• Steel and Composite Structures
• /
• 제35권5호
• /
• pp.671-685
• /
• 2020

This manuscript presents impacts of gradation of material functions and axial load functions on critical buckling loads and mode shapes of functionally graded (FG) thin and thick beams by using higher order shear deformation theory, for the first time. Volume fractions of metal and ceramic materials are assumed to be distributed through a beam thickness by both sigmoid law and symmetric power functions. Ceramic-metal-ceramic (CMC) and metal-ceramic-metal (MCM) symmetric distributions are proposed relative to mid-plane of the beam structure. The axial compressive load is depicted by constant, linear, and parabolic continuous functions through the axial direction. The equilibrium governing equations are derived by using Hamilton's principles. Numerical differential quadrature method (DQM) is developed to discretize the spatial domain and covert the governing variable coefficients differential equations and boundary conditions to system of algebraic equations. Algebraic equations are formed as a generalized matrix eigenvalue problem, that will be solved to get eigenvalues (buckling loads) and eigenvectors (mode shapes). The proposed model is verified with respectable published work. Numerical results depict influences of gradation function, gradation parameter, axial load function, slenderness ratio and boundary conditions on critical buckling loads and mode-shapes of FG beam structure. It is found that gradation types have different effects on the critical buckling. The proposed model can be effective in analysis and design of structure beam element subject to distributed axial compressive load, such as, spacecraft, nuclear structure, and naval structure.

• Structural Engineering and Mechanics
• /
• 제76권2호
• /
• pp.223-237
• /
• 2020

Transmission towers have come to represent one of the most important infrastructures in today's society, which may suffer severe earthquakes during their service lives. However, in the conventional seismic analyses of transmission towers, the towers are normally assumed to be fixed on the ground without considering the effect of soil-structure interaction (SSI) on the pile-supported transmission tower. This assumption may lead to inaccurate seismic performance estimations of transmission towers. In the present study, the seismic response and failure analyses of pile-supported transmission towers considering SSI are comprehensively performed based on the finite element method. Specifically, two detailed finite element (FE) models of the employed pile-supported transmission tower with and without consideration of SSI effects are established in ABAQUS analysis platform, in which SSI is simulated by the classical p-y approach. A simulation method is developed to stochastically synthesize the earthquake ground motions at different soil depths (i.e. depth-varying ground motions, DVGMs). The impacts of SSI on the dynamic characteristic, seismic response and failure modes are investigated and discussed by using the generated FE models and ground motions. Numerical results show that the vibration mode shapes of the pile-supported transmission towers with and without SSI are basically same; however, SSI can significantly affect the dynamic characteristic by altering the vibration frequencies of different modes. Neglecting the SSI and the variability of earthquake motions at different depths may cause an underestimate and overestimate on the seismic responses, respectively. Moreover, the seismic failure mode of pile-supported transmission towers is also significantly impacted by the SSI and DVGMs.

• 한국구조물진단유지관리공학회 논문집
• /
• 제18권3호
• /
• pp.101-107
• /
• 2014

구조물의 손상 추정은 동적응답신호로부터 고유주기와 모드형상을 구한 후 이를 역해석하여 손상위치와 손상정도를 파악함으로써 이루어 진다. 건축구조물의 경우 토목구조물에 비하여 구조형식이 복잡하고 비구조요소 및 노이즈 등의 영향으로 인하여 구조물 판별에 어려움이 있다. 동적응답신호를 이용한 건물의 손상추정에 관한 최근의 연구들은 손상추정을 위하여 민감도 또는 추정치 등 간접적 지표를 사용하고 있으나, 좀 더 합리적이고 명확한 손상추정을 위하여 운동방정식으로부터 직접 유도된 변수를 손상지수로 활용할 필요가 있을 것으로 판단된다. 따라서 본 연구에서는 전단형 건물의 운동방정식으로부터 직접 유도된 층강성 감소비를 손상지수로 하는 손상추정 방법을 제안하였다. 제안된 손상지수는 손상 전 모드형상과 손상 전 후 고유진동수 차이를 알면 구할 수 있다. 제안된 손상 추정방법을 수치해석예제에 적용한 결과 손상이 발생한 층에서 층강성 변화율이 (-)부호를 나타내었으며, 크기가 다른 층에 비하여 15배 정도 크게 나타나 전단형 건물의 손상 추정지수로서 활용될 수 있을 것으로 판단된다.

• 대한토목학회논문집
• /
• 제28권6D호
• /
• pp.801-807
• /
• 2008

본 연구는 시간-면적 방법론을 적용하여 도시교통수단의 토지소모 효율성을 비교분석하고자 하였다. 도시의 주요 교통수단을 대상으로 그간의 연구와 달리 각 수단에 적합한 교통조건과 운행여건을 고려한 토지소모효율성 산정식을 도출하였고, 도출된 식을 이용하여 각 수단별 1km 통행시의 인당 시간-면적 소모량을 계산하여 비교하였다. 또한 산정식을 이용하여 소모량과 운행속도와의 관계를 분석하여 각 수단의 소모량의 범위를 비교하였으며, 주차에 의한 시간-면적 소모량을 명확히 제시하기 위해 외곽으로부터 도심으로 통행하는 통근자의 가상 왕복통행을 가정하여 수단별 통행에 따른 총 시간-면적소모량을 비교분석하였다. 연구의 결과, 이용시설에 상관없이 승용차 이용자가 가장 소모량이 많은 것으로 나타났고, 도시철도를 포함한 대중교통수단의 효율성이 우수한 것으로 나타났다. 예상과는 달리 도보와 자전거는 높은 소모량을 보였다. 그럼에도 불구하고 단거리 통행시 버스를 대체할 수 있는 수단으로 나타났다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2005년도 춘계학술대회 논문집
• /
• pp.1640-1643
• /
• 2005

