• Journal of the Korean Society for Precision Engineering
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• v.13 no.2
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• pp.84-93
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• 1996

Non-destructive inspection techniques using laser have been broading their application areas as well as growing their measurement skills together with the rapid development of circumferential technology like fiber optics, computer and image processing. The ESPI technique is already on the stage of on-line testing with commercial products in developed country nations. Especially, this technique is expected to be applied to the nuclear industry, automobile and aerospace because it is proper for the vibration measurement and it can be applied to objects of a high temperature. This paper describes the use of the ESPI system for measuring vibration patterns on the reflecting objects. Using this system, high-quality Jo fringes for identifying mode shapes are displayed. A bias vibration is introduced into the reference beam to shift the Jo fringes so that fringe shift algorithms can be used to determine vibration amplitude. Using this method, amplitude fields for vibrating objects were obtained directly from the time-average interferograms recorded by the ESPI system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.444-449
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• 2009

An engine is one of the most dominant noise and vibration sources in vehicle systems. Therefore, in order to resolve noise and vibration problems due to engine, various types of engine mounts have been proposed. This work presents a new type of active engine mount system featuring a magneto-rheological (MR) fluid and a piezostack actuator. As a first step, six degrees-of freedom dynamic model of an in-line four-cylinder engine which has three points mounting system is derived by considering the dynamic behaviors of MR mount and piezostack mount. In the configuration of engine mount system, two MR mounts are installed for vibration control of roll mode motion whose energy is very high in low frequency range, while one piezostack mount is installed for vibration control of bounce and pitch mode motion whose energy is relatively high in high frequency range. As a second step, linear quadratic regulator (LQR) controller is synthesized to actively control the imposed vibration. In order to demonstrate the effectiveness of the proposed active engine mount, vibration control performances are evaluated under various engine operating speeds (wide frequency range) and presented in time domain.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.6
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• pp.583-590
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• 2009

An engine is one of the most dominant noise and vibration sources in vehicle systems. Therefore, in order to resolve noise and vibration problems due to engine, various types of engine mounts have been proposed. This work presents a new type of active engine mount system featuring a magneto-rheological (MR) fluid and a piezostack actuator. As a first step, six degrees-of freedom dynamic model of an in-line four-cylinder engine which has three points mounting system is derived by considering the dynamic behaviors of MR mount and piezostack mount. In the configuration of engine mount system, two MR mounts are installed for vibration control of roll mode motion whose energy is very high in low frequency range, while one piezostack mount is installed for vibration control of bounce and pitch mode motion whose energy is relatively high in high frequency range. As a second step, linear quadratic regulator (LQR) controller is synthesized to actively control the imposed vibration. In order to demonstrate the effectiveness of the proposed active engine mount, vibration control performances are evaluated under various engine operating speeds(wide frequency range) and presented in time domain.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.2
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• pp.124-131
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• 2002

This paper presents the design of an active vibration suppression controller for an air-spring type vibration isolation table. Firstly, isolation system model is constructed considering the isolation table, attached equipment and voice-coil actuator. An active control system is designed based on frequency-shaped sliding mode control theory rewarding high frequency uncertainties with respect to attached equipments on the isolation table. Finally. the performance of the active isolation system is evaluated by simulation under some disturbance conditions which are transmitted from base structure of the isolation system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1391-1395
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• 2006

In non-contact mode atomic force microscopy, the response of a resonating tip is used to measure the nanoscale topography and other properties of a sample surface. However, the tip-surface interactions can affect the tip response and destabilize the non-contact mode control. Especially it is difficult to obtain a good scanned image of high adhesion surfaces such as polymers using conventional hard NCHR tip and non-contact mode control. In this study, experimental investigation is made on the non-contact mode imaging and we report the microcantilever having low stiffness (OMCL) is useful to measure the properties of samples such as elasticity. In addition, we proved that it was adequate to use low stiffness microcantilever to obtain a good scanned image in AFM for the soft and high adhesion sample.

