• Advances in Computational Design
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• v.8 no.3
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• pp.191-217
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• 2023

The objective of this study was to evaluate the foundation structure of a 3.6-MW wind turbine generator (WTG) installed offshore in Western Korea. The ultimate limit state (ULS) and fatigue limit state (FLS) of the multi-pile steel foundation (MSF) installed at the Saemangeum offshore wind farm were structurally investigated using the finite element (FE) software, ANSYS Workbench 19.0. According to the ULS analysis, no plastic deformation was found in any of the components constituting the substructure. At the same time, the maximal stress value reached the calculation limit of 335 MPa. According to the FLS results, the stress concentration factor (SCF) ranged from 1.00 to 1.88 in all components. The results of this study can be applied to determine the optimal design for MSFs.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.1
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• pp.71-78
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• 1992

Zr-4 used for a cladding and an end plug of reactor component has creep deformation under operation at high temperature. Creep is regarded as the time dependent deformation of a material under constant applied stress. Although the major source of the deformation of zirconium component in water-cooled reactors is irradiation creep, the thermal creep may give a rise to significant deformation in reactor component especially at relatively high temperatures and at various constant stresses, and therefore it must be predicted accurately. Stress relaxation is the time dependent change of stress at constant strain and it is a process related intimately to creep. In this paper, the creep behavior and stress relaxation of Zr-4 is examined at the temperature of 50$0^{\circ}C$ that is 40% of the absolute melting temperature of Zr-4 under the stress below yield stress and under the various constant strains. The results obtained are summarized as follows: 1) With an increase of stress, the steady state creep rate increases and the creep rupture time decreases. 2) The steady state creep rate $\varepsilon$(%/s) for the stress $\sigma$sub(c) (kgf/mm super(2)) of Zr-4 increases outstandingly. All the empirical equations computed for Zr-4 increases outstandingly. All the empirical equations computed for Zr-4 are in accord with Norton's model equation($\varepsilon$=K$\sigma$ sub(c) super (n)). The constants of materials computed are as follows: K=3.9881$\times$10 super(-5), n=1.9608 3) The rupture time T sub(r) (hr) decreases linearly with the increase of stress on the log-log scaled graph. The empirical equations computed for Zr-4 are in accord with Bailey's model equation (T sub(r)=K sub(1)$\sigma$sub(c) super(m)). The constants of materials computed are as follows: K sub(1)=1.2875$\times$10 super(16), m=-3.467 4) It seems clear that the strain could be quantitatively dependent on the high temperature creep properties such as creep stress, rupture time, steady state creep rate and total creep rate. It is found that these relationships are linear on the log-log graph. 5) In stress relaxation test, as the critical constant strain that can be allowed to the specimen is larger, stress relaxation becomes more rapid, and as the constant strain is smaller, the stress relaxation becomes slower.

• Bulletin of the Korean Chemical Society
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• v.7 no.3
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• pp.204-210
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• 1986

It is shown that the linear stability coincides with the thermodynamic stability in the case of stress tensor evolution for simple dense fluids even if the constitutive (evolution) equation for the stress tensor is nolinear. The domain of coincidence can be defined in the space of parameters appearing in the constitutive equation and we find the domain is confined in an elliptical cone in a three-dimensional parameter space. The corresponding state theory in rheology of simple dense fluids is also further examined. The validity of the idea is strengthened by the examination.

• Computers and Concrete
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• v.12 no.4
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• pp.499-518
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• 2013

Fiber reinforced polymer (FRP) jackets have been widely used as an effective tool for the strengthening and rehabilitation of concrete structures, especially damaged concrete columns. Therefore, a clear understanding of the compressive behavior of FRP-confined concrete is essential. The objective of this paper is to develop a simple efficient method for predicting the compressive strength, the axial strain at the peak stress, and the stress-strain relationship of FRP-confined concrete. In this method, a compressive strength model is established based on Jefferson's failure surface. With the proposed strength model, the strength of FRP-confined concrete can be estimated more precisely. The axial strain at the peak stress is then evaluated using a damage-based formula. Finally, a modified stress-strain relationship is derived based on Lam and Teng's model. The validity of the proposed compressive strength and strain models and the modified stress-strain relationship is verified with a wide range of experimental results collected from the research literature and obtained from the self-conducted test. It can be concluded that, as a competitive alternative, the proposed method can be used to predict the compressive behavior of FRP-confined concrete with reasonable accuracy.

• Steel and Composite Structures
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• v.5 no.2_3
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• pp.159-168
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• 2005

Four design codes/regulations for steel structures in Japan are briefly reviewed. Some of them employ the limit state design concept while the others are still based on the allowable stress design concept. The process for revision is now in action. The directions in the development of structural design codes are also reported herein. It is noted that a current trend in this development is to employ the performance-based design concept that has been successfully implemented in some seismic design codes.

