• Geomechanics and Engineering
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• v.13 no.6
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• pp.907-928
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• 2017

The effects of seepage force and out-of-plane stress on cavity contracting and tunnel opening was investigated in this study. The generalized Hoek-Brown (H-B) failure criterion and non-associated flow rule were adopted. Because of the complex solution of pore pressure in an arbitrary direction, only the pore pressure through the radial direction was assumed in this paper. In order to investigate the effect of out-of-plane stress and seepage force on the cavity contraction and circular tunnel opening, three cases of the out-of-plane stress being the minor, intermediate, or major principal stress are assumed separately. A method of plane strain problem is adopted to obtain the stress and strain for cavity contracting and circular tunnel opening for three cases, respectively, that incorporated the effects of seepage force. The proposed solutions were validated by the published results and the correction is verified. Several cases were analyzed, and parameter studies were conducted to highlight the effects of seepage force, H-B constants, and out-of-plane stress on stress, displacement, and plastic radius with the numerical method. The proposed method may be used to address the complex problems of cavity contraction and tunnel opening in rock mass.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.12
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• pp.150-157
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• 2002

This paper presents an effective cutting force model that enable us to predict the instantaneous cutting force in face milling from a knowledge of the work material properties and cutting conditions. The development of the model is based on the orthogonal machining theory with the effective rake angle which is defined in the plane containing the cutting velocity and chip flow vectors. Face milling testes are performed at different feeds and, a fairly good agreement is shown between the predicted cutting forces and test results.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.3
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• pp.13-18
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• 2005

This paper presents an effective cutting force model that enables us to predict the instantaneous cutting force in face milling from knowledge of the work material properties and the cutting conditions. The development of the model is based on the orthogonal machining theory with the effective rake angle, which is defined in the plane containing the cutting velocity vector and the chip flow vector. Face milling tests are performed at different feeds and, a fairly good agreement is shown between the predicted cutting forces and the test results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1253-1261
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• 1993

Numerical analysis and measurements of the velocity and temperature distributions in buoyancy assisting laminar mixed convection flow over a vertically located, two-dimensional backward-facing step are reported. Laser-Doppler Velocimeter and Constant Temperature Anemometer operated in constant current were used to measure simultaneously the velocity and temperature distributions in the recirculation region downstream of the step. The reattachment length was measured by using flow visualization technique for different inlet velocities, wall temperatures and step heights. While the reattachment length $X_r$ increases as the inlet velocity or step height increase, it decreases as the buoyancy force increases, causing the size of the recirculation region to decrease. For the experimental range of $Gr_s$/$Re_{s}^{2}$$\times$$10^3$<17, a correlation equation for the reattachment length can be given by $X_{r}=1.05(2.13+0.021 Re_{s})exp$ $(-33.7_s^{-0.186}/Gr_{s}/Re_{s}^2).$ The Nusselt number is found to increase and the location of its maximum value moves closer to the step as the buoyancy force increases. The location of the maximum Nusselt number occurs downstream of the reattachment point, and distance between the reattachment point and the location of the maximum Nusselt mumber increases as the buoyancy force increases. Computational prediction agrees favorably well with measured results.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.243-247
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• 2015

The characteristics of the fluid force reduction of a square prism having a small triangular prism at the upstream side was investigated by measuring of lift and drag on the square prism The experimental parameters were the width ratios (H/B=0.2~0.6) of triangular prisms to the prism width and the gap ratios (G/B=0~3) between the square prism and the triangular prism. The drag reduction rate of the square prism was increased and then decreased with G/B in case of the same H/B, and was increased with H/B in case of the same G/B. The maximum drag reduction rate was represented by 78.5% at H/B=0.6 and G/B=1.5. The lift reduction rate of the square prism was hardly not affected by the width and gaps ratios, the average value was about 52.4%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.15-20
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• 2005

Two-dimensional incompressible Navier-Stokes flow solver is developed using SIMPLER method to study the unsteady viscous flow physics over two-dimensional ellipses. Unsteady viscous flows over various thickness-to-chord ratios of 0.6, 0.8, 1.0, and 1.2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000. This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces. The present numerical solutions are compared with available experimental and numerical results and show a good agreement. Through this study, it is observed that the Reynolds number and the cylinder thickness affect not only the frequency of the force oscillations but also the mean values and the amplitudes of the total drag and lift forces significantly.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.1
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• pp.25-33
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• 1986

Natural river channels usually have a deep section and one or two floodplains, which is called a compound channel. As the general method in the compound channel overestimates the discharge capacity, the momentum transfer due to interaction between the main channel flow and flow over its floodplain must be considered. Scale model experiments are performed for the rectangular main channel with an asymmetrical floodplain. Firstly, velocities are measured at various section grids. Secondary, boundary shear stresses are calculated from velocity distributions. Lastly, in order to determine the apparent shear force, the shear stress distributions are integrated along the wetted perimeter for the full cross-section and equated to the total weight force in the flow direction. The hydraulic characteristics in a compound channel are closely examined with the scales of length, velocity, boundary shear stress, and apparent shear force which are described with the various relationships.

