6,533 research outputs found
An analytical approach to grid sensitivity analysis for NACA four-digit wing sections
Sensitivity analysis in computational fluid dynamics with emphasis on grids and surface parameterization is described. An interactive algebraic grid-generation technique is employed to generate C-type grids around NACA four-digit wing sections. An analytical procedure is developed for calculating grid sensitivity with respect to design parameters of a wing section. A comparison of the sensitivity with that obtained using a finite difference approach is made. Grid sensitivity with respect to grid parameters, such as grid-stretching coefficients, are also investigated. Using the resultant grid sensitivity, aerodynamic sensitivity is obtained using the compressible two-dimensional thin-layer Navier-Stokes equations
Grid sensitivity for aerodynamic optimization and flow analysis
After reviewing relevant literature, it is apparent that one aspect of aerodynamic sensitivity analysis, namely grid sensitivity, has not been investigated extensively. The grid sensitivity algorithms in most of these studies are based on structural design models. Such models, although sufficient for preliminary or conceptional design, are not acceptable for detailed design analysis. Careless grid sensitivity evaluations, would introduce gradient errors within the sensitivity module, therefore, infecting the overall optimization process. Development of an efficient and reliable grid sensitivity module with special emphasis on aerodynamic applications appear essential. The organization of this study is as follows. The physical and geometric representations of a typical model are derived in chapter 2. The grid generation algorithm and boundary grid distribution are developed in chapter 3. Chapter 4 discusses the theoretical formulation and aerodynamic sensitivity equation. The method of solution is provided in chapter 5. The results are presented and discussed in chapter 6. Finally, some concluding remarks are provided in chapter 7
Interactive real time flow simulations
An interactive real time flow simulation technique is developed for an unsteady channel flow. A finite-volume algorithm in conjunction with a Runge-Kutta time stepping scheme was developed for two-dimensional Euler equations. A global time step was used to accelerate convergence of steady-state calculations. A raster image generation routine was developed for high speed image transmission which allows the user to have direct interaction with the solution development. In addition to theory and results, the hardware and software requirements are discussed
Meson Masses and Mixing Angles in 2+1 Flavor Polyakov Quark Meson Sigma Model and Symmetry Restoration Effects
The meson masses and mixing angles have been calculated for the scalar and
pseudoscalar sector in the framework of the generalized 2+1 flavor Polyakov
loop augmented quark meson linear sigma model. We have given the results for
two different forms of the effective Polyakov loop potential. The comparison of
results with the existing calculations in the bare 2+1 quark meson linear sigma
model, shows that the restoration of chiral symmetry becomes sharper due to the
influence of the Polyakov loop potential. We find that inclusion of the
Polyakov loop in quark meson linear sigma model together with the presence of
axial anomaly, triggers an early and significant melting of the strange
condensate. We have examined how the inclusion of the Polyakov loop
qualitatively and quantitatively affects the convergence in the masses of the
chiral partners in pseudoscalar (, , , ) and scalar
(, , ,) meson nonets as the temperature is varied on
the reduced temperature scale. The role of anomaly in determining the
isoscalar masses and mixing angles for the pseudoscalar ( and )
and scalar ( and )meson complex, has also been investigated in the
Polyakov quark meson linear sigma model. The interplay of chiral symmetry
restoration effects and the setting up of restoration trend has been
discussed and analyzed in the framework of the presented model calculations.Comment: 15 pages, 8 figures, 4 table
Non-collinear Magnetic Order in the Double Perovskites: Double Exchange on a Geometrically Frustrated Lattice
Double perovskites of the form A_2BB'O_6 usually involve a transition metal
ion, B, with a large magnetic moment, and a non magnetic ion B'. While many
double perovskites are ferromagnetic, studies on the underlying model reveal
the possibility of antiferromagnetic phases as well driven by electron
delocalisation. In this paper we present a comprehensive study of the magnetic
ground state and T_c scales of the minimal double perovskite model in three
dimensions using a combination of spin-fermion Monte Carlo and variational
calculations. In contrast to two dimensions, where the effective magnetic
lattice is bipartite, three dimensions involves a geometrically frustrated face
centered cubic (FCC) lattice. This promotes non-collinear spiral states and
`flux' like phases in addition to collinear anti-ferromagnetic order. We map
out the possible magnetic phases for varying electron density, `level
separation' epsilon_B - epsilon_B', and the crucial B'-B' (next neighbour)
hopping t'.Comment: 15 pages pdflatex + 19 figs, revision: removed redundant comment
State-space Correlations and Stabilities
The state-space pair correlation functions and notion of stability of
extremal and non-extremal black holes in string theory and M-theory are
considered from the viewpoints of thermodynamic Ruppeiner geometry. From the
perspective of intrinsic Riemannian geometry, the stability properties of these
