scholarly journals Tunable broadband-negative-permeability metamaterials by hybridization at THz frequencies

RSC Advances ◽  
2020 ◽  
Vol 10 (47) ◽  
pp. 28343-28350
Author(s):  
Thi Hien Nguyen ◽  
Son Tung Bui ◽  
Xuan Ca Nguyen ◽  
Dinh Lam Vu ◽  
Xuan Khuyen Bui
Keyword(s):  
Numerical Study ◽  
Second Order ◽  
Negative Permeability

We present a numerical study of thermo-tunable broadband-negative-permeability metamaterial based on second-order hybridization operating at the THz regime.

A case study in bifurcation theory

2017 ◽  
Vol 28 (08) ◽  
pp. 1750104 ◽  
Author(s):  
Youssef Khmou
Keyword(s):  
Dynamical Systems ◽  
Bifurcation Theory ◽  
Chaotic Behavior ◽  
Numerical Study ◽  
Logistic Map ◽  
Logistic Function ◽  
Second Order ◽  
Short Paper ◽  
Chaotic Region

This short paper is focused on the bifurcation theory found in map functions called evolution functions that are used in dynamical systems. The most well-known example of discrete iterative function is the logistic map that puts into evidence bifurcation and chaotic behavior of the topology of the logistic function. We propose a new iterative function based on Lorentizan function and its generalized versions, based on numerical study, it is found that the bifurcation of the Lorentzian function is of second-order where it is characterized by the absence of chaotic region.

scholarly journals AERODYNAMIC MODELING OF OSCILLATING WING IN HYPERSONIC FLOW: A NUMERICAL STUDY

2016 ◽  
Vol 42 ◽  
pp. 1660177
Author(s):  
JIAN ZHU ◽  
YING-YU HOU ◽  
CHEN JI ◽  
ZI-QIANG LIU
Keyword(s):  
Mach Number ◽  
Hypersonic Flow ◽  
Numerical Study ◽  
Unsteady Aerodynamics ◽  
Order Theory ◽  
Second Order ◽  
Double Wedge ◽  
Piston Theory ◽  
Impact Theory ◽  
Cfd Method

Various approximations to unsteady aerodynamics are examined for the unsteady aerodynamic force of a pitching thin double wedge airfoil in hypersonic flow. Results of piston theory, Van Dyke’s second-order theory, Newtonian impact theory, and CFD method are compared in the same motion and Mach number effects. The results indicate that, for this thin double wedge airfoil, Newtonian impact theory is not suitable for these Mach number, while piston theory and Van Dyke’s second-order theory are in good agreement with CFD method for Ma<7.

Numerical study of a transitional synthetic jet in quiescent external flow

2007 ◽  
Vol 581 ◽  
pp. 287-321 ◽  
Author(s):  
RUPESH B. KOTAPATI ◽  
RAJAT MITTAL ◽  
LOUIS N. CATTAFESTA III
Keyword(s):  
Numerical Study ◽  
Time Integration ◽  
Three Dimensional ◽  
Internal Flow ◽  
External Flow ◽  
Second Order ◽  
Synthetic Jet ◽  
Transition To Turbulence ◽  
Step Method ◽  
Fractional Step Method

The flow associated with a synthetic jet transitioning to turbulence in an otherwise quiescent external flow is examined using time-accurate three-dimensional numerical simulations. The incompressible Navier–Stokes solver uses a second-order accurate scheme for spatial discretization and a second-order semi-implicit fractional step method for time integration. The simulations are designed to model the experiments of C. S. Yao et al. (Proc. NASA LaRC Workshop, 2004) which have examined, in detail, the external evolution of a transitional synthetic jet in quiescent flow. Although the jet Reynolds and Stokes numbers in the simulations match with the experiment, a number of simplifications have been made in the synthetic jet actuator model adopted in the current simulations. These include a simpler representation of the cavity and slot geometry and diaphragm placement. Despite this, a reasonably good match with the experiments is obtained in the core of the jet and this indicates that for these jets, matching of these key non-dimensional parameters is sufficient to capture the critical features of the external jet flow. The computed results are analysed further to gain insight into the dynamics of the external as well as internal flow. The results indicate that near the jet exit plane, the flow field is dominated by the formation of counter-rotating spanwise vortex pairs that break down owing to the rapid growth of spanwise instabilities and transition to turbulence a short distance from the slot. Detailed analyses of the unsteady characteristics of the flow inside the jet cavity and slot provide insights that to date have not been available from experiments.

A preliminary numerical study of a swirling jet behind a circular disc

2008 ◽  
Vol 223 (5) ◽  
pp. 1127-1139
Author(s):  
H T Toh ◽  
R F Huang ◽  
M J Chern
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Saddle Points ◽  
Three Dimensional ◽  
Second Order ◽  
Circular Disc ◽  
Mean Velocity ◽  
Swirling Jet ◽  
First Case ◽  
Axis Of Symmetry

The three-dimensional flow fields behind a circular disc produced by an annular swirling jet alone and by an annular swirling jet with a central jet issuing from the disc centre are studied by solving the three-dimensional incompressible Navier—Stokes equations numerically using the solution algorithm of Hirt et al. ( Los Alamos Scientific Lab. Rept. LA-5852 (1970)). The swirl number and the Reynolds number based on the disc diameter and the volumetric mean axial velocity of the annular swirling jet are S=0.194 and Re=656, respectively. The convective and diffusive terms in the governing equations are discretized using the second-order central difference scheme. The resulting discretized equations are advanced in time using the second-order Runge—Kutta scheme. The simulation shows that the flow field behind the circular disc exhibit periodic oscillating behaviour, with the second case having a higher frequency due to the presence of the central jet. The mechanism responsible for this oscillating behaviour is identified and discussed. An analysis of the mean velocity fields in the mid-plane shows the existence of a stagnation point on the axis of symmetry in the first case and two saddle points off the axis of symmetry in the second case.

