• Journal of Advanced Marine Engineering and Technology
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• v.26 no.5
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• pp.596-606
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• 2002

The three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, PAM-FLOW based on FEM method has been applied to analyze the flow field around the high speed train which is entering into a channel. From the present study, the pressure and flow transients were calculated and analyzed. The generation of compression wave was observed ahead of train and the high pressure in the gap between the train and the tunnel was also found due to the blockage effects. It was found that abrupt fluctuation in pressure exists in the region from train nose to shoulder of train corresponding to 10％ of total length of train during tunnel entry. Computed time history of aerodynamic forces of train during tunnel entry show that drag coefficient rapidly rises and saturates at about non-dimensional time 0.31. The total increase of drag coefficient before and after tunnel entry is about 1.1%. Transient profile of lift force shows similar pattern to drag coefficient except abrupt drop after saturation and lift force in the tunnel increases 0.08% more than that before tunnel entry.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1020-1025
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• 2002

This paper exploits how vortex noise is generated around a cylinder. This is done by utilizing an acoustic holography. In this experiment. compressed air was Infected to tile cylinder through a hose. Therefore, major noise sources were at a hose end as well as around the cylinder： vortex shedding noise. The holography results show a resultant noise picture there it is not easy to clearly sort out the shedding noise and what is generated at the end of the tube. We attempted to separate those noise by the method we developed : contribution analysis scheme. The method, in fact, was found to be efficient and practical to separate the noise field into independent noise sources. The highlights of the results are. we believe, that lift and drag noise picture are now available. This procedure does not limit its application. therefore we may use this to visualize any noise field that we want to understand.

• Journal of Ship and Ocean Technology
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• v.12 no.2
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• pp.41-52
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• 2008

The development of a high-lift rudder is needed because low speed full ships such as the VLCC(Very Large Crude oil Carrier) have difficulty for obtaining enough lifting force from a common rudder. The rudder of a ship is generally positioned behind the hull and propeller. Therefore, rudder design should consider the interactions between hull, propeller, and rudder. In the present study, the FLUENT code and body fitted mesh systems generated by the GRIDGEN program are adopted for the numerical simulations of flow characteristics around a rudder that is interacting with hull and propeller. Sliding mesh model(SMM) is adopted to analyze the interaction between propeller rotation and wake flow behind hull. Several numerical simulations are performed to compare the interactions such as hull-rudder, propeller-rudder, and hull-propeller-rudder. Also, we consider relationships between the interactions. The results of present numerical simulations show the variation of flow characteristics by the interaction between hull, propeller, and rudder, and these results are compared with an existing experimental result. The present study demonstrates that numerical simulations can be used effectively in the design of high-lift rudder behind low speed full ship.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.18-25
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• 2006

Unsteady aerodynamic force measurements were carried out in order to investigate the effects of phase difference of a dragonfly-type model with two pairs of wing. A load-cell was employed to measure the aerodynamic force generated by a plunging motion of the dragonfly-type model. The dragonfly-type model has a dynamic similarity with real one, and incidence angles of fore- and hind-wing are 0° and 10°, respectively. Other experimental conditions are as follows: The freestream velocity was 1.6 m/sec and corresponding chord Reynolds number was 2.88×103, and phase differences of fore- and hind-wing were 0°, 90°, 180° and 270°. The variation of aerodynamic coefficients during one cycle of the wing motion is presented. Results show that the lift is generated during the downstroke motion and the drag generated during the hind-wing‘s downstroke motion with the lift generation.

• Journal of computational fluids engineering
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• v.19 no.2
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• pp.66-71
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• 2014

Aerodynamic design of a vehicle has very important meaning on the fuel economy, dynamic stability and the noise & vibration of a moving vehicle. In this study, the correlation of aerodynamic effect between two model vehicles moving inline on a road was studied with the basic SAE model vehicle. Drag and lift are two main physical forces acting on the vehicle and both of them directly effect on the fuel economy and driving stability of the vehicle. For the research, the distance between two vehicles is varied from 5m to 30m at the fixed vehicle speed, 100km/h and the side-wind was assumed to be zero. The main issue for this numerical research is on the understanding of the interaction forces; lift and drag between two vehicles formed inline. From the study, it was found that as the distance between two vehicles is closer, the drag force acting on both the front and rear vehicle decreases and the lift force has same trend for both vehicle. As the distance(D) is 5m, the drag of the front vehicle reduced 7.4% but 28.5% for the rear-side vehicle. As the distance is 30m, the drag of the rear vehicle is still reduced to 22% compared to the single driving.

