Today’s rules and regulations regarding emissions from combustion vehicles are very strict and the travel range per tank and/or charge, especially for electric vehicles, is a crucial factor which will always be considered by the customers. Hence, automotive manufacturers strive to boost fuel and battery economy. This can, to a great extent, be done by improving the aerodynamics of the vehicle for lower drag. The conventional CFD process for aerodynamic development is relatively time consuming and there is rarely enough timeor resources to find the optimal design in all regions of the vehicle. Hence, the adjoint solver was investigated to make the aerodynamic development process more efficient by providing sensitivities of the geometry with respect to drag force. The adjoint solver was investigated both through a literature review as well as by performing CFD and adjoint simulations. The CFD and adjoint simulations were performed using Fluent 2019 R1 and the realizable k-ε turbulence model. It was found that it is important to monitor surface sensitivities during the solution in addition to the adjoint residuals to assess convergence of the adjoint simulation. It is also recommended to analyse regions of high residuals in the domain to ensure that they are far away from the surface(s) of interest. Investigations regarding different stabilization schemes as well different meshes for the adjoint solver were performed. It was concluded that the residual minimization scheme (RMS) is the preferred stabilization scheme. It was found that a coarser mesh can be used to reduce localized transient behaviour if the adjoint solver has trouble converging. It was found that a simplified model of a fully detailed car geometry is necessary to reduce the complexity and the resolution of the mesh to be able to use the RMS and to avoid local instabilities. A proposed CFD and adjoint procedure with guidelines and recommendation was developed.

In this Licentiate of Engineering thesis, a method is proposed that identifies the mechanical properties of arteries in vivo. The mechanical properties of an artery are linked to the development of cardiovascular diseases. The possibility to identify the mechanical properties of an artery inside the human body could, thus, facilitate disease diagnostization, treatment and monitoring. Supplied with information obtainable in the clinic, typically limited to time- resolved pressure-radius measurement pairs, the proposed in vivo parameter identi- fication method calculates six representative parameters by solving a minimization problem. The artery is treated as a homogeneous, incompressible, residual stress- free, thin-walled tube consisting of an elastin dominated matrix with embedded collagen fibers referred to as the constitutive membrane model. To validate the in vivo parameter identification method, in silico arteries in the form of finite element models are created using published data for the human abdominal aorta. With these in silico arteries which serve as mock experiments with pre-defined material parameters and boundary conditions, in vivo-like pressure-radius data sets are generated. The mechanical properties of the in silico arteries are then determined using the proposed parameter identification method. By comparing the identified and the pre-defined parameters, the identification method is quantitatively validated. The parameters for the radius of the stress-free state and the material constant associated with elastin show high agreement in case of healthy arteries. Larger differences are obtained for the material constants associated with collagen, and the largest discrepancy occurs for the in situ axial prestretch. For arteries with a pathologically small elastin content, incorrect parameters are identified but the presence of a diseased artery is revealed by the parameter identification method. Furthermore, the identified parameters are used in the constitutive membrane model to predict the stress state of the artery in question. The stress state is thereby decomposed into an isotropic and an anisotropic component which are primarily associated with the elastin dominated matrix and the collagen fibers, respectively. In order to assess the accuracy of the predicted stress, it is compared to the known stress state of the in silico arteries.  