Publications
192 results found
Chabchoub A, Vitanov N, Hoffmann N, 2010, Experimental Evidence for Breather Type Dynamics in Freak Waves, PAMM, Vol: 10, Pages: 495-496, ISSN: 1617-7061
Withalm M, Röper J, Hoffmann NP, 2010, Linear stability analysis of oscillating Ekman boundary layers, PAMM, Vol: 9, Pages: 489-490, ISSN: 1617-7061
Hoffmann NP, Withalm M, 2010, Solitary Roll Vortices in the Mixed Convection of a Vertical Fluid Layer, PAMM, Vol: 9, Pages: 475-476, ISSN: 1617-7061
Withalm M, Hoffmann NP, 2010, Simulation of full-scale ice-structure-interaction by an extended Matlock-model, COLD REGIONS SCIENCE AND TECHNOLOGY, Vol: 60, Pages: 130-136, ISSN: 0165-232X
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- Citations: 23
Gdaniec P, Weiss C, Hoffmann NP, 2010, On chaotic friction induced vibration due to rate dependent friction, MECHANICS RESEARCH COMMUNICATIONS, Vol: 37, Pages: 92-95, ISSN: 0093-6413
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- Citations: 15
Kruse S, Hoffmann N, 2010, A Minimal Model to Explore the Influence of Distant Modes on Mode‐Coupling Instabilities, International Conference of Numerical Analysis and Applied Mathematics 2010, Pages: 1411-1414
Weiss C, Hothan A, Morlock M, et al., 2009, Friction-induced vibration of artificial hip joints, GAMM Mitteilungen, Vol: 32, Pages: 193-204, ISSN: 0936-7195
A hip replacement system is analysed with respect to its susceptibility to friction induced vibrations under laboratory conditions and in a pseudo-in vivo setup. The method of complex eigenvalue extraction within the framework of finite-element modelling and analysis is used to identify the geometric properties and system parameters that might lead to unstable sliding states. The approach presented reveals negatively damped eigenmodes for both the pseudo-in vivo setup and the not-implanted system under laboratory conditions without boundary conditions. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Wernitz B, Hoffmann N, 2009, New Approaches to Signal Analysisof Friction Noise and Vibration, IMechE International Conference of Braking 2009
Hoffmann NP, Ciavarella M, Stolz U, et al., 2009, The effect of long-wavelength stiffness variation on wear pattern generation, JOURNAL OF SOUND AND VIBRATION, Vol: 322, Pages: 785-797, ISSN: 0022-460X
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- Citations: 3
Withalm M, Hoffmann NP, 2009, On new localized vortex solutions in the couette-ekman layer, Advances in Turbulence XII - Proceedings of the 12th EUROMECH European Turbulence Conference, Pages: 111-114
Vitanov N, Hoffmann N, 2009, ON PROBABILITY FOR ROGUE WAVES IN THE NORTH SEA, COMPTES RENDUS DE L ACADEMIE BULGARE DES SCIENCES, Vol: 62, Pages: 187-194, ISSN: 1310-1331
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- Citations: 3
Withalm M, Hoffmann NP, 2009, On New Localized Vortex Solutions in the Couette-Ekman Layer, 12th EUROMECH European Turbulence Conference, Publisher: SPRINGER-VERLAG BERLIN, Pages: 111-114, ISSN: 0930-8989
Hoffmann N, Gaul L, 2008, Friction Induced Vibrations of Brake Systems: Research Fields and Activities, SAE 26th Brake Colloquium
Hoffmann N, 2008, An extended minimal modelfor wear pattern generation, International Journal of Pure and Applied Mathematics, Vol: 49, Pages: 349-355
Hoffmann N, 2008, On the role of the random nature of friction in friction induced mode-coupling instability, 7th European Conference on Structural Dynamics
Hoffmann NP, Gaul L, 2008, Friction induced vibrations of brakes: Research fields and activities, ISSN: 0148-7191
Friction induced vibrations in brakes are a topic of major interest and concern for the automotive industry. The structural vibrations that may occur, as well as the audible noise that can be related to them, may lead to consequences as diverse as driver discomfort, maintenance requirements, and even safety issues. Although friction induced vibrations are known already since the beginnings of friction brake design, a generally accepted consensus on many aspects, like fundamental mechanisms or generic solution approaches, seems still to be debated. The present paper attempts to shed some light on the reasons for these persisting difficulties. A review of the different classes of phenomena appearing is given, which could be understood as an attempt to limit the scope of phenomena considered as friction induced. Research topics and disciplines involved will be identified and a clarification of achievements and unanswered questions will be attempted. Due to the enormous amount of work that has been done on the general topic during the last at least five centuries, and in the context of vehicle friction brakes during at least one century, it is of course not claimed to give an exhaustive and in-depth review of each and any line of thought and investigation. However, by synoptically bringing together the phenomenological as well as the disciplinary points of view, a contribution to explaining remaining difficulties and to addressing open research tasks is attempted. © 2008 SAE International.
Hoffmann NP, Gaul L, 2008, Friction induced vibrations of brakes: Research fields and activities, ISSN: 0148-7191
Friction induced vibrations in brakes are a topic of major interest and concern for the automotive industry. The structural vibrations that may occur, as well as the audible noise that can be related to them, may lead to consequences as diverse as driver discomfort, maintenance requirements, and even safety issues. Although friction induced vibrations are known already since the beginnings of friction brake design, a generally accepted consensus on many aspects, like fundamental mechanisms or generic solution approaches, seems still to be debated. The present paper attempts to shed some light on the reasons for these persisting difficulties. A review of the different classes of phenomena appearing is given, which could be understood as an attempt to limit the scope of phenomena considered as friction induced. Research topics and disciplines involved will be identified and a clarification of achievements and unanswered questions will be attempted. Due to the enormous amount of work that has been done on the general topic during the last at least five centuries, and in the context of vehicle friction brakes during at least one century, it is of course not claimed to give an exhaustive and in-depth review of each and any line of thought and investigation. However, by synoptically bringing together the phenomenological as well as the disciplinary points of view, a contribution to explaining remaining difficulties and to addressing open research tasks is attempted. © 2008 SAE International.
