• Geomechanics and Engineering
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• 제14권6호
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• pp.519-532
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• 2018

In this work, two dimensional (2D) and quasi three-dimensional (quasi-3D) HSDTs are proposed for bending and free vibration investigation of functionally graded (FG) plates using hyperbolic shape function. Unlike the existing HSDT, the proposed theories have a novel displacement field which include undetermined integral terms and contains fewer unknowns. The material properties of the plate is inhomogeneous and are considered to vary continuously in the thickness direction by three different distributions; power-law, exponential and Mori-Tanaka model, in terms of the volume fractions of the constituents. The governing equations which consider the effects of both transverse shear and thickness stretching are determined through the Hamilton's principle. The closed form solutions are deduced by employing Navier method and then fundamental frequencies are obtained by solving the results of eigenvalue problems. In-plane stress components have been determined by the constitutive equations of composite plates. The transverse stress components have been determined by integrating the 3D stress equilibrium equations in the thickness direction of the FG plate. The accuracy of the present formulation is demonstrated by comparisons with the different 2D, 3D and quasi-3D solutions available in the literature.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.409-421
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• 2018

In the present paper, functionally graded (FG) materials are presented to investigate the bending analysis of simply supported plates. It is assumed that the material properties of the plate vary through their length according to the power-law form. The displacement field of the present model is selected based on quasi-3D hyperbolic shear deformation theory. By splitting the deflection into bending, shear and stretching parts, the number of unknowns and equations of motion of the present formulation is reduced and hence makes them simple to use. Governing equations are derived from the principle of virtual displacements. Numerical results for deflections and stresses of powerly graded plates under simply supported boundary conditions are presented. The accuracy of the present formulation is demonstrated by comparing the computed results with those available in the literature. As conclusion, this theory is as accurate as other shear deformation theories and so it becomes more attractive due to smaller number of unknowns. Some numerical results are provided to examine the effects of the material gradation, shear deformation on the static behavior of FG plates with variation of material stiffness through their length.

• Wind and Structures
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• 제22권4호
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• pp.429-454
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• 2016

In this paper, a shear deformation plate theory based on neutral surface position is developed for free vibration analysis of functionally graded material (FGM) plates. The material properties of the FGM plates are assumed to vary through the thickness of the plate by a simple power-law distribution in terms of the volume fractions of the constituents. During manufacture, defects such as porosities can appear. It is therefore necessary to consider the vibration behavior of FG plates having porosities in this investigation. The proposed theory is based on assumption that the in-plane and transverse displacements consist of bending and shear components, in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. The neutral surface position for a functionally graded plate which its material properties vary in the thickness direction is determined. The equation of motion for FG rectangular plates is obtained through Hamilton's principle. The closed form solutions are obtained by using Navier technique, and then fundamental frequencies are found by solving the results of eigenvalue problems. Numerical results are presented and the influences of the volume fraction index and porosity volume fraction on frequencies of FGM plates are clearly discussed.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2006년도 춘계종합학술대회
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• pp.957-960
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• 2006

본 논문에서는 2.45GHz대역 RTLS에서 2차원 평면 위치추정 알고리즘을 확장한 3차원 공간상의 위치추정 알고리즘을 연구하였으며, 태그의 송신시간 정보가 필요 없는 TDOA 기법을 이용하여 3차원 좌표를 추정하였다. 가로, 세로 300m의 탐색범위에서 시뮬레이터 구현을 통해 이차원 평면상의 쌍곡선 교점을 태그의 X, Y 좌표로 추정하였으며, 추정한 X, Y 좌표를 통해 Z 좌표를 최종적으로 추정하였다. RTLS 규격상 허용 오차 범위는 반경 3m 이내를 만족해야 하며, 실험결과 리더의 수신 옵셋이 이상적인 경우 태그의 3차원 위치는 실제 좌표와 근접함을 확인하였다. 수신옵셋이 32.76nsec 이내의 경우 옵셋의 차등적 증가시 RTLS 규격상의 반제 3m 이내의 오차범위를 벗어남을 확인하였다. 따라서 추후 연구를 통해 리더의 수신옵셋을 저감할 수 있는 기법이나 3차원 위치 추정시 적정 임계치 설정과 같은 판별 기법을 통해 위치 추정의 정확도를 향상시켜야 할 것으로 고려된다.

• 한국재난정보학회 논문집
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• 제19권3호
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• pp.572-581
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• 2023

연구목적:이력형 댐퍼에 하중이 작용할 때 편심에 의해서 부재가 면외 방향으로 거동하는 것을 방지하여 응력-변형율 곡선의 불규칙성을 개선하고 감쇠효과의 계산 시 정확성을 기하고자 하는 것이 본 연구의 목적이다. 연구방법:본 연구에서 사용하는 강재 스트립의 제원은 동일하게 하되 각각의 댐퍼를 구성할 스트립의 곡률은 다르게 한다. 곡률이 다른 각각의 강재 스트립을 댐퍼 1개당 3개씩 정삼각형으로 배치하여 곡률이 다른 5개의 댐퍼를 제작한 후 반복하중 실험을 수행하고, 에너지 소산량을 계산하여 댐퍼의 감쇠성능을 측정하였다. 연구결과: 시험 결과, 댐퍼 중에서 초기곡률이 조금이라도 있는 경우는 없는 경우보다 에너지 소산량은 상당히 감소하지만, 곡률의 크기에 따른 에너지 소산량의 변화는 크지 않으며, 곡률의 유무가 중요한 변수로 사료된다. 결론:댐퍼를 적용한 해석적 검토에서 주기는 T=0.3sec에서 T=0.536sec로 약 78.7% 정도 장주기화 되었고, 응답 스펙트럼 가속도는 Sa=0.54g에서 Sa =0.229g로 줄었으므로 댐퍼의 감쇠효과는 충분히 존재한다.