The comparison of the predicted and the in silico decomposed stress states show a close agreement for arteries exhibiting a low transmural stress gradient. With increasing transmural stress gradient the agreement deteriorates. The proposed in vivo parameter identification method is capable of identifying adequate parameters and predicting the decomposed stress state reasonably well for healthy human abdominal aortas from in vivo-like data. / In diesem Lizentiat der Ingenieurwissenschaften wird eine Methode zur Identifikation der mechanischen Eigenschaften von Arterien in vivo vorgestellt. Die mechanischen Eigenschaften einer Arterie sind mit der Ausbildung kardiovaskulärer Krankheiten verknüpft und deren Identifikation hat daher das Potenzial die Diagnose, die Behandlung und die Überwachung dieser Krankheiten zu verbessern. Basierend auf klinisch möglichen Messungen, die üblicherweise auf ein zeitaufgelöstes Druck-Radiussignal limitiert sind, werden sechs repräsentative Parameter durch Lösen eines Minimierungsproblems berechnet. Die sechs Parameter sind dabei die Eingangsparameter des zur Hilfe gezogenen konstitutiven Schalenmodells welches eine Arterie als eine homogene, inkompressible, restspannungsfreie und dünnwandige Röhre beschreibt. Weiterhin wird angenommen, dass die Arterienwand aus einer elastindominierten Matrix mit eingebetteten Kollagenfasern besteht. Um die in vivo Parameteridentifikationsmethode zu validieren, werden in silico Arterien in Form von Finite Elemente Modellen erstellt. Diese in silico Arterien beruhen auf publizierten Materialparametern der menschlichen Abdominalaorta und dienen als Pseudoexperimente mit vordefinierten mechanischen Eigenschaften und Randbedingungen. Mit diesen Arterien werden in vivo-ähnliche Druck-Radiussignale erstellt und anschliesend werden ihre mechanischen Eigenschaften mit Hilfe der Parameteridentifikationsmethode bestimmt. Der Vergleich der identifizierten und der vordefinierten Parameter ermöglicht die quantitative Validierung der Methode. Die Parameter des spannungsfreien Radius und der Materialkonstanten für Elastin weisen hohe Übereinstummung im Falle gesunder Arterien auf. Die Abweichung der Materialkonstanten für Kollagen sind etwas gröser und der gröste Unterschied tritt beim axialen in situ Stretch auf. Für Arterien mit einem pathologisch geringen Elastinbestandteil werden falsche Parameter identifiziert, wobei die Parameteridentifikationsmethode eine krankhafte Arterie offenlegt. Weiterhin werden mit Hilfe der identifizierten Parameter und des konstitutiven Schalenmodells der Spannungszustand in der Arterienwand berechnet. Dieser ist dabei aufgeteilt in einen isotropen und einen anisotropen Anteil. Der isotrope Anteil wird mit der elastindomierten Matrix und der anisotrope Anteil mit den Kollagenfasern verknüpft. Um die Genauigkeit des berechneten Spannungszustandes beurteilen zu können, wird dieser mit dem Zustand in den in silico Arterien verglichen. Im Fall von Arterien, die einen geringen transmuralen Spannungsgradienten aufweisen, entspricht der berechnete Spannungszustand dem in silico Zustand. Mit zunehmendem transmuralen Spannungsgradienten lässt die Übereinstimmung nach. Für die gesunde menschliche Abdominalaorta ist die entwickelte in vivo Parameteridentifikationsmethode in der Lage, basierend auf in vivo-ähnlichen Messsignalen, adäquate Parameter zu identifizieren und einen zufriedenstellenden Spannungszustand zu berechnen. / I denna licentiatavhandling föreslås en metod för att identifiera mekaniska egenskaper hos artärer in vivo. De mekaniska egenskaperna är kopplade till utvecklingen av hjärt-kärlsjukdomar, och möjligheten att identifiera dessa egenskaper skulle således kunna underlätta diagnostisering, behandling och uppföljning av dessa sjukdomar. Den förslagna metoden använder kliniskt mätbara tryck-radie-signaler och löser ett minimeringsproblem för att bestämma sex parametrar som beskriver kärlets mekaniska egenskaper. Artären modelleras som ett homogent, inkompressibelt och spänningsfritt tunnväggigt rör där kärlväggen utgörs av en elastindominerad matris armerad med inbäddade kollagenfibrer. För att validera parameteridentifieringen skapas en uppsättning representativa, virtuella artärer med hjälp av finita element. Dessa in silico-artärer baseras på publicerade data för mänsklig bukaorta och används för att generera fiktiva tryckradie-signaler vilka sedan matas in i den förslagna modellen. Genom att parametrar och randvillkor för in silico-artärerna är kända fungerar dessa som en kontroll mot vilka resultatet från parameteridentifieringen kan jämföras. Parametrarna som beskriver den icke trycksatta radien och den elastindominerade matrisen visar god överensstämmelse med de in silico-artärerna för friska kärl. Större diskrepans erhålls för de parametrar som associeras med kollagenet, och den största avvikelsen erhålls för den parameter som beskriver den axiella försträckningen. För artärer med