• Journal of Korean Academy of Nursing
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• v.36 no.7
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• pp.1123-1134
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• 2006

Purpose: The purpose of this study was to identify the effects of aromatherapy on blood pressure and stress responses of clients with essential hypertension. Method: There were fifty-two subjects divided into an essential oil group, placebo group, and control group by random assignment. The application of aromatherapy was the inhalation method of blending oils with lavender, ylangylang, and bergamot once daily for 4 weeks. To evaluate the effects of aromatherapy, blood pressure and pulse were measured two times a week and serum cortisol levels, catecholamine levels, subjective stress, and state anxiety were measured before and after treatment in the three groups. Data was analyzed by repeated measures of ANOVA, one-way ANOVA, and $X^2-test$ using the SPSS 10.0 program. Results: The blood pressure, pulse, subjective stress, state anxiety, and serum cortisol levels among the three groups were significantly statistically different. The differences of catecholamine among the three groups were not significant statistically Conclusion: The results suggest that the inhalation method using essential oils can be considered an effective nursing intervention that reduces psychological stress responses and serum cortisol levels, as well as the blood pressure of clients with essential hypertension.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.815-822
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• 2004

A knowledge of in situ stress state is important to design various engineering structures such as dams, tunnels and so on. There are about three wellknown indicators that is, borehole will breakouts, hydraulic fracturing, ellipsoidal cross section of borehole that have been attributed to the state of stress in the vicinity of borehole. Fortunately, Televiewer traveltime image can be used as a caliper log with 144 or 288 arms, which allows to determine the borehole shape. Televiewer amplitude image will give detailed information about the distribution and character of breakouts and hydraulic fracturing as well. For investigation purposes, a series of boreholes(total 195 boreholes: 12.239m) that have been logged all over the country during past 10 years are analyzed. The primary objective of this paper are to examnine the ability of a Televiewer to determine the shape of borehole, to present data inferred by stress indicators, to indicate their possible relationship with the anisotropic horizontal stresses. It is shown that in most cases the fracture orientation statistically estimated from observed fractures denotes an excellent correlation with the orientations inferred by stress indicators. Many intervals of breakouts are terminated at the intersection of oblique fracture with the borehole. The results from Televiewer data are further compared with those of hydraulic fracturing techniques.

• Journal of Korean Biological Nursing Science
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• v.13 no.2
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• pp.102-108
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• 2011

Purpose: The purpose of this study was to examine the effects of first clinical training on stress, anxiety and changes in autonomic nervous system in nursing students. Methods: Seventy-four nursing students were assigned to the experimental group (n=36) that had two weeks of clinical training, and the control group (n=38) that had only two weeks of regular classes. Perceived stress, state anxiety and heart rate variability (HRV) were measured at the beginning and end of the experiment. Results: Perceived stress in the experimental group was significantly higher than in the control group. However, State anxiety was not significantly different between the two groups. All indices of HRV except LF/HF ratio were significantly different between the two groups. LF norm in the experimental group was significantly higher than in the control group, and HF norm in the experimental group was significantly lower than in the control group. Conclusion: Based on these results, it can be suggested that clinical training increases the perceived stress and affects the changes in autonomic nervous system in nursing students.

• Geomechanics and Engineering
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• v.11 no.3
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• pp.325-343
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• 2016

A total stress-based bounding surface model is developed to predict the undrained behaviour of saturated soft clays under cyclic loads based on the anisotropic hardening modulus field and bounding-surface theories. A new hardening rule is developed based on a new interpolation function of the hardening modulus that has simple mathematic expression and fewer model parameters. The evolution of hardening modulus field is described in the deviatoric stress space. It is assumed that the stress reverse points are the mapping centre points and the mapping centre moves with the variation of loading and unloading paths to describe the cyclic stress-strain hysteresis curve. In addition, by introducing a model parameter that reflects the accumulation rate and level of shear strain to the interpolation function, the cyclic shakedown and failure behaviour of soil elements with different combinations of initial and cyclic stresses can be captured. The methods to determine the model parameters using cyclic triaxial compression tests are also studied. Finally, the cyclic triaxial extension and torsional shear tests are performed. By comparing the predictions with the test results, the model can be used to describe undrained cyclic stress-strain responses of elements with different stress states for the tested clays.

• Korean Journal of Adult Nursing
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• v.19 no.5
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• pp.115-126
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• 2007

Purpose: The present study is a quasi-experimental research for examining the effects of imagery on stress, anxiety and immune cells in acute leukemia patients receiving chemotherapy and utilizing the therapy for their self control and stress management. Methods: The subjects were 60 patients who were diagnosed with acute leukemia and scheduled to receive chemotherapy at A hospital in Seoul during the period from November 2006 to March 2007. After the start of chemotherapy, the experimental group received imagery for 4 weeks, three sessions a week, so a total of 12 sessions and 156 minutes. Results: The decrease of stress was larger in the experimental group than in the control group. Systolic blood pressure decreased significantly more in the experimental group than in the control group. In the experimental group, state anxiety decreased significantly in the 2nd week of the experiment and after the final stage of the experiment. The total number of white blood cells, and the absolute number of neutrophils and lymphocytes were showing significant differences between the time points. Conclusion: Imagery is an effective intervention for reducing stress and state anxiety and stabilizing blood pressure in acute leukemia patients receiving chemotherapy.