2018-08-22T02:17:24Z
http://ijstm.shirazu.ac.ir/?_action=export&rf=summon&issue=268
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
A two-dimensional thermo hydrodynamic analysis of journal bearings characteristics
A numerical thermohydrodynamic analysis of journal bearings operating under laminar flow and steady conditions is presented. Numerical solutions of full Navier-Stokes equations, coupled with energy equation in the lubricant field and heat conduction equation in the bearing, are obtained for a bearing of infinite length. Using conformal mapping, an orthogonal grid is generated and the governing equations are transformed for use in the computational plane. Finite difference forms of the transformed equations are obtained by control volume method, and the SIMPLE algorithm is used for the pressure-velocity coupling. Regarding the cavitated flow region, a cavitation criterion based on the lubricant vapor pressure is defined and the extent of the cavitated region is determined in the course of iterative numerical calculations. A homogenous mixture of lubricant and vapor is assumed in the cavitated region and the mean physical properties of the mixture are obtained based on the continuity requirement. To study the effect of different parameters, solutions are obtained for different values of eccentricity and radial clearance and also for different values of Reynolds number. To validate the computational results, comparison with experimental data of other investigators is made for several test examples, and reasonable agreement is obtained for each example
Journal bearing
thermohydrodynamic
lubrication
laminar
cavitation
infinite length
2013
02
16
203
220
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Dynamic mesh adaptation for two-dimensional unsteady flow
A method for adaptive refinement of a triangular mesh for solution of the steady and unsteady Euler equations is presented. An upwind, finite volume based on Roe’s flux difference splitting method is used to discretize the equations. By using advancing front method an initial regular Delaunay triangulation has been made. The adaptation procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal cost. Steady transonic results are shown to be of high spatial accuracy, primarily in that the shock waves are very sharply captured. Unsteady results obtained for a moving shock wave in a two-dimensional domain show the precise enrichment and coarsening procedure. The results were obtained with large computational savings when compared to results for globally-enriched mesh with cells subdivided as many times as the finest cells of the adapted grid.
Adaptive grid
Euler equations
unsteady solution
Delaunay triangulation
moving grid
2013
02
16
221
229
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Hydrodynamic phenomena of collision between a high-speed droplet and a rigid plane using second-order perturbation techniques
In this paper, the hydrodynamic phenomena of collision of a high-speed droplet with a rigid plane have been investigated by using perturbation techniques. Here, the velocity components, in contrast to other works, have been directly derived by solving Navier -Stokes equations. The ratio of initial droplet radius to the final droplet radius has been chosen as a perturbation parameter. Due to the interaction of a solid surface and moving fluid, a boundary layer forms and the field equations can be divided into two parts: inner and outer. By combining inner and outer solutions, we can determine velocity and pressure fields inside the droplet. As a result, final droplet radius, spreading rate, and final time up to the point that the droplet ceases to move will be determined. In the present study the problem is solved for high Reynolds numbers in which surface tension effects during the spreading process can be neglected. The results obtained agree well with other semi-analytic and also experimental studies which can be used for prediction of droplet impingement behavior.
Hydrodynamic
droplet
rigid plane
spread rate
perturbation techniques
2013
02
16
231
246
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Solution of three dimensional Euler equations using first and second order upwind algorithm
A code for computing three-dimensional steady Euler equations regions has been developed for supersonic and hypersonic inviscid flows. First-and second-order upwind schemes are used. The algorithm uses cell-centered implicit finite volume method. The flow fields around a secant ogive-cylinder (SOC) and 10° half-angle circular cone are computed and compared against experimental results of other references. Results of the second-order upwind scheme are in good agreement with experimental data except in the flow separation region. In addition, the results indicate that the second-order upwind scheme gives a more accurate pressure distribution on the body than the first-order before sectional separation occurs.
Steady Euler
upwind
Riemann problem
Roe’s scheme
supersonic
hypersonic
2013
02
16
247
258
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Wave length effect on Kelvin-Helmholtz instability criterion in two-phase stratified flow
Transient conditions of two-phase air-water flow were numerically analyzed. The wave growth from a stratified flow regime in a horizontal duct was considered. Conservation equations were solved by finite difference method. The analyses on the onset of wave initiation was compared with the empirical correlations of other researchers. This analysis clarified that the Kelvin-Helmholtz instability criterion is valid only for waves with long wavelengths. Also, the required air velocity for the initiation of waves with short wave lengths is well below that defined by the Kelvin-Helmholtz instability relation.
Wave length
Kelvin-Helmholtz instability
two-phase stratified flow
wave growth
2013
02
16
259
267
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Numerical analysis of second order wave diffraction on two-dimensional bodies
The problem of second-order wave diffraction around arbitrary two-dimensional bodies is studied and a numerical method in time-domain presented. The solution is based on separating the velocity potential into a known incident velocity potential and a scattered velocity potential. The initial condition corresponds to Stokes second order wave field in the domain, and the scattered potential is allowed to develop in time and space. The free surface boundary conditions and the radiation condition are satisfied to second order by an integral equation in time and the field solution at each time step is obtained by an integral equation method based on Green's theorem. Results are presented for three different geometries, a semi-submerged cylinder with axis at the still water level, a fully submerged circular cylinder and a semi-submerged rectangular cylinder. Comparison of the results of this work with theoretical and experimental ones shows good agreement.
