Search results for "Numerical stability"
showing 10 items of 29 documents
Using of reflections for expansion of frequency tuning in a THz-band gyrotron
2017
Effect of delayed reflection on operation of a second-harmonic THz-band gyrotron is studied. Theoretical analysis, numerical calculations and experimental observations for the 0.394 THz FU CW IIB gyrotron are presented.
Flow Control of Fluid in Pipelines Using PID Controller
2019
In this paper, a PID controller is utilized in order to control the flow rate of the heavy oil in pipelines by controlling the vibration in a motor pump. A torsional actuator is placed on the motor pump in order to control the vibration on a motor and consequently controlling the flow rates in pipelines. The necessary conditions for the asymptotic stability of the proposed controller are validated by implementing the Lyapunov stability theorem. The theoretical concepts are validated utilizing numerical simulations and analysis, which proves the effectiveness of the PID controller in the control of flow rates in pipelines.
A strain-difference-based nonlocal elasticity model
2004
Abstract A two-component local/nonlocal constitutive model for (macroscopically) inhomogeneous linear elastic materials (but constant internal length) is proposed, in which the stress is the sum of the local stress and a nonlocal-type stress expressed in terms of the strain difference field, hence identically vanishing in the case of uniform strain. Attention is focused upon the particular case of piecewise homogeneous material. The proposed model is thermodynamically consistent with a suitable free energy potential. It constitutes an improved form of the Vermeer and Brinkgreve [A new effective nonlocal strain measure for softening plasticity. In: Chambon, R., Desrues, J., Vardulakis, I. (E…
A nonhomogeneous nonlocal elasticity model
2006
Nonlocal elasticity with nonhomogeneous elastic moduli and internal length is addressed within a thermodynamic framework suitable to cope with continuum nonlocality. The Clausius–Duhem inequality, enriched by the energy residual, is used to derive the state equations and all other thermodynamic restrictions upon the constitutive equations. A phenomenological nonhomogeneous nonlocal (strain difference-dependent) elasticity model is proposed, in which the stress is the sum of two contributions, local and nonlocal, respectively governed by the standard elastic moduli tensor and the (symmetric positive-definite) nonlocal stiffness tensor. The inhomogeneities of the elastic moduli and of the int…
Robust Finite-Time Control of Switched Linear Systems and Application to a Class of Servomechanism Systems
2015
This paper investigates finite-time (FT) stability and stabilization problems for a class of switched linear systems with polytopic uncertainties. Both stable and unstable subsystems are considered to coexist in the system, and a new concept of extended FT stability is proposed as the first attempt. A stability criterion is first established, where the admissible maximum switching number is obtained while ensuring extended FT stability of switched linear systems with time-varying delays under a given maximum ratio between the running time of unstable subsystems and the running time of stable subsystems. Sufficient conditions on the existence of desired memory state-feedback controllers are …
A Boundary Element Formulation for Modelling Structural Health Monitoring Applications
2015
In this paper, a boundary element formulation for modelling pitch-catch damage detection applications is introduced. The current formulation has been validated by both finite element analyses and physical experiments. Comparing to the widely used finite element method, the current formulation does not only use less computational resources, but also demonstrates higher numerical stability. doi: 10.12783/SHM2015/221
A new solver for incompressible non-isothermal flows in natural and mixed convection over unstructured grids
2022
Abstract In the present paper we propose a new numerical methodology for the solution of 2D non-isothermal incompressible flows for natural and mixed convection in irregular geometries. The governing equations are the Incompressible Navier-Stokes Equations and the Energy Conservation Equation. Fluid velocity and temperature are coupled in the buoyancy term of the momentum equations according to the Oberbeck–Boussinesq approximation. The governing equations are discretized over unstructured triangular meshes satisfying the Delaunay property. Thanks to the Oberbeck–Boussinesq hypothesis, the flow and energy problems are solved in an uncoupled way, and two fractional time step procedures are s…
A shoreline boundary condition for a highly nonlinear Boussinesq model for breaking waves
2012
Abstract A physically based strategy was used to model swash zone hydrodynamics forced by breaking waves within a Boussinesq type of model. The position and the velocity of the shoreline were determined continuously in space by solving the physically-based equations of the shoreline motion; moreover, a fixed grid method, with a wet–dry interface, was adopted for integrating the Boussinesq model. The numerical stability of the model was improved by means of an extrapolation method. To validate the proposed methodology, the classical analytical solution for the shoreline motion of a monochromatic wave train over a plane beach was considered. The comparison between the analytical and numerical…
A fully adaptive wavelet algorithm for parabolic partial differential equations
2001
We present a fully adaptive numerical scheme for the resolution of parabolic equations. It is based on wavelet approximations of functions and operators. Following the numerical analysis in the case of linear equations, we derive a numerical algorithm essentially based on convolution operators that can be efficiently implemented as soon as a natural condition on the space of approximation is satisfied. The algorithm is extended to semi-linear equations with time dependent (adapted) spaces of approximation. Numerical experiments deal with the heat equation as well as the Burgers equation.
Three-dimensional linear stability analysis of the flow in a liquid spherical droplet driven by an alternating magnetic field
2003
The paper presents a numerical stability analysis of the flow driven by an alternating (AC) magnetic field in an electromagnetically levitated liquid metal droplet. The basic axisymmetric flow is found to become unstable at Reynolds numbers in the order of 100. The critical Reynolds number Rec and the corresponding most unstable azimuthal wave number m are found for several configurations of the magnetic field depending on the skin-depth d. For a uniform external AC magnetic field the azimuthal wave number of the most unstable mode is m=3. An additional steady (DC) magnetic field imposed along the axis of symmetry increases the stability of the flow.