Wolfgang Seemann

Resonance Tracking of Continua Using Self-Sensing Actuators

This paper proposes and develops an innovative method to solve the resonance tracking problem for actuator and sensor applications to obtain maximum power transmission or signal selectivity using a modified phase-locked loop (PLL). The tracking of a higher eigenfrequency is very useful in some cases, but it is more challenging than the excitation of the only eigenfrequency of a 1-DoF system. The resonances are identified through employing their characteristic phase difference. The conventional PLL was modified to track a certain phase difference without deviation. The closed loop is a nonlinear control system due to the conversion between harmonic signals and phase signals. However, a model simplification to linear elements allows the goal oriented determination of the controller parameters. The advantages of self-sensing in combination with resonance tracking are attractive for practical applications such as ultrasonic motors and compact force sensors. The conducted experiments approved the effectiveness of the resonant excitation of higher oscillation modes of continua using self-sensing actuators.

Guided Wave Generation and Sensing in an Elastic Beam Using MFC Piezoelectric Elements: Theory and Experiment

This article describes the results of experimental evaluation of capabilities of a pin-force mathematical model for guided wave generation and sensing in elastic beam-like structures using MFC piezoelectric elements. It is found that the model provides an adequate and convenient tool for fast parametric study of wave excitation and propagation at a frequency range of practical interest. The model is tested against both MFC and laser vibrometer-based signal measurements; the upper frequency limits of applicability for both sensing methods are demonstrated.

Control of Compliant Mechanisms with Large Deflections

Very often elastic joints are used in high precision applications. In the case of rotational joints flexure hinges do have some advantages compared to conventional ones. However, the most important disadvantages are the complicated and complex kinematics and kinetics. As consequence, the control of mechanisms comprised of flexure hinges gets more difficult. The strategy pursued here is to reduce flexure hinges to pseudo rigid-body systems that fit into the elaborated framework of multi-body dynamics, in particular pre-control in combination with a feedback controller. The inherent deviations of these reduced models are described as uncertainties. Methods from robust control are used to synthesize controllers for such systems with uncertainty. The procedure is illustrated by examining an example of a single flexure hinge (leaf spring type).

A computational model of human movement coordination

Due to the numerous degrees of freedom in the human motor system, there exists an infinite number of possible movements for any given task. Unfortunately, it is currently unknown how the human central nervous system (CNS) chooses one movement out of the plethora of possible movements to solve the task at hand. The purpose of this study is the construction of a computational model of human movement coordination to unravel the principles the CNS might use to select one movement from plethora of possible movements in a given situation. Thereby, different optimization criteria were examined. The comparison of predicted and measured movement patterns exhibited that a minimum jerk strategy on joint level yielded the closest fit to the human data.

Dynamic Stability of a Steady Flow in a Planar Channel

In flexible channels with internal flow the steady state may loose stability by divergence or flutter, thus leading to undesirable dynamic behaviour. A lot of investigations have already been done on this subject. The aim of this contribution is to investigate and compare systematically the influence of various parameters on the stability behaviour of the coupled problem. Therefore, a simple, yet general model is built. The fluid is assumed to be inviscid and irrotational and both compressible and incompressible fluid are considered. The steady flow is bounded by a planar channel with a rigid and a thin, flexible wall. The latter is modelled as a continuum on a viscoelastic foundation, which exhibits bending and extensional stiffness. The influence of the various characteristics on the complex eigenvalues and therefore on the stability of the steady state is discussed.

Hochlauf von Turboladerrotoren in Nichtlinear Modellierten Schwimmbuchsenlagern

Bei hochtourigen Rotoren kleiner Bauweise, wie beispielsweise Abgasturboladern in Pkw und Lkw, kommen Schwimmbuchsenlager zum Einsatz. Die Mehrkorpersimulation des Hochlaufes von Abgasturboladerrotoren mit nichtlinear modellierten Schwimmbuchsenlagern stellt eine grose Herausforderung fur die Hydrodynamik sowie fur die Rotordynamik dar. Sowohl die Entwicklung rechenzeiteffizienter Methoden und Modellierungstechniken als auch die Erklarung der verschiedenen Instabilitatsphanomene waren die Kernziele des FVV-Vorhabens „Hochlaufsimulation“ (Nr. 912). Die Aufgabe wurde von der Forschungsvereinigung Verbrennungskraftmaschinen e. V. (FVV) gestellt und am Karlsruher Institut fur Technologie (KIT) und an der Universitat Kassel gelost.

Support-Condition Analyses of Rotating Beams Under Distributed Imbalance Loading

In roll balancing the behaviour of the roll can be studied either experimentally with trial weights or, if the roll dimensions are known, analytically by forming a model of the roll to solve response to imbalance. Essential focus in roll balancing is to find the correct amount and placing for the balancing mass or masses. If this selection is done analytically the roll model used in calculations has significant effect to the balancing result. In this paper three different analytic methods are compared. In first method the mode shapes of the roll are defined piece wisely. The roll is divided in to five parts having different cross sections, two shafts, two roll ends and a shell tube of the roll. Two boundary conditions are found for both supports of the roll and four combining equations are written to the interfaces of different roll parts. Totally 20 equations are established to solve the natural frequencies and to form the mode shapes of the non-uniform roll. In second model the flexibility of shafts and the stiffness of the roll ends are added to the support stiffness as serial springs and the roll is modelled as a one flexibly supported beam having constant cross section. Finally the responses to imbalance of previous models are compared to finite element model using beam elements. Benefits and limitations of each three model are then discussed.© 2011 ASME

Nonlinear Vibrational Behaviour of an Elasto-Pneumatic Training Tool

This paper deals with the nonlinear vibrational response of a stepping-board with nonlinear elasto-pneumatic force elements. Experimental investigations often show too high vertical ground reaction forces (VGRF) between the test persons and the training tool during exercises. The goal of this contribution is to identify the main factors of the dynamical behaviour and thus the biomechanical impact on humans of this training tool. Therefore this paper presents a mechanical model in order to investigate the interaction between the nonlinear behaviour of the board and the athlete. The multiphysical modelling consists of the linear-elastic structural stiffness part and the nonlinear part due to the pneumatic components. This leads to a nonlinear ordinary differential equation.

Methods for Computing 3D Steady-State Vibrations of Composites Using Green’s Functions

Spatial steady-state harmonic vibrations of an infinite layered composite plate with an arbitrary elastic anisotropy of each layer are considered in this paper. The required vector of mechanical displacements of arbitrary points for a layered structure can be represented in the form of a double inverse Fourier transform of the product of the Fourier transform of the Green’s matrix and the Fourier transform of the surface load vector. An algorithm for computing the Fourier inverse transform with the given load vector is presented. Reducing of the initial double integral to the repeated one and using Jordan’s lemma make it possible to present the displacement vector in terms of residues in real and complex poles of the Green’s matrix. The stationary phase method is applied for computing asymptotic representations of the displacement field in the far-field zone. Displacements on the surface of some various composites on the basis of graphite-epoxy material for two types of surface load were computed as numerical examples.© 2010 ASME