@inbook{9536, abstract = {{This paper presents a model for unsteady longitudinal slippage of a loaded rubber wheel. The aim of modelling was to calculate the dynamical contact behavior in a numerical efficient way. Further on, simulation results are compared to experimental data.}}, author = {{Gutzeit, F and Sextro, Walter and Kröger, Matthias}}, booktitle = {{Analysis and Simulation of Contact Problems}}, editor = {{Wriggers, Peter and Nackenhorst, Udo}}, isbn = {{978-3-540-31760-9}}, pages = {{261--270}}, publisher = {{Springer Berlin Heidelberg}}, title = {{{Unsteady rolling contact of rubber wheels}}}, doi = {{10.1007/3-540-31761-9_29}}, volume = {{27}}, year = {{2006}}, } @inproceedings{9542, author = {{Hofmeisterro, Adolf and Sextro, Walter and Röschel, Otto}}, booktitle = {{Proceedings of EUCOMES, the first European Conference on Mechanism Science}}, pages = {{1--12}}, title = {{{Error-Workspace Analysis of Plane Mechanisms}}}, year = {{2006}}, } @inbook{9551, abstract = {{Friction occurs in the contact between tyre and road. The friction of rubber material on dry surfaces is dominated by hysteresis and adhesion effects. Hysterisis friction is characterised by the energy dissipation within the visco-elastic material, which is caused by its deformation while passing the surface roughness. Hysteresis effects are modelled by an extended linear visco-elastic material with several Maxwell elements. The development of a model in the time domain allows to consider nonlinear effects. Additionally temperature effects are taken into account based on the WLF-transformation. Adhesion forces originate from molecular bindings between the contact partners. This effect is simulated by applying a modified model of Achenbach on real surfaces. The temperature distribution within the friction contact region is investigated experimentally as well. Furthermore global stick-slip vibrations of a rubber block element are investigated using a global contact model. Numerical results are compared with experiments performed on a tribometer test rig.}}, author = {{Sextro, Walter and Moldenhauer, Patrick and Wangenheim, M and Lindner, Markus and Kröger, Matthias}}, booktitle = {{Analysis and Simulation of Contact Problems}}, editor = {{Wriggers, Peter and Nackenhorst, Udo}}, isbn = {{978-3-540-31760-9}}, pages = {{243--252}}, publisher = {{Springer Berlin Heidelberg}}, title = {{{Contact behaviour of a sliding rubber element}}}, doi = {{10.1007/3-540-31761-9_27}}, volume = {{27}}, year = {{2006}}, } @article{9266, abstract = {{The present paper deals with the forced vibration analysis of a test structure. The test structure consists of two parts, an upper and a lower half pipe, joint in two bolted flanges which represent the extended friction contacts. Depending on the clamping loads different normal pressure distributions can be established in the contact interfaces. Since the test structure is loaded with a harmonic external force relative displacements occur in the contact interface. This leads to microslip effects affecting the dynamic behaviour. The experimental validation of the calculation method accounting for these effects is shown by comparing measured and calculated frequency response functions (FRF). ({\^A}{\copyright} 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}}, author = {{Genzo, Alexander and Sextro, Walter and Popp, Karl}}, issn = {{1617-7061}}, journal = {{PAMM}}, number = {{1}}, pages = {{91--92}}, publisher = {{WILEY-VCH Verlag}}, title = {{{Analysis of the Forced Vibration of Two Bolted Half-Pipes with Extended Friction Contacts}}}, doi = {{10.1002/pamm.200510026}}, volume = {{5}}, year = {{2005}}, } @article{9526, abstract = {{The present paper deals with the forced vibration analysis of a test structure. The test structure consists of two parts, an upper and a lower half pipe, joint in two bolted flanges which represent the extended friction contacts. Depending on the clamping loads different normal pressure distributions can be established in the contact interfaces. Since the test structure is loaded with a harmonic external force relative displacements occur in the contact interface. This leads to microslip effects affecting the dynamic behaviour. The experimental validation of the calculation method accounting for these effects is shown by comparing measured and calculated frequency response functions (FRF). ({\^A}{\copyright} 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}}, author = {{Genzo, Alexander and Sextro, Walter and Popp, Karl}}, issn = {{1617-7061}}, journal = {{PAMM}}, number = {{1}}, pages = {{91--92}}, publisher = {{WILEY-VCH Verlag}}, title = {{{Analysis of the Forced Vibration of Two Bolted Half-Pipes with