When a highly deformable elastic sphere impacts a water surface at an oblique angle it can skip several times in a manner similar to a skipping stone. However, this sphere seems to skip more readily and with more ease than a traditional skipping stone. This thesis examines the improved skipping characteristics of highly deformable elastic spheres made from cured silicone rubber. The effect of impact velocity, impact angle, sphere diamter and material shear modulus on ricochet trajectory is experimentally examined using high speed photography and image processing techniques. Experimental evaluation shows that deformation is the primary contributor to an increased lift force upon impact. An analytical model is presented in addition to a regime diagram predicting ricochet results from impact conditions.

Soft and deformable silicone rubber spheres ricochet from a water surface when rigid spheres and disks (or skipping stones) cannot. This dissertation investigates why these objects are able to skip so successfully. High speed cameras allow us to see that these unique spheres deform significantly as they impact the water surface, flattening into pancake-like shapes with greater area. Though the water entry behavior of deformable spheres deviates from that of rigid spheres, our research shows that if this deformation is accounted for, their behavior can be predicted from previously established methods. Soft spheres skip more easily because they deform significantly when impacting the water surface. We present a diagram which enables the prediction of a ricochet from sphere impact conditions such as speed and angle. Experiments and mathematical representations of the sphere skipping both show that these deformable spheres skip more readily because deformation momentarily increases sphere area and produces an attack angle with the water which is favorable to skipping. Predictions from our mathematical representation of sphere skipping agree strongly with observations from experiments. Even when a sphere was allowed to skip multiple times in the laboratory, the mathematical predictions show good agreement with measured impact conditions through subsequent skipping events. While studying multiple impact events in an outdoor setting, we discovered a previously unidentified means of skipping, which is unique to deformable spheres. This new skipping occurs when a relatively soft sphere first hits the water at a high speed and low impact angle and the sphere begins to rotate very quickly. This quick rotation causes the sphere to stretch into a shape similar to an American football and maintain this shape while it spins. The sphere is observed to move nearly parallel with the water surface with the tips of this “football” dipping into the water as it rotates and the sides passing just over the surface. This sequence of rapid impact events give the impression that the sphere is walking across the water surface.

The Apollo Command Module had a tendency to flip over upon impact with the ocean surface after returning from space (9/19 times). In an effort to better characterize the inversion process for future water landing vehicles, experimental results for a simplified buoyant cylindrical puck impacting the water surface are presented. This study focuses on the dependence of inversion upon vertical velocity, horizontal velocity, and the pitch angle of the puck relative to the free surface. High-speed images reveal an asymmetric cavity that forms upon water impact. The asymmetric cavity then collapses, applying a moment, which can be sufficient to invert the puck after impact. Increasing the vertical velocity increases the likelihood of inversion. The puck never flipped over below a vertical velocity of 3.75 m/s. Increasing the horizontal velocity also slightly increases the likelihood of inversion. However, the largest effect of increasing horizontal velocity is to shift the range of impact angles for which the puck will invert to lower angles. The buoyant cylindrical puck used in this study requires a higher Froude number (4.34) to invert than previous geometries which have been studied.

<p>The work in this thesis focuses on the use of explicit finite element analysis (FEA) in the modelling of fluid-structure interaction of panel-water impacts. Paper A, considers modelling of a two-dimensional rigid wedge impacting a calm water surface. From analytical methods and results of a systematic parameter study a generalised approach for determination of fluid discretization and contact parameters in the modelling of arbitrary hull-water impact situations is developed and presented. In paper B the finite element modelling methodology suggested in paper A is evaluated for elastic structures by a convergence study of structural response and hydrodynamic load. The structural hydroelastic response is systematically studied by a number of FE-simulations of different impact situations concerning panel deadrise, impact velocity and boundary conditions. In paper B a tentative method for dynamic characterization is also derived. The results are compared with other published results concerning hydroelasticity in panel water impacts. The long-term goal of this work is to develop design criteria, by which it can be determined whether the loading situation of a certain vessel type should be regarded as quasi-static or dynamic, and which consequence on the design a dynamic loading has.</p>