patologiskt lågt elastininnehåll identifieras felaktiga parametrar, men resultatet avslöjar ändå tydligt en sjuk artär. De identifierade parametrarna har också använts för att jämföra spänningstillst åndet i membranmodellen och in silico-artäreren. Spänningstillståndet har delats upp i en isotrop och en anisotrop komponent svarande mot, i huvudsak, den elastindominerade matrisen samt kollagenfibrerna. Resultatet visar en mycket god överensstämmelse för bägge komponenterna hos in silico-artärer med låg spänningsgradient genom väggen. Med ökande spänningsgradient försämras dock överensstämmelsen. Resultatet visar att den förslagna metoden är kapabel att identifiera adekvata parametrar och att förutsäga spänningskomponenterna i en frisk aorta.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. September, 2017. / This study investigates the mineralogical, petrographic and geochemical characteristics of target rocks and impact-formed breccias (impactites) intersected by the 368 m long M4 drillcore located 18 km NNW from the estimated centre of the 145 ± 2 Ma, Morokweng impact structure (MIS), South Africa. M4 is the only core from the central parts of the Morokweng impact structure not to intersect fractionated granophyric impact melt directly beneath 35-100 m of Cenozoic Kalahari Group sediments. Instead it intersects highly fractured, cataclased and shocked, crystalline target rocks that are cut by mm- to m-scale melt-matrix breccia and suevite dykes. The target rocks comprise granitic, granodioritic, trondhjemitic and dioritic Archaean gneisses, metadolerite and dolerite. The gneisses and metadolerite show signs of quartz veining and metasomatism linked to localised mylonitic to brittle fault deformation that predated the impact. The suevite and meltmatrix breccia dykes make up ~10% of the core. All rocks show signs of low-T hydrothermal effects that occurred after the impact. The target rocks contain a complex network of shear fractures that contain cataclasite and which grade into monomict lithic breccia. The cataclasite contains shocked mineral fragments, which indicates that the shear fracturing postdated the initial shock stage of the impact. The melt-matrix breccia and suevite dykes show signs that they intruded along the fractures, although there is also evidence that shear fracturing continued after quenching of the melt. This suggests that the intrusion of the dykes overlapped the brittle deformation of the target rocks. Shock features in the M4 core lithologies include planar fractures, feather features, decorated planar deformation features (PDF), mosaic extinction and toasting in quartz; oblique lamellae, reduced birefringence and patchy (mosaic) extinction in plagioclase, and chevron-style spindleshaped lamellae in microcline, as well as kink bands in biotite and planar fractures in titanite and zircon. Universal Stage measurements of PDF sets in quartz from 8 target rocks and 6 impactite dykes revealed four dominant sets: 0°(0001), 22.95°{ 3 1 10 }, 17.62°{ 4 1 10 }, 32.42°{ 2 1 10 }; with no significant change in shock intensity with depth nor significant differences in PDF orientations or intensity between melt-matrix breccias, suevites and target rocks. Based on these observations the average peak shock pressures are estimated at 10 - 25 GPa. Apart from one suevite dyke that contains exotic clasts and an unusual bulk composition, all suevite and melt-matrix breccia dykes show major, trace and REE compositions and lithic and mineral clasts that indicate that they were formed from the target rocks found in the M4 core. The individual impactite dykes show good compositional correlation with their wallrocks, which supports limited transport of the melt and suevite. This is also supported by evidence of small-scale variation of the melt composition in the melt-matrix breccias, which indicates that not enough time was available for complete mixing to happen. The similarity in matrix composition and in lithic and mineral clast types in the melt-matrix breccias to their wallrocks, is consistent with a friction melt origin. These dykes are thus interpreted as pseudotachylite. Macroscopic and microscopic evidence suggests that the melts intruded cataclasite-filled fractures and that interfingering and infolding between the melts and incohesive cataclasite allowed the melt to assimilate cataclasite. The melt clasts in the suevite show the same composition and clast features as the melt-matrix breccias. Based on this evidence it is proposed that the melt clasts in the suevite in the M4 core are fragments of quenched pseudotachylite that became separated and mechanically