• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.864-869
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• 2004

A novel concept of feedback loop design for modal test and model updating is proposed. This method uses the closed -loop natural frequency information for parameter modification to overcome the problems associated with the conventional method employing the modal sensitivity matrix. To obtain new modal information from closed-loop system, controllers should be effective in changing modal data while guaranteeing the stability of closed-loop system. It is very hard to guarantee the stability of the closed-loop system with non-collocated sensor and actuator set. Ill this research, we proposed a controller called mode-decoupling controller that can change a target mode as much as the designer wants guaranteeing the stability of closed-loop system. This controller can be computed just using measured open-loop modeshape matrix. A simulation based on time domain input/output data is performed to check the feasibility of proposed control method.

• 한국공간구조학회논문집
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• 제2권2호
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• pp.59-67
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• 2002

In this study, a method that estimates stiffness and mass matrices of shear building from modal test data is presented. This method applied of building depends on the number of measurement points that are less in number than the total structural degrees of freedom, and on the first two orders of structural mode measured. By means of this method it is possible to use modal data of unmeasurable points to estimate total stiffness and mass matrices of structure. Some examples are studied in this paper, and its result shows that this method is reliable.

• 한국소음진동공학회논문집
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• 제14권10호
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• pp.955-961
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• 2004

A novel concept of feedback loop design for modal test and model updating is proposed. This method uses the closed-loop natural frequency information for parameter modification to overcome the problems associated with the conventional method employing the modal sensitivity matrix. To obtain new modal information from closed-loop system, controllers should be effective in changing modal data while guaranteeing the stability of closed-loop system. But it is very hard to guarantee the stability of the closed-loop system with non-collocated sensor and actuator set. In this research, we proposed a controller called mode-decoupling controller that can change a target mode as much as the designer wants guaranteeing the stability of closed-loop system. This controller can be computed Just using measured open-loop modeshape matrix. A simulation based on time domain input/output data is performed to check the feasibility of proposed control method.

• Structural Engineering and Mechanics
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• 제36권6호
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• pp.697-714
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• 2010

This paper presents an improved version of the Hilbert-Huang transform (HHT) for the modal evaluation of structural systems or signals. In this improved HHT, a well-designed bandpass filter is used as preprocessing to separate and determine each mode of the signal for solving the inherent modemixing problem in HHT (i.e., empirical mode decomposition, EMD, associated with the Hilbert transform). A screening process is then applied to remove undesired intrinsic mode functions (IMFs) derived from the EMD of the signal's mode. A "best" IMF is selected in each screening process that utilizes the orthogonalization coefficient between the signal's mode and its IMFs. Through mode-by-mode signal filtering, parameters such as the modal frequency can be evaluated accurately when compared to the theoretical value. Time history of the identified modal frequency is available. Numerical results prove the efficiency of the proposed approach, showing relative errors 1.40%, 2.06%, and 1.46%, respectively, for the test cases of a benchmark structure in the lab, a simulated time-varying structural system, and of a linear superimposed cosine waves.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.125-130
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• 2004

The vibration and buckling characteristics of the capsule for fuel irradiation test are studied. The natural frequencies of the capsule in air and under water are obtained by modal testing and finite element(FE) analysis using ANSYS program, and accelerations with flow are measured to estimate the compatibility with the operation requirement of the HANARO reactor. The experimental fundamental frequency of the capsule in the x and z direction is 8.5Hz and 8.75Hz in air, and 7.5Hz and 7.75Hz under water, respectively. The maximum amplitude of accelerations under the normal operating condition is measured as 11.0m/s$^2$ that is within the allowable vibrational limit(18.99m/s$^2$) of the reactor structure. Also, the maximum displacement at 100% flow is calculated as 0.13mm which is not interference with other nearby structures. FE analysis results show that the natural frequencies are found to be similar to those of the modal testing when three supporting parts are considered as simply supported conditions. From the buckling analysis, when the loading tool is applied, the critical buckling load of the capsule is 233N.

