Medical device-associated infections and corrosion behaviour of medical devices always impose considerable inconvenience and distress to patients and place a substantial economic burden on health care systems. The aim of this research is to solve this problem by developing a new coating which can reduce bacterial adhesion and slow down the corrosion behaviour efficiently. In this study, two kinds of Ni-P-PTFE based coatings including Ni-P-PTFE-ZrO2 and Ni-P-PTFE-ZrO2-TiO2 were developed by electroless plating technique. The assays of bacterial adhesion and removal were conducted on nano-composite Ni-P-PTFE-ZrO2 and Ni-P-PTFE-ZrO2-TiO2 coatings to see whether or not they have the capability of effectively resisting bacterial adhesion or reducing adhered bacteria. The anticorrosive properties of these Ni-P-PTFE based coatings were also investigated by electrochemical test. In the assay of bacterial adhesion and removal, two different bacteria were used including Escherichia coli and Staphylococcus aureus. The Ni-P-PTFE-ZrO2 and Ni-P-PTFE-ZrO2-TiO2 coatings prepared with the different concentrations of PTFE, ZrO2 and TiO2 showed that the concentrations had significant influence on the bacterial adhesion and removal using a dipping process. The effect of surface free energy and its components of the coatings on the performance of bacterial adhesion and removal were also investigated. Extended DLVO theory also explained why some coatings adhered less bacteria than others by analysing total interaction energy between bacteria and the coatings. While in the corrosion test, open circuit potential, polarization resistance (Rp), corrosion current density (Icorr), and corrosion rate (CR) were obtained by measuring the open circuit potential and anodic, cathodic tafel plots of Ni-P-PTFE-ZrO2 and Ni-P-PTFE-ZrO2-TiO2 coatings to evaluate their anticorrosive performances. V In conclusion, the new nano-composite Ni-P-PTFE-ZrO2 and Ni-P-PTFE-ZrO2-TiO2 coatings showed the better capability of resisting bacterial adhesion and reducing adhered bacteria after dipping process than Ni-P and Ni-P-PTFE coatings and also have better anticorrosive property than Ni-P and Ni-P-PTFE coatings. These two new coatings have great potential to be used in the medical device market.

Se establece la metodología, incluyendo la formulación necesaria, para el diseño térmico de subenfriadores criogénicos n2(i)-n2(i), observando en todo momento criterios de optimización para con los diferentes parámetros y dimensiones que han de caracterizar el resultado final del mismo. La metodología esta contrastada experimentalmente, a partir de los datos obtenidos tras los ensayos realizados con el prototipo construido en base a la propia metodología. Ello ha permitido proponer una correlación, inspirada en la de Kutateladze, y que es especifica para la pareja fluido superficie utilizada, en áreas a determinar el coeficiente de convección en ebullición nucleada.

The aim of this work is to study the thermal and fluid-dynamic behavior of vapor compression refrigerating systems and their constitutive elements (heat exchangers, expansion devices, compressors and connecting tubes) focused on the use of natural refrigerants (carbon dioxide, isobutane and ammonia). The specific topics analyzed throughout this thesis have arisen from the growing interest in environmentally friendly refrigerants that has led the CTTC group (Centro Tecnológico de Transferencia de Calor) to undertake significant research efforts and to take part in several projects with national and European institutions. The information reported herein represents a summary of the work carried out by the author during the last years together with the contributions provided by other members of the CTTC group. This thesis has led to the creation of some publications in International Conferences and indexed journals. The main achievement of this work has been the development of a flexible numerical tool based on several subroutines. The whole numerical infrastructure is the result of coupling the specific resolution procedures for each vapor compression refrigerating system component together with the whole system resolution algorithm. The simulations have been oriented to study the system thermodynamical characteristics as well as some relevant aspects of its particular elements. In addition to the numerical results a significant experimental work has also been carried out in the CTTC facilities due to the need for experimental validation. The author has been fully involved in data acquisition procedures and has also collaborated in the setting up of the experimental units. In general, all the studies conducted in this work have been presented following the same structure: i) numerical model and resolution procedure explanation; ii) model validation against experimental data; and iii) simulation results. The specific topics tackled