Lattice Boltzmann method and immersed boundary method for the simulation of viscous fluid flows

Most realistic fluid flow problems are characterised by high Reynolds numbers and complex boundaries. Over the last ten years, immersed boundary methods (IBM) that are able to cope with realistic geometries have been applied to Lattice- Boltzmann methods (LBM). These methods, however, have normally been applied to low Reynolds number problems. In the present work, an iterative direct forcing IBM has been successfully coupled with a multi-domain cascaded LBM in order to investigate viscous flows around rigid, moving and wilfully deformed boundaries at a wide range of Reynolds numbers. The iterative force-correction immersed boundary method of (Zhang et al., 2016) has been selected due to the improved accuracy of the computation, while the cascaded LB formulation is used due to its superior stability at high Reynolds numbers. The coupling is shown to improve both the stability and numerical accuracy of the solution. The resulting solver has been applied to viscous flow (up to a Reynolds number of 100000) passed a NACA-0012 airfoil at a 10 degree angle of attack. Good agreement with results obtained using a body-fitted Navier-Stokes solver has been obtained. At moving or deformable boundary applications, emphasis should be given on the influence of the internal mass on the computation of the aerodynamic forces, focusing on deforming boundary motions where the rigid body approximation is no longer valid. Both the rigid body and the internal Lagrangian points approximations are examined. The resulting solver has been applied to viscous flows around an in-line oscillating cylinder, a pitching foil, a plunging SD7003 airfoil and a plunging and flapping NACA-0014 airfoil. Good agreement with experimental results and other numerical schemes has been obtained. It is shown that the internal Lagrangian points approximation accurately captures the internal mass effects in linear and angular motions, as well as in deforming motions, at Reynolds numbers up to 4 • 104. Finally, an expanded higher-order immersed boundary method which addresses two major drawbacks of the conventional IBM will be presented. First, an expanded velocity profile scheme has been developed, in order to compensate for the discontinuities caused by the gradient of the velocity across the boundary. Second, a numerical method derived from the Navier-Stokes equations in order to correct the pressure distribution across the boundary has been examined. The resulting hybrid solver has been applied to viscous flows around stationary and oscillating cylinders and examined the hovering flight of elliptical wings at low Reynolds numbers. It is shown that the proposed scheme smoothly expands the velocity profile across the boundary and increases the accuracy of the immersed boundary method. In addition, the pressure correction algorithm correctly expands the pressure profile across the boundary leading to very accurate pressure coefficient values along the boundary surface. The proposed numerical schemes are shown to be very efficient in terms of computational cost. The majority of the presented results are obtained within a few hours of CPU time on a 2.8 GHz Intel Core i7 MacBook Pro computer with a 16GB memory

Analysis of employment's changes defining factors in E.U countries.

150 σ.Εισαγωγή στις βασικές έννοιες της απασχόλησης και της αγοράς εργασίας.Μεταβολή της απασχόλησης και της ανεργίας σε χώρες της Ε.Ε. κατά τη διάρκεια της κρίσης.Εισαγωγή στην έννοια της παραγωγικότητας και παράθεση των βασικών μέτρων μέτρησης αυτής. Αναλυτική παρουσίαση του μοντέλου αναλυτικής αποδόμησης LDMI (Logarithmic Divisia Mean Index) και εισαγωγή των προσδιοριστικών παραγόντων της απασχόλησης σε αυτό με παράλληλη σύγκριση του μοντέλου με άλλα ευρέως χρησιμοποιούμενα. Παράθεση αποτελεσμάτων για μεταβολές απασχόλησης , ακαθάριστης προστιθέμενης αξίας , ένταση εργασίας και διάρθρωσης της οικονομόιας των υπό μελέτη χωρών καθώς και αποτελεσμάτων Divisia.The aim of the present diploma thesis is to study the development of employment in countries of the EU and to analyse her defining factors with application of a decomposition analysis model. For the development of this work were used as primary data, tables that present elements for the structure of economies of each country, the Gross Value Added and the intensity of work and which emanate from the network place of European Statistical Service (EUROSTAT). In the first chapter of the thesis we achieve an import in the basic significances of job market, employment and unemployment. Followed by an extensive analysis of economic developments and developments in the job market of member states of the EU during the crisis. Finally becomes reason for the productivity as well as for the various metres of its measurement. Then we present the most basic models of decomposition analysis and after extensively comparing them we present the final LDMI (logarithmic mean divisia index) model that we used. In chapter 5 we focus on an analytic presentation of the decomposition analysis model that we used and which is followed by importing the defining parameters of employment in this. Still is presented the problem of null prices that often appears in such decomposition analysis studies and we propose various ways of confrontation. The usefulness of the LDMI method is big while it is applied in a lot of energy studies and allows us to study the exclusive action of each defining factor of an analysis while considering the remaining factors, immutable. Here it is stressed that it is the first time where such an attempt to apply a decomposition analysis method in an employment analysis problem was made, and it was applied with particular success. Closing we analytically present the results of our work starting from a general analysis of the employment development. Still we present elements and charts for the change of Gross Value Added in the under study countries in the time period between 2001 and 2008, the structure of their economies and the change of work intensity per sector of production. Finally we present an analytic, both graphic and quantitative analysis of the results of Divisia method which is followed by an extensive annotation of those.Εμμανουήλ Ι. Φαλαγκάρη