This paper presents analysis of dynamic characteristics of a high-speed milling spindle with a drawbar and a built-in motor. The spindle system with a built-in motor can be used to simplify the structure of machine tools, to improve the machining flexibility of machine tools, and to perform the high speed machining. In this system the shaft is usually assumed as a rigid rotor. In this paper, the modal characteristics of drawbar in high-speed milling spindle system due to supporting stiffness between drawbar and shaft and considering the mass and stiffness effects of the built-in motor's rotor are analyzed by numerical method. The result shows enough stiff supports must be provided between shaft and drawbar to prevent occurring drawbar vibration lower than the natural frequency of 1st bending mode of spindle. And considering the mass and stiffness of built-in motor's rotor is important thing to derive more accurate results.

• 한국정밀공학회지
• /
• 제16권12호
• /
• pp.126-132
• /
• 1999

The paper presents the modeling and optimal control for the reduction of transverse vibration of simply supported beam under a moving mass. The equations of motion are derived by using assumed mode method. The coriolis and centripetal accelerations are accommodated in the equations of motion to account for the dynamic effect of the traveling mass. In order to reduce the transverse vibration of the beam, an optimal controller with full state feedback is designed based on the linearized equations of motion. The optimal actuator locations are determined with the evaluation of an optimal cost functional defined by the worst initial condition with the trade-off of controlled mode performance. Numerical simulations are performed with respect to various velocities and different traveling masses. Even if the velocity of the traveling mass reaches to the critical speed which can cause the resonance of the beam, the controller with two piezoelectric actuators shows the excellent performance under severe time-varying disturbances of the system.

• Nuclear Engineering and Technology
• /
• 제31권2호
• /
• pp.202-213
• /
• 1999

Effects of the rotary inertia of concentrated masses on the natural vibrations of fluid conveying pipes have been studied by theoretical modeling and computer simulation. For analysis, two boundary conditions for pipe ends, simply supported and clamped-clamped, are assumed and Galerkin's method is used for transformation of the governing equation to the eigenvalues problem and the natural frequencies and mode shapes for the system have been calculated by using the newly developed computer code. Moreover, the critical velocities related to a system instability have been investigated. The main conclusions for the present study are (1) Rotary inertia gives much change on the higher natural frequencies and mode shapes and its effect is visible when it has small value, (2) The number and location of nodes can be changed by rotary inertia, (3) By introducing rotary inertia, the second natural frequency approaches to the first as the location of the concentrated mass approaches to the midspan of the pipe, and (4) The critical fluid velocities to initiate the system unstable are unchanged by introduction of rotary inertia and the first three velocities are $\pi$, 2$\pi$, and 3$\pi$ for the simply supported pipe and 2$\pi$, 8.99, and 12.57 for the clamped-clamped pipe.

• Earthquakes and Structures
• /
• 제15권4호
• /
• pp.411-417
• /
• 2018

To solve the seismic response problem of a vertical floating roof tank with base isolation, the floating roof is assumed to experience homogeneous rigid circular plate vibration, where the wave height of the vibration is linearly distributed along the radius, starting from the theory of fluid velocity potential; the potential function of the liquid movement and the corresponding theoretical expression of the base shear, overturning the moment, are then established. According to the equivalent principle of the shear and moment, a simplified mechanical model of a base isolation tank with a swinging effect is established, along with a motion equation of a vertical storage tank isolation system that considers the swinging effect based on the energy principle. At the same time, taking a 150,000 m 3 large-scale storage tank as an example, a numerical analysis of the dampening effect was conducted using a vibration mode decomposition response spectrum method, and a comparative analysis with a simplified mechanical model with no swinging effect was applied.

• 한국소음진동공학회논문집
• /
• 제15권5호
• /
• pp.620-628
• /
• 2005

In this paper, we studied about the dynamic behavior of a cracked rotating cantilever beam. The influences of a rotating angular velocity, the crack depth and the crack position on the dynamic behavior of a cracked cantilever beam have been studied by the numerical method. The equation of motion is derived by using the Lagrange's equation. The cracked cantilever beam is modeled by the Euler-Bernoulli beam theory. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The lateral tip-displacement and the axial tip-deflection of a rotating cantilever beam is more sensitive to the rotating angular velocity than the depth and position of crack. Totally, as the crack depth is increased, the natural frequency of a rotating cantilever beam is decreased in the first and second mode of vibration. When the crack depth is constant, the natural frequencies of a rotating cantilever beam are proportional to the rotating angular velocity in the each direction.

• 한국통신학회논문지
• /
• 제14권2호
• /
• pp.155-163
• /
• 1989

단일 링크 유연성 로보트 팔의 제어를 위해서 가정 모드 방법으로 유도된 동 특성 모델링에 QUADRATIC-최적제어 이론을 적용하였다. 이 제어 기법에 대한 제어 루우프 구성에는 모든 상태값의 피이트 백을 필요로 하지만 유연성 팔에 있어서 모드형태의 시 종속 변화율은 직접 출력으로부터 피이드백 될수 없기 때문에 최적 제어기를 실현하기 위해서는 상태 추정기의 도입이 필요하게 된다. 특히 시스템에 외란이나 측정에 노이즈가 발생할 때는 확률 추정 방법을 적용해서 상태를 추정해야 하는데 이를 위해서 칼만 필터를 사용하였다. 상태 추정기를 이용한 유연성 메니퓨레이터 팔의 시스템 모델을 모든 상태 값이 직접 측정될 수 있다고 가정한 유연성 시스템 모델과 시뮤레이션을 통해서 비교하였다.