within this thesis include the implementation of a two-phase numerical model to simulate the thermal and fluid-dynamic behavior of single- and two-phase flows inside ducts, the study of heat transfer coefficient empirical correlations for both cooling of carbon dioxide at transcritical conditions and evaporation of ammonia at overfeed conditions, the implementation of a numerical model to simulate capillary tubes in order to study their behavior at typical operational conditions found in household refrigerators working with isobutane, the development of a two-phase flow distribution model to simulate heat exchangers made up by manifold systems, and the study of vapor compression refrigeration cycles with special emphasis on carbon dioxide transcritical situations. The set of the numerical models implemented has demonstrated to be a flexible tool as several different aspects of refrigeration vapor compression systems have been successfully simulated and study. It has also demonstrated to be an accurate tool as the numerical results achieved have shown good agreement against experimental data / The aim of this work is to study the thermal and fluid-dynamic behavior of vapor compression refrigerating systems and their constitutive elements (heat exchangers, expansion devices, compressors and connecting tubes) focused on the use of natural refrigerants (carbon dioxide, isobutane and ammonia). The specific topics analyzed throughout this thesis have arisen from the growing interest in environmentally friendly refrigerants that has led the CTTC group (Centro Tecnológico de Transferencia de Calor) to undertake significant research efforts and to take part in several projects with national and European institutions. The information reported herein represents a summary of the work carried out by the author during the last years together with the contributions provided by other members of the CTTC group. This thesis has led to the creation of some publications in International Conferences and indexed journals. The main achievement of this work has been the development of a flexible numerical tool based on several subroutines. The whole numerical infrastructure is the result of coupling the specific resolution procedures for each vapor compression refrigerating system component together with the whole system resolution algorithm. The simulations have been oriented to study the system thermodynamical characteristics as well as some relevant aspects of its particular elements. In addition to the numerical results a significant experimental work has also been carried out in the CTTC facilities due to the need for experimental validation. The author has been fully involved in data acquisition procedures and has also collaborated in the setting up of the experimental units. In general, all the studies conducted in this work have been presented following the same structure: i) numerical model and resolution procedure explanation; ii) model validation against experimental data; and iii) simulation results. The specific topics tackled within this thesis include the implementation of a two-phase numerical model to simulate the thermal and fluid-dynamic behavior of single- and two-phase flows inside ducts, the study of heat transfer coefficient empirical correlations for both cooling of carbon dioxide at transcritical conditions and evaporation of ammonia at overfeed conditions, the implementation of a numerical model to simulate capillary tubes in order to study their behavior at typical operational conditions found in household refrigerators working with isobutane, the development of a two-phase flow distribution model to simulate heat exchangers made up by manifold systems, and the study of vapor compression refrigeration cycles with special emphasis on carbon dioxide transcritical situations. The set of the numerical models implemented has demonstrated to be a flexible tool as several different aspects of refrigeration vapor compression systems have been successfully simulated and study. It has also demonstrated to be an accurate tool as the numerical results achieved have shown good agreement against experimental data

Permanent magnet synchronous motors (PMSMs) are an alternative in critical applications where high-speed operation, compactness and high efficiency are required. In these applications it is highly desired to dispose of an on-line, reliable and cost-effective fault diagnosis method. Fault prediction and diagnosis allows increasing electric machines performance and raising their lifespan, thus reducing maintenance costs, while ensuring optimum reliability, safe operation and timely maintenance. Consequently this thesis is dedicated to the diagnosis of magnetic and electrical faults in PMSMs. As a first step, the behavior of a healthy machine is studied, and with this aim a new 2D finite element method (FEM) modelbased system for analyzing