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Numerical Study of Combined Natural Convection-surface Radiation in a Square Cavity
Get PDFCombined laminar natural convection and surface radiation in a differentially heated square cavity has been investigated by a finite volume method through the concepts of staggered grid and SIMPLER approach. A power scheme has been also used in approximating advection–diffusion terms, determining the view factors by means of analytical expressions. The effect of emissivity on temperature and velocity profiles within the enclosure has been analyzed. In addition, results for local and average convective and radiative Nusselt numbers are presented and discussed for various conditions
Nonlinear Symmetric Free Vibration Analysis of Super Elliptical Isotropic Thin Plates
Get PDFNonlinear symmetric free vibration analyses are first presented for super elliptical isotropic thin plates with simply supported edge and clamped edge based on classical plate theory. Approximate solutions of super elliptical thin plates are obtained by Ritz method, and the validity can be confirmed by comparison with related researchers’ results. Numerical results confirm that the characteristics of nonlinear vibration behaviors are significantly influenced by different boundary conditions, vibration amplitudes, the power of the super ellipse, as well as ratio of major to minor axis
Analysis on Flexural Behavior of UHPFRC Beams based on Tensile Stress-Crack Opening Relationship
Get PDFThe objective of this study is to investigate the differences between the tensile stress-crack opening relationships of the small size notched beam and the real size beam which were made of two ultra-high performance fiber reinforced concretes (UHPFRCs) having different volume fractions and lengths of fibers. The stress-crack opening relationships of two UHPFRCs were first obtained from the inverse analysis for the small size notched beam tests. In addition, the three types of real size beams were manufactured for each mix: (1) plain beam, (2) beam with tensile reinforcement, and (3) beam with both tensile and compressive reinforcements. The flexural tests of the plain and reinforced beams were conducted up to a failure state. The load-deflection curves of the plain and reinforced UHPFRC beams calculated based on the tensile stress-crack opening relationship of the notched beams did not give an accurate prediction on the measured load-deflection curves of the real size beams. The tensile stress-crack relationships accurately fitting the measured load-deflection curves were additionally found, and the difference in the tensile stress-crack opening relationships of the small size notched beams and the real size beams was analyzed in this study
Graded Dielectric Inhomogeneous Planar Layer Radome for Aerospace Applications
Get PDFControllable artificial dielectrics are used in the design of radomes to enhance their electromagnetic (EM) performance. The fabrication of such radome wall structures with controllable dielectric parameters seems to be an arduous task. Further even minor fluctuations of dielectric properties of radome wall due to fabrication uncertainties tend to result in drastic degradation of radome performance parameters. In the present work, a novel inhomogeneous radome with graded variation of dielectric parameters is proposed which limits the constraints on fabrication and facilitates excellent EM performance characteristics. This radome wall consists of five dielectric layers cascaded such that the middle layer has maximum dielectric constant and electric loss tangent. The dielectric parameters of the layers on both sides of the middle layer decrease in a graded (or step-wise) manner. The EM performance characteristics of the IPL radome with graded dielectric parameters are superior to that of conventional monolithic half-wave radome
From Geometric Transformations to Auxetic Metamaterials
Get PDFThe paper introduces a new alternative towards fabrication of auxetic metamaterials (materials with negative Poisson’s ratio) controlled by geometric transformations. These transformations are derived from the theory of small (infinitesimal) elastic deformation superimposed on finite elastic deformations. By using this theory, a cylindrical region filled with initial deformed foam is transformed through deformation into a cylindrical shell region filled with auxetic metamaterial. As an example, the realization of the seismic cloak device becomes a practical possibility
Comparing the Effect of Uniaxial Cyclic Mechanical Stimulation and Chemical Factors on Myogenin and Myh2 Expression in Mouse Embryonic and Bone Marrow Derived Mesenchymal Stem Cells
Get PDFBackground: Environmental factors affect stem cell differentiation. In addition to chemical factors, mechanical signals have been suggested to enhance myogenic differentiation of stem cells. Therefore, this study was undertaken to illustrate and compare the effect of chemical and mechanical stimuli on Myogenin (MyoG) and Myosin heavy chani 2 (Myh2) expression of mouse bone marrowderived mesenchymal stem cells (BMSCs) and embryonic stem cells (ESCs). Methods: After isolation and expansion of BMSCs and generation of embryoid bodies and spontaneous differentiation of ESCs, cells were examined in 4 groups: (1) control group: untreated cells; (2) chemical group: cells incubated in myogenic medium (5-azacythidine and horse serum for BMSCs, dimethyl sulfoxide (DMSO) and horse serum for ESCs) for 5 days; (3) mechanical group: cells exposed to uniaxial cyclic strain (8%, 1 Hz, 24 h) and (4) chemical + mechanical group: cells incubated in myogenic medium for 4 days and then exposed to uniaxial cyclic strain. Real-time PCR was used to examine the expression of MyoG and Myh2 as specific myogenic markers. Results: suggested that mechanical loading, as a single factor, could elevate MyoG and Myh2 expression. Combining chemical with mechanical factor increases expression and there was no significant difference in MyoG expression of ESCs- and MSCs-chemical + mechanical groups; however, Myh2 expression was significantly higher in ESCs-mechanical group than that in the same group of MSCs
