• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제29권4호
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• pp.212-218
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• 2003

Matrix metalloproteinases (MMPs) play an important role in the normal morphogenesis, maintenance, and repair of matrix and also have important functions in pathologic conditions characterized by excessive degradation of extracellular matrix, such as rheumatoid arthritis, osteoarthritis, periodontitis and in tumor invasion and metastasis. In this study, expression of MMP-1 and -2 mRNA in retrodiscal tissue of the temporomandibular joint (TMJ) was examined and compared with magnetic resonance imaging (MRI) and surgical findings. MMP mRNAs in the retrodiscal tissue samples were detected by reverse transcription - polymerase chain reaction. TMJ internal derangement (ID) was categorized as normal disc position, disc displacement with reduction, early stage of disc displacement without reduction (DDsR) and late stage of DDsR. TMJ osteoarthrosis (OA) was classified with normal, mild and advanced OA. The amount of synovial fluid collection was divided into not detected, small, large and extremely large amount on MR T2-weighted imaging. Perforation and adhesion were examined during open surgery of the TMJ. Six out of 37 samples were excluded because of little amount of extracted total mRNA. MMP-2 mRNA was detected whole joints, and so the MMP-2 mRNA seems to be expressed normally in retrodiscal tissue. However, MMP-1 mRNA was expressed in 8 of 31 joints. Frequencies of MMP-1 mRNA expression according to the TMJ IDs, amount of synovial fluid and surgical findings made no significant difference. MMP-1 mRNA was detected more frequently in OA groups (7/16 joints, 43.8%) than in normal bony structure group (1/15 joints, 6.7%). Expression of MMP-1 mRNA in retrodiscal tissue might be related with OA of the TMJ.

• 한국전산구조공학회논문집
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• 제15권3호
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• pp.463-469
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• 2002

탄성지반 위에 놓인 보-기둥 요소의 총포텐셜 에너지로부터 변분원리를 적용하여 지배방정식과 힘-변위 관계식을 유도하였다. 4계 상미분방정식 형태의 지배방정식을 4개의 변위 파라메타를 도입하여 1계 연립미분방정식 형태의 선형 고유치 문제로 전환하고, 힘-변위 관계식을 적용하여 엄밀한 정적, 동적 요소강성행렬을 유도하였다. 직접강성법을 이용하여 구조물 강성행렬을 구하고, 2차원 보-기둥구조의 엄밀한 좌굴하중과 고유진동수를 구하고, 결과를 유한요소해와 비교함으로써 본 연구의 타당성을 검증하였다. 이러한 엄밀한 해석방법은 Hermitian 다항식을 형상함수로 도입하여 요소의 강성행렬을 산정하는 유한요소법과 비교할 때, 요소의 수를 대폭 줄일 수 있는 장점이 있다.

• 한국소음진동공학회논문집
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• 제19권10호
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• pp.1069-1074
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• 2009

A sub-domain method for free vibration analysis of arbitrarily shaped, concave membranes with a deep groove is proposed in the paper. The proposed method divides the concave membrane of interest into two convex regions. The vibration displacement(approximate solution) of each convex region is assumed by linearly superposing plane waves generated at edges of the region. A sub-system matrix for each convex region is extracted by applying a provisional boundary condition to the approximate solution. Finally, a system matrix, which of the determinant gives eigenvalues of the concave membrane, is made by considering the fixed boundary condition(displacement zero condition) at edges and the compatibility condition(the condition of continuity in displacement and slope) at the interface between the two regions. Case studies show that the proposed method is valid and accurate when the eigenvalues by the proposed are compared to those by NDIF method, FEM, or the exact method.

• Steel and Composite Structures
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• 제23권1호
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• pp.1-16
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• 2017

This paper is presented to solve the buckling problem of functionally graded truncated conical shells subjected to displacement-dependent pressure which remains normal to the shell middle surface throughout the deformation process by the semi-analytical finite strip method. Material properties are assumed to be temperature dependent, and varied continuously in the thickness direction according to a simple power law distribution in terms of the volume fraction of a ceramic and metal. The governing equations are derived based on first-order shear deformation theory which accounts for through thickness shear flexibility with Sanders-type of kinematic nonlinearity. The element linear and geometric stiffness matrices are obtained using virtual work expression for functionally graded materials. The load stiffness also called pressure stiffness matrix which accounts for variation of load direction is derived for each strip and after assembling, global load stiffness matrix of the shell which may be un-symmetric is formed. The un-symmetric parts which are due to load non-uniformity and unconstrained boundaries have been separated. A detailed parametric study is carried out to quantify the effects of power-law index of functional graded material and shell geometry variations on the difference between follower and non-follower lateral buckling pressures. The results indicate that considering pressure stiffness which arises from follower action of pressure causes considerable reduction in estimating buckling pressure.

