• Journal of KSNVE
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• v.8 no.1
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• pp.180-186
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• 1998

Vibration test fixture is used in random vibration control testing. The specified reference spectrum should be transmitted equally to the specimen attachment points on the fixture. In most practical cases, however, spectrum at each of specimen attachment points may be quite different from the specified reference spectrum because of the dynamic characteristics of vibration test fixture. This paper proposes the method of experimental dynamic modification of fixture system for vibration test so that the reference spectrum can be transmitted to the specimen attachment points without distortion. The stiffness of mounts of specimen and the thickness of fixture are considered as design variables. The frequency response functions of specimen used for input data are obtained from vibration testing, and the frequency response functions of fixture are obtained from finite element modeling. The sensitivities of frequency response functions at specimen attachment points to the mount stiffness are derived from synthesis method of transfer function. And the sensitivities to the thickness of fixture are also derived from finite element modeling. The presented method is verified by computer simulation and vibration testing.

• Journal of KSNVE
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• v.6 no.2
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• pp.215-224
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• 1996

Active vibration control is generally used to reduce vibration level by the actuators based on measured signal. Dynamic properties of a structure can be easily modified by the active vibration control, so that the vibration level may be effectively reduced to the magnitude below the allowable limit over a wide frequency rangs. In this paper, an instantaneous optimal control algorithm including acceleration feedback is presented for the active vibration control of large structures considering facts that the acceleration response can be easily measured, but the displacement and velocity response are obtained by numerically integrating the measured acceleration response with some errors. The adverse effect of the time delay is overcomed by taking into account the dynamic characteristics of an actuator and filters in the design of controller. Performance test is carried out using a hydraulic active mass driver on a test structure$(L{\times}W{\times}H;=;1200mm{\times}800mm{\times}1600mm, about;500kg)$ supported by four columns under base excitations. It is confirmed that the vibration level of the test structure are reduced to about 1/6 near resonance.

• Journal of Biomedical Engineering Research
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• v.30 no.3
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• pp.247-254
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• 2009

We studied the postural response induced by plantar sole vibration with various frequencies(20, 60, 100Hz) and vibration zone(the anterior and posterior foot zone) of both soles during standing. Eight healthy young adults were exposed to 15s periods of plantar sole vibration while blindfolded. Body sway(COM, center of mass), the angle of neck, trunk, hip, knee, ankle and EMG of four lower limb muscles(tibialis anterior, lateral and medial gastrocnemial, soleus muscle) were recorded during 15s plantar sole vibration using 3D motion analysis system. Simulating each zone separately resulted in spatially oriented body tilts; oppositely directed backward and forward, respectively, the amplitude of which was proportional to the vibration frequency. EMG activity of lower limb muscles also varied according to the direction of the vibration zone and linearly according to the frequency. These findings led us to consider the plantar sole vibration as useful method of postural balance control and adjustment.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1439-1443
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• 2007

In this paper, vibration reduction techniques of a voice coil motor (VCM) actuator are presented for AFM imaging system. The damping coefficient of the actuator driven by VCM with a flexure hinge is quite low and it cause the about 30dB peak amplitude response at the resonance frequency. To decrease this peak response, we design and apply elliptical band-stop filters to xy and z axis VCM actuator. Frequency response of each actuator with filter is measured to verify the effect of the filters. As a sensor, capacitive sensor is used. Vibration reduction rate of the xy actuator with the filter is also measured while real AFM scanning condition. As another method, closed loop control with the capacitive sensor is applied to the xy axis actuator to add an electrical damping effect and vibration reduction rate measured. These vibration reduction rates with each method are compared. In the case of z axis actuator, the frequency response of force (gap) control loop is measured. For comparison, the frequency response using a conventional PID controller is also obtained. Finally, the AFM image of a standard grid sample is measured with the designed controller to analyze the effect in the AFM imaging.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.1
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• pp.17-24
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• 2013

The process of producing high precision and light weight product is always exposed to impact load or shock. Because of this, isolator device is required. To measure the response of the isolator, accelerometer is practically used. However, the measured response of the accelerometer is different to the response of the isolator. To predict the response of the accelerometer and the isolator, 2-DOF damped system with an input shock is modeled using numerical analysis. 1-DOF damped system with a base excitation is also used to predict the response of the isolator. The mass ratio, damping ratio, and natural frequency ratio are then varied. The predicted responses from the two modeling approaches are compared and large errors are found.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.6
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• pp.723-730
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• 2018

A well-designed flight vibration specification enables the optimum weight design of the Surface-to-Air or Air-to-Air Missile, improves the maneuverability of the flight vehicle, improves the engagement of target, and increases the price competitiveness of the components and the missile system. Conventional flight vibration specifications are used by using a somewhat higher standard as suggested in MIL-STD-810C, or based on accumulated data from developed similar missile systems. In this study, we confirmed the validity of FEA response analysis by comparing response data obtained by FEA and response data of real product. Also we proposed that each specification that reflects the structural characteristics of the place where the components are mounted is required instead of verifying all the components by a single flight vibration specification.

