• 제목/요약/키워드: fatigue spectrum

검색결과 166건 처리시간 0.021초

음향방출을 이용한 발전용 밸브 누설 진단 현장 적용 연구 (In-Situ Application Study on the Power Plant Valve Leak Diagnosis Using Acoustic Emission Technology)

  • 이상국
    • 비파괴검사학회지
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    • 제28권4호
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    • pp.315-322
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    • 2008
  • 발전소 밸브는 장시간 동안 고온고압하의 기혹한 조건으로 운전됨에 따라 밸브 시트(seat)면의 이물질 삽입, 시트의 균열, 스템(stem) 패킹(parking) 또는 용접부위 결함 및 피로균열 둥에 의해 누설손상이 발생하고 있다. 이러한 밸브 내부누설 상태를 정밀하게 진단하고 평가하기 위해서는 음향방출기술의 적용이 필요하며, 본 논문은 현장적용이 가능한 연구를 수행하고 그 결과를 소개하고자 한다. 또한 실제 발전소에서 운전되는 다양한 밸브 조건을 토대로 실험실 실험에 의해 주변잡음, 밸브누설시의 음향레벨 및 스펙트럼 특성을 분석하고, 발전소 현장실험 결과와의 비교분석을 통하여, 밸브 누설상태에 따른 주변잡음, 음향신호 및 측정 가능한 최소 누설검출량 등의 평가방법에 대해 고찰하였다. 실험실 실험 및 현장적용 연구결과로부터 밸브누설 여부를 포함한 상태 평가와 최소 측정가능 누설검출량 평가가 가능하였으며, 향후 본 연구는 발전설비 안전운전과 밸브누설로 인한 에너지 손실 예방에 크게 기여할 것으로 기대된다.

Relationship of EMG and Subjective Discomfort Ratings for Repetitive Handling of Lightweight Loads

  • Lee, Inseok;Jo, Sungpill
    • 대한인간공학회지
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    • 제33권6호
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    • pp.565-575
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    • 2014
  • Objective: The aim of this study is to evaluate the effect of weight of load and time on the physical workload of repetitive upper-limb tasks with handling light weight loads using EMG and perceived discomfort, and to investigate the relationship between EMG and perceived discomfort for those repetitive tasks of moving light weight loads. Background: Repetitive upper-limb motion is known as one of the main risk factors of musculoskeletal disorders, and a lot of repetitive tasks are carried out while handling light weight loads in the industry. In evaluating the workload of repetitive tasks handling light weight loads, EMG and perceived discomfort can be used, though their relationship in those work conditions are not much investigated. Method: A laboratory experiment with 18 healthy males were conducted to record EMG signals from 5 muscle sites of the right arm and shoulder and rate perceived discomforts for the body parts and the whole body while carrying out repetitive materials-handling tasks for 52min. The subjects were divided into 3 groups which handled the loads of 1kg, 2kg and 3kg, respectively. ANOVAs were conducted to analyze the effects of the weight and time on RMS of EMG amplitude (normalized RMS: NRMS), median frequency of power spectrum of EMG (normalized MDF: NMDF) and perceived discomfort. The correlations between NRMS and NMDF and perceived discomfort were also analyzed. Results: Statistically significant muscular fatigue effects were not found from NRMS and NMDF in most muscles, while there were significant increases of discomfort as the task time elapsed. It was shown that there were an increasing trend of the muscular activity as the weight of load increased and a decreasing trend of median frequency of EMG of upper and lower arms as time elapsed. It was found that there were significant negative correlations between NMDFs from the lower arm and discomfort ratings, though the relationships were weak. Conclusion: It can be concluded that the working conditions adopted in this study were not enough to induce muscular fatigue, while there was significant increase in perceived discomfort. A further study is necessary to integrate the objective and subjective measures for more reliable and sensitive evaluation of workload of repetitive tasks of handling light weight loads. Application: This study can be used as a basic study for the evaluation of workload of repetitive tasks handling light weight loads.

