The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Joy Merwin Monteiro - One of the best experts on this subject based on the ideXlab platform.
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tropical vorticity forcing and superrotation in the spherical shallow water equations
Quarterly Journal of the Royal Meteorological Society, 2017Co-Authors: D L Suhas, Jai Sukhatme, Joy Merwin MonteiroAbstract:The response of the nonlinear shallow-water equations (SWE) on a sphere to tropical vorticity forcing is examined, with an emphasis on momentum fluxes and the emergence of a superrotating state. Fixing the radiative damping and momentum drag time-scales to be of the order of a few days, a state of superrotation (SR) is shown to emerge under steady large-scale and random small-scale vorticity forcing. In the first example, the stationary response to a pair of equal and oppositely signed vortices placed on the Equator is considered. Here, the equatorial flux budget is dominated by the eddy fluxes and these drive the system into a state of SR. Eventually, the flux associated with the momentum drag increases to balance the eddy fluxes, resulting in a steady state with a superrotating jet at the Equator. The initial value problem with these twin vortices also exhibits SR driven by eddy fluxes. Curiously, this Transient Solution spontaneously propagates westward and continually circumnavigates the globe. It is worth emphasizing that this SR state does not rely on any particular form of dissipation at large scales and is, in fact, observed even in the absence of any large-scale damping mechanism. In the second example, a random small-scale vorticity forcing is applied across the Tropics. The statistically steady state obtained is fairly turbulent in nature, but here too the eddy fluxes dominate and the system exhibits SR. It is important to note that, in both these cases, the direct forcing of the zonal mean zonal flow is zero by construction and the eddy fluxes at the Equator are responsible for its eastward acceleration. Further, in both these examples, the rotational part of the flow dominates the momentum fluxes as well as the stationary zonal mean zonal flow itself. Arguments based on the nature of potential vorticity and enstrophy are put forth to shed some light on these results.
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tropical vorticity forcing and superrotation in the spherical shallow water equations
arXiv: Atmospheric and Oceanic Physics, 2016Co-Authors: Jai Sukhatme, Joy Merwin MonteiroAbstract:The response of the nonlinear shallow water equations (SWE) on a sphere to tropical vorticity forcing is examined with an emphasis on momentum fluxes and the emergence of a superrotating (SR) state. Fixing the radiative damping and momentum drag timescales to be of the order of a few days, a state of SR is shown to emerge under steady large-scale and random small-scale vorticity forcing. In the first example, the stationary response to a pair of equal and oppositely signed vortices placed on the equator is considered. Here, the equatorial flux budget is dominated by the eddy fluxes and these drive the system into a state of SR. Eventually, the flux associated with the momentum drag increases to balance the eddy fluxes, resulting in a steady state with a SR jet at the equator. The initial value problem with these twin vortices also exhibits SR driven by eddy fluxes. Curiously, this Transient Solution spontaneously propagates westward and continually circumnavigates the globe. It is worth emphasizing that this SR state does not rely on any particular form of dissipation at large scales, and is in fact observed even in the absence of any large-scale damping mechanism. In the second example, a random small-scale vorticity forcing is applied across the tropics. The statistically steady state obtained is fairly turbulent in nature, but here too, the eddy fluxes dominate, and the system exhibits SR. It is important to note that in both these cases, the direct forcing of the zonal mean zonal flow is zero by construction, and the eddy fluxes at the equator are responsible for its eastward acceleration. Further, in both these examples, the rotational part of the flow dominates the momentum fluxes as well as the stationary zonal mean zonal flow itself. Arguments based on the nature of potential vorticity and enstrophy are put forth to shed some light on these results.
Martyna Kobielnik - One of the best experts on this subject based on the ideXlab platform.
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Transient Solution for the queue size distribution in a finite buffer model with general independent input stream and single working vacation policy
Applied Mathematical Modelling, 2018Co-Authors: Wojciech M Kempa, Martyna KobielnikAbstract:Abstract A single-channel finite-buffer queueing model with a general independent input stream of customers, exponential processing times and a working vacation policy is considered. Every time , when the server becomes idle, an exponentially distributed single working vacation period is being initialized, during which the processing is provided with another (slower) rate. After the completion of the vacation period, the service is being continued normally, with the original speed. Using the idea of an embedded Markov chain, the systems of Volterra-type integral equations for the time-dependent queue-size distributions, conditioned by the initial buffer state and related to each other, are built for models beginning the operation in normal and working vacation modes, separately. The Solutions of the corresponding systems written for the Laplace transforms are obtained in compact forms using the linear algebraic approach. The numerical illustrative examples are attached as well.
