• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.163-168
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• 1991

During Compression molding of polymeric composite materials, the flow characteristics should be obtained. Understanding the flow states may be useful for determination of optimum molding conditions, charge pattern etc. So far, for obtaining the flow analysis, no-slip boundary condition was applied on the mold surface. However, The study under consideration of the slip was conducted by Barone and Caulk. They have introduced the nondimensional parameter which is the ratio of viscous to friction resistance and governs the frictional condition. But the method for determining the parameter could not be proposed. In our work, the parameter which explains the interfacial friction is measured under a variety of molding conditions. Two-dimensional rectangular part and circular hollow disk are simulated with the measured parameter using the finite element method. Effects of the parameter on shapes of flow fronts are also presented.

• Tribology and Lubricants
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• v.10 no.2
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• pp.43-50
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• 1994

The hydrodynamic bearing is accepted in many rotating systems because it has a large load carrying capacity. But the anisotropic pressure distribution of the bearing can arise the unstable vibration phenomenon over a certain speed. The magnetic bearing is an active element so that the unstable phenomenon of the hydrodynamic bearing, which is induced by the anisotropic support pressure of the oil film, can be controlled if the control algorithm and the controller gains are chosen appropriately. In this study, we investigate the stabilization method of the hydrodynamic bearing system composing the hybrid bearing which is the single unit of hydrodynamic bearing and magnetic bearing. The load carrying conditions of the hybrid bearing is modelled by the sum of the stiffness and damping coefficients of the hydrodynamic and the magnetic bearings in each direction. The dynamics of the rotor is analyzed by the Finite Element Method and the stability limit is determined by the eigenvalues of the hybrid bearings and shaft system. The eigenvalue study of the system shows that the stability limit of the hybrid bearing is increased compared to that of the hydrodynamic bearing. A Small increment of the stiffness and damping coefficient of the hybrid bearings by the magnetic actuators can increase the stability limit of the system. In this paper we tried to show the design references of the hybrid bearings by using the nondimensional bearing parameters. The analysis results show the possibilities of the stability limit increment of the hydrodynamic bearing system by combining the magnetic bearing.

• Water for future
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• v.21 no.3
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• pp.291-291
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• 1988

The two dimensional time dependent flow past a circular cylinder is analyzed numerically. In the analysis, equations of conservation of mass and momentum are transformed to equations of stream function-vorticity and vorticity transport, and nondimensionalized by nondimensional parameters representing flow characteristics, The resulting stream function-vorticity equstion and vorticity transport equation are solved by successive over relaxation scheme and alternating direct implicit scheme. Numerical experments are performed for the flow in the range of Reynolds number 125 to 275. The time dependent streamlines, vorticities, pressure on cylinder surface, separation angle, and drag and lift coefficients are calculated, and the method for estimation of pressure on cylinder surface and the outer boundary limit are developed.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.142-154
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• 1998

A stirling engine is a mechanism used to convert heat to power and operates on a closed regenerative thermodynamic cycle with compression and expansion of the working fluid at different temperature. The performance of a stilting cycle machine is a function of six independent parameters, namely; (1) speed N(r.p.m), (2) pressure of the working fluid p(Pa), (3) ratio of the temperature in the compression and expansion space ${\tau}(=T_C/T_E)$ , (4) ratio of the swept volumes in these two spaces K, (5) phase angle $\alpha$ and (6) dead volume ratio X. This paper describes the procedure and presents the results of computations carried out to establish the optimum combinations of these six parameters for maximum engine output for the machine acting as a prime mover, over a combined temperature range from $300^{\circ}K$ to $1000^{\circ}K$ and dead volume ratio X ranging from 0.1 to 2.0. The output of a stilting cycle machine can be expressed in terms of nondimensional power in several different ways. Four methods were studied in detail, the parameters optimized and design charts and engine power charts prepared. The results of this paper may be useful as a guide to the likely effects on the performance of some of the important design parameters and regenerator design.

