• 대한기계학회논문집B
• /
• 제27권12호
• /
• pp.1667-1672
• /
• 2003

In contrast to the high demand for MEMS devices, microflow analysis is not feasible even for single-phase flow with conventional Navier-Stokes equation because of non-continuum effect when characteristic dimension is comparable with local mean free path. DSMC is one of particle based DNS(Direct Numerical Simulation) methods that uses no continuum assumption. In this paper, gas flow in microchannel is studied using DSMC. Interfacial shear and flow characteristics are observed and compared with the results of gas flow that is in contact with liquid case and solid wall case. The simulation is limited to the case of equilibrium steady state and evaporation/condensation coefficient is assumed to be the same and unity. System temperature remains constant and the interfacial shear appears to be small compared to the result with solid wall. This is because particles evaporated and reflected from the liquid surface form high density layer near the interface with liquid flow.

• 한국가시화정보학회지
• /
• 제2권2호
• /
• pp.8-15
• /
• 2004

With all the recent progresses in computer hardware and software technology, the animation of fluids in real-time is still among the most challenging issues of computer graphics. The fluid animation is carried out in two steps - the physical simulation of fluids immediately followed by the visual rendering. The physical simulation is usually accomplished by numerical methods utilizing the particle dynamics equations as well as the fluid mechanics based on the Navier-Stokes equations. Particle dynamics method is usually fast in calculation, but the resulting fluid motion is conditionally unrealistic. The methods using Navier-Stokes equation, on the contrary, yield lifelike fluid motion when properly conditioned, yet the complexity of calculation restrains this method from being used in real-time applications. This article presents a rapid fluid animation method by using the continuum-based fluid mechanics and the enhanced particle dynamics equations. For real-time rendering, pre-integrated volume rendering technique was employed. The proposed method can create realistic fluid effects that can interact with the viewer in action, to be used in computer games, performances, installation arts, virtual reality and many similar multimedia applications.

• Structural Engineering and Mechanics
• /
• 제56권6호
• /
• pp.939-957
• /
• 2015

In this paper, a new approach based on the continuum model is proposed to estimate the main cable tension force of suspension bridges from measured natural frequencies. This approach considered the vertical vibration of a main cable hinged at both towers and supported by an elastic girder and hangers along its entire length. The equation reflected the relationship between vibration frequency and horizontal tension force of a main cable was derived. To avoid to generate the additional cable tension force by sag-extensibility, the analytical solution of characteristic equation for anti-symmetrical vibration mode of the main cable was calculated. Then, the estimation of main cable tension force was carried out by anti-symmetric characteristic frequency vector. The errors of estimation due to characteristic frequency deviations were investigated through numerical analysis of the main cable of Taizhou Bridge. A field experiment was conducted to verify the proposed approach. Through measuring and analyzing the responses of a main cable of Taizhou Bridge under ambient excitation, the horizontal tension force of the main cable was identified from the first three odd frequencies. It is shown that the estimated results agree well with the designed values. The proposed approach can be used to conduct the long-term health monitoring of suspension bridges.

• Geomechanics and Engineering
• /
• 제30권5호
• /
• pp.449-460
• /
• 2022

Safe underground construction in a rock mass requires adequate ground investigation and effective determination of rock conditions. The estimation of rock mass behavior is difficult, because rock masses are innately anisotropic and heterogeneous at different scales and are affected by various environmental factors. Quantitative rock mass classification systems, such as the Q-system and rock mass rating, are widely used for characterization and engineering design. The measurement of rock classification parameters is subjective and can vary among observers, resulting in questionable accuracy. Geophysical investigation methods, such as seismic surveys, have also been used for ground characterization. Torsional shear wave propagation characteristics in cylindrical rods are equal to that in an infinite media. A probabilistic quantitative relationship between the Q-value and shear wave velocity is thus investigated considering long-wavelength wave propagation in equivalent continuum jointed rock masses. Individual Q-system parameters are correlated with stress-dependent shear wave velocities in jointed rocks using experimental and numerical methods. The relationship between the Q-value and the shear wave velocity is normalized using a defined reference condition. This relationship is further improved using probabilistic analysis to remove unrealistic data and to suggest a range of Q-values for a given wave velocity. The proposed probabilistic Q-value estimation is then compared with field measurements and cross-hole seismic test data to verify its applicability.

• Structural Engineering and Mechanics
• /
• 제86권1호
• /
• pp.17-27
• /
• 2023

To investigate the mechanical behavior of the post-tensioned prestressed concrete lining (PPCL), the desilting tunnel of the Xiaolangdi Hydro Project in China is adopted as a case, and a detailed three-dimensional continuum model verified by the observation results is established for the PPCL. The radial stresses, longitudinal stresses, axial forces and bending moments of the PPCL under the completed cable tension condition (CCTC) and design water pressure condition (DWPC) are analyzed, respectively. The numerical results reveal that the PPCL concrete is significantly compressed in the circumferential direction by the prestress, while the prestress has a negligible influence on the radial stresses of the PPCL concrete. It should be noted that the concrete near the anchor slots has a complex and adverse stress state with stress concentration, longitudinal tensioning and large bending moment. In addition, a simplified shell model and a further simplified beam model which can take the influences of the prestress loss and the anchor slot into consideration are proposed for the PPCL. The results of the simplified models are in a good agreement with these of the three-dimensional continuum model, and they can be used as efficient approaches for the structural design and analysis of the PPCL.

