• 대한토목학회논문집
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• 제13권1호
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• pp.39-46
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• 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.

• 한국전산구조공학회논문집
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• 제15권2호
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• pp.351-365
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• 2002

현재 국내에서는 벽체와 바닥판으로만 구성된 벽식 구조형식의 아파트 건물이 많이 사용되고 있다. 또한 청력에 대한 저항이 뛰어나기 때문에 전단벽 코어를 갖는 입체골조구조물이 고층 빌딩의 구조시스템으로 자주 이용된다. 기능적인 이유로 인해 이러한 구조물들의 전단벽에는 하나 또는 여러 개의 개구부가 발생하게 된다. 개구부가 있는 전단벽을 정확하게 해석하기 위해서는 여러 개의 유한요소를 사용하여 구조물을 세분모형화하는 것이 필요하다. 그러나, 전체 구조물을 유한요소로 세분하여 모형화하는 것은 막대한 해석시간과 컴퓨터 메모리를 소요하게 된다. 개구부의 수, 크기, 위치에 상관없이 적용할 수 있는 효율적인 해석기법이 본 논문에서 제안되었다. 제안된 해석기법에서는 슈퍼요소와 부분구조, 행렬응축, 가상보 등을 이용하였고 제안된 해석기법의 효율성을 검증하기 위해 벽식구조물과 전단벽 코어를 갖는 입체골조구조물의 3차원 해석이 수행되었다. 예제구조물의 해석을 통해 제안된 해석기법이 해석시간과 컴퓨터메모리를 크게 감소시키고, 정확한 해석결과를 얻을 수 있음이 확인되었다.

• 한국레이저가공학회지
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• 제5권2호
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• pp.17-22
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• 2002

Characteristics of micro carbon structures fabricated with laser-induced chemical vapor deposition (LCVD) are investigated. An argon ion laser (λ＝514.5nm) and ethylene gas were utilized as the energy source and precursor, respectively. The laser beam was focused onto a graphite substrate to produce carbon deposit through thermal decomposition of the precursor. Average growth rate of a carbon rod increased for increasing laser power and pressure. Micro carbon rods with good surface quality were obtained at near the threshold condition. Micro carbon rods with aspect ratio of about 100 and micro tubular structures were fabricated to demonstrate the possible application of this method to the fabrication of three-dimensional microstructures. Laser Raman spectroscopic analysis of the micro carbon structures revealed that the carbon rods are consisting of amorphous carbon.

• Steel and Composite Structures
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• 제10권3호
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• pp.281-295
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• 2010

An experimental and a non linear finite element investigation on the behavior of steel-concrete composite beams stiffened in hogging moment region with Carbon Fiber Reinforced Plastics (CFRP) sheets is presented in this paper. A total of five specimens were tested under two-point loads. Three of the composite beams included concrete slab while the other two beams had composite slabs. The stiffening was achieved by attaching CFRP sheets to the concrete surface at the position of negative bending moment. The suggested CFRP sheets arrangement enhanced the overall beam behavior and increased the composite beam capacity. Valuable parametric study was conducted using a three dimensional finite element model using ANSYS program. Both geometrical and material nonlinearity were included. The studied parameters included CFRP sheet arrangement, concrete strength and degree of shear connection.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 Proceedings of 2004 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.1-13
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• 2004

A scanning stereo-PIV system was developed to measure the three-dimensional distribution of three-component velocity in a turbulent round jet. A laser light beam produced by a high repetition rate YLF pulse laser was expanded vertically by a cylindrical lens to form a laser light sheet. The light sheet is scanned in a direction normal to the sheet by a flat mirror mounted on an optical scanner, which is controlled by a programmable scanner controller. Two high-speed mega-pixel resolution C-MOS cameras captured the particle images illuminated by the light sheet, and stereoscopic PIV method was adopted to acquire the 3D-3C-velocity distribution of turbulent round jet in an octagonal tank filled with water. The jet Reynolds number was set at Re=1000 and the streamwise location of the measurement was fixed at approximately x = 40D. Time evolution of three-dimensional vortical structure, which is identified by vorticity, is visualized. It revealed that the existence of a group of hairpin-like vortex structures was quite evident around the rim of the shear layer of the jet. Turbulence statistics shows good agreement with the previous data, and divergence of a filtered (unfiltered) velocity vector field was $7\%\;(22\%)$ of root-me an-squared vorticity value.

