Time Steps V.S Cohesion in Non-Smooth Contact Dynamics Algorithm

We present the equations obeyed by contacts forces in a granular system solved by the Contact Dynamics algorithm. We consider their resolution in a very simple case of cohesive interaction, i.e.for a straightforward two-body 2D normal collision. The equations predict that increasing time steps should coincide with an increase of the effective cohesion of the systems. Numerical simulations are performed to verify the predictions, in the case of cohesive granular piles falling in the gravity field. A discussion on how a seemingly purely numerical quantity may end up being a non-trivial ingredient in the physics of the simulated system ensues

The Cohesive Granular Collapse as a Continuum : Parametrization Study

Although intensive research on the flow of dry granular materials has allowed for the proposition of continuum rheology and modelling, the behaviour of flowing cohesive material has attracted less attention so far. To start modelling such cohesive flows, we first focus on the configuration of a granular collapse, which is a simple benchmark test. Specifically, we compare granular-collapse experiments of cohesive grains with numerical simulations, where we test a simple rheology for the material : the so-called µ(I)-rheology, supplmented by a yield stress for cohesion. This document reports the sensitivity of our numerical simulations on the parameters of the rheology, often challenging to measure in experiments

On the Deformation of a Hyperelastic Tube Due to Steady Viscous Flow Within

In this chapter, we analyze the steady-state microscale fluid--structure interaction (FSI) between a generalized Newtonian fluid and a hyperelastic tube. Physiological flows, especially in hemodynamics, serve as primary examples of such FSI phenomena. The small scale of the physical system renders the flow field, under the power-law rheological model, amenable to a closed-form solution using the lubrication approximation. On the other hand, negligible shear stresses on the walls of a long vessel allow the structure to be treated as a pressure vessel. The constitutive equation for the microtube is prescribed via the strain energy functional for an incompressible, isotropic Mooney--Rivlin material. We employ both the thin- and thick-walled formulations of the pressure vessel theory, and derive the static relation between the pressure load and the deformation of the structure. We harness the latter to determine the flow rate--pressure drop relationship for non-Newtonian flow in thin- and thick-walled soft hyperelastic microtubes. Through illustrative examples, we discuss how a hyperelastic tube supports the same pressure load as a linearly elastic tube with smaller deformation, thus requiring a higher pressure drop across itself to maintain a fixed flow rate.Comment: 19 pages, 3 figures, Springer book class; v2: minor revisions, final form of invited contribution to the Springer volume entitled "Dynamical Processes in Generalized Continua and Structures" (in honour of Academician D.I. Indeitsev), eds. H. Altenbach, A. Belyaev, V. A. Eremeyev, A. Krivtsov and A. V. Porubo

Dimensional metrology of cylinders based on digital image processing: application to LHC corrector magnets

This paper presents the development of a method to measure relative deformations of bodies (basically cylinders) based on the analysis of images taken with a digital camera. The main application is the measurement of the deformation of the shrinking tubes of superconducting corrector magnets, which allows the calculation of the final prestress exerted to the coils. (4 refs)

Optimized low-level liquid scintillation spectroscopy of 35S for atmospheric and biogeochemical chemistry applications

Anthropogenic activities, dominated by emissions of sulfur dioxide (SO2), have perturbed the global sulfur (S) cycle. Uncertainties in timescales of S transport and chemistry in the atmosphere lead to uncertainties in the predicted impact of S emissions. Measurements of cosmogenic 35S may potentially be used to resolve existing uncertainties in the photochemical and chemical transformation of S in the environment. The lack of a simple, effective, and highly sensitive technique to measure 35S activity in samples with low activities may explain the scarcity of published measurements. We present a set of new sample handling and measurement procedures optimized for the measurement of 35S in natural samples with activities as low as 0.20 dpm above background (2σ, integration time = 2 hr). We also report simultaneous measurements of aerosol () and gas phase () collected at inland and coastal locations; the range of observed activities corresponds to SO2 residence lifetimes of 0.2 ± 0.04 (coastal) - 22.3 d ± 0.04 (inland). These optimized techniques offer the potential for resolving atmospheric processes that occur on 6–12-hour timescales as well as resolving transport phenomena such as stratospheric mixing into the troposphere

Final Design and Prototyping of the Superconducting Magnet Package for the Linear Accelerator of the European XFEL

Abstract—The electron beam of the European XFEL will beaccelerated to an energy up to 17 GeV in a linear acceleratorwhich is divided into 101 modules. Each module will be equippedwith eight superconducting cavities and a superconductingmagnet package. That package consists of a main superferricquadrupole and two nested corrector dipoles, horizontal andvertical, enclosed in a stainless steel vessel. Conduction cooledcurrent leads are used.Up to four prototypes were produced between 2005 and 2009.Some problems were detected which may complicate the seriesproduction, mainly that the wire diameter was too small for thewinding process, the solid iron yoke was too expensive to bemachined and the magnetization effects on the magnet transferfunction were too high. Therefore, it was decided to revisit thedesign to ease fabrication. The new magnet design is presented inthis paper. The fabrication process and test results of theprototype are reported as well.Finally, the helium vessel around the magnet needs to satisfythe European Standard for Pressure Vessels, namely PED97/23/EC. This paper also describes the modifications necessaryin the original design to achieve that specification

Design, fabrication and tests of a 600A HTc current lead for the LHC correction magnets

This paper describes the design and fabrication of four sets of HTc 600 A current leads manufactured by ANTEC in collaboration with three more Institutes to test the feasibility of industrial fabrication of these units. This development has been made in the framework of a CERN programme to build low thermal losses leads for the correction magnets of the LHC. Tests performed at the manufacturer installations are also presented. (5 refs)

Experience on Series Production of the Superconducting Magnet Package for the Linear Accelerator of the European XFEL

Abstract—The procurement of 103 superconducting magnetpackages is part of the Spanish in-kind contribution to theEuropean X-FEL. Each package consists of a main superferricquadrupole and two steerers, vertical and horizontal, fed byconduction-cooled current leads and enclosed in a stainless steelvessel. The operation temperature is 2 K, as they are embeddedin a superfluid helium bath. The magnetic and mechanicaldesigns are published elsewhere. The magnets are beingproduced in the Spanish company ANTEC, while the vessels arefabricated by another Spanish company, Trinos Vacuum-Projects, which is also responsible for the integration, under thesupervision of CIEMAT. The helium vessel manufacturer needsto accomplish the requirements given by the European PressureEquipment Directive, namely PED 97/23/EC. This paperdescribes the series fabrication techniques, the production followup,the quality assurance and the magnet testing at themanufacturer site. Cold tests are realized at DESY premises. Themain problems found during the fabrication of the first half ofthe series are also reported: a) the reproducibility of thequadrupole coil dimensions; b) the accuracy of the beam positionmonitor housing after final welding of the vessel; and c) theminimization of the magnetization effects on the transfer functionof the magnets