Engineering criticality analysis on an offshore structure using the first- and second-order reliability method

  • Kang, Beom-Jun;Kim, Jeong-Hwan;Kim, Yooil
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제8권6호
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    • pp.577-588
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    • 2016
  • Due to the uncertainties related to the flaw assessment parameters, such as flaw size, fracture toughness, loading spectrum and so on, the probability concept is preferred over deterministic one in flaw assessment. In this study, efforts have been made to develop the reliability based flaw assessment procedure which combines the flaw assessment procedure of BS7910 and first-and second-order reliability methods (FORM/SORM). Both crack length and depth of semi-elliptical surface crack at weld toe were handled as random variable whose probability distribution was defined as Gaussian with certain means and standard deviations. Then the limit state functions from static rupture and fatigue perspective were estimated using FORM and SORM in joint probability space of crack depth and length. The validity of predicted limit state functions were checked by comparing it with those obtained by Monte Carlo simulation. It was confirmed that the developed methodology worked perfectly in predicting the limit state functions without time-consuming Monte Carlo simulation.

고주파 유압시스템의 주파수 특성과 축압기 효과의 실험적 연구 (Research for the Effect of Accumulator and the High Frequency-Hydraulic System of Frequency Characteristics by Experimental Method)

  • 박남은;김재수;김양수;김종록;노형운;전승배;나홍철
    • 한국유체기계학회 논문집
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    • 제6권3호
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    • pp.51-57
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    • 2003
  • Characteristics of the high frequency pulsatile flow have been investigated experimentally to understand the flow phenomena in the hydraulic system. One axis fatigue test bed, which is widely used for automobile field test, is used. Four pressure transducers, an amplifier and a A/D convertor are used to obtain the high frequency pulsatile pressure waveform in hydraulic system. The characteristics of frequency are analyzed by power spectrum method. According to the variations of pump input pressure and actuator acceleration frequency, the pressure is measured with or without an accumulator. The amplitude of pressure with accumulator is very lower than those without accumulator due to absorbing function of accumulator. As the frequency of actuator acceleration is increased, the effect of accumulator become very important to decrease the amplitude of pulsatile pressure waveform with high frequencies.

와이블-역승법을 이용한 기계류부품의 가속시험 방법 개발 (Development of accelerated life test method for mechanical components using Weibull-IPL(Inverse Power Law) model)

  • 이근호;김형의;강보식
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 춘계학술대회
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    • pp.445-450
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    • 2003
  • This study was performed 10 develop the accelerated life test method using Weibull-IPL(Inverse Power Law) model for mechanical components. Weibull-IPL model is concerned with determining the assurance life with confidence level and the accelerated life test time From the relation of weibull distribution factors and confidence limit, the testing times on the no number of failure acceptance criteria arc determined. The mechanical components generally represent wear and fatigue characteristics as a failure mode. IPL based on the cumulative damage theory is applied effectively the mechanical components to reduce the testing time and to achieve the accelerating test conditions. As the actual application example, accelerated life test method of agricultural tractor transmission was described. Life distribution of agricultural tractor transmission was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (MTBF) 3,000 hours and 90% confidence level for one test sample. According to IPL, because test time call be shorten in case increase test load test time could be reduced by 482 hours when we put the load 1.1 times of rated load than 0.73 times of rated load that is equivalent load calculated by load spectrum of the agricultural tractor. This time, acceleration coefficient was 11.7.

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자동변속기 구성품의 가속수명평가 방법에 관한 연구 (A Study on Accelerated Life Evaluation Method of Component for Automatic Transmission)

  • 임홍수;조병철;김연규;이희용;김재훈
    • 한국자동차공학회논문집
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    • 제25권2호
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    • pp.250-256
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    • 2017
  • Automatic transmission(A/T) is one of a car's core components. The durability of A/T has an effect on the durability of the car. The input shaft of A/T passes the power directly from the engine, so the durability of the input shaft for A/T is likewise vital. In this study, the test method of the input shaft is considered and the load spectrum of A/T is analyzed to secure durability of the input shaft. The shape parameter, T-N curve of the input shaft torsional fatigue test are obtained for life evaluation and analysis. Results of this study can be used to get the basic background of the durability test for A/T components.