Nonlinear diffraction
second order wave theory
wave forces
nonlinear waves
2013
02
16
269
282
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Surface temperature and heat transfer measurements in cross-corrugated plate heat exchangers
Two variables of importance in the design of cross-corrugated plate heat exchangers are the size (i.e, height and pitch) of the corrugation embossed on the plates, and the orientation of the corrugation with respect to the main flow direction. In this paper, such effects on the heat transfer performance of the exchanger are investigated. For this purpose, measurements were made on two especially designed test samples which were constructed by placing four clear corrugated plastic plates against each other to form three flow channels. While the height and pitch of the corrugation were fixed, the angle of inclination of the two samples was 45o and 60o. These samples were tested in a closed-circuit using hot and cold water, and data regarding temperatures and flow rates were recorded. While the present results are in general agreement with those in the literature, contrary to what has been
reported has been found that, the 45o sample has a better thermal performance than the 60o sample for Re >1300; for lower Re’s, the trends are identical
Plate heat exchanger
cross-corrugation
thermography
thermochromic liquid crystal film
2013
02
16
283
297
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Heat transfer characteristics of turbulent flow in periodic channels
Periodic fully-developed fluid flow and heat transfer characteristics are obtained numerically for turbulent flow in a channel with repeated baffle blockages. The channel has a rectangular cross-section and the baffles are located on the upper and lower walls in a staggered array. The Lam–Bremhorst low-Reynolds number form of themodel is used for the computations. The computations are performed for a set of geometric parameters. Reynolds number ranges from 103 to 104,Prandtle number is 0.7 (air), and the wall temperature is assumed to be uniform. The computational results are compared with experimental data and close
agreement is observed. The results indicate that the baffles have an increasing effect on transfer coefficients
turbulent flow
heat transfer
low-Reynolds number
vorticity
periodic
2013
02
16
299
308
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Studies of Nox, Co, soot formation and oxidation from a direct-injection stratified-charge engine using k-e turbulence mode
In this investigation, a model has been developed to predict the performance and emissions – NOx, CO and soot-in a direct-injection stratified-charge engine with a Texaco controlled combustion system (TCCS). This model uses theturbulence model to determine characteristic velocities for heat transfer calculations, that has only an empirical constant by comparison with Woschni's equation in which separate constants are used for each process in the four stroke cycle to determine the velocity for use in the Reynolds number. The modified Keck and Blizard model is used for combustion calculation by considering the rapid compression effects on the turbulence intensity. Extended Zel'dovich mechanism has been used to predict NOx emissions. To predict CO emissions, the Zeleknik and McBride models have been used. A certain model has been used to predict the mass of soot formed and oxidized. Comparison of the model predictions with available experimental data shows good agreement. Moreover, the program has a high flexibility for parametric studies to calculate the effect of engine parameters such as fuel-air ratio, engine speed, injection timing period and percentage of exhaust gas recirculation (EGR) on the performance and emission characteristics of the engine.
emissions
NOx
CO
soot
stratified
turbulence
Texaco
2013
02
16
309
320
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
A hybrid method for domain decomposition in parallel computing
A hybrid method is presented for domain decomposition employing combinatorial and algebraic graph theoretical algorithms. The method uses combinatorial graph theory for partial decomposition, followed by a spectral bisection approach based on concepts from algebraic graph theory. Examples are presented to illustrate the efficiency of the mixed method. In this paper, the effects of nodal ordering on the performance of the spectral bisection and mixed method are investigated.
parallel computing
spectral bisection
Graph Theory
partitioning
hybrid method
2013
02
16
321
332
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
First order decoupling of equations of motion for multibody systems consisting of rigid and elastic bodies
An improved method for deriving elastic generalized coordinates is considered and Kane's equations of motion for multibody systems consisting of an arbitrary number of rigid and elastic bodies are presented. The equations are in general form and are applicable for any desired holonomic system. Flexibility in choosing generalized speeds in terms of generalized coordinate derivatives in Kane's method is used. It is shown that proper choice of a congruency transformation between generalized coordinate derivatives and generalized speeds leads to first order decoupled equations of motion for holonomic multibody systems consisting of an arbitrary number of rigid and elastic bodies. In order to demonstrate the use of this method, a simple system consisting of a lumped mass, a spring and a clamped-free elastic beam is modeled
Decoupling
rigid and elastic systems
Kane's equations
congruency transformation
2013
02
16
333
343
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2000
24
3
Robust controller design for multivariable nonlinear uncertain systems
A QFT-type frequency-domain controller design technique is presented for multiple input-multiple ouput (MIMO) nonlinear systems with significant structured (parametric) uncertainty. Hard time-domain constraints are imposed on the outputs and control inputs in response to step disturbances. The control design method is based on replacing the nonlinear MIMO system with an equivalent diagonal MIMO linear uncertain plant using compact and convex sets of output functions. Then, a diagonal controller is designed for the equivalent linear system by transferring the time-domain constraints into the frequency-domain to obtain a series of allowable regions for the frequency responses of the nominal loop transfer functions. Next, a loop-shaping procedure is used to shape the nominal loop transfer function and hence the controller for each loop. Finally, Schauder’s fixed point theorem is utilized to show that the same controller will also work for the nonlinear system. The proposed method is illustrated by an example.
robust control
nonlinear
multivariable
QFT
structured uncertainty
2013
02
16
345
356