• 한국유체기계학회 논문집
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• 제13권5호
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• pp.35-42
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• 2010

This paper deals with the development of analytical model of a turbocharger and its detail rotordynamic analysis. Two analytical models, which are verified by experimental modal testing, are proposed and the analytical model including rotor shaft extended to compressor and turbine wheel end side is chosen. A rotordynamic analysis includes the critical map, Campbell diagram, stability, and unbalance response, especially nonlinear transient response considering nonlinear fluid film force at bearings. Although the linearized analysis accurately predicts the critical speeds, stability limit, and stability threshold speed, the predicted vibration results are not valid for speeds above the stability threshold speed since the rotor vibrates with a subsynchronous component much larger than the one synchronous with rotor speed. Hence, for operating speed above the stability threshold, a nonlinear transient analysis considering nonlinear fluid film force must be performed in order to accurately predict vibration responses of rotor and guarantee results of analysis.

• 한국전산구조공학회논문집
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• 제25권4호
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• pp.315-321
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• 2012

본 연구에서는 분자동역학 전산모사와 유한요소해석 기반의 균질화 기법을 통해 나노복합재의 열전도 특성을 정확하고 효율적으로 예측할 수 있는 순차적 멀티스케일 균질화 해석기법을 제안하였다. 나노입자의 크기효과가 나노복합재의 유효 열전도 특성에 미치는 영향을 조사하기 위해 크기가 다른 구형 나노입자가 첨가된 나노복합재의 열전도 계수를 분자동역학 전산모사를 통해 예측했고, 그 결과 나노입자의 크기가 작아질수록 계면에서의 Kapitza열저항에 의해 나노복합재의 열전도 계수가 점차 감소하는 것으로 나타났다. 이러한 나노입자의 크기효과를 균질화 해석모델을 통해 정확하게 묘사하기 위해 Kapitza 열저항에 의한 계면에서의 온도 불연속 구간과 고분자 기지가 높은 밀도를 가지며 흡착되는 유효계면을 추가적인 상으로 도입하여 나노복합재를 입자, Kapitza 계면, 유효계면, 기지로 구성된 4상의 연속체 구조로 모델링하였다. 이후 순차적 멀티스케일 균질화 해석기법을 통해 유효계면의 열전도 계수를 나노복합재의 열전도 계수로부터 역으로 예측했으며, 이를 입자의 반경에 대한 함수로 근사하였다. 근사 함수를 토대로 다양한 입자 체적분율과 반경에 대한 나노복합재의 유효 열전도 특성을 예측하였으며, 유효계면에 대한 매개변수 연구를 수행하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.652-653
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• 2009

In this study, flow-induced vibration (FIV) analyses have been conducted for a 3D compressor blade model. Advanced computational analysis system based on computational fluid dynamics (CFD) and computational structural dynamics (CSD) has been developed in order to investigate detailed dynamic responses of designed compressor blades. Fluid domains are modeled using the computational grid system with local grid deforming and remeshing techniques. Reynolds-averaged Navier-Stokes equations with $\kappa-\varepsilon$ turbulence model are solved for unsteady flow problems of the rotating compressor model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D compressor blade for fluid-structure interaction (FSI) problems. Detailed dynamic responses and instantaneous pressure contours on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating compressor blade.

• 한국소음진동공학회논문집
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• 제19권6호
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• pp.551-559
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• 2009

In this study, flow-induced vibration(FIV) analyses have been conducted for a 3D compressor blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics(CSD) has been developed in order to investigate detailed dynamic responses of designed compressor blades. Fluid domains are modeled using the computational grid system with local grid deforming and remeshing techniques. Reynolds-averaged Navier-Stokes equations with $\kappa-\epsilon$ turbulence model are solved for unsteady flow problems of the rotating compressor model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D compressor blade for fluid-structure interaction(FSI) problems. Detailed dynamic responses and instantaneous pressure contours on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating compressor blade.

