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Found 5152 publications

On the Schur component preconditioners

B. Kiss A. Krebsz

Publication Name: Computers and Structures

Publication Date: 1999-01-01

Volume: 73

Issue: 1-5

Page Range: 537-544

Description:

Some representations of the H 1/2 norm are used as Schur complement preconditioners in PCG-based domain decomposition algorithms for elliptic problems. These norm representations are efficient preconditioners. Here we give a new matrix representation of the Ha (0 < a < 1) norms by a special sparse Toeplitz matrix. It contains O(log(N)) non-zero entries at each row, where N is the number of rows. The special properties of this matrix ensure that it can be used as preconditioner. This is proved by estimating spectral equivalence constants and this fact has also been verified by numerical tests.

Open Access: Yes

DOI: 10.1016/S0045-7949(98)00258-2

Test on railway vehicle-runway dynamic system for stress analysis of a carriage's body

Emil Halmos Laszlo Bozoky Vince Nagy Zoltan Varga

Publication Name: Proceedings of the Mini Conference on Vehicle System Dynamics Identification and Anomalies

Publication Date: 1998-12-01

Volume: Unknown

Issue: Unknown

Page Range: 115-122

Description:

Damages at vehicle bodies required an analysis to qualify the vehicle-runway system. The aim of the analysis is to declare critical effects and show the possible and necessary measurements. The running tests on the vehicle had many objects. Effects of waveform could be seen in the spectral density functions for vehicles running on runway with waved rail wearing. Effects of waveforms were found to be little on the mechanical stresses of vehicle body. The curve of the runway has major effect on the values of the mechanical stresses.

Open Access: Yes

DOI: DOI not available

Mechanics and energetics, the complex analysis of an industrial problem with the tools of up-to-date computer methods

I. Zsenak J. Egert F. Zsenak

Publication Name: Proceedings of the Conference on Mechanical Engineering

Publication Date: 1998-12-01

Volume: 2

Issue: Unknown

Page Range: 805-810

Description:

The arc furnaces are widely used to melt different kind of materials on high temperature. In the steel and the aluminum factories the so-called gurgling type Heroult furnaces are used. The shell's geometry an the used arc's parameters are the function of the local expectations. The most of the arcs agree on that the water taking up released heat during the melting goes out to channels or cooling towers, leaving the energy non-utilized.

Open Access: Yes

DOI: DOI not available

Test on railway vehicle-runway dynamic system for stress analysis of a carriage's body

No authors available

Publication Name: Proceedings of the Mini Conference on Vehicle System Dynamics, Identification and Anomalies

Publication Date: 1998-12-01

Volume:

Issue:

Page Range: 115-122

Description:

Damages at vehicle bodies required an analysis to qualify the vehicle-runway system. The aim of the analysis is to declare critical effects and show the possible and necessary measurements. The running tests on the vehicle had many objects. Effects of waveform could be seen in the spectral density functions for vehicles running on runway with waved rail wearing. Effects of waveforms were found to be little on the mechanical stresses of vehicle body. The curve of the runway has major effect on the values of the mechanical stresses.

Open Access: No

DOI: DOI not available

Analysis of a hidromechanical system's stability with a simple method

No authors available

Publication Name: Proceedings of the Mini Conference on Vehicle System Dynamics, Identification and Anomalies

Publication Date: 1998-12-01

Volume:

Issue:

Page Range: 283-294

Description:

Compact built hydraulic power steering with closed center valve is very sensitive for instability. The introduced method divide the nonlinear second order differential equation system into a linear and a non linear part. Applicating the Perron's theorem for the divided equation system it is possible to find such parameter's values which do not make the system instable.

Open Access: No

DOI: DOI not available

Analysis of a hidromechanical system's stability with a simple method

Zoltan Varga

Publication Name: Proceedings of the Mini Conference on Vehicle System Dynamics Identification and Anomalies

Publication Date: 1998-12-01

Volume: Unknown

Issue: Unknown

Page Range: 283-294

Description:

Compact built hydraulic power steering with closed center valve is very sensitive for instability. The introduced method divide the nonlinear second order differential equation system into a linear and a non linear part. Applicating the Perron's theorem for the divided equation system it is possible to find such parameter's values which do not make the system instable.

