Numerical Simu Research Articles

Distributed and Performance Guaranteed Robust Control for Uncertain MIMO Nonlinear Systems With Controllability Relaxation

In this paper, we investigate the distributed output tracking problem for networked uncertain nonlinear strict-feedback systems with intermittent actuator faults under a directed protocol. By embedding some performance functions into the control design, a distributed control scheme is developed that exhibits several salient features: 1)relaxing the system controllability conditions by inserting some differentiable compensation terms into the controllers; 2)dealing with mismatched uncertainties and accommodating actuation ineffectiveness automatically while achieving prescribed transient and steady-state tracking performance; 3)lowering structural and computational complexity by avoiding the derivatives of virtual controllers and desired trajectory, eluding the usage of extra observers to estimate the states of the neighbors, and demanding little prior information on system nonlinearities; and 4) reducing the communication burden by requiring only the output information from the neighbors for control design. All the closed-loop signals are ensured to be semi-globally ultimately uniformly bounded. Finally, the benefits of this method are verified via numerical simu

Numerical Study on the Effect of Angle of Inclination on Magnetoconvection Inside Enclosure with Heat Generating Solid Body

Convective ow and heat transfer of uid inside a square en- closure having heat generating solid body, with various thermal boundary conditions is investigated numerically. The top wall of the enclosure is adiabatic, both the bottom and right walls are kept at constant temper- ature, while the left wall is heated using sin function. Numerical simu- lations is carried out by solving the governing equations using SIMPLE algorithm by means of the nite-volume method with power-law scheme. The important parameters focused are angle of inclination of the enclo- sure, area ratio of solid-enclosure, Hartmann number and temperature dierence ratio of solid- uid, which are ranges 0 o - 90 o , 0:0625 - 0:5625, 0 - 100 and 0 - 50, respectively. Thermal conductivity ratio of solid- uid is xed as 5 and Rayleigh number as 10 5 .

Influence of aberrations in microholographic recording

The influence of various types of aberrations (spherical, coma, and astigmatic) of recording and read- out beams on the readout signal in a microholographic recording was investigated through a numerical simu- lation. The simulation conditions were that the wavelength of the laser was 405 nm and the numerical aperture of the objective lenses was 0.85. The tolerance of the root-mean-square (RMS) wavefront aberrations was defined as the aberration when the normalized signal level decreased to 0.8. Among the three types of aberrations, the influence of the spherical aberration was the most significant. When both the recording and readout beams were aberrated and the signs of the aberrations were in the worst case, the tolerance of the RMS wavefront aberra- tions was less than half of the Marechal's criterion. Moreover, when the RMS wavefront aberrations of the record- ing and readout beams were within the above tolerance, the bit intervals of 0.13 and 0.65 μm in the inplane and vertical directions, respectively, which correspond to the recording density of 91 bit∕μm 3 (recording capacity of 16 TB for a 120-mm-diameter optical disk having a 300-μm-thick recording layer), were shown to be feasible for confocal detection with an allowable signal-to-noise ratio. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.OE.54.11.117104)

The Effects of Temperature on Vortex-pairing Noise in Axisymmetric Subsonic Jets

Thermal effects on the sound generation by vortex pairing are investigated in axisymmetric subsonic jets. Direct numerical simu- lation of compressible Navier-Stokes equations is performed for an accurate description of near-field flow dynamics and far-field sound. As the core temperature increasing, the positions of vortex roll-up and pairing move upstream, and the noise intensity is enhanced. In addition, sound predicted by Lilley-Goldstein acoustic analogy is consistent with the result of simulation in all cases. A further analysis of sound sources of the Lilley-Goldstein equation shows that the thermodynamic component has remarkable influence in non-isothermal jets, especially in the cold one. Moreover, sound generation in the isothermal jet is specifically studied by a simple nonlinear interaction model based on instability waves which are obtained by solving linear parabolized stability equa- tions. The major radiation pattern given by the model is found to be in good agreement with the directly computed data, suggesting the great importance of nonlinear interaction in subsonic jet noise.

