• Proceedings of the KSR Conference
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• 2005.11a
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• pp.848-853
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• 2005

The objective of this paper is to address to the providing an adequate noise and vibration solution, required for High Speed Rail while maintaining the stability criteria of the ChonAn station structure, the first constructed in Korean High Speed Railway. The significant acoustic pressure level will be induced by the high speed trains passing-by. Therefore, the high level study of this case is necessary. The acoustic pressure level of 85 dB(A) inside the ChonAn station is expected, and the spaces below concrete slab are not suitable for commercial purpose, thus installation of filtering systems (spring boxes containing viscous dampers, ballast mats and acoustic shield) are provided to reduce the effect of the noise and vibration to acceptable level of 55 dB(A). But, a major drawback of application of the previously conducted experimental results was that the actual effect of installation of filtering system was never been validated. Therefore, the acquisition of noise and vibration on the present structure were obtained and compared to the computer simulations. These predicted the behavior of the station reasonably well. Also, the installation of filtering systems gave the superior reduction on noise and vibration. This application is successfully adapted without scarifying stability criteria related to the structural stability including excessive deformations or displacements. Three traffic operation safety limits: deck vertical acceleration, deflection of the structure, and longitudinal displacement of the slab were satisfactory.

• Smart Structures and Systems
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• v.14 no.3
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• pp.307-325
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• 2014

A newly developed method based on energy is presented to study the damage pattern of FRP material. Basalt fiber reinforced polymer (BFRP) is employed to monitor the damage under fatigue loading. In this study, acoustic emission technique (AE) combined with scanning electronic microscope (SEM) technique is employed to monitor the damage evolution of the BFRP specimen in an approximate continuous scanning way. The AE signals are analyzed based on the wavelet transform, and the analyses are confirmed by SEM images. Several damage patterns of BFRP material, such as matrix cracking, delamination, fiber fracture and their combinations, are identified through the experiment. According to the results, the cumulative energy (obtained from wavelet coefficients) of various damage patterns are closely related to the damage evolution of the BFRP specimens during the entire fatigue tests. It has been found that the proposed technique can effectively distinguish different damage patterns of FRP materials and describe the fatigue damage evolution.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.1
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• pp.45-52
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• 2016

Blast furnaces are crucial equipment for steel production. A typical furnace risks unexpected accidents caused by contraction and expansion of the walls under an environment of high temperature and pressure. In this study, an acoustic emission (AE) monitoring system was tested for evaluating the large-scale structural health of a blast furnace. Based on the growth of shell cracks with the emission of high energy levels, severe damage can be detected by monitoring increases in the AE energy parameter. Using this monitoring system, steel mill operators can establish a maintenance period, in which actual shell cracks can be verified by cross-checking the UT. From this study, we expect that AE systems permit early fault detection for structural health monitoring by establishing evaluation criteria based on the severity of shell cracking.

• Smart Structures and Systems
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• v.18 no.3
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• pp.471-484
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• 2016

Optical fiber sensors have been proven that they have the potential to detect high-frequency ultrasonic signals, in structural health monitoring field which generally refers to acoustic emission signals from active structural damages and guided waves excited by ultrasonic actuators and propagating in waveguide. In this work, the sensing properties of optical fiber sensors based on Mach-Zehnder interferometer were investigated in the metal plate. Analytical formulas were conducted first to explore the parameters affecting its sensing performances. Due to the simple and definable frequency component, the Lamb wave excited by the piezoelectric wafer was employed to study the sensitivity of the proposed optical fiber sensors with respect to the frequency, rather than the acoustic emission signals. In the experiments, according to above investigations, spiral shape optical fiber sensors with different size were selected to increase their sensitivity. Lamb waves were excited by a circular piezoelectric wafer, while another piezoelectric wafer was used to compare their voltage responses. Furthermore, by changing the excitation frequency, the tuning frequency characteristic of the proposed optical fiber sensor was also investigated experimentally.

• Journal of KSNVE
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• v.7 no.4
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• pp.589-596
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• 1997

A energy equation for a thin plate and surrounding fluid is derived. The equation essentially determines the relation between internal loss of thin plate, energy of acoustic radiation, and structure intensity. We attempted to use this relation to measure internal loss of thin plate. The significance of this approach is that internal loss at any point of a thin plate can be measured. The quality of this measure is dicated by the accuracy of associated measurement systems such as structure and acoustic intensity measurements. A strain gauge bridge system has been developed to measure structure intensity of thin plate. Its performance is tested by experiments.

