bluuebunny/crossref_metadata_2025_split huggingface dataset:
Retired occupational therapists' experiences in volunteer occupations
Authors: Cole Marilyn B. , Macdonald Karen C. 
Published: November 2010

AbstractAs the baby boomer generation, born 1945–1963, begins its transition to retirement, what might be the position of volunteering within their new life structure? Using retired occupational therapists as a purposive sample (n = 50), this survey provides a description of the volunteer experience in three distinct phases: 1) Pre‐retirement contemplation and preparation; 2) Actions, thoughts and feelings during the volunteer experience; and 3) Thoughts and feelings related to ending their volunteer roles. Results reveal that while retirees are highly motivated by altruism and the wish to stay engaged and connected with others through volunteering, they often find the existing structure of the organizations unable and unwilling to provide the kinds of volunteer roles that meet their needs and goals. These findings closely align with evidence from multidisciplinary and public health literature on civic engagement in the Third Age, retired but not disabled. In conclusion, results imply three new roles for occupational therapy practitioners with volunteering: 1) Promoting volunteer exploration and participation for older adult clients with disabilities; 2) Providing group interventions for Third Agers transitioning to retirement; and 3) Consulting with the organizations that depend on volunteers to guide them in revising the way they define and organize volunteer roles. Study is limited to one specific population but paves the way for replication with a broader range of participants. Copyright © 2010 John Wiley & Sons, Ltd.
Modelling of Wave Propagation using Spectral Finite Elements
Authors: Hennings Bianca , Lammering Rolf 
Published: November 2010

AbstractFor the analysis of wave propagation at high frequencies, the spectral finite element method (SFEM) is under investigation. In contrast to the conventional finite element method high‐order shape functions are used. They are composed of Lagrange polynomials with nodes at the Gauß‐Lobatto‐Legendre points. The Gauß‐Lobatto‐Legendre integration scheme is applied in order to obtain a diagonal mass matrix. So, the resulting system equations can be solved efficiently. In the numerical examples, spectral finite elements with shape functions of different order are applied to a plane strain problem. The numerical examples cover structures without and with stiffness discontinuities. It is shown that the results agree well with analytical solutions. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling Techniques for Coupled, Rotating Beams
Authors: Gattringer Hubert , Hubinger Stefan , Mayrhofer Karl , Höbarth Wolfgang , Bremer Hartmut 
Published: November 2010

AbstractBeams are parts of many industrial applications, like robot links, rolls in paper industry and turbo charger. In this work, a rotordynamical problem, the powertrain for a mill stand, is under consideration. Torsional and bending vibrations are used to describe the dynamical behavior. There are several methods for deriving the dynamical equations of motion. In this paper, the Projection Equation, a synthetical method, is used, leading to partial differential equations for the distributed parameter system. A simplification can be done by using the Ritz approximation method. This method requires the fulfillment of the geometric boundary conditions. For our example, a combination of rigid body modes and elastic modes is chosen. Also models for the gear box system and bearings are included. The solutions for the overall example are nonlinear ordinary differential equations which can be integrated numerically. The system is excited by constant torques and forces. Simulation results for this elastic multibody system are presented. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control Strategies for a Hybrid Articulated Robot
Authors: Höbarth Wolfgang , Gattringer Hubert , Staufer Peter , Bremer Hartmut 
Published: November 2010

AbstractDue to higher requirements in productivity and cost efficiency of production lines, robots and other manipulators have to move faster. One possibility to fulfill the mentioned goals is to build lightweight constructions having elastic deformations in joints and links. The elastic components tend to vibrations and static deflections. Methods that compensate or minimize these drawbacks are the focus of this paper.An articulated robot with 6 joints and flexibility in joints and links is under consideration. The joints are actuated by DC motors combined with Harmonic Drive gears which offer high gear ratios but undergo elastic deformations. The links are flexible in two bending directions and in torsional sense. To achieve ordinary differential equations, a Ritz approach together with the projection equation is used. The obtained model is used for feedforward and feedback control design.Based on reference trajectories and on a rigid body model, estimations for the elastic deflections are calculated. These deflections are used to alter the reference trajectory in order to minimize the error of the tool center point. For basic active damping, non‐local curvature feedback is used. Together with PD joint control and the feedforward control, satisfying results are obtained. Additionally, a sliding control approach is presented. The stiffness of the tool center point is enhanced with the drawback of less active damping.Simulation results and measured data are presented and compared. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy momentum consistent force formulation for the optimal control of multibody systems
Authors: Koch Michael W. , Leyendecker Sigrid 
Published: November 2010

