• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제23권4호
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• pp.367-380
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• 2019

A 1kW-class horizontal axis wind turbine (HAWT) rotor blade is taken into account to investigate elastic characteristics in 2-D. The elastic blade field is composed of symmetric cross-ply laminated composite material. Blade element momentum theory is applied to obtain the boundary conditions pressuring the blade, and the plane stress elasticity problem is formulated in terms of two displacement parameters with mixed boundary conditions. For the elastic characteristics a fair of differential equations are derived based on the elastic theory. The domain is divided by triangular and rectangular elements due to the complexity of the blade configuration, and a finite element method is developed for the governing equations to search approximate solutions. The results describe that the elastic behavior is deeply influenced by the layered angle of the middle laminate and the stability of the blade can be improved by controlling the layered angle of laminates, which can be evaluated by the mathematical approach.

• Structural Engineering and Mechanics
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• 제86권3호
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• pp.291-309
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• 2023

This paper addresses the finite element modeling of functionally graded porous (FGP) beams for free vibration and buckling behaviour cases. The formulated finite element is based on simple and efficient higher order shear deformation theory. The key feature of this formulation is that it deals with Euler-Bernoulli beam theory with only three unknowns without requiring any shear correction factor. In fact, the presented two-noded beam element has three degrees of freedom per node, and the discrete model guarantees the interelement continuity by using both C⁰ and C¹ continuities for the displacement field and its first derivative shape functions, respectively. The weak form of the governing equations is obtained from the Hamilton principle of FGP beams to generate the elementary stiffness, geometric, and mass matrices. By deploying the isoparametric coordinate system, the derived elementary matrices are computed using the Gauss quadrature rule. To overcome the shear-locking phenomenon, the reduced integration technique is used for the shear strain energy. Furthermore, the effect of porosity distribution patterns on the free vibration and buckling behaviours of porous functionally graded beams in various parameters is investigated. The obtained results extend and improve those predicted previously by alternative existing theories, in which significant parameters such as material distribution, geometrical configuration, boundary conditions, and porosity distributions are considered and discussed in detailed numerical comparisons. Determining the impacts of these parameters on natural frequencies and critical buckling loads play an essential role in the manufacturing process of such materials and their related mechanical modeling in aerospace, nuclear, civil, and other structures.

• 대한기계학회논문집
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• 제12권2호
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• pp.185-192
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• 1988

본 논문에서는 접촉문제를 보다 정교하게 수식화 함으로써 효율적인 볼 압입 시험 시뮬레이션 방법을 제시하고 이를 실제에 적용하여 방법의 유용성을 보이고자 한다. 아울러 실험을 병행하여 결과를 비교함으로써 해석결과의 신뢰성을 검토한다.

• Structural Engineering and Mechanics
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• 제45권6호
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• pp.759-777
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• 2013

In this paper, a topology optimization method based on the element independent nodal density (EIND) is developed for continuum solids with multiple load cases and multiple constraints. The optimization problem is formulated ad minimizing the volume subject to displacement constraints. Nodal densities of the finite element mesh are used a the design variable. The nodal densities are interpolated into any point in the design domain by the Shepard interpolation scheme and the Heaviside function. Without using additional constraints (such ad the filtering technique), mesh-independent, checkerboard-free, distinct optimal topology can be obtained. Adopting the rational approximation for material properties (RAMP), the topology optimization procedure is implemented using a solid isotropic material with penalization (SIMP) method and a dual programming optimization algorithm. The computational efficiency is greatly improved by multithread parallel computing with OpenMP to run parallel programs for the shared-memory model of parallel computation. Finally, several examples are presented to demonstrate the effectiveness of the developed techniques.

• Structural Engineering and Mechanics
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• 제55권1호
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• pp.29-46
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• 2015

A three-dimensional (3-D) method of analysis is presented for determining the natural frequencies of a truncated shallow and deep conical shell with linearly varying thickness along the meridional direction free at its top edge and clamped at its bottom edge. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components $u_r$, $u_{\theta}$, and $u_z$ in the radial, circumferential, and axial directions, respectively, are taken to be periodic in ${\theta}$ and in time, and algebraic polynomials in the r and z directions. Strain and kinetic energies of the truncated conical shell with variable thickness are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four-digit exactitude is demonstrated. The frequencies from the present 3-D method are compared with those from other 3-D finite element method and 2-D shell theories.

