The doctoral thesis describes the possibilities of numerical modelling of hollow core concrete panels, SPIROLL type. The commercial finite element program ANSYS 13.0 is used for the modelling. The focus is on the specific flexural support of the panel and on the distribution of the shear stresses in the panel ribs near the support. The goal is to valid actually used method for homogenization of the panel’s foreheads and its influence on the shear resistance by using four numerical models. The numerical models are compared and verified with two experiments. The first experiment is vacuum loading on the hollow core slab. Second experiment is about shear loading by applying the loading blocks. Four methods for design of hollow core panels are evaluated. It is the method based on main stresses, design according EN 1992 and EN 1168 and Yang’s method of prestress effects transfer. Based on the results, a method of considering flexural support for the evaluation of hollow core panels is proposed.

Timber-concrete composite (TCC) structures are becoming more popular in several industrial applications as an efficient method for optimizing the structural performance and the cost of construction as well as lowering the emissions of carbon dioxide. TCC floors are more sustainable than pure concrete floors and more resistant to vibrations and excessive deflections than pure wooden floors. The effectiveness of a TCC floor is dependent on the connection between the materials. The stiffness and strength of the composite element increases by having a rigid connection. An example of a rigid connection is an adhesive-bonded connection, however obtaining a connection without slip is difficult considering there will always be certain amount of slippage in the connection. In this thesis adhesive connections are investigated with two different types of adhesive, one called Sikasil SG-500 and the other Sika PS. The application of the adhesives for the test specimen differ. Since Sika PS is a more fluid glue, a different approach was necessary than for the Sikasil SG-500. Five test specimen were tested of each adhesive by performing double shear push out tests and comparing the results to a numerical model, which was performed in ABAQUS. In the numerical model, the adhesive was created as a cohesive element. Furthermore the properties of the modeled adhesive was based on the experimental results for respective adhesive. The experimental results showed that both adhesives managed the estimated shear force in the serviceability limit state and the ultimate limit state and yet remained in the elastic region. Sikasil SG-500 turned out to be more flexible while Sika PS specimen resulted in higher shear strength. The short creep tests (30 minutes of a constant load) showed that the deformation increased more for Sika PS than for Sikasil SG-500. However both adhesives had large deformations after only 30 minutes. There was also a difference in the average longitudinal shear strength, where it resulted in 1.06 MPa for Sikasil SG-500 and 2.02 MPa for Sika PS. This study indicates that Sika PS is more preferable in TCC structures than Sikasil SG-500.

<p>The fluid dynamics of blood in the systemic circulation modulates production of nitric oxide (NO), a potent vasodilator. Non-invasive techniques such as the flow-mediated dilation (FMD) test and physiologic phenomena associated with autonomic stress induce hyperemia and subsequently higher levels of wall shear stress (WSS), stimulating endothelial nitric oxide synthase (eNOS) expression. In the current clinical practice, WSS–a key regulator of endothelial function–is commonly estimated assuming a parabolic velocity distribution, despite the evidence that the temporal changes of pulsatile blood flow over the cardiac cycle modulate vasodilation in mammals. This work investigates the effect of cardiovascular stress on local WSS distributions and the potential for near-wall accumulation of nitrite, the vasoactive storage form of NO in the bloodstream. The specific aims of the project are therefore as follows: 1) develop a reduced-order model of the major systemic vasculature at rest, during a flight-or-flight response, and under moderate levels of aerobic exercise; 2) derive a velocity-driven Womersley solution for pulsatile flow to support accurate estimation of pulsatile WSS in the clinical setting; and 3) quantify cumulative transport of nitrite in a multiscale model of bifurcating vasculature utilizing computational fluid dynamics (CFD). Development of these open-source, translatable methods enable accurate quantification of hemodynamics and species transport during cardiovascular stress. Results detailed herein extend our knowledge about regulation of regional blood flow during autonomic stress, suggest a convergent evolutionary theory for having a complete circle of Willis, and potentially clarify reproducibility concerns associated with the FMD test. </p>

