• Journal of Satellite, Information and Communications
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• v.10 no.1
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• pp.22-28
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• 2015

In this paper, we propose a new computationally efficient joint iterative multi-input multi-output (MIMO) detection scheme using a soft interference cancellation and minimum mean squared-error (SIC-MMSE) method. The critical computational burden of the SIC-MMSE scheme lies in the multiple inverse operations of the complex matrices. We find a new way which requires only a single matrix inversion by utilizing the Taylor series expansion of the matrix, and thus the computational complexity can be reduced. The computational complexity reduction increases as the number of antennas is increased. The simulation results show that our method produces almost the same performances as the conventional SIC-MMSE with reduced computational complexity.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.88-97
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• 1996

This paper treats an adaptive finite-element method for the viscous compressible flow governed by Navier-Stokes equations in two dimensions. The numerical algorithm is the two-step Taylor-Galerkin mettled using unstructured triangular grids. To increase accuracy and stability, combined moving node method and grid refinement method have been used for grid adaption. Validation of the present algorithm has been made by comparing the present computational results with the existing experimental data and other numerical solutions. Four benchmark problems are solved for demonstration of the present numerical approach. They include a subsonic flow over a flat plate, the Carter flat plate problem, a laminar shock-boundary layer interaction. and finally a laminar flow around NACA0012 airfoil at zero angle of attack and free stream Mach number of 0.85. The results indicates that the present adaptive triangular grid method is accurate and useful for laminar viscous flow calculations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.27-37
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• 1993

An efficient method to solve the minimum weight design problem for frame structures subjected to stress and displacement constraints is presented. The different cross-sectional shapes are conside red in order to apply engineering design in which usually required custom fabrication. To increase the efficiency of the optimization process, the structural response quantities(nodal forces, displacements) are linearized with respect to cross-sectional properties or their reciprocal, based on first order Taylor series expansion, while cross-sectional dimensions are considered as design variables. Numerical examples are performed and compared with other methods to demonstrate the efficiency and reliability of approximation method for frame structural optimization with different cross-sectional shapes. It is shown that the number of finite element analysis is greatly reduced and it leads to a highly efficient method of optimization of frame structures.

• Journal of the Korean Society of Visualization
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• v.16 no.1
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• pp.21-29
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• 2018

Homogeneous and isotropic turbulence (HIT) with no mean flow is a very useful type of flow for basic turbulence research. However, it is difficult to generate HIT in the lab. In this study, we implemented HIT in a confined box through synthetic jet actuators using sub-woofer speakers. Characteristics of HIT are varied depending on the strength of the jets. We used 2D PIV to measure the velocity field. Turbulence statistics such as homogeneity, isotropy ratio, turbulence kinetic energy, dissipation rate, Taylor microscale, Kolmogorov scale, and velocity correlation coefficient were calculated. Most of the turbulence statistics increased exponentially according to the strength of the jets, and the Taylor Reynolds number reached up to 185.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.809-820
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• 2003

The present study investigates effects of flow velocity on the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewall are determined by using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The aspect ratio and corrugation angle of the wavy duct is fixed at 7.3 and 145$^{\circ}$ respectively, and the Reynolds numbers, based on the duct hydraulic diameter, vary from 100 to 5,000. The results show that there exist complex secondary flows and transfer processes resulting in non-uniform distributions of the heat/mass transfer coefficients on the duct side walls. At low Re (Re<1000), relatively high heat/mass transfer regions like cell shape appear on both pressure and suction side wall due to the secondary vortex flows called Taylor-Gortler vortices perpendicular to the main flow direction. However, at high Re (Re>1000), these secondary flow cells disappear and boundary layer type flow characteristics are observed on pressure side wall and high heat/mass transfer region by the flow reattachment appears on the suction side wall. The average heat/mass transfer coefficients are higher than those of the smooth circular duct due to the secondary flows inside wavy duct. And also friction factors are about two times greater than those of the smooth circular duct.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.215-218
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• 2011

