• Journal of the Korean Society of Marine Environment & Safety
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• 제21권2호
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• pp.130-139
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• 2015

To assess the noise stress of shrimp farms reasonably, we need a noise observation data underneath the waters first. But, it did not collect yet and airborne noise transfers to water noise wave using transition calculation. In case of construction of solar energy without noise stress protection wall, the threshold values (140 dB) from circumstance of underwater noise exceed within 17m at $S_2$ (15m away from source) and $S_3$ (15m away from source). Considering additional way to decrease the construction noise, all cases including minimum mode(Case A), general mode(Case B), and maximum mode(Case C) meet the guideline of underwater noise for fish farms. In case of the underwater noise could affect the fish farm, it is necessary to understand about farming species such as shrimp, monitoring of present states, and protection way under the construction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2010년도 추계학술대회 논문집
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• pp.380-384
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• 2010

A disturbance flow at piping bands and discontinuous regions such as a valve, a header has a intense broadband internal pressure field and a sound field which are propagated through the piping system The fields becomes the source of a vibration of this piping system. Intense broadband disturbance flow at a discontinuous region such as elbows, valves or headers generates an acoustical pulsation. The pulsation becomes the source of structural vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation affects the reliability of the plant piping system. This paper discusses the high vibration and the branch vent pipe's failure of condensate-water supply piping system due to the effect of acoustical pulsations by flow turbulence from the flow control valves of globe type in a power site.

• Safety and Health at Work
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• 제15권2호
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• pp.181-186
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• 2024

Background: This study aimed to analyze the trend of occupational noise-induced hearing loss (ONIHL) in Brazilian workers at a metallurgical plant with a hearing conservation program (HCP), which has been addressed in a previous study. Methods: All 152 workers in this time series (20032018) participated in the HCP and used personal protective equipment. All annual audiometry records in the company's software were collected from the electronic database. The trend of ONIHL was analyzed with the joinpoint regression model. The hearing thresholds of ONIHL cases at the end of the series were compared with those found in a national reference study. Results: The binaural mean hearing thresholds at 3, 4, and 6 kHz at the end of the series were higher for ages ≥50 years, exposures ≥85 dB (A), time since admission >20 years, and maintenance workers. Significance was found only in the group divided by age. There was an increasing time trend of ONIHL, though with a low percentage variation for the period (AAPC = 3.5%; p = 0.01). Hearing thresholds in this study differed from the reference one. Conclusion: Despite the unmet expectation of a stationary trend in the study period, the time pace of ONIHL evolution did not follow what was expected for a population exposed to noise. These findings signal to the scientific community and public authorities that good ONIHL control is possible when HCP is well implemented.

• Journal of Power System Engineering
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• 제12권5호
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• pp.65-70
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• 2008

The purpose of this study is to verify availability of the acoustic emission in-situ monitoring method to the internal leak and operating conditions of the turbine major valves relating to safety for turbine operating and prevention of turbine trouble at nuclear power plants. In this study, acoustic emission tests are performed when the pressurized electro-hydraulic control oil flowed through turbine electro-hydraulic controller oil check valve and turbine power/trip fluid solenoid valve in the condition of actual turbine operating. The acoustic emission method was applied to the valves at the site, and the background noise was measured far the abnormal plant condition. To judge for the leak existence ell the object valves, voltage analysis and frequency analysis of acoustic signal emitted from infernal leak in the valve operating condition are performed. It was conformed that acoustic emission method could monitor for valve internal leak to high sensitivity.

• Journal of KSNVE
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• 제9권6호
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• pp.1200-1209
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• 1999

This paper reports a peculiar example of flow-induced vibration in a very large plant and the whole procedure of reducing the vibration. During the operation of flue gas desurfurization unit of the thermal power plant, serious vibration was dtected at all around the plant. The worst vibration was recorded on the heat exchanger surface, which weighed 180 tones, as 17.8 m/$s^2$ in vibration amplitude at 34 Hz. To identify the vibration, frequency analysis on the response vibration as well as on the expected excitation forces and the system resonance was executed. This investigation revealed that the cause of the vibration was vortex shedding from the circular pipes in the heat exchanger. Vortices from the pipes excited acoustic resonance in the heat exchanger room, which, in turn, made the structure vibrate. Through inserting the baffles between the pipes, which had an effect of cutting the acoustic wave at resonance frequency, the vibration was eliminated dramatically.

