• Korean Chemical Engineering Research
• /
• v.53 no.1
• /
• pp.91-102
• /
• 2015

Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.7
• /
• pp.1789-1798
• /
• 1994

This paper aimed for numerical simulation of complicated gas turbine combustor with swirler. For the convenience of numerical analysis, fuel nozzle and air linear hole areas of secondary and dilution zone, which are issued to jet stream, were simplified to equivalent areas of annular type. In other to solve these problems, imaginary source terms which are corresponded to supplied fuel amount were added to those of governing equation. Chemical equilibrium model of infinite reaction rate and $k-{\epsilon}-g$ model with the consideration of density fluctuation were applied. As the result, swirl intensity contributed to mixing of supplied fuel and air, and to speed up the flame velocity than no swirl condition. Temperature profiles were higher than experimental results at the upstream and lower at the downstream, but total energy balance was accomplished. As these properties showed the similar trend qualitatively, simplified simulation method was worth to apply to complicated combustor for predicting combustion characteristics.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.6
• /
• pp.811-818
• /
• 2001

The wave characteristics for a non-reacting high-speed liquid jet were investigated using a linear stability theory. In this study, 2-D incompressible viscid momentum equation for a liquid jet was considered, and the effects of injection parameters, such as Weber number, Reynolds number, and density ratio, on the wave characteristics were investigated. With the wavelength obtained from the stability analysis, the atomization model was suggested. The droplet sizes after breakup were determined by the wavelengths of fast growing waves, and the mass of the shed droplets was determined by the breakup time derived by ORouke et al. It was found that in comparison with measurements of diesel fuel spray, the results of calculation had a similar trend of the decrease of overall SMD with the increase of Reynolds number.

• Journal of Magnetics
• /
• v.20 no.4
• /
• pp.421-426
• /
• 2015

This paper presents a practical method for estimation of average temperature in the permanent magnet (PM) of electric machine by using finite element analysis (FEA) and dynamo load experiment. First of all, the temperature effect of PM to the torque has been employed by FEA in order to evaluate the Temperature-Torque characteristic curve. The 1st order polynomial equation which is torque attenuation coefficient is derived by the FEA result of the Temperature-Torque curve. Next, torque saturation test with constant current condition is performed by dynamo load experiment. Then, the temperature trend can be estimated by adding the initial starting temperature using the torque attenuation coefficient and torque saturation curve. Lastly, estimated temperature is validated by infrared thermometer which measures temperature of PM surface. The comparison between the estimated result and experimental result gives a good agreement within a deviation of maximum $8^{\circ}C$.

• Journal of Institute of Control, Robotics and Systems
• /
• v.10 no.1
• /
• pp.10-14
• /
• 2004

We present a predictive control algorithm combined with the robust robot control that is constructed on the Lyapunov min-max approach. Since the control design of a real manipulator system may often be made on the basis of the imperfect knowledge about the model, it is an important trend to design a robust control law that guarantees the desired properties of the manipulator under uncertain elements. In the preceding robust control work, we need to tune several control parameters in the admissible set where the desired stability can be achieved. By introducing an optimal predictive control technique in robust control we can find out much more deterministic controller for both the stability and the performance of manipulators. A new class of robust control combined with an optimal predictive control is constructed. We apply it to a simple type of 2-link robot manipulator and show that a desired performance can be achieved through the computer simulation.

• The Korean Journal of Ecology
• /
• v.2 no.1
• /
• pp.1-8
• /
• 1978

Epiphytic lichens were sampled quantitatively on the cherry trees (Prunus serrulata) at Jeonju and Hadong along both north and south exposures of tat trees. Coverage of lichens was determinated for each species by 10*20cm quadrat. Lichen species diversities such as total diversity (D), mean diversity (D), Shannon diversity (D') and redundancy (R) were estimated according to Brillouin and Shannon equation. The importance value of lichen species was meassured by niche preemption model, The importance value transformed into some fraction k of the niche space. The value of k was compared with aggregation of lichens communities in to areas. The ten most important awariensis, Parmelia incurva, Parmelia crinita, Dirinaria applanta, Parmelia wallichiana, Parmelia austrosinensis and Cetraria platyphylla. The mean coverage epiphytic lichens on north side of tree was higher than of south side in two areas. The species diversities of epiphytic lichen of two areas shows that a change in the value of D' along vertical was not paralled with the D and R. In Kumsan-sa, D, D and D' increased upward along the tree of north exposure, but did not follow this trend in south, However in Sangge-sa, D, D and D' of both sides increased.

• 한국연소학회:학술대회논문집
• /
• 2003.12a
• /
• pp.43-47
• /
• 2003

Coke oven is used in an iron-making process for producing coke through devolatilization of the coking coal. An unsteady 2-dimensional model of solid bed is proposed to simulate a coke oven. The model contains governing equations with partial differential equation forms for the solid phase and the gas phase. Drying and devolatilization of coking coal, heat transfer, and generation of internal pores in the coking coal are also reflected to the source terms. Simulation results show a reasonable trend compared with the physical data.

• Transactions of Materials Processing
• /
• v.4 no.3
• /
• pp.222-232
• /
• 1995

The planar anisotripic FEM analysis for predicting earing profiles and draw-in amounts in the deep-drawing process is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-based unit vector and normal contact pressure. The consistent full set of governing relations, which is comprising euilbrium and geometric constraint equations, is appropriately linearized. Barlat's strain-rate potential is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and potential parameters. The linear triangular membrane elements are used for depicting the formed sheet. In the numerical simulations of deep drawing processes of a flat-top cylindrical cup for 2090-T3 aluminum alloy sheet show good agreement with experiments, although some discrepancies were observed in the directional trend of cup height and thickness strains.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.43 no.5
• /
• pp.132-144
• /
• 2001

Iln order to figure out criteria of bentonite for using as impervious material of waste landfill, laboratory experiments were performed to reveal the geotechnical properties of soil-bentonite mixtures such as compaction test, direct shear test, unconfined compression test, triaxial compression test, consolidation test and permeability test. The results of the study are summarized as follows ; 1. Based on the compaction test, optimum moisture content increased with the increase of bentonite content, but maximum dry density decreased. 2. In unconfined compression test, the maximum strength of the soil-bentonite mixtures appeared at 10% bentonite content. The correlation equation between stress($\sigma$) and strain($\varepsilon$) of the soil-bentonite mixtures is given by ; $\sigma=\frac{a\cdot\varepsilon}{\varepsilon^n+b}$ 3. In shear test of the mixtures. the shear strength showed an increasing trend with increase of bentonite content and the maximum shear strength appeared at 10% bentonite content. 4. In consolidation test, the coefficient of compressibility $(a_v)$$(m_v)$$(C_v)$

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1996.05a
• /
• pp.141-146
• /
• 1996

ABSTRACT : The aging characteristics of NEPE propellant is studied by HPLC analysis, cube crack test, swelling, and mechanical property test. The depletion of mixed stabilizer NMAI2-NDPA is analysed by Berthelot's law. The stabilizer NMA was completely comsumed after 16 weeks at $70{\circ}$ and after 6 weeks at $80{\circ}$ and the cracks developed in the sample. The aging trend of the propellant was shown hardening phenomena in the range of 20-$60{\circ}$ due to evaporation of energetic plasticizers.