• 한국추진공학회지
• /
• 제17권4호
• /
• pp.43-48
• /
• 2013

초음속 디퓨져에서 천이구간에 대해서 수치적 기법에 의한 분석을 수행하였다. 수치기법으로는 초음속 디퓨져의 내부유동해석을 위하여 2차원 축대칭 Navier-Stokes equation와 $k-{\epsilon}$ 난류모델을 사용하였으며, 로켓엔진 연소실의 천이 구간의 압력변화에 따라서 디퓨져 내부의 마하수 및 진공챔버의 온도 분포를 비교 검토하였다. 초음속 디퓨져의 작동과정에서 진공챔버 내부에 연소가스가 유입되어지고 이러한 현상에 따라서 진공챔버 내부의 압력 및 온도가 상승하는 결과를 확인하였다. 이러한 유동현상에 따라서 천이과정에서 압력 및 온도 상승을 방지하는 시스템이 필요하다.

• 대기
• /
• 제23권1호
• /
• pp.13-21
• /
• 2013

In this study, the effects of atmospheric stability and surface temperature on the microscale local airflow are investigated in a hydrological suburban area using a computational fluid dynamics (CFD) model. The model domain includes the river and industrial complex for analyzing the effect of water system and topography on local airflow. The surface boundary condition is constructed using a geographic information system (GIS) data in order to more accurately build topography and buildings. In the control experiment, it is shown that the topography and buildings mainly determine the microscale airflow (wind speed and wind direction). The sensitivity experiments of atmospheric stability (neutral, stable, and unstable conditions) represent the slight changes in wind speed with the increase in vertical temperature gradient. The differential heating of ground and water surfaces influences on the local meteorological factors such as air temperature, heat flow, and airflow. These results consequentially suggest that the meteorological impact assessment is accompanied by the changes of background land and atmospheric conditions. It is also demonstrated that the numerical experiments with very high spatial resolution can be useful for understanding microscale local meteorology.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 추계학술대회 논문집
• /
• pp.231-234
• /
• 2005

The high temperature deformation behavior of AZ 31 Mg alloy was investigated by designing a back propagation neural network that uses a gradient descent-learning algorithm. A neural network modeling is an intelligent technique that can solve non-linear and complex problems by learning from the samples. Therefore, some experimental data have been firstly obtained from continuous compression tests performed on a thermo-mechanical simulator over a range of temperatures $(250-500^{\circ}C)$ with strain rates of $0.0001-100s^{-1}$ and true strains of 0.1 to 0.6. The inputs for neural network model are strain, strain rate, and temperature and the output is flow stress. It was found that the trained model could well predict the flow stress for some experimental data that have not been used in the training. Workability of a material can be evaluated by means of power dissipation map with respect to strain, strain rate and temperature. Power dissipation map was constructed using the flow stress predicted from the neural network model at finer Intervals of strain, strain rates and subsequently processing maps were developed for hot working processes for AZ 31 Mg alloy. The safe domains of hot working of AZ 31 Mg alloy were identified and validated through microstructural investigations.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2007년도 춘계학술대회논문집
• /
• pp.1023-1026
• /
• 2007

Optimal damping layout of the constrained viscoelastic damping layer on beam is identified with temperatures by using a gradient-based numerical search algorithm. An optimal design problem is defined in order to determine the constrained damping layer configuration. A finite element formulation is introduced to model the constrained damping layer beam. The four-parameter fractional derivative model and the Arrhenius shift factor are used to describe dynamic characteristics of viscoelastic material with respect to frequency and temperature. Frequency-dependent complex-valued eigenvalue problems are solved by using a simple resubstitution algorithm in order to obtain the loss factor of each mode and responses of the structure. The results of the numerical example show that the proposed method can reduce frequency responses of beam at peaks only by reconfiguring the layout of constrained damping layer within a limited weight constraint.

• Structural Engineering and Mechanics
• /
• 제60권4호
• /
• pp.707-727
• /
• 2016

In this paper, thermal vibration of a nonlocal functionally graded (FG) plates with arbitrary boundary conditions under linear and non-linear temperature fields is explored by developing a refined shear deformation plate theory with an inverse cotangential function in which shear deformation effect was involved without the need for shear correction factors. The material properties of FG nanoplate are considered to be temperature-dependent and graded in the thickness direction according to the Mori-Tanaka model. On the basis of non-classical higher order plate model and Eringen's nonlocal elasticity theory, the small size influence was captured. Numerical examples show the importance of non-uniform thermal loadings, boundary conditions, gradient index, nonlocal parameter and aspect and side-to-thickness ratio on vibrational responses of size-dependent FG nanoplates.

