• 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.

• International Journal of Fluid Machinery and Systems
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• v.4 no.2
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• pp.229-234
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• 2011

For Lift-type Vertical Axis Wind Turbine (VAWT), it is difficult to evaluate the performance through the scale-model wind tunnel tests, because of the scale effect relating to Reynolds number. However, it is beneficial to figure out the critical value of Reynolds number or minimum size of the Lift-type VAWT, when designing this type of micro wind turbine. Therefore, in this study, the performance of several scale-models of Lift-type VAWT (Reynolds number : $1.5{\times}10^4$ to $4.6{\times}10^4$) was investigated. As a result, the Reynolds number effect depends on the blade chord rather than the inlet velocity. In addition, there was a transition point of the Reynolds number to change the dominant driving force from Drag to Lift.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2110-2117
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• 2003

A physics-based material removal model in various scales is described and a feature scale simulation for a chemical mechanical polishing (CMP) process is performed in this work. Three different scales are considered in this model, i.e., abrasive particle scale, asperity scale and wafer scale. The abrasive particle and the asperity scales are combined together and then homogenized to result in force balance conditions to be satisfied in the wafer scale using an extended Greenwood-Williamson and Whitehouse-Archard statistical model that takes into consideration the joint distribution of asperity heights and asperity tip radii. The final computation is made to evaluate the material removal rate in wafer scale and a computer simulation is performed for detailed surface profile variations on a representative feature. The results show the dependence of the material removal rate on the joint distribution, applied external pressure, relative velocity, and other operating conditions and design parameters.

• Wind and Structures
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• v.24 no.6
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• pp.579-611
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• 2017

Bora is a strong, usually dry temporally and spatially transient wind that is common at the eastern Adriatic Coast and many other dynamically similar regions around the world. One of the Bora main characteristics is its gustiness, when wind velocities can reach up to five times the mean velocity. Bora often creates significant problems to traffic, structures and human life in general. In this study, Bora velocity and near-ground turbulence are studied using the results of three-level high-frequency Bora field measurements carried out on a meteorological tower near the city of Split, Croatia. These measurements are analyzed for a period from April 2010 until June 2011. This rather long period allows for making quite robust and reliable conclusions. The focus is on mean Bora velocity, turbulence intensity, Reynolds shear stress and turbulence length scale profiles, as well as on Bora velocity power spectra and thermal stratification. The results are compared with commonly used empirical laws and recommendations provided in the ESDU 85020 wind engineering standard to question its applicability to Bora. The obtained results report some interesting findings. In particular, the empirical power- and logarithmic laws proved to fit mean Bora velocity profiles well. With decreasing Bora velocity there is an increase in the power-law exponent and aerodynamic surface roughness length, and simultaneously a decrease in friction velocity. This indicates an urban-like velocity profile for smaller wind velocities and a rural-like velocity profile for larger wind velocities. Bora proved to be near-neutral thermally stratified. Turbulence intensity and lateral component of turbulence length scales agree well with ESDU 85020 for this particular terrain type. Longitudinal and vertical turbulence length scales, Reynolds shear stress and velocity power spectra differ considerably from ESDU 85020. This may have significant implications on calculations of Bora wind loads on structures.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.8
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• pp.884-887
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• 2006

• Progress in Superconductivity and Cryogenics
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• v.13 no.3
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• pp.24-30
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• 2011

The stability issue of high temperature superconducting (HTS) racetrack coils is one of the most important factors for the development of large-scale rotating machines, such as ship propulsion motors and power generators. However, The stability and normal zone propagation characteristics of HTS racetrack pancake (RP) coils are not sufficient yet. In this study, quench tests for a GdBCO racetrack pancake coil were carried out under the condition of $LN_2$ at 77 K. Minimum quench energy and two-dimensional normal zone propagation velocities of the coil are also discussed. Normal zone propagation velocity in the coil's curved section is faster than in its straight section due to stress effects. The test results show that the protection of the straight section is of greater importance than that of the curved section when GdBCO racetrack pancake coils are applied to large-scale rotating machines.

