Mehrkörperdynamik elasitscher Bauteile mit Fügestellen

Florian Pichler

Mehrkörperdynamik elasitscher Bauteile mit Fügestellen

Florian Pichler

Research Center Wels

Publikation: Typen von Abschlussarbeiten › Dissertation

Abstract

Komplexe mechanische Strukturen bestehen häufig aus mehreren Substrukturen, welche durch Schraubverbindungen, Pressverbindungen oder andere Verbindungen zusammengebaut sind. Die nichtlinearen Kontakt- und Reibkräfte welche an den Fügestellen solcher Verbindungen auftreten, können das globale und lokale dynamische Verhalten maßgeblich beeinflussen. In die Mehrkörperdynamik werden lineare flexible Körper häufig via Modellreduktion (z.B. component mode synthesis) eingebunden. Solche Reduktionsmethoden erlauben im Allgemeinen keine genaue Berechnung der lokalen Deformationen innerhalb der Fügestelle. Infolgedessen führen unrealistische Kontakt- und Reibkräfte zu fragwürdigen Ergebnissen hinsichtlich der Verformungen und Spannungen. In der vorliegenden Dissertation wird eine vollständige Strategie für eine effiziente und genaue Berücksichtigung der nichtlinearen Fügestellenkräfte innerhalb eines flexiblen Mehrkörpersystems präsentiert. Dazu werden die Bewegungsgleichungen um den Vektor der generalisierten Fügestellenkräfte erweitert. Eine numerisch günstige Formulierung dieser generalisierten Fügestellenkräfte und den dazugehörenden Termen in der Jakobimatrix wird vorgestellt. Um Fügestellendeformationen mit der notwendigen Genauigkeit abbilden zu können wird eine problemorientierte Erweiterung klassischer Reduktionsbasen (wie z.B. Craig/Bampton) mit sogenannten Kontaktmoden (joint modes) präsentiert. Drei unterschiedliche Berechnungsansätze für diese Kontaktmoden werden vorgestellt und numerisch untersucht. Alle drei Methoden basieren auf sogenannten modalen Ableitungen. Für alle Berechnungsmethoden wurde eine Ergebnisgenauigkeit vergleichbar zu Ergebnissen der Finiten Elemente Methode erzielt. Dabei ist die Anzahl an Kontaktmoden um bis zu 95% geringer als die Fügestelle Knotenfreiheitsgrade hat. Für die praktische Anwendung werden schließlich jene Kontaktmoden vorgeschlagen die basierend auf einer gewichteten „proper orthogonal decomposition“ der modalen Ableitungen berechnet werden. Zusätzlich wird eine optimierte Berechnung dieser Kontaktmoden für vorgespannte Strukturen vorgestellt. Für eine realistische Abbildung von Trockenreibung innerhalb der Fügestelle werden unterschiedliche Kontakt- und Reibmodelle untersucht. Diese Modelle wurden hinsichtlich numerischer Effizienz und anderer Kriterien bewertet. Basierend auf numerischen Untersuchungen wird ein adaptiertes exponentielles Kontaktmodell und ein drei Parameter Coulomb Reibmodell empfohlen. Die vorgestellte Strategie erlaubt eine effiziente Mehrkörpersimulation von gefügten flexiblen Strukturen wobei die Ergebnisqualität hinsichtlich Verformungen und Spannungen mit der finiten Elemente Methode vergleichbar ist. Zwei exemplarische Anwendungen aus dem Gebiet der Fahrzeugtechnik (Zweimassenschwungrad und Lagerstuhl einer Verbrennungskraftmaschine) bestätigen die praktische Relev

Originalsprache	Englisch
Publikationsstatus	Veröffentlicht - 2018

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@phdthesis{a7168b042feb494d8a89988c5e1e4a35,

title = "Mehrk{\"o}rperdynamik elasitscher Bauteile mit F{\"u}gestellen",

abstract = "Complex mechanical structures are often an assembly of substructures which are connected by some type of joints, like screwed joints, crimp connections and others. The nonlinear contact and friction forces, which act on the involved surfaces of such joints, may influence the global and local dynamic behavior significantly. In multibody dynamic simulations, linear flexible bodies are often considered via model order reduction techniques like component mode synthesis. Such reduction methods do not allow an accurate computation of the local deformations inside the latter mentioned joints. Consequently, unrealistic contact and friction forces lead to questionable results in terms of deformations and stresses. In this thesis, a complete strategy for the efficient and accurate consideration of nonlinear joint forces within flexible multibody dynamics is presented. For this purpose, the jointed structure is considered as one flexible body in a multibody system. Furthermore, the equations of motion of a flexible multibody system are extended by the vector of generalized joint forces. A computational efficient formulation of these generalized joint forces and the associated terms in the system's Jacobian is derived. A problem-oriented extension of common reduction basis with so-called joint modes is introduced in order to enable an accurate approximation of the joint deformations. Three different approaches for the computation of these joint modes are presented. All three methods are based on the use of trial vector derivatives and were investigated with respect to the number of required joint modes for accurate results. An accuracy comparable to the finite element method was achieved by a number of joint modes which is up to 95% lower than the number of nodal degrees of freedom inside the joint. Joint modes computed by a stiffness weighted proper orthogonal decomposition of all trial vector derivatives are recommended for practical application. Furthermore, an optimized computation of these joint modes for preloaded structures has been developed. For the realistic representation of dry friction joint properties different contact and friction models are reviewed. These models have been rated in terms of numerical efficiency and other criteria. Based on different numerical studies, a joint adapted exponential contact penalty model and a three-parameter Coulomb-type friction model are recommended. In conclusion, the presented strategy permits efficient multibody simulation of jointed flexible structures with a result quality in terms of displacements and stresses comparable to the finite element method. Two exemplary applications from the field of automotive engineering confirm the practical relevance of the presented strategy.",

