Implicit large-eddy simulation of low-speed separated flows using high-resolution methods

Most flows of practical importance are governed by viscous near-wall phenomena leading to separation and subsequent transition to a turbulent state. This type of problem currently poses one of the greatest challenges for computational methods because its characteristics covers a wide range of physical processes that often place contradictory requirements on the numerics employed. This thesis seeks to investigate the physics of complex, separated flows pertinent to aeronautical engineering and to assess the performance of variants of the Implicit Large-Eddy Simulation approach in predicting this type of problem realistically. For this purpose, different numerical solution strategies based on high-resolution methods, distinguished by their order of accuracy, are used in precursor simulations and one selected approach is applied to a fully three-dimensional wing flow. In order to isolate the development from laminar to turbulent flow after separation has occurred, the prototype Taylor-Green Vortex is considered. Here, the behaviour of the numerical schemes during the linear, non-linear and fully turbulent stages in the flow evolution is tested for different grid sizes. It is found that the resolution power and the likelihood of symmetry breaking is increasing with the order of accuracy of the numerical method. These two properties allow the flow to develop more realistically on coarse grids if higher order schemes are employed. In the next step, flow separation from a gently curved surface is included. The fundamental study of a statistically two-dimensional channel flow with hill-type constrictions demonstrates the basic applicability of ILES to problems featuring massive separation. Without specific wall-treatment, high-resolution methods can improve prediction of the detachment location when compared to classical Large-Eddy Simulations. Finally, an ILES simulation of three-dimensional flow over a swept wing geometry at moderate angle of incidence is presented. The results are in excellent agreement with experiment in the fully separated and turbulent region and they are more accurate than a classical hybrid RANS/LES approach, using a grid twice the size, over the majority of the wing. This outcome will probably settle the dispute that has erupted in the past over the applicability of ILES to complex, wall-bounded flows

Enhanced Current Capability for Modular Multilevel Converters by a Combined Sorting Algorithm for Capacitor Voltages and Semiconductor Losses

The modular multilevel converter (MMC) has become very attractive for high- and medium-voltage applications, generating excellent waveforms at very high efficiencies. One of the main challenges is the appropriate selection of inserted submodules (SMs), commonly done by capacitor voltage balancing algorithms. However, the semiconductor stress can only be balanced up to a certain degree by conventional algorithms, since the stress is not directly monitored. An uneven stress distribution between the SMs does not only result in different lifetime expectations, but also in increased maximum temperatures, for which each SM needs to be designed. With the goal of more effective utilization of chip area, a new balancing approach is introduced for monitoring and balancing not only the capacitor voltages but also the average power losses in each SM. In this way, the MMC current capability is significantly increased only by software without deteriorating the system performance and efficiency

Diabetic Patients Foot Care Using Smart Materials to Prevent Ulcerations/Amputations

A major cause of illness and disability in diabetic patients is complications affecting the lower limbs, particularly the feet where loss of feeling may result in ulcerations, and ultimately to partial or total amputation. Traditional remedies for this problem still remains in measuring the foot pressures and then designing a passive shoe insert that absorbs the high pressures. This process may then be repeated multiple times during the lifetime of the patient. This paper describes the conceptual design of an automatic system that monitors and controls the pressure levels in diabetic patients’ feet in real time. The scheme is based on the constant measurement of pressure levels and then actively changing the shape of the shoe insert so as to decrease the high pressure levels. The sensing and the actuation is done by the use of smart materials powered by a battery pack in the insert. The sensing is done by using piezoceramic patches while the actuation is done by use of electroactive polymer (EAP) actuators. All the circuitry is envisioned to be on a single VLSI chip embedded in the shoe insert, hence making the shoe insert completely autonomous. The greatest strength of the system is that it is an active real time system that will adapt to changes in the locations of high stress points, and, hence, is far superior to currently used passive shoe inserts and other forms of diabetic foot care

Impact of Partial Power Processing Dual-Active Bridge Converter on Li-ion Battery Storage Systems