surface-mounted PSMSs with skewed rotor magnets is proposed. It is based on generating a geometric equivalent non-skewed permanent magnet distribution which accounts for the skewed distribution of the practical rotor, thus avoiding 3D geometries and greatly reducing the computational burden of the problem. To diagnose demagnetization faults, this thesis proposes an on-line methodology based on monitoring the zero-sequence voltage component (ZSVC). Attributes of the proposed method include simplicity, very low computational burden and high sensibility when compared with the well known stator currents analysis method. A simple expression of the ZSVC is deduced, which can be used as a fault indicator parameter. Furthermore, mechanical effects arising from demagnetization faults are studied. These effects are analyzed by means of FEM simulations and experimental tests based on direct measurements of the shaft trajectory through self-mixing interferometry. For that purpose two perpendicular laser diodes are used to measure displacements in both X and Y axes. Laser measurements proved that demagnetization faults may induce a quantifiable deviation of the rotor trajectory. In the case of electrical faults, this thesis studies the effects of resistive unbalance and stator winding inter-turn short-circuits in PMSMs and compares two methods for detecting and discriminating both faults. These methods are based on monitoring and analyzing the third harmonic component of the stator currents and the first harmonic of the ZSVC. Finally, the Vold-Kalman filtering order tracking algorithm is introduced and applied to extract selected harmonics related to magnetic and electrical faults when the machine operates under variable speed and different load levels. Furthermore, different fault indicators are proposed and their behavior is validated by means of experimental data. Both simulation and experimental results show the potential of the proposed methods to provide helpful and reliable data to carry out a simultaneous diagnosis of resistive unbalance and stator winding inter-turn faults.

In nowadays nanometer technology nodes, the semiconductor industry has to deal with the new challenges associated to technology scaling. On one hand, process developers face increasing manufacturing cost and variability, but also decreasing manufacturing yield. On the other hand, circuit designers and electronic design automation (EDA) developers have to reduce design turnaround time and provide the tools to cope with increasing design complexity and reduce the time-to-market. In this scenario, closer collaboration between all the actors involved is required. New approaches considering both design and manufacturing need to be explored. These are the so called design for manufacturability (DFM) techniques. A DFM trend that is becoming dominant is to make circuit layouts more regular and repetitive. The regular layout fabrics are based on the configuration of a simplied mask set, therefore reducing the manufacturing cost. Moreover, a reduced number of layout patterns is used, allowing better process variability control and optimization. Hence, regularity reduces layout complexity and therefore design complexity, allowing faster time-to-market. In this thesis, we explore forcing maximum layout regularity focusing on future technology nodes, with increasing design and manufacturability issues, where we expect layout regularity to be mandatory. With this objective, we have developed a new regular layout fabric called Via-Configurable Transistor Array (VCTA). The physical design is fully explained involving layout and geometrical considerations for transistors and interconnects. Initially, VCTA layouts developed manually have been evaluated in terms of manufacturability, but also in terms of area, energy and delay. For digital design, 32-bit binary adders designed with VCTA have been compared to standard cell layouts. For analog design, a delay-locked loop design using VCTA has been compared to its full custom version. We have also developed a physical synthesis tool that allows us to obtain VCTA circuit layouts in an automated way. Developing our own automation tool lets us controlling all the decisions made during the physical design flow to ensure that maximum layout regularity is respected. In this case the work is based on several algorithms, for instance for routing, that we have oriented to the area optimization of the layouts. Finally, in order to demonstrate the benefits of layout regularity, we have proposed a new layout regularity metric called Fixed Origin Corner Square Inspection (FOCSI). It is based on the geometrical inspection of the patterns in the layouts and it allows designers to compare regularity of designs but also how their regularity will impact their manufacturability. The FOCSI layout analysis tool can be used to optimize manufacturability.

