In conversation with simulation: The application of numerical simulation to the design of structural nodal connections

The thesis explores methods for integration of structural analysis, design and production in a digital design environment. The somewhat ambiguous title implies the ambition to make such integration in relation to the explorative phase of the design process which is described by Donald Sch\uf6n as having a conversational character. A conversation between the designer and the representation by the means of the tool. The tool is in this context a simulation and instead of exploring the potential of automatic optimisation, the simulation is used for designer driven exploration. The aim of the thesis is to give an overview of how this type of integration is currently being approached and to contribute with new tools and methods in that pursuit. The motivation behind the work is to lower the threshold for the application of structural analysis in early-stage design, with an ambition of architectural qualities and resource efficiency in mind. An overview of the historical context is portrayed with broad brush strokes, followed by a more precise account of the mathematical and physical context, which is complemented by an attempt to describe how our tools and roles tend to interplay in the composition of the design process. Methods such as the finite element method, isogeometric analysis, smoothed particle hydrodynamics and peridynamics, including their related geometrical representations are introduced in relation to this context. A variety of production techniques are also discussed in relation to material mechanical properties for conventional building materials such as steel, concrete and wood.The method development is approached through the use of numerical and physical experiments which are applied for design of material-efficient structural components, with a particular design process perspective. The nodal connection is chosen as an application because it combines geometrical and structural complexity in an element that is of crucial importance for a holistic spatial setting, while often being produced in a material inefficient way, with poor attention to detail.The three articles that are included follow a trajectory from large to small, from the holistic to the particular. The first article is a description of the computational design work with the roof for the new international airport of Mexico City. The second article aims to address one of the challenges that were faced in that project with material inefficiency for nodal connections, with a critical perspective on optimisation. The final article presents an extension/modification for the peridynamics theory enabling variable particle sizes and an irregular particle distribution through the introduction of a concept called force flux density. The development is motivated by limitations found in the present theory through numerical experiments. The method enables simulation of phenomena such as brittle fracture, for which correlation with Griffith\u27s theory of fracture is shown. Further work includes an extension of the force flux method from 2D to 3D, including calibration of material a model for 3D printed steel. Other possibilities involve the exploration of how such a method can adapt to the various stages of the design process, where requirements of accuracy, speed and interactivity will vary

Size-based indicators for assessments of ecological status of coastal fish communities

Human impact does not only affect the abundances of fish, but also the age- and size-distributions. Indicators of fish age and size-structures can hence be useful tools for fisheries- and environmental management. Size-based indicators have been tested and proposed for large, homogenous marine ecosystems with high fishing mortality, but rarely for fine-scaled heterogeneous ecosystems in coastal zones. Here we analyse a suite of size indicators for coastal fish communities in the Baltic Sea, including mean and median length, 10th and 90th-percentile of the length distribution (L10, L90), mean length of the 10% largest fish (Lmax), large fish indices, size-spectra, and size-diversity. Results show good precision and accuracy of most indicators at realistic sample sizes, except for size-spectra and size-diversity, making them less suitable. Different indicators showed correlations among sites, indicating similar responses to environmental variation. Most size indicators responded positively to lower fishing pressure, especially indicators emphasizing the largest individuals in the population (e.g. L90 and Lmax), whereas eutrophication and physical disturbances had less impact. We conclude that size-based indicators aiming at describing the occurrence of larger fish, like L90 and Lmax, are useful for establishing management targets and assessing the status of coastal fish

The numerical simulation of standard concrete tests and steel reinforcement using force flux peridynamics

Peridynamics is a numerical particle-based solid mechanics method that enables the simulation of brittle and quasi-brittle materials, as well as ductile materials. It allows cracking to appear spontaneously in the arms joining the particles and can therefore be used to simulate progressive fracture. In this article, we apply our version of peridynamics, which we call force flux peridynamics, to the simulation of concrete where the appearance of cracks plays an important role in the global mechanical properties. It is not difficult to modify the material parameters in peridynamics to achieve a given tensile strength or a given compressive strength. However, it is much more difficult to choose parameters which will model all the strength parameters of a material within the same model. When concrete fails in compression it may split or spall showing a complex relationship between compressive and tensile failure. We therefore set ourselves the simple task of producing a single peridynamics model which can predict the stiffness and strength behavior of concrete in standard compression and tension tests for which we chose the American Society for Testing and Materials standards for the cylinder compression test, the split cylinder test, and the modulus of rupture test. A parameter sensitivity study was performed based on the cylinder compression test to tune the key peridynamics parameters that determine the global material behavior. The compressive and tensile strengths were then determined from the combined simulation data. While the fracture modes, crack branching pattern and also the stress–strain curve show promising results, the maximum tensile strength was found to be significantly larger than physical experiments suggest. This is probably due to imperfections within real concrete at the interface between aggregate particles and cement paste and it shows that the detailed numerical modeling of the failure of concrete is highly complex with a large number of unknown material parameters

