• International Journal of Fluid Machinery and Systems
• /
• v.6 no.2
• /
• pp.87-93
• /
• 2013

In order to study the effect of the fluid-structure interaction (FSI) on the simulation results, the external characteristics and internal flow features of a diffuser pump were analyzed with a two-way flow solid coupling method. And the static and dynamic structure analysis of the blade was also caculated with the FEA method. The steady flow field is based on Reynolds Averaged N-S equations with standard $k-{\varepsilon}$ turbulent model, the unsteady flow field is based on the large eddy simulation, and the structure response is based on elastic transient structural dynamic equation. The results showed that the effect of FSI on the head prediction based on CFD really exists. At the same radius, the van mises stress on the nodes closed shroud and hub was larger than other nodes. A large deformation region existed near inlet side at the middle of blades. The strength of impeller satisfied the strength requirement with static stress analysis based on the fourth strength theory. The dynamic stress varied periodically with the impeller rotating. It was also found that the fundamental frequency of the dynamic stress is the rotating frequency and its harmonic frequency. The frequency of maximum stress amplitude at node 1626 was 7 times of the rotating frequency. The frequency of maximum stress amplitude at node 2328 was 14 times of the rotating frequency. No matter strength failure or fatigue failure, the root of blades near shroud is the key region to analyse.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.7
• /
• pp.751-757
• /
• 2012

An accelerated life test (ALT) is a test method that forces components to fail more quickly than they would under use conditions by applying higher overstresses. When two or more accelerating stresses are involved in an ALT, an interaction effect may occur. In previous studies, mostly ALTs without considering an interaction of accelerated stresses and accelerated life models were proposed. The life data obtained are extrapolated using a life-stress relationship to estimate the life distribution at use conditions. We use the general log-linear relationship to model the dependence of life in the Weibull distribution on stress. Therefore, this study suggests the acceleration factor model between the lives at use conditions and accelerated conditions by using mechanical component life data considering an interaction effect. Further, the accelerated life test method and acceleration factor model proposed in this paper will be the basis for adopting an accelerated life test with accelerated stress interactions.

• Journal of Ocean Engineering and Technology
• /
• v.34 no.2
• /
• pp.120-127
• /
• 2020

Evaluation of fatigue strength considering the springing effect of very large container ships is crucial in the design stage. In this study, we established a fatigue strength evaluation method considering a linear springing component in the frequency domain. Based on a three-dimensional global model, a fluid-structure interaction analysis was performed and the modal superposition method was applied to determine the hot spot stress at the hatch corner of very large container ships. Fatigue damage was directly estimated using the stress transfer function with a linear springing response. Furthermore, we proposed a new methodology to apply the springing effect to fatigue damage using hull girder loads. Subsequently, we estimated the fatigue damage contribution due to linear springing components along the ship length. Finally, we discussed the practical application of the proposed methods.

• Proceedings of the KSR Conference
• /
• 2010.06a
• /
• pp.50-57
• /
• 2010

Various installation faults may lie in fasteners in the construction of a direct-fixation track by the top-down method. At an extreme, they may cause excessive interaction between the train and track, compromise the running safety of the train, and cause damage to the track components. Therefore, the faults need to be kept within the allowable level through an investigation of their effects on the interactions between the train and track. In this study, the vertical dynamic stiffness of fasteners in installation faults was measured based on the dynamic stiffness test by means of an experimental apparatus that was devised to feasibly reproduce gap faults. This study proposes an effective analytical model for a train-track interaction system in which most elements, except the nonlinear wheel-rail contact and some components that behave bi-linearly, exhibit linear behavior. To investigate the effect of the behavior of fasteners in gap faults in a direct-fixation track on the vehicle and track, vehicle-track interaction analyses were carried out, targeting key review parameters such as the wheel load reduction factor, vertical rail displacement, rail bending stress, and mean stress of the elastomer. From the results, it was noted that the gap faults in the concrete bearing surface of a direct-fixation track need to be limited for the sake of the long-term durability of the elastomer than for the running safety of the train or the structural safety of the track.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1994.10a
• /
• pp.820-825
• /
• 1994

It is improtant to examine life or crack propagation behavior of structures because of its safety evaluation. The purpose of this study is to investigate the effect of crack-crack interaction to evaluate fatigue life and crack behavior. In this study, the behavior of the interaction of two cracks is studied by experiment. The vertical distance of two cracks is varied to make different interaction stress field. In addition, the effect of plastic zone is considered to examine crack propagation path and propagation rate.

• Korean Journal of Childcare and Education
• /
• v.16 no.6
• /
• pp.89-104
• /
• 2020

Objective: The purpose of this study was to examine the effects of maternal parenting stress and mother's ego-resilience on mother-child attachment. More specially, mother-child attachment for higher grade elementary school children was examined according to the internal working model. Methods: Participants were 190 mothers of fourth and fifth grade elementary school children. The Maternal Parenting Stress Scale(Shin, 1997), the Scales of Ego-resilience(Yoo & Shim, 2002), and Inventory of Parent Attachment(Yang, 2006) were used to measure variables. Collected data were analyzed by descriptive statistics, t-test, correlation analysis and multiple regression analysis. Results: The major findings were summarized as follows: First, there were no differences between mother-child attachment according to children's gender. Second, mother-child attachment was negatively correlated with maternal parenting stress and positively correlated with ego-resilience. Next, maternal parenting stress_interaction and ego-resilience explained mother-child attachment_trust. Last, maternal stress_interaction explained mother-child attachment_isolation. Conclusion/Implications: In conclusion, the study results showed that maternal parenting stress and ego-resilience influenced mother-child attachment. based on the results, the implications of this study were discussed.

