VORTEX GEOMETRY OF A JET-IN-CROSSFLOW DISCHARGE

KOLAR VACLAV 한국수자원학회 2005 한국수자원학회 학술대회 Vol.2005 No.1

Does the Endothelium of Competitive Athletes Benefit from Consumption of n-3 Polyunsaturated Fatty Acid-Enriched Hen Eggs?

Luka Kolar,Marko Stupin,Ana Stupin,Petar ?u?njara,Zrinka Mihaljevi?,Anita Mati?,Ivana Juki?,Nikolina Kolobari?,Ines Drenjan?evi? 한국식품영양과학회 2021 Preventive Nutrition and Food Science Vol.26 No.4

The present study aimed to determine the effect of n-3 polyunsaturated fatty acid (PUFA)-enriched hen eggs on microvascular vasodilation, microvascular responsiveness to a stress challenge and markers of oxidative stress in competitive athletes. Competitive athletes (n=23) were divided to a control group (n=9), who consumed three regular hens’ eggs daily (249 mg n-3 PUFAs/d), and n-3 PUFAs group (n=14), who consumed three n-3 PUFA-enriched hen eggs daily (1,053 g n-3 PUFAs/d) for 3 weeks. Endothelium-dependent responses [post-occlusive reactive hyperemia (PORH) and acetylcholine-induced dilation (AChID)] and endothelium-independent responses [sodium nitroprusside-induced dilation (SNPID)] of skin microvascular blood flow were assessed by laser Doppler flowmetry in pre- and post-acute exhausting exercise (AEE) sessions. Blood pressure, serum lipid, free fatty acids profiles, and biomarkers of oxidative stress were measured before and after each dietary protocol. Consumption of serum n-3 PUFAs significantly decreased the n-6/n-3 ratio and enhanced PORH and AChID, but did not affect SNPID at rest. Furthermore, serum glutathione peroxidase and superoxide dismutase activities were significantly decreased in the n-3 PUFAs group but remained unchanged in the control group. In both groups, PORH, AChID, and SNP were significantly reduced post-AEE compared with pre-AEE, both before and after consumption of each diet. Only AChID responsiveness to AEE (ΔAChID) significantly increased following consumption of n-3 PUFAs. Overall, n-3 PUFAs supplementation as n-3 PUFA-enriched hen eggs enhanced microvascular endothelial function at rest and may contribute to adaptation to AEE in competitive athletes.

Impact of Power Density Maximization on Efficiency of DC-DC Converter Systems

J.W. Kolar,J. Biela,U. Badstubner 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

The demand for decreasing costs and volume leads to a constantly increasing power density of industrial converter systems. In order to improve the power density further different aspects, like thermal management and electromagnetic effects must be considered in conjunction with the electrical design. Therefore, a comprehensive optimization procedure based on analytical models for minimizing volume of dc-dc converter systems has been developed at the Power Electronic Systems Laboratory of the ETH Zurich. Based on this procedure three converter topologies ? a phase shift converter with current doubler and with capacitive output filter and a series-parallel resonant converter ? are optimized with respect to power density for a telecom supply (400V/48V). There, the characteristic of the power density, the efficiency and the volume distribution between the components as function of frequency is discussed. For the operating points with maximal power density also the loss distribution is presented. Furthermore, the sensitivity of the optimum with respect to junction temperature, cooling and core material is investigated. The highest power density is achieved by the series-parallel resonant converter. For a 5 ㎾ supply a density of approximately 12 ㎾/ltr. and a switching frequency of ca. 130 ㎑ results.

A Novel Interactive Power Electronics Seminar (iPES) Developed at the Swiss Federal Institute of Technology (ETH) Zurich

Drofenik, Uwe,Kolar, Johann W. The Korean Institute of Power Electronics 2002 JOURNAL OF POWER ELECTRONICS Vol.2 No.4

This paper introduces the Interactive Power Electronics Seminar - iPES - a new software package for teaching of fundamentals of power electronic circuits and systems. iPES is constituted by HTML text with Java applets for interactive animation, circuit design and simulation and visualization of electromagnetic fields and thermal issues in power electronics. It does comprise an easy-to-use self-explaining graphical user interface. The software does need just a standard web-browser, i.e. no installations are required. iPES can be accessed via the World Wide Web or from a CD-ROM in a stand-alone PC by students and professionals. Due to the underlying software technology iPES is very flexible and could be used for on-line learning and could easily be integrated into an e-learning platform. The aim of this paper Is to give an introduction to the iPES-project and to show the different areas covered. The e- learning software is available at no costs at $\underline{www.ipes.ethz.ch}$ in English, German, Japanese, Korean, Chinese and Spanish. The project is still under development and the web page is updated in about 4 weeks intervals.