혼합배관 내의 열 경계층 이동으로 인한 고주기 온도요동에 관한 연구 (A Study on High Cycle Temperature Fluctuation Caused by Thermal Striping in a Mixing Tee Pipe)

  • 김석범;박종호
    • 한국유체기계학회 논문집
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    • 제10권5호
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    • pp.9-19
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    • 2007
  • Fluid temperature fluctuations in a mixing tee pipe were numerically analyzed by LES model in order to clarify internal turbulent flows and to develope an evaluation method for high-cycle thermal fatigue. Hot and cold water with an temperature difference $40^{\circ}C$ were supplied to the mixing tee. Fluid temperature fluctuations in a mixing tee pipe is analysed by using the computational fluid dynamics code, FLUENT, Temperature fluctuations of the fluid and pipe wall measured as the velocity ratio of the flow in the branch pipe to that in the main pipe was varied from 0.05 to 5.0. The power spectrum method was used to evaluate the heat transfer coefficient. The fluid temperature characteristics were dependent on the velocity ratio, rather than the absolute value of the flow velocity. Large fluid temperature fluctuations were occurred near the mixing tee, and the fluctuation temperature frequency was random. The ratios of the measured heat transfer coefficient to that evaluated by Dittus-Boelter's empirical equation were independent of the velocity ratio, The multiplier ratios were about from 4 to 6.

공기 동역학 하중이 부유식 해상 풍력 발전기의 계류선 응답에 미치는 영향에 관한 연구 (A Study on Effect of Aerodynamic Loads on Mooring Line Responses of a Floating Offshore Wind Turbine)

  • 김형준;한승오;정준모
    • 대한조선학회논문집
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    • 제52권1호
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    • pp.43-51
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    • 2015
  • This paper presents effect of aerodynamic loads on mooring line responses of a floating offshore wind turbine. A Matlab code based on blade element momentum (BEM) theory is developed to consider aerodynamic loads acting on NREL 5MW wind turbine. The aerodynamic loads are coupled with time-domain hydrodynamic analyses using one-way interaction scheme of the wave and wind loads. A semi-submersible floating platform which is from Offshore Code Comparison Collaborative Continuation(OC4) DeepCWind platform is used with catenary mooring lines simply composed of studless chain links. Average values of mooring peak tensions obtained from aerodynamic load consideration are significantly increased compared to those from simple wind drag force consideration. Consideration of aerodynamic loads also yield larger tension ranges which can be important factor to reduce fatigue life of the mooring lines.

하나로 침니내부지지대의 내진해석 및 진동시험 (Seismic Analysis and Vibration Test of HANARO In-Chimney Bracket)

  • 류정수;윤두병
    • 한국전산구조공학회:학술대회논문집
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    • 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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    • pp.481-488
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    • 2001
  • The HANARO in-chimney bracket was proposed as a structure which supports the guide tubes of irradiation facilities at the irradiation sites of CT, IR and OR4/5 in HANARO core for the reduction of flow-induced vibration and seismic response of the irradiation facilities. For the evaluation of the structural integrity of the in-chimney bracket, its finite element model is developed. The seismic response analysis was performed for the in-chimney bracket and related reactor structures, under the response spectrum of OBE and SSE. The analysis results show that stress values of the in-chimney bracket and reactor structures for the seismic loads are within the ASME code limits. It is also confirmed that its fatigue usage factor is much less than 1.0. For the verification of the implementation effects of the in-chimney bracket, the vibration level of the guide tube of the instrumented fuel assembly, which is subjected to fluid-induced vibration, was measured and analyzed. The vibration analysis results demonstrate that the vibration level of the instrumented fuel assembly has been remarkably reduced after installing the in-chimney bracket. Therefore, when the in-chimney bracket is installed at the reactor chimney, any damage on the structural integrity is not expected.

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유두컵 라이너의 물리화학적 특성 조사 (A Study on the Physical and Chemical Properties of Teat Cup Liners)

  • 이정치;박형련;김명선;이정길;이채용
    • 한국임상수의학회지
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    • 제22권2호
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    • pp.100-107
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    • 2005
  • This study was carried out to investigate the physical and chemical properties of teat cup liners. The hardness of the liners was $50\~67$, and their fatigue to failure 38-1,185 cycles. The elongation and tensile strength of these liners were about $134 kgf/cm^2\;and\;473\%$, respectively. The infrared spectrum and the gas chromatogram revealed that the liner A was consisted of NR, SBR, and BR, with a composition ratio of 60:20:20 (part per hundred rubber). The raw rubber materials used for liners B to G, on the other hand, were NBR only. However, the liner H was made of silicon rubber. The thermogravimetric analysis showed that the liners tested in this study contained raw rubber material, carbon black, organic compounds and metallic compounds.