There is currently a knowledge gap regarding the plastic material properties of many steel types that Atlas Copco use in their high torque power tools. This makes it difficult to fully utilise the capabilities of the Finite Element Method (FEM) to aid the developmental process. Case hardened steel is of special interest as there is not any established method on how to model it numerically.Test specimens of steel type 9195 and 2541 has been developed with two different geometries; hollow and solid. Specimen were heat treated to create case hardened specimens with different Case Depths (CD) as well as specimens made to mimic the material behaviour of the case and core of case hardened steel.Monotone torsion tests were conducted to generate stress-strain data for material models. Hardness tests of case hardened steel were made to determine hardness profiles. By combining these results, a spatially dependent case hardened steel material in an FE-model was created.Test results of the homogeneous specimen tests were successfully modelled using FEA. The case hardened steel could also be modelled, but with a discrepancy against the test results as the model core material were not representative actual core. However, the spatially dependent material model has high potential for simulating the case hardened steel, given the correct inputs. / Det finns för närvarnade bristfällig kännedom gällandes plastiska materialegenskaper hos många av de stål Atlas Copco använder i sina högmomentsverktyg för åtdragning av förband. Detta gör det svårt att fullt ut använda finita elementmetoden (FEM) som ett verktyg i produkters utvecklingsprocess. Sätthärdat stål är av intresse då det inte finns någon etablerad metod för hur det ska modelleras numeriskt.Provstavar gjorda av ståltyperna 9195 och 2541 har tagits fram med två olika geometrier; ihåliga och solida. Provstavarna var värmebehandlade vilket gav sätthärdade material med olika sätthärdningsdjup samt provstavar i material som skulle efterlikna materialet hos höljet och kärnan av sätthärdat stål.Monotona vridprov utfördes för att generera spännings-töjningsdata för användning i materialmodeller. Hårdhetstester gjordes för att fastställa hårdhetsprofiler hos sätthärdat stål. Genom att kombinera dessa provresultat skapades en numerisk material-model av sätthärdat stål med FEM.Testresultaten från de homogena provstavarna återskapades numeriskt med goda resultat. De sätthärdade provstavarnas beteende kunde också återskapas, men med ett något bristfälligt resultat då kärnmaterialet hos modellen inte var representativt av riktigt kärnmaterial hos sätthärdat stål. Modellen har dock hög potential för att återskapa sätthärdat stål, givet korrekt materialdata.

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Cardiovascular diseases are among the leading causes of deaths worldwide, but the fluid mechanics of many of these conditions and the devices used to treat them are only partially understood. This goal of this dissertation was to develop new experimental techniques that would enable translational research into two of these conditions. The first set of experiments examined <i>in-vitro</i> the changes in Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) caused by the implantation of coronary stents into the arteries of the heart using Particle Image Velocimetry. These experiments featured one-to-one scaling, commercial stents, and realistic flow and pressure waveforms, and are believed to be the most physiologically accurate stent experiments to date. This work revealed distinct differences in WSS and OSI between the different stent designs tested, and showed that changes in implantation configuration also affected these hemodynamic parameters. Also, the production of vortices near the stent struts during flow reversal was noted, and an inverse correlation between WSS and OSI was described. The second set of experiments investigated Left Ventricular Diastolic Dysfunction (LVDD) using phase contrast magnetic resonance imaging (pcMRI). Using this technique, ten patients with and without LVDD were scanned and a 2D portrait of blood flow through their heart was obtained. To augment this data, pressure fields were calculated from the velocity data using an omni-directional pressure integration scheme coupled with a proper-orthogonal decomposition-based smoothing. This technique was selected from a variety of methods from the literature based on an extensive error analysis and comparison. With this coupled information, it was observed that healthy patients exhibited different flow patterns than diseased patients, and had stronger pressure differences during early filling. In particular, the ratio of early filling pressure to late filling pressure was a statistically significant predictor of diastolic dysfunction. Based on these observations, a novel hypothesis was presented that related the motion of the heart walls to the observed flow patterns and pressure gradients, which may explain the differences observed clinically between healthy and diseased patients. / Ph. D.

Riparian buffers are promoted for water quality improvement, habitat restoration, and stream bank stabilization. While considerable research has been conducted on the effects of riparian buffers on water quality and aquatic habitat, little is known about the influence of riparian vegetation on stream bank erosion. The overall goal of this research was to evaluate the effects of woody and herbaceous riparian buffers on stream bank erosion. This goal was addressed by measuring the erodibility and critical shear stress of rooted bank soils in situ using a submerged jet test device. Additionally, several soil, vegetation, and stream chemistry factors that could potentially impact the fluvial entrainment of soils were measured. A total of 25 field sites in the Blacksburg, Virginia area were tested. Each field site consisted of a 2nd-4th order stream with a relatively homogeneous vegetated riparian buffer over a 30 m reach. Riparian vegetation ranged from short turfgrass to mature riparian forest. Multiple linear regression analysis was conducted to determine those factors that most influence stream bank erodibility and the relative impact of riparian vegetation. Results of this research indicated woody riparian vegetation reduced the susceptibility of stream bank soils to erosion by fluvial entrainment. Riparian forests had a greater density of larger diameter roots, particularly at the bank toe where the hydraulic stresses are the greatest. These larger roots (diameters > 0.5 mm) provided more resistance to erosion than the very fine roots of herbaceous plants. Due to limitations in the root sampling methodology, these results are primarily applicable to steep banks with little herbaceous vegetation on the bank face, such as those found on the outside of meander bends. In addition to reinforcing the stream banks, riparian vegetation also affected soil moisture and altered the local microclimate. While summer soil desiccation was reduced under deciduous riparian forests, as compared to herbaceous vegetation, winter freeze-thaw cycling was greater. As a result, in silty soils that were susceptible to freeze-thaw cycling, the beneficial effects of root reinforcement by woody vegetation were offset by increased freeze-thaw cycling. Using the study results in an example application, it was shown that converting a predominately herbaceous riparian buffer to a forested buffer could reduce soil erodibility by as much as 39% in soils with low silt contents. Conversely, for a stream composed primarily of silt soils that are prone to freeze-thaw cycling, afforestation could lead to localized increases in soil erodibility of as much as 38%. It should be emphasized that the riparian forests in this study were deciduous; similar results would not be expected under coniferous forests that maintain a dense canopy throughout the year. Additionally, because dense herbaceous vegetation would likely not develop in the outside of meander bends where hydraulic shear stresses are greatest, the reductions in soil erodibility afforded by the herbaceous vegetation would be limited to areas of low shear stress, such as on gently sloping banks along the inside of meander bends. As the first testing of this type, this study provided quantitative information on the effects of vegetation on subaerial processes and stream bank erosion. It also represents the first measurements of the soil erosion parameters, soil erodibility and critical shear stress, for vegetated stream banks. These parameters are crucial for modeling the effects of riparian vegetation for stream restoration design and for water quality simulation modeling. / Ph. D.