AbstractThis work considers the optimal control of multibody systems being actuated with control forces which impact the system's motion directly. The goal is to find a dynamically feasible trajectory of states and control leading from an initial to a desired final state, while minimising an objective function. The optimal control problem is solved using a direct transcription method, i.e. boundary conditions and a discrete version of the equations of motion serve as constraints for the minimisation of a cost function with respect to the discrete state and control trajectory. Here, a particular time stepping scheme, an energy momentum integrator based on discrete derivatives is used. Corresponding to a constrained formulation of multibody systems, we develop an energy momentum consistent discrete force formulation that fits into the energy momentum integrator. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A novel algorithm for the inverse problem in elasticity imaging by means of variational r‐adaption
Authors: Arnold Alexander , Bruhns Otto T. , Mosler Jörn 
Published: November 2010

AbstractElasticity imaging or elastography is a powerful technique in medicinal imaging for visualizing the stiffness distribution in soft tissue in vivo. It is motivated by the observation that the stiffness in soft tissue is affected by pathologies in many cases. More precisely, diseased tissue tends to be stiffer than the healthy surrounding tissue. The two steps involved in elasticity imaging are: first deforming the tissue and measuring the displacement field in the region of interest using ultrasound or MRI signals; second calculating the underlying stiffness distribution using an inverse analysis. While in common approaches this inverse analysis is based on minimizing the distance between the measured and the computed deformation field depending only on the unknown stiffness distribution, an additional variation of the underlying finite element discretization is the focus of the present work. In doing so, the triangulation is optimized improving the accuracy of the results and increasing the efficiency of the computational framework. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigations on physiological contact in the human hip joint
Authors: Fietz K. , Nackenhorst U. 
Published: November 2010

AbstractIn this contribution, an efficient computational approach for modeling the physiological contact conditions in synovial joints is presented. A detailed three‐dimensional finite element model of the hip joint is generated based on CT‐data. The synovial gap between the porous cartilage layers is discretized with shell‐like liquid interface elements. In these elements, the Stokes flow equations are solved and the contact conditions are treated in a staggered fluid structure interaction scheme. The development of the synovial contact elements is described and boundary conditions which represent the joint capsule are introduced. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structure Preserving Simulation of Optimal Index Finger Trajectories during Grasping
Authors: Maas Ramona , Leyendecker Sigrid 
Published: November 2010

AbstractTrajectory planning of human motion is done unconsciously by the central nervous system (CNS). To get a better understanding about how the human CNS controls movements in a particular example, we investigate the trajectory of the index finger during grasping. Varying forefinger movements are formulated as optimal control problems for constrained motion. For the solution of the optimal control problem, DMOCC (Discrete Mechanics and Optimal Control for Constrained Systems, introduced in [4]) is used. The structure preserving formulation distinguishes DMOCC from other direct transcription methods. It guarantees that certain characteristic properties of the real motion are inherited by the approximate trajectory. This is crucial, since numerical dissipation would lead to over‐ or underestimation of the joint torques. As in [2], the motion corresponding to different objective functions like total control effort, torque change, kinetic energy and jerk in the fingertip is compared. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stress‐triaxiality‐dependent modeling of ductile damage and fracture behavior
Authors: Brünig Michael , Gerke Steffen , Albrecht Daniel 
Published: November 2010

AbstractThe paper deals with the effect of stress triaxiality on the inelastic behavior of aluminum alloys. The proposed continuum model takes into account stress‐triaxiality‐dependence of the yield condition as well as of the damage criterion and the fracture condition with different branches corresponding to different micro‐mechanisms. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An enhanced model for probabilistic cleavage fracture assessment considering local constraint effects
Authors: Hardenacke Volker , Hohe Jörg , Luckow Sabrina , Siegele Dieter 
Published: November 2010

AbstractThe present study is concerned with the development of an enhanced probabilistic model for cleavage assessment of ferritic steels. An enhanced model for the probabilistic cleavage fracture assessment has to consider the conditions for both, nucleation and propagation of micro defects. Hence, a propagation based model is enhanced by a combination of the local plastic strain and the local stress triaxiality to account for the nucleation of potentially critical micro defects. The formulation of the new model is based on the local mechanical field quantities determined numerically at the cleavage origins for a variety of standard deep and shallow crack specimens as well as for small scale cruciform bending specimens. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fracture and Fragmentation of Silicon Dies
Authors: Laun Christoph , Pandolfi Anna , Ghisi Aldo , Weinberg Kerstin 
Published: November 2010

AbstractDifferent failure modes of silicon are observed. Experimental results are not able to explain these variations clearly and therefore numerical simulations have been performed. In order to reduce high computational costs a simplified method to introduce weakened areas on silicon chips is presented. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Residual capacities of uniaxially compressed, delaminated composite panels
Authors: Völlmecke Christina 
Published: November 2010

