Tech Science Press
Not a member yet
3972 research outputs found
Sort by
Mixed Convection and Heat Transfer in a “T” Form Cavity: The Effect of Inclination
Get PDFWe study the effect of inclination angle on mixed convection in a "T" form cavity containing two openings and two heated blocks mounted on its lower wall. The blocks are maintained at a constant temperature TH. The lower wall is adiabatic and submitted to a vertical air jet while the upper wall is kept cold at a constant temperature TC TH. The vertical walls are rigid and adiabatic. The governing equations are solved by a finite volume method. Special attention is devoted to the solution symmetry, the flow structure and the heat exchange through the cavity. The considered control parameters are: the inclination angle 0° ≤ φ ≤ 90°, the Rayleigh number 105 ≤ Ra ≤ 106, the Reynolds number 100 ≤ Re ≤ 1000, the Prandtl number Pr=0.72, the height of the blocks B=0.5, the opening width C=0.15 and the distance between blocks D=0.5. The results are presented in terms of streamlines, isothermal lines and variations of Nusselt number with Re or φ
Matrix Crack Detection in Composite Plate with Spatially Random Material Properties using Fractal Dimension
Get PDFFractal dimension based damage detection method is investigated for a composite plate with random material properties. Composite material shows spatially varying random material properties because of complex manufacturing processes. Matrix cracks are considered as damage in the composite plate. Such cracks are often seen as the initial damage mechanism in composites under fatigue loading and also occur due to low velocity impact. Static deflection of the cantilevered composite plate with uniform loading is calculated using the finite element method. Damage detection is carried out based on sliding window fractal dimension operator using the static deflection. Two dimensional homogeneous Gaussian random field is generated using Karhunen-Loeve (KL) expansion to represent the spatial variation of composite material property. The robustness of fractal dimension based damage detection method is demonstrated considering the composite material properties as a two dimensional random field
Finite Element Modeling of Compressive Deformation of Super-long Vertically Aligned Carbon Nanotubes
Get PDFThe super-long, vertically aligned carbon nanotubes (SL-VACNTs) are novel carbon nanomaterial produced from template-free synthesis. The mechanical responses of such material have been investigated by continuum finite element modeling and compared with experimental observations. The crushable foam model has been adequate in modeling the stress-strain curve and deformation of the SL-VACNTs under compression. SL-VACNTs are seen to exhibit transient elastic deformation at small displacement and then plastic deformation at large displacement. The deformation mostly occur at the position immediately beneath the compression platen (indenter face) due to the high stress/strain concentrations
Modelling of Nanoscale Friction using Network Simulation Method
Get PDFThe field of nanotribology in the last decades was established through the introduction of Atomic Force/Friction Force Microscopes. However, our theoretical understanding of the individual processes involved in friction force microscopy is limited. This work designs a reliable and efficient model for the stickslip phenomenon, following the rules of network simulation. The model is able to manage different types of potential between the tip and the sample surface, allowing different kinds of sample material and microscope tip properties to be simulated with only minor changes in the code. The most analysed tribological materials in technical literature are simulated to test the proposed model, while the results are close to experimentally obtained results
Exact Solutions of Finite Deformation for Everted Compressible Hyperelastic Cylindrical Tubes
Get PDFThe eversion problem for a class of compressible hyperelastic thinwalled cylindrical tubes is examined. The mathematical model is formulated as a second-order nonlinear ordinary differential equation based on the theory of nonlinear elasticity. The exact solution that describes the mechanism of the finite deformation of the everted cylindrical tube is obtained. Using numerical simulations, it is shown that the initial thickness of the tube plays a significant role in the eversion
A Systematic Review of Algorithms with Linear-time Behaviour to Generate Delaunay and Voronoi Tessellations
Get PDFTriangulations and tetrahedrizations are important geometrical discretization procedures applied to several areas, such as the reconstruction of surfaces and data visualization. Delaunay and Voronoi tessellations are discretization structures of domains with desirable geometrical properties. In this work, a systematic review of algorithms with linear-time behaviour to generate 2D/3D Delaunay and/or Voronoi tessellations is presented
Time Domain Inverse Problems in Nonlinear Systems Using Collocation & Radial Basis Functions