Fitted Mesh Method for a Class of Singularly Perturbed Differential-Difference Equations

2015 ◽  
Vol 8 (4) ◽  
pp. 496-514 ◽  
Author(s):  
Devendra Kumar
Keyword(s):  
Boundary Layer ◽  
Small Parameter ◽  
Uniform Convergence ◽  
Difference Equations ◽  
Numerical Study ◽  
Second Order ◽  
Singularly Perturbed ◽  
Uniform Mesh ◽  
Small Parameters ◽  
Spline Basis

AbstractThis paper deals with a more general class of singularly perturbed boundary value problem for a differential-difference equations with small shifts. In particular, the numerical study for the problems where second order derivative is multiplied by a small parameter ε and the shifts depend on the small parameter ε has been considered. The fitted-mesh technique is employed to generate a piecewise-uniform mesh, condensed in the neighborhood of the boundary layer. The cubic B-spline basis functions with fitted-mesh are considered in the procedure which yield a tridiagonal system which can be solved efficiently by using any well-known algorithm. The stability and parameter-uniform convergence analysis of the proposed method have been discussed. The method has been shown to have almost second-order parameter-uniform convergence. The effect of small parameters on the boundary layer has also been discussed. To demonstrate the performance of the proposed scheme, several numerical experiments have been carried out.

Numerical study of rotational diffusion in sheared semidilute fibre suspension

2011 ◽  
Vol 692 ◽  
pp. 153-182 ◽  
Author(s):  
Asif Salahuddin ◽  
Jingshu Wu ◽  
C. K. Aidun
Keyword(s):  
Evolution Equation ◽  
Chemical Engineering ◽  
Numerical Study ◽  
Rotational Diffusion ◽  
Hybrid Approach ◽  
Structural Evolution ◽  
Second Order ◽  
External Boundary ◽  
Aspect Ratios ◽  
Rigid Rod

AbstractFibre-level computer simulation is carried out to study the rotational diffusion and structural evolution of semidilute suspensions of non-Brownian, rigid-rod-like fibres under shear flow in a Newtonian fluid. The analyses use a hybrid approach where the lattice-Boltzmann method is coupled with the external boundary force method. The probability distribution of the orbit constant, $p({C}_{b} )$, in the semidilute regime is predicted with this method. The paper emphasizes assessment of the characteristics of a rotary diffusion model – anisotropic in nature (Koch, Phys. Fluids, vol. 7, 1995, pp. 2086–2088) – when used in suspensions with fibres of different aspect ratios (ranging from ${r}_{p} = 16$ to $72$) and with different volume concentrations (ranging from ${c}_{v} = 7. 58\ensuremath{\times} 1{0}^{\ensuremath{-} 3} $ to $6. 14\ensuremath{\times} 1{0}^{\ensuremath{-} 2} $). A measure of the scalar Folgar–Tucker constant, ${C}_{I} $, is extracted from the anisotropic diffusivity tensor, $ \mathbisf{C} $. The scalar ${C}_{I} $ is mostly $O(1{0}^{\ensuremath{-} 4} )$ in the semidilute regime and compares very well with the experimental observations of Stover (PhD thesis, School of Chemical Engineering, Cornell University, 1991) and Stover, Koch & Cohen (J. Fluid Mech., vol. 238, 1992, pp. 277–296). The ${C}_{I} $ values provide substantial numerical evidence that the range of ${C}_{I} $ (0.0038–0.0165) obtained by Folgar & Tucker (J. Rein. Plast. Compos., vol. 3, 1984, pp. 98–119) in the semidilute regime is actually overly diffusive. The paper also branches out to incorporate anisotropic diffusion (through the use of the Koch model) in the second-order evolution equation for $ \mathbisf{A} $ (a second-order orientation tensor). The solution of the evolution equation with the Koch model demonstrates unphysical behaviour at low concentrations. The most plausible explanation for this behaviour is error in the closure approximation; and the use of the Koch model in a spherical harmonics-based method (Montgomery-Smith, Jack & Smith, Compos. A: Appl. Sci. Manuf., vol. 41, 2010, pp. 827–835) to solve for the orientation moments corroborates this claim.

Numerical study of turbulent round jet in a uniform counterflow using a second order Reynolds Stress Model

2015 ◽  
Vol 9 (4) ◽  
pp. 482-495 ◽  
Author(s):  
Amani Amamou ◽  
Sabra Habli ◽  
Nejla Mahjoub Saïd ◽  
Philippe Bournot ◽  
Georges Le Palec
Keyword(s):  
Reynolds Stress ◽  
Numerical Study ◽  
Reynolds Stress Model ◽  
Second Order ◽  
Stress Model ◽  
Round Jet
Sign in / Sign up

Export Citation Format

Share Document