• 한국정밀공학회지
• /
• 제23권1호
• /
• pp.152-158
• /
• 2006

The AutoForm previously used the membrane element and it accomplished sheet metal forming analysis. The membrane analysis has been widely applied to various sheet metal forming processes because of its time effectiveness. However, it is well-known that the membrane analysis can not provide correct information for the processes which have considerable bending effects. In this research experimental results were compared with the analysis results obtained by using the shell element which is applied newly in the AutoForm commercial software. The shell element is a compromise element between continuum element and membrane element. The Finite element method by using shell element is the most efficient numerical method. From this research, it is known that FEA by using shell element can predict accurately the problems happened in actual experimental auto-body panel.

• 터널과지하공간
• /
• 제4권1호
• /
• pp.1-16
• /
• 1994

The study on the flow characteristics and analysis of groundwater in discontinuous rock mass is very important, since the water inflow into the underground opening during excavation induces serious stability and environmental problems. To investigate the flow through single rock joint, the effect of various aperture distribution on the groundwater flow has been analyzed. Observed through the analysis is the "channel flow", the phenomenon that the flow is dominant along the path of large aperture for given joint. The equivalent hydraulic conductivity is estimated and verified through the application of the joint network analysis for 100 joint maps generated statistically. Both the analytic aproach based on isotropic continuum premise and the joint network analysis are tested and compared analyzing the gorundwater inflow for underground openings of different sizes and varying joint density. The joint network analysis is considered better to reflect the geometric properties of joint distribution in analyzing the groundwater flow.ater flow.

• 지질공학
• /
• 제34권1호
• /
• pp.1-12
• /
• 2024

우리나라는 1980년까지 광물 지하자원 개발을 활발히 수행하였으나 이후 생산원가 대비 사업성이 크게 줄어들면서 많은 수의 폐광산이 발생되었다. 그 중 대부분은 광산개발 중단 후 오랜 시간이 지나 잔류성 침하가 발생할 가능성이 높은 상태에 있다. 하지만 그 발생 시기와 위치를 정확히 예측하기는 어려움이 있다. 따라서, 본 연구에서는 실제 지반침하가 발생한 사례를 분석하여 연속체 수치해석을 통해 지반침하의 발생 위치나 규모에 대한 예측 가능성을 살펴보고자 한다. 연구지역은 양산단층과 모량단층 사이에 위치하여 이들에 규제받는 ○○광산 지역이며, 이 지역에서는 2005~2009년에 걸쳐 3회의 지반침하가 발생된 바 있다. 지반침하지를 대상으로 시추조사 및 전기비저항 탐사를 수행하여 지층의 분포를 파악하였고, 실내시험을 통해 수치해석 시 적용되는 지반의 물리·역학적 특성을 파악하였다. 수치해석 결과 소성영역이 실제 지반침하 범위를 포함하는 형태로 나타나 연속체 해석으로도 채굴적에 의한 침하지 발생 위치 및 규모를 예측하는데 활용할 수 있을 것으로 판단된다.

• 대한토목학회논문집
• /
• 제13권1호
• /
• pp.39-46
• /
• 1993

양질의 근사화 방법을 이용하여 형상최적설계의 효율성을 증진시킬 수 있는 방법들을 개발하기 위한 필요성이 제기되어 왔다. 본 연구에서는 3차원 구조물의 형상적설계를 수행하기 위해 형상변수에 대한 절점력들의 Taylor급수 전개에 근거를 둔 효율적인 근사화 방법을 제안하였다. 수치예로서 캔틸레버보와 양단고정보를 취하여 제안된 방법에 의해 최적형상을 구하였다. 제안된 방법에 의해 얻어진 결과를 기 발표된 다른 방법들의 결과와 비교하여 효율성 및 수렴성에 관해 비교하였다. 그 결과 최적화를 위한 총 구조해석의 수가 크게 줄어들었고, 단면최적화만의 경우와 거의 같은 정도의 효율성을 갖게 됨을 알 수 있었다. 또한 최적형상을 얻기위해 적용된 다항식에 의한 경계표현기법은 최적형상을 얻기위한 유용한 방법임을 알 수 있었다.

• 자원환경지질
• /
• 제50권1호
• /
• pp.61-71
• /
• 2017

본 연구는 절리의 빈도 및 길이분포가 절리암반의 수리지질학적 특성에 미치는 영향을 평가하기 위하여 이차원 불연속절리망 (DFN; discrete fracture network) 유체유동 해석을 바탕으로 한 수치실험을 수행하였다. 두개의 절리군을 사용하여 절리의 빈도와 길이분포를 달리하며 추계론적으로 생성한 총 51개의 DFN 시스템에 대하여 $0^{\circ}$부터 매 $30^{\circ}$ 간격으로 총 12 방향으로 구현한 총 612개의 $20m{\times}20m$ DFN 블록에서 방향에 따른 블록수리전도도가 산정되었다. 또한, 각각의 DFN 시스템에서 이론적 블록수리전도도와 더불어 주 수리전도도텐서, 평균 블록수리전도도 등이 산정되었다. 절리군의 빈도의 증가 또는 길이의 평균 및 표준편차 증가에 따라 임의 방향으로의 블록수리전도도는 증가하며 DFN 시스템에 대한 등가연속체 취급 가능성이 높아지지만, 절리군 간의 빈도 차이가 커지면 블록수리전도도의 이방성 증대로 인하여 등가연속체 취급 가능성이 낮아질 수 있는 것으로 평가되었다. 두 절리군의 교차각이 작을수록 등가연속체 특성은 빈도 및 길이분포의 변화에 상대적으로 더욱 영향을 받는 것으로 평가되었다. 등가연속체로 취급하기 어려울 정도로 두 절리군의 교차각이 작아도 절리군의 빈도 또는 길이 분포가 증가하면 등가연속체 취급 가능성은 높아진다.