• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.184-191
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• 1997

A method, termed as the substructural sensitivity synthesis method, which utilizes the computational merits of the component mode synthesis technique is proposed to calculate design sensitivity of modal parameters of substructurally combined structures. In this method, the sensitivity analysis is combined with component mode synthesis thchnique. thus the degrees of freedom of a combined structure can be dramatically reduced. Free-interface mode method including the residual attachment modes among the component mode synthesis methods is used to calculate the modal sensitivity of the combined structure. For the design sensitivities of modal properties of structure, the Nelson's method, which is exact solving method is used. It is shown that the modal sensitivities of the entire structure can be obtained by synthesizing the substructural modal data, and the sensitivities of the modal data about the design variables of modifiable substructure. Using the proposed method, the final degrees of freedom of entire structure can be remarkably reduced to calculate the modal parameter sensitivities. With a structure composed of beams and plates, as an example, the sensitivities of the eigenvalues and eigenvectors obtained by this proposed method were compared with the exact solutions in terms of accuracy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.9 s.90
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• pp.801-810
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• 2004

Parameter modification of a linear finite element model(FEM) based on modal sensitivity matrix is usually performed through an effort to match FEM modal data to experimental ones. However, there are cases where this method can't be applied successfully; lack of reliable modal data and ill-conditioning of the modal sensitivity matrix constitute such cases. In this research, a novel concept of introducing feedback loops to the conventional modal test setup is proposed. This method uses closed-loop natural frequency data for parameter modification to overcome the problems associated with the conventional method based on modal sensitivity matrix. We proposed the whole procedure of parameter modification using the closed-loop natural frequency data including the modal sensitivity modification and controller design method. Proposed controller design method is efficient in changing modes. Numerical simulation of parameter estimation based on time-domain input/output data is provided to demonstrate the estimation performance of the proposed method.

• Journal of KSNVE
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• v.9 no.1
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• pp.163-173
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• 1999

Precise and reasonable modelling is necessary and indispensable to the analysis of dynamic characteristics of mechanical structures. Also. the effective prediction of the change of modal properties due to the variation of design parameters is required especially for the application of finite element method to the structural dynamics problems. To meet those necessity and requirement, three model updating algorithms are proposed for finite element methods. Those algorithms are based on sensitivity analysis of the modal data obtained from experimental modal analysis(EMA) and analytical modal analysis(AMA). The adapted sensitivity analysis methods of the algorithms are 1)eigensensitivity(EGNS) method. 2)frequency response function sensitivity(FRFS) method. 3)sensitivity based element-by-element method (SBEEM), Singular value decomposition(SVD) is used for performing eigenanalysis and parameter estimation in the updating process. Those algorithms are applied to finite element of a plate and the updating capability of each algorithm is compared in terms of accuracy. reliability and stability of the updating process. It is shown that the model updating method using frequency response function is superior to the other methods in view of various updating capabilities.

• Journal of Korean Society of Transportation
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• v.28 no.5
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• pp.117-129
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• 2010

This study presents a sensitivity analysis method for stochastic user equilibrium of multi-modal network flows. We consider a multi-modal network consisting of a road network for passenger cars physically separated from a transit network for public transport. We first establish a sensitivity analysis method with respect to arbitrary link parameters and perform a sensitivity analysis with respect to link capacity and transit line frequency as practical link parameters. Next, We establish a sensitivity analysis method and perform the sensitivity analysis with respect to modal split by passenger car and public transit. As with the elasticity of economics, these results can be important information for analyzing changes in travel behavior due to the changes in operation and policy of transportation facilities, as well as for analyzing the effects of these operational changes and policies. These results also can be utilized as a tool to constitute a multi-modal network design problem by using cooperative game theory.