• Water for future
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• v.31 no.4
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• pp.291-297
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• 1998

The two dimensional time dependent flow past a circular cylinder is analyzed numerically. In the analysis, equations of conservation of mass and momentum are transformed to equations of stream function-vorticity and vorticity transport, and nondimensionalized by nondimensional parameters representing flow characteristics, The resulting stream function-vorticity equation and vorticity transport equation are solved by successive over relaxation scheme and alternating direct implicit scheme. Numerical experiments are performed for the flow in the range of Reynolds number 125 to 275. The time dependent streamlines, vorticities, pressure on cylinder surface, separation angle, and drag and lift coefficients are calculated, and the method for estimation of pressure on cylinder surface and the outer boundary limit are developed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1437-1443
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• 2011

Thick plates produced by the rolling process are used as the basic elements of ship structures. In this paper, we present a setup model for controlling the asymmetric factors causing plate bending in the width direction during plate rolling. A series of three-dimensional finite element analyses is conducted to predict the relationship between various asymmetric factors and plate bending. The setup model is developed by performing regression on the relationship to produce linear equations with several nondimensional parameters. The setup model is verified with a pilot rolling test in which variations in thickness and temperature differences in the width direction exist. The results show that the bending curvatures predicted by the model are in fairly good agreement with the measured results for those asymmetric factors.

• Structural Engineering and Mechanics
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• v.5 no.3
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• pp.257-268
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• 1997

The elastic deflections and Euler buckling loads are investigated for a class of tapered and initially curved cantilevered beams subjected to loading at the tip. The beam's width increases linearly and its depth decreases linearly with the distance from the fixed end to the tip. Unloaded, the beam forms a circular are perpendicular to the axis of bending. The beam's deflection responses, obtained by solving the differential equations in closed form, are presented in terms of four nondimensional system parameters: taper ratio ${\kappa}$, initial shape ratio ${\Delta}_0$, end load ratio f, and load angle ${\theta}$. Laboratory measurements of the Euler buckling loads for scale models of tapered initially straight, corrugated beams compared favorably with those computed from the present analysis. The results are applicable to future designs of the end structures of highway guardrails, which can be designed to give the appropriate balance between the capacity to deflect a nearly head-on vehicle back to its right-of-way and the capacity to buckle sufficiently that penetration of the vehicle may be averted.

• Journal of ILASS-Korea
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• v.5 no.1
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• pp.13-22
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• 2000

The present study has numerically analyzed the vaporization characteristics of fuel droplets in the high temperature convective flow field. The axisymmetric governing equations for mass, momentum, energy, and species are solved by an iterative and implicite unstructured finite-volume method. The moving boundary due to vaporization is handled by the deformable unstructured grid technique. The pressure-velocity coupling in the density-variable flows is treated by the SIMPLEC algorithm. In terms of the matrix solver, Bi-CGSTAB is employed for the numerically efficient and stable convergence. The n-decane is used as a liquid fuel and the initial droplet temperature is 300K. Computations are performed for the nonevaporating and evaporating droplets with the relative interphase velocity(25m/s). The unsteady vaporization process has been simulated up to the nondimensional time, 25. Numerical results indicate that the mathematical model developed in this study succesfully simulates the main features of the droplet vaporization process in the convective environment.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.7
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• pp.537-544
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• 2007

To facilitate comparative analysis on the effects of numerous parameters concerning design and operation of a desiccant rotor, it is firstly required to represent the dehumidification performance as numerical indices. In this work is proposed two performance indices of a desiccant rotor: the humidity effectiveness and the enthalpy-leak ratio. The humidity effectiveness represents the actual dehumidification as compared with the dehumidification in an ideal case, while the enthalpy-leak ratio represents the enthalpy transfer from the regeneration side to the dehumidification side. In an ideal case, the two indices approach one and zero, respectively. The effects of numerous parameters on the dehumidification performance of a desiccant rotor are investigated through numerical simulation and represented with the two indices. The results show that the performance indices are mainly determined by three nondimensional parameters each representing the thermal capacity, the sorption capacity, and the transfer capacity of a desiccant rotor.

• Advances in nano research
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• v.7 no.2
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• pp.89-98
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• 2019

In this work, the thermal buckling characteristics of zigzag single-walled boron nitride (SWBNNT) embedded in a one-parameter elastic medium modeled as Winkler-type foundation are investigated using a nonlocal first-order shear deformation theory (NFSDT). This model can take into account the small scale effect as well as the transverse shear deformation effects of nanotubes. A closed-form solution for nondimensional critical buckling temperature is obtained in this investigation. Further the effect of nonlocal parameter, Winkler elastic foundation modulus, the ratio of the length to the diameter, the transverse shear deformation and rotary inertia on the critical buckling temperature are being investigated and discussed. The results presented in this paper can provide useful guidance for the study and design of the next generation of nanodevices that make use of the thermal buckling properties of boron nitride nanotubes.