Miroslav Byrtus

Variable speed pumping in thermal and nuclear power plants: Frequency converter versus hydrodynamic coupling

In this paper, a comprehensive case study analysis of flow control methods and appropriate technical implementations for high-power pump systems employed in thermal and nuclear power plants or heating plants will be presented. The main attention is focused on a comparison of two advanced variable speed control strategies employing VSD with frequency converter and VSD with hydrodynamic coupling.

Sophisticated software for design and optimization of VSDs for high-power pumps: Variable speed drive with frequency converter

This paper deals with a developed software for design and optimization of variable speed drives (VSDs) for high-power water pumps and fans in power and heating plants. The paper presents the physical background of modeling and proposed models of a variable speed drive with frequency converter.

Sophisticated software for design and optimization of variable speed drives for high-power pumps: Hydrodynamic coupling versus frequency converter

This paper deals with an analysis and comparison of high-power pump systems with flow control based on variable speed drives (VSDs). The attention is focused on a comparison of two advanced variable speed control strategies employing VSD with frequency converter and VSD with hydrodynamic coupling. Due to a very different nature of both drives it is a challenging task to compare them to each other, especially, in the area where a tiny efficiency improvement causes substantial energy consumption and/or CO2 emission reduction. The paper presents comparison of both VSDs in typical fields of their application (power plant, heating plant) in the form of case study. The calculations were performed using the software which we have developed for design, optimization and sophisticated comparison of these drives. Description of physical background of modeling and proposed models is also included.

Analysis of rotor's eccentricity influence on bearing load of induction machine

To ensure reliable drive with an induction machine requires deep insight in electro-mechanical dynamics during its operation. The flexible multibody modeling technique enables the simulation of dynamic loads on all drive components. This paper focuses on complex modeling of machines behavior in case of eccentrically placed rotor. The life time of machines bearing becomes very important issue of machines maintenance and reliability and is markedly influenced by any unbalanced forces acting on the rotor. The rotor eccentricity is one of the most significant aspects making machines bearing loaded by strong unbalanced magnetic pull. Only the complex flexible model of the rotor considering all unbalanced rotor forces can provide us the very detailed information about the bearing load. The methodology of determination of such loading is applied to the 11 kW squirrel-cage induction machine.

Original Research: Combined model of bladder detrusor smooth muscle and interstitial cells

Although patients with lower urinary tract symptoms constitute a large and still growing population, understanding of bladder detrusor muscle physiology remains limited. Understanding the interactions between the detrusor smooth muscle cells and other bladder cell types (e.g. interstitial cells, IC) that may significantly contribute to coordinating and modulating detrusor contractions represents a considerable challenge. Computer modeling could help to elucidate some properties that are difficult to address experimentally; therefore, we developed in silico models of detrusor smooth muscle cell and interstitial cells, coupled through gap junctions. The models include all of the major ion conductances and transporters described in smooth muscle cell and interstitial cells in the literature. The model of normal detrusor muscle (smooth muscle cell and interstitial cells coupled through gap junctions) completely reproduced the experimental results obtained with detrusor strips in the presence of several pharmacological interventions (ryanodine, caffeine, nimodipine), whereas the model of smooth muscle cell alone (without interstitial cells) failed to reproduce the experimental results. Next, a model of overactive bladder, a highly prevalent clinical condition in both men and women with increasing incidence at older ages, was produced by modifying several processes as reported previously: a reduction of Ca2+-release through ryanodine receptors and a reduction of Ca2+-dependent K+-conductance with augmented gap junctional coupling. This model was also able to reproduce the pharmacological modulation of overactive bladder. In conclusion, a model of bladder detrusor muscle was developed that reproduced experimental results obtained in both normal and overactive bladder preparations. The results indicate that the non-smooth muscle cells of the detrusor (interstitial cells) contribute significantly to the contractile behavior of bladder detrusor muscle and should not be neglected. The model suggests that reduced Ca2+-release through ryanodine receptors and Ca2+-dependent K+-conductance together with augmented gap junctional coupling might play a major role in overactive bladder pathogenesis.

Medium voltage fan save: Energy efficient fan systems in power engineering, part 1

Fan systems, pumping systems and compressed air systems consume approximately 60% of total electricity generated worldwide. At the same time, these systems have very significant cost-effective energy saving potential. Nevertheless, the major barriers to effectively and widely apply the generally known recommendations are i) the need of individual evaluation of each application for concrete facilities ii) the lack of methodology and/or tools that would be able to sufficiently and reliably quantify the real energy saving potential for the most suitable technology both from technological and economical point of view. In this paper, we present the results of the research project which is intended to overcome these barriers. By specific, we present the developed software tool, methodology and physical background of modeling with the emphasis on comparison of conventional flow control methods to variable speed drives (VSDs). Case study results are also included.

Rigid Jeffcott Rotor Bifurcation Behaviour Using Different Models of Hydrodynamic Bearings

The paper studies dynamical behaviour of Jeffcott rotor supported by a hydrodynamic bearings. It uses different analytical formulations for hydrodynamic bearing forces acting on Jeffcott rotor. The model is nonlinear due to the presence of hydrodynamic bearings and can show different subharmonic behaviour like oil whip and oil whirl. Such a system is subjected to dynamical analysis using numerical continuation aimed at detection of nonlinear phenomena like bifurcations and unstable behaviours with respect to basic system parameters.

Steady-State Behaviour of the Rigid Jeffcott Rotor Comparing Various Analytical Approaches to the Solution of the Reynolds Equation for Plain Journal Bearing

A planar 2 DOF model of an unbalanced rigid disc on a massless rigid shaft (rigid Jeffcott rotor) is extended considering nonlinear forces in plain journal bearings. To express the fluid-film forces in the journal bearings, several approximate analytical solutions of the Reynolds equation are used, including widely used approximations for infinitely long and infinitely short journal bearing and a method using correction polynomial functions to extend the area of aspect ratios. The differences in steady-state response of such a rotor are studied. The influence of the approximate solution type, eccentricity ratio and aspect ratio is analysed. The aim is to find out the more effective approach to journal bearing description which could be further used in detailed dynamical analyses of both stable and unstable dynamic behaviour along with nonlinear phenomena like bifurcations and transitions to chaotic motions.

Natural frequencies of small squirrel cage induction machine rotor — Finite element model optimization

The paper deals with possibilities of geometry simplification for FE structural model calculating natural frequencies and mode shapes of rotor of small squirrel-cage induction motor. Proposed simplifications lead to the computing time savings while good result accuracy is preserved. All results are verified by experimental measurement.

Dynamic load of induction machine due to rotor's eccentricity and bearing clearance

The most critical part of the induction machines which determines on their life time operation are rolling element bearings. To ensure reliable drive with an induction machine requires deep insight in electro-mechanical dynamics during its operation. The flexible multibody modeling technique enables the simulation of dynamic loads on all drive components. This paper focuses on complex dynamic modeling of machines behavior in case of eccentrically placed rotor supported by nonlinear bearing with radial clearance. The life time of machines bearing becomes very important issue of machines maintenance and reliability and is markedly influenced by any unbalanced forces acting on the rotor. Only the complex electro-mechanical models of the rotor considering all unbalanced electrical and mechanical rotor forces can provide the very detailed information about the bearing load. The methodology of determination of such loading is applied to the 11 kW squirrel-cage induction machine.