Clearance gap flow: simulations by discontinuous Galerkin method and experiments

Compressible viscous fluid flow in a narrow gap formed by two parallel plates in distance of 2 mm is investigated numerically and experimentally. Pneumatic and optical methods were used to obtain distribution of static to stagnation pressure ratio along the channel axis and interferograms including the free outflow behind the channel. Modern developing discontinuous Galerkin finite element method is implemented for numerical simu- lation of the fluid flow. The goal to make progress in knowledge of compressible viscous fluid flow characteristic phenomena in minichannels is satisfied by finding a suitable approach to this problem. Laminar, turbulent and transitional flow regime is examined and a good agreement of experimental and numerical results is achieved using γ − Reθt transition model.

Numerical modelling of tonal components of pressure pulsation spectra in the LRE booster turbopump screw stage

Booster pump unit providing the required NPSH for the main LRE turbopump feed system operates in high vibration activity. Numerical simu- lation of unsteady flow in the booster pump unit allows one to analyze the amplitude-frequency characteristics of pressure pulsations generating the pump casing vibration. The obtained results were analyzed, the signals of pressure pulsations at the inlet and the outlet of the pump screw rotor ob- tained. The sources of pressure pulsations are defined. The conducted com- putational experiment revealed the direction of work to reduce the influence of hydrodynamic sources of vibration on the total vibration level of booster pump unit.

Design of Plasmonic Perfect Absorbers for Quantum-well Infrared Photodetection

Based on analytic formulas and numerical simu- lations, we propose a plasmonic cavity with a top Au grating and bottom Au film to enhance quantum-well infrared pho- todetectors (QWIPs) operating at wavelengths between 2 and 30 μm. By using plasmonic cavity modes, QWIPs can detect light even at normal incidence. With using optimal structural parameters, light can be almost perfectly absorbed by the cavity and over 54 % of the light is absorbed by the QW active region. Compared with the reference structure (without Au layers and with an isotropic active region), the absorption enhancement is over 30 times in the QW active region at normal incidence and remains high value (> 4.5) for p -polarized light in a broad range of incident angle (|θ| < 60 0 ).

Energy localization and transport in two-dimensional electrical lattices

Intrinsic localized modes (ILMs) have been generated and characterized in two-dimensional nonlinear electrical lattices which were driven by a spatially-uniform voltage signal. These ILMs were found to be either stationary or mobile, depending on the details of the lattice unit-cell, as had already been reported in one-dimensional lattices; however, the mo- tion of these ILMs is qualitatively dierent in that it lacks a consistent direction. Furthermore, the hop- ping speed seems to be somewhat reduced in two di- mensions due to an enhanced Peierls-Nabarro (PN)- barrier. We investigate both square and honeycomb lattices composed of 6 6 elements. These direct ob- servations were further supported by numerical simu- lations based on realistic models of circuit components. The numerical study moreover allowed for an analysis of ILM dynamics and pattern formation for larger lat- tice sizes.

Modelling Effect of Toxic Metal on the Individual Plant Growth: A Two Compartment Model

A two co mpart ment mathematical model for the ind ividual plant growth under the stress of toxic metal is studied. In the model it is assumed that the uptake of to xic metal adsorbed on the surface of soil by the plant is through root compart ment thereby decreasing the root dry weight and shoot dry weight due to decrease in nutrient concentration in each compart ment. In order to visualize the effect of to xic metal on p lant growth, we have studied two models that is, mod el for plant growth with no toxic effect and model fo r plant growth with toxic effect. Fro m the analysis of the models the criteria for plant growth with and without toxic effects are derived. The numerical simu lation is done using Matlab to support the analytical results.

Effectsof Order of Chemical Reaction on a Boundary Layer Flow with Heat and Mass Transfer Over a Linearly Stretching Sheet

The heat and mass transfer characteristics over a linearly stretching sheet subjected to an order of chemical reaction are studied numerically.A similarity transformat ion is utilized to convert the governing nonlinear partial differential equations into ordinary differential equations. The numerical method of solution is based on the shooting method with six order Runge-Kutta iteration scheme. The numerical simu lations are conducted at Schmidt nu mber Sc varying fro m0.22to 0.78 and chemical reaction varying fro m 0.5 to 3. The effects of the governing parameters on the local skin friction and rateof mass transfer on the wall are accurately calculated.