• 한국전산구조공학회논문집
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• 제17권2호
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• pp.183-192
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• 2004

본 논문에서는 수직으로 시추된 해양 파일에 대한 새로운 동적 해석절차가 제안되고 전형적 설계문제에 의하여 검증된다. 해수에 잠긴 파일의 구조는 물론 해양파도와 조류에 의한 힘도 유한요소법에 의해서 정식화되고 모델링된다. 유한요소 방정식에 적합한 파력을 구하기 위해서 여러 가지 파도이론 가운데서도 Airy의 파도이론이 시험되고 선정되었다. 조류의 후방와류에 기인한 횡방향 양력은 Strouhal 진동수와 적절한 양력계수를 가진 간단한 조화함수에 기초한다 파일에 대한 고유진동수 해석과 주파수 응답해석은 정식화 결과를 NASTRAN에 입력하여 계산되었다. 여기서 제안된 절차에 의해 얻어진 동적 변위와 응력의 결과는 기본설계해석 단계로서 해양파일의 파력과 조류 양력에 의한 동적거동을 구할 수 있으며 설계에 응용될 수 있음을 보여준다

• Smart Structures and Systems
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• 제13권1호
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• pp.55-80
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• 2014

The present work pays emphasis on investigating the effect of different types of debonding on the bending behaviour of active sandwich beam, consisting of both extension and shear actuators. An active sandwich beam finite element is formulated by using Timoshenko's beam theory, characterized by first order shear deformation for the core and Euler-Bernoulli's beam theory for the top and bottom faces. The problem of debondings of extension actuator and face are dealt with by employing four-region model for inner debonding and three-region model for the edge debonding respectively. Displacement based continuity conditions are enforced at the interfaces of different regions using penalty method. Firstly, piezoelectric actuation of healthy sandwich beam is assessed through deflection analysis. Then the effect of actuators' debondings with different boundary conditions on bending behavior is computationally evaluated and experimentally clamped-free case is validated. The results generated will be useful to address the damage tolerant design procedures for smart sandwich beam structures with structural control and health monitoring applications.

• Structural Engineering and Mechanics
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• 제73권1호
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• pp.17-25
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• 2020

A finite element (FE) model for analyzing slender reinforced high-strength concrete (HSC) columns under biaxial eccentric loading is formulated in terms of the Euler-Bernoulli theory. The cross section of columns is divided into discrete concrete and reinforcing steel fibers so as to account for varied material properties over the section. The interaction between axial and bending fields is introduced in the FE formulation so as to take the large-displacement or P-delta effects into consideration. The proposed model aims to be simple, user-friendly, and capable of simulating the full-range inelastic behavior of reinforced HSC slender columns. The nonlinear model is calibrated against the experimental data for slender column specimens available in the technical literature. By using the proposed model, a numerical study is carried out on pin-ended slender HSC square columns under axial compression and biaxial bending, with investigation variables including the load eccentricity and eccentricity angle. The calibrated model is expected to provide a valuable tool for more efficiently designing HSC columns.

• 대한조선학회논문집
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• 제28권2호
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• pp.307-317
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• 1991

선체구조 및 해양구조물의 기본 구조요소로 사용되는 편심으로 보강된 평판이나 쉘 수조물의 기하하적 비선형 해석에 관한 논문으로서 사용된 유한요소는 격하 쉘요소와 편심된 격하보요소이며 total Lagrange(T.L.)수식과 updated Lagrange(U.L.)수식으로 정식화 하였다. 편심된 보강평판의 비선형 해석에서 사용된 모델은 보강재의 이상화 방법에 따라 평판과 보강재를 격하 쉘요소로 이상화한 모델과 평판은 격하 쉘요소로하고 보강재는 편심된 격하 보요소로 이상화한 모델로 각각 구분하여 비선형 해석을 수행하였으며 해석과정에서 편심 보강평판의 임계하중을 구하고 좌굴 후 비선형 거동을 조사하였다. 해석된 임계 좌굴하중은 선급에서 규정하고 있는 방식의 오일러의 좌굴하중값 보다는 낮게 조사되었다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.279-283
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• 2004

Thermal postbuckling and vibration analyses of functionally graded plates (FG plates) are performed. The nonlinear finite element equation based on the first-order shear deformation plate theory is formulated for the FG plate. The von Karman strain-displacement relation is used to account for the thermal large deflection. The incremental method considering the effect of the initial deflection and the initial stress is adopted for temperature-dependent material properties of functionally graded materials. The numerical result shows characteristics of the thermal postbuckling and vibration of FG plates in the pre- and post- buckled regions.