Hong-Gi Lee

Computational Study of the Scale Effect on Resistance and Propulsion Performance of VLCC

This article examines the scale effect of the flow characteristics, resistance and propulsion performance on a 317k VLCC. The turbulent flows around a ship in both towing and self-propulsion conditions are analyzed by solving the Reynolds-averaged Navier-Stokes equation together with the application of Reynolds stress turbulence model. The computations are carried out in both model- and full-scale. A double-body model is applied for the treatment of free surface. An asymmetric body-force propeller is used. The speed performances including resistance and propulsion factors are obtained from two kinds of methods. One is to analyze the computational results in model scale through the revised ITTC’78 method. The other is directly to analyze the computational results in full scale. Based on the computational predictions, scale effects of the resistance and the self-propulsion factors including form factor, thrust deduction fraction, effective wake fraction and various efficiencies are investigated. Scale effects of the streamline pattern, hull pressure and local flow characteristics including x-constant sections, propeller and center plane, and transom region are also investigated. This study presents a useful tool to hull-form and propeller designers, and towing-tank experimenters to take the scale effect into consideration.

Computational Prediction of Speed Performance for a Ship with Vortex Generators

Abstract The computational prediction method of speed performance for a ship with vortex generators is proposed. The Reynolds averaged Navier-Stokes equation has been solved together with the application of Reynolds stress turbulence mod el. The computations are carried out under identical conditions of the experimental method, i.e., towing and self-propulsion calculations without and with vortex generators. The speed performance in full scale is obtained through analyzing the computational results in model scale according to the revised model-ship performance analysis method of ITTC’78 with considering the vortex generators into account. The characteristics of resistan ce, self-propulsion and wake characteristics on the propeller plane are investigated. The proposed computational prediction clearly shows the effect of vortex generators and can be applicable to the design tool for vortex generators. ※Keywords: Vortex generator(와류생성기), Speed performance(속도성능), Computational prediction(수치적 추정), Revised ITTC’78 analysis method(수정된 ITTC’78 해석법), Resistance(저항), Self-propulsion(자항), Wake characteristics(반류특성)

2D WPS System for Measuring the Location Changes in Real Time of PAL-XFEL Devices

Several parts that comprise the large scientific equipment should be installed and operated at precise three-dimensional location coordinates X, Y, and Z through survey and alignment to ensure their optimal performance. As time goes by, however, the ground uplifts and subsides, which changes the coordinates of the installed components and leads to alignment errors ΔX, ΔY, and ΔZ. As a result, the system parameters change, and the performance of the large scientific equipment deteriorates accordingly. Measuring the change in the locations of the systems comprising the large scientific equipment in real time would make it possible to predict alignment errors, locate any region with greater changes, realign components in the fast changing region and shorten the time of survey and alignment. For this purpose, a hydrostatic leveling sensor (HLS) with 0.2 μm resolution was installed and is operated in the PAL-XFEL building. In addition, a 2D wire position sensor (WPS) with a 0.1 μm resolution was installed and is operated in the undulator sections where measurements of the two-dimensional changes of the systems (vertical & horizontal) are necessary. This paper is designed to introduce the operating principle of the 2D WPS, the installation and operation of the WPS system, and the way in which the WPS system is utilized in order to ensure beam stability.

Design of Switching Magnet for 20-MeV Beamlines at PEFP

The PEFP (Proton Engineering Frontier Project) proton linac is designed to have two proton beam extraction lines at the 20-MeV and 100-MeV end. The 20-MeV extraction line is branched out into 5 beamlines by using the switching magnet. The magnet bends the proton beam by +20, +10, 0, -10, -20 degrees, respectively, and has an AC frequency of 2.5 Hz with a programmable ac power supply. It employs an H-shape, 0.45 T magnetic fields, 500 mm effective length, and 50 mm pole gap. Laminated steel of 0.5 mm reduces the eddy currents in the yoke, but some heat radiation from the stainless steel of vacuum chamber is inevitable. This paper presents the magnet specification and primary design.