The work in this thesis focuses on the use of explicit finite element analysis (FEA) in the modelling of fluid-structure interaction of panel-water impacts. Paper A, considers modelling of a two-dimensional rigid wedge impacting a calm water surface. From analytical methods and results of a systematic parameter study a generalised approach for determination of fluid discretization and contact parameters in the modelling of arbitrary hull-water impact situations is developed and presented. In paper B the finite element modelling methodology suggested in paper A is evaluated for elastic structures by a convergence study of structural response and hydrodynamic load. The structural hydroelastic response is systematically studied by a number of FE-simulations of different impact situations concerning panel deadrise, impact velocity and boundary conditions. In paper B a tentative method for dynamic characterization is also derived. The results are compared with other published results concerning hydroelasticity in panel water impacts. The long-term goal of this work is to develop design criteria, by which it can be determined whether the loading situation of a certain vessel type should be regarded as quasi-static or dynamic, and which consequence on the design a dynamic loading has. / QC 20101126

L'objectif de ces travaux de thèse est de proposer des approches de modélisation et d'expérimentation de l'impact de structures déformables et indéformables sur différents milieux. Différents modèles analytiques et des simulations numériques sont développés en comparaison aux résultats expérimentaux. Une première partie se consacre à la caractérisation de la similitude entre la réponse à l'impact à l'eau d'un solide et la réponse d'un solide impactant une structure déformable. Des simulations éléments finis (EF) et SPH sont réalisées pour l'impact à l'eau d'un tube cylindrique (sans rupture). Un modèle analytique d'impact à l'eau est proposé pour prédire l'évolution de l'effort (pic, durée). L'analyse des résultats permet de dimensionner un programmateur d'impact solide reproduisant le pic d'effort. Des simulations EF de l'impact sur un tube cylindrique, à géométrie adapté, dans la direction longitudinale, sont réalisées et comparées à quelques expériences tests. Le «flambage dynamique» (dû au comportement inélastique du matériau et aux ondes de déformations) des tubes est alors observé. Une seconde partie traite du cas de la perforation sous impact d'une tôle mince à faibles vitesses d'impact (< 10 m/s, vitesse de déformation < 1000 s-1). Des essais sur puits de chute instrumenté (force, déplacement, déformée de tôle, avancée de fissure) sont analysés. Des simulations EF en éléments coques avec un critère de rupture ductile par endommagement sont réalisées. Les paramètres de rupture dynamique sont identifiés par méthode inverse à l'aide d'essais de résilience Charpy sur l'alliage d'aluminium de désignation 2024 T3. Une analyse des pics de force lors de l'impact permet une meilleure compréhension des mécanismes de perforation. En parallèle, un nouveau modèle analytique, basé sur les énergies impliquées lors de l'impact, est proposé et comparé aux simulations EF. L'étude numérique de la perforation est étendue aux grandes vitesses d'impact et de déformation (100 - 1000 m/s, vitesse de déformation <100 000 s-1) pour identifier les transitions des différents mécanismes de perforation connus (pétalisation, fragmentation des pétales, fragmentation complète). / The objective of this work is to propose approaches to model and to assess experimentally the structural impact on different media. A variety of analytic models and numerical simulations are developed comparing to experimental results. The first part of this work presents a discussion on the similitude between a water impact and an impact on a deformable solid structure. Water impact simulations of a deformable cylinder (without rupture) are performed by finite elements (FE, Coupled Eulerian Lagrangian) and SPH analysis. An analytical model of water impact is proposed for the prediction of peak force evolution. The analysis of results permits to design an impact programmer reproducing this peak force. FE longitudinal impact simulations on cylindrical tubes, with an adapted geometry, are performed and compared with some experiments. The “dynamic buckling” of tubes under impact (due to the material inelastic behavior and to strain waves) is observed. The second part deals with the low velocity perforation (< 10 m/s, strain rate < 1000 s-1) of thin plates. Some experiments on an instrumented drop test (force, displacement, plate shape, crack propagation) are analyzed. Shell FE simulations, with a damage rupture criteria implemented are performed. Parameters are identified by inverse method with the help of Charpy tests made on 2024 T3 aluminum alloy. An analysis of the peak force, during impact, leads to a good understanding of the perforation mechanism. In parallel, a new analytical model, based on an energetic approach of the perforation, is proposed and compared with FE simulations. The numerical perforation study is extended to high velocities and high strain rates (100 - 1000m/s, strain rate < 100 000 s-1) in order to identify different well-known transitions of perforation (Petalisation, petals' fragmentation, total plate's fragmentation).