Zweitveröffentlichung / Die moderne Gefäßchirurgie bedient sich bei hohen Stadien der pAVK, spezieller Gefäßrekonstruktionen in Form von distalen End-zu-Seit-Gefäßanastomosen. Das langfristige Versagen der Gefäßanastomose hängt primär von der Entstehung einer subendothelialen Intimahyperplasie (IH) ab. Diese IH-Gebiete befinden sich je nach Anastomosengeometrie im Gebiet der Hauben- und Fersenzone sowie am Boden der Anastomose. // Mit Hilfe der Particle Image Velocimetry-Technik wird eine Taylor-Patch-, eine Miller-Cuff-Anastomose und eine femoro-crurale Patch-Prothese bezüglich ihrer Flussmuster sowie ihrer hämodynamischen Eigenschaften wie Geschwindigkeit, Scherstress und Rotation in z-Richtung (Vorticity) untersucht. // In einem hydrodynamischen Kreislaufmodell werden elastische, transparente Silikonmodelle der Anastomosen hergestellt und mit einem blutanalogen Newtonschen Fluid (Glycerol-Wasser-Gemisch) unter Simulation der femorocruralen Druckkurve, pulsatil bei Variation der Strömungsbedingung perfundiert. Der periphere Widerstand beträgt 0,5 mmHg/ml/min (PRU) und die Phasenverschiebung -12 Grad (zwischen Druck- und Flusskurve). // Die Flussmuster variieren zwischen den unterschiedlichen Ausstromverhältnissen erheblich. Bei den unterschiedlichen Flussstärken hingegen ähneln sich die Flussmuster. Alle drei Modelle zeigen ausgeprägte Flussseparationszonen im Hauben- und Fersengebiet sowie geometrieabhängig auch eine Stagnationszone am Boden. Diese Bereiche wiesen die geringsten Fluidgeschwindigkeiten, deutlich unter normalem Wandscherstressniveau liegende Scherstressverhältnisse sowie geringe Vorticitywerte auf. Im Bereich der Übergangszonen finden sich hohe Scherstress- sowie Vorticitywerte. Geschwindigkeitsunterschiede des Fluids zeigten sich im Bereich der Ausstromsegmente. Variable Stressverteilungen zeigen sich auch innerhalb der Separationszonen. Eine Erklärung für die unterschiedlich beschriebenen Offenheitsraten der drei Anastomosenformen wird durch diese Arbeit nicht gefunden. / Modern vascular surgery uses special termino-lateral anastomoses for treating high levels of peripheral arterial disease (PAD). Long term stenoses and occlusions of vascular anastomoses mostly depend on the development of subendothelial myointimal hyperplasia (MIH). There are characteristic areas within the anastomoses, where this process can be examined: The heel, the tow and the floor zone. // This examination observes local hemodynamics like velocity, shear stress and vorticity (rotation in z-direction) and flow patterns of a Taylor-Patch-, a Miller-Cuff-Anastomosis and a feroro-crural patch prothesis (FCPP) with the usage of a Particle Image Velocimetry. In a hydrodynamic circulation model various elastic, transparent silicon phantoms of termino-lateral anastomoses are perfused with a Newton fluid blood analogon (glycerol-water mixture) while simulating the femorocrural pressure curve in a pulsatile manner under variation of the flow conditions. The outflow resistance is 0.5 mmHg/ml/min (PRU, peripheral resistance units) and a phase shift of -12° between flow and pressure curve is simulated. // The flow patterns differed extremely in accordance of the various outflow ratios. Using different flow intensity, the flow patterns are very similar. // All three anastomoses show characteristic heel and toe separation zones. In the FCPP centre a stagnation zone on the floor can not be examined. Shear stress inside the flow separations was significantly lower than normal wall shear stress. High shear stress levels were found inside the transition zones between flow separation and high velocity mainstream. An explanation for the different stenoses and occlusions time of the three different anastomoses can not be found.