Numerical solution of a free surface problem by a boundary element method

This paper describes a method for the numerical solution of a Riabouchinsky cavity flow. Application of a boundary element method leads to a system of non-linear equations. The mild singularity appearing at the separation point is treated with the introduction of a curved boundary element, which satisfies the exact behaviour of the free boundary in that neighbourhood.     

A combustion problem in cylindrical and spherical symmetry

Summary We study a system of partial differential equations describing the behaviour of a perfect, viscous, polytropic, compressible, chemically reactive gas in a bounded container, under assumptions of cylindrical symmetry. The global existence in the time of a classical solution is proved by some a priori estimates. One extension at the spherical case is given.

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Sommario Si studia un sistema di equazioni a derivate parziali che descrive il comportamento di un gas perfetto, viscoso, politropico, comprimibile che reagisce chimicamente in un recipiente limitato, con simmetria cilindrica. Si prova I'esistenza globale nel tempo di una soluzione classica per mezzo di stime a priori. Si estende poi questo procedimento al caso delta simmetria sferica.

     

Motion of a cylindrical cavity near a free boundary of a liquid

The dynamics of a cylindrical cavity in a liquid with no allowance for vertical displacement are considered in [1–3]. The present study investigates the pulsation motion of a cylindrical cavity near a free boundary of a liquid, allowing for displacement of the axis of the cavity in the vertical direction.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 173–176, November–December, 1988.     

A Stefan-type free boundary problem in a thermal switch

Summary We study a mathematical model of thermal switch in a glass under the Joule heating. We prove the existence of solutions for the free boundary problem related to the model. This problem is a Stefan-type problem with a source depending on the free boundary and the latent heat depending on the history of the free boundary.

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Sommario Si studia un modello matematico che descrive un fenomeno di cambiamento di fase in un vetro attraversato da una corrente elettrica. In particolare si dimostra l'esistenza di soluzioni per il problema a frontiera libera connesso con il modello. Questo problema è del tipo di Stafan, con sorgente funzione della frontiera libera e con calore latente che dipende dalla storia della frontiera.

     

Numerical solution of moving boundary problem in a finite domain

The temperature distribution in two regions and the location of moving interface during freezing in a finite domain is studied numerically. The differential equations governing the process of heat transfer in two regions are converted to initial value problem of vector matrix form. The solution of this initial value problem is utilized iteratively in the interface heat flux equation to determine interface location as well as the temperature distribution in two regions. The whole analysis is presented in a nondimensional form and the results thus obtained are discussed in detail. Received on 4 March 1998     

SOLVING THE FREE BOUNDARY PROBLEM IN CONTINUOUS CASTING BY USING BOUNDARY ELEMENT METHOD

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A free boundary problem arising in oil production

For a stable two-phase free boundary problem arising in oil production, we prove the existence of a weak solution and the continuity of the free boundary.

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Sommario Si prova un teorema di esistenza di una soluzione debole per un problema stazionario a contorno libero a due fasi che interessa la produzione di petrolio. Si dimostra inoltre la continuità del contorno libero.

     

Influence of boundary conditions on the solution of a hyperbolic thermoelasticity problem

We consider a series of problems with a short laser impact on a thin metal layer accounting various boundary conditions of the first and second kind. The behavior of the material is modeled by the hyperbolic thermoelasticity of Lord–Shulman type. We obtain analytical solutions of the problems in the semi-coupled formulation and numerical solutions in the coupled formulation. Numerical solutions are compared with the analytical ones. The analytical solutions of the semi-coupled problems and numerical solutions of the coupled problems show qualitative match. The solutions of hyperbolic thermoelasticity problems are compared with those obtained in the frame of the classical thermoelasticity. It was determined that the most prominent difference between the classical and hyperbolic solutions arises in the problem with fixed boundaries and constant temperature on them. The smallest differences were observed in the problem with unconstrained, thermally insulated edges. It was shown that a cooling zone is observed if the boundary conditions of the first kind are given for the temperature. Analytical expressions for the velocities of the quasiacoustic and quasithermal fronts as well as the critical value for the attenuation coefficient of the excitation impulse are verified numerically.     

