• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.2
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• pp.121-131
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• 2011

An object oriented programming(OOP) framework is presented to solve plane elastostatic contact problems by means of the boundary element method(BEM). Unified modeling language(UML) is chosen to describe the structure of the program without loss of generality, even though all implemented codes are written with C++. The implementation is based on computational abstractions of both mathematical and physical concepts associated with contact mechanics involving geometrical nonlinearities and the corner node problems for multi-valued traction. The overall class organization for contact analysis is discussed in detail. Numerical examples are also presented to verify the accuracy of the developed BEM program.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1075-1080
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• 2010

For the aeroelastic analysis of a wing with friction damping, coupled time integration method was used to obtain time responses in the subsonic and transonic regions. To take into account aerodynamic nonlinearity induced by shock wave on the lifting surface, transonic small disturbance equation with in-phase periodic boundary condition was used for unsteady aerodynamic calculation. For 2-DOF airfoil system with displace-dependent friction dampers, the effects of normal load slope and Mach number on flutter boundary were investigated.

• Geophysics and Geophysical Exploration
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• v.3 no.2
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• pp.61-69
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• 2000

The free-surface boundary conditions are persistent problem in elastic wave equation modeling by finite-difference method, which can be summarized with the degradation of the accuracy of the solution and limited stability range in Poisson's ratio. In this paper, we propose the mid-point averaging scheme as an alternative way of implementing the free-surface boundary conditions, and present the solution to Lamb's problem to verify our approach.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.1
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• pp.39-47
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• 2004

In this paper, the defects of two-dimensional anisotropic elastic bodies are identified by using the boundary element method. The use of numerical models that contain only boundary integral terns reduces the dimensionality of the problem by one. This advantage is particularly important in problems such as crack mechanics. Avoiding domain meshing is also particularly advantageous in the solution of inverse problems since it overcomes mesh perturbations and simplifies the procedure. In this paper, nondestructive approaches for the existing isotropic materials are extended to analyze the elastic bodies made of anisotropic materials such as composites. After verifying that the proposing boundary element model is in good agreement with numerical results reported by other investigators, the effect of noise in the measurements on the identifiability is studied with respect to different design parameters of layered composites. Sample studies are carried out for various layup configurations and loading conditions. The effects of the layup sequences in detecting flaw of composites is explored in this paper.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.574-577
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• 2010

이번 연구에서는 저속 비압축성 유체-구조 연성을 고려한 위상 최적화을 위해 새로운 모노리틱 해석을 개발한다. 이 새로운 해석 기법에서는 기존의 유체-구조 연성 시스템 해석 기법에서 유체와 구조 영역을 분리하고 연성 조건을 만족시키는 것과 다르게 하나의 일치된 해석 방정식을 유체 영역과 구조 영역에 동일하게 적용한다. 또한, 경계조건을 만족시키기 위하여 단일화 된 해석 방정식의 물성치를 바꾸어주는 새로운 방식을 제시하였다. 이 새로운 방법에서는 유체, 구조 영역을 분리하지 않고 Navier-Stoke's 방정식과 선형 탄성식을 동시에 사용하였다. 또한, 유체-구조 영역이 연성 해석 중 변화하는 것을 반영하기 위하여 구조 변위를 이용하여 Deformation tensor를 계산하였고 이를 이용하여 변형 후에서의 Navier-Stoke 방정식의 미분을 계산하는 방법을 제안하였다. 그리고, 정상 상태 유체를 가정하고 속도에 비례하는 마찰힘인 Darcy's force 항을 Navier-Stoke 방정식에 넣고 이 마찰 힘의 크기를 변화시킴으로 해서 유체 방정식에서의 연성 경계 조건을 만족시켰다. 선형 탄성 방정식에서 Divergence이론을 이용해서 경계에서 작용하는 외력이 하는 일을 내부 시스템에 하는 일로 계산하였다. 개발된 모노리스 해석 방법을 이용하여 저속 비압축성 유체가 구조에 미치는 압축력을 계산하였고 이용하여 컴플라이언트 미케니즘을 설계하였다.

• Composites Research
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• v.23 no.3
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• pp.19-30
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• 2010

The present study describes a method for analytical solution to elastic field in structural elements of general symmetric laminated composite materials. The two dimensional plane stress elasticity problems under mixed boundary conditions are reduced to the solution of a single fourth order partial differential equation, expressed in terms of a single unknown function, called displacement potential function. In addition, all the components of stress and displacement are expressed in terms of the same displacement potential function, which makes the method suitable for any boundary conditions. The method is applied to obtain analytical solutions to two particular problems of structural elements consisting of an angle-ply laminate and a cross-ply laminate, respectively. Some numerical results are presented for both the problems with reference to the glass/epoxy composite. The results are highly accurate and reliable as all the boundary conditions including those in the critical regions of supports and loads are satisfied exactly. This verifies the method as a simple and reliable one as well as capable to obtain exact analytical solution to elastic field in structural elements of composite materials under mixed and any other boundary conditions.