• Journal of Korean Society of Steel Construction
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• v.12 no.1 s.44
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• pp.83-91
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• 2000

The first Procedure to identify structural system by using measured data is transformation of data to frequency domain and try to recognize modal characteristics in graphical condition. Those methods are doubted about the reliability to the civil structures, especially bridges which has coupled and close modal characteristics. In this paper, feasibility of time domain modal Identification methods were examined and applied double least square method to overcome bias characteristics of the identification methods. To show the advantage of proposed method, simulation were carried out for mass-spring model. And to examine the usage of the method in realistic case, sensitivity of the methods to noise was performed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.802-807
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• 2002

The updating of FE model to match it with the experimental results needs the modal information. There are two cases where this methodology is ill-equip to deal with； under-determined and ill-conditioning problem. The feedback exciter that uses the summation of the white noise and the signals from the measurement sensors multiplied with feedback gains can deal with these problems as the new modal data from the closed loop system generate more constraints the updating parameters should obey. The new modal data from the closed loop system should be different to enhance the condition of the modal sensitivity matrix. In this research, a guide for the selection of the sensor locations and the decision of the corresponding output feedback gains is proposed. This method is based on the sensitivity of the modal data with respect to the feedback gains. Through the proper selection of the exciter and sensor locations and the feedback gain, the eigenvalue sensitivity of the updating parameters which cause the ill-conditioning of the modal sensitivity matrix can be modified and consequently the error contamination in updating parameters are reduced.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.59-64
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• 2003

The parameter modification of the initial FEM model to match it with the experimental results needs the modal information and the modal sensitivity matrix to the parameter change. There are two cases this methodology is ill-equip to deal with; the deficiency of the necessary modal information and the ill-conditioning of the sensitivity matrix. In this research, a novel concept of the feedback exciter that uses the summation of the white noise and the signals from the measurement sensors multiplied with feedback gains as the reference signal is proposed. There are 2 advantages using this external feedback excitation. First, we can use the change of the system response such as modal data by the active energy Path from the sensor to the exciter. This change of the system response can be additional clues to the system dynamics that we want to know. Secondly, the external energy Path alternates the offset of the Parameter change to the system response. That means the modal sensitivity of the parameters becomes different from the original sensitivities by the feedback excitation. Through the feedback loop, we can change the similar modal sensitivities of some updating parameters and consequently discriminate the parameters using the closed-loop modal data. To demonstrate the discrimination performance, the parameter estimation of an indeterminate structure by use of the feedback method is introduced.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.530-533
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• 2004

It is well known that many real systems have asymmetric mass, damping and stiffness matrices. In this case, the method for calculating eigenpair sensitivity is different from that of symmetric system. To determine the derivatives of the eigenpairs in asymmetric damped case, a modal method was recently developed by Adhikari. When a dynamic system has many degrees of freedom, only a few lower modes are available, and because the higher modes should be truncated to use the modal method, the errors may become significant. In this paper a procedure for determining the sensitivities of the eigenpairs of asymmetric damped system using a few lowest set of modes is proposed. Numerical examples show that proposed method achieves better calculating efficiency and highly accurate results when a few modes are used.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.2
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• pp.129-137
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• 2000

In the prototype stage of a car developing program, the efficiency of trouble shooting is an important factor to be considered. Structural modifications by the design sensitivity analysis are applied to a steering wheel system for improving the idle vibration of the prototype passenger car. For the design sensitivity analysis, the experimental modal analysis for the steering system attached to a body-in-white is fulfilled and the modal parameters extracted from the experimental data are used to predict the effect of structural modification, The design sensitivity results rank the locations to be reinforced in terms of frequency variation. The modification of steering system according to the sensitivity analysis results shifted the resonant frequency of the system effectively. In addition, the idle test of the car after the structural modifications f steering system shows that the proposed method can reduce vibration of the steering wheel efficiently.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.12
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• pp.3782-3791
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• 1996

A great deal of effert has been invested in upgrading the performance and the efficiency of mechanical structures. Using experimental modal analysis(EMA) or finite element analysis(FEA) data of mechanical structures, this performance and efficiency can be effectively evaluated. In order to analyze complex structures such as automobiles and aircraft, for the sake of computing efficiency, the dynamic substructuring techniques that allow to predict the dynamic behavior of a structure based on that of the composing structures, are widely used. By llinking a modal model obtained from EMA and an analytical model obtained from FEA, the best conditioned structures can be desinged. In this paper, a new algorithm for structural dynamic modification-SRFSM (substructure response function sensitivity method) is proposed by linking frequency responce function synthesis and response function sensitivity. A mehtod to obtain response function sensitivity using direct derivative of mechanical impedance, is also used.