In the general part of this diploma thesis are presented technical information collected on the issue of spontaneous decay of ozone in water solution and problems with analytical monitoring of these processes. Particular attention is paid to influence of pH value, bicarbonate and peroxide concentration on ozone decay kinetics. Experimental part is focused on the use of spectrophotometry in the study of chemical reactions associated with the spontaneous decay of ozone in distilled and tap water depending on pH and temperature after saturating of water by ozone prepared from air and pure oxygen. Direct photometry in UV range of spectrum (at 260 nm) was used to monitoring of ozone decomposition kinetics.

Cotton is one of the leading fibers in the textile industry due to its superior mechanical qualities. It accounts for high environmental impacts, especially water consumption and scarcity. Since cotton is a significant raw material for IKEA, it had set a target to source from only sustainable sources such as from the Better Cotton Initiative, and recycled cotton. At the same time, IKEA also has a commitment to transition to a circular business, which includes recycling. This comparative and accounting Life Cycle Assessment (LCA) analyzes virgin (two types - conventional cotton and Better Cotton) yarns, and mixed (virgin plus recycled) cotton yarns from some of the top supplier countries of the company, on a cradle-to-gate perspective. Water quantity and quality impacts are analyzed together with climate change. The Life Cycle Impact Assessment (LCIA) shows that there is a proportional reduction in impacts of the mixed yarns as recycled cotton percentage is increased, since the impacts of recycled yarns are much lower than virgin yarns. In virgin conventional yarns, the main stages that contributed the most to the impacts were cotton cultivation and spinning. Irrigation used in cotton cultivation accounted for the most impacts in water availability. For water quality, the impacts were mostly coming from electricity use and direct field emissions from cotton cultivation. In addition, this study demonstrated that there were high differences between the impacts in the countries studied. The results also suggested that there were water savings by using Better Cotton compared to conventional cotton yarns. / Bomull är en av de vanligaste fibrerna i textilindustrin på grund av dess överlägsna mekaniska egenskaper. Den orsakar dock hög miljöpåverkan, särskilt vattenförbrukning och -brist. Eftersom bomull är ett viktigt råmaterial för IKEA, har de satt ett mål att endast använda hållbara källor, som från Better Cotton Initiative, och återvunnen bomull. Samtidigt har IKEA också åtagit sig att övergå till en cirkulär affärsmodell som inkluderar återvinning. Denna jämförande studie beaktar livscykelanalys (LCA) och analyserar jungfruligt garn (två typer - konventionell bomull och Better Cotton) och blandat bomullsgarn (jungfru plus återvunna) från några av företagets främsta leverantörsländer ur ett vagga-till-port-perspektiv. Vattenmängder och kvalitetseffekter analyseras tillsammans med klimatförändringar. Livscykelbedömningen (LCIA) visar att det finns en proportionell minskning av effekterna av de blandade garnerna när andelen återvunnen bomull ökar, eftersom effekterna av återvunnet garn är mycket lägre än jungfruliga garner. I konventionellt jungfruligt garn var bomullsodling och spinning de främsta stegen som bidrog mest till effekterna. Bevattning som används vid bomullsodling svarade för de största effekterna på tillgången till vatten. För vattenkvaliteten kom effekterna huvudsakligen från elanvändning och direkta utsläpp från bomullsodling. Dessutom visade denna studie att det fanns stora effektskillnader mellan de studerade länderna. Resultaten antydde också att det fanns vattenbesparingar genom att använda Better Cotton jämfört med konventionella bomullsgarn.