216 research outputs found
Turbulence production and turbulent pressure support in the intergalactic medium
No full textThe injection and evolution of turbulence in the intergalactic medium is studied by means of mesh-based hydrodynamical simulations, including a subgrid-scale (SGS) model for small-scale unresolved turbulence. The simulations show that the production of turbulence has a different redshift dependence in the intracluster medium (ICM) and the warm-hot intergalactic medium (WHIM). We show that the turbulence in the ICM is produced chiefly by merger-induced shear flows, whereas the production in the WHIM is dominated by shock interactions. Secondly, the effect of dynamical pressure support on the gravitational contraction has been studied. This turbulent support is stronger in the WHIM gas at baryon overdensities 1 less than or similar to delta less than or similar to 100 and less relevant for the ICM. Although the relative mass fraction of the gas with large vorticity is considerable (52 per cent in the ICM), we find that for only about 10 per cent in mass this is dynamically relevant, namely not associated with an equally large thermal pressure support. According to this result, a significant non-thermal pressure support counteracting the gravitational contraction is a localized characteristic in the cosmic flow, rather than a widespread feature
Forming of metal-based composite parts
No full textIn the last few decades, metal-based composites and related manufacturing methods have attained a significant research attention thanks to the possibilities they offer to tailor both the material properties and the part in-service performances. A variety of metal-based composite parts is available for commercial applications since more affordable and robust manufacturing processes and quality control techniques have recently overcome many challenging technological issues. The paper aims at describing the forming processes applied to metal-based composites, with particular emphasis on the process features, part obtainable characteristics, and modelling issues for a convincing design and optimization of the process itself. The most recent progresses and challenges are illustrated in detail, including innovative materials and processes that are emerging to answer the requirements of advanced engineering applications as well as new modelling techniques and current approaches to face economic and environmental issues
Interlaboratory Comparison of Forming Limit Curves for Hot Stamping of High Strength Steels
No full textThe paper presents the approaches followed by two labs - LFT at the University of Erlangen-Nuremberg (Germany) and DIMEG at University of Padua (Italy) - in evaluating formability limits of 22MnB5 sheets when processed under hot stamping conditions. Details about the two testing apparatuses and the testing procedures are outlined, and the results in terms of Forming Limit Curves FLC compared and critically commented
Interlaboratory Comparison of Friction Conditions in Hot Stamping Operations
No full textThe paper presents results obtained at two labs, on in Germany and one in Italy, in terms of friction coefficient as function of hot stamping process parameters. Even if the testing procedures and analysis tools to evaluate tribological conditions are different for the two labs, both the approaches show a similar trend as regards the friction coefficient dependence from the process parameters
Interlaboratory comparison for heat transfer coefficient identification in hot stamping of high strength steels.
No full textThe topic of the paper is the identification of the heat transfer coefficient (HTC) in hot stamping of boron steel sheets under conditions very close to the industrial ones. Two approaches followed by one lab in Germany and one lab in Italy are presented for HTC identification, showing the two experimental apparatuses that were set-up to conduct the tests, the procedures developed and applied to identify the HTC. The obtained results are compared in terms of dependence of HTC from the applied contact pressure, the similarities and the differences of the two approaches are outlined and commented
Mechanical properties and plastic anisotropy of the quenchable high strength steel 22MnB5 at elevated temperatures
No full textWithin the scope of this paper, the formability of the press hardenable steel 22MnB5 will be investigated with regard to its anisotropic properties at elevated temperatures under the processing conditions of hot stamping. Two different experimental setups have been realized, one at the University of Erlangen-Nuremberg using conductive heating, and the other one at the University of Padova using inductive heating. Both of these equipments enable the characterization of the material anisotropy behavior by performing uniaxial, hot tensile tests in the range of hot stamping temperatures
Opto-electronic oscillator employing photonic-chip based stimulated Brillouin scattering
No full textWe demonstrate an optoelectronic oscillator based on stimulated Brillouin scattering as an active filter on a photonic chip
Energy and water fluxes above a cacao agroforestry system in Central Sulawesi, Indonesia, indicate effects of land-use change on local climate
No full textRapid conversion of tropical rainforests to agricultural land-use types occurs throughout Indonesia and South-East Asia. We hypothesize that these changes in land-use affect the turbulent heat exchange processes between vegetation and the atmosphere, and the radiative properties of the surface, and therefore, induce an impact on local climate and water flows. As part of the international research project (SFB 552, Stability of Rainforest Margins in Indonesia, STORMA) the turbulent heat fluxes over a cacao agroforestry system (AFS) were investigated, using the eddy covariance technique. These first heat flux observations above a cacao AFS showed an unexpectedly large contribution of the sensible heat flux to the total turbulent heat transport, resulting in an averaged day-time Bowen ratio of beta = H/lambda E approximate to 1. Seasonality of beta did mainly coincide with the seasonal course of precipitation, which amounted to 1970 mm yr(-1) during the investigated period. The findings are compared to invastigations at four neotropical rain forests where daytime beta were substantially smaller than 1. All discussed sites received similar incident short wave radiation, however, precipitation at the neotropical sites was much higher. Our first observations in a nearby Indonesian upland rain forest where precipitation was comparable to that at the cacao AFS showed an intermediate behaviour. Differences in beta between the cacao AFS and the tropical forests are discussed as a consequence of differing precipitation amounts, and albedo. From these comparisons we conclude that conversion from tropical forests to cacao AFS affects the energy fluxes towards increased heating of the day-time convective boundary-layer
- …