• Special Issue of the Society of Naval Architects of Korea
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• 2005.06a
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• pp.97-106
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• 2005

According to the trends of construction of large size vessel with high power the natural frequencies of the bending modes of propeller blades have been lower than the past. Therefore, it is expected that the noise and vibration problems of the marine propeller are frequently occurred. As main issue of the propeller noise and vibration problem, the cavitation noise and singing noise due to the flow induced excitation of the bending modes of propeller blade in the high frequency range has been studied by the hydrodynamic researchers in the view point of the excitation force reduction. In this paper, the vibration mode characteristics of propeller with a large diameter in very large vessel are investigated by the vibration analysis of the finite element method using MSC/Nastran and the vibration measurement by the impact test on the propeller blade. According to the results, the natural frequencies of various blade bending modes in water entrained condition could be estimated from the natural frequencies taken by the measurement and free vibration analysis in the dry condition, and it could be estimated how the high frequency noise such as singing is generated from the blade bending modes.

• Structural Engineering and Mechanics
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• v.42 no.2
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• pp.229-245
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• 2012

Bridge vibration displacements have been directly measured by LVDTs (Linear Variable Differential Transformers) or laser equipment and have also been indirectly estimated by an algorithm of integrating measured acceleration. However, LVDT measurement cannot be applied for a bridge crossing over a river or channel and the laser technique cannot be applied when the weather condition is poor. Also, double integration of accelerations may cause serious numerical deviation if the initial condition or a regression process is not carefully controlled. This paper presents an algorithm of estimating bridge vibration displacements using vibration strains measured by FBG (Fiber Bragg Grating) sensors and theoretical mode shapes of a simply supported beam. Since theoretically defined mode shapes are applied, even high modes can be used regardless of the quality of the measured data. In the proposed algorithm, the number of theoretical modes is limited by the number of sensors used for a field test to prevent a mathematical rank deficiency from occurring in computing vibration displacements.89The proposed algorithm has been applied to various types of bridges and its efficacy has been verified. The closeness of the estimated vibration displacements to measured ones has been evaluated by computing the correlation coefficient and by comparing FRFs (Frequency Response Functions) and the maximum displacements.

• Structural Engineering and Mechanics
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• v.57 no.3
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• pp.543-567
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• 2016

This study attempts to address the buckling and free vibration characteristics of an isotropic cylindrical panel subjected to non-uniform temperature rise using numerical approach. Finite element analysis has been used in the present study. The approach involves three parts, in the first part non-uniform temperature field is obtained using heat transfer analysis, in the second part, the stress field is computed under the thermal load using static condition and, the last part, the buckling and pre-stressed modal analysis are carried out to compute critical buckling temperature as well as natural frequencies and associated mode shapes. In the present study, the effect of non-uniform temperature field, heat sink temperatures and in-plane boundary constraints are considered. The relation between buckling temperature under uniform and non-uniform temperature fields has been established. Results revealed that decrease (Case (ii)) type temperature variation field influences the fundamental buckling mode shape significantly. Further, it is observed that natural frequencies under free vibration state, decreases as temperature increases. However, the reduction is significantly higher for the lowest natural frequency. It is also found that, with an increase in temperature, nodal and anti-nodal positions of free vibration mode shapes is shifting towards the location where the intensity of the heat source is high and structural stiffness is low.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.660-664
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• 2014

A diesel forklift truck under 3-ton class has disadvantages in the vibration transmission path. Because the weight ratio of body structure to powertrain which is source of excitation force is lower th an a mid-class forklift. In addition, the torsional and bending vibration mode frequencies of body structure are within the engine excitation frequency range, then high idle vibration generated by resonance. In this paper vehicle body structure design and optimization technique considering idle vibration reduction are presented. Design sensitivity analysis is applied to search the sensitive of design parameters in body structure. The design parameters such as thickness and pillar cross section were optimized to increase the torsional and bending vibration mode frequencies.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.473-477
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• 2001

In this paper, Firstly, it is shown that the high vibration and noise source of piping and pump system is the acoustic resonance. Secondly, in order to decrease the high vibration and noise of piping and pump system, the acoustic mode of piping have been changed and its effectiveness is investigated as applied it at piping system practically.