Tech Science Press
Not a member yet
3972 research outputs found
Sort by
An Alternative Approach to Minimize the Convection in Growing a Large Diameter Single Bulk Crystal of Si<sub>0.25</sub>Ge<sub>0.75</sub> Alloy in a Vertical Bridgman Furnace
No full textProducing homogeneous single bulk crystals requires a good understanding of the thermo-solutal behavior in the solvent region. This study explores simulation of the growth of large diameter single bulk crystals of silicon and germanium alloy from its melt utilizing Bridgman method. Both thermal and solutal diffusion of silicon and germanium in the molten SiGe alloy are of interest. It was observed that the diffusion dominates the transport phenomenon in the solvent region especially in the first 25 mm of the model due to having a PeT <<1. It was also found that the control of both radial and axial applied temperature can be considered as an alternative approach to obtain a homogeneous and uniform distribution of silicon in the solvent region, more specifically near the solid liquid interface. This of course was accompanied by applying a reduced pulling rate. The aforementioned parameters are integral part of obtaining a flat or near flat shape interface which is most sought after in industry
CFD Simulation of Magnetohydrodynamic Flow of a Liquid- Metal Galinstan Fluid in Circular Pipes
Get PDFIn this paper, the steady, laminar, incompressible viscous flow of an electrically conducting liquid-metal fluid is investigated numerically in a circular non-conducting pipe. The considered work fluid is Galinstan (GaInSn, i.e. Gallium-Indium-Tin). Such a liquid metal is subjected to a constant pressure gradient along the axial direction and a uniform transverse magnetic field in the spanwise direction. Numerical simulations are performed by means of the Fluent commercial software (used to solve the governing three dimensional fluid dynamics and electromagnetic field partial differential equations iteratively). The magnetic field induction, B, takes values between 0 and 1.5 T with a 0.5 T step size. The fluid velocity is found to decrease with an increase in the intensity of the applied magnetic field. The results, plotted as a function of system parameters, are critically discussed with respect to potential industrial applications
Numerical Study of Natural Convection in an Inclined Triangular Cavity for Different Thermal Boundary Conditions: Application of the Lattice Boltzmann Method
Get PDFA double-population Lattice Boltzmann Method (LBM) is applied to solve the steady-state laminar natural convective heat-transfer problem in a triangular cavity filled with air (Pr = 0.71). Two different boundary conditions are implemented for the vertical and inclined boundaries: Case I) adiabatic vertical wall and inclined isothermal wall, Case II) isothermal vertical wall and adiabatic inclined wall. The bottom wall is assumed to be at a constant temperature (isothermal) for both cases. The buoyancy effect is modeled in the framework of the well-known Boussinesq approximation. The velocity and temperature fields are determined by a D2Q9 LBM and a D2Q4 LBM, respectively. Comparison with previously published work shows excellent agreement. Numerical results are obtained for a wide range of parameters: the Rayleigh number spanning the range(103-106) and the inclination angle varying in the intervals (0° to 120°) and (0° to 360°) for cases I and II, respectively. Flow and thermal fields are given in terms of streamlines and isotherms distributions. It is observed that inclination angle can be used as a relevant parameter to control heat transfer in right-angled triangular enclosures
Multi-domain boundary knot method for ultra-thin coating problems
No full textThis paper develops a multi-domain boundary knot method (BKM) formulation to solve the heat conduction problems of ultra-thin coatings. This approach overcomes the troublesome singular integration difficulty in the boundary element method in the simulation of such ultra-thin coating problems. Our numerical results show that the present BKM is very promising with sufficient accuracy in predicting the temperature distributions and the other physical quantities in thin coated layers even when the thickness ranges from 10-1m to 10-9m. The present method can also easily be extended to the three-dimensional problems
Analysis and Prediction of Parallel Effect on Inherent Deformation during the Line Heating Process
No full textThis paper describes the effect of previous heating on inherent deformation by following heating, more specifically, the case of two heating lines applied parallel to each other. The novelty of the work lies in revealing the parallel effect and how, factors such as, for example, the heating condition and the plate geometry, influence the resulting inherent deformation of parallel heating. In addition, relationships to easily get these influences are provided. The results are suitable for a wide range of heating conditions and plate thickness
Analysis of Band Structure for 2D Acoustic Phononic Structure by BEM and the Block SS Method
No full textBy its very basis, the block Sakurai-Sugiura (SS) method may be applied to solving nonlinear eigenvalue problem formulated by boundary integral equation. In this paper, the methodology of BEM combined with the block SS method is applied to the computation of band structures of phononic structures for acoustic problems. Since the conventional boundary integral equation yields the real fictitious eigenfrequencies when it is applied to an exterior problem of scatters, Burton-Miller’s method is employed to remove the real fictitious eigenfrequencies resulted by the boundary of the scatterers. The application of the method is demonstrated through analyses of band structures of homogenous and composite structures