• Geomechanics and Engineering
• /
• v.16 no.3
• /
• pp.309-320
• /
• 2018

In this paper, a numerical study using finite element method with considering soil-structure interaction was conducted to investigate the stress and deformation behavior of a sheet pile wall structure. In numerical model, one of the nonlinear elastic material constitutive models, Duncan-Chang E-v model, is used for describing soil behavior. The hard contact constitutive model is used for simulating the behavior of interface between the sheet pile wall and soil. The construction process of excavation and backfill is simulated by the way of step loading. We also compare the present numerical method with the in-situ test results for verifying the numerical methods. The numerical analysis showed that the soil excavation in the lock chamber has a huge effect on the wall deflection and stress, pile deflection, and anchor force. With the increase of distance between anchored bars, the maximum wall deflection and anchor force increase, while the maximum wall stress decreases. At a low elevation of anchored bar, the maximum wall bending moment decreases, but the maximum wall deflection, pile deflection, and anchor force both increase. The construction procedure with first excavation and then backfill is quite favorable for decreasing pile deflection, wall deflection and stress, and anchor forces.

• Wind and Structures
• /
• v.31 no.4
• /
• pp.373-380
• /
• 2020

For large-scale 5MW offshore wind turbines, the discrete equation of fluid domain and the motion equation of structural domain with geometric nonlinearity were built, the three-dimensional modeling of the blade considering fluid-structure interaction (FSI) was achieved by using Unigraphics (UG) and Geometry modules, and the numerical simulation and the analysis of the vibration characteristics for wind turbine structure under rotating effect were carried out based on ANSYS software. The results indicate that the rotating effect has an apparent effect on displacement and Von Mises stress, and the response and the distribution of displacement and Von Mises stress for the blade in direction of wingspan increase nonlinearly with the equal increase of rotational speeds. Compared with the single blade model, the blade vibration period of the whole machine model is much longer. The structural coupling effect reduces the response peak value of the blade displacement and Von Mises stress, and the increase of rotational speed enhances this coupling effect. The maximum displacement difference between two models decreases first and then increases along wingspan direction, the trend is more visible with the equal increase of rotational speed, and the boundary point with zero displacement difference moves towards the blade root. Furthermore, the Von Mises stress difference increases gradually with the increase of rotational speed and decreases nonlinearly from the blade middle to both sides. The results can provide technical reference for the safe operation and optimal design of offshore wind turbines.

• Journal of Korean Biological Nursing Science
• /
• v.21 no.3
• /
• pp.224-230
• /
• 2019

Purpose: This study aimed to investigate sex differences in the effect of body mass index (BMI) and stress on high-risk diabetes mellitus (DM). Methods: Secondary analysis of data from 4,271 male and female adults participating in the Sixth Korea National Health and Nutrition Examination Survey 2015 was performed. The participants were evaluated using questionnaires and blood tests. Data were analyzed using descriptive statistics, t-test, ${\chi}^2-test$, and multiple logistic regression analysis (SPSS 24.0). Results: To identify sexspecific effects, interaction variables were included. Hemoglobin A1c (HbA1c) level was higher in men than in women, and the risk of DM decreased 0.31 times in women compared to that in men. As age increased, the odds of risk DM increased 1.03. The risk of DM increased 1.99 times in overweight individuals and 2.79 times for obese individuals compared to that in individuals with normal weight. Stress levels were higher in women than in men, but stress is not an influential factor in high-risk DM. In age-sex interaction, the odds of risk DM increased 1.02 in women compared to that in men as age increased. Conclusion: HbA1c level was affected by age-sex interaction, and age and sex should be considered in the application of HbA1c in the diagnosis of DM.

• Korean Journal of Child Studies
• /
• v.37 no.5
• /
• pp.33-52
• /
• 2016

Objective: This study aimed to investigate the trajectory of maternal parenting stress during infancy according to the employment status of mothers when each year's depression was controlled and examine the longitudinal effects of parenting stress on affective parenting and socioemotional developmental outcomes for preschoolers. Methods: Using latent growth modeling, the first 4 waves of panel data collected from 2,078 mothers and their babies were analyzed. This nationwide data was provided from the 2008 Panel Study on Korean Children, conducted by the Korea Institute of Child Care and Education. Results: First, maternal parenting stress showed a linear increasing pattern, and there were individual differences in intercept and slope. Second, when each year's maternal depression was controlled, the intercept of parenting stress was lower, but the rate of increase was higher. In multiple group analyses, this increasing pattern of parenting stress was significant only in unemployed mothers. Lastly, the increase of unemployed mothers' parenting stress had direct effects on child emotionality and peer interaction and had an indirect effect on child peer interaction (mediated by affective parenting). Conclusion: The current study verified that the longitudinal effects of increasing parenting stress of unemployed mothers on affective parenting and child socioemotional development when maternal depression level was controlled. These results imply that we need to pay more attention to emotional health and resources of unemployed mothers and provide them with social support as well as employed mothers.