@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}}, } @inproceedings{8921, author = {{Panning, Lars and Sextro, Walter and Popp, Karl}}, booktitle = {{Schwingungen in rotierenden Maschinen VI SIRM, Referate der Tagung in Wien}}, editor = {{Irretier, H and Nordmann, R and Springer, H}}, pages = {{297--306}}, publisher = {{Vieweg-Verlag}}, title = {{{Schwingungsanalyse verstimmter Schaufelkränze mit Reibelementen}}}, year = {{2001}}, } @article{8922, author = {{Sextro, Walter}}, journal = {{Zeitschrift für angewandte Mathematik und Mechanik (ZAMM)}}, pages = {{225--226}}, title = {{{Heat and Wear Generation for Rolling Contacts}}}, volume = {{81}}, year = {{2001}}, } @inproceedings{8923, author = {{Sextro, Walter}}, booktitle = {{ASME Design Engineering Technical Conferences}}, number = {{DETC2001/VIB-21512}}, pages = {{1--12}}, title = {{{Development and Experimental Validation of a Point Contact Model for Dynamical Problems with Friction}}}, year = {{2001}}, } @article{8924, abstract = {{In forced systems with cyclic symmetry localization can occur due toparameter uncertainties. Often, Monte-Carlo simulations are used to findregions, where the system response is sensitive to parameteruncertainties. These simulations require a large computation time.Therefore, an approximate method to calculate the envelopes of thefrequency response functions is developed in this paper. An example of anonlinear system with cyclic symmetry is a bladed disk assembly withfriction dampers. Friction dampers can be installed underneath the bladeplatforms of turbine blades. Due to dry friction and the relative motionbetween blades and dampers, energy is dissipated, which results in areduction of blade vibration amplitudes. By optimizing the mass of thefriction dampers, the best damping effects are obtained, which lead toan increase in the reliability of the turbine. In this paper, thecalculated response of a mistuned bladed disk assembly with frictiondampers is discussed. An approximate method is developed to calculatethe envelopes of the corresponding frequency response function forstatistically varying eigenfrequencies of the blades. Regions wherelocalization can occur with a high probability, are calculated by thismethod.}}, author = {{Sextro, Walter and Popp, Karl and Krzyzynski, Tomasz}}, issn = {{0924-090X}}, journal = {{Nonlinear Dynamics}}, keywords = {{bladed disk assembly, mistuning, sensitivity, localization}}, number = {{1-3}}, pages = {{207--220}}, publisher = {{Kluwer Academic Publishers}}, title = {{{Localization in Nonlinear Mistuned Systems with Cyclic Symmetry}}}, doi = {{10.1023/A:1012915002568}}, volume = {{25}}, year = {{2001}}, } @article{8918, abstract = {{The paper deals with cyclic periodic structures modelling bladed disk assemblies of blades with friction elements for vibration damping. These elements placed between adjacent blades reduce the vibration amplitudes by means of dry friction resulting from centrifugal forces acting on the elements and relative displacements of the blades. However, the application of these friction elements results in an additional dynamical coupling which together with mistuning of some system parameters (e.g., blade eigenfrequency or contact parameters) may cause localization of vibration. In the present paper a linear approximation of such a system is investigated. The structure composed of cyclic periodic cells modelled each as a clamped-free beam interacting with each other by means of viscoelastic elements of complex stiffness is applied for dynamic system analysis. In case of free vibrations as well as in case of steady-state dynamic response to a harmonic pressure field, a perfect periodic structure and the structures with periodically mistuned parameters (blade eigenfrequencies and contact parameters) are studied. Some regularities in the dynamic response of the systems with mistuning have been noticed. Despite the fact that only a linear approximation has been used, the results and conclusions can be applied for models which describe the blade interaction in a nonlinear way.}}, author = {{Krzyzynski, Tomasz and Popp, Karl and Sextro, Walter}}, issn = {{0960-0779}}, journal = {{Chaos, Solitons \& Fractals}}, number = {{10}}, pages = {{1597 -- 1609}}, title = {{{On some regularities in dynamic response of cyclic periodic structures}}}, doi = {{10.1016/S0960-0779(99)00080-6}}, volume = {{11}}, year = {{2000}}, }