black branes are divulged from the positivity of principle minors of the
space-state metric tensor. We have explicitly analyzed the state-space
configurations for (i) the two and three charge extremal black holes, (ii) the
four and six charge non-extremal black branes, which both arise from the string
theory solutions. An extension is considered for the ---
multi-centered black branes, fractional small black branes and two charge
rotating fuzzy rings in the setup of Mathur's fuzzball configurations. The
state-space pair correlations and nature of stabilities have been investigated
for three charged bubbling black brane foams, and thereby the M-theory
solutions are brought into the present consideration. In the case of extremal
black brane configurations, we have pointed out that the ratio of diagonal
space-state correlations varies as inverse square of the chosen parameters,
while the off diagonal components vary as inverse of the chosen parameters. We
discuss the significance of this observation for the non-extremal black brane
configurations, and find similar conclusion that the state-space correlations
extenuate as the chosen parameters are increased.Comment: 35 pages, Keywords: Black Hole Physics, Higher-dimensional Black
Branes, State-space Correlations and Statistical Configurations. PACS
numbers: 04.70.-s Physics of black holes; 04.70.Bw Classical black holes;
04.70.Dy Quantum aspects of black holes, evaporation, thermodynamics;
04.50.Gh Higher-dimensional black holes, black strings, and related object
Effects of quarks on the formation and evolution of Z(3) walls and strings in relativistic heavy-ion collisions
We investigate the effects of explicit breaking of Z(3) symmetry due to the
presence of dynamical quarks on the formation and evolution of Z(3) walls and
associated QGP strings within Polyakov loop model. We carry out numerical
simulations of the first order quark-hadron phase transition via bubble
nucleation (which may be appropriate, for example, at finite baryon chemical
potential) in the context of relativistic heavy-ion collision experiments.
Using appropriate shifting of the order parameter in the Polyakov loop
effective potential, we calculate the bubble profiles using bounce technique,
for the true vacuum as well as for the metastable Z(3) vacua, and estimate the
associated nucleation probabilities. These different bubbles are then nucleated
and evolved and resulting formation and dynamics of Z(3) walls and QGP strings
is studied. We discuss various implications of the existence of these Z(3)
interfaces and the QGP strings, especially in view of the effects of the
explicit breaking of the Z(3) symmetry on the formation and dynamical evolution
of these objects.Comment: 17 pages, 9 figures, PDFLate
Rotating light, OAM paradox and relativistic complex scalar field
Recent studies show that the angular momentum, both spin and orbital, of
rotating light beams possesses counter-intuitive characteristics. We present a
new approach to the question of orbital angular momentum of light based on the
complex massless scalar field representation of light. The covariant equation
for the scalar field is treated in rotating system using the general
relativistic framework. First we show the equivalence of the U(1) gauge current
for the scalar field with the Poynting vector continuity equation for paraxial
light, and then apply the formalism to the calculation of the orbital angular
momentum of rotating light beams. If the difference between the co-, contra-,
and physical quantities is properly accounted for there does not result any
paradox in the orbital angular momentum of rotating light. An artificial
analogue of the paradoxical situation could be constructed but it is wrong
within the present formalism. It is shown that the orbital angular momentum of
rotating beam comprising of modes with opposite azimuthal indices corresponds
to that of rigid rotation. A short review on the electromagnetism in
noninertial systems is presented to motivate a fully covariant Maxwell field
approach in rotating system to address the rotating light phenomenon.Comment: No figure
Hybrid Petri-nets for Modeling and Performance Evaluation of Supply Chains
Cataloged from PDF version of article.Modelling and analysis of complex and co-ordinated supply chains is a crucial task due to its inherent complexity and uncertainty. Therefore, the current research direction is to devise an efficient modelling technique that maps the dynamics of a real life supply chain and assists industrial practitioners in evaluating and comparing their network with other competing networks. Here an effective modelling technique, the hybrid Petri-net, is proposed to efficiently handle the dynamic behaviour of the supply chain. This modelling methodology embeds two enticing features, i.e. cost and batch sizes, in deterministic and stochastic Petri-net for the modelling and performance evaluation of supply chain networks. The model is subsequently used for risk management to investigate the issues of supply chain vulnerability and risk that has become a major research subject in recent years. In the test bed, a simple productive supply chain and an industrial supply chain are modelled with fundamental inventory replenishment policy. Subsequently, its performance is evaluated along with the identification and assessment of risk factors using analytical and simulation techniques respectively. Thus, this paper presents a complete package for industrial practitioners to model, evaluate performance and manage risky events in a supply chain
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