mixed into the cataclasite matrix when movement continued along the cataclasite-bearing fractures after the melt quenched. This was possible because the cataclasite was still incohesive and because strong vertical and horizontal displacements of the entire M4 sequence happened during the crater modification stage of the impact, possibly for 1-2 minutes after the impact. The melt-matrix breccias are compositionally distinct from the Morokweng granophyric impact-melt rock intersected in the other central borehole cores. Melt particles are pervasively hydrothermally altered to a secondary mineral assemblage of zeolites and smectites, attributed to impact-induced hydrothermal fluid circulation in the MIS. The upper parts of the core are marked by abundant haematite but in the deeper levels of the core, chlorite-epidote-andradite garnet is found, which may indicate a vertically-zoned hydrothermal system after the impact. The hydrothermal effects also explain the abundance of decorated PDF in shocked quartz grains and the lack of glass in the PDF in quartz. The 10-25 GPa shock levels in the target rocks support them lying close to the transient crater floor and initially close (<10 km) to the point of impact. The high structural position of the rocks relative to the impact-melt sheet suggests that the M4 sequence represents part of the peak ring of the Morokweng impact structure. The rocks of the peak ring would have experienced strong vertical and centrifugal displacement during the crater excavation and modification stages, which can explain the intense shear fracturing and cataclasis, brecciation and friction melting as well as the strong block movements that could disrupt and disperse the pseudotachylite melt dykes to produce suevite. A peak ring radius of 18 km would suggest that the original Morokweng crater rim diameter would have been >70 km, but between 1 and 2 km of post-impact erosion before the deposition of the Kalahari Group means that this could be a minimum estimate. / LG2018

Thesis (Ph.D.)--University of the Witwatersrand, Faculty of Science, 1995

This report is a bachelor thesis at Mälardalens University in Eskilstuna on the behalf of Scandinavian pile Driving AB in Sala.Scandinavian pile Driving AB is a relatively small company with high competitiveness that develops and manufactures drilling rigs and foundation mast in its factory in Sala.This report has investigated the development possibilities of Scandinavian Pile Driving AB's machine MD40, which is a smaller drilling rig which is usually used in smaller and special drilling operations. Where the company asks to find out what requirements the market demands and design suggestions on how their new machine can be designed.The work process in this report has strived to follow the six phases of the product development process presented in the book "Product Design and Development" by Karl T. Ulrich and Steven D. Eppinger up to and including Phase 3. Thereby, the work has completed market research in the form of benchmarking of competing companies drilling rigs and interviewing users of the MD40 drilling rig.With this reason, the work could have resulted in 11 concepts where one of the concepts has been transferred to a 3D CAD model with associated drawings. The goal of development has been to minimize the total volumes of the machine, maximize mobility and space controlsystem and make it as stable as possible. / Den här rapportenär ett examensarbete för högskoleexamen på grundnivå, det vill säga 15 hp på 50 procent arbetstakt. Arbetet görs vidMälardalens högskola i Eskilstuna mot Scandinavian pile Driving AB i Sala. Scandinavianpile Driving AB är relativt litet företag med hög konkurrenskraftighetsom utvecklar och tillverkar borriggar och borrmaster i sin fabrik i Sala. Denna rapport har undersök utvecklingsmöjligheter av Scandinavian pile Driving AB ́s maskin MD40 somär mindre borriggsomvanligen används vid mindre och speciella borrningsarbeten. Därföretaget efterfrågaratt ta reda på vilkakrav som marknaden efterfrågar och designförslag på hur deras nya maskin kan vara utformad.Arbetsprocessen hos denna rapport har strävat att följa den produktutvecklingsprocessens sex faser som presenteras i boken ”Product Design and Develepmonent” av Karl T. Ulrich och Steven D. Eppingersfram till och med fas 3. Där med har arbetet fullföljt en marknadsundersökningi form av benchmarking av konkurrerande företags borriggar och intervju med användare av MD40 borrigg.Med den grunden kunde arbetet resulterat i 11 stycket konceptdär ett av de koncepten har blivit överfört till en 3D CAD-modell med till hörande ritningar. Där målet av utvecklingen har varit att minimeraden totala volymen hos maskinen,maximera mobilitetochutrymme regleringssystemoch göra den så stabil som möjligt.