• Journal of computational fluids engineering
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• v.17 no.3
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• pp.68-74
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• 2012

Near-wall effect on wakes behind particles is one of the important factors in precise tracking of particles in turbulent flows. However, most aerodynamic force models for particles did not fully consider the wall effect. In the present study, we focused on changes of hydrodynamic forces acting on a particle depending on wall proximity. To this end, we developed an immersed boundary method with multi-direct forcing incorporated to a fully implicit decoupling procedure for incompressible flows. We validate the present immersed boundary method through two-dimensional simulations of flow over a circular cylinder. Comprehensive parametric studies on the effect of the wall proximity on the drag and lift forces acting on an immersed circular cylinder in a channel flow are performed in order to investigate general flow patterns behind the circular cylinder for a wide range of Reynolds number (0.01 ${\leq}$ Re ${\leq}$ 200). As the cylinder is closer to the wall, the drag coefficient decreases while the lift coefficient increases with a local maximum. Maximum drag and lift coefficients for different wall proximities decrease with increment of Reynolds number. Normalized drag and lift coefficients by their maximum values show universal correlations between the coefficients and wall proximity in a low Reynolds number regime (Re ${\leq}$ 1).

• The KSFM Journal of Fluid Machinery
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• v.13 no.5
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• pp.43-53
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• 2010

This study investigates a design optimization of a rotating two-pass rectangular cooling channel with staggered arrays of pin-fins. The radial basis neural network method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The ratio of the diameter to height of the pin-fins and the ratio of the streamwise spacing between the pin-fins to height of the pin-fin are selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Results are presented for streamlines, velocity vector fields, and contours of Nusselt numbers, friction coefficients, and turbulent kinetic energy. These results show how fluid flow in a two-pass square cooling channel evolves a converted secondary flows due to Coriolis force, staggered arrays of pin-fins, and a $180^{\circ}$ turn region. These results describe how the fluid flow affects surface heat transfer. The Coriolis force induces heat transfer discrepancy between leading and trailing surfaces, having higher Nusselt number on the leading surface in the second pass while having lower Nusselt number on the trailing surface. Dean vortices generated in $180^{\circ}$ turn region augment heat transfer in the turning region and in the upstream region of the second pass. As the result of optimization, in comparison with the reference geometry, thermal performance of the optimum geometry shows the improvement by 30.5%. Through the optimization, the diameter of pin-fin increased by 14.9% and the streamwise distance between pin-fins increased by 32.1%. And, the value of objective function decreased by 18.1%.

• Journal of Physiology & Pathology in Korean Medicine
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• v.16 no.3
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• pp.507-513
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• 2002

Jaeumgenby-tang(JGT) have been used in oriental medicine for many centries as a a therapeutic agent of vertigo caused by deficiency of qi and blood. The effects of JGT on the regional cerebral blood flow(rCBF), mean arterial blood pressure(MABP) and cardiac muscle contractile force(CMF) is not known. The purpose of this Study was to investigate effects of JGT on the rCBF, MABP, CMF and mechanism of JGT induced changed rCBF, MABP, CMF. The changes of rCBF, MABP and CMF were determinated by Laser-Doppler Flowmetry(LDF). The results were as follows; JGT extract was increased rCBF, MABP and CMF in a dose-dependent, specially JGT extract was significantly increased rCBF and MABP. Pretreatment with propranolol was significantly inhibited JGT induced increase of rCBF but pretreatment with indomethacin and methylene blue were accelerated JGT induced increase of rCBF. Pretreatment with propranolol and indomethacin were inhibited JGT induced increase of MABP, but pretreatment with methylene blue was accelerated JGT induced increase of MABP. Pretreatment with propranolol was significantly inhibited JGT induced increase of CMF but pretreatment with indomethacin and methylene blue were accelerated JGT induced increase of CMF. This results suggest that JGT increased rCBF by increasing MABP and CMF and the action of JGT is mediated by adrenergic β-receptor.