A boundary element method for a non-linear free surface problem

In this paper a numerical method to compute the wave resistance of a body submerged in a free stream of finite and infinite depth is presented. Non-linear effects on the free surface are taken into account by an iterative procedure; the solution is in the form of a single-layer potential. For the 2D problem, results are shown for both the cases of finite and infinite depth of the fluid domain, with special emphasis on the supercritical flow in which the consistency of the scheme is pointed out. The method is also extended to the 3D case of a spheroid submerged in deep water. All the results presented are compared with experimental data and analytical solutions available in the literature.     

Theoretical solution of the boundary problem of subsonic aerodynamics

A general theoretical solution of the boundary problem of aerodynamics of high subsonic velocities is presented. The solution of the partial differential equation for the velocity potential is carried out in the physical plane in streamline co-ordinates. The principle of the solution is the representation flow of a compressible fluid around a given profile to a hypothetical flow of an incompressible fluid around a different associated profile. In other words, the problem of compressible flow is transformed to the problem of incompressible flow, which can easily be solved. The results of this solution show very good agreement with solutions of other authors and with experiments.     

Constructive symmetry in the stability problem for a cylindrical shell reinforced by stiffening rings under hydrostatic pressure

We use the solution of the problem under study which was earlier obtained by the author [1—3] and which is based on a decomposition of the reinforced shell into separate constructive elements (the ribs and the shell itself) and then on deriving the equilibrium equations and consistency conditions for their strains. Under the assumption that the shell precritical state is momentless, this is a sufficiently exact solution. Its drawback is the significant complexity of the computational algorithm. In the present paper, we show that the laboriousness of the algorithm can be reduced dramatically if the shell under study has elements of design symmetry (identical ribs, their uniform spacing, or both). In addition, we present dependencies determining the stiffening rib rigidity needed to ensure that the shell remains stable for a given critical value of the external hydrostatic pressure.     

On the solution of nonlinear two-point boundary value problem

In this paper, a non-variational version of a max-min principle is proposed, andan existence and uniqueness result is obtained for the nonlinear two-point boundaryvalue problenl u"+g(t.u)=f(t),u(0)=u(2π)=0     

Estimates of the influence of the transverse strain in a contact problem with free boundary

We use the contact problem with free boundary for a “heavy cylindrical shell-over-support reinforcement ring” system as an example to study the influence of transverse shear on the stress state in the shell. To obtain the equilibrium equations for the shell and the reinforcement ring, we apply an express algorithm developed by one of the authors to take into account transverse strains in Kirchhoff versions of the theory of shells. The contact problem with free boundary is solved by the generalized reaction method proposed earlier. We use numerical examples to show that the corrections introduced in the stress state by taking into account the transverse shears are by an order of magnitude larger than the traditional estimate of errors in the Kirchhoff hypotheses.     

A Lie symmetry approach for the solution of the inverse kinematics problem

In this paper, it is considered the inverse kinematics problem, which is faced from a differential point of view. In particular, it is shown that an asymptotic inverse kinematics can be interpreted as a Lie symmetry of the direct kinematics. A parameterization of all Lie symmetries of the direct kinematics is proposed, and the classical Newton and gradient method are obtained as particular cases.     

Iterative solution of a non-linear boundary value problem for a rotating string

The problem of determining the motion of a rotating inextensible string of length l, free at one end and fixed at the other can, under certain assumptions, be treated by solving a non-linear boundary value problem. p]In this paper, two Picard-type iterative schemes are constructed and the sequences generated are proved to converge to a positive solution of that non-linear boundary value problem. Additionally, one sequence converges to the solution from above, the other from below. Moreover, the iterative scheme can be used to solve the inverse problem of determining the angular velocity of the rotating string, given two observations (at one point in time) of position of the string.     

Nonsteady-state problem of the emission of acoustic waves by a cylindrical piezoelectric transducer near a planar boundary

We study processes developing when a cylindrical piezoceramic shell with split electrodes located near a planar boundary is excited by nonsteady-state electrical signals. We solve the problem using the Laplace integral transform with respect to time. The boundary conditions are satisfied in the space of the originals. Under these conditions, the unknowns are found from a system of Volterra integral equations. We present the calculation results and their analysis. Translated from Prikladnaya Mekhanika, Vol. 33. No. 12, pp. 60–67, December, 1997.