• Structural Engineering and Mechanics
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• v.13 no.4
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• pp.355-368
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• 2002

In this paper, we address the numerical investigation on the effect of liquid compressibility onto the natural frequency of liquid-filled containers. Traditionally the liquid motion has been treated as an ideal fluid motion. However, from the numerical experiments for the axisymmetrical free-vibration of cylindrical liquid-storage tanks, we found that the relative difference in natural frequencies between ideal and compressible motions becomes remarkable, as the slenderness of tank or the relative liquid-fill height becomes larger. Therefore, in such cases of dynamic systems, the liquid compressibility becomes an important parameter, for the accurate vibration analysis. For the free-vibration analysis of compressible liquid-structure interaction we employed the coupled finite element formulation expressed in terms of the acoustic wave pressure and the structure deformation.

• Advances in aircraft and spacecraft science
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• v.5 no.2
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• pp.277-294
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• 2018

In the space industry, structures undergo several vibration and acoustic tests in order to verify their design and give confidence that they will survive the launch and other critical in-orbit dynamic scenarios. At component level, vibration tests are conducted with the aim to reach local or global interface loads without exceeding the design loads. So, it is often necessary to control and limit the input based on a load criterion. This means the test engineer should be able to assess the interface loads, even when load cannot be measured. This paper presents various approaches to evaluate interface loads using measured accelerations and by referring to mass operators. Various methods, from curve fitting techniques to finite element-based methods are presented. The methods are compared using signals with known imperfection to identify strengths and weaknesses of each mass operator definition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.797-801
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• 2003

The Statistical Energy Analysis is based on the power flow and the energy conservation between sub-systems, which enable the prediction of acoustic and structural vibration behavior in mid-high frequency ranges. This paper discusses the identification of SEA coupling loss factor parameters from experimental measurements of small reverberation chamber sound pressure levels and structural accelerations. As structural subsystems, steel plates with and without damping treatment are considered. Calculated CLFs were verified by both transmission loss values for air-borne CLF case and running SEA commercial software As a result, CLFs have shown a good agreement with those computed by software. Acoustical behavior of air-borne noise and structure-borne noise has been examined. which shows reasonable results, too.

• Transactions of the Society of Information Storage Systems
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• v.2 no.1
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• pp.50-55
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• 2006

As high performance and high speed have been accomplished by technology of optical disk drive. optical disk drives have gradually high percentage of the market share in market of storage devices. This technology helps to improve the quality of record/reproduction. However, simultaneously it causes various problems in the structural aspect and increases noise largely. Especially at high speed, dominant noise is more influenced by fluid noise than by structure-borne noise. The purpose of this study is that reduce the air-born noise in optical disk drive as it decreases a quantity of flow by using a micro muffler. The micro muffler is a miniaturized muffler. The muffler is used widely by solution to reduce air-borne noise which is generated by flow. According to frequency band of the noise source, it can be applied by muffler of various forms. In this study, we examined the acoustic characteristics of the micro muffler and applied it to reduction of the ODD noise. It could get an excellent noise reduction in high frequency band through the decrease of an inner flow. But it could not get a noise reduction in low frequency band.

• KIEAE Journal
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• v.7 no.2
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• pp.3-8
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• 2007

Recently, the structural system of public residential buildings has been changed from the reinforced concrete (RC) wall system to the (PC) wall and moment resisting systems. Thus, it is important to develop the suitable wall system in accordance with the trend of the modern structural system. This paper presents the basic study on the suitable boundary wall in high-rise buildings. The research also demonstrates the evaluation results on sound characteristics in the aspect of sound insulation. The evaluation of sound insulation capability for the commercialized wall structure was conducted based on literature survey while the measurement of sound insulation capability for the light-weght EPP concrete was performed in according to KS F2808 in laboratory. The main objective of this research is to propose the most suitable dry wall system as a sound insulation structure through the comparison and analysis of frequency characteristics and weight-acoustic attenuation.