• 대한기계학회논문집A
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• 제23권11호
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• pp.2058-2066
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• 1999

The present paper proposes a new dynamic analysis method for multi-span Timoshenko beam structures supported by joints with damping subject to moving loads. An exact dynamic element matrix method is adopted to model Timoshenko beam structures. A generalized modal analysis method is applied to derive response formulae for beam structures subject to moving loads. The proposed method offers an exact and closed form solution. Two numerical examples are provided for validating and illustrating the proposed method. In the first numerical example, a single span beam with multiple moving loads is considered. A dynamic analysis on a multi-span beam under a moving load is considered as the second example, in which the flexibility and damping of supporting joints are taken into account. The numerical study proves that the proposed method is useful for the vibration analysis of multi-span beam-hype structures by moving loads.

• Wind and Structures
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• 제38권3호
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• pp.215-229
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• 2024

Guyed mast structures exhibit characteristics such as high flexibility, low mass, small damping ratio, and large aspect ratio, leading to a complex wind-induced vibration response mechanism. This study analyzed the time- and frequency-domain characteristics of the wind-induced response of a guyed mast structure using measured acceleration response data obtained from the Shenzhen Meteorological Gradient Tower (SZMGT). Firstly, 734 sets of 1-hour acceleration samples measured from 0:00 October 1, 2021, to 0:00 November 1, 2021, were selected to study the vibration shapes of the mast and the characteristics of the generalized extreme value (GEV) distribution. Secondly, six sets of typical samples with different vibration intensities were further selected to explore the Gaussian property and modal parameter characteristics of the mast. Finally, the modal parameters of the SZMGT are identified and the identification results are verified by finite element analysis. The findings revealed that the guyed mast vibration shape exhibits remarkable diversity, which increases nonlinearly along the height in most cases and reaches a maximum at the top of the tower. Moreover, the GEV distribution characteristics of the 734 sets of samples are closer to the Weibull distribution. The probability distribution of the structural wind vibration response under strong wind is in good agreement with the Gaussian distribution. The structural response of the mast under wind loading exhibits multiple modes. As the structural response escalates, the first three orders of modal energy in the tower display a gradual increase in proportion.

• 대한기계학회논문집A
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• 제21권3호
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• pp.423-429
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• 1997

A simplified method for determining the mode components of the strain energy release rate of free-edge delaminations in laminated composite is proposed. The interlaminar stresses are evaluated as an interface moment and interface shear forces that are obtained from the equilibrium equations at the interface between the adjacent layers. Deformation of an edge-delaminated laminate is calculated by using a generalized quasi-three dimensional classical laminated plate theory developed by the authors. The analysis provides closed-form expression for the three components of the strain energy release rate. Comparison of results with a finite element solution using the virtual crack closure technique shows good agreement. In the present study, laminated composite with stacking sequences of [30/-30/90]$_{s}$ were examined. The simple nature of the method makes it suitable for primary design analysis for the delaminations of laminated composite.e.

• Journal of Mechanical Science and Technology
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• 제15권6호
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• pp.693-698
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• 2001

The analysis of actuating forces (or torques) and joint reaction forces (or moments) are essential to determine the capacity of actuators, to control the system and to design the components. This paper presents an inverse dynamic analysis algorithm for flexible multibody systems with closed-loops in the relative joint coordinate space. The joint reaction forces are analyzed in Cartesian coordinate space using the inverse velocity transformation technique. The joint coordinates and the deformation modal coordinates are used as the generalized coordinates of a flexible multibody system. The algorithm is verified through the analysis of a slider-crank mechanism.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.838-843
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• 2001

Internal damping plays an important role in some rotor dynamic systems with the use of various materials for shafts, for example, composite material. However, although the effects of internal damping have been investigated for a couple of decades, there are several different internal damping models in use, none of which are accepted as the most reliable model. The purpose of this paper is to compare the results of dynamic analysis of rotor systems with several different internal damping models. The exact dynamic element method is used to formulate and analyze the problem. The simulation results provided in this paper may be useful for the dynamic analysis of high rotor systems subject to significant internal damping.

