127 research outputs found
Boundary-Conforming Finite Element Methods for Twin-Screw Extruders: Unsteady - Temperature-Dependent - Non-Newtonian Simulations
We present a boundary-conforming space-time finite element method to compute
the flow inside co-rotating, self-wiping twin-screw extruders. The mesh update
is carried out using the newly developed Snapping Reference Mesh Update Method
(SRMUM). It allows to compute time-dependent flow solutions inside twin-screw
extruders equipped with conveying screw elements without any need for
re-meshing and projections of solutions - making it a very efficient method. We
provide cases for Newtonian and non-Newtonian fluids in 2D and 3D, that show
mesh convergence of the solution as well as agreement to experimental results.
Furthermore, a complex, unsteady and temperature-dependent 3D test case with
multiple screw elements illustrates the potential of the method also for
industrial applications
Combining Boundary-Conforming Finite Element Meshes on Moving Domains Using a Sliding Mesh Approach
For most finite element simulations, boundary-conforming meshes have
significant advantages in terms of accuracy or efficiency. This is particularly
true for complex domains. However, with increased complexity of the domain,
generating a boundary-conforming mesh becomes more difficult and time
consuming. One might therefore decide to resort to an approach where individual
boundary-conforming meshes are pieced together in a modular fashion to form a
larger domain. This paper presents a stabilized finite element formulation for
fluid and temperature equations on sliding meshes. It couples the solution
fields of multiple subdomains whose boundaries slide along each other on common
interfaces. Thus, the method allows to use highly tuned boundary-conforming
meshes for each subdomain that are only coupled at the overlapping boundary
interfaces. In contrast to standard overlapping or fictitious domain methods
the coupling is broken down to few interfaces with reduced geometric dimension.
The formulation consists of the following key ingredients: the coupling of the
solution fields on the overlapping surfaces is imposed weakly using a
stabilized version of Nitsche's method. It ensures mass and energy conservation
at the common interfaces. Additionally, we allow to impose weak Dirichlet
boundary conditions at the non-overlapping parts of the interfaces. We present
a detailed numerical study for the resulting stabilized formulation. It shows
optimal convergence behavior for both Newtonian and generalized Newtonian
material models. Simulations of flow of plastic melt inside single-screw as
well as twin-screw extruders demonstrate the applicability of the method to
complex and relevant industrial applications
Boundary-Conforming Finite Element Methods for Twin-Screw Extruders using Spline-Based Parameterization Techniques
This paper presents a novel spline-based meshing technique that allows for
usage of boundary-conforming meshes for unsteady flow and temperature
simulations in co-rotating twin-screw extruders. Spline-based descriptions of
arbitrary screw geometries are generated using Elliptic Grid Generation. They
are evaluated in a number of discrete points to yield a coarse classical mesh.
The use of a special control mapping allows to fine-tune properties of the
coarse mesh like orthogonality at the boundaries. The coarse mesh is used as a
'scaffolding' to generate a boundary-conforming mesh out of a fine background
mesh at run-time. Storing only a coarse mesh makes the method cheap in terms of
memory storage. Additionally, the adaptation at run-time is extremely cheap
compared to computing the flow solution. Furthermore, this method circumvents
the need for expensive re-meshing and projections of solutions making it
efficient and accurate. It is incorporated into a space-time finite element
framework. We present time-dependent test cases of non-Newtonian fluids in 2D
and 3D for complex screw designs. They demonstrate the potential of the method
also for arbitrarily complex industrial applications
Heat and water transport in soils and across the soil-atmosphere interface: 2. Numerical analysis
In an accompanying paper, we presented an overview of a wide variety of modeling concepts, varying in complexity, used to describe evaporation from soil. Using theoretical analyses, we explained the simplifications and parameterizations in the different approaches. In this paper, we numerically evaluate the consequences of these simplifications and parameterizations. Two sets of simulations were performed. The first set investigates lateral variations in vertical fluxes, which emerge from both homogeneous and heterogeneous porous media, and their importance to capturing evaporation behavior. When evaporation decreases from parts of the heterogeneous soil surface, lateral flow and transport processes in the free flow and in the porous medium generate feedbacks that enhance evaporation from wet surface areas. In the second set of simulations, we assume that the vertical fluxes do not vary considerably in the simulation domain and represent the system using one-dimensional models which also consider dynamic forcing of the evaporation process, for example, due to diurnal variations in net radiation. Simulated evaporation fluxes subjected to dynamic forcing differed considerably between model concepts depending on how vapor transport in the air phase and the interaction at the interface between the free flow and porous medium were represented or parameterized. However, simulated cumulative evaporation losses from initially wet soil profiles were very similar between model concepts and mainly controlled by the desorptivity, Sevap, of the porous medium, which depends mainly on the liquid flow properties of the porous medium
Heat and Water Transport in Soils and across the Soil-Atmosphere Interface: Comparison of Model Concepts.
