• Journal of the Korean Society for Precision Engineering
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• v.20 no.6
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• pp.47-54
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• 2003

As a tool for strain measurement to work with screw driven or hydraulic material test systems, in which mechanical vibration is inherent, SSDG (Speckle Strain/Displacement Gage), ESP (Electronic Speckle Photography) and its 3-dimension version SDSP are evaluated for the theory and practical appliance. Through tension test of steel strips, their validity and shortcomings are examined. As the results, it has been shown that, although SSDG and ESP provide direct measurement of in-plane strain in one direction, they are so sensitive to the out-plane displacement. On the other hand, SDSP which is aided with DIC (Digital Image Correlation) technique to trace the movement of the speckles provides not only in-plane 2-dimensional displacement field, but also out-of-plane displacement simultaneously. However, because the DIC is time-consuming, not automated yet and it needs post-processing to evaluate strain from the displacement field, SDSP appears to be not adequate as a real time sensor.

• Explosives and Blasting
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• v.37 no.4
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• pp.1-9
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• 2019

In this study the applicability of a Digital Image Correlation (DIC) method was investigated by measuring the displacement and vibration of rock pillar due to underground mining blasting. When combined with a high speed photography technology, the DIC method provides an excellent photographic image processing ability that can be used to convert the evolving full-field surface properties of structures to 2D or 3D set of coordinate values. The measured coordinate sets are then used to calculate the displacement, strain, and velocity of the target structure. This technique is widely used in science and engineering, and continuously finds its new application areas. In this study, the DIC system and the conventional seismograph were compared for their ability to measure the displacement and vibration produced by blasting. In the field test both methods showed similar results. Thus, it is concluded that the DIC method is feasible to measure the ground displacements and vibrations from blasting.

• Smart Structures and Systems
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• v.12 no.3_4
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• pp.381-397
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• 2013

In this paper, wireless health monitoring of stay cables using piezoelectric strain sensors and a smart skin technique is presented. For the cables, tension forces are estimated to examine their health status from vibration features with consideration of temperature effects. The following approaches are implemented to achieve the objective. Firstly, the tension force estimation utilizing the piezoelectric sensor-embedded smart skin is presented. A temperature correlation model to recalculate the tension force at a temperature of interest is designed by correlating the change in cable's dynamic features and temperature variation. Secondly, the wireless health monitoring system for stay cables is described. A piezoelectric strain sensor node and a tension force monitoring software which is embedded in the sensor are designed. Finally, the feasibility of the proposed monitoring technique is evaluated on stay cables of the Hwamyung Grand Bridge in Busan, Korea.

• Smart Structures and Systems
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• v.1 no.1
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• pp.83-101
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• 2005

This paper summarizes the application of a rational methodology for the structural assessment of older reinforced concrete Tunisian bridges. This methodology is based on ambient vibration measurement of the bridge, identification of the structure's modal signature and finite element model updating. The selected case study is the Boujnah bridge of the Tunis-Msaken Highway. This bridge is made of a continuous four-span simply supported reinforced concrete slab without girders resting on elastomeric bearings at each support. Ambient vibration tests were conducted on the bridge using a data acquisition system with nine force-balance accelerometers placed at selected locations of the bridge. The Enhanced Frequency Domain Decomposition technique was applied to extract the dynamic characteristics of the bridge. The finite element model was updated in order to obtain a reasonable correlation between experimental and numerical modal properties. For the model updating part of the study, the parameters selected for the updating process include the concrete modulus of elasticity, the elastic bearing stiffness and the foundation spring stiffnesses. The primary objective of the paper is to demonstrate the use of the Enhanced Frequency Domain Decomposition technique combined with model updating to provide data that could be used to assess the structural condition of the selected bridge. The application of the proposed methodology led to a relatively faithful linear elastic model of the bridge in its present condition.