• Wind and Structures
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• v.18 no.2
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• pp.135-154
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• 2014

Aerodynamic characteristics of crescent and D-shape bundled conductors were measured by high frequency force balance technique in the wind tunnel. The drag and lift coefficients of each sub-conductor and the whole bundled conductors were presented under various attack angles of wind. The galloping possibility of bundled conductors is discussed based on the Den Hartog criterion. The influence of icing thickness, initial ice accretion angle and sub-conductor on the aerodynamic properties were investigated. Based on the measured aerodynamic force coefficients, a computationally efficient finite element method is also implemented to analyze galloping of iced bundled conductors. The analysis results show that each sub-conductor of the bundled conductor has its own galloping feature due to the use of aerodynamic forces measured separately for every single sub-conductors.

• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.921-930
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• 2001

A new theoretical critical heat flux (CHF) model was developed for the forced convective flow boiling at high pressure, high mass velocity, and low quality. The present model for an intermittent vapor blanket was basically derived from the sublayer dryout theory without including any empirical constant. The vapor blanket velocity was estimated by an axial force balance, and the thickness of vapor blanket was determined by a radial force balance for the Marangoni force and lift force. Based on the comparison of the predicted CHF with the experimental data taken from previous studies, the present CHF model showed satisfactory results with reasonable accuracy.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.2
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• pp.70-78
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• 2004

The present study numerically investigates two-dimensional laminar flow past a circular cylinder in an aligned magnetic field using the spectral method. Numerical simulations are performed for flow fields with Re=100 and 200 in the range of 0$\leq$N$\leq$10, where Ν is the Stuart number that is the ratio of electromagnetic force to inertial force. The present study reports the detailed information of flow quantities on the cylinder surface at different Stuart numbers. It is shown that the vortex shedding can be controlled by the magnetic force representing the Stuart number. As Ν increases, the vortex shedding becomes weaker, resulting in drag reduction whose magnitude is the largest at a critical value. In addition, as the magnetic force increases, the lift amplitude decreases, reaching zero at the critical number.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1223-1228
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• 2001

We have been developing the pantograph for Korean High Speed Train for the last five years. To fulfil the following requirements at designed speed of 350km/h ： 1) contact loss less than 1 ％, 2) aerodynamic noise less than 91dB, 3) average uplift force less than 200N, the pantograph has been modified two times since the first prototype pantograph was manufactured, By means of the following up characteristic test, low speed wind tunnel test, and high speed wind tunnel test for the prototype pantographs, we found that the aerodynamic uplift force did not exceed l60N at speed up to 350km/h and the aerodynamic noise was less than 88dB, that the following up characteristics of the prototype pantograph was excellent.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.334-334
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• 2015

The results of flow feature around two circular cylinders in various arrangements are carried out using two-dimensional simulation at Reynolds number of 200. In this work, time-averaged fluid force acting on the upstream and downstream cylinders were calculated for staggered angle ${\alpha}=0{\sim}90^{\circ}$ in the range of L/D = 1.1~5, where ${\alpha}$ is the angle between the free-stream flow and the line connecting the centers of the cylinders, L is centre-to-centre distance and D is cylinder diameter. The dependence of magnitudes and trends of fluid force coefficient on the spacing ratio L/D and ${\alpha}$ are discussed. In all arrangements of two cylinders, tandem arrangement (${\alpha}=0^{\circ}$) is the case produced a minimum drag coefficient for downstream cylinder. Moreover, the locations of separation and stagnation points or pressure coefficient on surface of the cylinder were examined. Acknowledgement: "This research was a part of the project titled 'Development of integrated estuarine management system', funded by the Ministry of Oceans and Fisheries, Korea."