Evaluating k–∈ with One–equation Turbulence Model

Abstract An extended version of the isotropic one–equation model is proposed to account for the dis- tinct effects of low-Reynolds number (LRN) and wall proximity. The turbulent kinetic energy k and the dissipation rate ∈ are evaluated using the R (= k 2 /∈) transport equation together with some empirical relations. The eddy viscosity formulation maintains the positivity of normal Reynolds stresses and the Schwarz’ inequality for turbulent shear stresses. The model coef- ficients/functions preserve the anisotropic characteristics of turbulence in the sense that they are sensitized to rotational and nonequilibrium flows. The model is validated against a well- documented flow case, yielding predictions in good agreement with the direct numerical simu- lation (DNS) data. Comparisons indicate that the present model offers some improvement over the Spalart–Allmaras one–equation model.

Numerical Simulation of the Kinematic Behavior of a Twist Beam Suspension Using Finite Element Method

The use of numerical simu lations in the design of automotive components has contributed to reducing the design time, decreasing the prototypes costs and increasing reliability of the final product. In addition, the search for solutions of lo w cost and satisfactory performance is essential for the success of the product in the world market. Twist-beam suspensions are an examp le of this co mpetit ive environ ment. This solution presents a very satisfactory performance when applied to light vehicles and has an excellent relationship between cost / benefit in the automotive market. It is estimated that more than 90% of light vehicles manufactured in emergent countries use this type of suspension at the rear. Despite its acceptance in the automotive market there are few studies related to the twist -beam suspension, perhaps because of its simplicity and low cost design and ease of manufa cturing. Un like other types of suspension, the twist-beam has a flexib le torsion beam connecting the swing arms. The evaluation of the deformation of this flexib le element becomes essential to understand their kinemat ic behavior. Thus, the use of software based only on the rigid body dynamics is not suitable to analy ze this type of suspension. The main objective of this work was to evaluate through numerical simu lation based on finite element method, the influence of the torsion beam on the kinematic behavior of a twist-beam suspension. It was evaluated the influence of both the position and orientation of the torsion beam on the suspension, under symmetric and asymmetric loadings.

Modelling the Effects of Competing Toxin Producing Phytoplankton on a Zooplankton Population: Role of Holling Type-II Functional Response with Time-Lag

In this paper, a system consisting of two competing harmfu l phytoplankton and a zooplankton with Holling type-II functional response and discrete time lag is considered. A stable co-existence of all the species has been observed for the system without delay and the Hopf-b ifurcation phenomenon is observed for the interior equilibriu m po int. The Hopf-bifurcating solution is obtained for the critical values of parameters like predation rates and half saturation constants. Further, using the normal form theory, we have determined the direction and the stability of the Hopf-bifurcation solution. The introduction of time delay in the system also shows the Hopf-bifurcat ion as the delay parameter passes through a critical value. Finally, the numerical simu lation is carried out to support the theoretical results.

Influence of external perturbations on dynamical characteristics of dust clusters (simulation)

The results of a numerical study of the dynamics of interacting particles in cluster systems under the action of an external perturbing field on them are presented. The relaxation rates and characteristic relax� ation times of a cluster to its equilibrium state are analyzed. The conditions for the formation of dynamical structures of charged particles in the field of external nonpotential forces are investigated. The peculiarities of diagnosing the pair potential of particles in nonequilibrium systems are considered. The numerical simu� lation conditions for the problem were close to the conditions of experiments in a dusty plasma.