An air data acquisition algorithm has been developed for the supersonic flow at the preliminary design stage with pressure data acquisition device composed of major three total pressure sensors and two static pressure sensors. Through this algorithm, Mach number, angle of attack and sideslip angle can be very easily derived with simple interpolation algorithm and predefined data tables. In this preliminary design stage, to verify the developed algorithm, the data tables are constructed with data driven by Taylor Maccoll equation. Furthermore, these data are compared and modified with computational results based on CFD analysis. The present algorithm would be useful to get supersonic air data for the various aerial vehicles and their flight tests.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.3
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• pp.41-49
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• 2009

The present paper describes a mathematical modeling and simulation of the separation of a solid rocket booster from an air breathing engine vehicle. The vehicle and booster are considered as a multi-connected body and the booster is assumed to move only along the axial direction of the vehicle. The dynamic motion of the vehicle and the booster were modeled by using Kane's method. The aerodynamic forces on the whole system along various positions of booster were calculated by using DATCOM software and the internal pressure force acting on the effective surface during separation was simply calculated with gas dynamics and Taylor MacColl equation. Numerical simulation was done by using Mathworks-Matlab. From the result, the variation of Mach number and angle of attack are not large during the separation, so the variation of pitch angle and the characteristics of inlet flow for varying the Mach number and angle of attack during the separation test can be identified as neglectable values.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.5
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• pp.60-65
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• 2011

The development of an air data acquisition algorithm has been described in the supersonic flow at the preliminary design stage with pressure data acquisition device composed of major three total pressure sensors and two static pressure sensors which are installed on the surface of a cone type supersonic inlet. Through this algorithm, Mach number, angle of attack and sideslip angle can be very easily derived with simple interpolation algorithm and predefined data tables. The available range of Mach number is 1.6 to 4.0, angle of attack, $-12^{\circ}$ to $12^{\circ}$ and sideslip angle, $-12^{\circ}$ to $12^{\circ}$. In preliminary design stage, the data tables applied to the developed algorithm are constructed with data driven by Taylor Maccoll equation. The present algorithm would be useful to get supersonic flow air data for the various aerial vehicles and their flight tests.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.1-9
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• 2012

The gas jet from a coaxial porous injector for two-phase flows is discharged from the porous surface, which encloses the center liquid jet, and the gas and liquid jet interact with each other physically. The wall injected gas jet transfers the radial momentum effectively while the radial gas jet develops to axial jet, and the performance of atomizing and mixing can be improved. In this study, the Weber number and the ratio of momentum flux were controlled by changing the gas injection area and the mass flow rate of the gas jet, and a study on the spray characteristics at the cold-flow test using water and air simulant was performed. It is concluded that the radial momentum transfer concept of a coaxial porous injector gives a positive effect on the atomization and mixing of the two-phase spray.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.327-330
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• 2006

This paper represents the numerical analysis on effects of radius ratio in a concentric annulus with a rotating inner cylinder. The numerical model consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8mm, the numerical parameters are angular velocity and radius ratio. Also, the whole walls of numerical model have no-slip and the working fluid is used water at $20^{\circ}C$. The numerical analysis is assumed the transient state to observe the flow variations by time and the 3-D cylindrical coordinate system. The calculation grid adopted a non-constant grid for dense arrangement near the wall side of cylinder, the standard $k-{\omega}$ high Reynolds number model to consider the effect of turbulence flow and wall, the fully implicit method for time term and the quick scheme for momentum equation. The numerical method is compared with the experimental results by Wereley and Lueptow, and the results are very good agreement. As the results, TVF isn't appeared when Re is small because of the initial flow instability is disappear by effect of the centrifugal force and viscosity. The vortex size is from 0.8 to 1.1 for TVF at various $\eta$, and the traveling distance for wavy vortex have the critical traveling distance for each case.