• 대한기계학회논문집A
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• 제29권12권
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• pp.1574-1585
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• 2005

In this paper, a spectral element model is developed for the uniform straight pipelines conveying internal unsteady fluid. Four coupled pipe-dynamics equations are derived first by using the Hamilton's principle and the principles of fluid mechanics. The transverse displacement, the axial displacement, the fluid pressure and the fluid velocity are all considered as the dependent variables. The coupled pipe-dynamics equations are then linearized about the steady state values of the fluid pressure and velocity. As the final step, the spectral element model represented by the exact dynamic stiffness matrix, which is often called spectral element matrix, is formulated by using the frequency-domain solutions of the linearized pipe-dynamics equations. The FFT-based spectral dynamic analyses are conducted to evaluate the accuracy of the present spectral element model and also to investigate the structural dynamic characteristics and the internal fluid transients of an example pipeline system.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1638-1642
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• 2003

Piezoactuator using a flexure hinge mechanism is often used in the precision stages. When the total size of the hinge mechanism become small compared with the deformation of the hinge mechanism, the geometrical nonlinearity makes a considerable error in the output displacement. In this research, the incremental method based on the matrix method is developed to model the effect of the geometrical nonlinearity. Developed modeling method is applied to derive the error of output displacement of the bridge-type hinge mechanism and its results are derived with respect to the design parameters. This method can be easily used to the design optimization of the hinge mechanism and analysis results show that the geometrical nonlinearity error should be considered to achieve a high accuracy to the piezoactuators.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.475-480
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• 2003

Latex modification of concrete provides the material with higher flexural strength. This increase in flexural strength can attribute to the crack-arresting action of polymer in concrete, and also to the bonding they provide between the matrix and aggregates. This experimental study presents the fracture behavior of 12 flexural reinforced concrete beams repaired or strengthened by latex-modified concrete with the main experimental variables such as overlay thickness, strength thickness, and shear reinforcement. The results are as follow: All beam specimens having shear reinforcement were failed by delamination rupture at concrete interface at about 80% of ultimate loading after flexural cracking. All specimens overlayed and strengthened by latex-modified concrete (LMC) showed higher ultimate flexural strength than OPC control specimen, but lower than LMC control specimen. This increase in flexural strength could attribute to the high bonding they provide between the matrix and aggregates. All specimens except two shear unreinforced showed quite similar and consistent displacement behavior. The effect of overlay and strength thickness on the load-displacement relationship were a small at this study.

• 전산구조공학
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• 제10권2호
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• pp.139-148
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• 1997

A finite element method is programmed to analyse the nonlinear behavior of axisymmetric structures. The lst order Mindlin shell theory which takes into account the transversal shear deformation is used to formulate a conical two node element with six degrees of freedom. To evade the shear locking phenomenon which arises in Mindlin type element when the effect of shear deformation tends to zero, the reduced integration of one point Gauss Quadrature at the center of element is employed. This method is the Updated Lagrangian formulation which refers the variables to the state of the most recent iteration. The solution is searched by Newton-Raphson iteration method. The tangent matrix of this method is obtained by a finite difference method by perturbating the degrees of freedom with small values. For the moment this program is limited to the analyses of non-linear elastic problems. For structures which could have elastic stability problem, the calculation is controled by displacement.

• Structural Engineering and Mechanics
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• 제30권4호
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• pp.387-402
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• 2008

The Integrated Force Method (IFM) has been developed in recent years for the analysis of civil, mechanical and aerospace engineering structures. In this method all independent or internal forces are treated as unknown variables which are calculated by simultaneously imposing equations of equilibrium and compatibility conditions. The solution by IFM needs the computation of element equilibrium and flexibility matrices from the assumed displacement, stress-resultant fields and material properties. This paper presents a general purpose code for the automatic generation of element equilibrium and flexibility matrices for plate bending elements using the Integrated Force Method. Kirchhoff and the Mindlin-Reissner plate theories have been employed in the code. Paper illustrates development of element equilibrium and flexibility matrices for the Mindlin-Reissner theory based four node quadrilateral plate bending element using the Integrated Force Method.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.178-179
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• 2017

Input filter is an essential component in a practical matrix converter (MC) system to generate the sinusoidal input currents. However, the input filter causes a displacement angle between the input current of MC and the source current. In this paper, we investigate the input filter design for MCs by considering the displacement angles of the input current and the input voltage to guarantee high input power factor (IPF) operation as well as low input current harmonic contents. Simulation results are provided to validate the input filter design with near unity input power factor and low total harmonic distortion (THD) of the input current.