• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.14 no.4
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• pp.293-299
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• 1985

This paper describes an economical prediction procedure for heat transfer phenomenon through a channel containing an abrupt asymmetric expansion in flow cross-seetional area. Numerical solutions for the flow field are obtained by the finite difference numerical method applied to the modified boundary layer equations. Modified boundary energy equation is used to analyze heat transfer as modified boundary momentum equation. Predictions of the method compare very favorable with exprimental data. Results of this study by modified boundary layer equation are as follows : 1. The computation time required for the scheme is at least an order of magnitude less than for the numerical solution of the full Navier-stokes and Energy eguations. 2. In laminar flow, the maximum heat transfer occurs downstream of the reattachment point.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.2
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• pp.10-19
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• 2009

The working of diesel particulate filters(DPF) needs to periodically burn soot that has been accumulated during loading of the DPF. The prediction of the relation between an uniformity of gas velocity and soot regeneration efficiency with simulations helps to make design decisions and to shorten the development process. This work presents a comprehensive combined 'DOC+CDPF' model approach. All relevant behaviors of flow fluid are studied in a 3D model. The obtained flow fields in the front of DPF is used for 1D simulation for the prediction of the thermal behavior and regeneration efficiency of CDPF. Validation of the present simulation are performed for the axial and radial direction temperature profile and shows goods agreement with experimental data. The coupled simulation of 3D and 1D shows their impact on the overall regeneration efficiency. It is found that the flow non-uniformity may cause severe radial temperature gradient, resulting in degrading regeneration efficiency.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.74-82
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• 2010

Power flow analysis(PFA) methods have shown many advantages in noise predictions and vibration analysis in medium-to-high frequency ranges. Applying the finite element technique to PFA has produced power flow finite element method(PFFEM) that can be effectively used for analysis of vibration of complicated structures. PFADS(power flow analysis design system) based on PFFEM as the vibration analysis program has been developed for vibration predictions and analysis of coupled structural systems. In this paper, to improve the function of vibro-acoustic coupled analysis in PFADS, the PFFEM has been extended for analysis of the interior noise problems in the vibro-acoustic fully coupled systems. The vibro-acoustic fully coupled PFFEM formulation based on energy coupled relations is extended to structural system model by using appropriate modifications to structural-structural, structural-acoustic and acoustic-acoustic joint matrices. It has been applied to prediction of the interior noise in two room model coupled with panels, and the PFFEM results are compared to those of statistical energy analysis(SEA).

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.427-733
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• 2003

Adiabatic shear bands have been observed in the serrated chip during high strain rate metal cutting process of medium carbon steel and titanium alloy. The recent microscopic observations have shown that dynamic recrystallization occurs in the narrow adiabatic shear bands. However the conventional flow stress models such as the Zerilli-Armstrong model and the Johnson-Cook model, in general, do not predict the occurrence of dynamic recrystallization (DRX) in the shear bands and the thermal softening effects accompanied by DRX. In the present study, a strain hardening and thermal softening model is proposed to predict the adiabatic shear localized chip formation. The finite element analysis (FEA) with this proposed flow stress model shows that the temperature of the shear band during cutting process rises above 0.5T$\sub$m/. The simulation shows that temperature rises to initiate dynamic recrystallization, dynamic recrystallization lowers the flow stress, and that adiabatic shear localized band and the serrated chip are formed. FEA is also used to predict and compare chip formations of two flow stress models in orthogonal metal cutting with AISI 1045. The predictions of the FEA agreed well with the experimental measurements.

