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This paper is a numerical simulation that was made in the three-dimensional flow, carried out in a modified centrifugal compressor, having vaned diffuser stage, used as an auto-motive turbo charger. Moreover, the performance of the centrifugal compressor was dependent on the proper matching between compressor impeller and vaned diffuser, influencing significantly surge and the efficiency of centrifugal compressor stages. In addition, a modified compressor impeller, coupled with vane and vaneless diffuser, has been found to have similar internal flow patterns for both the vaneless and vaned diffuser design. The vaned diffuser effect has been paid particular attention in terms of better analysis where the diffuser was designed for high sub-sonic inlet conditions. Another aim of this research was to study and simulate the effect of vaned diffuser on the performance of a centrifugal compressor. The simulation was undertaken by using a commercial software, the so-called ANSYS CFX, to predict numerically the performance in terms of pressure ratio, poly tropic efficiency and mass flow rate for the centrifugal compressor stage. The results were generated from CFD and were analyzed for better understanding of the fluid flow through centrifugal compressor stage. Conclusively, it was observed that the effect of the vaned diffuser is to convert the kinetic energy into a high static pressure after analyzing the results of the simulation.
Residual stress in MEMS is of inherent importance in various respects. This study proposes a specific method using ANSYS including the birth and death method and combined with the optimal method (SCGM) to reduce the residual stresses during the CMOS fabrication process. The suitable cooling temperature for decreasing the residual stress is proposed and available. It demonstrates that the suitable parameter on the fabrication can reduce the residual stress in MEMS devices without any extra manufacturing process or external apparatus. The proposed method can expand to simulate the realistic MEMS model effectively.
The attractive feature of the singularity method for steady Stokes flows is that the hydrodynamic forces acting on the particle can be calculated by the total strength of distributed singularities. For unsteady Stokes flows, however we have to derive hydrodynamic forces acting on a solid body in terms of the strengths of both unsteady Stokeslets as well as unsteady potential dipoles if mass and force sources are both taken into consideration. Since the hydrodynamic force formulation results in a Volterra integral equation of the first kind, and the strengths are numerically approximated by means of the Lubich convolution quadrature method (CQM) in this study. As far as the numerical solutions of time-domain integral formulations of the unsteady Stokes equations are concerned, this paper requires only the Laplace-domain instead of the time- domain fundamental solutions of the governing equations. The stability and accuracy of the proposed method are verified through some well selected numerical examples. In total we include two examples presenting the accuracy of Lubich CQM, and another two examples for calculating general hydrody-namic forces of a sphere in oscillating or non-oscillating unsteady Stokes flows. It is concluded that this study is able to extend the unsteady Stokes flow theory to more general transient motions instead to limit to the oscillating flow assumption.
In this study, the region-point-matching technique (RPMT) is applied to examine the scattering problem of truncated semi-elliptic canyons under plane SH-wave excitation. The partition of the entire analyzed region into two subregions is carried out via an introduction of the elliptic-arc auxiliary boundary. Taking advantage of appropriate wavefunctions in elliptic coordinates, the expression of antiplane motions for each subregion can be obtained. To accomplish the indispensable coordinate shift, the coordinate-transformed relation, intended as a substitute for the addition theorem involving Mathieu functions, is well utilized. Integration of the coordinate-transformed relation into the RPMT brings about the rapid construction of simultaneous equations. Effects of pertinent parameters on steady-state and transient surface motions are demonstrated. Computed results show that, for horizontal incidence, the potential high level of ground shaking may occur near the illuminated upper corner of the canyon. In such a small localized region, due to the occurrence of constructive interference between the reflected waves from the horizontal ground surface and the scattered waves from the corners of the canyon, the peak amplifaction may be at least two times that of free-field response.
In this research, the effect of the surface inclination on the hydrodynamics and heat transfer of droplets impinging on very hot surfaces is studied. The applied numerical algorithm is based on the accurate calculation of the vaporization rate in the simulation process using a combination of the level set and ghost fluid methods. Also a mesh clustering technique is utilized to create sufficient mesh resolution near the surface in order to take into account the effect of the thin vapor layer between droplet and very hot surface. The results are verified against available experiments. The effect of the surface inclination on the droplet maximum spreading radius, droplet contact time and total heat removal from the surface is considered. Results show that for the studied regime, the maximum spreading radius of the droplet is decreased with an increase in the surface inclination while the droplet contact time on the surface is independent from the surface inclination. For inclinations greater than 45°, the total heat removal is decreased considerably with an increase in the inclination angle. For smaller inclinations, the dependency of the total heat removal on the surface inclination is not strong.
