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Turbulent Inlet Conditions Modeling using Large-eddy Simulations
Get PDFTurbulence is a phenomenon which presents peculiarities when it is experimented or simulated. This occurs due to its complexity and high sensibility to the inlet conditions of the turbulent flow fields, as well as the presence of a large range of time and length scales. A simplification for this situation is obtained with the use of approximations and turbulence models. In the present work, the Largeeddy Simulations methodology was applied, aiming the modeling of the previously mentioned complexity, which consists in using a filter to resolve the large scales while the remaining scales were determined by classical and dynamic Smagorinsky models. Three different approximations for the inlet conditions were applied: white noise, Random Flow Generation (RFG) and Synthetic Eddy Method (SEM). It was possible to realize that the use of the dynamic Smagorinky model and the RFG or SEM methodologies resulted in a better characterization of the studied flow
A Jacobi Spectral Collocation Scheme Based on Operational Matrix for Time-fractional Modified Korteweg-de Vries Equations
Get PDFIn this paper, a high accurate numerical approach is investigated for solving the time-fractional linear and nonlinear Korteweg-de Vries (KdV) equations. These equations are the most appropriate and desirable definition for physical modeling. The spectral collocation method and the operational matrix of fractional derivatives are used together with the help of the Gauss-quadrature formula in order to reduce such problem into a problem consists of solving a system of algebraic equations which greatly simplifying the problem. Our approach is based on the shifted Jacobi polynomials and the fractional derivative is described in the sense of Caputo. In addition, the presented approach is applied also to solve the timefractional modified KdV equation. For testing the accuracy, validity and applicability of the developed numerical approach, we apply it to provide high accurate approximate solutions for four test problems
A 3-D Visco-Hyperelastic Constitutive Model for Rubber with Damage for Finite Element Simulation
Get PDFA constitutive model to describe the behavior of rubber from low to high strain rates is presented. For loading, the primary hyperelastic behavior is characterized by the six parameter Ogden’s strain-energy potential of the third order. The rate-dependence is captured by the nonlinear second order BKZ model using another five parameters, having two relaxation times. For unloading, a single parameter model has been presented to define Hysteresis or continuous damage, while Ogden’s two term model has been used to capture Mullin’s effect or discontinuous damage. Lastly, the Feng-Hallquist failure surface dictates the ultimate failure for element deletion. The proposed model can accurately predict the response of rubber using a limited set of experimental data. The model has been validated here for the case of rubber but can be extended to a wide range of polymers
Three Dimensional Natural Frequency Analysis of Sandwich Plates with Functionally Graded Core Using Hybrid Meshless Local Petrov-Galerkin Method and Artificial Neural Network
Get PDFPresent study is concerned with three dimensional natural frequency analysis of functionally graded sandwich rectangular plates using Meshless Local Petrov-Galerkin (MLPG) method and Artificial Neural Networks (ANNs).The plate consists of two homogeneous face sheets and a power-law FGM core. Natural frequencies of the plate are obtained by 3D MLPG method and are verified with available references. Convergence study of the first four natural frequencies for different node numbers is the next step. Also, effects of two parameters of “FG core to plate thickness ratio” and “volume fraction index” on natural frequencies of plate are investigated. Then, four distinct ANNs are used to predict the first four natural frequencies of the plate. Back-Error Propagation (BEP) method is used to train the ANNs. The predicted data shows a good agreement with respect to the actual data. Finally, the trained ANNs are used for prediction of natural frequencies of some conditions where MLPG data are not available
High-Order Fully Coupled Scheme Based on Compact Integrated RBF Approximation for Viscous Flows in Regular and Irregular Domains
Get PDFIn this study, we present a numerical discretisation scheme, based on a direct fully coupled approach and compact integrated radial basis function (CIRBF) approximations, to simulate viscous flows in regular/irregular domains. The governing equations are taken in the primitive form where the velocity and pressure fields are solved in a direct fully coupled approach. Compact local approximations, based on integrated radial basis functions, over 3-node stencils are introduced into the direct fully coupled approach to represent the field variables. The present scheme is verified through the solutions of several problems including Poisson equations, Taylor-Green vortices and lid driven cavity flows, defined on domains of different shapes. The numerical results obtained by the present scheme are highly accurate and in good agreement with those reported in earlier studies of the same problems
Fast Generation of Smooth Implicit Surface Based on Piecewise Polynomial
