• 한국해양공학회지
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• 제32권3호
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• pp.151-157
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• 2018

Offshore structures are exposed to low- and high-frequency responses due to environmental loads, and fatigue damage models are used to calculate the fatigue damage from these. In this study, we tried to optimize the main parameters used in fatigue damage calculation to derive a new fatigue damage model. A total of 162 bi-modal spectra using the elliptic equation were defined to describe the response of offshore structures. To calculate the fatigue damage from the spectra, time series were generated from the spectra using the inverse Fourier transform, and the rain-flow counting method was applied. The considered optimization variables were the size of the frequency increments, ratio of the time increment, and number of repetitions of the time series. In order to obtain optimized values, the fatigue damage was calculated using the parameter values proposed in previous work, and the fatigue damage was calculated by increasing or decreasing the proposed values. The results were compared, and the error rate was checked. Based on the test results, new values were found for the size of the frequency increment and number of time series iterations. As a validation, the fatigue damage of an actual tension spectrum found using the new proposed values and fatigue damage found using the previously proposed method were compared. In conclusion, we propose a new optimized calculation process that is faster and more accurate than the existed method.

• 한국정밀공학회지
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• 제30권2호
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• pp.231-235
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• 2013

The purpose of this paper is to compare with estimation of equivalent fatigue load in time domain and frequency domain and estimate the fatigue life of structure with multi-axial vibration loading. The fatigue analysis with two methods is implemented with various signals like random, sinusoidal signals. Also an equivalent fatigue life estimated by rainflow cycle counting in time domain is compared with results estimated with probability density function of each signal in frequency domain. In case of frequency domain, equivalent fatigue life can estimate through Dirlik's method with probability density function. And the work proposed in this paper compared the fatigue damage accumulated under uni-axial loading to that induced by multi-axial loading. The comparison is preformed for a simple cantilever beam, which is exposed to vibrations of several directions. For verification of estimation performance of fatigue life, results are compared to those of FEM analysis (ANSYS).

• 대한의용생체공학회:의공학회지
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• 제32권4호
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• pp.319-327
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• 2011

Skeletal muscle fatigue is defined as a 'any reduction in the maximal capacity to generate force or power output', and is the reduction of oxygen consumption and by-product of metabolism. For the muscle fatigue therapy, low level laser has been introduced that leads the mitochondrial respiratory and attributes the muscle fatigue recovery. This study analyzed the muscle fatigue signals from electromyography(EMG) during low-level laser therapy (LLLT). Healthy subjects performed voluntary elbow flexion-extension excercise and received placebo LLLT and active LLLT using a 830 nm laser diode. Then, EMG were measured for the evaluation of muscle fatigue. The acquired EMG data were analyzed with median frequency and short time fourier transform methods. The results showed that the LLLT had a significant symptomatic relief of muscle fatigue based on the EMG frequency analysis. Therefore, the muscle fatigue analysis with EMG signals can be applied to quantitative evaluation for the monitoring of LLLT effects.

• The Journal of Korean Physical Therapy
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• 제11권1호
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• pp.71-77
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• 1999

The purpose of this study was to investigate the changes of muscle power by transcutaneous electrical nerve stimulation(TBNS), low frequency-low intensity(20pps, invisible muscle contraction intensity), low frequency-high intensity(20pps, visible muscle contraction), high frequency-low intensity(100pps, invisible muscle contraction intensity) and high frequency-high intensity(100pps, visible muscle contraction). The results were as follows. 1. Increased muscle power after 30 minutes of treatment by low frequency-low intensity TENS, and post-treatment 30 minutes muscle power were increased more than pre-treatment power(p<0.05). 2. Decreased muscle power after a 30 minute treatment by low frequency-high intensity TENS, and after the 30 minute treatment was terminated muscle power didn't recover to pre-treatment levels. 3. Decreased muscle power after 30 minute treatment by high frequency-low intensity TENS, but post-treatment 30 minute, muscle power didn't recover to pre-treatment levels. 4. The muscle power was remarkably decreased by high frequency-high intensity TENS after 30 minute treatment, in addition treatment terminated after 30minutes didn,t recover to pre-treatment power(p<0.05). 5. Lower frequency-low intensity TENS are good methods for preventing muscle fatigue, buty high intensity (TENS) are increased muscle fatigue. 6. Traditional TENS by high frequency-low intensity is a good method for preventing muscle fatigue.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권7호
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• pp.344-351
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• 2006

The fatigue of back muscle in the repetitive lifting motion was studied using multiple parameters(FFT_MDF, RMS, 2C, NT) in this study. Recent developments in the time-frequency analysis procedures to compute the IMDF(instantaneous median frequency) were utilized to overcome the nonstationarity of EMG signal using Cohen-Posch distribution. But the above method has a lot of computation time because of its complexity. So, in this study, FFT_MDF(median frequency estimation based on FFT) algorithm was used for median frequency estimation of back muscle EMG signal during muscle work in uniform velocity portion of lumbar movement. The analysis period of EMG signal was determined by using the run test and lumbar movement angle in dynamic task, such as lifting. Results showed that FFT_MDF algorithm is well suited for the estimation of back muscle fatigue from the view point of computation time. The negative slope of a regression line fitted to the median frequency values of back muscle EMG signal was taken as an indication of muscle fatigue. The slope of muscle fatigueness with FFT_MDF method shows the similarity of 77.8% comparing with CP_MDF(median frequency estimation based on Cohen Posch distribution) method.

