• 한국지반환경공학회 논문집
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• 제10권4호
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• pp.65-71
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• 2009

수압파쇄기술은 가스나 석유, 지열 등 자원추출을 하기 위해 다양한 분야에서 전세계적으로 응용되고 있는 기술이다. 이러한 수압파쇄 작업 시 복수의 균열이 필수적으로 발생하여 균열간 기계적인 상호작용을 유발하는데 이러한 상호작용은 수압파쇄시 얻어질 수 있는 결과(균열 폭, 균열 길이, 보어홀 내 압력)에 큰 영향을 끼치게 된다. 수치해석기법인 경계병치법은 이러한 균열간의 역학적 상호작용을 고려하는데 유효한 수치해석적 기법으로 개발이 되고 있으나 응력확대계수를 계산하는 해석식과의 비교 등을 통한 검증이 필요하다. 이를 위해 무한평면에 일축 인장 응력과 전단응력이 작용하는 단일균열의 경우 및 임의의 두 균열이 존재하는 경우의 응력확대계수 및 균열폭 해석식과 본 수치해석기법을 통해 얻은 값을 비교하였다. 그 결과, 본 연구에서 제시한 경계병치법은 해석식과 상당히 근접한 결과를 나타내어, 균열간의 기계적인 상호작용을 고려하는데 유효함을 검증하였으며, 추후 수압파쇄 시 설계에 필요한 균열폭 등의 변수를 계산하는데 사용할 수 있음을 나타내었다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2002년도 추계공동학술대회논문집
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• pp.95-100
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• 2002

표면효과익선이란 동체의 날개가 해수면 가까이 비행할 때 수면과 날개 사이에서 양력이 증가되는 표면효과를 이용하는 에너지 절약형 선박이다. 표면효과익선은 낮은 고도로 공기 중에서 비행하여야 되므로 박판으로 이루어져야 한다. 그러므로, 표면효과익선 구조에서 외판의 두께는 얇고 가벼우며 Stringer와 Frame등의 보강재는 외판에 비하여 단면적이 훨씬 크다. 이와 같은 구조에 있어서는 외판이 면내방향의 하중을 받으면 박판인 외판은 순전단장에 가깝게 된다. 이와같이 외판과 큰 단면적을 갖는 String를 서로 조합하여 이루어진 구조는 표면효과익선 구조물의 구조응답해석이 가능하다. 본 연구에서는 기본설계 단계에서 간단하게 기체 구조강도해석을 할 수 있는 기존의 해석적인 방법으로 동체와 표면익의 구조강도를 계산할 수 있는 해석적인 방법을 제시하였다.

• Structural Engineering and Mechanics
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• 제48권4호
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• pp.547-567
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• 2013

Nonlinear behavior of functionally graded material (FGM) plates under thermal loads is investigated here using an efficient sinusoidal shear deformation theory. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the sinusoidal distribution of transverse shear stress through the thickness in such a way that shear stresses vanish on the plate surfaces. Therefore, there is no need to use shear correction factor. Unlike the conventional sinusoidal shear deformation theory, the proposed efficient sinusoidal shear deformation theory contains only four unknowns. The material is graded in the thickness direction and a simple power law based on the rule of mixture is used to estimate the effective material properties. The neutral surface position for such FGM plates is determined and the sinusoidal shear deformation theory based on exact neutral surface position is employed here. There is no stretching-bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The non-linear strain-displacement relations are also taken into consideration. The thermal loads are assumed as uniform, linear and non-linear temperature rises across the thickness direction. Closed-form solutions are presented to calculate the critical buckling temperature, which are useful for engineers in design. Numerical results are presented for the present efficient sinusoidal shear deformation theory, demonstrating its importance and accuracy in comparison to other theories.