Evaporation from the soil surface represents a water flow and transport process in a porous medium that is coupled with a free air flow and with heat fluxes in the system. We give an overview of different model concepts that are used to describe this process. These range from non-isothermal two-phase flow two-component transport in the porous medium that is coupled with one-phase flow two-component transport in the free air to isothermal water flow in the porous with upper boundary conditions defined by a potential evaporation flux when available energy and transfer to the free air flow are limiting or by a critical threshold water pressure when soil water availability is limiting. The latter approach corresponds with the classical Richards equation with mixed boundary conditions. We formulated the different equations and identified assumptions behind simplified forms. Conditions for which lateral and up and downward air flow in the porous medium and vapor diffusion in the pore space play an important role were identified using simulations for a set of scenarios. When comparing cumulative evaporation fluxes from initially wet soil profiles, only small differences between the different models were found. The effect of vapor flow in the porous medium on cumulative evaporation could be evaluated using the desorptivity, Sevap, which represents a weighted average of liquid and vapor diffusivity over the range of soil water contents between the soil surface water content and the initial soil water content. Vapor flow influences the shape of the moisture front close to the soil surface. Simulated evaporation fluxes under dynamic forcing, e.g. due to diurnal variations in net radiation, differed considerably between the models. Experimental methods that allow monitoring of diurnal evaporation fluxes are therefore essential for model discrimination and parameterization
The Global Atmosphere Watch reactive gases measurement network
Long-term observations of reactive gases in the troposphere are important for understanding trace gas cycles and the oxidation capacity of the atmosphere, assessing impacts of emission changes, verifying numerical model simulations, and quantifying the interactions between short-lived compounds and climate change. The World Meteorological Organizationâs (WMO) Global Atmosphere Watch (GAW) program coordinates a global network of surface stations some of which have measured reactive gases for more than 40 years. Gas species included under this umbrella are ozone, carbon monoxide, nitrogen oxides, and volatile organic compounds (VOCs). There are many challenges involved in setting-up and maintaining such a network over many decades and to ensure that data are of high quality, regularly updated and made easily accessible to users. This overview describes the GAW surface station network of reactive gases, its unique quality management framework, and discusses the data that are available from the central archive. Highlights of data use from the published literature are reviewed, and a brief outlook into the future of GAW is given. This manuscript constitutes the overview of a special feature on GAW reactive gases observations with individual papers reporting on research and data analysis of particular substances being covered by the program. - See more at: http://elementascience.org/article/info:doi/10.12952/journal.elementa.000067#sthash.cHvHu0T6.dpu
Common Household Chemicals and the Allergy Risks in Pre-School Age Children
The risk of indoor exposure to volatile organic compounds (VOCs) on allergic airway diseases in children remains unknown.We examined the residential concentrations of VOCs, emitted from building materials, paints, furniture, and other lifestyle practices and the risks of multiple allergic diseases as well as the IgE-sensitization in pre-school age children in Sweden.In a case-control investigation (198 case children with asthma and allergy and 202 healthy controls), air samples were collected in the room where the child slept. The air samples were analyzed for the levels of eight classes of VOCs.A natural-log unit of summed propylene glycol and glycol ethers (PGEs) in bedroom air (equal to interquartile range, or 3.43 - 15.65 ”g/m(3)) was associated with 1.5-fold greater likelihood of being a case (95% CI, 1.1 - 2.1), 1.5-fold greater likelihood of asthma (95% CI, 1.0 - 2.3), 2.8-fold greater likelihood of rhinitis (95% CI, 1.6 - 4.7), and 1.6-fold greater likelihood of eczema (95% CI, 1.1 - 2.3), accounting for gender, secondhand smoke, allergies in both parents, wet cleaning with chemical agents, construction period of the building, limonene, cat and dog allergens, butyl benzyl phthalate (BBzP), and di(2-ethylhexyl)phthalate (DEHP). When the analysis was restricted to the cases, the same unit concentration was associated with 1.8-fold greater likelihood of IgE-sensitization (95% CI, 1.1 - 2.8) compared to the non-IgE sensitized cases. No similar associations were found for the other classes of VOCs.We propose a novel hypothesis that PGEs in indoor air exacerbate and/or induce the multiple allergic symptoms, asthma, rhinitis and eczema, as well as IgE sensitization respectively
Commitment zu aktivem Daten- und -softwaremanagement in groĂen ForschungsverbĂŒnden
Wir erkennen die Wichtigkeit von Forschungsdaten und -software fĂŒr unsere Forschungsprozesse an und ordnen die Veröffentlichung von Forschungsdaten und -software als wesentlichen Bestandteil der wissenschaftlichen PublikationstĂ€tigkeit ein. DafĂŒr unterstĂŒtzen wir als Verbund unsere Forschenden im Umgang mit Daten und Software nach den FAIR-Prinzipien in Einvernehmen mit dem DFG-Kodex âLeitlinien zur Sicherung guter wissenschaftlicher Praxisâ. In Zusammenarbeit mit unseren Institutionen und Fachcommunities stellen wir adĂ€quate Forschungsdatenmanagement-Werkzeuge und -Dienste bereit und befĂ€higen unsere Forschenden zum Umgang damit. Dabei bauen wir vorzugsweise auf existierenden Angeboten auf und bemĂŒhen uns im Gegenzug um deren Anpassung an unsere BedĂŒrfnisse. Wir streben MaĂnahmen fĂŒr die Definition und Sicherstellung der QualitĂ€t unserer Forschungsdaten und -software an. Wir verwenden vorzugsweise existierende Daten-/Metadatenstandards und vernetzen uns nach Möglichkeit fĂŒr die Erstellung und Implementierung neuer Standards mit entsprechenden nationalen und internationalen Initiativen. Wir verfolgen die Entwicklungen im Bereich des Forschungsdaten- und -softwaremanagements und prĂŒfen neu entstehende Empfehlungen und Richtlinien zeitnah auf ihre Umsetzbarkeit
Ăbermorgen war gestern - the Revolution (not only) in Military Affairs
Albert M, Helmig J. Ăbermorgen war gestern - the Revolution (not only) in Military Affairs. In: Helmig J, Schörnig N, eds. Die Transformation der StreitkrĂ€fte im 21. Jahrhundert. Studien der Hessischen Stiftung Friedens- und Konfliktforschung. Vol 54. Frankfurt a. M.: Campus-Verl.; 2008: 289-299
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