• 터널과지하공간
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• 제15권1호
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• pp.47-54
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• 2005

암반 불연속면의 조사 및 분석 과정에서 거쳐야할 필수적인 단계 중 하나는 방대한 불연속면 자료로부터 군을 판별하는 것이다. 불연속면 군 분류는 암반분류, 키블록 해석. 개별요소해석 및 불연속연결망 생성과 같은 암반공학적 업무에 있어서 필수적이다. 일반적으로 등고선도를 이용한 수작업 군 분류가 적용되었으나 이 방법은 수작업에 의존한 주관적인 결과를 제공한다는 단점이 있다. 본 연구에서는 유전자알고리즘을 이용한 불연속면 군 분석기법을 도입하였으며 방향성 자료에 적용하기 위해 기본적인 유전자알고리즘을 변경하였다. 최종적으로 이러한 이론을 적용한 FORTRAN 프로그램 GAC를 개발하였으며 두 가지 형태의 불연속면 자료의 군 분석에 적용하였다. 적용 결과 GAC를 적용한 군 분류는 빠르고 효율적인 군 분석방법임을 확인하였으며 최적의 불연속면 군 수를 결정하는 데 있어서 분산에 근거한 적합도 함수가 Davis-Bouldin 지수에 근거한 적합도 함수보다 효율적인 것으로 나타났다.

• 터널과지하공간
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• 제27권2호
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• pp.100-108
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• 2017

균열텐서 파라미터는 절리의 기하학적 속성이 결합된 효과를 지시하는 척도로 사용할 수 있으며 불연속절리망(DFN)에서 유체 유동통로의 연결 상태를 정량화할 수 있다. 본 연구는 이차원 DFN의 균열텐서 파라미터와 수리적 특성 간의 상관성 분석을 수행하였다. DFN에서 임의 방향으로의 수리전도도는 이에 직교하는 방향으로 산정된 균열텐서성분과 강한 비선형 관계를 갖는 것으로 평가되었다. 서로 다른 규모의 이차원 DFN 블록에서 방향에 따른 균열텐서의 일차불변량($F_0$)을 방사형 도표로 나타내었을 때, 방향에 따른 $F_0$ 값의 유의미한 변화가 없는 원형의 플롯은 절리성 암반을 대표요소체적으로 취급하기 위한 필요조건이 될 수 있다. DFN 블록에서 임의 방향으로 개별체 해석기법으로 산정한 수리전도도와 이론적 수리전도도 사이의 상대오차(ER)는 $F_0$의 증가에 따라 감소한다. $F_0$는 평균 블록수리전도도와 강한 함수관계를 갖는 것으로 분석되었다.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1157-1164
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• 2001

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few research have been carried out on predicting the noise because of the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan. We assume that the impeller rotates with a constant angular velocity and the flow field of the impeller is incompressible and inviscid. So, a discrete vortex method(DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowsons method is used to predict the acoustic source. In order to compare the experimental data, a centrifugal impeller and wedge introduced by Weidemann are used in the numerical calculation and the results are compared with the experimental data. Reasonable results are obtained not only for the peak frequencies but also for the amplitudes of the tonal.

• 한국농공학회지
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• 제38권3호
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• pp.82-91
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• 1996

This is a basic study for the static and dynamic analysis on the elasto-plastic and elasto-viscoplastic of an axi-symmetric shell. The objective of this study was to investigate the mechanical characteristics of a nuclear reinforced concrete containment structure, which was selected as a model, by a numerical analysis using a finite element method. The structure was modeled with discrete ring elements of 8-noded isoparametric element rotating against the symmetrical axis, and the interaction between the foundation and the structure was modeled by Winkler's model. Also, the meridional tendon was modeled with 2-node truss elements, and the hoop tendon was done with point elements in two degrees of freedom. The effect of the tendon was considered without the increasement in total degree of freedom as the stiffness matrix of modeled tendon elements was assembled on the stiffness matrix of ring elements linked with the tendon. The results obtained from the analysis of an example were summarized as follows : 1. The stresses in the hoop direction on the interior and exterior surfaces of the structure were shown in changes of similar trend, and high stresses appeared on the structure wall 2. The stresses in the meridional direction on the interior and exterior surfaces were shown in change of different trend. Especially, the stresses at the junctions between the dome and the wall and between the wall and the bottom plate of the structure were very high, compared with those at other parts of the structure. 3. The stress changes in the direction of thickness on the crown of the dome were much linearly distributed. However, as the amount of tendon increased, the stresses in the upper and lower parts of the wall established with the tendon were shown stress concentration. 4. The stress changes in the direction of thickness on the center of the structure wall was linearly distributed in the all cases, and special stress due to the use of the tendon was not shown.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.281-284
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• 2009