• Geomechanics and Engineering
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• 제10권3호
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• pp.357-386
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• 2016

In this research work, an exact analytical solution for thermal stability of solar functionally graded rectangular plates subjected to uniform, linear and non-linear temperature rises across the thickness direction is developed. It is assumed that the plate rests on two-parameter elastic foundation and its material properties vary through the thickness of the plate as a power function. The neutral surface position for such plate is determined, and the efficient hyperbolic plate theory based on exact neutral surface position is employed to derive the governing stability equations. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the quadratic distribution of transverse shear stress through the thickness in such a way that shear stresses vanish on the plate surfaces. Therefore, there is no need to use shear correction factor. Just four unknown displacement functions are used in the present theory against five unknown displacement functions used in the corresponding ones. The non-linear strain-displacement relations are also taken into consideration. The influences of many plate parameters on buckling temperature difference will be investigated. Numerical results are presented for the present theory, demonstrating its importance and accuracy in comparison to other theories.

• Tribology and Lubricants
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• 제38권3호
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• pp.84-92
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• 2022

In Part I, developed was a method to obtain the stress field due to an edge dislocation that locates in an elastic half plane beneath the contact edge of an elastically similar square wedge. Essential result was the corrective functions which incorporate a traction free condition of the free surfaces. In the sequel to Part I, features of the corrective functions, F_kij,(k = x, y;i,j = x,y) are investigated in this Part II at first. It is found that F_xxx(ŷ) = F_xyx(ŷ) where ŷ = y/η and η being the location of an edge dislocation on the y axis. When compared with the corrective functions derived for the case of an edge dislocation at x = ξ, analogy is found when the indices of y and x are exchanged with each other as can be readily expected. The corrective functions are curve fitted by using the scatter data generated using a numerical technique. The algebraic form for the curve fitting is designed as F_kij(ŷ) = $\frac{1}{\hat{y}^{1-{\lambda}}I+yp}$$\sum_{q=0}^{m}{\left}$$\left[A_q\left(\frac{\hat{y}}{1+\hat{y}} \right)^q \right]$ where λ_I=0.5445, the eigenvalue of the adhesive complete contact problem introduced in Part I. To investigate the exponent of F_kij, i.e.(1 - λ_I) and p, Log|F_kij|(ŷ)-Log|(ŷ)| is plotted and investigated. All the coefficients and powers in the algebraic form of the corrective functions are obtained using Mathematica. Method of analyzing a surface perpendicular crack emanated from the complete contact edge is explained as an application of the curve-fitted corrective functions.

• 한국지구과학회지
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• 제34권1호
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• pp.59-68
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• 2013

본 연구는 최근 2005년 1월부터 2011년 3월까지 발생한 한반도 남서부지역($34^{\circ}N-36^{\circ}N$, $126^{\circ}E-128^{\circ}E$)의 지진 중 규모 2.0 이상의 22개 지진에 대한 단층운동의 해를 구하여 분석하였다. 본 연구를 통해 각 지진의 진앙을 재결정하고, 이를 기상청과 한국지질자원연구원의 진앙자료와 비교한 결과 대부분 $0.05^{\circ}$ 이내로 대체적으로 유사한 값을 보이나, 해안지역에서 관측망의 편중 혹은 부족으로 인해 약간 더 커진다. 진원깊이가 구해진 한국지질자원연구원의 진원깊이 자료와 비교하면 최대 12.7 km 이내에서 다양한 차이를 보인다. 대부분의 진앙은 지구조선에 인접하여 분포한다. 단층면 해는 P파 초동극성을 이용하는 방법과 SH파의 극성 및 SH/P 진폭비를 추가하는 방법으로 구한 결과 대부분 주향이동운동 혹은 역단층 성분이 포함된 주향이동단층 운동의 특징을 보인다. 주 응력장인 P축은 동북동-서남서 혹은 동서 방향이 우세하게 나타나고, 이는 전반적인 한반도의 응력장 분포와 잘 일치한다. 단층면해는 주로 'NNE-SSW와 WNW-ESE 방향' 또는 'NE-SW와 NW-SE 방향'의 단층면과 보조단층면을 보이는데, 이는 지표의 지구조선 방향과 전반적으로 잘 일치하는 경향을 보인다.

