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Suneet Singh - One of the best experts on this subject based on the ideXlab platform.

  • Non-Linear Stability Analysis of pressure drop oscillations in a heated channel
    Chemical Engineering Science, 2018
    Co-Authors: Emadur Rahman, Suneet Singh
    Abstract:

    Abstract A study of non-Linear Stability Analysis using co-dimension two (i.e., two free parameters being varied) bifurcations related to pressure drop oscillations (PDO) in a heated channel has been carried out in this paper. In the existing literature, in the context of PDO, mostly Linear Stability Analysis is done. A few works on non-Linear Stability Analysis are available; however, only co-dimension one bifurcation studies of PDO have been carried out in these works. However, in practice, since the inlet temperature of the coolant is also an independent operating parameter, both inlet temperature, and inlet mass flow rate need to be considered for Stability Analysis. It is also noted that the existing plethora of studies on PDO is limited to the prediction of supercritical Hopf bifurcation only. However, in the current study, two types of Hopf bifurcations have been identified namely subcritical and supercritical. A subcritical Hopf bifurcation exhibits unstable limit cycles, which is a signature of the existence of unstable solutions for slightly larger perturbations even in the Linearly stable region. The existence of unstable solutions indicates that Linear Stability Analysis is not sufficient to identify the overall Stability behavior. Also, a generalized Hopf point on the Stability boundary has been identified which denotes a boundary between subcritical and supercritical Hopf bifurcation. Furthermore, numerical simulations are carried out in different regions (both stable and unstable) of the parameter space to understand the non-Linear phenomena of the system. Moreover, the bifurcations are explained in terms of the interaction of the external and internal characteristic curves of the system. The large and small amplitude cycles are shown in the characteristic curves of the system.

  • Non Linear Stability Analysis of parallel channels with natural circulation
    Nuclear Engineering and Design, 2016
    Co-Authors: Ashish Mishra, Suneet Singh
    Abstract:

    Abstract Linear Stability Analysis of two-phase flow in natural circulation loop is quite extensively studied by many researchers in past few years. It can be noted that Linear Stability Analysis is limited to the small perturbations only. It is pointed out that such systems typically undergo Hopf bifurcation. If the Hopf bifurcation is subcritical, then for relatively large perturbation, the system has unstable limit cycles in the (Linearly) stable region in the parameter space. Hence, Linear Stability Analysis capturing only infinitesimally small perturbations is not sufficient. In this paper, bifurcation Analysis is carried out to capture the non-Linear inStability of the dynamical system and both subcritical and supercritical bifurcations are observed. The regions in the parameter space for which subcritical and supercritical bifurcations exist are identified. These regions are verified by numerical simulation of the time-dependent, nonLinear ODEs for the selected points in the operating parameter space using MATLAB ODE solver.

  • Non-Linear Stability Analysis of uniformly heated parallel channels for different inclinations
    Applied Thermal Engineering, 2016
    Co-Authors: Ashish Mishra, Suneet Singh
    Abstract:

    Abstract The Linear Stability for two phase flow in parallel channels has been studied quite extensively. However, the Analysis is valid only for infinitesimally small perturbations. Therefore, there is a need to carry out non-Linear Stability Analysis for small finite sized perturbations. Moreover, earlier studies do not consider inclination of these channels, which exist for various applications. The focus of the present work is to carry out Linear as well as non-Linear Stability Analysis of parallel channels for various inclinations (including vertical and horizontal). The bifurcation Analysis is carried out to capture the non-Linear dynamics of the system and to identify regions in the parameter space for which subcritical and supercritical bifurcations exist. The study is carried out for different inclination angles in order to characterize the effect of inclination on the Stability of the system. The Analysis shows that, at all inclinations, a GH point and BT point exist. The subcritical and supercritical bifurcations are confirmed by numerical simulation of the time-dependent, nonLinear ODEs for the selected points in the operating parameter space using MATLAB ODE solver. The identification of these points is important because the Stability characteristics of the system for finite (though small) perturbations are dependent on them.

Desiderio A. Vasquez - One of the best experts on this subject based on the ideXlab platform.

  • Linear Stability Analysis of convective chemical fronts
    Physical Review E, 1997
    Co-Authors: Desiderio A. Vasquez
    Abstract:

