• Journal of the Korean Society for Precision Engineering
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• v.30 no.2
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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).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.416-422
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• 2007

Prime movers in most large merchant ships adapt two stroke low speed diesel engine which has higher efficiency, mobility and durability. However, severe torsional vibration in these diesel engines may be induced by higher fluctuation of combustion pressures. Consequently, it may lead sometimes to propulsion shafting failure due to the accumulated fatigue stresses. Shaft fatigue strength analysis had been done traditionally in time domain but this method is complicated and difficult in analysing bi-modal vibration system such as the case of cylinder misfiring condition. In this paper authors introduce an assessment method of fatigue strength estimation for propulsion shafting system with two stroke low speed diesel engine in the frequency domain.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.667-679
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• 2022

Fatigue damage analysis of ships includes parameters considering operational factors. Due to these operational variables, there is a difference between the fatigue damage estimated during the design stage and the actual accumulated fatigue damage. Likewise, there are various loading conditions for the real container ships, but at design stage the fatigue damage is calculated by applying the representative loading conditions. Moreover, although the difference in fatigue damages is expected when the actual and design loading conditions are applied, there are few studies on the contributions of the fatigue damage based on the loading conditions of container ships. In this paper, fatigue contributions were investigated from various cargo weight distributions. The hull girder loads calculated through seakeeping analysis and fatigue damages obtained by performing spectral fatigue analysis were identified under new loading conditions. As a result, it was found that the variation of cargo weight distribution in the container ship brought about changes in the hull girder loads and fatigue damage by affecting the hull girder stress.

• Journal of the Ergonomics Society of Korea
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• v.16 no.3
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• pp.37-48
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• 1997

It is very common for women wear shoes with a high heel. It has been known that the high heel could disfigure the foot shape and cause various joint problems including back pain. However, few quantitative studies have been conducted. Therefore, in this study, the low back muscle has been investigated in order to find fatifue effect due to different heights of the heel. In particular, 0, 4, 6 and 8cm heel and two different shapes of heel have been used for an experiment. Ten healthy female subjects volunteered for the study. Isometric Trunk Exertion Frame(ITEF) and Electromyography were used to measure tha Median Frequency via Spectral analysis. The results indicated that the heel height significantly affected the local muscle fatigue of the back. After post hoc analysis, it was found that a proper heel height ougth to be lower than 5cm not to have severely fatigued back muscle after a casual walk for an hour. Such results could be applies to female industrial workers in order to prevent a cumulative trauma disorder of the back, and also to design a female dress shoes minimizing low back fatigue.

• Journal of Energy Engineering
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• v.29 no.3
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• pp.7-17
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• 2020

Heat recovery steam generator(HRSG) generate steam using the high-temperature exhaust energy of gas turbines. Structures of HRSG are damaged by flow induced vibration of flue gas in some cases. In order to evaluate fatigue life to predict damage to a structure, a vibration analysis caused from flue gas should be used to derive the Power Spectral Density(PSD). However, it is very difficult to experimentally derive the vibrations generated by the exhaust gas form of gas turbines, which is very fast and complex. It was able to establish a way to identify vibration characteristics depending on the location of the structure by using high computing resources, large eddy simulation (LES). Random vibration analysis through these vibration characteristics(PSD) can evaluate the fatigue life of a structure.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.1
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• pp.1-9
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• 2023

The skin structure of sensor pod mounted on the exterior of aircraft can be exposed to the acoustic dynamic load and static load such as aerodynamic pressure and inertial load during flight. Fatigue life prediction of structural model under acoustic load should be performed and also differential stiffness of model modified by static load should be considered. The acoustic noise test spectrum of MIL-STD-810G was applied to the structural model and the stress response power spectral density (PSD) was calculated. The frequency response analysis was performed with or without prestress induced by inplane static load, and the response spectrum was compared. Time series data was generated using the calculated PSD, and the time and frequency domain fatigue life were predicted and compared. The variation of stress response spectrum due to static load and predicted fatigue life according to the different structural model considering mean stress were examined and decreasing fatigue life was observed in the model with prestress of compressive static load.