author = "Florian Pichler",

year = "2018",

language = "English",

}

TY - BOOK

T1 - Mehrkörperdynamik elasitscher Bauteile mit Fügestellen

AU - Pichler, Florian

PY - 2018

Y1 - 2018

N2 - Complex mechanical structures are often an assembly of substructures which are connected by some type of joints, like screwed joints, crimp connections and others. The nonlinear contact and friction forces, which act on the involved surfaces of such joints, may influence the global and local dynamic behavior significantly. In multibody dynamic simulations, linear flexible bodies are often considered via model order reduction techniques like component mode synthesis. Such reduction methods do not allow an accurate computation of the local deformations inside the latter mentioned joints. Consequently, unrealistic contact and friction forces lead to questionable results in terms of deformations and stresses. In this thesis, a complete strategy for the efficient and accurate consideration of nonlinear joint forces within flexible multibody dynamics is presented. For this purpose, the jointed structure is considered as one flexible body in a multibody system. Furthermore, the equations of motion of a flexible multibody system are extended by the vector of generalized joint forces. A computational efficient formulation of these generalized joint forces and the associated terms in the system's Jacobian is derived. A problem-oriented extension of common reduction basis with so-called joint modes is introduced in order to enable an accurate approximation of the joint deformations. Three different approaches for the computation of these joint modes are presented. All three methods are based on the use of trial vector derivatives and were investigated with respect to the number of required joint modes for accurate results. An accuracy comparable to the finite element method was achieved by a number of joint modes which is up to 95% lower than the number of nodal degrees of freedom inside the joint. Joint modes computed by a stiffness weighted proper orthogonal decomposition of all trial vector derivatives are recommended for practical application. Furthermore, an optimized computation of these joint modes for preloaded structures has been developed. For the realistic representation of dry friction joint properties different contact and friction models are reviewed. These models have been rated in terms of numerical efficiency and other criteria. Based on different numerical studies, a joint adapted exponential contact penalty model and a three-parameter Coulomb-type friction model are recommended. In conclusion, the presented strategy permits efficient multibody simulation of jointed flexible structures with a result quality in terms of displacements and stresses comparable to the finite element method. Two exemplary applications from the field of automotive engineering confirm the practical relevance of the presented strategy.

AB - Complex mechanical structures are often an assembly of substructures which are connected by some type of joints, like screwed joints, crimp connections and others. The nonlinear contact and friction forces, which act on the involved surfaces of such joints, may influence the global and local dynamic behavior significantly. In multibody dynamic simulations, linear flexible bodies are often considered via model order reduction techniques like component mode synthesis. Such reduction methods do not allow an accurate computation of the local deformations inside the latter mentioned joints. Consequently, unrealistic contact and friction forces lead to questionable results in terms of deformations and stresses. In this thesis, a complete strategy for the efficient and accurate consideration of nonlinear joint forces within flexible multibody dynamics is presented. For this purpose, the jointed structure is considered as one flexible body in a multibody system. Furthermore, the equations of motion of a flexible multibody system are extended by the vector of generalized joint forces. A computational efficient formulation of these generalized joint forces and the associated terms in the system's Jacobian is derived. A problem-oriented extension of common reduction basis with so-called joint modes is introduced in order to enable an accurate approximation of the joint deformations. Three different approaches for the computation of these joint modes are presented. All three methods are based on the use of trial vector derivatives and were investigated with respect to the number of required joint modes for accurate results. An accuracy comparable to the finite element method was achieved by a number of joint modes which is up to 95% lower than the number of nodal degrees of freedom inside the joint. Joint modes computed by a stiffness weighted proper orthogonal decomposition of all trial vector derivatives are recommended for practical application. Furthermore, an optimized computation of these joint modes for preloaded structures has been developed. For the realistic representation of dry friction joint properties different contact and friction models are reviewed. These models have been rated in terms of numerical efficiency and other criteria. Based on different numerical studies, a joint adapted exponential contact penalty model and a three-parameter Coulomb-type friction model are recommended. In conclusion, the presented strategy permits efficient multibody simulation of jointed flexible structures with a result quality in terms of displacements and stresses comparable to the finite element method. Two exemplary applications from the field of automotive engineering confirm the practical relevance of the presented strategy.

M3 - Doctoral Thesis

ER -

Mehrkörperdynamik elasitscher Bauteile mit Fügestellen

Abstract

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