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Complete Solid Buckling Analysis With Boundary Face Method
Get PDFIn this paper, we will propose a new concept, namely the Complete Solid Buckling Analysis, in which the deformation assumptions for rods, beams and plates are all discarded, and the entire structure, including all its local smallsized features, is modeled as a three-dimensional (3D) solid according to its real shape and dimensions. Firstly, we derive a new control equation, in which physical variables in three directions are considered. Then, an equivalent Boundary Integral Equation (BIE) is derived from the control equation. In the numerical implementation, the Boundary Face Method is employed, by which analyses can be performed directly on the CAD geometry model. And the Dual Reciprocity Method is used to deal with the domain integrals. Finally, several numerical examples with different geometries and boundary conditions are presented to test our method. Results are in good agreements with the known ones
Heat and Mass Transfer due to Natural Convection along a Wavy Vertical Plate with Opposing Thermal and Solutal Buoyancy Effects
Get PDFIn the present work, a numerical analysis is performed of the combined effects of (opposing) thermal and solutal buoyancy in the presence of a wavy (vertical) surface. The boundary layer equations and related boundary conditions are discretized using a finite volume scheme and solved numerically using a Gauss-Seidel algorithm. The influence of the wavy geometry (in terms of related wavelength L and amplitude a) and the buoyancy ratio N on the local Nusselt and Sherwood numbers and on the skin-friction coefficient are studied in detail. Results show that when Pr Sc, the flow is completely perturbed; the thickness of the mass boundary layer is larger than that of the thermal boundary layer
Heat Transfer Related to a Self-Sustained Oscillating Plane Jet Flowing Inside a Rectangular Cavity
Get PDFComputations related to a heat transfer and fluid flow of a plane isothermal fully developed turbulent plane jet flowing into a rectangular hot cavity are reported in this paper. Both velocity and temperature distributions are computed by solving the two-dimensional Unsteady Reynolds Averaged Navier--Stokes (URANS) equations. This approach relies on one point statistical modeling based on the energy - specific dissipation (k-ω) turbulence model. The numerical simulations are carried out in the framework of a finite volume method. This problem is relevant to a wide range of practical applications including forced convection and the ventilation of mines, enclosure or corridors. The structural properties of the flow and heat transfer are described for several conditions. An oscillatory regime is evidenced for particular jet location, inducing for each variable a periodic behavior versus time. The jet flapping phenomena is detailed numerically through the instantaneous streamlines contours and the vorticity magnitude contours within one period of oscillation. The heat transfer along the cavity walls is also periodic. Time average of mean Nusselt number is correlated with some problem parameters
Rupture and Instability of Soft Films due to Moisture Vaporization in Microelectronic Devices
Get PDFIn this paper, a damage mechanics-based continuum theory is developed for the coupled analysis of moisture vaporization, moisture absorption and desorption, heat conduction, and mechanical stress for a reflow process in microelectronic devices. The extremely compliant film has been used in wafer level lamination process. Such a soft film experiences cohesive rupture subjected to moisture absorption during reflow. The numerical simulation results have demonstrated that vapor pressure due to moisture vaporization is the dominant driving force for the failures. The correlation between the vapor pressure evolution and the film rupture observed from the experiments have been established through two case studies. The results are in excellent agreement with experimental observations. Further, to understand the mechanism of soft film rupture, the instability theory for rubbery material undergoing large deformation is introduced. Neo-Hookean, Mooney–Rivlin, and Ogden’s models are used to derive the analytical solutions. For any thickness of the spherical void with neo-Hookean materials, maximum vapor pressure is up to 2.5 times of shear modulus. The instability of the void with Mooney-Rivlin material depends on material property, coefficient of asymmetry, and thickness of the wall. In either case, it has been found that the hoop stress always increases monotonically even though the vapor pressure starts to fall below the cavitation pressure, and eventually this leads to the void to collapse. However, if the vapor pressure falls at a greater rate, the collapse may not occur
A Numerical Modeling of Failure Mechanism for SiC Particle Reinforced Metal-Metrix Composites
Get PDFThe present work is to investigate the failure mechanisms in the deformation of silicon carbide (SiC) particle reinforced aluminum Metal Matrix Composites (MMCs). To better deal with crack growth, a new numerical approach: the MLPG-Eshelby Method is used. This approach is based on the meshless local weak-forms of the Noether/Eshelby Energy Conservation Laws and it achieves a faster convergent rate and is of good accuracy. In addition, it is much easier for this method to allow material to separate in the material fracture processes, comparing to the conventional popular FEM based method. Based on a statistical method and physical observations, the hard SiC particles are distributed randomly over the cubic space of the matrix. Four failure mechanisms are found to be critical to the accurate prediction of the mechanical properties of MMCs: a) the failure inside the matrix; b) the failure between the interface of aluminum matrix and the SiC particles; c) the fracture of the SiC particles; and d) the separation of two neighboring SiC particles. Plastic work is used as a failure criterion. It is found that the current approach can accurately predict the mechanical behavior of MMCs, including Young's moduls, stress strain curve, tensile strength, and limit strain. When the SiC volume fraction is low, the interface failure is more important; while for the case of high SiC volume fraction, all the four failure mechanisms work together to affect the mechanical property for the composite structure
