On the Use of Piezoelectric Sensors in Structural Mechanics: Some Novel Strategies

In the present paper, a review on piezoelectric sensing of mechanical deformations and vibrations of so-called smart or intelligent structures is given. After a short introduction into piezoelectric sensing and actuation of such controlled structures, we pay special emphasis on the description of some own work, which has been performed at the Institute of Technical Mechanics of the Johannes Kepler University of Linz (JKU) in the last years. Among other aspects, this work has been motivated by the fact that collocated control of smart structures requires a sensor output that is work-conjugated to the input by the actuator. This fact in turn brings into the play the more general question of how to measure mechanically meaningful structural quantities, such as displacements, slopes, or other quantities, which form the work-conjugated quantities of the actuation, by means piezoelectric sensors. At least in the range of small strains, there is confidence that distributed piezoelectric sensors or sensor patches in smart structures do measure weighted integrals over their domain. Therefore, there is a need of distributing or shaping the sensor activity in order to be able to re-interpret the sensor signals in the desired mechanical sense. We sketch a general strategy that is based on a special application of work principles, more generally on displacement virials. We also review our work in the past on bringing this concept to application in smart structures, such as beams, rods and plates

Quasi-static Response of a Timoshenko Beam Loaded by an Elastically Supported Moving Rigid Beam

The present paper is concerned with the quasi-static response of an elastic beam, loaded by a rigid beam, which is slowly transported along the elastic beam. The elastic beam is modelled as a Timoshenko beam. The present paper provides a limiting case of the model with constant distributed load that is often considered in the study of transported masses. The rigid beam is connected to the Timoshenko beam by means of an interface modelled as a Winkler foundation. We present a non-dimensional study on the influence of the interface stiffness upon the displacement, bending moment and shear force of the Timoshenko beam, when the rigid beam is assumed to suffer a prescribed transverse displacement. Special emphasis is laid on the distribution of pressure transmitted by the interface between the Timoshenko beam and the rigid beam. Considerable pressure concentrations are found to take place and the locations of the maximum bending moments in the Timoshenko beam move towards the ends of the rigid beam

Loading of slender cylindrical piles due to non-breaking and breaking waves - large scale laboratory tests and theoretical investigations -