Get PDFTo speed up generating a scalar field g(x) based on a piecewise polynomial, a new method for determining field values that are indispensable to generate g(x) has been proposed. In the proposed method, an intermediate for generating g(x) does not required, i.e., the field values can directly be determined from given point data. Numerical experiments show that the computation time for determining the field values by the proposed method is about 10.4–12.7 times less than that of the conventional method. In addition, on the given points, the accuracy of g(x) obtained by using the proposed method is almost the same as that of the conventional method. Furthermore, the computation time of the proposed method is almost not affected by the number of given points for the case where the number of all cells is large
Structural-Acoustic Design Sensitivity Analysis based on Direct Differentiation Method with Different Element Types
Get PDFEngineers have started to develop ways to decrease noise radiation. Structural-acoustic design sensitivity analysis can provide information on how changes in design variable affect the radiated acoustic performance. As such, it is an important step in the structural-acoustic design and in optimization processes. For thin structures immersed in water, a full interaction between the structural domain and the fluid domain needs to be taken into account. In this work, the finite element method is used to model the structure parts and the boundary element method is applied to the exterior acoustic problem. The formula of the sound pressure sensitivity based on the direct differentiation method is presented. The design variable can be chosen as the material parameters, structure and fluid parameters, such as the fluid density, structural density, Poisson’s ratio, Young’s modulus, structural shape size and so on. Numerical examples are presented to demonstrate the validity of the proposed algorithm. Different types elements are used for the numerical solution, and the performance of different types of FE/BE element is presented and compared
An Advanced ACA/BEM for Solving 2D Large-Scale Elastic Problems with Multi-Connected Domains
Get PDFAn advanced Boundary Element method (BEM) accelerated via Adaptive Cross Approximation (ACA) and Hierarchical Matrices (HM) techniques is presented for the solution of large-scale elastostatic problems with multi-connected domains like in fiber reinforced composite materials. Although the proposed ACA/ BEM is demonstrated for two-dimensional (2D) problems, it is quite general and it can be used for 3D problems. Different forms of ACA technique are employed for exploring their efficiency when they combined with a BEM code. More precisely, the fully and partially pivoted ACA with and without recompression are utilized, while the solution of the final linear system of equations is accelerated via an iterative GMRES solver. The proposed methodology is demonstrated with the solution of large scale, plane strain elastic problems dealing with the bending of unidirectional fiber composite plates with large numbers of periodically or randomly distributed cylindrical elastic fibers embedded in a matrix medium
Extreme Learning Machines Based on Least Absolute Deviation and Their Applications in Analysis Hard Rate of Licorice Seeds
Get PDFExtreme learning machine (ELM) has demonstrated great potential in machine learning and data mining fields owing to its simplicity, rapidity and good generalization performance. In this work, a general framework for ELM regression is first investigated based on least absolute deviation (LAD) estimation (called LADELM), and then we develop two regularized LADELM formulations with the l2-norm and l1-norm regularization, respectively. Moreover, the proposed models are posed as simple linear programming or quadratic programming problems. Furthermore, the proposed models are used directly to analyze the hard rate of licorice seeds using near-infrared spectroscopy data. Experimental results on eight different spectral regions show the feasibility and effectiveness of the proposed models
Large Deformation Hyper-Elastic Modeling for Nonlinear Dynamic Analysis of Two Dimensional Functionally Graded Domains Using the Meshless Local Petrov-Galerkin (MLPG) Method
Get PDFA meshless method based on the local Petrov-Galerkin approach is developed for elasto-dynamic analysis of geometrically nonlinear two dimensional (2D) problems in hyper-elastic functionally graded materials. The radial point interpolation method (RPIM) is utilized to build the shape functions and the Heaviside step function is used as the test function. The mechanical properties of functionally graded material are considered to continuously vary in a certain direction and are simulated using a nonlinear power function in volume fraction form. Considering the large deformations, it is assumed that the domain be made of large deformable neo-Hookean hyperelastic materials. Rayleigh damping is employed to model energy dissipation in analyses. The Newmark finite difference method is used to treat the time dependence of the variables. At any time step of Newmark method, the Newton-Raphson iteration technique is employed to solve the nonlinear governing equations. Accuracy of the proposed method is verified using the results available in the literature. It is shown that the present MLPG method is a suitable meshless method for large deformation problems. The nonlinear time histories and wave propagations of displacement field for various FG distributions and damping ratios are studied in detail