scholarly journals On an ill-posed problem for a biharmonic equation

Filomat ◽  
2017 ◽  
Vol 31 (4) ◽  
pp. 1051-1056 ◽  
Author(s):  
Tynysbek Kal’menov ◽  
Ulzada Iskakova
Keyword(s):  
Boundary Value Problem ◽  
Biharmonic Equation ◽  
Sufficient Conditions ◽  
Rectangular Domain ◽  
Problem Solution ◽  
Local Boundary ◽  
Stability Of Solution ◽  
Ill Posed ◽  
The Stability ◽  
Necessary And Sufficient

A local boundary value problem for the biharmonic equation in a rectangular domain is considered. Boundary conditions are given on all boundary of the domain. We show that the considered problem is self-adjoint. Herewith the problem is ill-posed. We show that the stability of solution to the problem is disturbed. Necessary and sufficient conditions of existence of the problem solution are found.

On a criterion for the solvability of one ill-posed problem for the biharmonic equation

2016 ◽  
Vol 24 (6) ◽  
Author(s):  
Tynysbek S. Kal’menov ◽  
Makhmud A. Sadybekov ◽  
Ulzada A. Iskakova
Keyword(s):  
Biharmonic Equation ◽  
Sufficient Conditions ◽  
Adjoint Problem ◽  
Rectangular Domain ◽  
Solution Stability ◽  
Well Posedness ◽  
Local Boundary ◽  
Ill Posed ◽  
Necessary And Sufficient ◽  
Isolated Point

AbstractA local boundary value problem for an inhomogeneous biharmonic equation in a rectangular domain is considered. Boundary conditions are given on the whole boundary of the domain. It is shown that the problem turns out to be self-adjoint. And herewith the problem is ill-posed. An example is constructed demonstrating that the solution stability to the problem is violated. Necessary and sufficient conditions of the existence of a strong solution to the investigated problem are found. The idea of the method is that the solution to the problem is constructed in the form of an expansion on eigenfunctions of this self-adjoint problem. This problem has an isolated point of continuous spectrum in zero. It is shown that there exists a series (a sequence) of eigenvalues converging to zero. Asymptotics of these eigenvalues is found. Namely this asymptotics defines a reason for the ill-posedness of the investigated problem. A space of well-posedness for the investigated problem is constructed.

scholarly journals DIRICHLET PROBLEM FOR LOADED DEGENERATING EQUATION OF THE MIXED TYPE IN THE RECTANGULAR AREA

2017 ◽  
Vol 19 (6) ◽  
pp. 40-53
Author(s):  
E.P. Melisheva
Keyword(s):  
Dirichlet Problem ◽  
Boundary Problem ◽  
Mixed Type ◽  
Sufficient Conditions ◽  
Rectangular Domain ◽  
One Dimensional ◽  
Rectangular Area ◽  
The Stability ◽  
Necessary And Sufficient ◽  
Uniqueness Of A Solution

In this work necessary and sufficient conditions for uniqueness of a solution to the first boundary problem for Lavrentiev-Bitsadze equation in rectangular domain are established. The solution to the problem is constructed as a sum of series with respect of eigenfunctions of a corresponding one-dimensional Stour-m-Liouviele problem. The stability is shown.

Nonlinear boundary-value problems for degenerate differential-algebraic systems

2020 ◽  
Vol 17 (3) ◽  
pp. 313-324
Author(s):  
Sergii Chuiko ◽  
Ol'ga Nesmelova
Keyword(s):  
Boundary Value Problem ◽  
Boundary Value Problems ◽  
Algebraic System ◽  
Boundary Value ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Weakly Nonlinear ◽  
Differential Algebraic System ◽  
Linear Differential ◽  
Necessary And Sufficient