    A chemical front propagating upward in a fluid separates heavy unreacted fluid from light reacted fluid. The density difference caused by the front propagation leads to convection. Convection enhances the front speed and curves the front as it propagates upward in a tube. The convective front propagates with constant speed and is steady in a frame of reference comoving with the front. This paper presents a Linear Stability Analysis of the convective front. The fronts are modeled using a front evolution equation coupled to Darcy's law for flow in porous media and the Navier-Stokes for viscous flow. The solutions can be either axisymmetric or nonaxi- symmetric as observed in experiments in tubes. For flow in porous media, there is a region of biStability between both types, whereas in viscous flow the axisymmetric front is always unstable. Chemical waves generate thermal and compositional gra- dients that lead to convection. Recent experimental and the- oretical work have shown that convection significantly alters the behavior of the chemical wave. Miike, Muller, and Hess showed that convective rolls are associated with the chemi- cal waves in the Belousov-Zhabotinsky ~BZ! reaction @1#. Menzinger et al. observed convective turbulence as the BZ reaction takes place in a vertical tube @2#. Chemical waves propagating upward are different than propagating down- ward due to convection in the iron ~II!-nitric acid reaction @3#, the chlorite-thiosulfate reaction @4#, and the iodate- arsenous acid reaction in vertical cylinders @5#. Experiments by Masere et al. in the iodate-arsenous acid reaction showed that a front propagating upward in a vertical cylinder can be either flat, nonaxisymmetric, or axisymmetric depending on the diameter of the tube @6#. For diameters less than 1.1 mm, the front is flat; if the diameter is between 1.1 and 2.3 mm, the front is nonaxisymmetric; and for larger diameters the front is axisymmetric. Fronts propagating downward are al- ways flat with the same speed. They have the same speed of the flat front propagating upward, indicating no convection, thus the curvature of the front and speed enhancement is due to convective fluid motion. In this reaction, a single front propagating upward separates heavy unreacted fluid from light reacted fluid. This density difference leads to convec- tion. Previous theoretical work consisted of the Linear Stability Analysis of the convectionless flat fronts in the iodate- arsenous reaction @7#. This calculation showed that the flat front is unstable to nonaxisymmetric perturbations near the onset of convection, and unstable to axisymmetric perturba- tions for larger diameters @8#. However, this calculation can- not predict when the transition from a nonaxisymmetric to an axisymmetric front takes place. In order to describe this pro- cess, a Linear Stability Analysis of the convective fronts is required. Theoretical work on convective fronts in the iodate-arsenous acid reaction consisted of numerical solu- tions of the equations of motion in two dimensions. The front was modeled with reaction-diffusion equations @9# and with a front evolution equation @10#. The reaction-diffusion solu- tions are computationally more expensive, but they showed the transition from flat, to nonaxisymmetric, and later to axi- symmetric fronts as the width of the tube is increased @11#. The solutions of the front evolution equations showed only nonaxisymmetric fronts. Theoretical work for flow in porous media are relevant to experiments where the reaction takes place between two ver- tical walls, a Hele-Shaw cell @12#. The reaction-diffusion equation coupled to Darcy's law showed a region of bista- bility where the front can be either axisymmetric or nonaxi- symmetric @13#. This property was not observed for the vis- cous fluid equations described by the Navier-Stokes equations. In this work, we carry out the Linear Stability Analysis of convective fronts using the front evolution equa- tion. We considered flow in porous media using Darcy's law, and viscous flow using the Navier-Stokes equations.

Laurens E. Howle - One of the best experts on this subject based on the ideXlab platform.

S. Waiyapot - One of the best experts on this subject based on the ideXlab platform.

  • Linear Stability Analysis of dispersion-managed solitons controlled by filters
    Journal of Lightwave Technology, 2000
    Co-Authors: J. Kumasako, Masayuki Matsumoto, S. Waiyapot
    Abstract:

    We present a Linear Stability Analysis of dispersion-managed (DM) solitons controlled by inline narrow-band filters. We show that the filters can destabilize the pulse if they are unsuitedly located in the dispersion map, which is contrary to the case of standard solitons in fibers with constant dispersion. We also show that for such an inStability to take place the pulse energy and the dispersion-map strength should be significantly larger than those usually required for practical long-distance transmission. The filter-induced inStability of DM solitons will be an issue in the operation of stretched-pulse mode-locked fiber lasers.

  • Linear Stability Analysis of dispersion-managed solitons controlled by filters
    Technical Digest. Summaries of papers presented at the Conference on Lasers and Electro-Optics. Postconference Edition. CLEO '99. Conference on Lasers, 1
    Co-Authors: Masayuki Matsumoto, S. Waiyapot
    Abstract:

    Summary form only given. We quantify how bandpass filters can stabilize (or destabilize) the propagation of DM solitons by using a Linear Stability Analysis. Both ideal lossless systems and realistic systems composed of single-mode and dispersion-compensating fibers (SMF and DCF) are analyzed.

Jeffrey J. Hoyt - One of the best experts on this subject based on the ideXlab platform.

  • Linear Stability Analysis of phase separation in nanoscale systems
    Acta Materialia, 2009
    Co-Authors: Jeffrey J. Hoyt
    Abstract:

    Abstract A Linear Stability Analysis of the early stages of spinodal decomposition in nanospheres has been performed. The dominant decomposition mode is described in terms of a Stability map, which defines regions of the fastest growing composition modulation in a space of particle radius and km, where km is the most unstable mode in the bulk system. It is shown that at sufficiently small particle size the first unstable mode is the non-radially symmetric first-order spherical harmonic. The Analysis is extended to the case of nanowires and the interplay between decomposition along the wire length vs. radial and angular perturbations is discussed.