For 10-15 years, the Powder-In-Tube (PIT) process has been one of the leading manufacturing methods for producing the highest critical current density (Jc) Nb₃Sn wires for at small effective filament diameter (deff), both required for future applications in high energy physics. Since Nb₃Sn first became commercially available in the 1960's, non-Cu Jc values have steadily climbed until a plateau was reached at about 3,000~A/mm (12~T, 4.2~K) in the year 2000. Comprehensive analysis of recent wires suggests that both PIT and the other high Jc wire design, Rod Restack Process (RRP), have yet to achieve their maximum potential as high Jc conductors. Currently, PIT wires obtain a maximum Jc(12~T, 4.2~K) of about 2700~A/mm2 and do so by converting up to 60% of the non-Cu cross section into superconducting Nb₃Sn. However, about a quarter of this volume fraction is made of large grains of Nb₃Sn which are too large or otherwise disconnected to carry current in transport, wasting both real estate, as well as Sn and Nb that would be better used to make the desired small grain A15. The most recent RRP wires typically achieve Jc values of around 3000~A/mm2 by also converting about 60% of the non-Cu cross section into A15, however nearly all of that has the desired small grain morphology with high vortex pinning, ideal for current transport. Studies at the Applied Superconductivity Center have shown that one route to improvement for both wires may be in controlling the formation of intermediate phases which form before Nb₃Sn . An intermetallic Nb-Cu-Sn, commonly referred to as Nausite, is considered responsible for the formation of the undesirable large grains. We studied the phase evolution in PIT Nb₃Sn from the starting powder mixture at room temperature up to 690°C to better understand what role Nausite ((Nb0.75Cu0.25)Sn₂) actually plays in forming large grain A15 with the goal of preventing its formation and making better use of the Sn available to form the desired small grain A15 morphology. After heat treatment, all wires were imaged in an SEM and then processed through digital image analysis software, extracting area fractions of each phase and their morphology. For heat treatments which showed interesting metallographic results, additional measurements were made by transport, resistivity, magnetization, and/or heat capacity to develop a complete picture of how the microstructure affects critical wire properties. Based on these results, novel heat treatments were developed and demonstrated our ability to reduce the undesired large grain A15 while simultaneously producing more current-carrying small grain A15, increasing the ratio of small:large grain A15 from 3.0 to 3.8. Another possible path to improvement is to reduce the non-uniform deformation incurred during wire fabrication. A PIT Nb₃Sn wire begins as a mono-filament consisting of a thick Nb7.5wt%Ta tube clad in high-purity Cu, inscribed with a Cu sleeve, and filled with a Sn-rich NbSn₂ powder. The external Cu cladding will later provide a low resistance normal conducting path around superconducting filaments, a necessity for magnet stability. The final wire diameter is between 0.7-1.25~mm with 156 or 192 filaments, whose diameters are 33-50~μm, organized into 6-7 concentric rings. Through advanced digital image analysis software, we can extract geometric information which describes how the wire and filaments deform from their nominally circular shape, becoming elliptical or otherwise having non-uniform deformation which can be detrimental to wire properties. We found that the non-uniform deformation incurred during wire fabrication can degrade the wire performance. The most severe effect is caused by the different deformation rates of the Nb-Ta tube compared to its powder core, which leads to the Sn-rich core drifting from the center of the Nb-Ta tube, leading to an uneven A15 reaction front. This is referred to here as 'centroid drift'. In PIT wires, the diffusion barrier must be consumed to form A15 while still leaving a thin, protective annulus behind to protect the Cu. Centroid drift then causes a large inefficiency as it creates a thick and thin side of diffusion barrier, the thin side limiting the reaction if Sn leaks are to be prevented, while the thick side becomes wasted Nb-Ta. Up to 30% of the final non-Cu cross-section remains as unused diffusion barrier. When Sn leaks out of the filaments it increases the resistivity of the Cu stabilizer, lowering the Residual