Finite element analysis of a fluid-structure interaction in flexible pipe line

This paper describes the basic theory and computing method for transient flow of liquid in flexible pipe such as rubber tubing and arterial system. A mathematical model taking into account tube wall axial and radial motion (in which the dynamic fluid pressure causes circumferential and axial motion of the tube wall) is presented. The tube wall is assumed to be elastic material and the compressibility of the liquid is neglected. Circumferential and axial strain-stress relationships for the tube are considered. The obtained mathematical system is constituted of four non-linear hyperbolic partial differential equations describing the wave  propagation in both pipe wall and liquid flow. The fluid-structure interaction is found to be governed by Poisson’s ratio. In this steady finite element method based on Galerkin formulation is applied. Numerical results show a good similarity with those of the literature obtained by the characteristics method.Key words : Fluid-structure interaction, flexible pipe, rubber, finite element method

Computer Forensics

84 σ.Το θέμα της διπλωματικής εργασίας είναι η μελέτη της επιστήμης της δικανικής υπολογιστών η οποία είναι κλάδος της ψηφιακής δικανικής. Στην εισαγωγή, αναφέρονται χαρακτηριστικά, εφαρμογές, μεθοδολογίες και κλάδοι της ψηφιακής δικανικής. Στο δεύτερο κεφάλαιο περιγράφονται βασικά χαρακτηριστικά της διαδικασίας απόκτησης ψηφιακών δεδομένων από υπολογιστές. Στο τρίτο κεφάλαιο παρουσιάζονται στοιχεία για τη διαδικασία της ανάλυσης των ψηφιακών δεδομένων ενός σκληρού δίσκου. Συγκεκριμένα παρουσιάζονται σημαντικά αρχεία και τοποθεσίες του λειτουργικού συστήματος Windows με ενδιαφέρον για έναν αναλυτή καθώς και χαρακτηριστικά της ανάλυσης βασικών τύπων αρχείων. Στο τέταρτο κεφάλαιο παρουσιάζονται σημαντικά εργαλεία για τη διεξαγωγή μιας έρευνας στα πλαίσια της δικανικής υπολογιστών. Το τελευταίο κεφάλαιο περιλαμβάνει τρία εργαστήρια όπου φαίνονται στην πράξη τεχνικές της δικανικής υπολογιστών. Στο πρώτο αναλύονται τα βήματα της απόκτησης ψηφιακών δεδομένων σε πλατφόρμα εργασίας Windows και Linux. Στο δεύτερο αναζητούνται ίχνη της δραστηριότητας ενός χρήστη σε σύστημα με Windows, ενώ στο τελευταίο αναζητούνται ίχνη μιας μνήμης usb σε ένα σύστημα Windows.The theme of this diploma thesis is the study of computer forensics science which is branch of digital forensics. Firstly, we refer to characteristics, applications, methods and branches of digital forensics. In chapter 2, details of digital data’s acquisition from computers are being described. In chapter 3, we present elements of the analysis of digital evidence, retrieved from a hard disc. More specifically, not only do we refer to important locations and artifacts of Windows operating systems, but also we present the basics of file types’ analysis. In chapter 4, essential tools for forensic investigations are being involved. The last chapter includes three labs which show computer forensics’ techniques in practice. In the first lab we state detailed steps for a forensic acquisition in Windows and Linux platforms. In the second lab, we trace a user’s activities in a Windows operating system whereas in the last lab we search for the traces of a flash drive in a Windows system.Καρρά Τανισκίδου Ευθυμί

A model for the degradation of polyimides due to oxidation

Polyimides, due to their superior mechanical behavior at high temperatures, are used in a variety of applications that include aerospace, automobile and electronic packaging industries, as matrices for composites, as adhesives etc. In this paper, we extend our previous model in [S. Karra, K. R. Rajagopal, Modeling the non-linear viscoelastic response of high temperature polyimides, Mechanics of Materials, In press, doi:10.1016/j.mechmat.2010.09.006], to include oxidative degradation of these high temperature polyimides. Appropriate forms for the Helmholtz potential and the rate of dissipation are chosen to describe the degradation. The results for a specific boundary value problem, using our model compares well with the experimental creep data for PMR-15 resin that is aged in air.Comment: 13 pages, 2 figures, submitted to Mechanics of Time-dependent Material

A thermodynamic framework to develop rate-type models for fluids without instantaneous elasticity

In this paper, we apply the thermodynamic framework recently put into place by Rajagopal and co-workers, to develop rate-type models for viscoelastic fluids which do not possess instantaneous elasticity. To illustrate the capabilities of such models we make a specific choice for the specific Helmholtz potential and the rate of dissipation and consider the creep and stress relaxation response associated with the model. Given specific forms for the Helmholtz potential and the rate of dissipation, the rate of dissipation is maximized with the constraint that the difference between the stress power and the rate of change of Helmholtz potential is equal to the rate of dissipation and any other constraint that may be applicable such as incompressibility. We show that the model that is developed exhibits fluid-like characteristics and is incapable of instantaneous elastic response. It also includes Maxwell-like and Kelvin-Voigt-like viscoelastic materials (when certain material moduli take special values).Comment: 18 pages, 5 figure