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Dnipropetrovsk, Ukraine

Zabolotnyy P.,Institute of Technical Mechanics
International Conference on Mathematical Methods in Electromagnetic Theory, MMET

The eigenfrequencies of a truncated biconical cavity with a dielectric cylinder are calculated as a function of the dielectric permittivity of the cylinder and the cone angles. The results of analytical calculation by the quasiregular approximation method are compared with the numerical results obtained using the classical scheme of the finite-element method. The range of cone angles in which the quasiregular approximation method is applicable is reported. © 2014 IEEE. Source

Sherif K.,Linz Center of Mechatronics | Witteveen W.,Magna Powertrain | Puchner K.,Magna Powertrain | Irschik H.,Johannes Kepler University | Irschik H.,Institute of Technical Mechanics
AIAA Journal

The present paper modifies and extends the recently developed equivalent static load method for the optimization of dynamically loaded linear elastic finite element systems with a huge number of degrees of freedom. In the equivalent static load method, dynamic loads have been transformed into equivalent static loads. This leads to an equivalent static response optimization with multiple loading conditions instead of a dynamic optimization problem. In the present paper, the equivalent static load algorithm is modified and extended by introducing a fatigue analysis in the iterative optimization procedure, where damage is used as suitable termination criterion of the iteration, as well as for the determination of a single and meaningful equivalent static load that leads to maximal damage in the structure. During the evolution process the structure is systematically stiffened by using the solid isotropic microstructure with penalization approach until a user-defined damage level is reached. Three standard examples from literature and an industrial application with a large number of degrees of freedom (600,000) demonstrate the computational efficiency of the proposed method. Copyright © 2010. Source

Kovalenko Y.,CINVESTAV | Gorev N.B.,Institute of Technical Mechanics | Kodzhespirova I.F.,Institute of Technical Mechanics | Prokhorov E.,CINVESTAV | Trapaga G.,CINVESTAV
Water Resources Management

This paper analyzes the convergence of a pressure-driven analysis (PDA) model of a water distribution network solver based on Todini's global gradient algorithm. The PDA model is constructed by embedding a pressure-demand relationship in the EPANET simulator code. To avoid spurious convergence, a residual-based convergence error was used. The introduction of pressure-dependent demands is shown to result in a far poorer convergence. The study of solver convergence as a function of the smoothness of the pressure-demand curve has demonstrated that, statistically, a smooth pressure-demand relationship gives a somewhat better convergence. To improve convergence, use was made of a quadratic approximation of the Hazen-Williams head loss-flow relationship in the vicinity of zero and the correct implementation of the Darcy-Weisbach formula in the solver. To further improve convergence, an iteration step control technique called the line search was used. The analysis of solver convergence for different line search variants has shown that the line search in its usual form is not efficient enough and may result in poorer convergence. A necessary error decrease algorithm, whose use in the line search improves solver convergence, is proposed. It is shown that due to the convergence improvement methods the convergence of the PDA solver is somewhat better than that of the demand-driven analysis solver and sufficient for direct problems such as design, for example. © 2014 Springer Science+Business Media Dordrecht. Source

Gorev N.B.,Institute of Technical Mechanics | Kodzhespirova I.F.,Institute of Technical Mechanics | Prokhorov E.,CINVESTAV
Journal of Hydraulic Engineering

This paper presents and discusses an extension of the pseudotransient continuation-based steady state solver for hydraulic networks proposed previously to the case of zero flow rates. The original solver, which reduces the solution of the governing nonlinear algebraic equations to the numerical integration of an initial-value problem, has problems in situations in which the head derivative of the flow rate tends to infinity, as is the case with zero flow rates. The extension is on the basis of the use of a model headloss-flow relationship that coincides with the true one at zero and has a finite head derivative at that point. This modified steady state solver is free from some convergence problems that occur in Newton-Raphson method-based solvers when analyzing a pipe network with control devices. The paper includes the results of the numerical analysis of test networks, which demonstrate the convergence of the modified steady state solver for cases in which existing steady state solvers have troubles. © 2011 American Society of Civil Engineers. Source

Gorev N.B.,Institute of Technical Mechanics | Kodzhespirova I.F.,Institute of Technical Mechanics | Prokhorov E.,CINVESTAV
Journal of Hydraulic Engineering

A procedure for the experimental convergence evaluation of a hydraulic-network solver is proposed, based on using genetic algorithms to search for network parameter values that maximize the number of iterations of the hydraulic-network solver under test. The efficiency of the method is demonstrated by the example of convergence evaluation for the EPANET hydraulic simulator. Examples of a pipe network and of combinations of parameter values for which the static solver of the simulator fails to converge in a reasonable number of iterations are given. The features of the EPANET 2.00.12 solver responsible for loss of convergence are discussed. New criteria for the automatic start of solution damping aimed at improving the convergence of the solver are proposed. The better convergence of the EPANET solver modified in accordance with these criteria is confirmed by the random and the proposed search-based testing method. © 2010 ASCE. Source

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