Resistance Ratio (RRR). A high RRR is required for magnet stability, and such Sn leaks can be detrimental to magnet performance. In addition, we found that filaments farther from the center of the wire tend to be those with highest centroid drift, and they are also the most susceptible to leaking Sn. Moreover, we observed that in leaks severe enough to produce a Kirkendall void, the A15 volume is also reduced. By comparison, RRP type wires manage a similar reaction with less than 10% residual barrier in the non-Cu cross section. Recently, Bruker EAS, the manufacturer of PIT Nb₃Sn wires, developed a new wire design which added a bundle barrier around the filament pack to contain Sn leaks and maintain a high RRR, as well as increasing the Sn content in the powder core to produce more A15. We believe that by improving deformation properties and optimizing new heat treatments to account for the higher Sn content, Jc can be substantially enhanced while maintaining RRR at small filament diameters. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / April 16, 2018. / CERN, magnets, nb3sn, powder in tube, superconductivity, wires / Includes bibliographical references. / David C. Larbalestier, Professor Directing Thesis; Jennifer Proffitt, University Representative; Fumitake Kametani, Committee Member; Emmanuel Collins, Committee Member; Chiara Tarantini, Committee Member; Peter J. Lee, Committee Member.

The company Falcken Forshaga are manufacturing lifting tools for the steel, paper and concrete industry. The company wants a lifting tool for L-supports which they want to be able to sell to the concrete industry. The reason for this is that todays ways of lifting and rotation of the supports are done by slings which are time consuming to use because the process is done in multiple steps. The reason why the supports are rotated is because they are casted lying down and are transported standing up which means that the supports needs to be lifted and then rotated. The purpose of this project is to simplify the process between casting and transport as well as learn to work on a project at a company. The goal of the work is to design a lifting tool which follows the requirements set by Falcken for the lifting tool and so it can gain CE-mark in the future. To design a lifting tool the product development process was used as it best fits this project. The work started with status analysis to be able to study the steps which occur in the process today from casting to transport. This is today made possible in three steps lift, rotation and movement to make it ready for transportation. A project plan was developed where the project was divided into different parts with goals to always have something to work against which brings the work forward. A risk analysis over the project was constructed at the beginning to analyze potential risks with the aim to minimize them. The biggest risk that was analyzed was that the project will become delayed, to counter this the project plan needs to be up to date as well as to get help if in need. The next step in the process is to list all the specifications and requests from Falcken and summarize them to be able to generate concepts. A second risk analysis was made to analyze the potential risks with or around the lifting tool during lift where the biggest risks is those who involve people getting injured and are the most important to minimize. To generate the concepts the 6-3-5-method was used and resulted in five different concepts which was analyzed further and filtered through an elimination matrix where the best concept was selected. The concept that was chosen and was designed in Autodesk Inventor was a support arm lift which locks in the sides of the L-support and has beams which run along the sides of the support and in underneath the lower edge of the support with plates. The tool is designed to lift in front of the center of gravity of the support which means that when the support is lifted the whole thing will rotate by itself which means that the steps from casting to transport will be done in one step instead of three. To ensure the strength of the construction it is calculated against safety factor of three as well as it is controlled with a FEM-analyze in Creo parametric 5 and inventor 2019 on details with are too complicated to calculate by hand. The tool which was designed meets all the requirement that was set but to achieve a tool which is sellable and is CE-marked more risks must be analyzed according to SS-EN ISO 12100:2010 and its life span has to be calculated via fatigue calculations as well as it must be manufactured and tested.

