• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.11 s.242
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• pp.1472-1479
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• 2005

Multiple surface crack distributed randomly along a weld toe influences strongly on the fatigue crack propagation life of welded joint. It is investigated by using statistical approaches based on series of systematic experiments. From the statistical results, initial crack numbers and its locations follow the normal distribution, and the probability of initial crack depths and lengths can be described well by tile Weibull distribution. These characteristics are used to calculate the fatigue crack propagation life, in which the mechanisms of mutual interaction and coalescence of the multiple cracks are considered as well as the Mk-factors obtained from a parametric study on the crack depths and lengths. The automatic calculation is achieved by the NESUSS, where the parameters such as the number, location and size of the cracks are all treated as random variables. The random variables are dealt through the Monte-Carlo simulation with sampling random numbers of 2,000. The simulation results show that the multiple cracks lead to much shorter crack propagation life compared with those in single crack situation. The sum of the simulation and tile fatigue crack initiation life derived by the notch strain approach agrees well with the experiments.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.6
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• pp.813-820
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• 2010

The spread mooring system for FPSO is developed to explore deep sea area, in which swell is dominant. It is known that the tension response of mooring lines in this sea area shows bimodal spectrum. Assuming normal distribution of tension profile and Rayleigh distribution of tension amplitude, the power spectral density function (PSD) of the mooring tension under the bimodal stationary random process is applied for the calculation of spectrum fatigue. Three popular methods, which are simple summation method, combined spectrum method and Jioa-Moan method, are used to combine fatigue damages from bimodal spectrum characteristics. Each damage value is compared with damage using Rainflow Cycle Counting (RCC) method which is believed to be close to exact solution. Vanmarcke' parameter and RMS(Root Mean Square) ratio are employed to assess relative damage variations between from RCC method and from three combination methods. Finally the most reliable fatigue damage combining method for spread mooring system is suggested.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.301-306
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• 2002

The characteristics of parameters for the probability distribution of fatigue crack growth lives by the non-Gaussian random process simulation method is investigated. In this paper, the material resistance to fatigue crack growth is treated as a spatial random process, which varies randomly on the crack surface. Using the previous experimental data, the crack length - the number of cycles curves are simulated. The results are obtained for constant stress intensity factor range conditions with stress ratio of R=0.2, three specimen thickness of 6, 12 and 18mm, and the four stress intensity level. The probability distribution function of fatigue crack growth lives seems to follow the 3-parameter Wiubull and shows a slight dependence on specimen thickness and stress intensity level. The shape parameter, ${\alpha}$, does not show the dependency of thickness and stress intensity level, but the scale parameter, ${\beta}$, and location parameter, ${\upsilon}$, are decreased by increasing the specimen thickness and stress intensity level. The slope for the stress intensity level is larger than the specimen thickness.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.984-994
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• 2020

It is reported that about 20% of accidents at nuclear power plants in Korea and abroad are caused by human error. One of the main factors contributing to human error is fatigue, so it is necessary to prevent human errors that may occur when the task is performed in an improper state by grasping the status of the operator in advance. In this study, we propose a method of evaluating operator's fitness-for-duty (FFD) using various parameters including eye movement data, subjective fatigue ratings, and operator's performance. Parameters for evaluating FFD were selected through a literature survey. We performed experiments that test subjects who felt various levels of fatigue monitor information of indicators and diagnose a system malfunction. In order to find meaningful characteristics in measured data consisting of various parameters, hierarchical clustering analysis, an unsupervised machine-learning technique, is used. The characteristics of each cluster were analyzed; fitness-for-duty of each cluster was evaluated. The appropriateness of the number of clusters obtained through clustering analysis was evaluated using both the Elbow and Silhouette methods. Finally, it was statistically shown that the suggested methodology for evaluating FFD does not generate additional fatigue in subjects. Relevance to industry: The methodology for evaluating an operator's fitness for duty in advance is proposed, and it can prevent human errors that might be caused by inappropriate condition in nuclear industries.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.111-122
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• 2000

