The essence of Biot waves in an oscillator with two degrees of freedom

In poroelastic media, i.e., porous structures whose pores contain fluid, a kind of waves can be observed that does not occur in elastic media, the so-called slow P-waves or Biot waves, which may be perceived as opaque when first encountered. In this paper, we pursue two goals: firstly, we want to provide a simple explanatory model of these waves and, secondly, we want to prepare the reader for Biot’s seminal paper. We discretize a finite poroelastic waveguide by Galerkin’s method to arrive at a mechanical system with 2 degrees of freedom and solve the eigenvalue problem of free oscillations. This oscillator representation (ODE) is simpler than the wave representation (PDE) while maintaining salient features of poroelastodynamics and offering a different perspective. In fact, an oscillation is a standing wave with wave velocity and wave length being related to frequency and domain length. In this reduced model, slow P-waves, when they exist, correspond to an oscillation with large phase shift and fast P-waves to an oscillation with small phase shift. The intended audience are engineering or physics graduate students with basic knowledge of linear oscillations, linear differential equations and some understanding of biphasic media

A Brief Survey on Non-standard Constraints: Simulation and Optimal Control

In terms of simulation and control holonomic constraints are well documented and thus termed standard. As non-standard constraints, we understand non-holonomic and unilateral constraints. We limit this survey to mechanical systems with a finite number of degrees of freedom. The long-term behavior of non- holonomic integrators as compared to structure-preserving integrators for holonomically constrained systems is briefly discussed. Some recent research regarding the treatment of unilaterally constrained systems by event-driven or time-stepping schemes for time integration and in the context of optimal control problems is outlined

Neighbourhood watch in mechanics: non-local models and convolution

This paper is intended to serve as a low-hurdle introduction to non-locality for graduate students and researchers with an engineering mechanics or physics background who did not have a formal introduction to the underlying mathematical basis. We depart from simple examples motivated by structural mechanics to form a physical intuition and demonstrate non-locality using concepts familiar to most engineers. We then show how concepts of non-locality are at the core of one of the moste active current research fields in applied mechanics, namely in phase-field modelling of fracture. From a mathematical perspective, these developments rest on the concept of convolution both in its discrete and in its continuous form. The previous mechanical examples may thus serve as an intuitive explanation of what convolution implies from a physical perspective. In the supplementary material we highlight a broader range of applications of the concepts of non-locality and convolution in other branches of science and engineering by generalizing from the examples explained in detail in the main body of the article.Comment: article (16 pages, 7 figures) and supplementary material (9 pages, 8 figures

Neuartige Drehgelenke für reibungsarme Mechanismen : Auslegungskriterien und Berechnungsmethoden

In many branches of technology is a need for mechanisms with minimum friction and minimum bearing play. Such mechanisms are neither feasible with conventional hinges nor with hinges from the micro- and nanopositioning. This thesis proposes novel hinges in order to bridge the gap between the precision of micropositioning and the workspace of applications in manufacturing. The proposed implementations are flexure hinges for large displacements and dry slide bearings with friction reduction

Neuartige Drehgelenke für reibungsarme Mechanismen : Auslegungskriterien und Berechnungsmethoden

In vielen Bereichen der Technik, insbesondere der Mikrofertigung, gibt es einen Bedarf an spiel- und reibungsarmen Mechanismen. Solche Mechanismen können bisher weder mit konventionellen Gelenken noch mit Gelenken der Mikro- oder Nanopositionierung erreicht werden. Die vorliegende Arbeit setzt an diesen Defiziten an und entwickelt neue Lösungsansätze. Zu den erarbeiteten Vorschlägen gehören Festkörpergelenke für große Ausschläge und Trockengleitlager mit Reibwertglättung

Aviator: a web service for monitoring the availability of web services

With Aviator, we present a web service and repository that facilitates surveillance of online tools. Aviator consists of a user-friendly website and two modules, a literature-mining based general and a manually curated module. The general module currently checks 9417 websites twice a day with respect to their availability and stores many features (frontend and backend response time, required RAM and size of the web page, security certificates, analytic tools and trackers embedded in the webpage and others) in a data warehouse. Aviator is also equipped with an analysis functionality, for example authors can check and evaluate the availability of their own tools or those of their peers. Likewise, users can check the availability of a certain tool they intend to use in research or teaching to avoid including unstable tools. The curated section of Aviator offers additional services. We provide API snippets for common programming languages (Perl, PHP, Python, JavaScript) as well as an OpenAPI documentation for embedding in the backend of own web services for an automatic test of their function. We query the respective APIs twice a day and send automated notifications in case of an unexpected result. Naturally, the same analysis functionality as for the literature-based module is available for the curated section. Aviator can freely be used at https://www.ccb.uni-saarland.de/aviator

How to write an article for GAMMAS and a longer title

This tutorial is a ready-to-run LaTeX example that prospective authors of GAMMAS may substitute with their own content. Moreover, it contains information about some journal policies