Hoffmann NP, Weiß C, 2007, Effects of rate and state dependent friction on the stability of steady sliding, VDI Berichte, Pages: 195-205, ISSN: 0083-5560
The influence of LuGre-type friction on the fundamental mechanisms resulting in linear instability of steady sliding is investigated. Both a velocity-dependent kinetic friction coefficient as well as mode-coupling are considered. It turns out that the destabilizing effect of a kinetic friction coefficient that decreases with relative sliding velocity is reduced when the rate-dependent effects of LuGre-type friction are introduced and become more pronounced. Mode-coupling instability however seems to be much more robust with respect to underlying rate-dependencies.
Hoffmann NP, Misol M, 2007, On the role of varying normal load and of randomly distributed relative velocities in the wavelength selection process of wear-pattern generation, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, Vol: 44, Pages: 8718-8734, ISSN: 0020-7683
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- Citations: 7
Hoffmann N, 2007, On wear pattern generation in elastic systems, PAMM, Vol: 7, Pages: 4050003-4050004, ISSN: 1617-7061
Hoffmann NP, 2007, Linear stability of steady sliding in point contacts with velocity dependent and LuGre type friction, JOURNAL OF SOUND AND VIBRATION, Vol: 301, Pages: 1023-1034, ISSN: 0022-460X
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- Citations: 27
Keitzel H, Hoffmann N, 2006, Influence of the contact model on the onset of sprag‐slip, PAMM, Vol: 6, Pages: 311-312, ISSN: 1617-7061
<jats:title>Abstract</jats:title><jats:p>In systems with sliding‐friction often strong self‐excited vibrations do occur. One of the possible underlying mechanisms is the so‐called sprag‐slip instability. In the present work the onset of sprag‐slip is investigated by a simple model in which an inclined elastic beam slides over a rigid belt moving with constant velocity. For a Coulomb friction law and a contact model with constant contact stiffness for a certain range of parameters the system loses its static solution corresponding to the steady sliding state. Simultaneously with this loss of existence of the static solution the qualitative properties of the system's flow field in phase space change, resembling a transition from stable to unstable behavior. To investigate the influence of contact models and related parameters on the details of this onset of sprag‐slip also Hertz theory of elastic contact is applied. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)</jats:p>
Hoffmann N, 2006, Transient growth and stick-slip in sliding friction, JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME, Vol: 73, Pages: 642-647, ISSN: 0021-8936
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- Citations: 11
Hoffmann N, Gaul L, 2006, A stochastic averaging approach for printed circuit boards with nonlinear damping characteristics subjected to random vibration loads, MECHANICS RESEARCH COMMUNICATIONS, Vol: 33, Pages: 385-393, ISSN: 0093-6413
Hoffmann N, Wagner N, Gaul L, 2005, Quenching mode-coupling friction-induced instability using high-frequency dither, JOURNAL OF SOUND AND VIBRATION, Vol: 279, Pages: 471-480, ISSN: 0022-460X
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- Citations: 25
Abele M, Leohold J, Müller W, et al., 2004, Modellierung und Bewertung fehlertoleranter Energiebordnetz-Architekturen für X-by-Wire-Systeme, VDI Berichte, Pages: 259-280, ISSN: 0083-5560
Hoffmann N, Gaul L, 2004, Non-conservative beating in sliding friction affected systems: transient amplification of vibrational energy and a technique to determine optimal initial conditions, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, Vol: 18, Pages: 611-623, ISSN: 0888-3270
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- Citations: 11
Hoffmann N, Gaul L, 2004, A sufficient criterion for the onset of sprag-slip oscillations, ARCHIVE OF APPLIED MECHANICS, Vol: 73, Pages: 650-660, ISSN: 0939-1533
Hoffmann N, Bieser S, Gaul L, 2004, Harmonic Balance and Averaging Techniques for Stick-Slip Limit-CycleDetermination in Mode-Coupling Friction Self-Excited Systems, Technische Mechanik, Vol: 24, Pages: 185-197
Barthlott J, Schlechter V, Hoffmann N, et al., 2004, Modeling and simulation of future vehicle powernets, SAE Technical Papers, ISSN: 0148-7191
Future vehicle electrical systems will differ substantially from current ones due to rising requirements. For example driver-assistance and drive-by-wire systems will lead to novel and demanding electrical load profiles which in turn will pose new requirements on the electrical system. Furthermore safety concepts, reliability, availability and diagnosis are getting increasingly important in such systems and thus also in the vehicle's electrical system. In order to meet the upcoming requirements new concepts for future vehicle electrical systems have to be developed such that the new powernet is able to adapt flexibly to different situations or failures by routing the energy through different channels. For efficiency the corresponding development process should be based on modeling and simulation techniques. Depending on the design or analysis task, the powernet is represented through different modeling descriptions. One representation is the description with function objects which can be arranged modularly or hierarchically. For computation of reliability and other characteristics of electrical system topologies the net is represented as a graph or flow network. For the description of the global network state and the local states of the subsystems the power distribution points are described as discrete event systems. The modeling methodology developed in this work is a core competence, needed to design future vehicle electrical systems with regard to safety and reliability. Copyright © 2004 SAE International.
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