• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.285-295
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• 2001

The transport phenomena in a wedge-shaped pool of twin-roll continuous caster are affected by the various operating parameters such as the melt-feed pattern, roll-gap thickness, melt-superheat, and casting speed. A computer program has been developed for analyzing the two-dimensional, steady conservation equations for transport phenomena during twin-roll continuous casting process in order to estimate the turbulent melt-flow, temperature fields, and solidification in the wedge-shaped pool. The turbulent characteristics of the melt-flow were considered using a low-Reynolds-number K-$\xi$ turbulence model. Based on the computer program, the effects of the different melt-feed patterns, roll-gap thicknesses, and superheats of melt on the variations of the velocity and temperature distributions, and the mushy solidification were examined. The results show that the liquidus line is located considerably at the upstream region, and in the lower region appear the well-mixed melt-flow and most widely developed mushy zone. Besides, the variation of melt-flow due to varying melt-feed patterns, affects mainly the liquidus line, and scarcely has effects on the solidus line in the outlet region.

• Journal of Biomedical Engineering Research
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• v.25 no.4
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• pp.289-293
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• 2004

In the present study, knee varus torque and mediolateral accelerations were measured using the three-dimensional motion analysis system and a linear accelerometry in odor to determine the effect of heel wedges during walking. Wedges were inclined with 10$^{\circ}$ and 15$^{\circ}$ in medial and lateral directions respectively Both knee varus torques and mediolateral accelerations showed two distinct positive peaks in loading response and preswing. Medial wedges resulted in significantly increased both knee varus torque and lateral acceleration in loading response, compared with the barefoot walking(p<0.05). On the other hand, lateral wedges decreased them in loading response(p<0.05). This became more significant for more inclined wedges. However, no significant correlations were found between knee varus torque and lateral acceleration according to the angle of heel wedges in preswing. From this study, it was found that a lateral wedge would be helpful to treat osteoarthritis, decreasing knee varus torque in loading response. In addition, lateral acceleration of the knee joint might be an alternative to determine the effect of wedges and the alignment of the knee joint during walking, instead of measuring knee torque by the three-dimensional motion analysis.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.557-560
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• 2002

In this study, simulation of weak shock waves are peformed by a two-dimensional thermal fluid or compressible fluid model of the lattice Boltzmann method. The shock wave represents an abrupt change in fluids properties, in which finite variations in pressure, internal energies, and density occur over the shock thickness. The characteristics of the proposed model with a simple distribution function is verified by calculation of the sound speeds, and the shock tube problem. The reflection of a weak shock wave by wedge propagating in a channel is performed. The results agree well with those by finite difference method or by experiment. In the simulation of unsteady shock wave diffraction around a sharp corner, we show a flow field of vortical structure near the comer.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.6
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• pp.436-449
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• 2013

In this paper, a numerical analysis is carried out to study the characteristics of supercavitating flows and the drag of relatively simple two-dimensional and axisymmetric bodies which can be used for supercavity generation device, cavitator, of a high-speed underwater vehicle. In order to investigate the suitability of numerical models, cavity flows around the hemispherical head form and two-dimensional wedge are calculated with combinations of three turbulence models(standard $k-{\epsilon}$, realizable $k-{\epsilon}$, Reynolds stress) and two cavitation models(Schnerr-Sauer, Zwart-Gerber-Belamri). From the results, it is confirmed that the calculated cavity flow is more affected by the turbulence model than the cavitation model. For the calculation of steady state cavity flows, the convergence in case of the realizable $k-{\epsilon}$ model is better than the other turbulence models. The numerical result of the Schnerr-Sauer cavitation model is changed less by turbulence model and more robust than the Zwart-Gerber-Belamri model. Thus the realizable $k-{\epsilon}$ turbulence model and the Schnerr-Sauer cavitation model are applied to calculate supercavitating flows around disks, two dimensional $10^{\circ}$ and $30^{\circ}$ wedges. In case of the disk, the cavitation number dependences of the cavity size and the drag coefficient predicted are similar to either experimental data or Reichardt's semi-empirical equations, but the drag coefficient is overestimated about 3% higher than the Reichardt's equation. In case of the wedges, the cavitation number dependences of the cavity size are similar to experimental data and Newman's linear theory, and the agreement of the cavity length predicted and Newman's linear theory becomes better as decreasing cavitation number. However, the drag coefficients of wedges agree more with experimental data than those of Newman's analytic solution. The cavitation number dependences of the drag coefficients of both the disk and the wedge appear linear and simple formula for estimating the drag of supercavitating disks and wedges are suggested. Consequently, the CFD scheme of this study can be applied for numerical analysis of supercavitating flows of the cavitator and the cavitator design.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.362-364
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• 2010

Shock wave interaction with droplet-gas medium is investigated in this paper. In the present computation, the shock wave is initially started in a pure gas and reflected from the wedge to interact with the droplet-ridden gas flows. We used the compressible two-fluid two-phase model that is solved by the two-fluid version of the HLL scheme. The interfacial drag force and heat transfer were included to model the interaction between continuous and dispersed phases. The parametric effect of void fraction on the shock wave reflection in the two-phase media was investigated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.32-33
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• 2003

