Computational Homogenisation of Polycrystalline Elastoplastic Microstructures at Finite Deformation

During sheet bulk metal forming processes, both flat geometries and three-dimensional structures change their shape while undergoing large plastic deformations. As for metal forming processes, FE-simulations are often done before in-situ experiments, a very accurate model for respective structures is required, performing well at small geometries possessing small curvatures as forms with wide as well as lateral characteristics.Because of the crystalline nature of metals, certain anisotropies have to be taken into account. Macroscopically observable plastic deformation is traced back to dislocations within considered slip systems in the crystals causing plastic anisotropy on the microscopic and the macroscopic level.A crystal plasticity model for finite deformations is used to model the behaviour of polycrystalline materials in representative volume elements (RVEs) on the microstructure. In order to circumvent singularities stemming from the linear dependency of the slip system vectors, a viscoplastic power-law is introduced providing the evolution of the plastic slips and slip resistances. The model is validated with experimental microstructural data under deformation. Through homogenisation and optimisation techniques, effective stress-strain curves are determined and can be compared to results from real forming processes, leading to an effective elastoplastic material model which is suitable for processes in the sheet bulk metal forming field

Non-local ductile damage formulations for sheet bulk metal forming

A ductile damage model for sheet bulk metal forming processes and its efficient and accurate treatment in the context of the Finite Element Method is presented. The damage is introduced as a non-local field to overcome pathological mesh dependency. Since standard elements tend to show volumetric locking in the bulk forming process a mixed formulation is implemented in the commercial software simufact.forming to obtain better results.DFG/SFB/TR 7

Surrogate cloud fields generated with the Iterative Amplitude Adapted Fourier Transform algorithm

A new method of generating two-dimensional and three-dimensional cloud fields is presented, which share several important statistical properties with real measured cloud fields.Well-known algorithms such as the Fourier method and the Bounded Cascade method generate fields with a specified Fourier spectrum. The new iterative method allows for the specification of both the power spectrum and the amplitude distribution of the parameter of interest, e.g. the liquid water content or liquid water path. As such, the method is well suited to generate cloud fields based on measured data, and it is able to generate broken cloud fields. Important applications of such cloud fields are e.g. closure studies. The algorithm can be supplied with additional spatial constraints which can reduce the number of measured cases needed for such studies. In this study the suitability of the algorithm for radiative questions is evaluated by comparing the radiative properties of cloud fields from cloud resolving models of cumulus and stratocumulus with their surrogate fields at nadir, and for a solar zenith angle of 0◦ and 60◦. The cumulus surrogate clouds ended up to be identical to the large eddy simulation (LES) clouds on which they are based, except for translations and reflections. The root mean square differences of the stratocumulus transmittance and reflectance fields are less than 0.03% of the radiative budget. The radiances and mean actinic fluxes fit better than 2%. These results demonstrate that these LES clouds are well described from a radiative point of view, using only a power spectrum together with an amplitude distribution

Lean buildings: energy efficient commercial buildings in Germany

The paper presents the description and initial evaluation of a number of commercial large scale buildings (>1000m2) situated across Germany. The study has been carried out within the framework of the evaluation program, SolarBau, which has been initiated and funded by the German Ministry of Economy and Technology. The program funds up to 25 demonstration buildings and their collective evaluation. Funding is only provided at the design stage of the buildings for additional investigations and simulations of variants, which feature elements of passive cooling, and after construction for a thorough monitoring of the finished buildings. The absence of investment subsidies ensured that all design solutions were realized under representative economic conditions. The technical requirements for admittance of a building to the program were an anticipated total primary energy use (heating, cooling and lighting) below 100 kWh/(m2a) [31,700 Btu/(ft2a)] combined with excellent vis ual and thermal comfort conditions. These ambitious goals can only be reached by a lean building featuring increased thermal insulation, intensive use of daylight and a strategy for passive cooling. The reduced HVAC-system relies heavily on a building whose design carefully considers the given climatic boundary conditions. In the moderate German climate, the focus usually lies on the avoidance of unwanted solar gains in the summer. The remaining internal loads can often be counterbalanced by controlled ventilation, additional nocturnal ventilation or by earth-to-air heat exchangers