• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.4
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• pp.112-119
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• 1994

This study is investigated into the dynamic effect of the manifold configuration during the gas exchange processes using both simulation and experiment, In theoretical study on the flow analysis, the characteristic method is applied to solve the compressible unsteady flow equation, involving the several steady flow boundary conditions. In order to excute the engine experiment efficiently, a data acquisition system is configured by using A/D converter and PC. Good results which coincided experimental data with simulation output were obtained, and it shows that this simulation method can be applied to obtain the optimal design parameters in the intake and exhaust systems.

• Nuclear Engineering and Technology
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• v.41 no.7
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• pp.893-906
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• 2009

The present work presents the development of a Large Eddy Simulation (LES) methodology viable for complex geometries and suitable for the simulation of rod-bundles. The use of LES and Direct Numerical Simulation (DNS) allows for a deeper analysis of the flow field and the use of stochastical tools in order to obtain additional insight into rod-bundle hydrodynamics. Moreover, traditional steady-state CFD simulations fail to accurately predict distributions of velocity and temperature in rod-bundles when the pitch (P) to diameter (D) ratio P/D is smaller than 1.1 for triangular lattices of cylindrical pins. This deficiency is considered to be due to the failure to predict large-scale coherent structures in the region of the gap. The main features of the code include multi-block capability and the use of the fractional step algorithm. As a Sub-Grid-Scale (SGS) model, a Dynamic Smagorinsky model has been used. The code has been tested on plane channel flow and the flow in annular ducts. The results are in excellent agreement with experiments and previous calculations.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.170-178
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• 1999

In general, an impeller of centrifugal turbomachinery is designed at isolated condition without considering the presence of a volute, but when the impeller is operating with its volute, the performance of impeller can be different. This is largely caused by the interaction between the impeller and volute flow fields. The magnitude of distortion is increased as the operating point is away from the design point and, as a result, the interaction between the impeller and volute is stronger. In the present calculation, the flow through the impeller is simulated using coarse grids. The flow within the impeller and the volute is naturally unsteady, but the flow is assumed to be steady across the interface between the volute and impeller flow fields. Under the assumption of steady three-dimensional incompressible turbulent flow, the time averaged N-S equations involving standard k-$\epsilon$ turbulent model was solved by the F.V.M. The calculation results are compared with the experimental results obtained for an industrial fan by Sakai etc. and the Hood agreement is demonstrated. And the effects of the impeller-volute interaction are studied.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.5
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• pp.185-190
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• 2006

The security analysis relates to the ability of the electric systems to survive sudden disturbances such as electric short circuits or unanticipated loss of system elements. It is composed of both steady state and dynamic security analyses, which are not two separate issues but should be considered together. In steady state security analysis including voltage security analysis, the analysis checks that the system is operated within security limits by OPF (optimal power flow) after the transition of a new operating point. On the other hand, dynamic security analysis deals that the transition will lead to an acceptable operating condition. Transient stability, which is the ability of power systems to maintain synchronism when subjected to a large disturbance, is a principal component in dynamic security analysis. Usually any loss of synchronism will cause additional outages. They make the present steady state analysis of the post-contingency condition inadequate for unstable cases. This is the reason of the need for dynamics of systems. Probabilistic criterion can be used to recognize the probabilistic nature of system components and shows the possibility of system security. A comprehensive conceptual framework for probabilistic static and dynamic assessment is presented in this paper. The simulation results of the Western System Coordinating Council (WSCC) system compare an analytical method with Monte-Carlo simulation (MCS). Also, a case study of the extended IEEE Reliability Test System (RTS) shows the efficiency of this approach.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.53-61
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• 2004

Condenser tube which is used for a cooling system of automobiles is mainly manufactured by conform extrusion. However, direct extrusion using porthole die in comparison with conform extrusion has many advantages such as improvement of productivity, reduction of production cost etc. In general, the porthole die extrusion process is useful for manufacturing long tubes with hollow sections and consists of three stages(dividing, welding and forming stages). Especially, Porthole die for producing condenser tube is very complex. Thus, in order to obtain the detailed mechanics, to assist in the design of proper die shapes and sizes, and to improve the quality of products, porthole die extrusion should be analyzed in as non-steady state as possible. This paper describes FE analysis of non-steady state porthole die extrusion for producing condenser tube with multi-hole through 3D simulation in the non-steady state during the entire process to evaluate detailed metal flow, temperature distribution, welding pressure and extrusion load. Also to validate FE simulation of porthole die extrusion, a comparison of simulation and experiment results was presented in this paper.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.8-23
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• 1997