• Journal of the KSME
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• v.30 no.3
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• pp.246-251
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• 1990

마이크로폴라 탄성이론은 다른 마이크로연속체(microcontinuum) 이론에 비해 적용이 간단하며, 실제 많은 물리적인 현상을 규명하는 데 다양하게 이용할 수 있다. 특히 고전 탄성이론에 의해 적절하게 해결될 수 없는 덤벨(dumbell) 분자로 이루어진 물체, 액체 결정체(liquid crystals), 과립상(granular)의 분자로 구성된 물체와 복합 섬유재료(composite fibrous materials) 등은 마 이크로폴라 탄성이론에 의해 잘 해결될 수 있다. 또한 마이크로폴라 탄성이론은 고체 내에서의 파의 전파(propagation)와 분산(dispersion), 구멍 주위의 응력집중과 외부 하중을 받는 물체에 있어 균열끝에서의 응력 분포 등의 고체역학 문제들은 물론이고, 경계층(boundary layer), 난 류(turbulence), 유체 유동의 불안정(instability)과 표면장력 현상 등의 유체역학에서의 복잡한 문제들을 해결하는 데에도 이용할 수 있다. 마이크로폴라 탄성이론은 고전 탄성이론에 비해 상 대적으로 새롭고 미개척 분야이긴 하지만 이론의 기반이 확고하기 때문에 앞으로의 회전응력 측정장치의 개발을 통해 미소구조의 영향을 고려해야 하는 많은 문제들을 해결하는데 큰 기여를 할 것으로 전망된다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.3
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• pp.187-195
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• 2024

This paper presents two-dimensional boundary value problems of the stress-based gradient elasticity within the smoothed finite element method (S-FEM) framework. Gradient elasticity is introduced to address the limitations of classical elasticity, particularly its struggle to capture size-dependent mechanical behavior at the micro/nano scale. The Ru-Aifantis theorem is employed to overcome the challenges of high-order differential equations in gradient elasticity. This theorem effectively splits the original equation into two solvable second-order differential equations, enabling its incorporation into the S-FEM framework. The present method utilizes a staggered scheme to solve the boundary value problems. This approach efficiently separates the calculation of the local displacement field (obtained over each smoothing domain) from the non-local stress field (computed element-wise). A series of numerical tests are conducted to investigate the influence of the internal length scale, a key parameter in gradient elasticity. The results demonstrate the effectiveness of the proposed approach in smoothing stress concentrations typically observed at crack tips and dislocation lines.

• International Journal of Highway Engineering
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• v.7 no.3 s.25
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• pp.11-21
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• 2005

To examine adequacy of existing multi-layer elastic analysis of layer interface conditions, this study compared outputs of finite element analysis and multi-layer elastic analysis as vertical load was applied to the surface of asphalt pavements. Structural pavement analysis considering influence of a horizontal load was also carried out in order to simulate passing vehicle loads under various interface conditions using ABAQUS, a three dimensional finite element program. Pavement performance depending on interface conditions was quantitatively evaluated and fundamental study of layer interface effect was performed in this study. As results of the study, if only vertical load is applied, subdivision of either fully bonded or fully unbonded is enough to indicate interface condition. On the other hand, when horizontal load is applied with vertical load, pavement behavior and performance are greatly changed with respect to layer interface condition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.5
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• pp.413-420
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• 2012

In this study, the Kernel integration scheme for 2D linear elastic direct boundary element method has been discussed on the basis of subparametric element. Usually, the isoparametric based boundary element uses same polynomial order in the both basis function and mapping function. On the other hand, the order of mapping function is lower than the order of basis function to define displacement field when the subparametric concept is used. While the logarithmic numerical integration is generally used to calculate Kernel integration as well as Cauchy principal value approach, new formulation has been derived to improve the accuracy of numerical solution by algebraic modification. The subparametric based direct boundary element has been applied to 2D elliptical partial differential equation, especially for plane stress/strain problems, to demonstrate whether the proposed algebraic expression for integration of singular Kernel function is robust and accurate. The problems including cantilever beam and square plate with a cutout have been tested since those are typical examples of simple connected and multi connected region cases. It is noted that the number of DOFs has been drastically reduced to keep same degree of accuracy in comparison with the conventional isoparametric based BEM. It is expected that the subparametric based BEM associated with singular Kernel function integration scheme may be extended to not only subparametric high order boundary element but also subparametric high order dual boundary element.