• Transactions of the KSME C: Technology and Education
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• v.5 no.2
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• pp.81-87
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• 2017

315Fr compressor motor exceeds vibration specifications. To find the reason, first a modal impact test with free-free condition is done. Second a modal test with fixed condition is done. Thereafter the test results are compared with FEM simulation results. Using free-free condition modal impact test, FEM simulation conditions (boundary, mesh..) are modified. The motor has rolling motion around 120Hz. FEM simulation also shows same result. FEM simulation will be used to develop other series compressor motors. Using this, manufacturing test model and doing test will be useless.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.258-261
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• 2006

The structure of small launch vehicle can be divided into engine section and payload section. This paper introduces modal test of the payload section of small launch vehicle which is composed to satellite, PLA (Payload Adapter), VEB (Vehicle Equipment Bay), KMS (Kick Motor Support) and KM (Kick Motor). From this test, dynamic properties of the 2nd stage structure of small launch vehicle can be obtained. In this test, to simulate free-free boundary condition, test object was hung by 4 bungee cords and excited by using impact hammer Modal test data are analyzed by using TDAS(Test Data Analysis Software). As the result, modal parameters and mode shapes below 100Hz of the 2nd stage of small launch vehicle were identified.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.2
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• pp.75-84
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• 2010

An in-cabinet response spectrum should be generated to perform the seismic qualification of devices and instruments mounted inside safety-related electrical equipment installed in nuclear power plants. The response spectrum is available by obtaining accurate seismic responses at the device mounting location of the cabinet. The dynamic behavior of most of electrical equipment may not be easily analyzed due to their complex mass and stiffness distributions. Considering these facts, this study proposes a procedure to estimate the seismic responses of a structure by a combination of a test and subsequent analysis. This technique firstly constructs the modal equations of the structure by using the experiment modal parameters obtained from the impact test. Then the seismic responses of the structure may be calculated by a mode superposition method. A simple steel frame structure was fabricated as a specimen for the validation of the proposed method. The seismic responses of the specimen were estimated by using the proposed technique and compared with the measurements obtained from the shaking table tests. The study results show that it is possible to accurately estimate the seismic response of the structure by using the experimental modal parameters obtained from the impact test.

• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.391-405
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• 2019

Compared to the ambient vibration test mainly identifying the structural modal parameters, such as frequency, damping and mode shapes, the impact testing, which benefits from measuring both impacting forces and structural responses, has the merit to identify not only the structural modal parameters but also more detailed structural parameters, in particular flexibility. However, in traditional impact tests, an impacting hammer or artificial excitation device is employed, which restricts the efficiency of tests on various bridge structures. To resolve this problem, we propose a new method whereby a moving vehicle is taken as a continuous exciter and develop a corresponding flexibility identification theory, in which the continuous wheel forces induced by the moving vehicle is considered as structural input and the acceleration response of the bridge as the output, thus a structural flexibility matrix can be identified and then structural deflections of the bridge under arbitrary static loads can be predicted. The proposed method is more convenient, time-saving and cost-effective compared with traditional impact tests. However, because the proposed test produces a spatially continuous force while classical impact forces are spatially discrete, a new flexibility identification theory is required, and a novel structural identification method involving with equivalent load distribution, the enhanced Frequency Response Function (eFRFs) construction and modal scaling factor identification is proposed to make use of the continuous excitation force to identify the basic modal parameters as well as the structural flexibility. Laboratory and numerical examples are given, which validate the effectiveness of the proposed method. Furthermore, parametric analysis including road roughness, vehicle speed, vehicle weight, vehicle's stiffness and damping are conducted and the results obtained demonstrate that the developed method has strong robustness except that the relative error increases with the increase of measurement noise.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.308-314
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• 1999

This paper presents the results of structural identification of a safety-related valve for nuclear power plant by impact hammer test as well as shaking table tests by using broadband random wave and sine sweep excitation. The test specimen is a Y-type motor operated globe valve. The test was performed as a "support test" to validate the analytically obtained modal parameters of the valve during its seismic qualification process by analytical method. From the study results it has been found that the shaking table test generally yields higher natural frequencies and lower damping values compared with those of impact hammer test. And it has been recognized that impact hammer test for modal identification of complex structures should be applied very carefully to get reasonable results.e results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1455-1458
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• 2007

Vibration characteristics of concrete slabs were investigated using a 1:10 scale model and finite element method. A 1:10 scale model of a test building with 150 and 200mm slab thicknesses was made of acrylic materials. Modal test was conducted to investigate mode shape and modal frequencies. Results show that the mode shapes of two slabs with different thickness are similar each other, whereas natural frequency is different. Through modal analysis using FEM, it was revealed that both mode shapes and natural frequencies calculated from the FEM model are similar to those of the scale model measurement. It was also found that natural frequencies increased with increment of the slab thickness.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1261-1266
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• 2000

In the impact echo method, a stress pulse is introduced into an object at on accessible surface by a transmitter. The pulse propagates into the test object and is reflected by flaws or interfaces. In this paper, void and crack locations of concrete specimens were detected using impact echo method. In their modal identification procedures, the double least squares solution for Ibrahim Time Domain technique was used.

• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.114-119
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• 2007

This paper introduces modal test of the 2nd stage structure of KSLV-I which is composed to satellite, PLA(Payload Adapter), EB(Equipment Bay), KMS(Kick Motor Support) and KM(Kick Motor) without PLF(Payload Fairing). In this test, to simulate free-free boundary condition, test object was hung by 4 bungee cords and excited by using impact hammer. From this test, dynamic properties of the 2nd stage structure of KSLV-I can be obtained. Modal test data are analyzed by using TDAS(Test Data Analysis Software). As the result, modal parameters and mode shapes below 100Hz of the 2nd stage of KSLV-I were identified.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.885-890
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• 2007

Fast Fourier Transformation(FFT) is one of the most useful way to analyze response signal for the purpose of grasping the dynamic characteristics of system. Vibration test using impact hammer is typical and simple experimental method widely used for catching hold of dynamic peculiar characters and modal behaviors of system. In this thesis, impact testing module for NI-PXI equipment is developed. The analyzing and visualizing module are developed with LabVIEW tool. A user can see quickly and easily modal shape of system after analyzing acquired data. This developed module will be expected to build up more convenient and serviceable measurement system.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.911-916
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• 2008

Impact noise caused by the collision of bodies is difficult to estimate because of the complexity of impact phenomenon. In this study, impact noise is estimated using two different methods when the noise is caused by the vibration due to impact. First, impact noise is analyzed using impact analysis and boundary element analysis. Second, modal expansion technique is applied to the estimation of impact noise. Experiment is carried out to validate the analysis results.