Steady and unsteady numerical simulations are conducted for the comparison with the experiments performed to investigate the ram accelerator flow field by using an expansion tube facility in Stanford University. Wavier-Stokes equations for chemically reacting flows are analyzed by fully implicit and time accurate numerical methods with Jachimowski's detailed chemistry model for hydrogen-air combustion involving 9 species and 19 reaction steps. Although the steady state numerical simulation shows a good agreement with the experimental schlieren and OH PLIF images for the case of $2H_2$＋$O_2$＋$17N_2$ fails in reproducing the combustion region behind the shock intersection point shown in the case of $2H_2$＋$O_2$＋$12N_2$ mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. From the result of unsteady numerical simulation, the experimental result seems to be an instantaneous state during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.535-540
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• 2000

The objective of the present study is to visualize the pulsatile flow fields by using three-dimensional computer simulation and the PIV system. A closed flow loop system was built for the steady and unsteady experiments. The Harvard pulsatile pump was used to generate the pulsatile pressure and velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow field. Two consecutive particle images were captured by a CCD camera for the image processing. The cross-correlation method in combination with the moving searching area algorithm was applied for the image processing of the flow visualization. The pulsatile flow fields were visualized effectively by the PIV system in conjunction with the applied algorithm. The range validation and the area interpolation methods were used to obtain the final velocity vectors with high accuracy. The finite volume predictions were used to analyze three-dimensional flow patterns in the bifurcation model. The results of the PIV experiment and the computer simulation are in good agreement and the results show the recirculation zones and formation of the paired secondary flow distal to the apex of the bifurcated model. The results also show that the branch flow is pushed strongly to the inner wall due to the inertial force effect and helical motions are generated as the flow proceeds toward the outer wall.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.81-85
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• 2005

Three-dimensional steady incompressible laminar entry flows in a square duct of $90^{\circ}$ bend are numerically simulated by a new solution code(PowerCFD) using unstructured cell-centered method. Solutions are obtained with three unstructured grid types of hexahedron, prism and hybrid at a Reynolds number, based on the hydraulic diameter and bulk velocity, of 790. Interesting features of the flow are presented in detail. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a $90^{\circ}$ bend of a square duct with fully-developed entry flows. It is found that the code is capable of producing the nature of laminar flow in curved square duct with no grid type dependency.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.153-158
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• 2005

Numerical simulations of two-dimensional steady incompressible lid-driven flow in a square cavity are presented to verify the validity of a new solution code(PowerCFD) with unstructured grids. The code uses the non-staggered(collocated) grid approach which is very popular for incompressible flow analysis because of its numerical efficiency on the curvilinear or unstructured grids. Solutions are obtained for configurations with a Reynolds number as high as 10,000 with both rectangular and hybrid types of unstructured grid mesh. Interesting features of the flow are presented in detail and comparisons are made with benchmark solutions found in the literature. It is found that the code is capable of producing accurately the nature of the lid-driven cavity flow at high Reynolds numbers.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.748-753
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• 2001

The objective of the present study is to visualize the pulsatile flow fields by using three-dimensional computer simulation and the PIV system. A closed flow loop system was built for the steady and unsteady experiments. The Harvard pulsatile pump was used to generate the pulsatile pressure and velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow field. Two consecutive particle images were captured by a CCO camera for the image processing at several cross section. The range validation and the area interpolation methods were used to obtain the final velocity vectors with high accuracy. The finite volume predictions were used to analyze three-dimensional flow patterns in the bifurcation model. The results of the PIV experiment and the computer simulation are in good agreement and the results show the recirculation zones and formation of the paired secondary flow distal to the apex of the bifurcated model. The results also show that the branch flow is pushed strongly to the inner wall due to the inertial force effect and helical motions are generated as the flow proceeds toward the outer wall.