This paper deals with an analytical solution of an oscillatory flow in a channel filled with a porous medium saturated with a viscous fluid. The consideration of porosity in the channel is the basic idea of the paper. The oscillatory waves in the channel with porous medium are produced due to self-excited pressure disturbances caused by inevitable fluctuation in a suction rate at the porous walls. The ensuing steady axial velocity and the time dependent oscillatory axial velocity are found analytically using perturbation method and WKB approximation. The important physical quantities like the velocity profile, amplitude of the oscillation and penetration depth of the oscillatory velocity have been given special emphasis in this analysis. The effects of porosity of the medium on these quantities are calculated analytically and examined graphically. We find that the amplitude of oscillatory velocity and the penetration depth of the oscillatory axial velocity decrease with increasing values of inverse Darcy parameter. The oscillations in the fluid can be minimized by decreasing the permeability of the medium.
Based on the Timoshenko beam model, the nonlinear vibration of microbeams made of functionally graded (FG) materials is investigated under different boundary conditions. To consider small scale effects, the model is developed based on the most general form of strain gradient elasticity. The nonlinear governing equations and boundary conditions are derived via Hamilton's principle and then discretized using the generalized differential quadrature technique. A pseudo-Galerkin approach is used to reduce the set of discretized governing equations into a time-varying set of ordinary differential equations of Duffing-type. The harmonic balance method in conjunction with the Newton-Raphson method is also applied so as to solve the problem in time domain. The effects of boundary conditions, length scale parameters, material gradient index and geometrical parameters are studied. It is found that the importance of the small length scale is affected by the type of boundary conditions and vibration mode. Also, it is revealed that the classical theory tends to underestimate the vibration amplitude and linear frequency of FG microbeams.
For economizing the space of equipment and increasing the throughput of product, a vertical transportation is usually used for manufacturing a large and thin glass substrate. Due to the fragile characteristic of the large and thin glass substrate, investigation of a method for maintaining the glass substrate stably and safely on a supporting frame during manufacturing processes becomes an important subject. This subject belongs to a kind of moving boundary problem and the method of Arbitrary Lagrangian Eulerian (ALE) with a finite element scheme is suitably used to solve it. Also, related methods of the generalized minimal residual method (GMRES) and pressure convection diffusion method are adopted to calculate pneumatic pressures distributed on the glass substrate. The results show that under a low frequency of the vertical transportation the glass substrate stably lies on the supporting frame, oppositely under a high frequency of the vertical transportation the glass substrate has possibility to depart from the supporting frame. The later situation is disadvantageous to the glass substrate and should be avoided as much as possible.
With the increasing use of plastic gears in substitution of conventional steel ones, a plastic involute helical gear has been introduced to engage with a steel involute worm thus forming a novel plastic-steel worm-gear pair. The geometry and kinematics of this kind of worm-gear pair has been established first to derive its meshing properties which have been further verified by the finite element simulation. And it turns out that the contact area of this worm-gear pair is a point or an ellipse instead of a line. Further, a discrete dynamic model has been applied to investigate the dynamic transmission of motion and power of this worm-gear pair through the dynamic mesh force and the driven plastic involute helical gear. And the effects of angular and distance assembling errors have also been included.
A new type of large semi-rigid solar array structure with a new structural concept of rigid-flexible combination has developed for space application. Due to the good features of large scale and lightweight, such structure can well satisfy to the large power requirements of spacecraft and thus has drawn increasing attention recently. However, its structural weakness of inherently flexibility makes low frequency vibrations happen much easier. It is highly required to obtain an accurate dynamic model for predicting the dynamic characteristics of this kind of semi-rigid space structure. Because this structure is composed of different components that have quite different stiffness properties respectively, it is very difficult to build up an accurate dynamic model of this complex structure. In this paper, a novel analytical dynamic model is developed for solving this problem. To validate the correctness of the proposed model, experiment studies are conducted. By comparing the simulation results with experimental results, it can be concluded that this dynamic modeling method presented in the paper is credible. The present study is significant for the structural construction and application of this special structure.
The effect of space and temperature dependent heat generation/absorption on an unsteady laminar boundary layer flow of viscous, incompressible, radiating and electrically conducting fluid over a vertical stretching permeable surface is investigated numerically in the presence of applied magnetic field and buoyancy force. By applying similarity analysis, the governing partial differential equations are transformed into a set of non-linear coupled ordinary differential equations and they are solved by Runge-Kutta-Fehlberg method along with shooting technique. The numerical values obtained within the boundary layer for the dimensionless velocity, temperature, skin friction coefficient and heat transfer rate are presented through graphs and tables for several set of values of governing parameters.
Of concern in this paper is a problem motivated towards studying the influence of slip velocity on heat and mass transfer in the unsteady flow of blood through a porous vessel, when the lumen of the vessel has turned into a porous structure with internal heat generation or absorption in the presence of chemical reaction. It is assumed that the influence of a uniform magnetic field acts normal to the flow and the permeability of the porous medium fluctuates with time. The suction velocity is also taken to be oscillates periodically. The problem is solved numerically by using Crank-Nicolson scheme. The computational results are presented graphically for the velocity, temperature and concentration distribution as well as the variation of skin-friction co-efficient, Nusselt number and Sherwood number for various values of the parameters involved in this analysis. The study reveals that the flow is appreciably influenced by the presence of a magnetic field and slip velocity.