Probing gas motions in the intra-cluster medium: a mixture model approach

Upcoming high spectral resolution telescopes, particularly Astro-H, are expected to finally deliver firm quantitative constraints on turbulence in the intra-cluster medium (ICM). We develop a new spectral analysis technique which exploits not just the line width but the entire line shape, and show how the excellent spectral resolution of Astro-H can overcome its relatively poor spatial resolution in making detailed infer- ences about the velocity field. The spectrum is decomposed into distinct components, which can be quantitatively analyzed using Gaussian mixture models. For instance, bulk flows and sloshing produce components with offset means, while partial volume- filling turbulence from AGN or galaxy stirring leads to components with different widths. The offset between components allows us to measure gas bulk motions and separate them from small-scale turbulence, while component fractions and widths con- strain the emission weighted volume and turbulent energy density in each component. We apply mixture modeling to a series of analytic toy models as well as numerical simu- lations of clusters with cold fronts and AGN feedback respectively. From Markov Chain Monte Carlo and Fisher matrix estimates which include line blending and continuum contamination, we show that the mixture parameters can be accurately constrained with Astro-H spectra: at a \sim 10% level when components differ significantly in width, and a \sim 1% level when they differ significantly in mean value. We also study error scalings and use information criteria to determine when a mixture model is preferred. Mixture modeling of spectra is a powerful technique which is potentially applicable to other astrophysical scenarios.

Prediction of Nitrogen Injection Performance in Conventional Reservoirs Using the Correlation Developed by the Incorporation of Experimental Design Techniques and Reservoir Simulation

Enhanced oil recovery using nitrogen injection is a commonly applied method for pressure maintenance in conventional reservoirs. Numerical s imulations can be practiced for the prediction of a reservoir performance in the course of injection process; however, a detailed simulation might take up enormous computer processing time. In such cases, a simple statistical model may be a good approach to the preliminary prediction of the proce ss without any application of numerical simulation. In the current work, seven rock/fluid r eservoir properties are considered as screening parameters and those parameters having the most considerable effect on the process are determined using the combination of experimental design techni ques and reservoir simulations. Therefore, the statistical significance of the main effects and in teractions of screening parameters are analyzed utilizing statistical inference approaches. Finally , the influential parameters are employed to create a simple statistical model which allows the prelimina ry prediction of nitrogen injection in terms of a recovery factor without resorting to numerical simu lations.

Hyperchaotification and Synchronization of Chaotic Systems

This paper addresses the hyperchaotification and the synchronization of chaotic systems. A nonlinear state feedback controller was designed to generate hyperchaos from the original chaotic system. The hyperchaos was identified by the existence of two positive Lyapunov exponents, bifurcation diagram and phase diagrams. Furthermo re, effective active controllers are designed for synchronizing the obtained hyperchaotic system with different chaotic systems. To illustrate the effectiveness of the proposed approach, numerical simu lation results obtained with the Lu and Qi chaotic systems are given.

Planification de trajectoire d'un système non linéaire de type FitzHugh Nagumo

This paper concerns the nonlinear ID FitzHugh Nagumo system with a Robin bound-ary control. We prove that this system is flat-like with the outflow electrical potential playing the role of the flat output. Indeed, the solution can be expressed in terms of an infini- te series depending on the derivatives and the integrals of the flat output. This series is shown to be convergent provided that the flat output is Gevrey of order 1 < a ≤ 2. Numerical simu- lalions are also presented.

Stability and Hopf Bifurcation Analysis for Functional Differential Equation with Distributed Delay

In some applications of delay differential equations in population dynamics, the need for incorporation of distributed delay is often the result of the existence of some processes or structures. The main objective of this paper is to provide some information on the stability and Hopf bifurcation analysis in a general functional differential equation with distributed delay. The local stability parameter regions related to time delay are given and compared for a general distribution delay function and three frequently used distributed delays including Dirac, uniform, and Gamma distributions. With the loss of stability at the boundary of these regions, we discuss the Hopf bifurcation using a normal-form method; there the computation of the coefficients is given explicitly in the form of the corresponding characteristic equation. Using the theoretical results, we study two examples of white blood cell models and address the effect of the distributed time delay on the physiological oscillations. Numerical simu...

Global Periodic Solutions in a Delayed Predator-Prey System with Holling II Functional Response

We consider a delayed predator-prey system with Holling II functional re- sponse. Firstly, the paper considers the stability and local Hopf bifurcation for a delayed prey-predator model using the basic theorem on zeros of general transcendental function, which was established by Cook etc.. Secondly, special attention is paid to the global ex- istence of periodic solutions bifurcating from Hopf bifurcations. By using a global Hopf bifurcation result due to Wu , we show that the local Hopf bifurcation implies the global Hopf bifurcation after the second critical value of delay. Finally, several numerical simu- lations supporting the theoretical analysis are given.