• Wind and Structures
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• v.1 no.2
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• pp.127-144
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• 1998

In this paper, the wake structures behind a square cylinder at the Reynolds number of 22,000 are simulated using the large eddy simulation, and the main features of the wake structure associated with unsteady vortex-shedding are investigated. The Smagorinsky model is used for parametrization of the subgrid scales. The finite element method with isoparametric linear elements is employed in the computations. Unsteady computations are performed using the explicit method with streamline upwind scheme for the advection term. The time integration incorporates a subcycling strategy. No-slip condition is enforced on the wall surface. A comparative study between two-and three-dimensional computations puts a stress on the three-dimensional effects in turbulent flow simulations. Simulated three-dimensional wake structures are compared with numerical and experimental results reported by other researchers. The results include time-averaged, phase-averaged flow fields and numerically visualized vortex-shedding pattern using streaklines. The results show that dynamics of the vortex-shedding phenomenon are numerically well reproduced using the present method of finite element implementation of large eddy simulation.

• Journal of Biomedical Engineering Research
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• v.12 no.4
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• pp.261-266
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• 1991

As the ensemble averaged dz/dt signal during exercise gets smoothed, it is difficult to find the distinctive marks for estimation of stroke volume. The cross correlation function was made use of estimating these marks for automatic calculation by computer from the ensemble averaged dz/dt signal. LVET( Left Ventricular Ejection Time) and stroke volume were estimated based on the calculated parameters from the characteristic points. LVET, stroke volume calculated by hand, by the ensemble average and the cross correlation were compared for accuracy validation.

• Journal of Korean Foot and Ankle Society
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• v.6 no.1
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• pp.73-79
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• 2002

Purpose: To evaluate the effectiveness of callotasis using the external fixator for the treatment of brachymetatarsia. Materials and Methods: Eleven patients(15 cases) who underwent callotasis were available. Follow-up averaged 23 months(15-38 months). Both the patients' postoperative satisfaction and the postoperative radiographic results were retrospectively evaluated. Results: The duration from applying the external fixator to remove averaged 15 weeks (8-21 weeks). We did osteotomy again in two cases because of early consolidation at the osteotomy site during distraction period. All cases were evaluated mild claw toe deformity and motional pain in metatarsophalangeal joint, but all patients satisfied the postoperative results except one complained motional pain and stiffness in metatarsophalangeal joint. The metatarsal shortening averaged 13mm(9-18mm) before operation. The amount of distraction for shortened metatarsals averaged 15mm(5-22mm). We found the 6 cases of narrowing of the metatarsophalangeal joint, 2 cases of subluxation of the metatarsophalangeal joint. Conclusion: We think that callotasis with external fixator is good operative method for the brachymetatarsia.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.595-601
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• 2001

We applied PIV method to obtain instantaneous and ensemble averaged velocity fields from the first row to the fifth row of a staggered tube bundle. The Reynolds number based on the tube diameter and the maximum velocity was set to be 4,000. Remarkably different natures are observed in the developing bundle flow. Such differences are depicted in the mean recirculating bubble length and the vorticity distributions. The jet-like flow seems to be a dominant feature after the second row and usually skew. However, the ensemble averaged fields show symmetric profiles and the flow characteristics between the third and fourth measuring planes are not so different. comparison between the PIV data and the RANS simulation yields severe disagreement in spite of the same Reynolds number. It can be explained that the distinct jet-like unsteady motions are not to be accounted in th steady numerical analysis.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.100-103
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• 2011

In the present work, a numerical study of fluid flow and heat transfer on the concave surface with impinging jet has been performed by solving three-dimensional Reynods-averaged Naver-Stokes(RANS) equations. The constant temperature condition was applied to the concave impingement surface. The inclination angle of jet nozzle and the distance between jet nozzles are chosen as design variables under equivalent mass flow rate of working fluid into cooling channel, and area averaged Nusselt number on concave impingement surface is set as the objective function. Thirteen training points are obtained by Latin Hypercube sampling method, and the PEA model is constructed by using the objective function values at the trainging points. And, the sequential quadratic programming is used to search for the optimal paint from the PBA model. Through the optimization, the optimal shape shows improved heat transfer rate as compared to the reference geometry.

• The Korean Journal of Rehabilitation Nursing
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• v.8 no.2
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• pp.94-101
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• 2005

Purpose: The purpose of this study is to investigate the degree of sleep disorder and its related factors in hemodialysis patients. Method: The subjects of this study consisted of 210 hemodialysis patients. Data were analyzed by descriptive statistics, t-test, ANOVA, pearson's correlation coefficient, or stepwise multiple regression analysis by using SPSS/PC+ program. Result: Sleep disorder degree averaged 2.24. Stress of hemodialysis patients averaged 2.52. Depression degree of hemodialysis patients averaged 1.14. There was significant difference in sleep disorder according to age, marriage status, education, family income and help-givers. Sleep disorder was significantly associated with stress and depression. Stress, depression and marriage status explained 31.3% of the variance in the sleep disorder. Conclusion: In conclusion, the sleep disorder of hemodialysis patients is the nursing problem. The sleep disorder degree relates with stress, depression. Especially, it is strongly affected by stress among them.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1199-1201
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• 2003

This paper presents an averaged switch model for an on-line deterioration analysis of inverters. The model is based on the operational characteristics of power diodes and IGBTS. Switching loss mechanisms are described and divided into the diode reverse-recovery mechanism, the IGBT current-tailing phenomenon, the IGBT turn-on time, and the output capacitances of the IGBTS and diodes. The deterioration analysis parameters are derived from the averaged switch modeling and the parameters can determinate the deterioration of the inverters.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.7
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• pp.547-551
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• 2013

Mass averaged and core enthalpy in the arc jet flow are obtained experimentally. The experiment is made for the 150kW Huels type arc-jet applying the test condition for the research of gasturbine engine injection cooling technique. The mass averaged enthalpy value determined by the sonic throat method is 5.5MJ/kg. The core enthalpy value determined by the heat transfer rate method is 14.3MJ/kg. Based on result of experiment, the ratio of the core to mass averaged enthalpies is 2.6.

• Interaction and multiscale mechanics
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• v.5 no.1
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• pp.27-40
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• 2012

The two-dimensional incompressible flow of a linear viscoelastic fluid we considered in this research has rapidly oscillating initial conditions which contain both the large scale and small scale information. In order to grasp this double-scale phenomenon of the complex flow, a multiscale analysis method is developed based on the mathematical homogenization theory. For the incompressible flow of a linear viscoelastic Maxwell fluid, a well-posed multiscale system, including averaged equations and cell problems, is derived by employing the appropriate multiple scale asymptotic expansions to approximate the velocity, pressure and stress fields. And then, this multiscale system is solved numerically using the pseudospectral algorithm based on a time-splitting semi-implicit influence matrix method. The comparisons between the multiscale solutions and the direct numerical simulations demonstrate that the multiscale model not only captures large scale features accurately, but also reflects kinetic interactions between the large and small scale of the incompressible flow of a linear viscoelastic fluid.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.2
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• pp.67-73
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• 2003

The algorithm (or calculating the base-collector breakdown voltage of NPN BJT(Bipolar Junction Transistor) for integrated circuits is Proposed. The method for calculating the electric field using the solution of Poisson's equation is presented and the method for calculating the breakdown voltage using the integration of ionization coefficients is presented. The base-collector breakdown voltage of NPN BJT using 20V process obtained from the proposed method shows an averaged relative error of 8.0% compared with the measured data and the base-collector breakdown voltage of NPN BJT using 30V process shows an averaged relative error of 4.3% compared with the measured data