AbstractThe mechanical buckling and postbuckling behaviour of a delaminated panel under uniaxial compression is investigated using a semi‐analytical geometrically nonlinear panel model. A Rayleigh‐Ritz procedure based on trigonometric displacement functions is used in conjunction with minimum energy principles to ascertain the mechanical response of the panels. The model includes the effect of delamination propagation resulting from the buckling of the laminates utilizing a discrete cohesive zone model. With the model developed, a detailed assessment of the residual capacity of the panel is provided due to its capability of tracing the equilibrium paths far into the postbuckling range. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A coupled transport and damage model for concrete at high temperatures
Authors: Cramer Friedhelm , Ostermann Lars , Dinkler Dieter 
Published: November 2010

AbstractA model for the numerical analysis of hygro‐thermal behavior of concrete at high temperatures which includes transport and reaction processes is presented. For the description of transport the model comprises the balance equation for mass and enthalpy and the constitutive equations for concrete at high temperatures. The degradation of the cement minerals C‐S‐H and portlandite is described by two chemical reactions. Finally, the finite element formulation for solving the coupled balance equations regarding the primary variables temperature and relative humidity is presented and the results of a 3‐D example are discussed. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Postbuckling of Composite Airframe Structures: Closed‐Form Approximate Solutions
Authors: Mittelstedt Christian , Schröder Kai‐Uwe 
Published: November 2010

AbstractIn this contribution, the postbuckling behaviour of imperfect rectangular composite plates under compression is treated in a closed‐form analytical manner. Based on rather simple shape functions for the postbuckling deflections and the plate imperfections, the requirement for compatibility of the membrane strains leads to an explicit solution for Airy's stress function. The equilibrium condition in the out‐of‐plane direction is not fulfilled explicitly, but rather in an integral sense using a Galerkin‐type formulation, leading to an approximate closed‐form solution for the postbuckling deflections. Eventually, rather simple closed‐form approximate solutions for all postbuckling state‐variables can be derived that can be used conveniently in engineering practice. The quality of the closed‐form solution is established by comparison with the results of other authors. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strain‐gradient viscoplasticity in one‐dimensional structural dynamics
Authors: Nguyen A.D. , Stoffel M. , Weichert D. 
Published: November 2010

AbstractBased on the static theory of strain‐gradient viscoplasticity proposed by [1], a one‐dimensional dynamic analysis is derived for finite element computation of isotropic hardening materials. The kinetic energy is assumed to be composed of the conventional and internal kinetic energy. The internal energy is described phenomenologically in terms of the equivalent plastic strain in order to capture the heterogeneity of plastic flow. Herein, the microscopic density is assumed to be related to the macroscopic one through a microscopic‐inertia parameter. The macroscopic‐ and microscopic‐force balances including inertia effects are derived. The performance of the proposed formulation is illustrated through the numerical simulation of a one‐dimensional dynamic problem. A parameter study to find the microscopic‐inertia parameter is carried out. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessment of structural sensitivity on the basis of artificial neural networks
Authors: Pannier Stephan , Graf Wolfgang 
Published: November 2010

AbstractIn engineering practice, the assessment of sensitivity is utilized to detect influential parameters in order to facilitate subsequent numerical simulation techniques. As sensitivity analyses are preprocessing methods for sophisticated numerical simulation techniques, e.g. reliability based optimization procedures, their application is always linked to an increase of the computational expense. In result, it is reasonable to couple sensitivity analysis and artificial neural networks (ANN). Therefore, multi‐faceted global sensitivity measures (GSM) may be formulated, taking advantage of different characteristics of the ANNs. Additionally, to take into account nonlinearities of the response surface, a new approach of sectional global n sensitivity measures is introduced. Generally, the sensitivity can be determined with $S_{i}=\hat{S}_{i}/\sum\limits_{j=1}^{n}\hat{S}_{j}$. Thereby, $S_{i}$ denotes the sensitivity of interest and $\hat{S}_{i}$ a characteristic of the function $f:\mathcal{R}^n\rightarrow\mathcal{R}$ under investigation. This can be either the response $f$ itself or the first partial derivative thereof $\partial_{i}f$. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
About the stress‐strain state of growing viscoelastic systems
Authors: Pulyaevskiy Denis V. , Potapov Vadim D. 
Published: November 2010