• Steel and Composite Structures
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• v.45 no.5
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• pp.621-640
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• 2022

In the present article, the vibration response of a geometrically imperfect bi-directional functionally graded plate (2D-FGP) with geometric discontinuities and micro-structural defects (porosities) has been investigated. A porosity model has been developed to incorporate the effective material properties of the bi-directional FGP which varies in two directions i.e. along the axial and transverse direction. The geometric discontinuity is also introduced in the plate in the form of a circular cut-out at the center of the plate. The structural kinematic formulation is based on the non-polynomial trigonometric higher-order shear deformation theory (HSDT). Finite element formulation is done using C° continuous Lagrangian quadrilateral four-noded element with seven degrees of freedom per node. The equations of motion have been derived using a variational approach. Convergence and validation studies have been documented to confirm the accuracy and efficiency of the present formulation. A detailed investigation study has been done to evaluate the influence of the circular cut-out, geometric imperfection, porosity inclusions, partial supports, volume fraction indexes (along with the thickness and length), and geometrical configurations on the vibration response of 2D-FGP. It is concluded that after a particular cut-out dimension, the vibration response of the 2D FGP exhibits non-monotonic behavior.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.5
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• pp.558-563
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• 2008

Vibration/shock affects biggest taking a train subtraction of vehicle and durability decline. Therefore, absorber is used for vibration/shock isolation and various qualities of the material and design are applied to isolation. This paper proposes vibration/shock absorber that applies 'Disc' spring. Through comparison with 'Disc' spring that has nonlinearity and coil spring that is having linearity, see effect that nonlinearity of isolation gets in vibration/shock Isolation. Coil spring and 'Disc' spring are non-linear numerical analysis and simulation through theory for this, get and investigate comparison result through an experiment finally. Expressed and formulated shock through 'Runge-Kutta' method/impact response to nonlinear-vibration-equation of 1 degree of freedom for numerical analysis. Double half sine pulse of excitation used and analyzed result through spectrum response analysis here. Response of disc spring is compared to response of coil spring by changing $h_o/t$ ratio with computer simulation and the usage of disc spring is increased through analysis of effect of design factors. The purpose of this paper is that the shock response of disc spring is calculated through numerical simulation and to design the optimal absorber under the limited condition. And then, the isolation effect was analyzed through the shock test.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.990-993
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• 2008

Vibration/shock affects biggest taking a train subtraction of vehicle and durability decline. Therefore, absorber is used for vibration/shock isolation and various qualities of the material and design are applied to isolation. This paper proposes vibration/shock absorber that applies 'Disc'spring. Through comparison with 'Disc' spring that has nonlinearity and coil spring that is having linearity, see effect that nonlinearity of isolation gets in vibration/shock isolation. Coil spring and 'Disc' spring are non-linear numerical analysis and simulation through theory for this, get and investigate comparison result through an experiment finally. Expressed and formulated shock through 'Runge-Kutta' method/impact response to nonlinear-vibration-equation of 1 degree of freedom for numerical analysis. Double half sine pulse of excitation used and analyzed result through spectrum response analysis here. Response of disc spring is compared to response of coil spring by changing ho/t ratio with computer simulation and the usage of disc spring is increased through analysis of effect of design factors. The purpose of this paper is that the shock response of disc spring is calculated through numerical simulation and to design the optimal absorber under the limited condition. And then, the isolation effect was analyzed through the shock test.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.04a
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• pp.120-127
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• 1994

Noise and vibration induced by subway operation are one of the major factor which annoy residents living near railway tracks. While lateral vibration is a major factor in analyzing seismic effect of the structure, vertical vibration became a major concern in considering the subway induced vibration because relatively smaller energy affects only nearby areas than that of earthquake. A characteristics of structural response induced by subway operation has been studied with different total height of the building and different number of spans. Also the frame with different span length has been studied. As the numbers of degrees freedom increase the higher mode effect on vertical vibration increases. Accordingly, the total affecting vertical modes are distributive as the numbers of degrees of freedom increase. Though the total degree of freedom increases, only some of the dominant modes actively affects to the vertical response of the structure. A frame with the number of equal spans could be analyzed by replacing the whole frame as one when we want to predict the response of the vertical vibration. Also it has been found that the seperate frame analysis will give little different result when adjacent span is relatively longer than others.