1,122 research outputs found

    Proceedings of SIRM 2023 - The 15th European Conference on Rotordynamics

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    It was our great honor and pleasure to host the SIRM Conference after 2003 and 2011 for the third time in Darmstadt. Rotordynamics covers a huge variety of different applications and challenges which are all in the scope of this conference. The conference was opened with a keynote lecture given by Rainer Nordmann, one of the three founders of SIRM “Schwingungen in rotierenden Maschinen”. In total 53 papers passed our strict review process and were presented. This impressively shows that rotordynamics is relevant as ever. These contributions cover a very wide spectrum of session topics: fluid bearings and seals; air foil bearings; magnetic bearings; rotor blade interaction; rotor fluid interactions; unbalance and balancing; vibrations in turbomachines; vibration control; instability; electrical machines; monitoring, identification and diagnosis; advanced numerical tools and nonlinearities as well as general rotordynamics. The international character of the conference has been significantly enhanced by the Scientific Board since the 14th SIRM resulting on one hand in an expanded Scientific Committee which meanwhile consists of 31 members from 13 different European countries and on the other hand in the new name “European Conference on Rotordynamics”. This new international profile has also been emphasized by participants of the 15th SIRM coming from 17 different countries out of three continents. We experienced a vital discussion and dialogue between industry and academia at the conference where roughly one third of the papers were presented by industry and two thirds by academia being an excellent basis to follow a bidirectional transfer what we call xchange at Technical University of Darmstadt. At this point we also want to give our special thanks to the eleven industry sponsors for their great support of the conference. On behalf of the Darmstadt Local Committee I welcome you to read the papers of the 15th SIRM giving you further insight into the topics and presentations

