• Journal of Environmental Science International
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• v.28 no.11
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• pp.1047-1059
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• 2019

To address the increase of weather hazards and the emergence of new types of such hazards, an optimization technique for three-dimensional (3D) representation of meteorological facts and atmospheric information was examined in this study as a novel method for weather analysis. The proposed system is termed as "meteorological and air quality information visualization engine" (MAIVE), and it can support several file formats and can implement high-resolution 3D terrain by employing a 30 m resolution digital elevation model. In this study, latest 3D representation techniques such as wind vector fields, contour maps, stream vector, stream line flow along the wind field and 3D volume rendering were applied. Implementation of the examples demonstrates that the results of numerical modeling are well reflected, and new representation techniques can facilitate the observation of meteorological factors and atmospheric information from different perspectives.

• The Korean Journal of Rheology
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• v.10 no.4
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• pp.217-226
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• 1998

The anisotropy caused by the fiber orientation, which is inevitably generated by the flow during injection molding of short fiber reinforced polymers, greatly influences dimensional accuracy, mechanical properties, and other quality of the final product. Since the filling stage of the injection molding process plays a vital role in determining fiber orientation, an accurate analysis of flow field for the filling stage is needed. Unbalanced filling occurs when a complex or a multi-cavity mold is used leading to development of regions where the fiber suspension is under compression. It is impossible to make an accurate calculation of the flow field during filling with the analysis assuming incompressible fluid. A mold with four cavities with different filling times was produced to compare the numerical analysis results with the experimental data. There was a good agreement between the experimental and theoretical results when the compressibility of the polymer melt was considered for the numerical simulation. The fiber orientation states for compressible and incompressible fluids were also compared qualitatively as well as quantitatively in this study.

• Journal of Environmental Science International
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• v.14 no.3
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• pp.297-309
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• 2005

Recently air quality modeling studies for industrial complex and large cities located in the coastal regions have been carried out Especially, the representation of atmospheric flow fields within a model domain is very important, because an adequate air quality simulation requires an accurate portrayal of the realistic three­dimensional wind fields. Therefore this study investigated effect of using high resolution terrain height data and FDDA with observational data to reflect local characteristics in numerical simulation. So the experiments were designed according to FDDA and the detail terrain height with 3sec resolution or not Case 30s was the experiment using the terrain height data of USGS without FDDA and Case 3s was the experiment using the detail terrain height data of Ministry of Environment without FDDA and Case 3sF was experiment using the detail terrain height data of Ministry of Environment with FDDA. The results of experiments were more remarkable, In Case 3s and Case 3sF, temperature indicated similar tendency comparing to observational data predicting maximum temperature during the daytime and wind speed made weakly for difference of terrain height Also Case 3sF had more adequate tendency than Case 3s at dawn.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.11-21
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• 2005

A three-dimensional parallel Euler flow solver has been developed for the simulation of unsteady rotor-fuselage interaction aerodynamics on unstructured meshes. In order to handle the relative motion between the rotor and the fuselage, the flow field was divided into two zones, a moving zone rotating with the blades and a stationary zone containing the fuselage. A sliding mesh algorithm was developed for the convection of the flow variables across the cutting boundary between the two zones. A quasi-unsteady mesh adaptation technique was adopted to enhance the spatial accuracy of the solution and to better resolve the wake. A low Mach number pre-conditioning method was implemented to relieve the numerical difficulty associated with the low-speed forward flight. Validations were made by simulating the flows around the Georgia Tech configuration and the ROBIN fuselage. It was shown that the present method is efficient and robust for the prediction of complicated unsteady rotor-fuselage aerodynamic interaction phenomena.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.41-50
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• 1989

A basic formulation of the panel method, which is based on the potential field formulation, is reviewed for the case of two-dimensional hydrofoil problems. Numerical procedures to improve the computational efficiency of the panel method are suggested. By investigating local behavior of the flow around the trailing edge, a wedge type Kutta condition is formulated. By subdividing the trailing edge panels, where dipole strengths of the subdivided panels follow the local behavior of the potential values of the flow outside a wedge, the circulation around a hydrofoil is calculated accurately with a relatively small number of panels. The subdividing technique to improve the accuracy of the numerical Kutta condition is proved to be efficient. A local behavior of the flow around the leading edge is also investigated. By matching the flow around the leading edge with that around a parabola, a very accurate velocity distribution is obtained with relatively small number of panels. An accurate prediction of the stagnation point and the pressure distribution near the leading edge may contribute to improve the accuracy of cavity predictions and boundary layer calculations around hydrofoils.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.10
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• pp.901-906
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• 2010