Extended Friction Contacts}}}, doi = {{10.1002/pamm.200510026}}, volume = {{5}}, year = {{2005}}, } @article{9529, abstract = {{In dieser Arbeit wird ein analytisches Berechnungsverfahren vorgestellt, mit dem der gesamte Positions- und Orientierungsraum (ErrorWorkspace) ebener Mechanismen mit spielbehafteten Gelenken kinematisch beschrieben bzw. dargestellt werden kann. Für die Berechnung wird der gesamte Positions- und Orientierungsraum im Kinematischen Bildraum dargestellt, wobei auf besondere Merkmale eingegangen wird. Der ErrorWorkspace, der mit Hilfe des Berechnungsverfahren bestimmt wird, wird an einem Koppelgetriebe, an einem Filmgreifergetriebe und an einem Double-rocker four-bar mechanism mit Kurbelantrieb dargestellt und analysiert. ({\copyright} 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}}, author = {{Hofmeister, Adolf and Sextro, Walter and Röschel, Otto}}, issn = {{1617-7061}}, journal = {{PAMM}}, number = {{1}}, pages = {{201--202}}, publisher = {{WILEY-VCH Verlag}}, title = {{{Unkontrollierbare Bewegungen ebener Mechanismen mit Gelenkspiel}}}, doi = {{10.1002/pamm.200510078}}, volume = {{5}}, year = {{2005}}, } @inproceedings{8952, abstract = {{In turbomachinery, friction contacts are widely used to reduce dynamic stresses in turbine blades in order to avoid expensive damages. As a result of energy dissipation in the friction contacts the blade vibration amplitudes are reduced. In case of so-called friction dampers, which are pressed on the platforms of the blades by centrifugal forces, the damping effect can be optimized by varying the damper mass. This optimization can be done by means of a simulation model applying the so-called component mode synthesis and the Harmonic Balance Method to reduce computation time. It is based on the modal description of each substructure. In a real turbine or compressor blading great differences in the magnitude of the individual blade amplitudes occur caused by unavoidable mistuning of all system parameters like contact parameters and natural frequencies of the blades. It may happen that most of the blades experience only small stresses whereas a few blades experience critical stresses. Therefore, it is necessary to consider mistuning for all system parameters to simulate the forced response of bladed disk assemblies with friction contacts. For a mistuned bladed disk the complete system has to be modeled to calculate the dynamic response. In practice, usually the standard deviations instead of the distributions of the system parameters are known. Therefore, Monte-Carlo simulations are necessary to calculate the forced response of the blades for given mean values and standard deviations of the system parameters. To reduce the computational time, an approximate method has been developed and extended for small and moderate standard deviations of the system parameters to calculate the distribution and the envelopes of the frequency response functions for statistically varying system parameters, in the following called statistical mistuning. The approximate method is based on a sensitivity analysis and the assumption of a Weibull distribution of the vibration amplitudes of the blades. Both, the approximate method and the assumption of a Weibull distribution of the vibration amplitudes are validated by Monte-Carlo simulations. By these investigations the influence of different arrangements of the system parameters for given mean values and standard deviations of the vibration amplitudes of the blades can be determined, too. For the present investigations only a small influence of the arrangement of blades with respect to their natural frequencies has been observed. On the other hand, an intentional mistuning of the damper masses and the natural frequencies of the blades in a systematic way, in the following called systematic mistuning, can be investigated to reduce the amplitudes of the system. The simulation results of a systematic mistuning has been validated by a test rig with a rotating bladed disk assembly with friction dampers. The investigations show a good agreement between the simulations and the measurements but only a slight decrease of the maximum amplitudes in case of a systematic mistuning. Copyright {\copyright} 2004 by ASME}}, author = {{Götting, Florian and Sextro, Walter and Panning, Lars and Popp, Karl}}, booktitle = {{Proceedings of ASME TURBO Expo, Power for Land, Sea, and Air}}, keywords = {{Friction, Disks}}, number = {{GT2004-53310}}, pages = {{257--267}}, title = {{{Systematic mistuning of bladed disk assemblies with friction contacts}}}, volume = {{6}}, year = {{2004}}, } @article{9520, abstract = {{Friction, especially friction of elastomers, can cause acoustic problems