    Strategies for Red-Light Photoswitching

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    Vuorovaikutteiset, muotoutuvat ja jopa älykkäät molekyylirakenteet ovat avain uuden sukupolven lääkeaineisiin ja toiminnallisiin materiaaleihin. Valokytkimet eli yhdisteet, jotka isomeroituvat reversiibelisti valon vaikutuksesta johtaen makroskooppisten ominaisuuksien muutoksiin, ovat erottamaton osa tätä tulevaisuutta. Mahdolliset sovelluskohteet ulottuvat lääketieteestä elektroniikkaan ja robotiikkaan. Valitettavasti useimmat valokytkinrakenteet, esimerkiksi laajalti käytetyt atsobentseenit, absorboivat ultraviolettivaloa, joka on vahingollista monille materiaaleille ja erityisesti eläville soluille. Jotta valokytkinten koko potentiaali voidaan hyödyntää, tarvitaan harmittomalla näkyvällä valolla toimivia yhdisteitä. Puna- tai infrapunavalo olisi ihanteellinen ärsyke biologian alalla käytettäville kytkimille. Sama pätee myös molekyylimoottoreihin eli yhdisteisiin, jotka pyörivät valon vaikutuksesta yksisuuntaisesti. Lisäksi sekä kytkinten että moottorien tulisi isomerisoitua valon vaikutuksesta tehokkaasti ja nopeasti, termisten isomerisaatioreaktioiden tulisi olla sovelluskohteesta riippuen hitaita tai nopeita ja yhdisteiden tulisi toimia hyvin erilaisissa ympäristöissä. Näiden ominaisuuksien hallitsemiseksi on tärkeää ymmärtää niiden taustalla olevat mekanismit. Tässä väitöskirjassa tutkimme kolmea keinoa toteuttaa valokytkentä punaisella valolla: (i) atsobentseenien absorptiospektrin siirtäminen rakennetta muokkaamalla, (ii) uusien, valmiiksi punaista valoa absorboivien rakenteiden hyödyntäminen ja (iii) epäsuora valokytkentä punavalolla aktivoitavia katalyyttejä hyödyntäen. Tarkastelemme strategioita teoreettiselta kannalta ja osoitamme, että niistä jokainen mahdollistaa valokytkennän punaista valoa käyttäen. Kullakin strategialla on etunsa ja haasteensa tehokkaan, nopean ja kestävän valokytkennän toteuttamiseksi. Tästä johtuen yksi ihanteellinen valokytkinmalli ei voi saavuttaa kaikkia eri sovelluksille asetettuja tavoitteita, vaan tulevaisuuden haaste on löytää kuhunkin käyttöön paras ratkaisu. Samoja periaatteita voidaan soveltaa myös molekyylimoottoreihin, jolloin molekulaarisen tason yksisuuntainen kiertoliike voidaan saada aikaan näkyvällä valolla. Lisäksi punaisella valolla toimivien valokytkinten rakenteita hyödyntämällä moottorien rotaatiota saadaan tehostettua.Responsive, adaptive and even intelligent molecular systems have been identified as the key to next-generation pharmaceuticals and functional materials. Photoswitches, compounds that isomerise reversibly between two distinct ground-state species upon excitation with light and consequently give rise to a macroscopic effect, are an integral part of this future. Their potential application areas range from photopharmacology to optoelectronics and soft robotics. However, most conventional photoswitch structures such as azobenzenes absorb ultraviolet light, high-energy photons that are detrimental to many artificial materials and especially to living systems. To harness their full potential, photoswitches should function efficiently with visible light that is benign to the environment. Red or near-infrared light would be the ideal stimulus for switches utilised in biological context, as these wavelengths are least absorbed by living tissue. The same applies to light-driven molecular motors, compounds that exhibit unidirectional rotation upon photoexcitation. In addition to absorption in the red part of the visible spectrum, both switches and motors should exhibit efficient and fast photoisomerisation, favourable thermal isomerisation kinetics and tolerance towards different environments in order to be useful in real-life applications. In this light, it is crucial to understand the underlying fundamental mechanisms that govern these attributes. In this thesis, we explore three different approaches to realise photoswitching with red light: (i) synthetic modifications of azobenzenes, (ii) utilisation of new photoswitch cores that inherently absorb low-energy photons, and (iii) indirect isomerisation with red-light photocatalysts. We study each strategy from a theoretical viewpoint and demonstrate that they all provide means to induce isomerisation with red light, each with unique advantages and challenges in terms of promoting efficient, fast and robust switching. As a result, a single optimal photoswitch system cannot be designed; instead, the challenge lies in identifying the best design for each application. The same principles can also be applied to molecular motors, giving rise to visible-light-powered unidirectional rotary motion on a molecular level. We show that drawing inspiration from red-light-absorbing photoswitches has repercussions not only on the visible-light absorption but also on enhanced rotation dynamics

    30th European Congress on Obesity (ECO 2023)

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    This is the abstract book of 30th European Congress on Obesity (ECO 2023

    Circulation Statistics in Homogeneous and Isotropic Turbulence

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    This is the committee version of a Thesis presented to the PostGrad Program in Physics of the Physics Institute of the Federal University of Rio de Janeiro (UFRJ), as a necessary requirement for the title of Ph.D. in Science (Physics). The development of the Vortex Gas Model (VGM) introduces a novel statistical framework for describing the characteristics of velocity circulation. In this model, the underlying foundations rely on the statistical attributes of two fundamental constituents. The first is a GMC field that governs intermittent behavior and the second constituent is a Gaussian Free field responsible for the partial polarization of the vortices in the gas. The model is revisited in a more sophisticated language, where volume exclusion among vortices is addressed. These additions were subsequently validated through numerical simulations of turbulent Navier-Stokes equations. This revised approach harmonizes with the multifractal characteristics exhibited by circulation statistics, offering a compelling elucidation for the phenomenon of linearization of the statistical circulation moments, observed in recent numerical simulation. In the end, a field theoretical approach, known as Martin-Siggia-Rose-Janssen-de Dominicis (MSRJD) functional method is carried out in the context of circulation probability density function. This approach delves into the realm of extreme circulation events, often referred to as Instantons, through two distinct methodologies: The First investigates the linear solutions and, by a renormalization group argument a time-rescaling symmetry is discussed. Secondly, a numerical strategy is implemented to tackle the nonlinear instanton equations in the axisymmetric approximation. This approach addresses the typical topology exhibited by the velocity field associated with extreme circulation events.Comment: Ph.D. Thesis - preliminary versio

