• Tribology and Lubricants
• /
• 제14권4호
• /
• pp.44-50
• /
• 1998

This paper describes the simulation of the levitation force between permanent magnet and high Tc(critical temperature) superconductor(HTSC). Levitation force is evaluated numerically on the basis of the magnetic vector potential method and the critical state model. The superconductor is approximated to 2-D slab model. By performing computations, the following characteristics have been investigated: the process of the generation of hysteresis, the various hysteretic behaviors. The characteristics of hysteresis are important for the application to magnetic bearing, for the damping and the nonlinear stiffness is related to hysteresis.

• 대한기계학회논문집B
• /
• 제30권10호
• /
• pp.950-956
• /
• 2006

A mathematical heat transfer model for the prediction of heat flux on the slab surface and temperature distribution in the slab has been developed by considering the thermal radiation in the furnace and transient conduction governing equations in the slab, respectively. The furnace is modeled as radiating medium with spatially varying temperature and constant absorption coefficient. The slab is moved with constant speed through non-firing, charging, preheating, heating, and soaking zones in the furnace. Radiative heat flux which is calculated from the radiative heat exchange within the furnace modeled using the FVM by considering the effect of furnace wall, slab, and combustion gases is applied as the boundary condition of the transient conduction equation of the slab. Heat transfer characteristics and temperature behavior of the slab is investigated by changing such parameters as absorption coefficient and emissivity of the slab. Comparison with the experimental work shows that the present heat transfer model works well for the prediction of thermal behavior of the slab in the reheating furnace.

• Computers and Concrete
• /
• 제23권2호
• /
• pp.121-131
• /
• 2019

Due to the heterogeneity nature of the concrete, it is difficult to simulate the hyperdynamic behaviour and crack trajectory of concrete material when subjected to explosion loads. In this paper, a 3D nonlinear numerical study was conducted to simulate the hyperdynamic behaviour of concrete under various loading conditions using Riedel-Hiermaier-Thoma (RHT) model. Detailed calibration was conducted to identify the optimal parameters for the RHT model on the material level. For the component level, the calibrated RHT parameters were used to simulate the failure behaviour of plain concrete (PC) slab under free air blast load. The response was compared with an available experimental result. The results show the proposed numerical model can accurately simulate the crack trajectory and the failure mode of the PC slab under free air blast load.

• International Journal of Railway
• /
• 제5권4호
• /
• pp.163-166
• /
• 2012

Many different types of floating slab track have been developed and installed around the world to reduce vibrations and noise originating in the surrounding environment. The main objective of this study is to examine the influence of slab length on behavior of floating slab track based on rail-slab-isolator interaction. The floating slab track is modeled by the connection between rail, slab, isolator, and slab mat in the transition zone. All elements were assembled in a simplified two-dimensional (2D) finite element model (FEM). The maximum length of FST is then investigated based on the maximum additional rail stress criterion as described in UIC 774-3R since no fully accepted design criteria for the slab length in FST systems currently exist.

• 한국정보통신학회논문지
• /
• 제12권7호
• /
• pp.1165-1172
• /
• 2008

본 논문에서는 2차원 시간영역 유한차분법(2D-FDTD)을 이용하여 메타물질(Metamaterial) Slab의 주파수 영역 특성을 구하는 방법을 연구하였다. 일반적으로 메타물질의 해석 방법에는 FDTD가 가장 광범위하게 사용되고 있는데 주파수 분산특성을 갖는 유전율과 투자율 모델을 가정하기 때문에, 정확한 주파수 응답특성을 구하기가 힘들다는 단점이 있다. 본 논문에서는 2차원 구조치 메타물질 Slab에 이미 광대역 특성을 갖는 가우시안 펄스와 제한된 대역폭 특성을 갖는 m-n-m 주기를 갖는 Sine 입력펄스를 각각 인가하여 주파수특성으로서 산란계수를 구하는 방법을 제안하고 비교하여 제한된 대역폭에 대한 주파수 특성 결과를 제시하였다. 본 논문에서 제안한 방법을 사용하면 메타물질을 이용한 다양한 회로구조에 대하여 제한된 대역폭에 대한 주파수 특성을 얻을 수 있다.

• 한국농공학회논문집
• /
• 제49권6호
• /
• pp.47-54
• /
• 2007

This paper is on the research of the special character of the dynamic response according to a design of the clamped reinforced concrete slab. In this study, the 20-node solid element has been used to analyze the dynamic characteristics of RC slabs with clamped edges. The elasto-visco plastic model for material non-linearity and the smeared crack model have been adopted in the finite element formulation. The design factor, which affect the dynamic response of the reinforced concrete slab, are the steel layer thickness, steel layer depth, steel layout method, steel layout angle and the slab thickness and span ratio. The main purpose of this study was to find out the dynamic response of the reinforced concrete slab according to above variables. The reduction of deflection/thickness ratio appeared less than 2% when the slab thickness between 20 and 21cm. It is desirable that the slab thickness must be above 20-21cm. The reduction ratio of deflection is appeared greatly when the value of the span/thickness ratio is between 25 and 30. In conclusion, the steel layer depth and thickness had a little effect on deflection of the dynamic response, but had no effect on the steel layout angle.