• 한국소음진동공학회논문집
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• 제14권8호
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• pp.741-748
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• 2004

The vibration and buckling characteristics of the capsule for fuel irradiation test are studied. The natural frequencies of the capsule in air and under water are obtained by modal testing and finite element (FE) analysis using ANSYS program, and accelerations with flow are measured to estimate the compatibility with the operation requirement of the HANARO reactor. The experimental fundamental frequencies of the capsule in the x and z direction are 8.5 Hz and 8.75 Hz in air, and 7.5 Hz and 7.75 Hz under water, respectively. The maximum amplitude of accelerations under the normal operating condition is measured as 11.0 m/s$^2$ that is within the allowable vibrational limit(18.99 m/s$^2$) of the reactor structure. Also, the maximum displacement at 100％ flow is calculated as 0.13 mm which is not interference with other nearby structures. FE analysis results show that the natural frequencies are found to be similar to those of the modal testing when three supporting parts are considered as simply supported conditions. From the buckling analysis, when the loading tool is applied, the critical buckling load of the capsule is 233 N.

• Structural Engineering and Mechanics
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• 제70권3호
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• pp.339-350
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• 2019

This research focuses on finite element model updating and damage assessment of structures at element level based on global nondestructive test results. For this purpose, an optimization system is generated to minimize the structural dynamic parameters discrepancies between numerical and experimental models. Objective functions are selected based on the square of Euclidean norm error of vibration frequencies and modal assurance criterion of mode shapes. In order to update the finite element model and detect local damages within the structural members, modern optimization techniques is implemented according to the evolutionary algorithms to meet the global optimized solution. Using a simulated numerical example, application of genetic algorithm (GA), particle swarm (PSO) and artificial bee colony (ABC) algorithms are investigated in FE model updating and damage detection problems to consider their accuracy and convergence characteristics. Then, a hybrid multi stage optimization method is presented merging advantages of PSO and ABC methods in finding damage location and extent. The efficiency of the methods have been examined using two simulated numerical examples, a laboratory dynamic test and a high-rise building field ambient vibration test results. The implemented evolutionary updating methods show successful results in accuracy and speed considering the incomplete and noisy experimental measured data.

• 한국소음진동공학회논문집
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• 제15권12호
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• pp.1332-1339
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• 2005

The vibration of Powertrain are one of the import design characteristics of a vehicle. Powertrain is mostly mounted to the front subframe and powertrain mounting has an important role in determining the vehicle vibration characteristics. In this paper, the accuracy of the vibration analysis for the front subframe is discussed. The dynamic characteristic of subframe are measured from vehicle test and the finite element model updating are performed that natural frequency, mass and MAC of the experimental and theoretical modal analysis are compared. The subframe mounting stiffness are obtained the iteration method based on the vibration of subframe from vehicle test. Finally, the result of dynamic analysis which is operated dynamic load is compared with experimental one of vehicle test.

• 대한기계학회논문집A
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• 제33권7호
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• pp.700-705
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• 2009

In order to enhance the dynamic stiffness of automotive panel, effect of bead and curved surface was investigated. Modal test was performed for principle specimens which have various kinds of beads, holes and curved surfaces. Test was also performed for conventional dash panel assembly and rear floor panel assembly and curved shaped ones. Results showed that curved shape increased the natural frequency of automotive panel more effectively than the bead. Finite element analysis was also performed and yielded good match with the test results.

• 한국자동차공학회논문집
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• 제19권3호
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• pp.57-64
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• 2011

In general, the durability performance of a large-sized military truck has been checked through a field durability test which required many man-hours and costs. To reduce these expenses, the durability analysis using a VTL(Virtual Test Lab) at an initial design stage was introduced recently. In this paper, the VTL with a multi-post testrig template for a large-sized truck was developed to compute the load histories transferred to cabin and chassis frame. The VTL consisted of trimmed FE models of cabin, chassis frame, and deck, dynamic models of front and rear suspensions, and a 8-post testrig template. The basic characteristics of the VTL were correlated with experimental results which had been extracted from actual driving test, modal test, and static weight test. The fatigue analysis using MSM(Modal Superposition Method) was applied to evaluate the durability performance of a large-sized military truck. From a series of analytic methods, it is shown that the fatigue analysis process using the VTL could be a useful tool to estimate the fatigue lives and weak areas of a large-sized military truck.