• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1139-1146
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• 2000

The frequencies of principal noise in interior permanent motor originate form two sources. One is torque ripple that is composed of cogging torque, magnetic torque ripple and reluctance torque ripple. The other is induced by natural frequencies. In this paper, the torque ripple and its influence on noise was examined by theoretical analysis. Understanding relation of dynamic characteristics and noise, natural frequencies and mode shapes were obtained by experimentation and operational deflection shape was observed. Finally, the method of predicting frequencies of principal noise was proposed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.944-949
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• 2003

A High-speed cutter, a kind of electric tool is studied to reduce its vibration and noise. The experimental modal analysis, the operational deflection shapes(ODS) and the time domain analysis(TDA) are used in the SMS software to analyze the vibration signals from an operating high-speed cutters under steady state operating condition. The second mode and fifth m,)do of the base plate coincide with the driving frequencies of the motor, And the vibration of the wheel cover is caused by the gap between the main wheel cover and the sub wheel cover. The structural modification for the base plate was done to reduce the vibration. The effect of modification is verified through the test.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.600-604
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• 2013

A CTBA(Coupled Torsion Beam Axle) is a general type for rear suspension of small/compact sedans. It connects left and right knuckles using torsion beam axle and trails rear wheels. Therefore, a CTBA performs a main role of ride & handing. But, a CTBA suspension has main bending mode around 120Hz and causes road booming noise in the interior of a car. Therefore, the mode control of a CTBA is very important for reducing road noise. In this paper, we optimized the shape of a CTBA to reduce road noise considering R&H performance, simultaneously. The vibration mechanism of CTBA was investigated using ODS(Operational Deflection Shape) and mode shape.

• Smart Structures and Systems
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• v.26 no.5
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• pp.667-680
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• 2020

This study aims at reporting a systematic procedure for evaluating the static and dynamic structural performance of steel bridges based on a short-period structural health monitoring measurement. Sungsu bridge located in Korea is considered as a case study presenting the most recent tests carried out to examine the bridge condition. Short-period measurements of Structural Health Monitoring (SHM) system were used during the bridge testing phase. A novel symmetry index is introduced using statistical analyses of deflection and strain measurements. Frequency Domain Decomposition (FDD) is implemented to the strain measurements to estimate the bridge mode shapes and damping ratios. Furthermore, Markov Chain Monte Carlo (MCMC) is also implemented to examine the reliability of bridge performance while ambient design trucks are in static or moving at different speeds. Strain, displacement and acceleration were measured at selected locations on the bridge. The results show that the symmetry index can be an efficient and useful measure in assessing the steel bridge performance. The results from the used method reveal that the performance of the Sungsu bridge is safe under operational conditions.

• Journal of Biosystems Engineering
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• v.32 no.1 s.120
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• pp.6-12
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• 2007

This study was conducted to investigate the drying characteristics of oak mushroom using stationary far-infrared dryer. Drying characteristics was measured at drying air velocity 0.4 to 0.6 m/s and drying temperature 50, 60, and 70$^{\circ}C$, respectively. With high temperature of far-infrared heater and fast air velocity, the far-infrared drying rate of double air flow system was better than conventional heated-air drying as much as 39%. The value of color difference (E) of oak mushroom before and after drying was 8.95 by using heated air drying and was in the range of 3.76$\sim$6.98 by the far-infrared drying. The shrinkage rate of oak mushroom after heated air drying was higher than that of air velocity, 0.6 m/s of far-infrared drying conditions, and was lower than that of air velocity, 0.4 m/s of far-infrared drying conditions. The content of free amino acid was higher in far-infrared drying than heated air drying.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.980-985
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• 2002

Several tests are performed to evaluate road booming noise. Baseline test delivers the information of road noise characteristics. Coupling effect between structure and acoustics is obtained from the mode shapes and the natural frequencies by the modal test. Equivalent stiffness at joint areas between chassis and car-body system can be determined by the input point inertance test. Noise sensitivity of body mounting point of a chassis part can be obtained from the noise transfer function test with input point inertance test. Operational deflection shape makes us analyze the actual vibration modes of the chassis system under actual loading and find noise sources very easily. finally, the transfer function analysis is used to identify noise paths through the chassis system. However, all of the tests above mentioned must be performed to evaluate road booming noise. The objectives and the procedures of the tests are described in this paper. Also, the guideline for efficient road noise evaluation test can be found.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.661-673
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• 2010

This paper presents recent developments in an extremely compact, wireless impedance sensor node (the WID3, $\underline{W}$ireless $\underline{I}$mpedance $\underline{D}$evice) for use in high-frequency impedance-based structural health monitoring (SHM), sensor diagnostics and validation, and low-frequency (< ~1 kHz) vibration data acquisition. The WID3 is equipped with an impedance chip that can resolve measurements up to 100 kHz, a frequency range ideal for many SHM applications. An integrated set of multiplexers allows the end user to monitor seven piezoelectric sensors from a single sensor node. The WID3 combines on-board processing using a microcontroller, data storage using flash memory, wireless communications capabilities, and a series of internal and external triggering options into a single package to realize a truly comprehensive, self-contained wireless active-sensor node for SHM applications. Furthermore, we recently extended the capability of this device by implementing low-frequency analog-to-digital and digital-to-analog converters so that the same device can measure structural vibration data. The compact sensor node collects relatively low-frequency acceleration measurements to estimate natural frequencies and operational deflection shapes, as well as relatively high-frequency impedance measurements to detect structural damage. Experimental results with application to SHM, sensor diagnostics and low-frequency vibration data acquisition are presented.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.561-578
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• 2010

This study proposes a multi-level damage localization strategy to achieve an effective damage detection system for civil infrastructure systems based on wireless sensors. The proposed system is designed for use of distributed computation in a wireless sensor network (WSN). Modal identification is achieved using the frequency-domain decomposition (FDD) method and the peak-picking technique. The ASH (angle-between-string-and-horizon) and AS (axial strain) flexibility-based methods are employed for identifying and localizing damage. Fundamentally, the multi-level damage localization strategy does not activate all of the sensor nodes in the network at once. Instead, relatively few sensors are used to perform coarse-grained damage localization; if damage is detected, only those sensors in the potentially damaged regions are incrementally added to the network to perform finer-grained damage localization. In this way, many nodes are able to remain asleep for part or all of the multi-level interrogations, and thus the total energy cost is reduced considerably. In addition, a novel distributed computing strategy is also proposed to reduce the energy consumed in a sensor node, which distributes modal identification and damage detection tasks across a WSN and only allows small amount of useful intermediate results to be transmitted wirelessly. Computations are first performed on each leaf node independently, and the aggregated information is transmitted to one cluster head in each cluster. A second stage of computations are performed on each cluster head, and the identified operational deflection shapes and natural frequencies are transmitted to the base station of the WSN. The damage indicators are extracted at the base station. The proposed strategy yields a WSN-based SHM system which can effectively and automatically identify and localize damage, and is efficient in energy usage. The proposed strategy is validated using two illustrative numerical simulations and experimental validation is performed using a cantilevered beam.