Diese Arbeit stellt einen Beitrag zur Wellenbelastung schlanker Zylindern dar. Als einer der Kernbeiträge der Arbeit gilt ein neu implementiertes Verfahren für die systematische Analyse von Versuchen zur Belastung schlanker Zylinder durch sehr steile und brechende Wellen. Das Verfahren dient als Grundlage für die Entwicklung/Verifizierung theoretischer Beschreibungen der für die Belastung relevanten Prozesse. Das Verfahren wird in den Kapiteln 4-7 beschrieben und implementiert. Als Hauptgrundlage der Arbeit dienen großmaßstäbliche Versuche - KC= 3 bis 14, Re= 4.0E5 bis 1.2E6 - im Großen Wellenkanal (Kapitel 3). Zur Klassifikation nach Lastfällen werden (i) die Distanz des Brechpunkts zur Zylinderfront und (ii) der Brechertyp mittels einer neu implementierten Methode berücksichtigt. Dabei werden gebrochene und brechende Wellen, steile Wellen und flache Wellen unterschieden. Für die Krafttrennung in quasi-statischen und dynamischen Kraftanteil wurde ein neues robustes Verfahren erfolgreich eingesetzt (Kapitel 4). Als weiterer Schlüsselbeitrag folgt die Analyse des dynamischen Kraftanteils (Kapitel 5). Die von Wienke & Oumeraci (2005) ermittelten curling Faktoren wurden für wassertiefenbedingte Sturzbrecher bestätigt. Bei Kollapsbrechern ist eine Anpassung aufgrund einer steileren Wellenfront erforderlich. Die Analyse des quasi-statische Kraftanteils erfolgt in den Kapiteln 6 & 7. Zunächst wird die gängige Praxis bei der Anwendung der Morison-Formel kritisch im Hinblick auf sehr steile Wellen diskutiert. Anschließend werden in Kapitel 7 die Kraftkoeffizienten CM und CD anhand der gemessenen Orbitalströmung und Linienkräfte auf das Bauwerk ermittelt. Es zeigt sich, dass Werte aus den Regelwerken korrigiert werden sollten. Außerdem werden potentialtheoretische Erweiterungen der Morison-Formel getestet. Abschließend konnten nicht lineare Effekte wie das sog. „ringing“ sehr gut anhand der gemessenen Wasserspiegelauslenkung ermittelt werden.This research study aims at the contribution to the wave loading of slender cylinders. Among the key result of this study, a consistent methodology for a systematic analysis of the tests on wave loads induced by near-breaking and breaking waves on slender cylinders is proposed. This provides the basis for the development and verification of theoretical descriptions of relevant processes. The methodology is described and successfully implemented in chapters 4-7. This study is based on systematic large scale model tests - KC= 3 bis 14, Re= 4.0E5 bis 1.2E6 - performed in the Large Wave Flume (GWK), Hannover. For the classification of individual wave events (i) distance of the breaking point to the cylinder front, and (ii) breaker type are considered. Here broken and breaking waves, near-breaking waves, non-breaking flat waves due to a more reliable and automated data analysis are distinguished. For the force separation in a quasi-static force and a dynamic force a new robust method combining FFT and EMD filtering has successfully been applied (chapter 4). A further key contribution is the analysis of the impact load for depth limited wave breaking waves (chapter 5). The curling factors determined by Wienke & Oumeraci (2005) for plunging breakers were confirmed. A slight adjustment is however required for collapsing breakers due to a steeper wave front. The quasi-static load to near breaking waves is analysed in chapters 6 & 7. The validity for near breaking waves of the commonly applied Morison formula is critically discussed. Further on in chapter 7 drag and inertia coefficients are determined on the basis of the measured orbital flow and wave-induced line forces on the pile. It is shown that adjustments to recommendations in the design standrards would be required. Modifications of the Morison formula based on potential theory were also tested. Finally, non-linear effects such as “ringing” could be determined from the analysis of the measured surface elevation

On the influence of material properties in sheet bending processes

In order to achieve the high performance and precision requirements of modern sheet bending processes, an appropriate implementation of material properties is essential. Experiments have shown that even variations within a lot of a specific material play an important role. For this sake, detailed knowledge of the influence of the specific properties like flow curve, rolling direction, strain rate, anisotropy etc. is required. In a first step, tension tests have been performed for some materials which are frequently used in industrial applications. In order to simulate the sheet bending process, advanced simulation models have been implemented. Detailed parameter studies have been performed, and the essential parameters and their influence on the bending process have been found out. The results have been compared to measurement results of the bending process

Marine Myxobacteria as a Source of Antibiotics—Comparison of Physiology, Polyketide-Type Genes and Antibiotic Production of Three New Isolates of Enhygromyxa salina

Three myxobacterial strains, designated SWB004, SWB005 and SWB006, were obtained from beach sand samples from the Pacific Ocean and the North Sea. The strains were cultivated in salt water containing media and subjected to studies to determine their taxonomic status, the presence of genes for the biosynthesis of polyketides and antibiotic production. 16S rDNA sequence analysis revealed the type strain Enhygromyxa salina SHK-1T as their closest homolog, displaying between 98% (SWB005) and 99% (SWB004 and SWB006) sequence similarity. All isolates were rod-shaped cells showing gliding motility and fruiting body formation as is known for myxobacteria. They required NaCl for growth, with an optimum concentration of around 2% [w/v]. The G + C-content of genomic DNA ranged from 63.0 to 67.3 mol%. Further, the strains were analyzed for their potential to produce polyketide-type structures. PCR amplified ketosynthase-like gene fragments from all three isolates enhances the assumption that these bacteria produce polyketides. SWB005 was shown to produce metabolites with prominent antibacterial activity, including activity towards methicillin resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE)

LEAN PANEL BENDER – Einige mechanische Aspekte der Modellierung in Echtzeit für Produktion in Losgröße 1