• The KSFM Journal of Fluid Machinery
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• v.3 no.3 s.8
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• pp.31-40
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• 2000

A computer program is developed for the prediction of the aerodynamic performance and the noise characteristics in the basic design step of axial flow fan. The flow field and the performance of fan are analyzed by using the streamline curvature computing scheme with total pressure loss and flow deviation models. Fan noise is assumed to be generated due to the pressure fluctuations induced by wake vortices of fan blades and to radiate via dipole distribution. The vortex-induced fluctuating pressure on blade surface is calculated by combining thin airfoil theory and the predicted flow field data. The predicted performances, sound pressure level and noise directivity patterns of fan by the present method are favorably compared with the test data of actual fan. Furthermore, the present method is shown to be very useful in optimizing design variables of fan with high efficiency and low noise level.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1348-1357
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• 2006

For the rational aseismatic design of a structure constructed on the ground which has weakness for liquefaction or flow, it is necessary to predict ground deformation as well as force acting on the ground. In general, the prediction of liquefaction is based on solid mechanics while the prediction of flow is basis of fluid mechanics. Since liquefaction and flow occur continuously, unified analysis methods have been developed. Among of them is Rue-elasto plastic model that is based on small deformation theory. This methods, however, is not adequate for such a large deformable ground condition. In this paper, a large deformaion theory using the finite deformation theory proposed by Dietal and the updated lagrangian method is presented. In addition, the applicability of the theory is verified by 1-d consolidation analysis and flow tests.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.610-620
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• 1999

Recently, numerous modifications of low Reynolds number $k-{\epsilon}$ model have boon carried out with the aid of DNS data. However, the previous models made in this way are too intricate to be used practically. To overcome this shortcoming, a new low Reynolds number $k-{\epsilon}$ model has boon developed by considering the distribution of turbulent properties near the wall. This study proposes the revised a turbulence model for prediction of turbulent flow with adverse pressure gradient and separation. Nondimensional distance $y^+$ in damping functions is changed to $y^*$ and some terms modeled for one dimensional flow in $\epsilon$ equations are expanded into two or three dimensional form. Predicted results by the revised model show an acceptable agreement with DNS data and experimental results. However, for a turbulent flow with severe adverse pressure gradient, an additive term reflecting an adverse pressure gradient effect will have to be considered.

• Transactions of Materials Processing
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• v.9 no.1
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• pp.72-79
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• 2000

Dynamic recrystallization (DRX), which may occur during hot deformation, is important for the microsturctural evolution of 304 stainless steel. Especially, the current interest in modelling hot rolling demands quantitative relationships among the thermomechanical process variables, such as strain, temperature, strain rate, and etc. Thus, this paper individually presents the relationships for flow stress and volume fraction of DRX as a function of processing variables using torsion tests. The hot torsion tests of 304 stainless steel were performed at the temperature range of 900~110$0^{\circ}C$ and the strain rate range of 5x10-2~5s-1 to study the high temperature softening behavior. For the exact prediction of flow stress, the equation was divided into two regions, the work hardening (WH) and dynamic recovery (DRV) region and the DRX region. Especially, The flow stress of DRX region could be expressed by using the volume fraction of DRX (XDRX). Since XDRX was consisted of the critical strain($\varepsilon$c) for initiation of dynamic recrystallization (DRX) and the strain for maximum softening rate ($\varepsilon$*), that were related with the evolution of microstructure. The calculated results predicted the flow stress and the microstructure of the alloy at any deformation conditions well.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.2
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• pp.69-74
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• 2016

Most hot water heating valves for apartments are constant-flow types, which limit the flow rate through an individual household for even distribution of heating water to other households. The constant-flow type is implemented by an on-off control. As a result, heating water is supplied intermittently and hence, indoor air temperature also fluctuates. Returning water temperature is also high, which reduces energy efficiency. To implement continuous feedback control, the indoor temperature dynamics was simulated to fit a measured temperature history by a state-of-the-art physical model. From the model, it was found that the most important disturbance is outdoor temperature and its effect on indoor temperature lasts about an hour. To cope with the slow response and the significant disturbance, a prediction control with proportional feedback is proposed. The control was found to be successful in implementing continuous heating water flow and improved indoor temperature control.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.477-478
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• 2010

It was in the mid-1980s when the shipboard noise analysis was introduced to the Korean shipbuilding industry. Since then through the continued efforts of the industries in the last decades, native computational codes dedicated to the shipboard noise prediction have been developed based on empirical formula and/or sophisticated theories such as SEA and PFM. This paper addresses some problems in dealing with predicting shipboard noise and the way how to overcome the uncertainties in the prediction.