Adaptive bone re-modelling for optimization of porous structural components

This paper presents a speculative application of adaptive bone-remodelling to generate porous structures for building components using a numerical meshless method. We hypothesize that such porous structures could then be 3d printed to achieve light weight and material efficientbuilding components. The meshless model is built up of particles that are connected by arms to their neighbours within a distance called a horizon. The re-modelling adaption is then based on the ratio of arms strain over average arm strain which is mapped to a third-order polynomial function and used to scale the arm stiffness in a way that mimics the resorption and densification of bone tissue. The method is shown to work rather well in the recreation of the structural patterns found in cross section of a femur bone. The translation to a geometry which can be manufactured with additive techniques is not tackled specifically and suggest a direction for further work

The Use of Peridynamic Virtual Fibres to Simulate Yielding and Brittle Fracture

The forces in the ‘arms’ joining the particles in a peridynamic analysis depend upon the state of stress in the equivalent continuum and the orientation, length and density of the arms. Short and long arms carry less force than medium length arms as controlled by the weighting kernel. We introduce an intermediate step of imagining a mat of long fibres in which the fibre forces only depend upon the stress, the fibre orientation and the length of fibres per unit volume without the added complexity of the arm lengths. The effect of the arm lengths can then be considered as a separate exercise, which does not involve the continuum properties. The arm length is proportional to size of the particles and the separation of length from the state of stress allows for modelling of variable particle density in the discretisation of a problem domain, which enables computationally efficient accurate analysis. We then introduce the concept of arm elongation to fracture in order to model surface energy in fracture mechanics. This means that shorter arms have a larger strain to fracture than longer arms. The numerical implementation demonstrates that this produces a fracture stress that is inversely proportional to the square root of the crack length as predicted by the Griffith theory

Increasing NADH oxidation reduces overflow metabolism in Saccharomyces cerevisiae

Respiratory metabolism plays an important role in energy production in the form of ATP in all aerobically growing cells. However, a limitation in respiratory capacity results in overflow metabolism, leading to the formation of byproducts, a phenomenon known as “overflow metabolism” or “the Crabtree effect.” The yeast Saccharomyces cerevisiae has served as an important model organism for studying the Crabtree effect. When subjected to increasing glycolytic fluxes under aerobic conditions, there is a threshold value of the glucose uptake rate at which the metabolism shifts from purely respiratory to mixed respiratory and fermentative. It is well known that glucose repression of respiratory pathways occurs at high glycolytic fluxes, resulting in a decrease in respiratory capacity. Despite many years of detailed studies on this subject, it is not known whether the onset of the Crabtree effect is due to limited respiratory capacity or is caused by glucose-mediated repression of respiration. When respiration in S. cerevisiae was increased by introducing a heterologous alternative oxidase, we observed reduced aerobic ethanol formation. In contrast, increasing nonrespiratory NADH oxidation by overexpression of a water-forming NADH oxidase reduced aerobic glycerol formation. The metabolic response to elevated alternative oxidase occurred predominantly in the mitochondria, whereas NADH oxidase affected genes that catalyze cytosolic reactions. Moreover, NADH oxidase restored the deficiency of cytosolic NADH dehydrogenases in S. cerevisiae. These results indicate that NADH oxidase localizes in the cytosol, whereas alternative oxidase is directed to the mitochondria

Coastal fish community indicators in Sweden - variation along environmental gradients

Coastal fish communities have a central role in both environmental and fisheries management. The following report summarizes the current state (2014) of indicator-based approaches in Sweden, to assess the status of coastal fish communities in relation to internationally agreed directives. Coastal fish is not included as a biological quality element in the European Water Framework Directive (WFD), with the exception of transitional waters, but they are included in the European Marine Strategy Framework Directive (MSFD). The report is particularly focused on potential connection points between the MSFD and WFD, in order to facilitate the harmonisation of assessments of different ecosystem components and geographical areas. One important aspect would be to develop geographically based assessment methods, to make better use of data from inventory studies. Key aspects for this development are explored in an example case study, which is based on data with wide geographical coverage. The study addresses general patterns in the distribution of species and indicators among geographical areas in the Baltic Sea, and explores the relationship between indicators and environmental variables. Changes in the indicators were to a large extent attributed to gradients in natural environmental variables, such as temperature, salinity and wave exposure. The results indicate that all these variables should be included in a geographically based assessment. Variables attributed to eutrophication were important for five of the eight studied indicators. This was mainly coupled to a gradient in water transparency. Variables attributed to the mortality of fish were less influential. Possibly, the indicators assessed were not sensitive enough, or the studied gradient was not strong enough for evaluating this pressure. Potentially, also, the explanatory variables that were used were not quantified in an adequate way. A need was seen to update information on the geographical distribution of recreational fisheries and top predators (cormorants, seals), in order to support the assessment of pressure-state relationship, and identify connection points to management measures. All these aspects need to be considered further in the continued indicator development. The environmental variables explained a reasonable part of the observed variation in the data set, although a relatively large part of the variation was left unexplained. The unexplained variability may potentially be reduced by more refined quantitative analyses, which can also explain variation at different geographical scales. The study was also limited by available environmental data. In terms of additional explanatory variables, habitat quality is often expected to have high influence on species abundances, and hence on indicators. However, this variable could not be included, due to a lack of data with sufficient geographical coverage