Partial Power Processing converters (PPPCs) provide economical and highly efficient solutions to integrate battery energy storages systems (BSSs) into DC grids. Beside these significant advantages, direct connection of the batteries by PPPCs to DC grids imposes challenges on the operation of batteries which need more evaluation. DC grid imperfections such as harmonics and faults may directly propagate into BSS and result in battery capacity fade acceleration and/or battery failure. In this paper, low voltage (LV) grid imperfection impacts are compared for conventional dual-active bridge (DAB) and Partial Power Processing DAB (PPP-DAB) converters. Both theoretical and experimental studies are carried out. The obtained results show that PPP-DAB exposes the BSS to high amount of current harmonics and safety issues

Limits on nu_e and anti-nu_e disappearance from Gallium and reactor experiments

The deficit observed in the Gallium radioactive source experiments is interpreted as a possible indication of the disappearance of electron neutrinos. In the effective framework of two-neutrino mixing we obtain $\sin^{2}2\vartheta \gtrsim 0.03$ and $\Delta{m}^{2} \gtrsim 0.1 \text{eV}^{2}$. The compatibility of this result with the data of the Bugey and Chooz reactor short-baseline antineutrino disappearance experiments is studied. It is found that the Bugey data present a hint of neutrino oscillations with $0.02 \lesssim \sin^{2}2\vartheta \lesssim 0.08$ and $\Delta{m}^{2} \approx 1.8 \text{eV}^{2}$, which is compatible with the Gallium allowed region of the mixing parameters. This hint persists in the combined analyses of Bugey and Chooz data, of Gallium and Bugey data, and of Gallium, Bugey, and Chooz data.Comment: 21 pages. Final version to be published in Phys. Rev.

UseDa - un nouvel outil de base de données sur les utilisations ethnobotaniques des plantes de l'Afrique de l'Ouest

Das Wissen über die Nutzung von Wildpflanzen in Westafrika und ihre verschiedenen Anwendungen ist in zahlreichen, breit gestreuten Publikationen dokumentiert und oft in Form von grauer Literatur schwer zugänglich. Mehrere Online-Datenbanken umfassen Informationen aus diesen Quellen und bieten zusammenfassende Kurzbeschreibungen der Pflanzen Nutzungen. Unser Ziel ist es, zusätzlich eine Datenbank (UseDa) für ethnobotanische Primärdaten aus Interviews aufzubauen. Damit können quantitative Daten extrahiert und synthetisiert werden. Es können Datensätze nach verschiedenen Fragestellungen analysiert werden, z.B. der Frage nach verwendeten Arten in bestimmten Gebieten, durch verschiedene ethnische Gruppen oder unterschiedliche Nutzergruppen, was für die praktische Anwendung auf lokaler Ebene von Bedeutung ist. In diesem Artikel geben wir einen Überblick über den technischen Aufbau und den Inhalt der Datenbank und diskutieren am Ende den möglichen Output für die praktische Anwendung. Die Datenbank wurde im Rahmen des EU-geförderten Projekt UNDESERT aufgebaut.Knowledge about useful plants and their various applications in West Africa is scattered over many publications and often in form of grey literature difficult to access. Several online-databases compile large scale information from these sources and provide comprehensive summarized descriptions of plant usages. Our aim is to additionally build up a database (UseDa) for primary ethnobotanical interview data. Thus, quantitative data can be extracted and synthesized and data sets can be treated according to different research questions analyzing for example uses in specific areas, of different ethnic groups or user groups, which is essential for practical applications on a local level. In this article we give an overview on the technical structure and the content of the database and discuss at the end the possible output for practical application. The database was set up in the frame of the EU-funded Project UNDESERT.La connaissance sur les plantes utiles et leurs diverses applications en Afrique de l'Ouest sont dispersées sur de nombreuses publications et souvent difficiles d'accès car souvent publiées sous la forme de littérature grise. Plusieurs bases de données en ligne compilent à grande échelle des informations provenant de ces sources et fournissent des descriptions synthétiques des usages des plantes. Notre objectif est de construire une base de données (UseDa) pour les données primaires des enquêtes ethnobotaniques. Ainsi, les données quantitatives peuvent être extraite et synthétisée et elles peuvent être traitées selon différentes questions de recherche analysant par exemple leurs utilisations dans des zones spécifiques, par différents groupes ethniques ou groupes d'utilisateurs, ce qui est essentiel pour les applications pratiques au niveau local. Dans cet article, nous donnons un aperçu sur la structure technique et le contenu de la base de données et discutons à la fin les options possibles pour une application pratique. La base de données a été mise en place dans le cadre du projet UNDESERT financé par l'UE