Probabilistic Risk Assessment for the evaluation of procedures in the Nuclear Safety field. Application to a pressurized water reactor. The studies contained in this PhD are involved in the Nuclear Safety research field. Both are related to the Risk Informed philosophy with the improvement of the risk decision-making as a main target. Probabilistic Safety Assessment is the main tool for the development of the PhD and it is also the common research field for the assessment of its applications and limitations. The Nuclear Engineering Research Group (NERG) in the Technical University of Catalonia (UPC) decided to research in the development of new techniques and methodologies for a better assessment of the nuclear safety.The carried out studies contained in the PhD are based on a three loops Westinghouse Pressurised Water Reactor (PWR). Plant documentation (operation instructions, procedures, design basis, databases, safety studies, technical specifications, etc.) as well as scientific reviews; have made possible the achievement of the results and publications related to the PhD. The safety standards of the Nuclear Regulatory Commission (NRC) and the International Atomic Energy Agency (IAEA) have always been taken into account during the research. The thesis consists of two main parts: I) Quantification of the Outage Key Safety Functions using the Probabilistic Safety Assessment. II) Risk assessment of the spent fuel pool associated risk from the probabilistic view. The first study is based on the risk quantification of a deterministic procedure using the Probabilistic Safety Assessment. The analysed procedure contains the key safety functions during the outage. The result is the creation of a methodology which gives values to risk associated to the non-compliance of the key safety functions. It makes easier the decision-making during the plant operation. Second part, consists first in the development of the Probabilistic Safety Assessment (PSA) of a spent fuel pool. It is a Level 1 PSA containing all tasks for the performance of the study: Initiating events analysis, scenarios and consequences quantification, human reliability analysis, etc. Afterwards, using the developed PSA, the interaction with the deterministic analysis begins. Risk associated to design, technical specifications, operation and procedures is quantified. Again, the interaction between both risk assessment philosophies as a main find of this PhD is achieved. The evaluation of risk associated to deterministic studies using probabilistic tools makes possible the detection weaknesses in both techniques. Some of the numerical values presented in that thesis, may be slightly different to their real quantification result. Some of the technical names of components or systems may also defer. That is because of the existing data confidentiality associated to the project agreement. / La seguridad es el marco principal en el que se sitúan los dos estudios recogidos en esta tesis. Ambos se integran en el programa de investigación de la industria nuclear y tratan de implementar aplicaciones basadas en la información relativa al riesgo, con el objeto de facilitar la toma de decisiones en el campo de la planificación y explotación óptima de las centrales nucleares. Los Análisis Probabilistas de Seguridad son la herramienta común para el desarrollo de los estudios así como el campo dónde se investiga durante la Tesis para mejorar sus limitaciones y aplicaciones. Desde en Nuclear Engineering Research Group (NERG) de la Universitat Politècnica de Catalunya (UPC) se apostó por la línea de investigación de desarrollo de nuevas técnicas y metodologías de análisis de seguridad aplicadas a la industria nuclear. Un reactor Westinghouse de agua a presión (PWR) de tres lazos ha sido la base sobre la que se han aplicado los estudios de esta tesis. La documentación de la planta (instrucciones de operación, procedimientos, bases de diseño, criterios de éxito, bases de datos, estudios de seguridad, etc.) junto a un amplio espectro de publicaciones científicas en el campo, han permitido el hallazgo de resultados que se publican en esta tesis doctoral. Siempre, bajo los estándares de seguridad de la Nuclear Regulatory Commission y la Agencia Internacional de la Energía Atómica. La Tesis se compone de dos partes principales: I) Cuantificación de las Funciones Clave de Seguridad en parada mediante el Análisis Probabilista de Seguridad. II) II) Análisis del riesgo asociado a una Piscina de Combustible Gastado (PCG) de un reactor de agua a presión desde la óptica probabilista. La primera parte es fruto de la aplicación del análisis probabilista para la cuantificación del riesgo de un procedimiento determinista de la central nuclear en cuestión. Se consigue desarrollar una metodología que permita dar valores numéricos al riesgo que supone un mal cumplimiento de las funciones clave de seguridad de un procedimiento de