Size-Dependent Flexural Dynamics of Ribs-Connected Polymeric Micropanels
Get PDFThis study investigates the sensitivity of the flexural response of a ribconnected system of coupled micro-panels with traction-free surfaces. Idealized as a two-dimensional elastic continuum with a finite transverse stiffness, each micropanels’ behavior is examined within the framework of the biharmonic mathematical model derived from the higher-order, size-dependent strain energy formulation. The model incorporates the material length scale, which bears an associative relationship with the underlying polymer’s averaged Frank elastic constant. Upper estimates of the eigenvalue of the system, under fully clamped edges and simplysupported edges, are determined by the Rayleigh method. The adopted theory for the micro-panel’s behavior takes into account the rotary inertia, the small-scale effect, the Poisson’s ratio and the effective stiffness of the ribs, but neglects shear distortion. Frequency shifts of the rib-connected coupled micro-panels are systematically identified and presented. Results indicate the critical thickness for which the polymeric micro-panel’s resonant frequency starts to experience stiffened responses based on the magnitude of the size-effect. The Rayleigh method of eigenvalue extraction is augmented with the applied statistical method of design of experiment for the discovery of notable interaction effects between the aspect ratio, rotary inertia, small-scale effect, and thickness-to-span ratio of the system
Predicting Effective Elastic Moduli and Strength of Ternary Blends with Core–Shell Structure by Second–Order Two–Scale Method
Get PDFCore–shell particle–filled PA6/EPDM–g–MA/HDPE ternary blend has excellent mechanical properties. In this paper, effective elastic properties and tensile yield strength of the ternary blend are predicted by the second–order two– scale method, to investigate the relationship between morphology and mechanical properties. The method and the limit analysis for predicting mechanical properties of random heterogeneous materials are briefly introduced. Realistic morphology of the ternary blend including both core–shell particles and pure particles is simulated, and finite element mesh is generated. The unified strength theory is embedded in the method for the convenience of selecting a suitable yield criterion. The effective elastic moduli and tensile yield strength predicted by the method in this paper are compared with analytical and experimental results. Finally, effect of shell thickness in the core–shell particles on the effective elastic moduli and tensile yield strength is investigated
Homotopy Method for Parameter Determination of Solute Transport with Fractional Advection-dispersion Equation
Get PDFThe unknown parameters are critical factors in fractional derivative advection-dispersion equation describing the solute transport in soil. For examples, the fractional derivative order is the index of anomalous dispersion, diffusion coefficient represents the dispersion ability of media and average pore-water velocity denotes the main trend of transport, etc. This paper is to develop a homotopy method to determine the unknown parameters of solute transport with spatial fractional derivative advection-dispersion equation in soil. The homotopy method can be easily developed to solve parameter determination problems of fractional derivative equations whose analytical solutions are difficult to obtain. The sigmoid function is involved to adjust the homotopy parameter during the iterative processes. Numerical results show that the presented method is efficient and feasible in several benchmark examples
CFD and Experimental Investigations of Drag Force on Spherical Leak Detector in Pipe Flows at High Reynolds Number
Get PDFSpherical leak detectors can detect very tiny leakage in pipelines and have low risk of blockage. In this paper the passing ability of the detector in the vertical segment of a pipe was studied using CFD simulations and experiments. The Reynolds number for the sphere exceeds 104 at the economical velocity range for oil pipelines, and there were few researches related to the hydrodynamic force on the sphere by the pipe flow at high Reynolds number. For sphere with different sizes and density, and at different flow rates, more than 100 3-D steady numerical simulations were carried out. The simulation data was verified by comparing the experimental critical velocity with that of the simulation, the results shows that they agree well with each other. The drag on the sphere is related to the flow velocity V and the diameter ratio λ. The effect of flow velocity was more significant at λ > 0.65. An empirical formula for the drag with λ and V is established for 0.2 ≤ λ ≤ 0.9, 4000 ≤ Res ≤ 54000. The passing ability of the sample detector in 8-28 inch pipelines is predicted; it shows that the detector could go through the vertical pipe under normal economical flow velocity (0.7m/s-1.5m/s) in 8 or 10-inch pipelines. A passing ability test of the sample detector was carried out in an 8-inch pipe loop The optimal range for λ (0.7~0.8) is given based on the analysis results
Improved MPS-FE Fluid-Structure Interaction Coupled Method with MPS Polygon Wall Boundary Model
Get PDFThe MPS-FE method, which adopts the Finite Element (FE) method for structure computation and the Moving Particle Simulation (MPS) method for fluid computation involving free surfaces, was developed to solve fluid-structure interaction problems with free surfaces. The conventional MPS-FE method, in which MPS wall boundary particles and finite elements are overlapped in order to exchange information at a fluid-structure interface, is not versatile and reduces the advantages of the software modularity. In this study, we developed a nonoverlapping approach in which the interface in the fluid computation corresponds to the interface in the structure computation through an MPS polygon wall model. The accuracy of the improved MPS-FE method was verified by solving a dam break problem with an elastic obstacle and comparing the result obtained with that of the conventional MPS-FE method and particle FEM