Wave Propagation in Piezoelectric Rods with Rectangular Cross Sections
Get PDFOrthogonal polynomial approach has been used to deal with the wave propagation in structures that have finite dimension in only one direction, such as horizontally infinite flat plates, axially infinite hollow cylinders. In order to solve wave propagation in two-dimensional piezoelectric rod with rectangular cross section, i.e. the piezoelectric plate with finite dimensions in two directions, an extended orthogonal polynomial approach is proposed in this paper. For validation and illustration purposes, the proposed approach is applied to solving the wave propagation in a square steel rod. The results obtained are in good agreement with the results from the semi-analytical finite element method. The dispersion curves and displacement and electric potential distributions of various rectangular piezoelectric rods are calculated, and the effects of the different width to height ratio, material parameters and different polarizing directions on the dispersion curves and displacement and electric potential distributions are discussed
Boundary Element Analysis of Shear Deformable Shallow Shells Under Harmonic Excitation
Get PDFIn this work, the harmonic analysis of shallow shells using the Boundary Element Method, is presented. The proposed boundary element formulation is based on a direct time-domain integration using the elastostatic fundamental solutions for both in-plane elasticity and shear deformable plates. Shallow shell was modeled coupling boundary element formulation of shear deformable plate and two-dimensional plane stress elasticity. Effects of shear deformation and rotatory inertia were included in the formulation. Domain integrals related to inertial terms were treated using the Dual Reciprocity Boundary Element Method. Numerical examples are presented to demonstrate the efficiency and accuracy of the proposed formulation
A Simple, Fast, and Accurate Time-Integrator for Strongly Nonlinear Dynamical Systems
Get PDFIn this study, we consider Initial Value Problems (IVPs) for strongly nonlinear dynamical systems, and study numerical methods to analyze short as well as long-term responses. 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 of positions as well as velocities. For each discrete-time interval 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. Three numerical examples are provided to compare the present algorithm with explicit as well implicit methods in terms of accuracy, required size of time-interval (or step) and computational cost. The present algorithm is compared against, the second order central difference method, the classical Runge-Kutta method, the adaptive Runge-Kutta- Fehlberg method, the Newmark-β and the Hilber-Hughes-Taylor methods. First the highly nonlinear Duffing oscillator is analyzed and the solutions obtained from all algorithms are compared against the analytical solution for free oscillation at long times. A Duffing oscillator with impact forcing function is next solved. Solutions are compared against numerical solutions from state of the art ODE45 numerical integrator for long times. Finally, a nonlinear 3-DOF system is presented and results from all algorithms are compared against ODE45. It is shown that the present RBF-Coll algorithm is very simple, efficient and very accurate in obtaining the solution for the nonlinear IVP. Since other presented methods require a much smaller step size and higher computational cost, the proposed algorithm is advantageous and has promising applications in solving nonlinear dynamical systems. The extension of the present algorithm to orbit propagation problems with perturbations, will be pursued in our future studies. Issues of numerical stability for various time-integrators will also be explored in future studies
Coupled ABC and Spline Collocation Approach for a Class of Nonlinear Boundary Value Problems over Semi-Infinite Domains
Get PDFIn this article, we introduce a numerical scheme to solve a class of nonlinear two-point BVPs on a semi-infinite domain that arise in engineering applications and the physical sciences. The strategy is based on replacing the boundary condition at infinity by an asymptotic boundary condition (ABC) specified over a finite interval that approaches the given value at infinity. Then, the problem complimented with the resulting ABC is solved using a fourth order spline collocation approach constructed over uniform meshes on the truncated domain. A number of test examples are considered to confirm the accuracy, efficient treatment of the boundary condition at infinity, and applicability of the approach. The computational results show that the scheme is reliable and converges fast with a fourth order rate of convergenc