• Smart Structures and Systems
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• 제16권5호
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• pp.781-806
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• 2015

A unified formulation of finite layer methods (FLMs), based on the Reissner mixed variational theorem (RMVT), is developed for the three-dimensional (3D) coupled electro-elastic analysis of simply-supported, functionally graded piezoelectric material (FGPM) plates with open- and closed-circuit surface conditions and under electro-mechanical loads. In this formulation, the material properties of the plate are assumed to obey an exponent-law varying exponentially through the thickness coordinate, and the plate is divided into a number of finite rectangular layers, in which the trigonometric functions and Lagrange polynomials are used to interpolate the in- and out-of-plane variations of the primary field variables of each individual layer, respectively, such as the elastic displacement, transverse shear and normal stress, electric potential, and normal electric displacement components. The relevant orders used for expanding these variables in the thickness coordinate can be freely chosen as the linear, quadratic and cubic orders. Four different mechanical/electrical loading conditions applied on the top and bottom surfaces of the plate are considered, and the corresponding coupled electro-elastic analysis of the loaded FGPM plates is undertaken. The accuracy and convergence rate of the RMVT-based FLMs are assessed by comparing their solutions with the exact 3D piezoelectricity ones available in the literature.

• Journal of Magnetics
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• 제21권3호
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• pp.476-489
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• 2016

In the present study, squeezing flow of micropolar nanofluid between parallel infinite disks in the presence of magnetic field perpendicular to plane of the disks is taken into account. The constitutive equations that govern the flow configuration are converted into nonlinear ordinary differential with the help of suitable similarity transforms. HAM package BVPh2.0 has been employed to solve the nonlinear system of ordinary differential equations. Effects of different emerging parameters like micropolar parameter K, squeezed Reynolds number R, Hartmann number M, Brownian motion parameter Nb, thermophoresis parameter Nt, Lewis number Le for dimensionless velocities, temperature distribution and concentration profile are also discussed graphically. In the presence of strong and weak interaction (i.e. n = 0 and n = 0.5), numerical values of skin friction coefficient, wall stress coefficient, local Nusselt number and local Sherwood number are presented in tabulated form. To check the validity and reliability of the developed algorithm BVPh2.0 a numerical investigation is also a part of this study.

• 한국해양공학회지
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• 제15권3호
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• pp.75-80
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• 2001

The elastic plastic fracture toughness of this material is evaluated by the an unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the material tearing modulus and characterizes the crack tip field under the plane stress and strain. SG-365 steel is observed that J-R curve and Tmat value decrease as 0%, 20%, 30%, and 40%. The 40% side grooved specimen is very useful in estimation of the $J_IC$. Because it is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides. it improves the accuracy of toughness values, decreases the scattering the them and tunneling and shear lip by the side groove. Applicability of tearing modulus($T_J$ proposed by paris et al as instability panameter for this material is investigated.

• 한국전기전자재료학회논문지
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• 제30권12호
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• pp.757-761
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• 2017

The computational fourier-transform moire (CFTM) method has been briefly explained and this method was used to perform strain analysis of a misfit dislocation in a strained $Si/Si_{0.55}Ge_{0.45}$ layer. An essential advantage of the CFTM method is that it does not require unwrapping, such that errors due to improper unwrapping can be excluded. The analysis results revealed that the Si layer was grown with tensile stress on $Si_{0.55}Ge_{0.45}$ and lattice constant of the Si layer along the growth direction was 1.9% smaller than that of $Si_{0.55}Ge_{0.45}$. On the other hand, strain of the misfit dislocation in the strained $Si/Si_{0.55}Ge_{0.45}$ layer was maximum at the dislocation core due to an extra half-plane and the $e_{xx}$ and $e_{yy}$ values were positive and negative, respectively, along the direction of a burgers vector.