• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.605-611
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• 2000

Presented in this paper is a new method of identifying the critical speed of rotor-bearing systems without actually reaching at the critical speed itself. Using the method, it is not only possible to calculate the critical speed by measuring a series of rotor responses at much lower rotating speeds away from and without reaching at the critical speeds but also the damping ratio and eccentricity of the system can be identified at the same time. Two types of test rotors were tested on the Rotor Dynamics Test Facility at the Rotordynamics Lab., KIMM, and the theory has been confirmed experimentally. The method can be adopted to monitor changes of the dynamic characteristics of critical rotating machinery before and after overhauls, repairs, exchanges of various parts, or to detect trends of direction of subtle changes in the dynamic characteristic parameters over a long periods of time.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.12
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• pp.1229-1236
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• 2008

A set of modal parameters of a stay-cable have been extracted fi:on a moving picture captured by a digital camera supported by shaking hands. It is hard to identify the center of targets attached on the cable surface from the blurred cable motion image, because of the high speed motion of cable, low sampling frequency of camera, and the shaking effect of camera. This study proposes a multi-template matching algorithm to resolve such difficulties. In addition, a sensitivity-based system identification algorithm is introduced to extract the natural frequencies and damping ratios from the ambient cable vibration data. Three sets of vibration tests are conducted to examine the validity of the proposed algorithms. The results show that the proposed technique is pretty feasible for extracting modal parameters from the severely shaking motion pictures.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.770-774
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• 1994

The volume of an acoustic source is important in determining various acoustic parameters. One of the suggested techniques is the internal pressure method incorporating a loudspeaker attached to a chamber wall and a microphone inserted into the cavity. Although the method is easy to handle with a very simple measurement setup, the coupling effects between the dynamic system of the loudspeaker and acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic field should be considered for precise result. In this study, higher order modes due to the discontinuities of loudspeaker and microphone boundaries are included and the electro-acoustic coupling effects are compensated for by using the results of two cylinders with different lengths. The volume velocity of a loudspeaker thus obtained agrees very with that measured by laser sensor.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.369-378
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• 1998

When a high-speed train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel. This wave subsequently emerges form the exit portal of the tunnel, which causes an impulsive noise. In the present study, experimental investigation is carried out on the sonic boom noise with parameters of train speed, blockage ratio, nose shape of train and airshaft. These experimental results show that several countermeasures could be used to efficiently reduce the sonic boom. In addition, numerical analysis is performed to predict the sonic boom. The predicted sound waves are in a good agreement with the experimental results.

• The Journal of the Acoustical Society of Korea
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• v.40 no.1
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• pp.73-83
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• 2021

Wind power energy harvesting has a big potential as a future clean energy resource, but accompanies infrasonic noises. The infrasound is difficult to shield and can induce various negative physiological effects. In this study, the Wind Turbine Syndrome (WTS) caused by the infrasonic noises are introduced, and the technical aspects for the measurement and management of the infrasonic noises from wind power plants are discussed.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.2
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• pp.119-126
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• 2022

This paper presents a method to reduce the vibration-induced noise effect of an inertial measurement device mounted on a self-driving vehicle. The inertial sensor used in the GNSS/INS integrated navigation system of a self-driving vehicle is fixed directly on the chassis of vehicle body so that its navigation output is affected by the vibration of the vehicle's engine, resulting in the degradation of the navigational performance. Therefore, these effects must be considered when mounting the inertial sensor. In order to solve this problem, this paper proposes to use an in-house manufactured vibration suppression device and analyzes its impact on reducing the vibration effect. Experimental test results in a static scenario show that the vibration-induced noise effect is more clearly observed in the lateral direction of the vehicle, but can be effectively suppressed by using the proposed vibration suppression device compared to the case without it. In addition, the dynamic positioning test scenario shows the position, speed, and posture errors are reduced to 74%, 67%, and 14% levels, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.339.2-339
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• 2002