operación. A parte del valor científico, que supone esta metodología, se obtienen unos resultados de la aplicación que posibilitan la toma de decisiones en planta. El segundo bloque de esta tesis consiste inicialmente en el desarrollo del Análisis Probabilista de Seguridad de la PCG de una central nuclear. Se trata de un estudio de Nivel 1 y contiene todas las tareas para un análisis de riesgo: evaluación inicial de los sucesos, cuantificación de las probabilidades de escenarios y consecuencias, análisis de fiabilidad humana, et. Al igual que en la parte I, una vez disponible la visión probabilista de la instalación, da comienzo la interacción con los diversos análisis deterministas referentes a la PCG. Se evalúa y cuantifica el riesgo asociado al diseño, especificaciones técnicas, operación y procedimentación. Una vez más, se consigue la integración de ambas persepectivas como principal hallazgo de esta tesis. Tanto el objeto como el alcance de ambos estudios se detallan en la memoria. El estado del arte de la Tesis se podría situar en un distanciamiento de las filosofías determinista y probabilista en la industria nuclear. Se consigue con estos estudios, una complementación entre ambas perspectivas sobretodo con la publicación de la metodología desarrollada. Evaluar métodos deterministas mediante técnicas probabilistas hace posible detectar debilidades en ambas formas de percibir el riesgo. Algunos de los valores presentados en la memoria de tesis, difieren de los calculados durante las tareas de cuantificación de los estudios. De la misma manera, algunos nombres específicos de componentes o sistemas analizados. Esto es debido a la confidencialidad de datos que rige el convenio entre la central nuclear y el grupo de investigación NERG.

Six synthetic manganese dioxides (coded SBPA, Faradiser WSZ, IBA no.14, IBA no.19, R2 and Faradiser M) covering the range of crystal structures exhibited by battery active materials were studied by XRD (X-Ray Diffraction) and FTIR (Fourier Transform Infra-Red) spectroscopy when H was inserted with organic reductants. Initial x-ray diffraction patterns (i.e. before H insertion) indicated a structural series, the γ-γt-MnO2 series. where γ-MnO2 designates the phase defined by de Wolff's intergrowth model. This model described γ-MnO2 as a random alternation of two types of layers derived from the known structures of the minerals ramsdellite and pyrolusite. γ-MnO2 may be characterised by one parameter, p, the pyrolusite type layer fraction. p=0 corresponds to ramsdellite whereas p=1 corresponds to pyrolusite. The additional structural defect responsible for the γ-γt-MnO2 series was found to be that of microtwinning in accordance with the model proposed by Pannetier et al. Material SBPA possessed a low degree of microtwinning with p=0.204±O.OO5 whereas typical battery active manganese dioxides IBA no.19 and R2 possessed x-ray diffraction patterns consistent with a high degree of microtwinning and p-0.2. The other materials, except Faradiser M, displayed x-ray diffraction patterns intermediate between those of SBPA and IBA no. 19/R2. Faradiser M possessed a high degree of microtwinning but with p-0.7. The most H inserted compounds (i.e. of composition MnOOH1.0) also formed an analogous structural series. the δ-δt-MnOOH series. δ-MnOOH may be described as a random alternation of two types of layers derived from the known structures of the minerals groutite and manganite which are reduced isostructural derivatives of ramsdellite and pyrolusite. δ-MnOOH was successfully analyzed for the concentration of (presumed) manganite type layer defects (m) in an analogous manner to that required to determine p, which confirmed the existence of reduced intergrowth structures. m was found to be less than p unless the H insertion reaction temperature was lowered (-2°C) in which case m=p. This was consistent with the observed precipitation of small amounts of γ-MnOOH when H was inserted with chemical reductants in non-aqueous solvents. The level of H insertion may be represented by the formula r in MnOOHr, where -0.1≤r≤1.0 (r starts at a value greater than zero due to the non-stoichiometry of battery active materials). H insertion into EMD (Electrodeposited Manganese Dioxide) R2 led to approximate isotropic lattice expansion in the H insertion region 0.11≤r≤0.80. This observation was consistent with a homogeneous solid state reduction with formation of a solid solution in which H+ and e- were mobile. In the region 0.80≤r≤1.01'new' non-moving peaks emerged characteristic of the final product while the original lines continued to move. The line shift indicated anisotropic lattice expansion. The 'new' non moving peaks could not be interpreted on the basis that a new phase was emerging. An explanation for this behaviour based on the properties of the defect crystal structure of the original material has been found. It involved identification of a type