Mechanism of a periodic oscillation of shock-induced combustion over a two- dimensional wedges and axi-symmetric cones were investigated through a series of numerical simulations at off-attaching condition of oblique detonation waves(ODW). A same computational domain over 40 degree half-angle was considered for two-dimensional and axi-symmetric shock-induced combustion phenomena. For two-dimensional shock-induced combustion, a 2H2+02+17N2 mixture was considered at Mach number was 5.85with initial temperature 292 K and initial pressureof 12 KPa. The Rankine-Hugoniot relation has solution of attached waves at this condition. For axi-symmetric shock-induced combustion, a H2+2O2+2Ar mixture was considered at Mach number was 5.0 with initial temperature 288 K and initial pressure of 200 mmHg. The flow conditions were based on the conditions of similar experiments and numerical studies.[1, 3]Numerical simulation was carried out with a compressible fluid dynamics code with a detailed hydrogen-oxygen combustion mechanism.[4, 5] A series of calculations were carried out by changing the fluid dynamic time scale. The length wedge is varied as a simplest way of changing the fluid dynamic time scale. Result reveals that there is a chemical kinetic limit of the detached overdriven detonation wave, in addition to the theoretical limit predicted by Rankine-Hugoniot theory with equilibrium chemistry. At the off-attaching condition of ODW the shock and reaction waves still attach at a wedge as a periodically oscillating oblique shock-induced combustion, if the Rankine-Hugoniot limit of detachment isbut the chemical kinetic limit is not.Mechanism of the periodic oscillation is considered as interactions between shock and reaction waves coupled with chemical kinetic effects. There were various regimes of the periodicmotion depending on the fluid dynamic time scales. The difference between the two-dimensional and axi-symmetric simulations were distinct because the flow path is parallel and uniform behind the oblique shock waves, but is not behind the conical shock waves. The shock-induced combustion behind the conical shockwaves showed much more violent and irregular characteristics.From the investigation of characteristic chemical time, condition of the periodic instability is identified as follows; at the detaching condition of Rankine-Hugoniot theory, (1) flow residence time is smaller than the chemical characteristic time, behind the detached shock wave with heat addition, (2) flow residence time should be greater than the chemical characteristic time, behind an oblique shock wave without heat addition.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4A
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• pp.325-328
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• 2011

In this paper, we present a new and simple derivation of the Craig representation for the two-dimensional (2-D) Gaussian Q-function in the viewpoint of geometry. The geometric derivation also leads to an alternative Craig form for the 2-D Gaussian Q-function. The derived Craig form is newly obtained from the geometry of two wedge-shaped regions generated by the rotation of Cartesian coordinates over two correlated Gaussian noises. The presented Craig form can play a important role in computing the probability represented by the 2-D Gaussian Q-function.

• Journal of Ocean Engineering and Technology
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• v.32 no.1
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• pp.36-42
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• 2018

Unlike a slender body, vortices are shed off alternately in the wake of a blunt body. In the case of liquid flows, when the pressure falls below the vapor pressure, cavitation occurs in the vortex core and affects the formation of the vortex street. This phenomenon is of major importance in many practical cases because the alternate shedding of vortices creates imbalanced forces on the body. Hence, it is very important to determine the shedding frequency of cavitating vortices. In this paper, the unsteady cavitating flow around a two-dimensional wedge-shaped submerged body was simulated using the commercial code STAR-CCM+. A numerical investigation of the structure of cavitating vortices was performed for a model with an apex angle of $20^{\circ}C$. The results were validated by comparing them with experimental measurements carried out at a cavitation tunnel of Chungnam National University (CNU-CT). It was found that the shedding frequency of the vortex increased by up to 18%, which was strongly affected by the development of cavitation.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.113-118
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• 2004

This paper presents a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method (FDLBM). We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of $\alpha=23^0$. At a stand-off distance $\omega$, the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and th propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. The lattice BGK model for compressible fluids is shown to be one of powerful tool for computing sound generation and propagation for a wide range of flows.

• Journal of the Korean Society of Combustion
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• v.7 no.1
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• pp.23-30
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• 2002

Instability of oblique detonation waves (ODW) at off-attaching condition was investigated through a series of numerical simulations. Two-dimensional wedge of finite length was considered in $H_2/O_2/N_2$ mixtures at superdetonative condition. Numerical simulation was carried out with a compressible fluid dynamics code and a detailed hydrogen-oxygen combustion mechanism. Present result reveals that there is a chemical kinetic limit of the ODW detachment, in addition to the theoretical limit predicted by Rankine-Hugoniot theory with equilibrium chemistry. Result also presents that ODW still attaches at a wedge as an oblique shock-induced flame showing periodically unstable motion, if the Rankine-Hugoniot limit of detachment is satisfied but the chemical kinetic limit is not. Mechanism of the periodic instability is considered as interactions of shock and reaction waves coupled with chemical kinetic effects. From the investigation of characteristic chemical time, condition of the periodic instability is identified as follows; at the detaching condition of the Rankine-Hugoniot theory, (1) flow residence time is smaller than the chemical characteristic time, behind the detached shock wave with heat addition, (2) flow residence time should be greater than the chemical characteristic time, behind an oblique shock wave without heat addition.