• Structural Engineering and Mechanics
• /
• 제76권5호
• /
• pp.579-590
• /
• 2020

This paper's objective is to investigate the effect of gravity on a micropolar thermoelastic medium with voids. The problem is assessed according to the three-phase-lag model. An analysis of the resulting non-dimensional displacement, temperature variation, and internal stress of the study material is carried out and presented graphically. The non-dimensional displacement, temperature, micro-rotation, the change in the volume fraction field and stress of the material are obtained and illustrated graphically. Comparisons are made with the results predicted by different theories for different values of gravity, the phase-lag of the heat flux and the phase-lag of the temperature gradient. The numerical results reveal that gravity and relaxation times have a significant influence on the distribution of the field quantities. Some notable insights of interest are deduced from the investigation.

• Advances in aircraft and spacecraft science
• /
• 제8권1호
• /
• pp.31-51
• /
• 2021

Selective laser melting (SLM), one of the most widely used powder bed fusion (PBF) additive manufacturing (AM) technology, enables the fabrication of customized metallic parts with complex geometry by layer-by-layer fashion. However, SLM inherently poses several problems such as the discontinuities in the molten track and the steep temperature gradient resulting in a high degree of residual stress. To avoid such defects, thisstudy proposes a temperature thread multiscale model of SLM for the evaluation of the process at different scales. In microscale melt pool analysis, the laser beam parameters were evaluated based on the predicted melt pool morphology to check for lack-of-fusion or keyhole defects. The analysis results at microscale were then used to build an equivalent body heat flux model to obtain the residual stress distribution and the part distortions at the macroscale (part level). To identify the source of uneven heat dissipation, a liquid lifetime contour at macroscale was investigated. The predicted distortion was also experimentally validated showing a good agreement with the experimental measurement.

• 한국수소및신에너지학회논문집
• /
• 제26권3호
• /
• pp.260-270
• /
• 2015

One-dimensional packed bed reactor model accounting for interfacial and intra-particle gradients was developed and based on it numerical analyses were performed to investigate the dynamic behavior of a commercial scale methanation reactor. Methanation reaction was almost complete near the reactor inlet and gases with equilibrated composition were discharged from the reactor. Both the intra-particle temperature gradient and differential surface temperature rise were found to be severe near the reactor inlet. To reduce the possible degradation or fracture of catalyst particles and prevent local overheating on the catalyst, addition of inert material can be an effective way.

• 대한기계학회논문집A
• /
• 제38권2호
• /
• pp.193-203
• /
• 2014

터빈의 운전온도와 세라믹 입자크기를 고려한 경사기능재료(FGM)로 만들어진 회전하는 가스터빈 블레이드의 열전달해석 및 응력해석을 수행하였다. 경사기능성 블레이드는 벽 두께에 따라서 연속적인 재료물성 변화를 나타낸다. 이러한 경사기능재료의 특성과 온도에 따른 열전 재료물성 변화를 고려하여 블레이드의 시스템 강성을 얻기 위해 블레이드의 열전달해석을 먼저 수행하였다. 이 열전달해석으로 얻은 시스템 강성으로부터 복합 변형 변수를 사용한 회전하는 가스터빈 블레이드의 운동방정식을 유도하였다. 유도된 운동방정식은 상용 유한요소 모델과 해석결과 비교를 통해 그 정확성을 입증하였으며 회전주파수와 구배 지수에 따른 최대 응력의 변화를 조사하였다. 또한, 열전달해석을 통해 가장 낮은 블레이드 온도를 나타내는 구배 지수를 조사하였다.

• 대기
• /
• 제31권2호
• /
• pp.185-198
• /
• 2021

In this study, we examined a spatial downscaling method based on Gradient and Inverse Distance Squared (GIDS) weighting to produce high-resolution grid data from a numerical weather prediction model over Korean Peninsula with complex terrain. The GIDS is a simple and effective geostatistical downscaling method using horizontal distance gradients and an elevation. The predicted meteorological variables (e.g., temperature and 3-hr accumulated rainfall amount) from the Limited-area ENsemble prediction System (LENS; horizontal grid spacing of 3 km) are used for the GIDS to produce a higher horizontal resolution (1.5 km) data set. The obtained results were compared to those from the bilinear interpolation. The GIDS effectively produced high-resolution gridded data for temperature with the continuous spatial distribution and high dependence on topography. The results showed a better agreement with the observation by increasing a searching radius from 10 to 30 km. However, the GIDS showed relatively lower performance for the precipitation variable. Although the GIDS has a significant efficiency in producing a higher resolution gridded temperature data, it requires further study to be applied for rainfall events.