• Journal of Power System Engineering
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• 제11권1호
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• pp.39-44
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• 2007

The purpose of this study is to verify availability of the acoustic emission in-situ monitoring method to the internal leak and operating conditions of the major valves at nuclear power plants. In this study, acoustic emission tests are performed when the pressurized temperature water and steam flowed through glove valve(main steam dump valve) and check valve(main steam outlet pump check valve) on the normal size of 12 and 18". The valve internal leak monitoring system for practical field was designed. The acoustic emission method was applied to the valves at the site, and the background noise was measured for the abnormal plant condition. To improve the reliability, a judgment of leak on the system was used various factors which are AE parameters, trend analysis, frequency analysis, voltage analysis and amplitude analysis of acoustic signal emitted from the valve operating condition internal leak.

• The Transactions of the Korean Institute of Electrical Engineers
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• 제37권5호
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• pp.311-318
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• 1988

An adaptive control problem for a plant with unmodelled dynamics is studied. The upper bounds of the output due to the unmodelled dynamics and measurement noise is assumed to be known. This problem was studied by Middleton et al. They used a modified form of the least square method in estimating the plant paramaters. In this paper, the bounds of the parameters are estimated by linear programming and the parameters are estimated by the projetion type algorithm incorporating the bounds of the parameters. The stability of the proposed adaptive control system can be proved in nearly the same way as the proof of Middleton. The performance of the proposed method is found to be much better than the method of Midlleton's with respect to the parameter convergence and plant output in computer simulations.

• Plant Journal
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• 제17권4호
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• pp.53-60
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• 2021

The purpose of this study was to develop a portable vibration analyzer that is effective for acquiring and analyzing vibration data of rotating equipment of a power plant and a domestic vibration monitoring system manufacturer Nada Co., Ltd. The hardware of the developed portable vibration analyzer minimizes measurement errors by calibrating the measured values obtained through measurement uncertainty for calibration of the measuring devices in the system, and is composed of a signal processing device with high resolution through high speed data processing. The software structure implements a variety of vibration plots to execute a detailed analysis program, and applies algorithms to measure and remove noise caused by disturbances while operating a rotating machine. The developed product contributed greatly to increase the user's mobility and performance, as well as to reduce the purchase cost due to localization.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.41-45
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• 2007

Palo Verde Unit 1 nuclear power station which is located in Arizona, USA had been operating at reduced power levels around 25% since December 25, 2005 due to vibration in one of its shutdown cooling lines. During an outage from March 18, 2006 to July 7, 2006 the necessary work and modifications to remedy the situation were performed. It cost approximately $46million to buy electricity to replace that lost as a result of this event. Therefore in this study, the vibration of shutdown cooling lines in the same nuclear power plant in Korea as Palo Verde Unit 1 should be measured by the operating condition of power plant. And it was evaluated using the expression for allowable velocity in ASME OM-S/G-2003. From the result of this study it is evaluated whether it is safe or not. If not the countermeasure should be considered in this study.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제17권7호
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• pp.572-578
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• 2007

Two stroke low speed diesel engines are widely used for marine propulsion or as power plant prime mover. These engines have many merits which includes higher thermal efficiency, mobility and durability. Yet various annoying vibrations occur sometimes in ships or at the plant itself. Of these vibrations, torsional vibration is very important and dictates a careful investigation during the engme's initial design stage for safe operation. With the rule and limit on torsional vibration in place, shaft strength fatigue due to torsional vibration however demands further analysis which possibly can be incorporated in the classification societies' rule and limit. In addition, the shaft's torsional vibration stresses can be calculated equivalently from accumulated fatigue cycles number due to transient torsional vibration in time domain. In this paper, authors suggest a new estimation method combined with Palmgren-Miner equation. A 6S70MC-C ($25,320ps{\times}91rpm$) engine for ship propulsion was selected as a case study. Angular velocity was measured, instead of shaft's strain, for simplified measurement and it was converted to torsional vibration stress for accumulated fatigue cycle numbers in shafting life time. Likewise, the accumulated fatigue calculation was compared with shaft fatigue strength limit. This new method can be further realized and confirmed in ship with two stroke low speed diesel engine.