of x-ray line shift characteristic of random layer structures. The effects observed were consistent with random precipitation of δ-MnOOH micro-domains within the solid solution. The 'new lines' which emerged represented a re-emergence of lines originally overlapped with other lines due to the particular effects of microtwinning. The appearance of microdomains of the end product crystallizing within the solid solution implied that H+ and e- were no longer mobile in the crystal structure but located or 'frozen' in position. The presence of 'frozen' H (i.e δ-MnOOH micro-domains) was supported by measurements of FTIR band areas at wavenumber regions where OH vibration modes occurred. The onset of OH vibration modes with increasing H insertion supported the interpretation of the x-ray patterns. Interpretation of the FTIR spectra of material SBPA indicated no OH bond formation in the H insertion region 0.068≤r≤0.35 and OH bond formation in the region 0.35≤r≤0.882. Examination of the XRD patterns indicated heterogeneous solid state reduction had occurred in the H insertion region 0.40≤r≤0.882. The onset of OH bond formation at r=0.35 was interpreted as a necessary precursor to heterogeneous reduction starting at r=OAO. Heterogeneous reduction was presumed to have occurred by H location in an outer particulate layer which propagated into the bulk. H insertion into the remaining materials was interpreted in a similar manner. That is beyond a certain r in MnOOHr H location, as indicated by OH bond formation, led to crystallization of δ-MnOOH micro-domains which either randomly precipitated in the solid solution or they associated in such a way that led to heterogeneous reduction. The r in MnOOHr at which H started to locate appeared to depend on the relative rates at which H was inserted and diffused into the solid. H location occurred at r-0.20 for Faradiser M in contrast to R2 in which it located at r=0.80. A complementary study of the stability of the H inserted compounds in 7M KOH was carried out. Results from potential measurements, x-ray diffraction and SEM were obtained. Over a period of six weeks potential measurements indicated development of a heterogeneous potential at deep H insertion levels. X-ray diffraction and SEM signified formation of δ-MnO2 and γ-MnOOH. The results confirm the proposition of Holton et al. that H inserted compounds are unstable in KOH and disproportionate into δ-MnO2 and γ–MnOOH. This work removes doubt concerning the above proposition since formation of δ-MnO2 n their work was not simply the result of instability. The H insertion level at which instability was observed appeared related to the formation of δ-MnOOH micro-domains, particularly for R2 in which instability occurred between 0.80≤r≤1.0. This coincides with the oxidation state, MnO1.6, beyond which alkaline manganese batteries cease to deliver useful power on prolonged intermittent discharge. Faradiser M possessed the largest instability region (0.48≤r≤1.0) and would, on this basis, be unsuitable for alkaline manganese batteries.

Non-ferrous surfaces such as diamond-like carbon (DLC) coatings are becoming potential candidates for automotive engine parts because of fuel economy gains that these surfaces offer by operating with very low friction. In recent years, a wide range of DLC coatings have been developed and it is important to understand their film-forming, friction reduction and wear resistance mechanisms under lubricated conditions. This aim of the work described in this thesis is to improve our understanding of the tribological behaviour of DLC coatings with different engine oil additives. The main focus of the thesis is to study a wide range of available DLC coating types with currently available and widely-used additives such as ZDDP, friction modifiers, MoDTC etc., in order to establish general rules of their tribological behaviour that will help lubricant manufacturers produce new oil formulations. The research shows that tribofilms are formed on all DLCs by most of the currently used additives and that the film thickness depends on various factors such as type of DLC coating, doping elements present in the coatings, concentration of hydrogen and tungsten present in the coatings and the counterpart. Hydrogen-free coatings (a-C and ta-C) give lower boundary friction compared to the other coatings whereas hydrogenated amorphous carbon (a-C:H) coatings give better wear resistance properties. Study of a-C:H:W coatings shows that the concentration of tungsten present in the coatings has a significant influence on wear resistance properties but negligible influence on the friction properties when additives are present. The steel/steel couple is known to form a thick ZDDP tribofilm. If one of the contact surfaces is coated with DLC, the tribofilm forming properties on the steel vary and, for some cases, the low boundary friction properties of DLCs are degraded.

