• Aerospace Engineering and Technology
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• v.3 no.1
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• pp.1-8
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• 2004

In this study, the method of computing and extracting the generalized unsteady aerodynamic matrices using MSC/NASTRAN and MSC/NASTRAN DMAP ALTER has been suggested for the analysis and control of aeroelastic phenomena such as flutter and gust response analysis. In addition to that, the method of approximating the generalized unsteady aerodynamic matrices using minimum state approximation method has been proposed in order to cast the aeroelastic equations of motion in state space form for aeroelastic analysis and control application. Simplified aircraft wing box model has been used for the validation of the methods suggested in this study.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.496-500
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• 2010

Understanding train-wind is the best method to know how to optimize subway ventilation system. The capacity and efficiency of the subway ventilation system are known by pressure and velocity while train runs. Analysis of the internal flow in subway tunnel and around subway station are studied using numerical methods. Characteristics of internal flow and influence of subway ventilation system for the subway station with platform screen door and tunnel are analyzed by unsteady state analysis. Velocity and pressure of train wind transformation are compared at around subway ventilation system and the internal flow is investigated at the subway tunnel.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.201-206
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• 2007

In this paper, we apply a three-dimensional rigid-plastic finite element method to simulate an unsteady-state roll forming process. A typical roll forming process is investigated from the standpoint of computer simulation and its realistic analysis model is proposed. The material is considered as bulk material and discretized into hexahedral finite elements. The presented approach is applied to simulating the roll forming process of straight stringer used for aircraft structure.

• Nuclear Engineering and Technology
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• v.18 no.2
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• pp.107-116
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• 1986

The steady and unsteady state models were established for the performance analysis and design of heavy water distillation columns packed with corrugated wire mesh. After the steady state model was derived with pressure drops, separated D$_2$O concentration and temperature profiles and pressure gradients in the column were obtained by solving MESH equations with equation tearing method. For the analysis of unsteady state behavior, the equilibrium stage transient model deduced from modifying the Cohen's ideal cascade equation was used to predict the concentration change of heavy water with time. These models were in good agreement with the experimental results of heavy water distillation at total reflux. And the newly developed packing material turned out to be very efficient separation device for very small HETP, pressure drop and holdup.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.8
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• pp.150-159
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• 1999

Exhaust system is composed of several parts. Among, them , design of muffler system strongly influences on engine efficiency and noise reduction. So , through comprehension of flow characteristics inside muffler is necessary . In this study , three-dimensional steady and unsteady compressible flow analysis was performed to understand the flow characteristics, pressure loss and amplitude variation of pulsating pressure. The computational grid generation was carried out using commercial preprocessor ICEM CFD/CAE. And the three-dimensional fluid motion inside the muffler was analyzed by STAR-CD, the computational fluid dynamics code. RNG k-$\varepsilon$ tubulence model was applied to consider the complexity of the geometry and fluid motion. The steady and unsteady flow field inside muffler such as velocity distribution, pulsating pressure and pressure loss was examined. In case of unsteady state analysis, velocity of inlet region was converted from measured pulsating pressure. Experimental measurement of pressure and temperature was carried out to provide the boundary and initial condition for computational study under three engine operating conditions. As a result of this study, we could identify the flow characteristics inside the muffler and obtain the pressure loss, amplitude variation of pulsating exhaust gas.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.4
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• pp.108-120
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• 1998

A theoretical study of three-dimensional unsteady compressible non-reacting flow inside double flow of monolith catalytic converter system attached to 6-cylinder engine was performed for the achievement of performance improvement, reduction of light-off time, and longer service life by improving the flow distribution of pulsating exhaust gases. The differences between unsteady and steady-state flow were evaluated through the numerical computations. To obtains the boundary conditions to a numerical analysis, one dimensional non-steady gas dynamic calculation was also performed by using the method of characteristics in intake and exhaust system. Studies indicate that unsteady representation is necessary because pulsation of gas velocity may affect gas flow uniformity within the monolith. The simulation results also show that the level of flow maldistribution in the monolith heavily depends on curvature and angles of separation streamline of mixing pipe that homogenizes the exhaust gas from individual cylinders. It is also found that on dual flow converter systems, there is severe interactions of each pulsating exhaust gas flow and the length of mixing pipe and junction geometry influence greatly on the degree of flow distribution.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2169-2180
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• 1992

Solid propellant combustion is investigated for its response to several imposed pressure histories. For this purpose, it is assumed that combustion takes place in a premixed gas evaporated from a uniform melt of solid propellant. One-dimensional unsteady problem is than numerically solved for a pressure coupling, with a steady state as an initial state. The results in response to pressure of finite sinusoidal waves show that unsteady mass fluxes are sometimes quite different from those predicted by the classical quasisteady burning law of Vieile. In addition, abnormal mass flux excursions are captured for a large pressure exponent and a lower melting point.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.29-34
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• 2008

A modeling technique for the 2-way coupling of heat transfer and conduction currents has been performed to inspire a combined analytical simulation. The 3-D finite element method is used to solve steady conduction currents and heat generation in an aluminum film deposited on a silicon substrate. The model investigates the temperature in the device after the current is applied. The conservation equation of energy, the Maxwell equations for conduction currents, the unsteady state heat transfer equation and the Fourier's law for heat transfer are implemented as a bidirectionally coupled problem. It is found that the strongly coupled temperature and time dependent heat equations give a reasonable results and an explicit solving technique.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.79-88
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• 1997

An analysis of unsteady heat and mass transfer in the Modified Chemical Vapor Deposition has been carried out including the effects of chemical reaction and variable properties. It was found that commonly used quasi-steady state assumption could be used to predict overall efficiency of deposition, however, the assumption would not provide detailed deposition profile. The present unsteady calculations of wall temperature profile and deposition profile have been compared with the existing experimental data and were in good agreement. The effects of variable torch speed were studied. Linearly varying torch speed case until time=120s resulted in much shorter tapered entry than the constant torch speed case.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.12 s.243
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• pp.1574-1585
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• 2005

In this paper, a spectral element model is developed for the uniform straight pipelines conveying internal unsteady fluid. Four coupled pipe-dynamics equations are derived first by using the Hamilton's principle and the principles of fluid mechanics. The transverse displacement, the axial displacement, the fluid pressure and the fluid velocity are all considered as the dependent variables. The coupled pipe-dynamics equations are then linearized about the steady state values of the fluid pressure and velocity. As the final step, the spectral element model represented by the exact dynamic stiffness matrix, which is often called spectral element matrix, is formulated by using the frequency-domain solutions of the linearized pipe-dynamics equations. The FFT-based spectral dynamic analyses are conducted to evaluate the accuracy of the present spectral element model and also to investigate the structural dynamic characteristics and the internal fluid transients of an example pipeline system.