• Physical Therapy Korea
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• v.19 no.1
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• pp.76-85
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• 2012

The purpose of this study was to identify the factors determining the participation restriction of chronic stroke patients based on international classification of functioning, disability, and health (ICF) model. Sixty-eight stroke patients participated. The participants were assessed participation restriction using the Korean version of London handicap scale (K-LHS), modified Barthel index (K-MBI) to measure activities of daily living, Berg balance scale (K-BBS) to assess balance, and the center for epidemiologic studies depression (K-CES-D) to gauge depression. Also, 3 minutes walking test (3MWT), gait velocity, asymmetric posture, and family support were assessed. A stepwise multiple regression analysis was used to explore the factors determining participation restriction. There were no significant different in the K-LHS and K-MBI results by gender (p>.05). Correlations between the K-LHS and K-MBI (r=-.656), K-BBS (r=-.543), K-CES-D (r=.266), 3MWT (r=-.363), gait velocity (r=.348), and family support (r=-.389) were significant (p<.05). Also, the K-MBI and family support were the factors that determined participation restriction (p<.05) and that 40.2% of the variation in the K-LHS can be explained. Therefore, it is suggested that evaluation and intervention of patient's activity level and extent of family support is necessary to reduce participation restriction of chronic stroke patients.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.67-70
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• 2004

An investigation was performed to study the impact damage of the laminated composite plates caused by a low- velocity foreign object with multi-scale modeling based on the concepts of Direct Numerical Simulation (DNS)[4]. In the micro-scale part, we discretize the composite plates through separate modeling of fiber and matrix for the local microscopic analysis. A micro-scalemodel was developed for predicting the initiation of the damage and the extent of the final damage as a function of material properties, laminate configuration and the impactor's mass, etc. Anda macro-scale model was developed for description of global dynamic behavior. The connection betweenmicroscopic and macroscopic is implemented by the tied interface constraints of LS-DYNA contact card. A transient dynamic finite element analysis was adopted for calculating the contact force history and the stresses and strains inside the composites during impact resulting from a point-nose impactor. The low-velocity impact events such as contact force, deformation, etc. are simulated in the macroscopic sense and the impact damages, fiber-breakage, matrix cracking and delamination etc. are examined in the microscopic sense.

• Journal of Mechanical Science and Technology
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• v.20 no.2
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• pp.262-270
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• 2006

Direct numerical simulations (DNS) of turbulent channel flows up to $Re_{\tau}=1270$ are performed to investigate an elliptic feature and strain rate field on cross sections of coherent fine scale eddies (CFSEs) in wall turbulence. From DNS results, the CFSEs are educed and the strain rate field around the eddy is analyzed statistically. The principal strain rates (i.e. eigenvalues of the strain rate tensor) at the CFSE centers are scaled by the Kolmogorov length $\eta$ and velocity $U_k$. The most expected maximum (stretching) and minimum (compressing) eigenvalues at the CFSE centers are independent of the Reynolds number in each $y^+$ region (i. e. near-wall, logarithmic and wake regions). The elliptic feature of the CFSE is observed in the distribution of phase-averaged azimuthal velocity on a plane perpendicular to the rotating axis of the CFSE $(\omega_c)$. Except near the wall, phase-averaged maximum $(\gamma^{\ast}/\gamma_c^{\ast})$ and minimum $(\alpha^{\ast}/\alpha_c^{\ast})$ an eigenvalues show maxima on the major axis around the CFSE and minima on the minor axis near the CFSE center. This results in high energy dissipation rate around the CFSE.

• Physical Therapy Korea
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• v.13 no.2
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• pp.1-8
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• 2006

The main purposes of this study were to find the correlation between walking ability assessment tools using the Modified Barthel Index (MBI), Functional Independence Measure (FIM), Spinal Cord Injury Measurement II (SCIM II), Walking Index for Spinal Cord Injury (WISCI), walking velocity, and walking endurance. The study population consisted of 56 patients with spinal cord injury referred to the department of Rehabilitative Medicine in the National Rehabilitation Hospital. All subjects were ambulatory with or without an assistive device. All participants were assessed by MBI, FIM, SCIM II, WISCI, walking velocity, and walking endurance. The data were analyzed using Pearson correlation analysis and X2. There was significant correlation between the MBI, FIM, SCIM II, WISCI, walking velocity, and walking endurance (p<.01). In particular, WISCI has a significant correlation with SCIM II(p<.001). Therefore the WISCI scale is an appropriate assessment tool to predict the gait ability of patients with spinal cord injury. Further study about MBI, FIM, SCIM II, WISCI, walking velocity, and walking endurance is needed using a longitudinal study design.