• Journal of KSNVE
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• v.11 no.1
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• pp.125-131
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• 2001

There is a clearance between the parts of a machine due to design tolerance, manufacturing error, wear, looseness, or misalignment. If the clearance is large, the vibration and noise of the machine is generally large. Therefore, the analysis on the nitration and noise of a machine can tell the clearance of the machine, which reveals the condition of the machine, i.e., the existence of faults and the safety of the machine. The investigation of this kind of research should be on the basis of experimental results. A link mechanism with a clearance at a joint between the coupler and locker is made for the investigation of the condition monitoring of a machine due to clearance. The vibration and sound are measured from the link driving system during the operation. The signals are clarified using line enhancement technique. The noise removed signals are used to develop the dynamic model of the system for a model based fault diagnosis. Also this study showed that the clarified signals can be used for the calculation of the joint forces between the coupler and rocker and for the correlation between the vibration and sound levels and the clearance sizes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.8
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• pp.698-706
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• 2013

Structural vibration induced by excitation forces under turbulent boundary layer is investigated in terms of the numerical analysis in this paper. Since the responses of structures excited by the wall pressure fluctuation(WPF) are described by the power spectral density functions, they are calculated and reviewed theoretically for finite and infinite length beams. For the use of numerical approaches, the WPF needs to be discretized but conventional finite element method is not much effective for that purpose because the WPF lose the spatial correlation characteristics. As an alternative numerical technique for WPF modelling, a wavenumber domain finite element approach, called waveguide finite element method, is examined here for infinite length beams. From the comparison between the numerical and theoretical results, it was confirmed that the WFE method can effectively and easily cope with the excitation from WPF and hence the suitable approach.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.3
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• pp.284-292
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• 2008

The active control technique mostly uses the least-mean-square(LMS) algorithm, because the LMS algorithm can easily obtain the complex transfer function in real-time, particularly when the Filtered-X LMS(FXLMS) algorithm is applied to an active noise control(ANC) system. However, FXLMS algorithm has the demerit that stability of the control is decreased when the step size become larger but the convergence speed is faster because the step size of FXLMS algorithm is fixed. As a result, the system has higher probability which the divergence occurs. Thus the Co-FXLMS algorithm was developed to solve this problem. The Co-FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. In this paper, the performance of the Co-FXLMS algorithm is presented in comparison with the FXLMS algorithm. Simulation and experimental results show that active noise control using Co-FXLMS is effective in reducing the noise in duct system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.737-742
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• 2007

The method of the reducing duct noise can be classified by passive and active control techniques. However, passive control has a limited effect of noise reduction at low frequencies (below 500Hz) and is limited by the space. On the other hand, active control can overcome these passive control limitations. The active control technique mostly uses the Least-Mean-Square (LMS) algorithm, because the LMS algorithm can easily obtain the complex transfer function in real-time particularly when the Filtered-X LMS (FXLMS) algorithm is applied to an active noise control (ANC) system. However, the convergence performance of the LMS algorithm decreases slightly so it may delay the convergence time when the FXLMS algorithm is applied to the active control of duct noise. Thus the Co-FXLMS algorithm was developed to improve the control performance in order to solve this problem. The Co-FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. In this paper, the performance of the Co-FXLMS algorithm is presented in comparison with the FXLMS algorithm. Simulation results show that active noise control using Co-FXLMS is effective in reducing duct noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.598-603
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• 2007

The active control technique mostly uses the Least-Mean-Square (LMS) algorithm, because the LMS algorithm can easily obtain the complex transfer function in real-time, particularly when the Filtered-X LMS (FXLMS) algorithm is applied to an active noise control (ANC) system. However, FXLMS algorithm has the demerit that stability of the control is decreased when the step size become larger but the convergence speed is faster because the step size of FXLMS algorithm is fixed. As a result, the system has higher probability which the divergence occurs. Thus the Co-FXLMS algorithm was developed to solve this problem. The Co-FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. In this paper, the performance of the Co-FXLMS algorithm is presented in comparison with the FXLMS algorithm. Simulation results show that active noise control using Co-FXLMS is effective in reducing the noise in duct system.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.2
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• pp.96-103
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• 2005

The early detection of the bearing defects in rotating machinery is very important since the critical failure of bearing causes a machinery shutdown. However it is not easy to detect the vibration signal caused by the initial defects of bearing because of the high level of random noise. A signal processing technique, called the adaptive line enhancer(ALE) as one of adaptive filter, is used in this study. This technique is to eliminate random noise with little a prior knowledge of the noise and signal characteristics. Also we propose the optimal methods fir selecting the three main ALE parameters such as correlation length filter order and adaptation constant. Vibration signals f3r three abnormal bearings, including inner and outer raceways and ball defects, were acquired by Anderon(angular derivative of radius on) meter. The experimental results showed that ALE is very useful f3r detecting the bearing defective signals masked by random noise.