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Transient Solution for queue size distribution in a certain finite buffer model with server working vacations
International Conference on Information and Software Technologies, 2016Co-Authors: Wojciech M Kempa, Martyna KobielnikAbstract:A finite-buffer queueing model with Poisson arrivals and exponential processing times is investigated. Every time when the system empties, the server begins a generally distributed single working vacation period, during which the service is provided with another (slower) rate. After the completion of the vacation period the processing is being continued normally, with original speed. The next working vacation period is being initialized at the next time at which the system becomes empty, and so on. The system of Volterra-type integral equations for Transient queue-size distribution, conditioned by the initial level of buffer saturation, is built. The Solution of the corresponding system written for Laplace transforms is given in a compact-form using the linear algebraic approach and the corresponding result obtained for the ordinary model (without working vacation regime). Numerical examples are attached as well.
Hao Lin - One of the best experts on this subject based on the ideXlab platform.
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a Transient Solution for vesicle electrodeformation and relaxation
Physics of Fluids, 2013Co-Authors: Jia Zhang, Jeffrey D Zahn, Wenchang Tan, Hao LinAbstract:A Transient analysis for vesicle deformation under direct-current electric fields is developed. The theory extends from a droplet model, with the additional consideration of a lipid membrane separating two fluids of arbitrary properties. For the latter, both a membrane-charging and a membrane-mechanical model are supplied. The vesicle is assumed to remain spheroidal in shape for all times. The main result is an ordinary differential equation governing the evolution of the vesicle aspect ratio. The effects of initial membrane tension and pulse length are examined. The model prediction is extensively compared with experimental data, and is shown to accurately capture the system behavior in the regime of no or weak electroporation. More importantly, the comparison reveals that vesicle relaxation obeys a similarity law regardless of the means of deformation. The process is governed by a single time scale that is a function of the vesicle initial radius, the fluid viscosity, and the initial membrane tension. This similarity scaling law can be used to calculate membrane properties from experimental data.
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Transient Solution for droplet deformation under electric fields
Physical Review E, 2013Co-Authors: Jia Zhang, Jeffrey D Zahn, Hao LinAbstract:A Transient analysis to quantify droplet deformation under DC electric fields is presented. The full Taylor-Melcher leaky dielectric model is employed where the charge relaxation time is considered to be finite. The droplet is assumed to be spheroidal in shape for all times. The main result is an ODE governing the evolution of the droplet aspect ratio. The model is validated by extensively comparing predicted deformation with both previous theoretical and numerical studies, and with experimental data. Furthermore, the effects of parameters and stresses on deformation characteristics are systematically analyzed taking advantage of the explicit formulas on their contributions. The theoretical framework can be extended to study similar problems, e.g., vesicle electrodeformation and relaxation.
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a Transient Solution for vesicle electrodeformation and relaxation
arXiv: Biological Physics, 2012Co-Authors: Jia Zhang, Jeffrey D Zahn, Wenchang Tan, Hao LinAbstract:A Transient analysis for vesicle deformation under DC electric fields is developed. The theory extends from a droplet model, with the additional consideration of a lipid membrane separating two fluids of arbitrary properties. For the latter, both a membrane-charging and a membrane-mechanical model are supplied. The vesicle is assumed to remain spheroidal in shape for all times. The main result is an ODE governing the evolution of the vesicle aspect ratio. The effects of initial membrane tension and pulse length are examined. The model prediction is extensively compared with experimental data, and is shown to accurately capture the system behavior in the regime of no or weak electroporation. More importantly, the comparison reveals that vesicle relaxation obeys a universal behavior regardless of the means of deformation. The process is governed by a single timescale that is a function of the vesicle initial radius, the fluid viscosity, and the initial membrane tension. This universal scaling law can be used to calculate membrane properties from experimental data.