• 한국도로학회논문집
• /
• 제10권3호
• /
• pp.209-220
• /
• 2008

본 논문은 지반위에 놓인 콘크리트 슬래브가 환경하중에 의해 컬링 할 때의 거동을 해석할 경우에 하부층의 모델링 방법에 따른 해석 결과의 차이를 분석한 내용을 기술하였다. 지반위에 놓인 슬래브 시스템을 전체 3차원 모델, 3차원 슬래브와 하부층을 스프링으로 구성한 모델, 그리고 2차윈 슬래브와 하부층을 스프링으로 구성한 모델 등으로 개발하여 해석을 수행하였다. 먼저 하부층이 단일 층으로 구성되어 있을 경우에 하부층 모델링 방법에 따른 컬링 거동의 차이를 분석하였다. 그리고 하부층이 서로 다른 재료와 두께로 구성되어 있는 복층일 경우에 하부층 모델링에 따른 컬링 거동의 특성을 비교 분석하였다. 연구결과 하부층을 무인장 스프링으로 모델링 하면 하부층이 단층일 경우에는 일반적으로는 상당히 정확한 해석결과를 얻을 수 있으나, 하부층이 복층일 경우에는 상위하부층의 탄성계수가 클 때, 하위하부층의 탄성계수가 작을 때, 그리고 상위하부층과 하위하부층의 두께가 두꺼울 때는 컬링 시에 슬래브의 수직변위 차이를 과대평가하게 되며 최대응력은 과소평가하게 된다.

• Geomechanics and Engineering
• /
• 제17권2호
• /
• pp.119-131
• /
• 2019

Time dependent creep settlements are one of the most important causes of material deteriorations for the huge water structures such as concrete faced rockfill dams (CFRDs). For this reason, performing creep analyses of CFRDs is vital important for monitoring and evaluating of the future and safety of such dams. In this study, it is observed how changes viscoplastic behaviour of a CFR dam depending the time. Ilısu dam that is the longest concrete faced rockfill dam (1775 m) in the world is selected for the three dimensional (3D) analyses. 3D finite difference model of Ilısu dam is modelled using FLAC3D software based on the finite difference method. Two different special creep material models are considered in the numerical analyses. Wipp-creep viscoplastic material model and burger-creep viscoplastic material model were rarely used for the creep analyses of CFRDs in the last are taken into account for the concrete slab and rockfill materials-foundation, respectively. Moreover, interface elements are defined between the concrete slab-rockfill materials and rockfill materials-foundation to provide interaction condition for 3D model. Firstly, dam and foundation are collapsed under its self-weight and static behaviour of the dam is evaluated for the empty reservoir conditions. Then, reservoir water is modelled considering maximum water level of the dam and time-dependent creep analyses are performed for maximum reservoir condition. In this paper, maximum principal stresses, vertical-horizontal displacements and pore pressures that may occur on the dam body surface during 30 years (from 2017 to 2047) are evaluated in detail. According to numerical analyses, empty and maximum reservoir conditions of Ilısu dam are compared with each other in detail. 4 various nodal points are selected under the concrete slab to better seen viscoplastic behaviour changes of the dam and viscoplastic behaviour differences of these points during 30 years are graphically presented. It is clearly seen that horizontal-vertical displacements and principal stresses for maximum reservoir condition are more than the empty reservoir condition of the dam and significant pore pressures are observed during 30 years for maximum reservoir condition. In addition, horizontal-vertical displacements, principal stresses and pore pressures for 4 nodal points obviously increased until a certain time and changes decreased after this time.

• 소성∙가공
• /
• 제20권2호
• /
• pp.132-139
• /
• 2011

Three dimensional simulations were performed for the deformation of a slab in a roller hearth type slab reheating furnace. The main objective of this study was to examine the deformation pattern of the slab due to the shadow effect, i.e., the temperature difference between the upper and lower slab surfaces, in particular, the variations of displacement and effective stress in the vertical direction. A commercially available FE code, ANSYS Workbench $12.1^{TM}$, was used in a fully coupled thermo-elasticity analysis. Several cases with different slab surface temperatures were selected for the simulations. For the sake of simplicity, the temperature environment inside the furnace was assumed to be homogeneous for the upper and lower faces of the slab. Two cases of with different slab width were selected as model geometry. The deformation patterns were computed and explained in terms of periodicity and symmetry. The results indicated that the shadow effect leads to a significant displacement in the vertical direction and, thereby, is one of the main reasons for the separation of the slab and its supports. These simulations also predicted that the deformation is more severe along the transverse direction than along the longitudinal direction.

• 한국도로학회논문집
• /
• 제10권2호
• /
• pp.145-157
• /
• 2008

하중전달효율은 다웰이 설치되었거나 설치되지 않은 콘크리트포장 줄눈의 구조적 성능을 나타내기 위해 사용된다. ABAQUS 소프트웨어를 사용한 줄눈 콘크리트장의 3차원 모형이 본 연구를 통하여 구축되었다. 기층과 노상이 접착되어 구성된 하부층 위에 3개의 슬래브가 놓였으며, 스프링 요소를 사용하여 인접한 슬래브를 줄눈에서 연결하였다. 콘크리트포장의 다양한 줄눈강성을 모사하기 위하여 다양한 값의 스프링 상수를 입력값으로 사용하여 그 관계를 조사하였으며, 스프링 상수가 커질수록 줄눈의 하중전달효율이 증가하는 것으로 나타났다. 슬래브와 기증의 다양한 탄성계수와 두께를 사용하여 슬래브의 거동과 하중전달효율에 미치는 재료물성과 기하학적 형상의 영향을 분석하였다. 그 결과 노상의 탄성계수는 기층의 탄성계수와 슬래브 및 기층의 두께보다 더 큰 영향을 미치는 것으로 나타났다. 또한 양 또는 영의 온도구배에서보다는 음의 온도구배에서 슬래브의 거동과 하중 전단효율이 더 민감 하게 변화하였으며, 낮은 강성의 줄눈은 슬래브의 온도구배에 더 민감한 것으로 나타났다.