• 한국산학기술학회논문지
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• 제19권12호
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• pp.887-895
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• 2018

본 논문은 수송량 증대를 위한 열차제어시스템의 안전거리 설계와 전동차 제동설계에 활용할 수 있는 제동모델을 제시한다. 제동모델을 위해 6량 1편성으로 운행되는 전동차의 제동특성을 시험하였다. 제동특성에 영향을 줄 수 있는 인자로는 마찰계수, 제동압력의 변화, 회생제동 등이 있으며 시험을 통해 확인하였다. 제동압력은 상용제동과 비상제동으로 구분하고 차량의 특성을 반영하였다. 주행하는 철도차량에 작용하는 외력은 주행저항을 측정 시험과 후처리 방법을 제시하고 있는 KS R 9217에 따라 시험을 수행하고 2차 다항식 형태로 해당 열차의 주행저항을 제시하였다. 차량의 재원, 마찰계수, 제동압력, 주행저항을 바탕으로 직선 평탄 선로를 주행하는 전동차의 동적 거동은 다물체 동역학 해석 소프트웨어를 이용하여 해석하였다. 해석결과는 상용제동과 비상제동에 대하여 시험결과와 비교 검증하였으며 상당히 합리적인 결과를 도출하였다. 검증된 모델은 제동초기 속도에 따른 정지거리를 분석하고 감속도 중심의 제동모델과 비교하였다. 또한, 운영기관의 마찰계수 한계치에 따라 열차제어시스템을 위한 안전거리는 변화할 수 있음을 확인하였다. 본 연구의 결과는 철도차량들을 연결하여 운행하는 열차의 동적 거동해석에 활용할 수 있을 뿐 아니라 차량 설계에서 제동에 영향을 미치는 다양한 선로환경 분석과 제동 성능향상의 기초자료로 활용할 수 있을 것으로 기대된다.

• 한국유체기계학회 논문집
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• 제16권3호
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• pp.26-31
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• 2013

In present 3D CFD study, the method for determining leakage and rotordynamic coefficients of a plain-gas seal is suggested by using the relative coordinate system for steady-state simulation. In order to find the effect of pre-swirl speed at seal inlet, pre-swirl velocity is included as a parameter. Present analysis is verified by comparison with results acquired from Bulk-flow analysis code and published experimental results. The results of 3D CFD rotordynamic coefficients of direct stiffness(K) and cross-coupled stiffness(k) show improvements in prediction. As pre-swirl speed at seal inlet increases, k also increases to destabilize system. However, pre-swirl speed at seal inlet does not show sensitivity to the leakage and rotordynamic coefficients of K and damping(C).

• 동력기계공학회지
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• 제13권5호
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• pp.34-39
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• 2009

In this paper, the CFD analysis using various turbulent models has been performed to evaluate which type of turbulent models can predict well the mixing flow structure of $45^{\circ}$ impinging round jet. This CFD analysis has been carried out through the commercial Fluent software. As a result, any of turbulent models cannot predict the experimental results definitely all over the flow range. However, as compared with the experimental results, the turbulent model of realizable(RLZ) k-$\varepsilon$ only predicts well in the limited range between X/$X_0=1.1$ and X/$X_0=2.0$.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.858-861
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• 2014

This paper presents a simplified finite element tire model for vehicle dynamics analysis. The classical finite element tire model was too big to simulate dynamic properties of the tire. In the simplified model, number of nodes of the tire model was dramatically reduced, and thus its simulation time was several times less than the classical model. Bead, carcass, belt which have an important role to the dynamic characteristics of tire were replaced by simple axis symmetric membrane elements. Also the rebar element was deleted. The tire model has been verified by comparing vertical stiffness data of the simulation model to the test data.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.547-550
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• 2004

We present a multiscale scheme which describes the dynamic pictures of atoms in the multiple length-scale systems. Large-scale atomic systems are reduced to coarse grained system by the quasicontinuum, of which the dynamic pathways are rendered by the action-derived molecular dynamics proved effective for multiple time-scale problems such as rare events. Adatom diffusions on the metal (001) surface are selected for our numerical examples. The energy barriers of the diffusions and the real dynamic trajectories of the adatoms are calculated.

• 한국정밀공학회지
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• 제29권12호
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• pp.1296-1303
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• 2012

There is a certain limit to reproduce phenomena between the real vehicle and road, since the existing methods to verify durability of the wheel are mostly uni-axial tests. And the change of durability of the wheel can't be predicted since these tests don't consider the camber angle and lateral force as important factors. In this paper, the FE models of the wheel-tire and drum are created. Then, the vertical and lateral loads are applied to wheel-tire assembly and the camber angle is applied by inclining the wheel-tire assembly to the drum. Based on the analysis result, the crack position is predicted to be created in the body of the wheel. The variation of the stress according to the camber angle is verified and the maximum spot of the stress changes continually.