An approximately H<sup>1</sup>-optimal Petrov-Galerkin meshfree method: application to computation of scattered light for optical tomography
No full textNearly pollution-free solutions of the Helmholtz equation for k-values corresponding to visible light are demonstrated and verified through experimentally measured forward scattered intensity from an optical fiber. Numerically accurate solutions are, in particular, obtained through a novel reformulation of the H1 optimal Petrov-Galerkin weak form of the Helmholtz equation. Specifically, within a globally smooth polynomial reproducing framework, the compact and smooth test functions are so designed that their normal derivatives are zero everywhere on the local boundaries of their compact supports. This circumvents the need for a priori knowledge of the true solution on the support boundary and relieves the weak form of any jump boundary terms. For numerical demonstration of the above formulation, we used a multimode optical fiber in an index matching liquid as the object. The scattered intensity and its normal derivative are computed from the scattered field obtained by solving the Helmholtz equation, using the new formulation and the conventional finite element method. By comparing the results with the experimentally measured scattered intensity, the stability of the solution through the new formulation is demonstrated and its closeness to the experimental measurements verified
A set-based method for structural eigenvalue analysis using Kriging model and PSO algorithm
No full textThe set-based structural eigenvalue problem is defined, by expressing the uncertainties of the structural parameters in terms of various convex sets. A new method based on Kriging model and Particle Swarm Optimization (PSO) is proposed for solving this problem. The introduction of the Kriging model into this approach can effectively reduce the computational burden especially for largescale structures. The solutions of the non-linear and non-monotonic problems are more accurate than those obtained by other methods in the literature with the PSO algorithm. The experimental points for Kriging model are sampled according to Latin hypercube sampling method. Two approaches of imposing the constraint of the hyper-ellipsoid are presented for global optimization. One is by adding penalty terms to the original objective function; the other one is use objective function with interval spherical coordinates by coordinate transformation. An engineering example revealed the feasibility and accuracy of the proposed method
Dynamic Route Guidance Based on Model Predictive Control
No full textRoute selections for vehicles can be equivalent to determine the optimized operation processes for vehicles which intertwine with each other. This paper attempts to utilize the whole methodology of model predictive control to engender rational routes for vehicles, which involves three important parts, i.e. simulation prediction, rolling optimization and feedback adjustment. The route decisions are implemented over the rolling prediction horizon taking the real-time feedback information and the future intertwined operation processes into account. The driving behaviors and route selection speculations of drivers and even traffic propagation models are on-line identified and adapted for the simulation prediction in next prediction horizon. The mesoscopic traffic model is utilized for the simulation prediction so as to achieve both computing efficiency and prediction accuracy, where the partial link density in front of the vehicle rather than the density of total link is utilized to calculate the vehicle propagation velocity. The path traveling time is accumulated in a way related to the departure time and the operation process of a vehicle. The system architecture is composed of two parts. One is to simulate the true traffic system with stochastic behaviors such as speed fluctuations and inclinations to obey or disobey navigation commands, and the other one is the simulation prediction, rolling optimization and feedback adjustment system. In this way, the case study of medium traffic network shows that the simulation prediction-based rolling-horizon feedback implementation can prevent possible congestion in advance. It provides an engineering solution to the real-time closed-loop predictionbased traffic navigation
Fracture Behavior of Heat Affected Zone of Laser-welded Joint for Ti-6Al-4V titanium alloy: Experimental and Computational Study
No full textIn order to study failure perspective of Ti-6Al-4V titanium alloy welded joint, fracture behavior of the heat affected zone is researched. Microhardness, tensile test and microstructure are used to study the mechanical properties of the titanium alloy laser welded joint. The tensile and microhardness results show that heat affected zone near the base metal is the weakest in welded joints. This paper is based on the results from in-situ tension test to observe the process of crack expansion in heat affected zone. And then, in-situ test is simulated via the finite element method on ABAQUS Standard; therefore the fracture criteria are generated by comparing the applied force between simulation and in-situ test. Meanwhile, the GTN model is used to describe the damage behavior of the titanium alloy. The grain structure is simplified as voronoi convex polyhedron. And then, based on the in-situ test and its simulation, we conduct research on the fracture driving force under micro-scale condition. The simulation result indicates that the driving forces for metal fracture are jointly from the normal stress and shear stress