• Structural Monitoring and Maintenance
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• 제5권3호
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• pp.379-390
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• 2018

In this paper, a novel and effective damage diagnosis algorithm is proposed to detect and estimate damage using two stages least squares support vector machine (LS-SVM) and limited number of attached sensors on structures. In the first stage, LS-SVM1 is used to predict the unmeasured mode shapes data based on limited measured modal data and in the second stage, LS-SVM2 is used to predicting the damage location and severity using the complete modal data from the first-stage LS-SVM1. The presented methods are applied to a three story irregular frame and cantilever plate. To investigate the noise effects and modeling errors, two uncertainty levels have been considered. Moreover, the performance of the proposed methods has been verified through using experimental modal data of a mass-stiffness system. The obtained damage identification results show the suitable performance of the proposed damage identification method for structures in spite of different uncertainty levels.

• 한국기계가공학회지
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• 제20권6호
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• pp.26-32
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• 2021

The antenna is mounted on the vehicle and operated, so its components must be able to withstand the shock that may occur while driving. In this study, the stability of antenna mounted on the vehicle is verified through the connection between modal analysis and transient analysis. The shock data used was taken from MIL-STD-810H, METHOD 516.8. As a result of the analysis of antenna, the maximum equivalent stress 169.49MPa and minimum margin of safety 2.31 has occurred on the bracket of antenna. Thus, it was found that the antenna has enough stability during the operation.

• 소음진동
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• 제6권3호
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• pp.287-296
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• 1996

A virtual work form of flexible multibody dynamic formulation with rotary inertia has been derived. For the analysis of large flexible multibody systems, deformation modal coordinates have been employed to represent coupled motion between gross and vibrational motion. For the efficient evaluation of the entries in the mass matrix, a flexible body has been treated as a collection of mass points. The rotary inertia was generated from the consistent mass matrix in a finite element model. Deformation mode shapes were obtained from finite element analysis. Bending and twisting vibration analyses of a cantilever have been carried out to see rotary inertia effects. A space flexible robot simulation has been also carried out to show effectiveness of the proposed formulation. This formulation is effective to the model that consists of beam, plate, or shell element that contains rotational degree of freedom at the nodal point. It is also effective to the flexible body model to which a large lumped rotary inertia is attached.

• 대한기계학회논문집
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• 제10권3호
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• pp.383-391
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• 1986

본 논문에서는 이들 기본모우드형태가 검토되었고 또한 두께효과와 비대칭성 효과에 따른 고유진동주파수, 모우드형태, 울림주파수의 변화를 수치적 해석과 실험 적 해석방법에 의해 비교검토되었다. 수치해석방법은 유한요소법으로 이용된 프로그 램은 NASTRAN 프로그램이고 모우드의 형태는 Tectronics컴퓨터그래픽을 이용하여 나타 내었다. 실험적방법은 충격햄머법과 F.F.T. 분석장치(Fast Fourier Transformation Analyzer)를 이용하였다.

• 대한기계학회논문집A
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• 제29권3호
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• pp.387-394
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• 2005

Accurate predictions and simulations of the behavior of space structures based on analytical models become more important. In order to perform analysis to support the design of Ku-band transponder panel for the Communications and Broadcasting Satellite(CBS), mathematical models of the panel were generated in the form of finite element models. Test verification of these models is required before the transponder panel can be certified for launch environments. A modal identification was performed to obtain modal parameters which can be compared with the test results using correlation techniques. This paper approaches the sensor placement from the standpoint of the structural dynamicist who uses the modal parameter obtained during launch environmental test. The models were validated by performing a test-analysis correlation and updating analysis. It was proved that the Ku-band transponder panel satisfies the environmental test requirements.

• 한국소음진동공학회논문집
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• 제22권6호
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• pp.495-501
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• 2012

In this study, the natural frequencies and mode shape of an external mounting pod were verified using the modal analysis and modal testing technique for a pod mounted on an aircraft. The procedure associated with the FE model building of an external mounted pod to predict the dynamic behavior of aircraft structures is described. The simplified FE model reflecting the results of the modal testing of a pod is built through the optimization and will be applied to the structural dynamic model of an aircraft which is used to verified the stability of vibration and flutter of an aircraft.