    ReMKiT1D -- A framework for building reactive multi-fluid models of the tokamak Scrape-Off Layer with coupled electron kinetics in 1D

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    In this manuscript we present the recently developed flexible framework for building both fluid and electron kinetic models of the tokamak Scrape-Off Layer in 1D - ReMKiT1D (Reactive Multi-fluid and Kinetic Transport in 1D). The framework can handle systems of non-linear ODEs, various 1D PDEs arising in fluid modelling, as well as PDEs arising from the treatment of the electron kinetic equation. As such, the framework allows for flexibility in fluid models of the Scrape-Off Layer while allowing the easy addition of kinetic electron effects. We focus on presenting both the high-level design decisions that allow for model flexibility, as well as the most important implementation aspects. A significant number of verification and performance tests are presented, as well as a step-by-step walkthrough of a simple example for setting up models using the Python interface

    Simulations numériques d'allumages des moteurs aéronautiques en conditions réalistes de hautes altitudes

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    La capacité de rallumage est un aspect critique de la conception des moteurs aéronautiques et les normes de sureté exigent l'allumage du moteur en conditions de haute altitude (basse pression : P = 0.3 bar et basse température : T = 233 K ). Ainsi, l'influence des conditions de basse pression et de basse temperature doit être mieux comprise. Pour cela, l'effet de ces conditions sur les phenomènes chimiques a tout d'abord été étudié en configurations purement gazeuses. Les résultats ont alors montré que les conditions sub-atmosphériques étaient désavantageuses à cause d'un ralentissement de la réactivité chimique et donc d'une réduction de la puissance dégagée. De plus, des simulations numériques directes ont été réalisées en utilisant une chimie ARC multi-composante ce qui a permis de comparer le développement des noyaux de flamme en fonction des conditions de pression et de température. Les résultats indiquent alors que les noyaux formés en condition de basse pression sont moins robustes aux phénomènes d'extinctions. D'autre part, l'influence des conditions de haute altitude sur le diphasique a aussi été évaluée. Premièrement, au niveau de l'injection de carburant, les données expérimentales disponibles ont montré que les basses pressions réduisent les processus d'atomisation ce qui conduit à la formation d'un spray composé de gouttes plus larges et moins nombreuses. Des simulations d'allumage diphasique ont alors été réalisées en prenant en compte la modification de la distribution de goutte induite par les conditions de haute altitude. Un changement complet du régime de combustion a alors été observé par rapport au cas gazeux. Pour finir, ce travail a permis de développer de nouvelles méthodes numériques qui ont pu être utilisées pour simuler l'allumage en condition réaliste de haute altitude dans le banc MERCATO. Ce calcul a mis en évidence le rôle critique des phénomènes diphasiques dans la formation et le développement du noyau. De plus, l'effet néfaste des basses pressions et des basses températures sur l'allumage a été retrouvé. The relight capability is a critical aspect of the aeronautical engine design and safety standards require the ignition of the engine under high altitude conditions (low pressure: P = 0.3 bar and low temperature: T = 233 K). Therefore the influence of low pressure and low temperature conditions on the ignition processes must be better understood. For this purpose, the effect of these conditions on the chemical phenomena has been first evaluated with purely gaseous configurations. The results have shown the detrimental effect of sub-atmospheric conditions via a slowing down of the chemical reactivity and thus a reduction of the power released. In addition, direct numerical simulations performed using a multi-component ARC chemistry enable to compare the kernel developments depending on the pressure and temperature conditions and indicate that low pressure kernels are less robust to extinction phenomena. On the other hand, the influences of high altitude conditions on the two-phase flow have also been evaluated. Firstly, at the fuel injection, the available experimental measurements have shown that low pressure reduces the atomization phenomenon resulting in a spray with larger and fewer droplets. Two-phase ignition simulations have thus been performed taking into account the different droplet distribution due to the high altitude conditions. A complete modification of the combustion regime has then been observed compared to the gaseous case. Finally, this work enables to develop new numerical methods which have been used to simulate the ignition under realistic high altitude conditions in the MERCATO configuration. This computation highlighted the critical role of the two-phase phenomena in the formation and development of the kernel. Furthermore, the detrimental effect of low pressure and low temperature on the ignition has been recovered once again

