arXiv subjects

Arkady I. Leonov

Publications and source records attributed to Arkady I. Leonov.

12 recordsLinked to original sources

arXiv2008

Aerodynamic Models for Hurricanes III. Modeling hurricane boundary layer

The third paper of the series (see previous ones in Refs.[1-2]) discusses basic physicalprocesses in the (quasi-) steady hurricane boundary layer (HBL), develops an approximate airflow model, establishes the HBL structure, and presents integral balance relations for dynamic and thermodynamic variables in HBL. Models of evaporation and condensation are developed, where the condensation is treated similarly to the slow combustion theory. A turbulent approximation for the lower sub-layer of HBL is applied to the sea-air interaction to establish the observed increase in angular momentum in the outer region of HBL.A closed set of balance relations has been obtained. Simple analytical solution of the set yields expressions for the basic dynamic variables - maximal tangential and radial velocities in hurricane, maximal vertical speed in eye wall, the affinity speed of hurricane travel, and the maximal temperature increase after condensation. Estimated values of the variables seem to be realistic. An attempt is also made to describe the radial distributions of wind velocity and surface pressure observed in the hurricane Frederic (1979).

physics.ao-ph↗

arXiv2008

Aerodynamic Models for Hurricanes IV. On the hurricane genesis and maturing

This, fourth paper of the series (see previous papers in Refs.[1-3]) derives approximate equations for future numerical studies of initial evolution of hurricanes, develops new analytical models of hurricane genesis and maturing, and presents simple results, which seems to be in accord with observations. Several remarks on tornados are also made at the end of the paper.

physics.ao-ph↗

arXiv2008

Aerodynamic Models For Hurricanes I. Model description and horizontal motion of hurricane

Aerodynamic models are developed to describe coherent structures and transport processes in hurricanes moving over open seas. The models consist of the lower boundary layer and upper adiabatic layer. Except friction at the air/sea interface,proposed modeling avoids the common turbulent approximations while using explicitly or implicitly basic stability constraints. The models analyze dynamics of upper hurricane adiabatic layer, dynamics and transport processes in hurricane boundary layer, and genesis and maturing of hurricane. The proposed modeling provides a rude enough but consistent analytical description of basic processes in hurricanes. The present paper qualitatively describes the model of mature hurricane, briefly discusses the basic thermodynamic relations and aerodynamic equations, and establishes the principles of horizontal motion for mature hurricane.

physics.ao-ph↗

arXiv2008

Aerodynamic Models for Hurricanes II. Model of the upper hurricane layer

This second paper of the series (see the first one in [1]) models the dynamics and structure of upper hurricane layer in adiabatic approximation. Formulation of simplified aerodynamic model allows analytically express the radial istributions of pressure and wind speed components. The vertical evolution of these distributions and hurricane structure in the layer are described by a coupled set of equations for the vertical mass flux and vertical momentum balance, averaged over the eye wall cross section. Several realistic predictions of the model are demonstrated, including the change of directions for the component of radial wind speed and angular velocity of hurricane with altitude.

physics.ao-ph↗

arXiv2005

A model of weak viscoelastic nematodynamics

The paper develops a continuum theory of weak viscoelastic nematodynamics of Maxwell type. It may describe the molecular elasticity effects in mono-domain flows of liquid crystalline polymers as well as the viscoelastic effects in suspensions of uniaxially symmetric particles in polymer fluids. Along with viscoelastic and nematic kinematics, the theory employs a general form of weakly elastic thermodynamic potential and the Leslie-Ericksen-Parodi type constitutive equations for viscous nematic liquids, while ignoring inertia effects and the Frank (orientation) elasticity in liquid crystal polymers. In general case, even the simplest Maxwell model has many basic parameters. Nevertheless, recently discovered algebraic properties of nematic operations reveal a general structure of the theory and present it in a simple form. It is shown that the evolution equation for director is also viscoelastic. An example of magnetization exemplifies the action of non-symmetric stresses. When the magnetic field is absent, the theory is simplified to the symmetric, fluid mechanical case with relaxation properties for both the stress and director. Our recent analyses of elastic and viscous soft deformation modes are also extended to the viscoelastic case. The occurrence of possible soft modes minimizes both the free energy and dissipation, and also significantly decreases the number of material parameters. In symmetric linear case, the theory is explicitly presented in terms of anisotropic linear memory functionals. Several analytical results demonstrate a rich behavior predicted by the developed model for steady and unsteady flows in simple shearing and simple elongation.

cond-mat.soft↗

arXiv2004

Algebraic theory of linear viscoelastic nematodynamics Part 1: Algebra of nematic operators

This first part of the paper develops algebraic theory of linear anisotropic, six-parametric nematic "N-operators" build up on the additive group of traceless second rank 3D tensors. These operators have been implicitly used in continual theories of nematic liquid crystals and weakly elastic nematic elastomers. It is shown that there exists a noncommutative, multiplicative group N6 of N-operators build up on a manifold in 6D space of parameters. Positive N-operators, which in physical applications holds thermodynamic stability constraints, form a subgroup of group N6 on a more complicated manifold in parametric space. A three-parametric, commutative transversal-isotropic subgroup S3 < N6 of positive symmetric nematic operators is also briefly discussed. The special case of singular, non-negative symmetric N-operators reveals the algebraic structure of nematic soft deformation modes.