Open Access: Yes

DOI: DOI not available

A multipole expansion technique in solving boundary integral equations

Csaba Gáspár

Publication Name: Computer Methods in Applied Mechanics and Engineering

Publication Date: 1998-05-11

Volume: 157

Issue: 3-4

Page Range: 289-297

Description:

The Boundary Integral Equation Method reduces the spatial dimension of an elliptic problem by converting the original n-dimensional partial differential equation to an (n - 1)-dimensional boundary integral equation defined on the boundary of the domain of the original problem. At the same time, the discretisation of the problem is also remarkably simplified. The price of these advantages, however, is that the structure, as well as the algebraic properties of the resulting boundary element matrices, are somewhat unpleasant, since they are neither sparse nor self-adjoint in general, even if the original problem is self-adjoint. Consequently, the computational cost of the Boundary Integral Equation Method seems to be unnecessarily high. To make the method more economic from a computational point of view, we present a numerical technique based on the multipole expansion method, which reduces the computational cost of the appearing matrix-vector multiplications (i.e. the evaluations of the discretized boundary integrals) by a remarkable amount. The method is applicable also to die reconstruction problem, when the inner solution is to be reconstructed from the boundary solutions. © 1998 Elsevier Science S.A.

Open Access: Yes

DOI: 10.1016/S0045-7825(97)00241-7

An Efficient Method for Checking Object-Oriented Database Schema Correctness

Michele Missikoff Anna Formica H. Dietmar Groger

Publication Name: ACM Transactions on Database Systems

Publication Date: 1998-01-01

Volume: 23

Issue: 3

Page Range: 333-369

Description:

Inheritance is introduced in object-oriented systems to enhance code reuse and create more compact and readable software. Powerful object models adopt multiple inheritance, allowing a type (or class) definition to inherit from more than one supertype. Unfortunately, in applying this powerful modeling mechanism, inheritance conflicts may be generated, which arise when the same property or operation is defined in more than one supertype. Inheritance conflicts identification and resolution is the key issue of this article. In strongly typed object-oriented systems the resolution of inheritance conflicts depends on the compatibility of the types of the conflicting definitions. In case of incompatible types, a contradiction arises. This article focuses on object-oriented databases (ODBs), providing a method aimed at supporting the designer in the construction of correct ODB schemas. The first necessary condition for schema correctness is the absence of contradictions. A second cause of schema incorrectness is due to the presence of structurally recursive types that, when defined within certain hierarchical patterns, cause the nontermination of the inheritance process. In the article, after the formal definition of a correct schema, two graph-theoretic methods aimed at verifying ODB schema correctness are analyzed. Although the first method is intuitive but inefficient, the second allows schema correctness to be checked in polynomial time, in the size of the schema. The results of this study are included in the implementation of Mosaico, an environment for ODB application design.

Open Access: Yes

DOI: 10.1145/293910.293152

Positivity of Runge-Kutta and diagonally split Runge-Kutta methods

Zoltán Horváth

Publication Name: Applied Numerical Mathematics

Publication Date: 1998-01-01

Volume: 28

Issue: 2-4

Page Range: 309-326

Description:

In this paper we study positivity of general Runge-Kutta (RK) and diagonally split Runge-Kutta (DSRK) methods when applied to the numerical solution of positive initial value problems for ordinary differential equations. Here we mean by positivity that the nonnegativity of the components of the initial vector is preserved. First we state and prove a theorem that gives conditions under which a general RK or DSRK method is positive on arbitrary positive problem set. Then we study problems which are simultaneously positive and dissipative. For such problems we give the maximal step size that - under a solvability assumption on the algebraic equations defining the method - guarantees positivity. We show how the step size threshold is governed by the radius of positivity, which is an inherent property of the scheme. This result ensures that we can construct DSRK methods which are unconditionally positive and have an order higher than 1. Note that such a method does not exist between the classical methods. Investigating the radius of positivity of RK methods further we can get rid of the additional solvability condition. In this way we can give a complete positivity analysis for RK methods. We calculate the positivity threshold for some methods, which are of practical interest. Finally we prove a theorem which generalizes the well-known result of Bolley and Crouzeix to nonlinear problems. © 1998 Elsevier Science B.V. and IMACS. All rights reserved.

Open Access: Yes

DOI: 10.1016/S0168-9274(98)00050-6