• Journal of Biosystems Engineering
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• 제29권2호
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• pp.101-108
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• 2004

The objectives of this study were to determine the natural frequency of a walking-type cultivator's handle using a modal analysis, to determine whether or not the handle resonates with forcing frequency induced by its engine, and to determine a method to reduce the handle vibration using a technique of the operational deflection shapes(ODS). Results of the study are as follows: The natural frequencies of the handle up to third harmonics were found to be 20.4, 22.5 and 92.1 Hz in the vertical direction and 14.9, 93, and 132 Hz in the horizontal direction. It was found that the handle does not resonate with the forcing frequency of the engine, which is 52 Hz. The operational deflection shape analysis revealed the deflected shapes of the handle in the vertical and horizontal directions and suggested that the handle vibration can be reduced by adding some mass to the place where the largest deflection occurs. Attaching of 1.1 kg mass adjacent to the largely deflected area resulted in reductions of vibration from 9.45 to 8.03 m/s$^2$ in x-axis direction from 3.89 to 3.16 m/s$^2$ in y-axis direction and from 7.89 to 3.09 m/s$^2$ in z-axis direction, which are respectively 15, 19 and 61% reductions. The total vibration level was reduced by 29%, indicating that mass-adding method by the ODS is very effective for reducing the handle vibrations of the cultivators.

• Interaction and multiscale mechanics
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• 제3권4호
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• pp.321-331
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• 2010

A new technique is proposed for bridge structural damage detection based on spatial wavelet analysis of the time history obtained from vehicle body moving over the bridge, which is different from traditional detection techniques based on the bridge response. A simply-supported Bernoulli-Euler beam subjected to a moving spring-mass unit is established, with the crack in the beam simulated by modeling the cracked section as a rotational spring connecting two undamaged beam segments, and the equations of motion for the system is derived. By using the transfer matrix method, the natural frequencies and mode shapes of the cracked beam are determined. The responses of the beam and the moving spring-mass unit are obtained by modal decomposition theory. The continuous wavelet transform is calculated on the displacement time histories of the sprung-mass. The case study result shows that the damage location can be accurately determined and the method is effective.

• 한국소음진동공학회논문집
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• 제20권12호
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• pp.1168-1175
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• 2010

Excessive torsional vibrations from marine engine shafting systems can be reduced by using torsional vibration dampers. But in order to be tuned effectively, the dampers should be designed through the optimum design procedure. In this paper, the procedure to get the optimum values of system parameters of spring-viscous dampers using effective modal mass of inertia and stiffness is suggested and the damping is determined by the exact algebra optimization method. The validity of the suggested method is confirmed through the application to a 1800 kW four cycle diesel engine and generator system.

• Advances in aircraft and spacecraft science
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• 제10권3호
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• pp.223-243
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• 2023

There is a burgeoning demand for minimizing the mass of satellites because of its direct impact on reducing launch-to-orbit cost. This must be done without compromising the structure's efficiency. The present paper introduces a relatively low-cost and easily implementable approach for optimizing structural mass to a maximum natural frequency. The natural frequencies of the satellite are of utmost pertinence to the application requirements, as the sensitive electronic instrumentation and onboard computers should not be affected by the vibrations of the satellite structure. This methodology is applied to a realistic model of Al-Azhar University micro-satellite in partnership with the Egyptian Space Agency. The procedure used in structural design can be summarized in two steps. The first step is to select the most favorable primary structural configuration among several different candidate variants. The nominated variant is selected as the one scoring maximum relative dynamic stiffness. The second step is to use perforation patterns reduce the overall mass of structural elements in the selected variant without changing the weight. The results of the presented procedure demonstrate that the mass reduction percentage was found to be 39% when compared to the unperforated configuration that had the same plate thickness. The findings of this study challenge the commonly accepted notion that isogrid perforations are the most effective means of achieving the goal of reducing mass while maintaining stiffness. Rather, the study highlights the potential benefits of exploring a wider range of perforation unit cells during the design process. The study revealed that rectangular perforation patterns had the lowest efficiency in terms of modal stiffness, while triangular patterns resulted in the highest efficiency. These results suggest that there may be significant gains to be made by considering a broader range of perforation shapes and configurations in the design of lightweight structures.