like noise, squeal and comfort drawbacks like vibrations and wear. Therefore, rubber friction affects the function of many products in technical applications, e.g. seals, belts and tires. It can be classified according to different physical phenomena like adhesion, hysteresis, cohesion and viscous friction, see [3]. The topic of this paper is hysteresis friction of rubber that is caused by the energy dissipation due to internal material damping during the process of deformation. The deformation itself occurs during the sliding of a rubber element across the micro-scaled asperities of a rough surface. In this paper, the sliding process of a rubber element over real surfaces is simulated in time domain and compared to experiments. ({\^A}{\copyright} 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}}, author = {{Lindner, Markus and Sextro, Walter and Popp, Karl}}, issn = {{1617-7061}}, journal = {{PAMM}}, number = {{1}}, pages = {{101--102}}, publisher = {{WILEY-VCH Verlag}}, title = {{{Hysteretic Friction of a Sliding Rubber Element}}}, doi = {{10.1002/pamm.200410032}}, volume = {{4}}, year = {{2004}}, } @inproceedings{9523, abstract = {{During operation, the rotating blades of a gas turbine are subjected to centrifugal forces as well as fluctuating gas forces, resulting in blade vibrations. In addition to material damping, aerodynamical and blade root damping, underplatform dampers are widely used to increase the amount of damping and to decrease blade vibration amplitudes. The friction forces generated by the relative displacements between the underplatform damper and the blade platforms provide a significant amount of energy dissipation. In practice, a number of different underplatform damper designs are applied. Basically, these are wedge dampers with flat contact areas, cylindrical dampers with curved surfaces or asymmetrical dampers with both flat contact surfaces on one side and curved contact surfaces on the other. The latter damper type combines the advantages of both the wedge and the cylindrical damper by preventing the damper from pure rolling on the one hand as it has been observed for cylindrical dampers and on the other hand, avoiding a diverged plane area contact in case of a wedge damper, causing a damper lift-off. This paper will focus on the investigation of cylindrical and asymmetrical underplatform dampers. A comparison between measurements of rotating assemblies in Siemens PG gas turbines (V84.2, V64.3A and V94.3A(2)) under test and real operating conditions with cylindrical and asymmetrical underplatform dampers and the predictions of the developed theoretical model are presented. Special attention is paid to the frequency shift due to the application of an underplatform damper, since in particular for stationary gas turbines, in addition to the amplitude reduction, the accurate prediction of the resonance frequency is of major interest. Copyright {\copyright} 2004 by ASME}}, author = {{Panning, Lars and Popp, Karl and Sextro, Walter and Götting, Florian}}, booktitle = {{Proceedings of ASME TURBO Expo, Power for Land, Sea, and Air}}, keywords = {{Dampers, Gas turbines}}, number = {{GT2004-53316}}, pages = {{269--280}}, title = {{{Asymmetrical Underplatform Dampers in Gas Turbine Bladings: Theory and Application}}}, doi = {{10.1115/GT2004-53316}}, volume = {{6}}, year = {{2004}}, } @inproceedings{8933, author = {{Götting, Florian and Sextro, Walter and Panning, Lars and Popp, Karl}}, booktitle = {{Schwingungen in rotierenden Maschinen VI SIRM, Referate der Tagung in Darmstadt}}, editor = {{Irretier , H and Nordmann, R and Springer, H}}, pages = {{201--210}}, publisher = {{Vieweg-Verlag}}, title = {{{Schwingungsverhalten von verstimmten Beschaufelungen mit Reibelementen}}}, year = {{2003}}, } @article{8934, abstract = {{Im Folgenden wird eine Berechnungsmethode vorgestellt, die es erlaubt, das räumliche Schwingungsverhalten eines elastischen Mehrkörpersystems (EMKS) mit Reibkontakten in rechenzeit- und speicherplatzsparender Form zu analysieren. Der von trockener Reibung und Mikroschlupf geprägte, nichtlineare Dämpfungsmechanismus in den Reibkontakten eines EMKS wird dabei realitätsnahe abgebildet. Die Plausibilität der mit der Methode gewonnenen Berechnungsergebnisse wird beispielhaft an einem einfachen EMKS, einem in Längsrichtung geteilten, einseitig eingespannten Balken gezeigt. Für den geteilten Balken werden die Frequenzgänge des Torsionswinkels um die Längsachse und der Auslenkung um die biegeweiche Achse berechnet.