Nachfolgend werden einige wissenschaftliche Aspekte der Echtzeit-Materialerkennungsstrategie MAC diskutiert, die in der neuen Maschinenfamilie LEAN PANEL BENDER der Firma Salvagnini Maschinenbau realisiert ist und die eine hochpräzise und hocheffiziente Herstellung von komplex geformten Blechprodukten sowohl bei Losgröße 1 als auch in der Serie erlaubt.(VLID)342339

Dynamic displacement tracking in viscoelastic solids by actuation stresses: a one-dimensional analytic example involving shock waves

A one-dimensional (1D) analytic example for dynamic displacement tracking in linear viscoelastic solids is presented. Displacement tracking is achieved by actuation stresses that are produced by eigenstrains. Our 1D example deals with a viscoelastic half-space under the action of a suddenly applied tensile surface traction. The surface traction induces a uni-axial shock wave that travels into the half-space. Our tracking goal is to add to the applied surface traction a transient spatial distribution of actuation stresses such that the total displacement of the viscoelastic half-space coincides with the shock wave produced by the surface traction in a purely elastic half-space. We particularly consider a half-space made of a viscoelastic Maxwell-type material. Analytic solutions to this tracking problem are derived by means of the symbolic computer code MAPLE. The 1D solution presented below exemplifies a formal 3D solution derived earlier by the present authors for linear viscoelastic solids that are described by Boltzmann hereditary laws. In the latter formal solution, no reference was made to shock waves. Our present solution demonstrates its validity also in the presence of singular wave fronts. Moreover, in our example, we show that, as was also indicated in our earlier work, the actuation stress can be split into two parts, one of them producing no stresses, and the other no displacements in two properly enlarged problems

Advanced mechanical simulation models for automatic panel benders

With automatic panel benders complete products are manufactured from sheet metal. In order to achieve short cycle times with high flexibility, a deep insight into the non-linear bending process is required. For this reason, efficient mechanical simulation models have been implemented, combining Finite Element Method, multibody dynamics simulation tools, contact mechanics algorithms and substructuring. Scope of this work is the comparison of several simulation models with measurement results performed on a Salvagnini P4XeD automatic panel bender

Industrial application of advanced adaptive concepts for automatic panel benders

Recently, the requirements on sheet metal production processes have increased significantly. Highest precision and flexibility with efficient energy consumption and short cycle times can be achieved by advanced concepts only. This requires a deep insight into the non-linear bending process. For this sake, efficient simulation models have been implemented to model the bending process: two and three dimensional finite element models combined with multibody simulation tools, contact mechanics algorithms and substructure techniques. The simulation tools have been successfully calibrated by measurement results. With the obtained detailed process knowledge, new adaptive concepts have been introduced, e.g. a smart crowning system in order to achieve straight profiles. The industrial application has shown the advantage of utilizing the above mentioned techniques. The straightness of the bends has been significantly increased, while energy consumption and cycle times have been reduced. Secondly, the development time of new machine concepts has been drastically reduced, such that the first prototype can be transferred to series production within short time. Moreover, the applied strategies show a large potential for future developments

The motion of whips and chains

We study the motion of an inextensible string (a whip) fixed at one point in the absence of gravity, satisfying the equations $$\eta_{tt} = \partial_s(\sigma \eta_s), \qquad \sigma_{ss}-\lvert \eta_{ss}\rvert^2 = -\lvert \eta_{st}\rvert^2, \qquad \lvert \eta_s\rvert^2 \equiv 1$$ with boundary conditions $\eta(t,1)=0$ and $\sigma(t,0)=0$. We prove local existence and uniqueness in the space defined by the weighted Sobolev energy $$\sum_{\ell=0}^m \int_0^1 s^{\ell} \lvert \partial_s^{\ell}\eta_t\rvert^2 \, ds + \int_0^1 s^{\ell+1} \lvert \partial_s^{\ell+1}\eta\rvert^2 \, ds,$$ when $m\ge 3$. In addition we show persistence of smooth solutions as long as the energy for $m=3$ remains bounded. We do this via the method of lines, approximating with a discrete system of coupled pendula (a chain) for which the same estimates hold.Comment: 47 pages, 8 figure