Get PDFIn this study, we consider ill-posed time-domain inverse problems for dynamical systems with various boundary conditions and unknown controllers. Dynamical systems characterized by a system of second-order nonlinear ordinary differential equations (ODEs) are recast into a system of nonlinear first order ODEs in mixed variables. Radial Basis Functions (RBFs) are assumed as trial functions for the mixed variables in the time domain. A simple collocation method is developed in the time-domain, with Legendre-Gauss-Lobatto nodes as RBF source points as well as collocation points. The duffing optimal control problem with various prescribed initial and final conditions, as well as the orbital transfer Lambert’s problem are solved by the proposed RBF collocation method as examples. It is shown that this method is very simple, efficient and very accurate in obtaining the solutions, with an arbitrary solution as the initial guess. Since methods such as the Shooting Method and the Pseudo-spectral Method can be unstable and require an accurate initial guess, the proposed method is advantageous and has promising applications in optimal control and celestial mechanics. The extension of the present study to other optimal control problems, and other orbital transfer problems with perturbations, will be pursued in our future studies
On the First-principles Density Functional Theory Calculation of Electromigration Resistance Ability for Sn-based Intermetallic Compounds
Get PDFThe aim of the study is to investigate the interactions between Sn adatoms in a solder bump and three typical Sn-based intermetallic compounds (IMCs) surface, i.e., Cu3Sn, Cu6Sn5, and Ni3Sn4, at the atomistic scale. The adsorption energy, average bond length, and bond population of the Sn/Cu3Sn, Sn/Cu6Sn5,and Sn/Ni3Sn4 systems are calculated through the first-principles density functional theory (DFT) calculation to investigate how the Sn adatoms influence the IMC surface. The calculated results show that the Sn atoms on the Cu3Sn (0 0 1) surface hold the largest adsorption energy, average bond length and bond population, implying that the Cu3Sn (0 0 1) surface is the most stable surface for Sn adatoms. Moreover, the electromigration resistance ability of three typical Snbased IMCs can be further identified according to the nominal the adsorption energy, average bond length, and bond population, which are estimated through averaging the adsorption energy, average bond length, and bond population for the Cu3Sn, Cu6Sn5 and Ni3Sn4 IMCs at seven crystal surfaces, i.e., (1 0 0), (0 1 0), (0 0 1), (1 1 0), (1 0 1), (0 1 1) and (1 1 1). The results reveal that Cu3Sn holds the best electromigration resistance ability, followed by Ni3Sn4 and Cu6Sn5
A Universal Model-Independent Algorithm for Structural Damage Localization
Get PDFAlthough the model-independent damage localization algorithms have been extensively developed in recent years, the theoretical relationship between these damage indicators and the definition of damage is not clear. Moreover the existing damage localization methods are usually dependent on the boundary conditions and the type of structure. In view of this, the paper presents a universal model-independent algorithm for structural damage localization. To this end, the explicit relationship between the damage and damage-induced displacement variation is firstly clarified by using the well-known Sherman-Morrison and Woodbury formulas. A theorem is then presented for structural damage localization. According to the theorem, the universal model-independent damage localization algorithm has been concluded and verified in some common structures. Presented in this article also can be seen as a theoretical proof of the existing non model methods for structural damage localization. It has been shown that the presented algorithm may be useful in the long term health monitoring and the damage localization
Static, Free Vibration and Buckling Analysis of Functionally Graded Beam via B-spline Wavelet on the Interval and Timoshenko Beam Theory
Get PDFThe application of B-spline wavelet on the interval (BSWI) finite element method for static, free vibration and buckling analysis in functionally graded (FG) beam is presented in this paper. The functionally graded material (FGM) is a new type of heterogeneous composite material with material properties varying continuously throughout the thickness direction according to power law form in terms of volume fraction of material constituents. Different from polynomial interpolation used in traditional finite element method, the scaling functions of BSWI are employed to form the shape functions and construct wavelet-based elements. Timoshenko beam theory and Hamilton’s principle are adopted to formulate the governing motion equations of FG beam. On account of the excellent approximation property of B-spline function for structure analysis, the proposed BSWI method could achieve a fast convergence and satisfying numerical results with fewer degrees of freedoms. In the end, different numerical examples are employed to demonstrate the validity and high accuracy of the formulated FGM BSWI element comparing with the exact solutions and other existing approaches in literatures. The numerical results also show that the proposed numerical algorithm is very suitable to investigate the static, free vibration and buckling analysis of FG beam