Molecular dynamics (MD) is a discrete modelling technique that is used to capture the nanoscale motion of molecules. MD can be used to accurately simulate a range of physical problems where the continuum assumption breaks down. Examples include surface interaction, complex molecules, local phase changes, shock waves or the contact line between fluids. However, beyond very small systems and timescales (μm and msec), MD is prohibitively expensive. Continuum computational fluid dynamics (CFD), on the other hand, is easily capable of simulating scales of engineering interest, (m and s). However, CFD is unable to capture micro-scale effects vital for many modern engineering fields, such as nanofluidics, tribology, nano-electronics and integrated circuit development. This work details the development of a set of techniques that combine the advantages of both continuum and molecular modelling methodologies, allowing the study of cases beyond the range of either technique alone. The present work is split into both computational and theoretical developments. The computational aspect involves the development of a new high-performance MD code, as well as a coupler (CPL) library to link it to a continuum solver. The MD code is fully verified, has similar performance to existing MD software and allows simulation of a wide range of cases. The CPL library is a robust, flexible and language independent API and the source code has been made freely available under the GNU GPL v3 license. Both MD and CPL codes are developed to allow very large scale simulation on high performance computing (HPC) facilities. The theoretical aspect includes the development of a rigorous mathematical framework and its application to develop novel coupling methodologies. The mathematical framework allows a discrete molecular system to be expressed in terms of the control volume (CV) formulation from continuum fluid dynamics. A discrete form of Reynolds’ transport theorem, is thus obtained, allowing both molecular and continuum systems to be expressed in a consistent manner. This results in a number of important insights into the molecular definition of stress. This CV framework allows mathematical operations to be localised to a control volume in space. It is ideally suited to apply coupling constraints to a region in space. To link the CFD and MD solvers in a rigorous and physically consistent manner, the CV framework is combined with the variational principles of classical mechanics. The result is a unification of a number of existing forms used in the coupling literature and a rigorous derivation of a new and more general coupling scheme.

The transition to turbulence of a laminar boundary layer can be affected by free-stream turbulence (FST). High levels of FST can cause the exponentially growing Tollmien-Schlichting wave to be replaced by algebraically growing streaks. Transient growth theory successfully identified counter-rotating, streamwise-oriented vortices as optimal flow configuration for maximum streaks’ amplification. The introduction of a wall film can significantly alter the amplification and evolution of streaks, influencing the penetration of FST inside the boundary layers, and its effects on modal and non-modal stability are yet to be addressed within the appropriate spatially-developing framework. In this work, the outcome of the introduction of a wall film on spatial transient amplification is analysed. Under base flow parallelism, optimal disturbances are computed by solving an optimal evolution problem. This study demonstrates that decreasing the viscosity of the film has a direct impact on the efficacy of the vortex tilting mechanism, leading to transient growth reduction. The different spreading rates of the boundary layer edge and the interface height imply that the effects of stratification vary in the streamwise direction. The assumption of base flow parallelism is therefore relaxed and a framework for the determination of optimal disturbances and spatial transient amplification in two-phase spreading boundary layers is presented, using adjoint optimization techniques. It is shown that spreading effects can alter the prediction of linear stability on streaks amplification. Beyond the early linear stage, the amplitude of the instability waves and interface deformation become appreciable and nonlinear effects cannot be neglected. As a result, an accurate description of the evolution of disturbances in two-fluid boundary layers must account for nonlinear interactions and mean flow distortion. Direct Numerical Simulation (DNS) with interface tracking is used to study the nonlinear evolution of the optimal disturbances in the two-fluid flow.