Flexible forming process for sheet metal using reconfigurable die is introduced based on numerical simulation. Numerical simulation of sheet metal forming process is carried out by using flexible dies model instead of conventional matched die set. Elastic cushion which has high resilience behavior from excessive deformation are inserted between forming punches and blank material for smoothing the forming surface which has discrete due to characteristics of the flexile die. As an elastic cushion, urethane pads are utilized using hyperelastic material model in the simulation. Formability in view of surface defect such as onset of dimple is compared with regard to various punch sizes. Consequently, it is confirmed that the flexible forming process for sheet material has appropriate capability and feasibility for manufacturing of smoothly curved surface instead of conventional die forming process.

• Structural Engineering and Mechanics
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• 제30권6호
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• pp.699-712
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• 2008

The effectiveness of wavelet transform in detecting delamination damages in multilayered composite beams and plates is studied here. The damaged composite beams and plates are modeled in finite element software ABAQUS and the first few mode shapes are obtained. The mode shapes of the damaged structures are then wavelet transformed. It is observed that the distribution of wavelet coefficients can identify the damage location of beams and plates by showing higher values of wavelet coefficients at the position of damage. The effectiveness of the method is studied for different boundary conditions, damage location and size for single as well as multiple delaminations in composite beams and plates. It is observed that both discrete wavelet transform (DWT) and continuous wavelet transform (CWT) can detect the presence and location of the damaged region from the mode shapes of the structures. DWT may be used to approximately evaluate the size of the delamination area, whereas, CWT is efficient to detect smaller delamination areas in composites.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.265-271
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• 1997

A bond graph modeling approach which is equivalent to a finite element method is formulated in the case of the piezoelectric thickness vibrator. This formulation suggests a new definition of the generalized displacements for a continuous system as well as the piezoelectric thickness vibrator. The newly defined coordinates are illustrated to be easily interpreted physically and easily used in analysis of the system performance. Compared to the Mason equivalent circuit model, the bond graph model offers the primary advantage of physical realizability. Compared to circuit models based on standard discrete electrical elements, the main advantage of the bond graph model is a greater physical accuracy because of the use of multiport energic elements. While results are presented here for the thickness vibrator, the modeling method presented is general in scope and can be applied to arbitrary physical systems.

• International Journal of Aeronautical and Space Sciences
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• 제11권3호
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• pp.227-233
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• 2010

In this study, a genetic algorithm was utilized to optimize the stacking sequence of a composite plate subjected to a high velocity impact. The aim is to minimize the maximum backplane displacement of the plate. In the finite element model, we idealized the impactor using solid elements and modeled the composite plate by shell elements to reduce the analysis time. Various tests were carried out to investigate the effect of parameters in the genetic algorithm such as the type of variables, population size, number of discrete variables, and mutation probability.

• 한국분말재료학회지
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• 제7권4호
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• pp.189-196
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• 2000

Effect of ball filling ratio on the behavior of balls motion and their collision characteristic in a tumbler-ball milling of metal powder are investigated by a computer simulation. The discrete element method and the extended Kelvin model composed of nonlinear spring and nonlinear dashpot were employed in the simulation. It can be possible that analysis of the individual balls motion in a three-dimensional actual mill by the two-dimensional model simulation, since the simulated trajectories of ball paths are in relatively good agreement with the actual ones. It knows that the balls motion in the tumbler-ball mill is strongly influenced by the surface conditions of the balls and mill container wall. The energy consumption of the individual balls during impact and the impact frequency of the individual balls increased with an increase in the ball filling ratio and showed maximum values at about 50-60% ball filling ratio, and then decreased.

• Advances in aircraft and spacecraft science
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• 제2권1호
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• pp.1-16
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• 2015

In this paper, geometrical and mechanical approaches are proposed for the simulation of the draping of woven fabric onto complex parts. The geometrical discrete approach allows to define the ply shapes and fibres orientation in order to optimize the composite structural properties and the continuum meso-structural mechanical approach allows to take into account the mechanical properties of fibres and resin and the various dominating mode of deformation of woven fabrics during the forming process. Some numerical simulations of forming process are proposed and compared with the experimental results in order to demonstrate the efficiency of our approaches.