• 열처리공학회지
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• 제8권4호
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• pp.326-332
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• 1995

Using natural frequency measurement method, which is one of NDT method, natural frequency of the hot-rolled mild steel plate(specimen) under fatigue loading was measured. Between the degradation of the specimen under fatigue loading and the variation of the natural frequency of the specimen was investigated. As a result, the degradation of the specimen was described and monitored as variation of natural frequency of specimen. The natural frequency of specimen decreased gradually under fatigue loading. This means the variation of material properties of specimen. Especially. It means the variation of Young's modulus of specimen.

• 기본간호학회지
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• 제16권1호
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• pp.83-91
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• 2009

Purpose: The purpose of this study was to compare fatigue and fatigue-regulation behaviors in undergraduates courses related to public health (group A) and undergraduates in courses not related to public health (group B). Method: Using a structured questionnaire, data were collected from 236 undergraduates. Descriptive statistics, Pearson correlation coefficient, t-test with SAS package were used for data analysis, Results: There was a statistically significant difference between group A and group B in t-test comparison by group for fatigue, and all subcategories of fatigue and fatigue-regulation behaviors. The frequency of fatigue-regulation behavior of group A was 12.23 and the mean for total efficiency of fatigue-regulation behavior was 2.17, while the frequency of fatigue-regulation behavior for group B was 10.47 and the mean for total efficiency of fatigue-regulation behavior was 1.75. Finally, total fatigue and all subcategories of fatigue were positively related to fatigue-regulation behaviors. Conclusion: It is necessary to develop an intervention program for regulating fatigue in undergraduates courses related to public health.

• 한국음향학회지
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• 제28권7호
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• pp.646-652
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• 2009

본 논문에서는 점용접 너깃의 피로수명을 고려한 차량 서브프레임의 용접간격 최적화 설계기법이 제안된다. 주파수영역 피로해석기법에 의해 점용접 너깃의 피로수명이 평가된다. 피로해석에서 사용되는 입력 데이터는 벨지안로 프로파일을 통과하는 차량동역학 해석과 차량 서브프레임 유한요소모델의 모드 주파수 해석을 통해 얻는다. 주파수 영역 피로해석으로 부터 얻은 피로수명 결과로부터 용접간격 최적화를 수행 할 설계점들이 선정된다. 점용접 너깃의 피로수명을 최대화시키는 용접간격을 얻기 위하여 4-요인, 3-수준 직교배열 실험계획법이 사용된다. 본 연구를 통하여 최적화된 서브프레임은 초기모델에 비하여 최소 피로수명을 갖는 용접 너깃의 피로수명이 약 65.8 % 증대되는 것을 알 수 있다.

• The Journal of Korean Physical Therapy
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• 제34권5호
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• pp.205-211
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• 2022

Purpose: This study investigated the effects of an intervention that combined the abdominal drawing-in maneuver and frequency-specific neuromuscular electrical stimulation on changes in trunk muscle activity, muscle fatigue, and balance in stroke patients. Methods: Thirty stroke patients were randomly assigned to two groups. Fifteen subjects were assigned to group I which performed the abdominal drawing-in maneuver combined with low-frequency neuromuscular electrical stimulation and the other 15 subjects to group II where the abdominal drawing-in maneuver was combined with high-frequency neuromuscular electrical stimulation. Muscle activity and fatigue were measured using surface electromyography before the intervention. Balance was measured using the Trunk Impairment Scale and re-measured after six weeks of intervention for comparative analysis. Results: Both groups showed a significant increase in muscle activity and balance (p<0.05), and there was no significant difference between the groups (p>0.05). In the changes in muscle fatigue, only the experimental group II showed a significant increase in muscle fatigue (p<0.05). The difference between the groups was statistically significant (p<0.05). Conclusion: It was confirmed that among stroke patients, the combination of the abdominal drawing-in maneuver and low-frequency neuromuscular electrical stimulation was more effective in changing the muscle activity and balance of the trunk by minimizing the occurrence of muscle fatigue compared to the combination of the abdominal drawing-in maneuver and high-frequency stimulation. These results can be used as basic data for clinical trunk stabilization training.

• 한국자동차공학회논문집
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• 제22권6호
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• pp.68-74
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• 2014

This study analyzes structural stress and fatigue about three types of automotive wheels. As maximum equivalent stresses at 1, 2 and 3 types become lower than the yield stress of material and deformations become minute, theses types are thought be safe on durability. Type 2 model has the most fatigue life among three kinds of types and the rest of models with fatigue lives are shown in the order of type 1 and 3. As the most fatigue frequency of type 2 model happens at the state of average stress and amplitude stress on the stress range narrower than type 1 or 3, type 2 model becomes most stable. In case of type 2 with the state near the average stress of 0 MPa and the amplitude stress of 300MPa, the possibility of maximum damage becomes 30%. This stress state can be shown as the most damage possibility. These study results can be effectively utilized with the design on automotive wheel by anticipating and investigating prevention and durability against its damage.