• Geomechanics and Engineering
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• 제35권4호
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• pp.367-383
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• 2023

The present paper examines the natural frequency responses of the bi-directional (n_x-n_y, n_y-n_z and n_z-n_x) and multidirectional (n_x-n_y-n_z) functionally graded (FG) plate and curved structures with and without porosity. The even and uneven kind of porosity pattern are considered to observe the influence of porosity type and porosity index. The numerical findings have been obtained using a higher order shear deformation theory (HSDT) based isometric finite element (FE) approach generated in a MATLAB platform. According to the convergence and validation investigation, the proposed HSDT based FE model is adequate to predict free vibrational responses of multidirectional porous FG plates and curved structures. Further a parametric analysis is carried out by taking various design parameters into account. The free vibrational behavior of bidirectional (2D) and multidirectional (3D) perfect-imperfect FGM structure is examined against various power law index, support conditions, aspect, and thickness ratio, and for the curvature of curved structures. The results indicate that the maximum non-dimensional fundamental frequency (NFF) value is observed in perfect FGM plates and curved structures compared to porous FGM plates and curved structures and it is maximum for FGM plates and curved structures with uneven kind of porosity than even porosity.

• Structural Engineering and Mechanics
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• 제88권1호
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• pp.83-94
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• 2023

An accurate and highly efficient inverse element labelled iPCB is developed based on the inverse finite element method (iFEM) for real-time shape estimation of plane-curved structures (such as arch bridges) utilizing onboard strain data. This inverse problem, named shape sensing, is vital for the design of smart structures and structural health monitoring (SHM) procedures. The iPCB formulation is defined based on a least-squares variational principle that employs curved Timoshenko beam theory as its baseline. The accurate strain-displacement relationship considering tension-bending coupling is used to establish theoretical and measured section strains. The displacement fields of the isoparametric element iPCB are interpolated utilizing nonuniform rational B-spline (NURBS) basis functions, enabling exact geometric modelling even with a very coarse mesh density. The present formulation is completely free from membrane and shear locking. Numerical validation examples for different curved structures subjected to different loading conditions have been performed and have demonstrated the excellent prediction capability of iPCBs. The present formulation has also been shown to be practical and robust since relatively accurate predictions can be obtained even omitting the shear deformation contributions and considering polluted strain measures. The current element offers a promising tool for real-time shape estimation of plane-curved structures.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.101-109
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• 2004

Ship structures is thin-walled structures and she has lots of curved platings. In these days, lots different kinds of closed-formulas are development for ultimate strength of flat plate but for curved panels, there are not enough study or papers for this field. In this study, the ultimate strength characteristics for ship curved plates are studied. The ship plating is generally subjected to combined in-plane and lateral pressure loads. In-plane loads included biaxial compression/tension and edge shear. This is first report about the developing of ultimate compressive strength for ship curved plating. A closed-form formula for predicting the ultimate compressive strength of curved plates are empirically derived by curve fitting based on the computed results. The results and insights developed in the present study will be useful for damage tolerant design of curved plated structures.

• 한국공간구조학회논문집
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• 제17권3호
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• pp.45-55
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• 2017

The objective of this study is to estimate the mechanical characteristics and nonlinear behaviors on the geometric nonlinear analysis of curved cable-membrane roof systems for long span lightweight roof structures. The weight of a cable-membrane roof dramatically can reduce, but the single layer cable-membrane roof systems are too flexible and difficult to achieve the required structural stiffness. A curved cable roof system with reverse curvature works more effectively as a load bearing system, the pretension of cables can easily increase the structural stiffness. The curved cable roof system can transmit vertical loads in up and downward direction, and work effectively as a load bearing structure to resists self-weights, snow and wind loads. The nonlinear behavior and mechanical characteristics of a cable roof system has greatly an affect by the sag and pretension. This paper is carried out analyzing and comparing the tensile forces and deflection of curved roof systems by vertical loads. The elements for analysis uses a tension only cable element and a triangular membrane element with 3 degree of freedom in each node. The authors will show that the curved cable-membrane roof system with reverse curvature is a very lightweight and small deformation roof for external loads.

