• Journal of Acupuncture Research
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• 제22권6호
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• pp.173-180
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• 2005

Objectives : The purpose of this study was to assess the effect auricular acupuncture for acute mental stress using power spectrum analysis of the heart rate variability(HRV). Methods : 10 healthy volunteers participated in this study. After 5 minute rest, the first mental stress was provided for 5 minute. And then subjects rested for 15 minute. The second mental stress was provided for 5 minute. The acupoint, Shin-Mun point of the ear was stimulated for 15 minute. HRV was recorded before and after the first and second mental stress, and after auricular acupuncture stimulation. Results : After mental stress, normalized LF and LF/HF ratio is significantly increased. Before and after simple rest, normalized LF and normalized HF is significantly changed, but LF and LF/HF ratio is not significantly changed. On the other hand, before and after auricular acupuncture treatment, normalized LF, normalized HF is significantly changed, and also LF and LF/HF ratio is significantly decreased. Conclusion : The result suggest that auricular acupuncture can decrease more significantly in cardiac sympathetic activity due to mental stress than simple rest.

• 한국군사과학기술학회지
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• 제6권4호
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• pp.89-99
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• 2003

Smoothed particle hydrodynamics, SPH, is a gridless Lagrangian technique which is a useful alternative numerical analysis method to simulate high velocity deformation problems as well as astrophysical and cosmological problems. The SPH method brings about some difficulties such as tensile Instability and stress oscillation. A new SPH method, so called normalized algorithm, was introduced to overcome these difficulties. In this paper we aimed to estimate this method and have developed an one-dimensional normalized SPH program. The high velocity impact model of an aluminum bar has been analysed by using the developed program and a commercial hydrocode, LS-DYNA. The obtained numerical results showed good agreement with the results of the same model in reference. The program also showed more stable results than those of LS-DYNA in stress oscillation. We hopefully expect that the developed one-dimensional normalized SPH program can be used to solve hydrodynamic problems especially for explosive detonation analysis.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1557-1564
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• 2000

When the half infinite crack in the orthotropic material strip with a large anisotropic ratio(E11>>E22) propagates with constant velocity, dynamic stress component $\sigma$y occurre d along the $\chi$ axis is derived by using the Fourier transformation and Wiener-Hopf technique, and the dynamic stress intensity factor is derived. The dynamic stress intensity factor depends on a crack velocity, mechanical properties and specimen hight. The normalized dynamic stress intensity factors approach the maximum values when normalized time(=Cs/a) is about 2. They have the constant values when the normalized time is greater than or equal to about 2, and decrease with increasing a/h(h: specimen hight, a: crack length) and the normalized crack propagation velocity( = c/Cs, Cs: shear wave velocity, c: crack propagation velocity).

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.730-739
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• 2010

Stress history increases in penetration resistance due to the increase in residual horizontal stress of granular soil. This study analyzes the effect of stress history on the results of CPT and DMT from calibration chamber specimen in OC as well as NC state. Test results show that the normalized cone resistance by mean effective stress correlates well with the relative density and the state parameter, whereas the normalized cone resistance with regard to vertical effective stress is a little affected by stress history. The horizontal stress index($K_D$) in DMT more reflects the influence of stress history on granular soil than the dilatometer modulus($E_D$) and cone resistance($q_c$). The $K_D/K_0$, in which the effect of stress history on $K_D$ is compensated by the at-rest coefficient of earth pressure, $K_0$, is related to relative density, state parameter and the normalized cone resistance by mean effective stress. It is also observed that the normalized dilatometer modulus by mean effective stress($E_D/{\sigma_m}'$) is unique correlated with the state parameter, regardless of stress history.

• 대한기계학회논문집A
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• 제28권6호
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• pp.701-708
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• 2004

This paper discusses applicability of the enhanced reference stress method to estimate J-integral along the semi-elliptical surface crack front. It is found that angular variations of normalized J­integral are strongly dependent on the geometry, loading mode and loading magnitude. As application of the reference stress approach to semi-elliptical surface cracks implies proportional increases in the normalized J-integral, the present results pose a question in applicability of the reference stress approach. However, investigation of the error in the estimated J-integral in the present work suggests that the enhanced reference stress approach, recently proposed by authors, provides an effective engineering tool fur estimating crack driving force along the semi-elliptical surface crack front.