A three-dimensional flow simulation was performed to investigate the flow field in a wind farm on a complex terrain. The present study aims to examine the effects of mountainous terrain and turbine arrangement on the performance of wind power generation. A total of 49 wind turbines was modeled in the computational domain; detailed blade shape of the turbines was considered. Frozen rotor method was used to simulate the rotating operation. The torque acting on the turbine blades was calculated to evaluate the performance of the wind turbines. The numerical results showed details of the flow structure in the wind farm including the velocity deficit in the separated flow regions; this velocity deficit was due to the topographical effect. The effect of the wake induced by the upstream turbine on the performance of the downstream wind turbine could also be observed from the results. The methodology of the present study can be used for selecting future wind-farm sites and wind-turbine locations in a selected site to ensure maximum power generation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.205-217
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• 2006

Rock and discontinuities are main factors consisting of a rock mass and the physical properties of each factor have direct effects on the mechanical stability of artificial structures in the rock mass. Because physical properties of the rock and discontinuities change a lot according to the size of test materials, a close attention is needed when the physical properties, obtained from laboratory tests, are used for the design of field structures. In this study, change of physical properties of intact materials due to the change of their size are studied. Six kinds of artificial materials including crystal, instead of an intact rock, are adopted for the study to guarantee the homogeneity of specimen materials even with relatively large size. Uniaxial strength and Young's modulus of each artificial material are checked out for a size effect and compared with the predicted values by Buckingham's theorem - dimensional analysis. A numerical analysis using PFC (Particle Flow Code) is also applied and primary factors influencing on the size effect are investigated.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.2
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• pp.24-32
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• 2008

A non-reacting experimental study on a normal injection into a Mach 1.92 crossflow which flows over various geometries(flat plate, small cavity, large cavity) was carried out to investigate the effect of the momentum flux ratio(J). The aft ramp of the cavity advances the increase of the penetration height and the strong two-dimensional shock from recompression region mainly affects the shock structure and mixing layer at the downstream flow. As flow runs downward, the transverse penetration height increases with increasing J(J = 0.9, 1.7, 3.4). However, above some critical ratio, jet penetration height growth with increasing J is not appeared in flow-field. Large scale cavity has a good mixing efficiency but it increases the drag loss in the combustor.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.3 s.153
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• pp.267-278
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• 2007

This experimental study investigated on the eddy making effect on the roll motion of a rectangular barge in a two-dimensional wave tank. The structure was used to simulate a simplified rectangular barge in the beam sea condition. The structure with a draft one half of its height was hinged at the center of gravity and free to roll by waves. The rectangular barge was tested with regular waves with a range of wave periods that are shorter, equal to, and longer than its roll natural period. Particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The coupled interactions between the incident wave and the barge were demonstrated by examining the vortical flow fields to elucidate the eddy making effect during the roll motion. For incoming wave with a wave period same as the roll natural period, the barge roll motion was reduced by the eddy making damping effect. At the wave period shorter than the roll natural period, the structure roll motion was slightly reduced by the vertical flow around the barge. However, at the wave period longer than the roll natural period, the eddy making effect due to flow separation at structure corners indeed amplifies the roll motion. This indicates that not only can the eddy making effect damp out the roll motion, it can also increase the roll motion.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.2
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• pp.200-207
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• 2017

The purpose in having a control surface on ships is to control the motion of the ship. The control surface may be composed entirely of a single movable surface or of a combination of fixed and movable portions. A control surface has one sole function to perform in meeting its purpose, and that is to develop a control force in consequence of its orientation and movement relative to the water. The forces and moments generated as a result of this rotation and angle of attack then determine the manoeuvring characteristics of the ship. In this paper, two-dimensional flow characteristics of a flapped rudder and a water-blowing control rudder were accomplished respectively by PIV method in a circulating water channel. Model test has been carried out with different angles of attack of main foil (NACA 0012) and flap's deflection angles to predict the performance of the flapped rudder and the water-blowing control rudder. The 2-frame particle tracking method has been used to obtain the velocity distribution in the flow field. $Re{\fallingdotseq}3.0{\times}10^4$ has been used during the whole experiments and measured results have been compared with each other.