Fraunhofer Chalmers Research Centre for Industrial Mathematics
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Itererade slumpmässiga funktioner
No full textVi ger en kort introduktion till hur itererade slumpmässiga funktioner inducerar en markovkedja, samt till konvergens av sannolikhetsmått. Vi presenterar sedan Letacs sats, som ger förutsättningar för existensen hos en stationär fördelning i termer av Lipschitzkonstanterna för funktionerna. Vi studerar sedan till vilken grad satsen överlever utan Lipschitzkonstanter, och presenterar en generell sats som ger existens av en stationär fördelning, med andra förutsättningar. Vi studerar också huruvida satsen fortfarande håller om vi släpper på antaganden om oberoende och likafördelning, alltså släpper på att processen skall vara markovsk och tidshomogen. Vi ger en generalisering av Letacs sats som delvis innetäcker även detta fall
Mechanical analysis methods for ultra-stiff CFRP from thin tapes
No full textToday there is an increasing demand for more environmentally friendly transport systems. One way to decrease the fuel consumption of vehicles such as cars or airplanes is to decrease their weight. By replacing heavy construction material such as steel, which is often used in for example cars, with a material that has just as
good mechanical properties as steel but a fraction of the weight, more fuel efficient vehicles could be made.
A carbon fibre composite material, constructed out of uniformly distributed ultrathin high modulus carbon fibre reinforced polymer tapes, with mechanical properties
approaching those of steel but with about a fifth of the density is the subject of study for this Master’s thesis. The focus of the study was to construct mechanical analysis methods, i.e. models for predicting the stiffness and the strength in tensile loading,
for the composite material that was manufactured and tested in an accompanying study with this thesis work.
The model was constructed in the numerical computation environment MATLAB an shows good agreement with the experimental results obtained from the tensile tests.
The model predicts the stiffness, strength and failure modes most likely to occur in the laminate when loaded in tension. The model takes in-situ effects into account.
The first test and analysis results indicate great potential for the composite material as it exhibits tremendous mechanical properties even before the manufacturing has been perfected. The model also indicate failure of the laminate to initiate by tape pull-out followed by longitudinal tape fracture, and that transverse tape fracture is unlikely to occur for the simulated laminates
Omfattande renovering utifrån ett boendeperspektiv samt en utvärdering av Riksbyggens kommunikation
No full textFUNDAMENTAL, DESIGN OF A YOUTH CENTER THROUGH APPEALING ARCHITECTURE OF OPERATIVE SURFACES
No full textElectrochemical removal of mercury from contaminated aqueous solutions
No full textBecause mercury is one of the most toxic heavy metals known, there are multiple
techniques for the removal of mercury from aqueous solutions. A new technique introduced
uses electrochemical alloy formation to reduce mercury concentrations. By
controlling the potential applied, this method has been proven to reduce mercury in
aqueous solutions from different initial concentrations. The main conclusion is that
the method can reduce the amount of mercury in solution to under 6 µg/L, which is
the World Health Organisation’s guideline value for drinking water
Bio-Inspired Transportation Network Optimisation Reinforcement Rules in Physarum Vein Networks
No full textThe decision making process of unicellular organisms such as the amoeba Physarum
polycephalum may represent primitive forms of computation. Such non neuronal
organisms exhibit complex optimisation behaviour, apparently solving NP hard
problems in linear time. Understanding such behaviour may be relevant for many
different fields besides biology, from metaheuristics to neuroscience or information
theory. This master thesis explores possible reinforcement mechanisms Physarum
polycephalum that influence vein network formation and biomass density distribution.
The state-of-the-art Flow Conductivity Model (Tero et al 2006) that describes
vein development will be tested for the first time experimentally using time-lapseimaging-
techniques. If this model (also called the Physarum Solver) is the one used
to reproduce the slime mold’s solving capacities it lacks many of the Physarum’s
biological features, such as growth. However, we show that the Physarum expansion
neglected by the Flow Conductivity Model was not necessary, as the order in which
food sources were met did not influence the final distribution of biomass. By using
fluorescence microscopy, we have been able to quantify the flow within the veins of
the slime mold, extracting both the local diameter and the local flow rate within
the veins. We notes that the contractile cycles missing from the model may have a
strong impact on the decision making process. The fast contractile cycle creates the
flow by dilating the vein and creating low-pressure points; while the phase of the
slow contractile cycle distinguishes veins that will be reinforced from the other veins.
The fit to the empirical data has a different form to the various model functions that
have been used. However, even if the model does not fit experimental data trend,
it still has utility for bio-inspired optimisation and pedagogical purposes. Furthermore,
the Flow Conductivity Model may give us a better insight of the mechanic of
the slime mold’s vein selection than a new model over-fitting experimental data
Numerical and experimental analysis of the mechanical response of thin-ply cross-ply composites
No full textOne of the major strivings of today is to reduce the emission of green house gases. Within the transport vehicle industry this can be achieved by reducing their structural weight, which lowers the fuel consumption. That strive motivates the use of fibre reinforced polymers, which offers an increased weight to stiffness ratio compared to metallic materials.
Moreover, it has been shown that further advantages can be achieved if the thickness of certain plies in a composite is reduced. More specifically, if the thickness of a transversely loaded ply embedded in a multidirectional laminate is reduced, the onset of transverse cracks can be substantially delayed. This is called the in-situ effect. The aim of this project is to, with one experimental study and one numerical study, investigate this in-situ effect for thinner plies for which it has not yet been fully established.
The thickness range considered is between 20 μm and 240 μm. For the experimental study test specimens are manufactured and subjected to a tensile load while the edges are inspected for cracks. The numerical analysis is conducted within the framework of Abaqus, where a cohesive zone model is developed in combination with extended FEM. The outcome of the experiments show a small delay in the onset of transverse cracks when
the thickness of the 90°-ply is reduced. For some cases it is also seen that the crack density decreases when the thickness is reduced. Finally, the stiffness of the adjacent plies does not seem to have a large impact on the in-situ effect. However, difficulties related
to manufacturing complicates the interpretation of those results and their validity can be questioned.
The numerical study shows an in-situ effect in a model in which no in-situ properties are used. For the thinner case, the result aligns well with analytical models. It is shown that an extremely fine mesh is necessary in order to resolve the crack zone correctly, and
the dependency of input variables such as the critical energy release rate and interface strength is demonstrated. It is also shown that for one of the studied material a transition from stable to unstable crack growth occurs at the thickness 80 μm, where a crack grows stably for thinner plies and unstably for a thicker plies. Taking into account the manufacturing complications, the results still, on the whole, indicate
that the in-situ effect exist for the thin-ply composites studied in this project. This further motivates the development and research connected to thin-ply composites