In this study, A series of fatigue tests have been performed on the fillet welded joints of cover plates in steel plate girders in order to quantitatively assess the fatigue characteristics according to the shapes of cover plates. From the results of fatigue tests, it has been shown that the fatigue strengths were slightly different according to their shapes, but satisfied the fatigue design curves in Korea and other countries. Also, from the results of beachmark tests, it has been confirmed that the points of fatigue crack initiation were closely related to the shapes of weld bead toes, and fatigue cracks simultaneously initiated from several points in weld bead toes have been grown as semi-elliptical surface cracks, and these cracks have been coalesced each other, and grown as through thickness cracks, and finally reached to fracture. Besides, from the results of fracture mechanics approaches, stress gradient factors were the most dominant factors among crack correction factors obtained from the existing equations and finite element analysis, and the fatigue life on fillet welded joints of cover plates could be estimated using the relations between fatigue crack growth rate and stress intensity factor range obtained from finite element analysis.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.1
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• pp.50-56
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• 2010

Fatigue has been known as a major degradation mechanism of ASME class 1 components in nuclear power plants. Fatigue damage could be accelerated by combined interaction of several loads and environmental factors. However, the environmental effect is not explicitly addressed in the ASME S-N curve which is based on air at room temperature. Therefore many studies have been performed to understand the environmental effects on fatigue behavior of materials used in nuclear power plants. As a part of efforts, we performed low cycle fatigue tests under various environmental conditions and analyzed the environmental effects on the fatigue life of SA508 Gr. 1a low alloy steel by comparing with higuchi's model. Test results show that the fatigue life depends on water temperature, dissolved oxygen and strain rate. But strain rate over 0.4%/s has little effect on the fatigue life. To find the cause of different fatigue life with ANL's and higuchi's model, another test performed with different heat numbered and heat treated materials of SA508 Gr. 1a. On a metallurgical point of view, the material with bainite microstructure shows much longer fatigue life than that with ferrite/pearlite microstructure. And the characteristics of crack propagation as different microstructure seem to be the main cause of different fatigue life.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.4
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• pp.239-251
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• 2015

In this study, a spectral fatigue analysis was performed for the topside structure of an offshore floating vessel. The topside structure was idealized using beam elements in the SACS program. The fatigue analysis was carried out considering the wave and wind loads separately. For the wave-induced fatigue damage calculation, motion RAOs calculated from a direct wave load analysis and regular waves with different periods and unit wave heights were utilized. Then, the member end force transfer functions were generated covering all the loading conditions. Stress response transfer functions at each joint were produced using the specified SCFs and member end force transfer functions. fatigue damages were calculated using the obtained stress ranges, S-N curve, wave spectrum, heading probability of each loading condition, and their corresponding occurrences in the wave scatter diagrams. For the wind induced fatigue damage calculation, a dynamic wind spectral fatigue analysis was performed. First, a dynamic natural frequency analysis was performed to generate the structural dynamic characteristics, including the eigenvalues (natural frequencies), eigenvectors (mode shapes), and mass matrix. To adequately represent the dynamic characteristic of the structure, the number of modes was appropriately determined in the lateral direction. Second, a wind spectral fatigue analysis was performed using the mode shapes and mass data obtained from the previous results. In this analysis, the Weibull distribution of the wind speed occurrence, occurrence probability in each direction, damping coefficient, S-N curves, and SCF of each joint were defined and used. In particular, the wind fatigue damages were calculated under the assumption that the stress ranges followed a Rayleigh distribution. The total fatigue damages were calculated from the combination with wind and wave fatigue damages according to the DNV rule.

• Korean Journal of Adult Nursing
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• v.13 no.4
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• pp.620-631
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• 2001

Purpose: Fatigue is one of the most common complaints of cancer patients. In this study, we analyzed the change of fatigue level and general symptoms as time go by, so that, we could explain more on the mechanism and change of fatigue in relation with treatment, and explore the influencing factors. Method: The subjects of this study were 50 GI cancer patients who have visited the cancer center of A hospital in Suwon. We measured fatigue by using the Revised Piper Fatigue Scale(RPFS) at the time of starting and finishing induction chemotherapy, and starting the 2nd cycle of chemotherapy. Results: 1) The fatigue score was 2.81, 3.73, and 3.82 in a 10 point scale at the time of starting and finishing induction chemotherapy, and starting the 2nd chemotherapy, respectively. This means fatigue persisted until after the treatment. 2) Fifty two percent of participants complained of some kinds of symptoms when starting the treatment, and the proportion increased up to 92% when finishing the treatment. 3) Fatigue scores were significantly high in patients with fatigue-related symptoms than for patients without those symptoms. 4) Fatigue scores showed significant differences according to patients' general characteristics such as age, educational level, economic status, occupation, diagnosis, hematocrit, weight, and amount of sleepy. Conclusion: We have to develop intervention strategies to reduce fatigue in cancer patients in the consideration of influencing factors.