In recent years, the demand of mobile device, such as digital camera, camcoder and PDA, increases remarkably. So, requirements of the mobile information data storage used in the mobile devices increase noticeably also. 1" micro storage is a kind of mobile storage, which has a CF type II form factor, and the similar structure of the general 3.5" HDD. In this paper, we performed the vibration analysis and experimental study of disk-spindle system in 1 " micro storage, such as measurement of the NRRO of the disk, and modal analysis. (omitted)

• Bulletin of the Korean Mathematical Society
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• v.60 no.1
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• pp.93-111
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• 2023

In this paper we study a nudging continuous data assimilation algorithm for the three-dimensional Leray-α model, where measurement errors are represented by stochastic noise. First, we show that the stochastic data assimilation equations are well-posed. Then we provide explicit conditions on the observation density (resolution) and the relaxation (nudging) parameter which guarantee explicit asymptotic bounds, as the time tends to infinity, on the error between the approximate solution and the actual solution which is corresponding to these measurements, in terms of the variance of the noise in the measurements.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.832-842
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• 2009

Automatic speech recognition (ASR) has been successfully applied to many real human computer interaction (HCI) applications; however, its performance tends to be significantly decreased under noisy environments. The invention of audio visual speech recognition (AVSR) using an acoustic signal and lip motion has recently attracted more attention due to its noise-robustness characteristic. In this paper, we describe our novel integration scheme for AVSR based on a late integration approach. Firstly, we introduce the robust reliability measurement for audio and visual modalities using model based information and signal based information. The model based sources measure the confusability of vocabulary while the signal is used to estimate the noise level. Secondly, the output probabilities of audio and visual speech recognizers are normalized respectively before applying the final integration step using normalized output space and estimated weights. We evaluate the performance of our proposed method via Korean isolated word recognition system. The experimental results demonstrate the effectiveness and feasibility of our proposed system compared to the conventional systems.

• Journal of environmental and Sanitary engineering
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• v.11 no.3
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• pp.53-61
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• 1996

The subject of this study was to analyse overviews of companies which exceed TLV by industry, hazardous factors, and to estimate the numbers of companies measured in 1993 and the implementation rate of working environment measurement by the act of industrial safety and health The result of this study was as follow. 1. The number of cases which exceed TLV was 5,937 companies. In distribution of excess companies by the scale of workers, small scale cases under the 49 workers were 3,150 companies(53.0%) of total cases, medium scale cases between 50 - 299 workers were 2,248 companies(37.9%), and large scale cases over 300 workers were 539 companies(9.1%). By the industry of excess companies, it was marked high rate in manufacture of fabricared metal products(except machinary and equipment), manufacture of textiles of each 1,048 companies(17.7%), and 1,018 companies(17.1%). By the area of excess companies, it was shown high rate in Kyeongki area marked 1,679 companies(28.3%) and Daegu-Kyeongbuk area were marked 1,417 companies (23.9%). By the hazardous factors of excess companies, noise was recorded high rate in 5,160 companies (86.9%), dust was shown in 1,245 companies(21.0%), organic solvent was marked 130 companies(7.9%). The number of excess factors by the company was 1.2. In this result, the more it was bigger scale companies, the more excess factors were much more and the more it was recorded higher rate in noise organic solvent heavy metals, etc. 2. The measured cases in institutes during 1994 were 1,596 companies, and excess cases were 157 companies(9.8%) among them. By the scale of workers, small scale cases under the 49 workers were 190 companies (17.9%) among 1,064 companies, cases of medium scale cases between 50-299 workers were 127 companies (27.9%) among 463 companies, and large scale cases over 300 workers were 31 companies(44.9%) among 69 companies. In this result industry of the highest rate shown was manufacture of basic metals in 20 companies exceeded among 53 companies (37.7%), and was manufacture of pulp, paper production in 14 companies exceeded among 40 companies(35.0%), and the excess rate were high in bigger scale. 3. Companies estimated by the data of excess cases and excess rate in 1993 were 30,474 implementation rate estimated for measurement of working environment was 34.3% of companies in korean industry. In this result, it was comparatively shown of measurement rate for the working environment in manufacture of pulp, paper product, manufacture of machinary and equipment n.e.c., and of high measurement rate and excess rate in manufacture of electrial machinary and apparatus, and manufacture of basic metals.