and a 3 -D calibration based reconstruction method. The evaluation method based on NCC is one of the most accurate correlation-based methods. We validated the developed algorithm through a benchmarking comparison with 3-D artificial SPIV images and calibration target images.

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