• Structural Engineering and Mechanics
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• 제91권5호
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• pp.527-538
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• 2024

The standard numerical approximation of structural displacement field leads to the thickness-wise transverse shear stress distributions which are quite different from the exact ones. To overcome this inherent problem, an effective and reliable post-processing method is presented based on the strain recovery and the stress equilibrium, particularly for functionally graded cylindrical and conical elastic panels. The present method is developed in the framework of locking-free 2-D natural element method. Through the recovery of displacement component-wise derivatives, the element-wise discontinuous in-plane strain distributions are enhanced to be globally continuous and smoothened. And, using the continuous in-plane strains, the troublesome poor transverse shear stress distributions are enhanced through the thickness-wise integration of static equilibrium equations. The validity of present post-processing method is verified through the comparison with the reference solutions. In addition, the comparative experiments are also performed to investigate the difference between the present method and other available post-processing methods. The numerical results confirm that the present method provides the accurate transverse shear stress distributions which are consistent with the reference solutions and much better than other available methods.

• Structural Engineering and Mechanics
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• 제18권1호
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• pp.79-90
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• 2004

A high precision shear deformable triangular element has been proposed for bending analysis of triangular plate. The element has twelve nodes at the three sides and four nodes inside the element. Initially the element has thirty-five degrees of freedom, which has been reduced to thirty by eliminating the degrees of freedom of the internal nodes through static condensation. Plates having different boundary conditions, side ratios (b/a) and thickness ratios (h/a = 0.001, 0.1 and 0.2) have been analyzed using the proposed shear locking free element. Concentrated and uniformly distributed transverse loads have been used for the analysis. The formulation is made based on first order shear deformation theory. For validation of the present element and formulation few results of thin triangular plate have been compared with the analytical solutions. Results for thick plate have been presented as new results.

• Structural Engineering and Mechanics
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• 제26권1호
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• pp.69-86
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• 2007

A four-noded plate bending quadrilateral (PBQ4) and an eight-noded plate bending quadrilateral (PBQ8) element based on Mindlin plate theory have been adopted for modeling the thick plates on elastic foundations using Winkler model. Transverse shear deformations have been included, and the stiffness matrices of the plate elements and the Winkler foundation stiffness matrices are developed using Finite Element Method based on thick plate theory. A computer program is coded for this purpose. Various loading and boundary conditions are considered, and examples from the literature are solved for comparison. Shear locking problem in the PBQ4 element is observed for small value of subgrade reaction and plate thickness. It is noted that prevention of shear locking problem in the analysis of the thin plate is generally possible by using element PBQ8. It can be concluded that, the element PBQ8 is more effective and reliable than element PBQ4 for solving problems of thin and thick plates on elastic foundations.

• Steel and Composite Structures
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• 제3권3호
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• pp.213-229
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• 2003

A high precision shear deformable triangular element has been proposed for free vibration analysis of composite trapezoidal plates. The element has twelve nodes at the three sides and four nodes inside the element. Initially the element has fifty-five degrees of freedom, which has been reduced to forty-eight by eliminating the degrees of freedom of the internal nodes through static condensation. Plates having different side ratios (b/a), boundary conditions, thickness ratios (h/a=0.01, 0.1 and 0.2), number of layers and fibre angle orientations have been analyzed by the proposed shear locking free element. Trapezoidal laminate with concentrated mass at the centre has also been analyzed. An efficient mass lumping scheme has been recommended, where the effect of rotary inertia has been included. For validation of the present element and formulation few results of isotropic trapezoidal plate and square composite laminate have been compared with those obtained from open literatures. The numerical results for composite trapezoidal laminate have been given as new results.

• 한국전자파학회논문지
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• 제22권3호
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• pp.292-298
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• 2011

본 논문에서는 전압 제어 특성을 이용하여 광대역에서 사용 가능한 주입 동기 발진기를 제안하였다. 주입 동기 발진기의 공진 회로에 바렉터 다이오드를 포함시켜 다이오드의 바이어스 전압을 제어하여 자유 발진 주파수를 가변 가능하도록 하였으며, 이를 통해 주입 동기 신호의 입력 레벨이 낮더라도 광대역에서 동작이 가능하도록 하였다. 제안된 주입 동기 발진기는 0.8 mm 두께를 갖는 FR-4 기판을 사용하여 제작되었으며, 0~5 V의 제어 전압을 주어졌을 때, 자유 발진 주파수는 2.39~2.52 GHz로 가변이 가능하였다. 주파수 고정시 -10 dBm의 입력 신호 레벨에서 주파수 동기 범위가 50 MHz 이상이며, 주파수 가변을 통해 -30 dBm의 낮은 주입 신호레벨에서 90 MHz의 주파수 동기 범위를 얻을 수 있었다.