• Journal of Korean Public Health Nursing
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• v.16 no.1
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• pp.105-114
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• 2002

This study was to investigate the level of fatigue and its associated variables in patients with systemic lupus erythematosus(SLE) in Korea. From March to June, 2001, 100 patients, registered at one university hospital rheumatology clinic in Seoul, were accepted as subjects for this study. The sampling method was adopted a non-probability, purposive technique. The instruments used for this study were The Multidimensional Assessment Fatigue scale developed by Tack and Beck Depression Instrument develped by Beck. The collected data were analyzed by SAS program using t-test, ANOVA with Scheffe-test, Pearson correlation coefficients and stepwise multiple regression. The results were as follows: 1. Total scores of fatigue of the subjects averaged $24.46(\pm10.85)$, degree of fatigue was $5.08(\pm2.29)$, and influence of fatigue was $3.52(\pm2.12)$. 2. Regarding characteristics, more depressive(p=.0001) and more painfuI(p=.0122) patients revealed more fatigue. Also, the subjects with spouse(p=.0337) and having poor quality of sleep(p=.0445) revealed more fatigue. 3. The subjects' total fatigue score, depression, pain and age was correlated positively(r=.53; r=.48; r=.24), and total fatigue score, and exercise time, quality of sleep was correlated negatively(r=-.45; r=-.21). 4. The main influencing factors on the fatigue were depression$(52.92\%)$ and quality of sleep $(8.10\%)$. These two main variables made it possible to explain $61.02\%$ of the varience in fatigue. In conclusion, this study revealed depression and quality of sleep is an important factor that can improve quality of life in patients with SLE. It is recommended that nursing intervention for SLE patients would be focused to decrease depression and to enhance quality of sleep.

• Journal of The Korean Society of Integrative Medicine
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• v.10 no.3
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• pp.53-62
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• 2022

Purpose : This research is a descriptive study that aimed to identify the levels of health promotion behaviors, fatigue, and depression of nursing students and confirm the effect of health promotion behaviors on fatigue and depression. Methods : Data were collected from September 27 to October 15, 2021 through survey questionnaires on 178 nursing students of 2 universities in G-do who voluntarily agreed to participate. The collected data were analyzed using SPSS 23.0, the general characteristics of nursing students were analyzed by frequency and percentage, and the levels of their health promotion behaviors, fatigue, and depression of nursing students was analyzed by mean and standard deviation. The relationship among the health promotion behaviors, fatigue, and depression was analyzed by Pearson's Correlation Coefficient. Multiple regression analysis was performed for the effects of health promotion behaviors on fatigue and depression of nursing students. Results : The nursing students' health promotion behaviors averaged 2.25±.43 points out of 5, and for each sub-factor, interpersonal relationship was the highest at 2.66±.49 points and physical activity was the lowest at 2.01±.60 points. Fatigue was 4.89±1.02 points out of 7 and depression was 10.52±9.10 points out of 63. A statistically significant correlation was found among health promotion behaviors, fatigue, and depression. Health promotion behaviors that significantly affected fatigue were stress management (𝛽=-.263, p=.004) and physical activity (𝛽=-.208, p=.026), which showed 35 % explanatory power on fatigue. Health promotion behaviors that significantly affected depression were spiritual growth (𝛽=-.342, p=.002), and physical activity (𝛽=-.231, p=.016), which showed 31 % explanatory power for depression. Conclusion : This study is meaningful in that it provided basic data to develop an effective health promotion behavior program to prevent and manage nursing students' fatigue and depression, by identifying and analyzing the sub-factors of health promotion behaviors affecting their fatigue and depression.