The study of the differential-algebraic boundary value problems, traditional for the Kiev school of nonlinear oscillations, founded by academicians M.M. Krylov, M.M. Bogolyubov, Yu.A. Mitropolsky and A.M. Samoilenko. It was founded in the 19th century in the works of G. Kirchhoff and K. Weierstrass and developed in the 20th century by M.M. Luzin, F.R. Gantmacher, A.M. Tikhonov, A. Rutkas, Yu.D. Shlapac, S.L. Campbell, L.R. Petzold, Yu.E. Boyarintsev, V.F. Chistyakov, A.M. Samoilenko, O.A. Boichuk, V.P. Yacovets, C.W. Gear and others. In the works of S.L. Campbell, L.R. Petzold, Yu.E. Boyarintsev, V.F. Chistyakov, A.M. Samoilenko and V.P. Yakovets were obtained sufficient conditions for the reducibility of the linear differential-algebraic system to the central canonical form and the structure of the general solution of the degenerate linear system was obtained. Assuming that the conditions for the reducibility of the linear differential-algebraic system to the central canonical form were satisfied, O.A.~Boichuk obtained the necessary and sufficient conditions for the solvability of the linear Noetherian differential-algebraic boundary value problem and constructed a generalized Green operator of this problem. Based on this, later O.A. Boichuk and O.O. Pokutnyi obtained the necessary and sufficient conditions for the solvability of the weakly nonlinear differential algebraic boundary value problem, the linear part of which is a Noetherian differential algebraic boundary value problem. Thus, out of the scope of the research, the cases of dependence of the desired solution on an arbitrary continuous function were left, which are typical for the linear differential-algebraic system. Our article is devoted to the study of just such a case. The article uses the original necessary and sufficient conditions for the solvability of the linear Noetherian differential-algebraic boundary value problem and the construction of the generalized Green operator of this problem, constructed by S.M. Chuiko. Based on this, necessary and sufficient conditions for the solvability of the weakly nonlinear differential-algebraic boundary value problem were obtained. A typical feature of the obtained necessary and sufficient conditions for the solvability of the linear and weakly nonlinear differential-algebraic boundary-value problem is its dependence on the means of fixing of the arbitrary continuous function. An improved classification and a convergent iterative scheme for finding approximations to the solutions of weakly nonlinear differential algebraic boundary value problems was constructed in the article.

scholarly journals Sufficient conditions for hyperbolicity and consistency of the dynamic equations for fluid-saturated solids

2021 ◽  
Author(s):  
Vladimir A. Osinov
Keyword(s):  
Boundary Value Problem ◽  
Wave Speed ◽  
Boundary Value ◽  
Sufficient Conditions ◽  
Positive Definiteness ◽  
Dynamic Equations ◽  
Necessary Condition ◽  
Systems Of Equations ◽  
Acoustic Tensor ◽  
Ill Posed

AbstractPrevious studies showed that the dynamic equations for a porous fluid-saturated solid may lose hyperbolicity and thus render the boundary-value problem ill-posed while the equations for the same but dry solid remain hyperbolic. This paper presents sufficient conditions for hyperbolicity in both dry and saturated states. Fluid-saturated solids are described by two different systems of equations depending on whether the permeability is zero or nonzero (locally undrained and drained conditions, respectively). The paper also introduces a notion of wave speed consistency between the two systems as a necessary condition which must be satisfied in order for the solution in the locally drained case to tend to the undrained solution as the permeability tends to zero. It is shown that the symmetry and positive definiteness of the acoustic tensor of the skeleton guarantee both hyperbolicity and the wave speed consistency of the equations.

On the Necessary and Sufficient Conditions for the Stability of Linear Generalized Ordinary Differential, Linear Impulsive and Linear Difference Systems

2009 ◽  
Vol 16 (4) ◽  
pp. 597-616
Author(s):  
Shota Akhalaia ◽  
Malkhaz Ashordia ◽  
Nestan Kekelia
Keyword(s):  
Linear System ◽  
Difference Equations ◽  
Closed Interval ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Difference Systems ◽  
The Stability ◽  
Necessary And Sufficient ◽  
Generalized Ordinary Differential Equations ◽  
Lyapunov Sense

Abstract Necessary and sufficient conditions are established for the stability in the Lyapunov sense of solutions of a linear system of generalized ordinary differential equations 𝑑𝑥(𝑡) = 𝑑𝐴(𝑡) · 𝑥(𝑡) + 𝑑𝑓(𝑡), where and are, respectively, matrix- and vector-functions with bounded total variation components on every closed interval from . The results are realized for the linear systems of impulsive, ordinary differential and difference equations.

IDENTIFICATIONS OF HASLER'S CLASSES OF LINEAR RESISTIVE CIRCUIT STRUCTURES

2004 ◽  
Vol 13 (05) ◽  
pp. 957-980
Author(s):  
J. CEL
Keyword(s):  
Sufficient Conditions ◽  
Input Power ◽  
Maximal Entropy ◽  
Cactus Graph ◽  
Resistance Function ◽  
Total Input ◽  
Feedback Structure ◽  
Ill Posed ◽  
System Of Parameters ◽  
Necessary And Sufficient