    Discontinuous Galerkin methods for Liouville’s equation of geometrical optics

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    International Academic Symposium of Social Science 2022

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    This conference proceedings gathers work and research presented at the International Academic Symposium of Social Science 2022 (IASSC2022) held on July 3, 2022, in Kota Bharu, Kelantan, Malaysia. The conference was jointly organized by the Faculty of Information Management of Universiti Teknologi MARA Kelantan Branch, Malaysia; University of Malaya, Malaysia; Universitas Pembangunan Nasional Veteran Jakarta, Indonesia; Universitas Ngudi Waluyo, Indonesia; Camarines Sur Polytechnic Colleges, Philippines; and UCSI University, Malaysia. Featuring experienced keynote speakers from Malaysia, Australia, and England, this proceeding provides an opportunity for researchers, postgraduate students, and industry practitioners to gain knowledge and understanding of advanced topics concerning digital transformations in the perspective of the social sciences and information systems, focusing on issues, challenges, impacts, and theoretical foundations. This conference proceedings will assist in shaping the future of the academy and industry by compiling state-of-the-art works and future trends in the digital transformation of the social sciences and the field of information systems. It is also considered an interactive platform that enables academicians, practitioners and students from various institutions and industries to collaborate

    GEAR-RT: Towards Exa-Scale Moment Based Radiative Transfer For Cosmological Simulations Using Task-Based Parallelism And Dynamic Sub-Cycling with SWIFT

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    The development and implementation of GEAR-RT, a radiative transfer solver using the M1 closure in the open source code SWIFT, is presented, and validated using standard tests for radiative transfer. GEAR-RT is modeled after RAMSES-RT (Rosdahl et al. 2013) with some key differences. Firstly, while RAMSES-RT uses Finite Volume methods and an Adaptive Mesh Refinement (AMR) strategy, GEAR-RT employs particles as discretization elements and solves the equations using a Finite Volume Particle Method (FVPM). Secondly, GEAR-RT makes use of the task-based parallelization strategy of SWIFT, which allows for optimized load balancing, increased cache efficiency, asynchronous communications, and a domain decomposition based on work rather than on data. GEAR-RT is able to perform sub-cycles of radiative transfer steps w.r.t. a single hydrodynamics step. Radiation requires much smaller time step sizes than hydrodynamics, and sub-cycling permits calculations which are not strictly necessary to be skipped. Indeed, in a test case with gravity, hydrodynamics, and radiative transfer, the sub-cycling is able to reduce the runtime of a simulation by over 90%. Allowing only a part of the involved physics to be sub-cycled is a contrived matter when task-based parallelism is involved, and is an entirely novel feature in SWIFT. Since GEAR-RT uses a FVPM, a detailed introduction into Finite Volume methods and Finite Volume Particle Methods is presented. In astrophysical literature, two FVPM methods are written about: Hopkins (2015) have implemented one in their GIZMO code, while the one mentioned in Ivanova et al. (2013) isn't used to date. In this work, I test an implementation of the Ivanova et al. (2013) version, and conclude that in its current form, it is not suitable for use with particles which are co-moving with the fluid, which in turn is an essential feature for cosmological simulations.Comment: PhD Thesi
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