• Steel and Composite Structures
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• 제35권1호
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• pp.129-145
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• 2020

In typical, structural topology optimization plays a significant role to both increase stiffness and save mass of structures in the resulting design. This study contributes to a new numerical approach of topologically optimal design of Mindlin-Reissner plates considering Winkler foundation and mathematical formulations of multi-directional variable thickness of the plate by using multi-materials. While achieving optimal multi-material topologies of the plate with multi-directional variable thickness, the weight information of structures in terms of effective utilization of the material at the appropriate thickness location may be provided for engineers and designers of structures. Besides, numerical techniques of the well-established mixed interpolation of tensorial components 4 element (MITC4) is utilized to overcome a well-known shear locking problem occurring to thin plate models. The well-founded mathematical formulation of topology optimization problem with variable thickness Mindlin-Reissner plate structures by using multiple materials is derived in detail as one of main achievements of this article. Numerical examples verify that variable thickness Mindlin-Reissner plates on Winkler foundation have a significant effect on topologically optimal multi-material design results.

• 한국항공우주학회지
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• 제31권2호
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• pp.25-34
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• 2003

본 논문에서는 압전 작동기가 삽입되거나 부착된 구조를 해석하기 위하여, 기존의 기계적 문제만을 고려한 9 절점 가정변형률 쉘 요소의 정식화를 전기-기계연성 문제에도 적용 가능하도록 확장하였다. 본 쉘요소는 잠김현상을 완화할 수 있고, 두께변형을 고려하기 위해 각 절점에서 6개의 자유도를 갖는 특징이 있다. 전기-기계 자유도들은 구성방정식을 이용하여 연계시켰다. 변위장은 요소의 전체 두께방향으로 선형으로 가정하였고, 전기적 포텐셜은 각각의 압전재료층에 대해 선형으로 가정하였다. 확장된 정식화에 기초한 유한요소 프로그램을 개발하였고, 수치예제들을 통해 프로그램을 검증하였다. 개발된 쉘 요소에 의한 결과는 다른 참고문헌들의 결과들과 잘 일치하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 추계학술대회논문집; 한국과학기술회관; 6 Nov. 1997
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• pp.396-401
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• 1997

Dynamic stability of cylindrical shells subjected to follower forces is analyzed in this paper. Motion of shells is formulated in curvilinear coordinates that is consistent with assumptions made in the Timoshenko beam and the Mindlin plate. Using the finite element method, the induced equations are reduced to an equation with finite degrees of freedom. The 9-node Lagrangian element is used, and reduced integration is used to avoid shear and membrane locking. The effects of thickness ratio on the dynamic stability of cylindrical shells are studied.

• Structural Engineering and Mechanics
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• 제43권2호
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• pp.253-271
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• 2012

To analyze the bending and transverse shear effects of laminated composite plates, a thirteen nodes triangular element will be presented. The suggested formulations consider a parabolic variation of the transverse shear strains through the thickness. As a result, there is no need to use shear correction coefficients in computing the shear stresses. The proposed element can model both thin and thick plates without any problems, such as shear locking and spurious modes. Moreover, the effectiveness of $w_{,n}$, as an independent degree of freedom, is concluded by the present study. To perform the accuracy tests, several examples will be solved. Numerical results for the orthotropic materials with different boundary conditions, shapes, number of layers, thickness ratios and fiber orientations will be presented. The suggested element calculates the deflections and stresses more accurate than those available in the literature.

• 한국통신학회논문지
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• 제18권6호
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• pp.793-801
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• 1993

본 논문에서 우리는 외부공진기 내에 고 피네스 훼브리 페롯(F-P) 에탈론을 삽입시킴으로서 외부공진기 레이저의 주파수 잠김 및 주파수 잡음축소 등의 성능특성을 크게 개선시킬 수 있음을 이론적으로 보였다. 예를들면, 피네스가 30이고 광학적 두께가 1.5cm 인 F-P 에탈론은 3cm 길이의 외부공진기 내에 삽입한 경우, 동일한 조건에서 동작하는 종래의 외부공진기 레이저보다 7.6배의 주파수 잠김 정확도와 86배에 이르는 레이저 선폭 축소 특성의 개선 효과를 얻을 수 있었다.