}}, author = {{Genzo, Alexander and Sextro, Walter and Popp, Karl}}, issn = {{1617-7061}}, journal = {{PAMM}}, number = {{1}}, pages = {{120--121}}, publisher = {{WILEY-VCH Verlag}}, title = {{{Erzwungene Schwingungen von elastischen Mehrkörpersystemen mit Reibkontakten}}}, doi = {{10.1002/pamm.200310046}}, volume = {{2}}, year = {{2003}}, } @article{8937, abstract = {{Friction damping devices such as underplatform dampers are widely used in turbomachinery applications to reduce blade vibration amplitudes. In this paper, a model is presented briefly to calculate the forced response of mistuned bladed systems with friction dampers. Some results will give an insight in the vibrational behavior of frictionally damped bladed disks and how the damping gain is affected by the damper properties.}}, author = {{Panning, Lars and Sextro, Walter and Popp, Karl}}, issn = {{1617-7061}}, journal = {{PAMM}}, number = {{1}}, pages = {{118--119}}, publisher = {{WILEY-VCH Verlag}}, title = {{{Design of Friction Dampers for Mistuned Bladed Disks}}}, doi = {{10.1002/pamm.200310336}}, volume = {{3}}, year = {{2003}}, } @article{8938, author = {{Panning, Lars and Sextro, Walter and Popp, Karl}}, journal = {{International Journal of Rotating Machinery}}, number = {{3}}, pages = {{219--228}}, publisher = {{Hindawi Publishing Corporation}}, title = {{{Spatial dynamics of tuned and mistuned bladed disks with cylindrical and wedge-shaped friction dampers}}}, volume = {{9}}, year = {{2003}}, } @article{8939, author = {{Popp, Karl and Panning, Lars and Sextro, Walter}}, journal = {{Journal of Vibration and Control}}, pages = {{419--448}}, title = {{{Vibration Damping by Friction Forces -Theory and Applications}}}, volume = {{9}}, year = {{2003}}, } @inproceedings{8940, author = {{Sextro, Walter and Popp, Karl}}, booktitle = {{Forschungsvereinigung Verbrennungskraftmaschinen (FW)}}, number = {{753}}, pages = {{40}}, title = {{{Optimierung des Schwingungsverhaltens elastischer Strukturen mit Reibfugen am Beispiel von Turbomaschinenschaufeln}}}, year = {{2003}}, } @inproceedings{8941, abstract = {{Numerical predictions of the forced vibration of a disc assembly including frictional effects between the shrouds are presented concerning engineering needs for the blade design process. Assuming a tuned disc assembly, numerical static, free and then forced vibration analyses of a shrouded turbine blade measured in the spin pit are performed systematically. For the excitation forces of an air jet evaluated from the fairly linear behavior of the experimental blade resonance peaks, the reliability of the proposed approach is validated through the very close agreement of the computed and measured resonant peaks. These resonant peaks demonstrate either a fairly linear behavior or a non-linear one like the jump effect of blade resonance amplitudes, or elastic impacts between the shrouds. Also, the damping performance for different contact configurations between the shrouds is numerically analyzed. These numerical results indicate that the shrouds generate higher frictional damping for small angles (0--30 deg) between the circumferential direction and the normal vector to the contact surface. Copyright {\copyright} 2003 by ASME}}, author = {{Szwedowicz, J and Sextro, Walter and Visser, R and Masserey, P.A}}, booktitle = {{ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference}}, isbn = {{0-7918-3687-8}}, keywords = {{Turbine blades, Vibration}}, number = {{GT2003-38808}}, title = {{{On forced vibration of shrouded turbine blades}}}, doi = {{doi:10.1115/GT2003-38808}}, year = {{2003}}, } @inproceedings{8928, author = {{Panning, Lars and Sextro, Walter and Popp, Karl}}, booktitle = {{Proceedings of ASME TURBO Expo, Power for Land, Sea, and Air}}, number = {{GT- 2002-30429}}, title = {{{Optimization of the Contact Geometry between Turbine Blades and Underplatform Dampers with respect to Friction Damping}}}, year = {{2002}}, } @inproceedings{8929, author = {{Panning, Lars and Sextro, Walter and Popp, Karl}}, booktitle = {{Proceedings of the 9th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC}}, title = {{{Spatial dynamics of tuned and mistuned bladed disks with cylindrical and wedge-shaped friction dampers}}}, year = {{2002}}, } @inproceedings{8931, author = {{Sextro, Walter and Panning, Lars and Götting, Florian}}, booktitle = {{Proceedings of ASME TURBO Expo, Power for Land, Sea, and Air}}, number = {{GT- 2002-30427}}, title = {{{Fast Calculation of the Statistics of the Forced Response of Mistuned Bladed Disk Assemblies with Friction Contacts}}}, year = {{2002}}, } @inproceedings{8932, author = {{Sextro, Walter and Popp, Karl}}, booktitle = {{Forschungsvereinigung Verbrennungskraftmaschinen (FW) - lnformationstagung Turbinen}}, number = {{518}}, pages = {{157--183}}, title = {{{Optimierung des Schwingungsverhaltens elastischer Strukturen mit Reibfugen}}}, year = {{2002}}, }