Hydrodynamic instability of a compressible shear mixing layer plays a very important role in controlling and promoting the mixing processes in supersonic combustion problems. At supersonic convective Mach numbers the natural mixing rates of the shear layer are observed to be very small. The current research interest is in the mixing enhancement. In the first part of the present study, the linear spatial instability problem of a supersonic shear mixing layer inside a rectangular channel is solved. A systematic way of calculating and classifying all the normal modes is developed. It is demonstrated that a vortex sheet at high supersonic convective Mach number, neutrally stable when unconfined, becomes unstable when confined. Extensive numerical computations indicate that two classes of unstable waves, named as class A and class B supersonic instability waves, can be identified. In addition to unstable waves, two families of neutral waves, named as class C and class D neutral acoustic waves, can also be identified. The characteristics of the unstable waves as well as the neutral waves are determined. It is concluded that the new supersonic instabilities found in this study are the dominant instabilities of a confined mixing layer at high supersonic convective Mach numbers. As such they are very relevant to the supersonic combustion problem. The second part of the study explores the possibility of enhancing the rate of supersonic mixing by means of a periodic Mach wave system. The Mach wave system may be generated by small amplitude waviness of the confining channel walls. The stability of the periodic basic flow is analyzed numerically by the Floquet theory and the spectral-collocation method. The convergence of the numerical solutions is discussed. New secondary instabilities of the shear layer induced by the periodic Mach waves are found computationally. The / growth rate of the new instabilities is found to vary nearly linearly with the ratio of the wavy wall amplitude to the wave length. Therefore it is a potentially promising scheme for the enhancement of supersonic mixing. / Source: Dissertation Abstracts International, Volume: 51-05, Section: B, page: 2446. / Major Professor: Christopher K. W. Tam. / Thesis (Ph.D.)--The Florida State University, 1990.

Com base em exemplos, nos fundamentos da Mecânica estatística e na teoria ergódiga, é dada uma definição de atrator como uma medida invariante. Vários resultados que corroboram esta definição são demostrados. Caos é relacionado à presença de um atrator com entropia métrica maior que zero. O papel dos expoentes de Lyapunov é analisado e é provado que um atrator caótica possui expoentes de Lyapunov positivos em quase todo ponto, e também que, se um atrator possui todos expoentes de Lyapunov estritamente negativos num conjunto de medida atratora maior que zero, então seu suporte é uma órbita periódica assintoticamente estável. / Here, a definition of an attractor as an invariant measure is given based on Ergodic Theory, foundations of Statistical Mechanics and some examples. Chaos is related to the presence of an attractor with metric entropy grater zero. It is proved that a chaotic attractor has positive Lyapunov exponents almost everywhere, and that, if an attractor has every Lyapunov exponents less than zero in a set of nonzero measure then the support set of the attractor is an asymptotic stable periodic orbit.

Sobre as equações de Vertogen e de Vries no modelo de Dicke generalizado / On the Vertogen and de Vries equations in the generalized Dicke model