Formulae on first and second derivatives of various functions associated with a linear nullator–norator–resistance network such as total input power, driving-point and transfer resistances with respect to parameters are established. As a consequence, the concavity of the driving-point resistance with respect to the system of parameters is obtained which generalizes a scalar result of Schneider. An example is given showing that the driving-point resistance R of a nonreciprocal one-port is not monotone or convex or concave with respect to the system of resistances which shows that the Cohn–Vratsanos and the Shannon–Hagelbarger theorems which characterize R of reciprocal one-port cannot be extended in this way. Next, a simplified variant of the Shannon–Hagelbarger theorem is used to derive separate necessary and sufficient conditions characterizing always well-posed, sometimes ill-posed and always ill-posed classes of linear resistive circuit structures introduced and characterized by Hasler, both new in formulation and proof. This reveals that the form of the second partial derivative of the resistance function is responsible for various kinds of the structural solvability of linear circuits. Alternative "if and only if" criteria for these classes are established. They involve replacements of reciprocal circuit elements by combinations of contractions and removals leading to pairs of complementary directed nullator and directed norator trees with appropriately defined signs, and resemble therefore earlier famous Willson–Nielsen feedback structure and Chua–Nishi cactus graph criteria for circuits containing traditional controlled sources. Finally, the qualitative parts of the Cohn–Vratsanos and the Shannon–Hagelbarger theorems are shown to be simple consequences of much more general principles governing all aspects of life, such as maximal entropy and energy conservation laws.

Quasi-Periodic Motion and Hopf Bifurcation of a Two-Dimensional Aeroelastic Airfoil System in Supersonic Flow

2021 ◽  
Vol 31 (02) ◽  
pp. 2150018
Author(s):  
Wentao Huang ◽  
Chengcheng Cao ◽  
Dongping He
Keyword(s):  
Hopf Bifurcation ◽  
Sufficient Conditions ◽  
Theoretical Method ◽  
Simulation Method ◽  
Runge Kutta Method ◽  
Complex Roots ◽  
The Stability ◽  
Necessary And Sufficient ◽  
2D And 3D ◽  
Imaginary Roots

In this article, the complex dynamic behavior of a nonlinear aeroelastic airfoil model with cubic nonlinear pitching stiffness is investigated by applying a theoretical method and numerical simulation method. First, through calculating the Jacobian of the nonlinear system at equilibrium, we obtain necessary and sufficient conditions when this system has two classes of degenerated equilibria. They are described as: (1) one pair of purely imaginary roots and one pair of conjugate complex roots with negative real parts; (2) two pairs of purely imaginary roots under nonresonant conditions. Then, with the aid of center manifold and normal form theories, we not only derive the stability conditions of the initial and nonzero equilibria, but also get the explicit expressions of the critical bifurcation lines resulting in static bifurcation and Hopf bifurcation. Specifically, quasi-periodic motions on 2D and 3D tori are found in the neighborhoods of the initial and nonzero equilibria under certain parameter conditions. Finally, the numerical simulations performed by the fourth-order Runge–Kutta method provide a good agreement with the results of theoretical analysis.

Coupled Stability of Multiport Systems—Theory and Experiments

1994 ◽  
Vol 116 (3) ◽  
pp. 419-428 ◽  
Author(s):  
J. E. Colgate
Keyword(s):  
Stability Property ◽  
Force Feedback ◽  
Linear Time ◽  
Experimental Studies ◽  
Sufficient Conditions ◽  
Direct Drive ◽  
Property A ◽  
Linear Time Invariant ◽  
The Stability ◽  
Necessary And Sufficient

This paper presents both theoretical and experimental studies of the stability of dynamic interaction between a feedback controlled manipulator and a passive environment. Necessary and sufficient conditions for “coupled stability”—the stability of a linear, time-invariant n-port (e.g., a robot, linearized about an operating point) coupled to a passive, but otherwise arbitrary, environment—are presented. The problem of assessing coupled stability for a physical system (continuous time) with a discrete time controller is then addressed. It is demonstrated that such a system may exhibit the coupled stability property; however, analytical, or even inexpensive numerical conditions are difficult to obtain. Therefore, an approximate condition, based on easily computed multivariable Nyquist plots, is developed. This condition is used to analyze two controllers implemented on a two-link, direct drive robot. An impedance controller demonstrates that a feedback controlled manipulator may satisfy the coupled stability property. A LQG/LTR controller illustrates specific consequences of failure to meet the coupled stability criterion; it also illustrates how coupled instability may arise in the absence of force feedback. Two experimental procedures—measurement of endpoint admittance and interaction with springs and masses—are introduced and used to evaluate the above controllers. Theoretical and experimental results are compared.

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