cond-mat.soft↗

arXiv2004

Algebraic theory of linear viscoelastic nemattodynamics Part 2: Linear viscoelastic nematic viscoelasticity

This second part of paper develops a theory of linear viscoelastic nematodynamics applicable to LCP. The viscous and elastic nematic components in theory are described by using the LEP approach for viscous nematics and de Gennes free energy for weakly elastic nematic elastomers. The case of applied external magnetic field exemplifies the occurrence of non-symmetric stresses. In spite of multi- (10) parametric character of the theory, the use of nematic operators presents it in an elegant form. When the magnetic field is absent, the theory is simplified for symmetric case with 6 parameters, and takes an extremely simple, 2-parametric form for viscoelastic nematodynamics with possible soft deformation modes. It is shown that the linear nematodynamics is always reduced to the LEP-like equations where the coefficients are changed for linear memory functionals whose parameters are calculated from original viscosities and moduli.

cond-mat.soft↗

arXiv2004

Weak Viscoelastic Nematodynamics of Maxwell Type

A constitutive theory for weak viscoelastic nematodynamics of Maxwell type is developed using the standard local approach of non-equilibrium thermodynamics. Along with particular viscoelastic and nematic kinematics, the theory uses the weakly elastic potential proposed by de Gennes for nematic solids and the LEP constitutive equations for viscous nematic liquids, while ignoring the Frank (orientation) elasticity and inertia effects. In spite of many basic parameters, algebraic properties of nematic operations investigated in Appendix, allowed us to reveal a general group structure of the theory and present it in a simple form. It is shown that the evolution equation for director is also viscoelastic. An example of magnetization clarifies the situation with non-symmetric stresses. When the sources of stress asymmetry are absent, the theory is simplified and its relaxation properties are described by a symmetric subgroup of nematic algebraic operations. A purely linear constitutive behavior exemplifies the symmetric situation.

cond-mat.soft↗

arXiv2004

A Hybrid Model of Rubber Elasticity in Simple Extension

A thermodynamically related model is developed for describing elastic rubber-like behavior of amorphous and crystallizing polymers and demonstrated on example of simple extension. Both the “entropic” and “energetic” motions of polymer chains that contribute in macroscopic elastic deformation are taken into account. The model displays a continuous transition from entropy to energetic elasticity, without common singularity caused by finite extensibility of polymer chains. A multi-scale molecular approach, based on recent literature concepts has been employed for evaluations of continuum parameters. For crystallizing polymers, a simple model is developed for the stress-induced crystallization, which describes the stress reinforcement caused by the formation of long, needle-like polymer crystals.

cond-mat.soft↗

arXiv2003

Soft Dissipative Modes in Nematodynamics

The paper analyses a possible occurrence of soft and semi-soft dissipative modes in uniaxially anisotropic nematic liquids as described by the five parametric Leslie-Ericksen-Parodi (LEP) constitutive equations (CEs). As in the similar elastic case, the soft dissipative modes theoretically cause no resistance to flow, nullifying the corresponding components of viscous part of stress tensor, and do not contribute in the dissipation. Similarly to the theories of nematic elastic solids, this effect is caused by a marginal thermodynamic stability. The analysis is trivialized in a specific rotating orthogonal coordinate system whose one axis is directed along the director. We demonstrate that depending on closeness of material parameters to the marginal stability conditions, LEP CEs describe the entire variety of soft, semi-soft and harder behaviours of nematic viscous liquids. When the only shearing dissipative modes are soft, the viscous part of stress tensor is symmetric, and LEP CE for stress, scaled with isotropic viscosity is reduced to a one-parametric, stress - strain rate anisotropic relation. When additionally the elongation dissipative mode is also soft, this scaled relation has no additional parameters and shows that the dissipation is always less than that in isotropic phase. Simple shearing and simple elongation flows illustrate these effects.

cond-mat.soft↗

arXiv2003

Quasi-1D Modeling of Polymer Melt Die Swell in Short Dies

This paper describes the isothermal die swell using our recent quasi-1D model for fast (high Deborah number) contraction flows of polymers melts. Because the model analyzes the flow in several flow regions as one continuous process, it makes possible to evaluate the die swell as a qusi-1D extrudate flow in dies of various lengths. Using the asymptotic matching condition for the change in flow type at the die exit allowed us to find the swelling profile for extrudate along the flow direction. The calculations in paper performed using a multi-mode viscoelastic constitutive equation of differential type, are compared with the experimental/direct numerical data including basic rheological tests. The presented swelling model involves no fitting parameter and is applicable for calculations using any viscoelastic constitutive equation.

physics.flu-dyn↗

arXiv2003

The Model of Fast Contraction Flows for Polymeric Melts

The present paper develops an isothermal model for fast (high Deborah number) contraction flows of polymers from a reservoir to a die of circular or rectangular cross-sections. Two components of composite flow models in different regions of the flow domain are connected in succession with the use of asymptotic matching boundary conditions. These components are inhomogeneous elongation and a modified unsteady shearing. It is constructed based on a stable and descriptive set of viscoelastic constitutive equations with the specified material parameters. The present model demonstrates a reasonable good agreement to the experimental/direct numerical data and improves for the higher values of Deborah number and contraction ratio cases without any adjustable parameters. Also it is applicable to any constitutive equation and performs with easy PC numerical calculations.

physics.flu-dyn↗