• 한국전자파학회논문지
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• 제11권3호
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• pp.464-473
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• 2000

The method is presented which predicts voltage waveforms at each nodes inter-connected arbitrarily on the coupled transmission lines by extracting the node connection condition to be included in the modal telegrapher's equation, hence analyzing the mechanism of waveform propagation on transmission lines. It is shown that it is also possible to analyze efficiently the coupled nonuniform lines. And then the nonuniformity of coupled lines is demonstrated for suppressing the crosstalk spikes using the one-dimensional inverse-scattering control theory. The predicted waveforms by presented method are analyzed and verified by comparison with those by the generalized S-parameter technique.

• 소음진동
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• 제2권4호
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• pp.305-315
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• 1992

In order to investigate the effects of layer-wise in-plane displacements on vibration and damping characteristics of composite laminated plates, the finite element method based on the generalized laminated plate theory(GLPT) has been formulated. Specific damping capacity of each mode was obtained by modal strain energy method. To see the effect of transverse shear on deformation, the strain energy of stress components was computed. The accuracy of this study was examined for the cylindrical bending vibration of cross-ply plate strip. The results were very accurate compared with 3-D solutions. The numerical results show that through-thickness variation of in-plane displacements has not so much influence on the natural frequency, but has a great influence on the damping of composite plates, especially on the damping of thick composite plates since the damping is affected by local behavior while the natural frequency is affected by global behavior.

• 한국소음진동공학회논문집
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• 제19권2호
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• pp.200-207
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• 2009

Complex systems are made of many subsystems, those are developed and manufactured by many part companies. Even though the information for a part is necessary to analyze the performance of the other part, it is not so easy to get the information for that part from other companies due to many reasons like security or compatibilities. If the modal parameters of a system between the connecting points are available, we can reconstruct a reduced model for that system in a physical coordinate not in a generalized coordinate. The assemble of the equations of motion for the main system and the reduced equations of motion for the connected system can give a response of the main system considering the effects of connected systems. The results show that the proposed method can give the response of a system accurately. The rule for the selection of modes is to use the fundamental modes whose natural frequencies are low.

• 대한기계학회논문집
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• 제12권5호
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• pp.976-983
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• 1988

본 연구에서는 회전체 베어링계에 대한 불균형 응답 계산시 회전속도 의존성 을 손쉽게 고려할 수 있는 방법에 대해 논하고자 한다. 그 방법은 람다행렬(lamda matrix)을 도입하여, 회전속도 의존성을 지닌 고유치 문제를 회전속도 의존성이 없는 문제로 변환시킨 후 기존의 모우드 해석기법을 적용하여 불균형 응답특성을 알아내는 방법이다. 이때 베어링의 회전속도 의존성을 다항식(polynomial)으로 근사화할 수 있다는 기본 가정을 두었는데, 이러한 가정은 실제 베어링이 관심있는 회전수 영역에서 고차의 다항식으로 충분히 정확하게 근사화 될 수 있으므로 응용성을 크게 약화시키지 는 않는다. 특별히 회전속도 의존성이 자이로 효과(gyroscopic effect)에 의해서만 기인할 때는 여기서 제시하는 방법은 전혀 오차를 주지 않게 된다.

• Wind and Structures
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• 제11권2호
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• pp.153-178
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• 2008

Based on the empirical formulas for power spectra of generalized modal forces and local fluctuating wind forces in across-wind and torsional directions, the wind-induced lateral-torsional coupled response analysis of a representative rectangular tall building was conducted by setting various parameters such as eccentricities in centers of mass and/or rigidity and considering different torsional to lateral stiffness ratios. The eccentricity effects on the lateral-torsional coupled responses of the tall building were studied comprehensively by structural dynamic analysis. Extensive computational results indicated that the torsional responses at the geometric center of the building may be significantly affected by the eccentricities in the centers of mass and/or rigidity. Covariance responses were found to be in the same order of magnitude as the along-wind or across-wind responses in many eccentricity cases, suggesting that the lateral-torsional coupled effects on the overall wind-induced responses can not be neglected for such situations. The calculated results also demonstrated that the torsional motion contributed significantly to the total responses of rectangular tall buildings with mass and/or rigidity eccentricities. It was shown through this study that the framework presented in this paper provides a useful tool to evaluate the wind-induced lateral-torsional coupled responses of rectangular buildings, which will enable structural engineers in the preliminary design stages to assess the serviceability of tall buildings, potential structural vibration problems and the need for a detailed wind tunnel test.