• 한국지반공학회논문집
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• 제26권7호
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• pp.7-16
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• 2010

응력이력은 사질토 지반의 잔류 수평응력을 증가시켜 현장시험의 관입저항을 증가시킨다. 본 연구에서는 챔버에 조성된 정규 및 과압밀 시료에 대한 콘관입시험과 딜라토미터 시험을 수행하고 응력이력이 시험결과와 측정값의 상관관계에 미치는 영향을 분석하였다. 시험결과, 평균 유효응력으로 정규화된 콘선단저항은 상대밀도 및 상태정수와 높은 상관성을 보였다. 딜라토미터의 수평응력지수($K_D$)는 콘선단저항($q_c$) 뿐만 아니라, 딜라토미터 계수($E_D$) 보다도 응력이력 영향을 효과적으로 반영하였다. 수평응력지수에 반영된 응력이력의 영향을 정지토압계수인 $K_0$로 보정한 $K_D/K_0$는 상대밀도 뿐만 아니라, 상태정수, 평균 유효응력으로 정규화된 콘선단저항과 응력이력에 관계없는 높은 상관성을 보였다. 또한 평균 유효응력으로 정규화된 딜라토미터 계수($E_D/{\sigma}_m'$)와 상태정수의 관계도 응력이력에 관계없이 유일한 식으로 표현되었다.

• Structural Engineering and Mechanics
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• 제47권6호
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• pp.839-856
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• 2013

Metallic annular discs with their outer boundary fully constrained are studied with newly derived semi-analytical solutions for the effects of thickness variations under thermal loading and unloading. The plane stress and axisymmetric assumptions were adopted, and the thickness of the disk depends on the radius hyperbolically with an exponent n. Furthermore, it is assumed that the stress state is two dimensional and temperature is uniform in the domain. The solutions include the elastic, elastic-plastic and plastic-collapse behavior, depending on the values of temperature. The von Mises type yield criterion is adopted in this work. The material properties, Young's modulus, yield stress and thermal expansion coefficient, are assumed temperature dependent, while the Poisson's ratio is assumed to be temperature independent. It is found that for any n values, if the normalized hole radius a greater than 0.6, the normalized temperature difference between the elastically reversible temperature and plastic collapse temperature is a monotonically decreasing function of inner radius. For small holes, the n values have strong effects on the normalized temperature difference. Furthermore, it is shown that thickness variations may have stronger effects on the strain distributions when temperature-dependent material properties are considered.

• 한국해양공학회지
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• 제29권6호
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• pp.454-462
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• 2015

An extended study was conducted on the fracture criterion by Choung et al. (2011; 2012) and Choung and Nam (2013), and the results are presented in two parts. The theoretical background of the fracture and the results of new experimental studies were reported in Part I, and three-dimensional fracture surface formulations and verifications are reported in Part II. How the corrected true stress can be processed from the extrapolated true stress is first introduced. Numerical simulations using the corrected true stress were conducted for pure shear, shear-tension, and pure compression tests. The numerical results perfectly coincided with test results, except for the pure shear simulations, where volume locking appeared to prevent a load reduction. The average stress triaxialities, average normalized lode parameters, and equivalent plastic strain at fracture initiation were extracted from numerical simulations to formulate a new three-dimensional fracture strain surface. A series of extra tests with asymmetric notch specimens was performed to check the validity of the newly developed fracture strain surface. Then, a new user-subroutine was developed to calculate and transfer the two fracture parameters to commercial finite element code. Simulation results based on the user-subroutine were in good agreement with the test results.

• 한방재활의학과학회지
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• 제20권4호
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• pp.147-157
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• 2010

Objectives : The study is performed to investigate the influence of psychological stress on neck muscles tone and heart rate variability(HRV). Methods : This study was carried out with the data from stress response index score(SRI), surface electromyography(sEMG) and HRV. First subjects were divided into two group according to the SRI points. Subjects in group A had points of SRI in which lower than 30 points. Subjects in group B had points of SRI in which higher than 30 points. Then we investigated how to difference of the index of sEMG and HRV according to each groups. Results : In this study, the muscle contraction of both upper trapezius muscle in stress group were higher than non-stress group significantly. Complexity, root mean square of successive differences of R-R intervals(RMSSD), standard deviation difference between adjacent normal to normal intervals(SDSD), high frequency oscillation power(Ln(HF)), normalized HF(Norm HF) in stress group were lower than non-stress group significantly and normalized LF(Norm LF) was higher. Conclusions : This results show that the stress was associated with neck muscle condition and autonomic nervous system.

• 한국음향학회지
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• 제10권3호
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• pp.13-18
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• 1991

본 연구에서는 취약한 고체의 표면에 존재하는 crack에 탄성표면파를 입사 시켰을 때 발생하는 반사계수를 측정하여 파괴응력을 해석하는 방법을 연구 분석하였다. Crack이 존재하는 취약한 고체에서의 파괴응력은 임계응력확대계수와 정규화된 최대응력확대계수의 함수로써 나타나며, 이 때 정규화된 최대응력확대계수는 탄성표면파의 반사계수를 측정하여 구할 수 있었다. 실험을 위하여 Pyrex glass원판 중앙에 깊이가 0.5mm~0.9mm인 crack을 제작하였고, SAW wedge transducer를 피치캐치(pitch-catch) 모드로 구성하여 반사계수를 측정하고 파괴응력값을 산출하였으며 UTM(Universal Testing Machine)으로 측정한 값과 비교 분석하였다.