arXiv subjects
Publications and source records attributed to Vassil M. Vassilev.
In these notes, using the method of differential constraints, novel exact kink-like solutions are obtained for certain classes of complex Ginzburg--Landau equations with cubic-quintic nonlinearity. The foregoing solutions are presented in terms of the Lambert W function.
The shape equation for an axisymmetric fluid membrane is derived, assuming action of an uniform external electric field. The flexoelectric contribution to the free energy of the membrane, stemming from the latter is accounted within the theory by Steigmann and Agrawal. Additionally, we have introduced, in the aforementioned functional, another term associated with a curvature induced membrane polarization, as the latter was first hypothesized by A. Petrov. Some exact Naito-type solutions of the studied equation are given, with the free parameters linked to the model ones.
When masless excitations are limited or modified by the presence of material bodies one observes a force atcing between them generally called Casimir force. Such excitations are present in any fluid system close to its true bulk critical point. We derive exact analytical results for both the temperature and external ordering field behavior of the thermodynamic Casimir force within the mean-field Ginzburg-Landau Ising type model of a simple fluid or binary liquid mixture. We investigate the case when under a film geometry the boundaries of the system exhibit strong adsorption onto one of the phases (components) of the system. We present analytical and numerical results for the (temperature-field) surface of the force in both the critical region of the film close to its finite-size or bulk critical points as well as in the capillary condensation regime below the finite-size critical point.
We investigate the dependence of the order parameter profile, local and total susceptibilities on both the temperature and external magnetic field within the mean-filed Ginzburg-Landau Ising type model. We study the case of a film geometry when the boundaries of the film exhibit strong adsorption to one of the phases (components) of the system. We do that using general scaling arguments and deriving exact analytical results for the corresponding scaling functions of these quantities. In addition, we examine their behavior in the capillary condensation regime. Based on the derived exact analytical expressions we obtained an unexpected result -- the existence of a region in the phase transitions line where the system jumps below its bulk critical temperature from a less dense gas to a more dense gas before switching on continuously into the usual jump from gas to liquid state in the middle of the system. It is also demonstrated that on the capillary condensation line one of the coexisting local susceptibility profiles is with one maximum, whereas the other one is with two local maxima centered, approximately, around the two gas-liquid interfaces in the system.
The parametric equations of the plane curves determining the equilibrium shapes that a uniform inextensible elastic ring or tube could take subject to a uniform hydrostatic pressure are presented in an explicit analytic form. The determination of the equilibrium shape of such a structure corresponding to a given pressure is reduced to the solution of two transcendental equations. The shapes with points of contact and the corresponding (contact) pressures are determined by the solutions of three transcendental equations. The analytic results presented here confirm many of the previous numerical results on this subject but the results concerning the shapes with lines of contact reported up to now are revised.
In the present work we study acceleration waves in plate-like bodies using the balance laws for the time-dependent von Karman equations presented in [P. A. Djondjorov and V. M. Vassilev, Conservation Laws and Group-Invariant Solutions of the von Karman Equations, Int. J. Nonlinear Mech. 31 (1), pp. 73-87, (1986)]. Two of these balance laws correspond to the time-dependent von Karman equations themselves. They are used to define acceleration waves in thin isotropic elastic plates as discontinuity solutions with finite jumps of second derivatives of the displacement field at a certain curve - the wave front. These two balance laws lead through Hadamard's lemma and Kotchin's theorem to a set of jump conditions on the wave front. Similarly, the other balance laws lead to additional and independent jump conditions on the curve of discontinuity. Several examples are given to illustrate the effect of involving jump conditions of that kind in analysis of acceleration waves in plates. The examples are composed on the basis of three families of group-invariant solutions to the time-dependent von Karman equations. They present three kinds of waveforms pertaining to the class of the so-called relatively undistorded progressive waves. We analyze the propagation of this special kind of acceleration waves into a known state of plate motion.
In the present paper, a class of partial differential equations related to various plate and rod problems is studied by Lie transformation group methods. A system of equations determining the generators of the admitted point Lie groups (symmetries) is derived. A general statement of the associated group-classification problem is given. A simple intrinsic relation is deduced allowing to recognize easily the variational symmetries among the ''ordinary'' symmetries of a self-adjoint equation of the class examined. Explicit formulae for the conserved currents of the corresponding (via Noether's theorem) conservation laws are suggested. Solutions of group-classification problems are presented for subclasses of equations of the foregoing type governing stability and vibration of plates, rods and fluid conveying pipes resting on variable elastic foundations and compressed by axial forces. The obtained group-classification results are used to derive conservation laws and group-invariant solutions readily applicable in plate statics or rod dynamics.
In the case of transversely only loaded shallow shells, the nonlinear Donnell-Mushtari-Vlasov theory for large deflection of isotropic thin elastic shells leads to a system of two coupled nonlinear forth-order partial differential equations known as Marguerre's equations. This system involves two arbitrary elements -- the curvature tensor of the shell middle-surface and the function of transversal load per unit surface area. In the present note, the point symmetry groups of Marguerre's equations are established, the corresponding group classification problem being solved. It is shown that Marguerre's equations are equivalent to the von Karman equations for large deflection of plates in the time-independent case and in the time-dependent case as well. It is also observed that the same holds true in respect of the field equations for anisotropic shallow shells.