• Steel and Composite Structures
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• 제39권1호
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• pp.1-20
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• 2021

An exact solution based on refined third-order theory (TOT) has been presented for functionally graded porous curved beams having deep curvature. The displacement field of the refined TOT is derived by imposing the shear free conditions at the outer and inner surfaces of curved beams. The properties of the two phase composite are tailored according the power law rule and the effective properties are computed using Mori-Tanaka homogenization scheme. The equations of motion as well as consistent boundary conditions are derived using the Hamilton's principle. The curved beam stiffness coefficients (A, B, D) are obtained numerically using six-point Gauss integration scheme without compromising the accuracy due to deepness (1 + z/R) terms. The porosity has been modeled assuming symmetric (even) as well as asymmetric (uneven) distributions across the cross section of curved beam. The programming has been performed in MATLAB and is validated with the results available in the literature as well as 2D finite element model developed in ABAQUS. The effect of inclusion of 1 + z/R terms is studied for deflection, stresses and natural frequencies for FG curved beams of different radii of curvature. Results presented in this work will be useful for comparison of future studies.

• 대한토목학회논문집
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• 제8권2호
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• pp.227-238
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• 1988

본 논문에서는 인터체인지나 램프시설 등에서 볼 수 있는 공간 곡선부재들을 나선형 곡선부재로 이상화시켰다. 나선의 기하학적 특성치와 초기 곡률을 고려하여 평형방정식을 유도하였으며 모우드 형상함수를 가정하여 단순지지된 나선형 곡선부재의 규준화된 고유진동수를 계산할 수 있는 모우드 방정식을 유도하였다. 이러한 모우드 방정식을 이용하여 나선형 곡선부재의 고유진동수, 모우드 형상 그리고 고유진동수의 분포를 규명하였다.

• Steel and Composite Structures
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• 제26권5호
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• pp.607-620
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• 2018

Vibration analysis of deep curved FG nano-beam has been carried out based on modified couple stress theory. Material properties of curved Timoshenko beam are assumed to be functionally graded in radial direction. Governing equations of motion and related boundary conditions have been obtained via Hamilton's principle. In a parametric study, influence of length scale parameter, aspect ratio, gradient index, opening angle, mode number and interactive influences of these parameters on natural frequency of the beam, have been investigated. It was found that, considering geometrical deepness term leads to an increase in sensitivity of natural frequency about variation of aforementioned parameters.

• 대한토목학회논문집
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• 제8권2호
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• pp.215-225
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• 1988

인터체인지나 램프시설과 같은 구조물은 일정한 나선기울기를 갖는 나선형 곡선부재로 이상화시킬 수 있다. 이러한 나선형 곡선부재의 정적 및 자유진동 해석을 하기 위해 7차 hermite 형상함수를 이용한 유한요소 모델을 제시하였다. 다른 유한요소를 이용한 기존연구결과와 비교하여 나선형 유한요소는 적은수의 유한 요소로서, 보다 더 정확한 결과를 보였으며 직선 부재, 원형곡선 부재등에도 적용할 수 있음을 보였다.

• 한국공간구조학회논문집
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• 제7권1호
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• pp.55-62
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• 2007

곡선보의 고유진동수를 측정하기 우하여 이론적인 해석과 실험 및 유한요소법해석을 실시하였다. 본 논문에서는 모우드해석을 위한 실험에서 얻어지는 결과로부터 곡선보의 동특성의 하나인 고유진동수를 구하였다 먼저, 이론식을 통해 구조물의 동특성을 파악하고, 유한요소해석과 실험에 의한 결과를 비교 검토하여 구조물의 동적해석에 있어서 모우드해석법의 적용성을 보였다.

• 한국인터넷방송통신학회논문지
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• 제16권6호
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• pp.239-242
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• 2016

본 논문에서는 이중 곡률을 갖는 오목 렌즈를 제안하였다. 이중 곡률 렌즈는 HDPE (High Density Polyethylene)를 이용하여 제작하였다. 이중 곡률 렌즈는 두 개의 오목 구조로 구성되었다. 두 개의 오목 구조의 역할은 빔을 균일하게 넓게 보내기 위함이다. 작은 오목 구조는 큰 오목 구조 보다 더 큰 곡률 반경을 갖는다. 이러한 이중 곡률 렌즈는 밀리미터파 이미징 시스템에 적용 가능하다. 제작된 이중 곡률 렌즈를 250 GHz VDI 소스를 이용하여 검증하였다. 광학 시뮬레이션 툴인 ZEMAX를 이용하여 설계하고 제작된 렌즈는 균일한 빔과 확장 성능을 충분히 수행함을 확인하였다.