Comparison of Winding Concepts for Bearingless Pumps

K. Raggl,J. W. Kolar,T. Nussbaumer 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

Bearingless slice motors as employed in semiconductor, pharmaceutical and medical industry perform magnetic levitation by radial bearing forces and rotation by tangential forces. This requires bearing and drive windings, which can be realized as separate bearing and drive coils or as identical, concentrated coils on the stator claws. In this paper, a detailed comparison between these two winding concepts is undertaken, where the coil losses, the coil volume, the power electronics requirements and the achievable rotation speed are evaluated. Furthermore, practical features such as control complexity, cabling effort and manufacturability are taken into account. Finally, the trade-off between losses, volume and realization effort will be discussed in order to give a guideline for the selection of the appropriate winding concept for a specific application of a bearingless pump.

A Novel Low-Loss Modulation Strategy for High-Power Bi-directional Buck+Boost Converters

S. Waffler,J. W. Kolar 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

A novel low-loss, constant-frequency, zerovoltage-switching (ZVS) modulation strategy for bi-directional, cascaded, buck-boost DC/DC converters, used in a hybrid electrical vehicle (HEV), is presented and its benefits over state-of-the-art converters and soft-switching solutions are discussed in a comparative evaluation. To obtain ZVS with the purposed modulation strategy, the buck+boost inductance is selected and the switches are gated in a way that the inductor current has a negative offset current at the beginning and the end of each pulse period. This allows the MOSFET switches to turn on when the anti-parallel body diode is conducting. As the novel modulation strategy is a software-only solution, there are no additional expenses for active or passive components compared to conventional modulation implementations. Furthermore, an analytical and simulation investigation predicts an excellent efficiency over the complete operating range and a higher power density for a multi-phase converter equipped with the low-loss modulation. Experimental measurements performed with a converter prototype verify the mode of operation and the ZVS principle.

A Novel Approach for 3D Air Gap Reluctance Calculations

J. Muhlethaler,J. W. Kolar,A. Ecklebe 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

An approach to accurately calculate the reluctance of an air gap is introduced. The approach is easy to handle as it is based on a modular concept where a simple basic geometry is used as a building block to describe different three dimensional air gap shapes. A high degree of accuracy is achieved as the approach is based on an analytical field solution.

Optimization of Wheat Harvest

Kim, S.H.,Kolaric, W.J. Korean Society for Agricultural Machinery 2000 Agricultural and Biosystems Engineering Vol.1 No.1

Optimization was considered from three perspectives : minimum grain loss, minimum damaged grain loss, and minimum power consumption. Factors affecting combine performance were classified as control, adjustable, and environmental. Control and adjustable factors were optimized by the parameter design developed by Taguchi. Environmental factors were used as input for optimization. Optimum range for control and adjustable factors are presented. Parameter design was adequate to obtain the optimum levels of control factors and optimum range of adjustable factors.

Loss Modeling of Inductive Components Employed in Power Electronic Systems

J. Muhlethaler,J. W. Kolar,A. Ecklebe 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Loss models of inductive components are thoroughly investigated, thereby all different aspects of loss modeling are considered. The impact of peak-to-peak flux density ?B, frequency f, DC premagnetization HDC, temperature T, core shape, minor and major loops, flux waveform, and material on core loss calculation are considered. In order to calculate winding losses, formulas for round conductors and litz wires, each including skin- and proximity effects (including the influence of an airgap fringing field) are included. A high level of accuracy is achieved by combining the best state-of-the-art approaches and by embedding newly-developed approaches into a novel loss calculation framework. The loss models are verified by FEM simulations and experimental measurements.

A Comparison of Separated and Combined Winding Concepts for Bearingless Centrifugal Pumps

Raggl, Klaus,Nussbaumer, Thomas,Kolar, Johann W. The Korean Institute of Power Electronics 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.2

Bearingless centrifugal pump systems are employed in the semiconductor, pharmaceutical and medical industries due to their facility for pumping high purity fluids without particle contamination. Two types of forces have to be generated by the stator units, namely bearing forces for achieving magnetic levitation, and drive forces for producing the needed pump torque. The generation of these forces requires bearing and drive windings, which can be realized as separate bearing and drive coils or as identical, combined coils on the stator claws. In this paper, a detailed comparison between these two winding concepts is undertaken, whereby the copper losses, the power electronics losses, and the achievable pump output pressure are evaluated for both concepts. For each criterion a ratio of improvement is calculated analytically which allows evaluation of the performance of the two winding concepts for any given pump operating point and design. Finally, also practical features such as control complexity, cabling effort and manufacturability are discussed and measurements on prototype systems are carried out to validate the considerations.