• Smart Structures and Systems
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• 제19권3호
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• pp.309-322
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• 2017

In this paper, the buckling, and free vibration analysis of tapered functionally graded carbon nanotube reinforced composite (FG-CNTRC) micro Reddy beam under longitudinal magnetic field using finite element method (FEM) is investigated. It is noted that the material properties of matrix is considered as Poly methyl methacrylate (PMMA). Using Hamilton's principle, the governing equations of motion are derived by applying a modified strain gradient theory and the rule of mixture approach for micro-composite beam. Micro-composite beam are subjected to longitudinal magnetic field. Then, using the FEM, the critical buckling load, and natural frequency of micro-composite Reddy beam is solved. Also, the influences of various parameters including ${\alpha}$ and ${\beta}$ (the constant coefficients to control the thickness), three material length scale parameters, aspect ratio, different boundary conditions, and various distributions of CNT such as uniform distribution (UD), unsymmetrical functionally graded distribution of CNT (USFG) and symmetrically linear distribution of CNT (SFG) on the critical buckling load and non-dimensional natural frequency are obtained. It can be seen that the non-dimensional natural frequency and critical buckling load decreases with increasing of ${\beta}$ for UD, USFG and SFG micro-composite beam and vice versa for ${\alpha}$. Also, it is shown that at the specified value of ${\alpha}$ and ${\beta}$, the dimensionless natural frequency and critical buckling load for SGT beam is more than for the other state. Moreover, it can be observed from the results that employing magnetic field in longitudinal direction of the micro-composite beam increases the natural frequency and critical buckling load. On the other hands, by increasing the imposed magnetic field significantly increases the stability of the system that can behave as an actuator.

• Computers and Concrete
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• 제15권4호
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• pp.687-707
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• 2015

A finite element computer code for short-term analysis of steel-concrete composite structures is extended to study long-term effects under service loads, in the present work. Long-term effects are important in engineering design because they influence stress and strain distribution of the structural system and therefore contribute to the increment of deflections in these structures. For creep analysis, a rheological model based on a Kelvin chain, with elements placed in series, was employed. The parameters of the Kelvin chain were obtained using Dirichlet series. Creep and shrinkage models, proposed by the CEB FIP 90, were used. The shear-lag phenomenon that takes place at the concrete slab is usually neglected or not properly taken into account in the formulation of beam-column finite elements. Therefore, in this work, a three-dimensional numerical model based on the assemblage of shell finite elements for representing the steel beam and the concrete slab is used. Stud shear connectors are represented for special beam-column elements to simulate the partial interaction at the slab-beam interface. The two-dimensional representation of the concrete slab permits to capture the non-uniform shear stress distribution in the horizontal plane of the slab due to shear-lag phenomenon. The model is validated with experimental results of two full-scale continuous composite beams previously studied by other authors. Results are given in terms of displacements, bending moments and cracking patterns in order to shown the influence of long-term effects in the structural response and also the potentiality of the present numerical code.

• Steel and Composite Structures
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• 제37권1호
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• pp.37-49
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• 2020

In this paper, free vibration finite element analysis of axially moving laminated composite beams subjected to axial tension is studied. It is assumed that the beam has a constant axial velocity and is subject to uniform axial tension. The analysis is based on higher-order theories that have been presented by Carrera Unified Formulation (CUF). In the CUF technique, the three dimensional (3D) displacement fields are expressed as the approximation of the arbitrary order of the displacement unknowns over the cross-section. This higher-order expansion is considered in equivalent single layer (ESL) model. The governing equations of motion are obtained via Hamilton's principle. Finally, several numerical examples are presented and the effect of the ply-angle, travelling speed and axial tension on the natural frequencies and beam stability are demonstrated.

• Structural Engineering and Mechanics
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• 제29권4호
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• pp.355-380
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• 2008

In this study, the new three-dimensional finite element analysis model of guideway structures considering ultra high-speed magnetic levitation train-bridge interaction, in which the various improved finite elements are used to model structural members, is proposed. The box-type bridge deck of guideway structures is modeled by Nonconforming Flat Shell finite elements with six DOF (degrees of freedom). The sidewalls on a bridge deck are idealized by using beam finite elements and spring connecting elements. The vehicle model devised for an ultra high-speed Maglev train is employed, which is composed of rigid bodies with concentrated mass. The characteristics of levitation and guidance force, which exist between the super-conducting magnet and guideway, are modeled with the equivalent spring model. By Lagrange's equations of motion, the equations of motion of Maglev train are formulated. Finally, by deriving the equations of the force acting on the guideway considering Maglev train-bridge interaction, the complete system matrices of Maglev train-guideway structure system are composed.

• Computers and Concrete
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• 제19권2호
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• pp.191-201
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• 2017

External pre-stressing is often used in strengthening or retrofitting of steel-concrete composite beams. In this way, a proper numerical model should be able to trace the completely nonlinear response of these structures at service and ultimate loads. A three dimensional finite element model based on shell elements for representing the concrete slab and the steel beam are used in this work. Partial interaction at the slab-beam interface can be taken into account by using special beam-column elements as shear connectors. External pre-stressed tendons are modeled by using one-dimensional catenary elements. Contact elements are included in the analysis to represent the slipping at the tendon-deviator locations. Validation of the numerical model is established by simulating seven pre-stressed steel-concrete composite beams with experimental results. The model predictions agree well with the experimental results in terms of collapse loads, path failures and cracking lengths at negative moment regions due to service loads. Finally, the accuracy of some simplified formulas found in the specialized literature to predict cracking lengths at interior supports at service loading and for the evaluation of ultimate bending moments is also examined in this work.