• Journal of Convergence for Information Technology
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• v.11 no.10
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• pp.10-19
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• 2021

In this paper, we tried to derive characteristic parameters that reflect mental fatigue through EEG measurement and analysis. For this purpose, mental fatigue was induced through a resting state with eyes closed and performing subtraction operations in mental arithmetic for 30 minutes. Five subjects participated in the experiment, and all subjects were right-handed male students in university, with an average age of 25.5 years. Spectral analysis was performed on the EEG collected at the beginning and the end of the experiment to derive feature parameters reflecting mental fatigue. As a result of the analysis, the absolute power of the alpha band in the occipital lobe and the temporal lobe increased as the mental fatigue increased, while the relative power decreased. Also, the difference in power between resting state and task state showed that the relative power was larger than the absolute power. These results indicate that alpha relative power in the occipital lobe and temporal lobe is a feature parameter reflecting mental fatigue. The results of this study can be utilized as feature parameters for the development of an automated system for mental fatigue determination such as fatigue and drowsiness while driving.

• Physical Therapy Korea
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• v.11 no.2
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• pp.17-25
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• 2004

The purpose of this study was to assess the effect of applied insole types to lower extremities muscle fatigue during treadmill exercise. The control group and each different insole type group consisted of ten healthy male subjects. In the control group and each different insole type (soft type; 10 shore, semi-rigid type; 33 shore, rigid type; 50 shore) treadmill exercise was performed in twenty-five minutes. The electromyography (EMG) signals of four muscle (tibialis anterior, gastrocnemius medialis, rectus femoris, biceps femoris) were recording at sampling rate of 1024 Hz during treadmill exercise. The localized muscle fatigue (LMF) can be investigated using power spectral analysis. When did data analysis that excepted initial five minutes. The raw EMG signals was processed using the fast Fourier Transformation (FFT) and the median power frequency value was determined in initial ten second period and in last ten second period. Fatigue index was calculated and collected data were statistically analyzed by SPSS version 10.0 two-way using analysis of variance (ANOVA) with repeated measures ($4{\times}4$) was used to determine the main effect and interaction. Post hoc was performed with least significant difference. A level of significance was .05. Muscles fatigue index were significantly decreased in insole types (p<.05) and not significantly different in muscle (p>.05). Post hoc analysis shows that fatigue index in soft insole type, semi-rigid insole type and rigid insole type were lower than that control group (p=.028, p=.146, p=.095). There were no interaction between insole type and muscles (p>.05). The finding of this study can be used as a fundamental data when insole is applied and insole can be used to decreased of a fatigue during the dynamic exercise.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.3
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• pp.31-41
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• 1988

Recently, the offshore structures are increasingly constructed to explore the natural resources. These offshore structures are to be designed to resist the repetitive wave forces. A probabilistic method for the fatigue analysis of offshore concrete structures is presented in this study. The present spectral fatigue analysis calculates wave forces first and then the transfer functions for unit waves from which stress spectra are determined. The calculated fatigue stresses may then be used to evaluate the fatigue damage of concrete structures. A simplified model for the estimation of fatigue damage of the structures, which employs only the probabilistic moments of the peak stress distribution without direct integration, is also proposed. The present study allows more realistic fatigue analysis of offshore concrete structures.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.4 no.1
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• pp.44-50
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• 2001

Existing surface defects in structural members often act as sites of fatigue crack initiation, and if undetected, these cracks may grow through the thickness of the member, leading to catastrophic failure of the structure. Thus, in-service monitoring of fatigue cracks through reliable and effective nondestructive techniques is an important ingredient in the leak-before-break (LBB) design and safe operation of defects critical structures. An advanced, waveform-based, acoustic emission (AE) technique has been used in this paper to study the characteristics of the signals emanating from the initiation, growth and through-the -thickness penetration of surface fatigue crack in a 6061 aluminum plate. The goal of this experimental study is to determine whether the evolution of the fatigue crocks could be identified from the properties of the waveforms produced during the tests. The AE waveform signals detected at different stages of crack growth was found to have different temporal and spectral characteristics. The data analysis technique presented here can be applied to real-time monitoring of the initiation and propagation of fatigue cracks in structural components.