AbstractA problem of calculation of the stress‐strain state of viscoelastic heterogeneously ageing growing systems at the various moments of time is considered. The efficient numerical technique based on the Finite Element Method (FEM) is suggested. The constitutive equation between stresses and strains in the viscoelastic growing solid is corresponded with the Maslov‐Arutyunyan theory. The general system of equations of the FEM‐based technique is being formed for nodal displacement increments on the basis of variation of the total energy functional by components of the vector of nodal displacement increments. The numerical technique allows to take into account linear and nonlinear creep of the material, shrinkage (if it is necessary) and the instantly‐elastic modulus time‐dependence. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stabilized Mixed Tetrahedrals with Volume and Area Bubble Functions at Large Deformations
Authors: Widany Kai‐Uwe , Caylak Ismail , Mahnken Rolf 
Published: November 2010

AbstractIn this contribution, stabilized mixed finite tetrahedral elements are presented in order to avoid volume locking and stress oscillations. Geometrically non‐linear elastic problems are addressed. The mixed method of incompatible modes is considered. As a key idea, volume and area bubble functions are used for the method of incompatible modes [1], thus giving it the interpretation of a mixed finite element method with stabilization terms. Concerning non‐linear problems these are non‐linearly dependent on the current deformation state, however, linearly dependent stabilization terms are used. The approach becomes most attractive for the numerical implementation, since the use of quantities related to the previous Newton iteration step is completely avoided. The variational formulation for the standard two‐field method, the method of incompatible modes in finite deformation problems is derived for a hyper elastic Neo‐Hookean material. In the representative examples Cook's membrane problem and a block under central pressure illustrate the good performance of the presented approaches compared to existing finite element formulations. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comments on Membrane Locking
Authors: Winkler Robert 
Published: November 2010

AbstractMembrane locking is a severe issue frequently neglected in the context of low‐order (four node isoparametric) shell elements. From a theoretical point of view, the present contribution illustrates the underlying mechanism by means of shallow shell theory. From a numerical point of view, different element formulations based on standard enhanced assumed membrane strains and reduced integration methods have been compared to each other applying standard as well as modified benchmark examples. A modified integration scheme is proposed. According to preliminary results it behaves virtually optimal within the limits of finite element perfectibility. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Validierung eines Simulationsmodells für Wälzlager durch Abgleich von Simulations‐ mit Messdaten
Authors: Fritz Felix , Bücheler David , Seemann Wolfgang 
Published: November 2010

AbstractWälzlager besitzen abhängig von Drehwinkel und Belastung unterschiedliche Steifigkeit sowie Dämpfungs‐ und Reibverluste. Um das dynamische Verhalten und die Lebensdauer einer Maschine durch Simulationen zu beurteilen, werden daher die nichtlinearen Reaktionskräfte des Lagers als generisches Maschinenelement implementiert.Um die Güte dieses Elements zu validieren werden verschiedene Messungen an einem Wälzlagerprüfstand durchgeführt. Anschließend wird ein Modell dieses Prüfstandes in MSC/ADAMS aufgebaut und zum Abgleich die Experimente als Simulationen nachgebildet. Die untersuchten Größen sind die Lagersteifigkeit sowie das Reibmoment im Wälzlager. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear Vibrations with Friction: A Multiharmonic Approach
Authors: Herzog Anna , Panning Lars 
Published: November 2010

AbstractTurbine blades are subjected to vibrations caused by static and dynamic loads. To avoid damage, the arising dynamic stresses can be reduced by generating friction contacts between the blades leading to additional damping. The resulting nonlinear equations of motion of the blade dynamics can be solved by the Multiharmonic Balance Method (MHBM), which is described in this paper. With the MHBM, it is possible to consider a multiharmonic excitation as well as a response consisting of several harmonics. In this paper, the MHBM is applied to both a simple 1 DOF nonlinear oscillator and a cyclic model of a blade integrated disk (blisk). (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Dynamic Aspects and Pattern Generation in Vehicle‐Road Interaction
Authors: Vogt Heike , Seemann Wolfgang 
Published: November 2010

AbstractIncreasing transport capacity leads to new vehicle designs and increasing axle loads. Still it has to be better understood until which extend especially heavy vehicles cause corrugation of roads. Therefore, basic investigations concerning vehicle‐road interaction are helpful to augment the understanding of the basic mechanisms. Firstly, in order to investigate the oscillatory behavior of a vehicle a MDoF oscillator moving with constant velocity on a rippled road is considered. From this, general results about wear pattern generation of the road are derived from analytical considerations concerning the dynamic contact force between vehicle and road. Secondly, a simple vehicle road interaction model is presented which consists of a vehicle model and a road exhibiting viscoelastic plastic characteristics. Results of numerical simulations are compared with the findings deduced from the analytical MDoF model. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)