Charbel Farhat - One of the best experts on this subject based on the ideXlab platform.
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partitioned procedures for the Transient Solution of coupled aeroelastic problems part ii energy transfer analysis and three dimensional applications
Computer Methods in Applied Mechanics and Engineering, 2001Co-Authors: Serge Piperno, Charbel FarhatAbstract:Abstract We consider the problem of solving large-scale nonlinear dynamic aeroelasticity problems in the time-domain using a fluid/structure partitioned procedure. We present a mathematical framework for assessing some important numerical properties of the chosen partitioned procedure, and predicting its performance for realistic applications. Our analysis framework is based on the estimation of the energy that is artificially introduced at the fluid/structure interface by the staggering process that is inherent to most partitioned Solution methods. This framework also suggests alternative approaches for time-discretizing the transfer of aerodynamic data from the fluid subsystem to the structure subsystem that improves the accuracy and the stability properties of the underlying partitioned method. We apply this framework to the analysis of several partitioned procedures that have been previously proposed for the Solution of nonlinear Transient aeroelastic problems. Using two- and three-dimensional, transonic and supersonic, wing and panel aeroelastic applications, we validate this framework and highlight its impact on the design and selection of a staggering algorithm for the Solution of coupled fluid/structure equations.
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Partitioned procedures for the Transient Solution of coupled aroelastic problems Part I: Model problem, theory and two-dimensional application
Computer Methods in Applied Mechanics and Engineering, 1995Co-Authors: S. Piperno, Charbel Farhat, Bernard LarrouturouAbstract:In order to predict the dynamic response of a flexible structure in a fluid flow, the equations of motion of the structure and the fluid must be solved simultaneously. In this paper we present several partitioned procedures for time-integrating this focus coupled problem and discuss their merits in terms of accuracy, stability, heterogeneous computing, I/O transfers, subcycling and parallel processing. All theoretical results are derived for a one-dimensional piston model problem with a compressible flow, because the complete three-dimensional aeroelastic problem is difficult to analyze mathematically. However, the insight gained from the analysis of the coupled piston problem and the conclusions drawn from its numerical investigation are confirmed with the numerical simulation of the two-dimensional Transient aeroelastic response of a flexible panel in a transonic non-linear Euler flow regime. © 1995.
Wojciech M Kempa - One of the best experts on this subject based on the ideXlab platform.
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Transient Solution for the queue size distribution in a finite buffer model with general independent input stream and single working vacation policy
Applied Mathematical Modelling, 2018Co-Authors: Wojciech M Kempa, Martyna KobielnikAbstract:Abstract A single-channel finite-buffer queueing model with a general independent input stream of customers, exponential processing times and a working vacation policy is considered. Every time , when the server becomes idle, an exponentially distributed single working vacation period is being initialized, during which the processing is provided with another (slower) rate. After the completion of the vacation period, the service is being continued normally, with the original speed. Using the idea of an embedded Markov chain, the systems of Volterra-type integral equations for the time-dependent queue-size distributions, conditioned by the initial buffer state and related to each other, are built for models beginning the operation in normal and working vacation modes, separately. The Solutions of the corresponding systems written for the Laplace transforms are obtained in compact forms using the linear algebraic approach. The numerical illustrative examples are attached as well.
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Transient Solution for queue size distribution in a certain finite buffer model with server working vacations
International Conference on Information and Software Technologies, 2016Co-Authors: Wojciech M Kempa, Martyna KobielnikAbstract:A finite-buffer queueing model with Poisson arrivals and exponential processing times is investigated. Every time when the system empties, the server begins a generally distributed single working vacation period, during which the service is provided with another (slower) rate. After the completion of the vacation period the processing is being continued normally, with original speed. The next working vacation period is being initialized at the next time at which the system becomes empty, and so on. The system of Volterra-type integral equations for Transient queue-size distribution, conditioned by the initial level of buffer saturation, is built. The Solution of the corresponding system written for Laplace transforms is given in a compact-form using the linear algebraic approach and the corresponding result obtained for the ordinary model (without working vacation regime). Numerical examples are attached as well.
