Investigation of earth pressure distributions on multi-tied flexible retaining walls

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) "Δομοστατικός Σχεδιασμός και Ανάλυση των Κατασκευών"112 σ.Στην παρούσα μεταπτυχιακή διπλωματική εργασία διερευνήθηκε το πρόβλημα της κατανομής των εδαφικών ωθήσεων πάνω σε πολλαπλά αγκυρωμένα εύκαμπτα πετάσματα. Για τον υπολογισμό των ανωτέρω ωθήσεων, έχουν προταθεί αρκετές αναλυτικές ημι–εμπειρικές μεθοδολογίες από διάφορους ερευνητές. Για την αξιολόγηση των παραπάνω μεθόδων και για μια κατά το δυνατόν πιο ρεαλιστική προσομοίωση του εν λόγω προβλήματος, μορφώθηκε ένα κατάλληλο αριθμητικό προσομοίωμα, το οποίο αναλύθηκε με τη μέθοδο των πεπερασμένων στοιχείων. Έγινε προσπάθεια να καλυφθεί ένα εύρος εδαφών, ώστε να αξιολογηθεί η δυνατότητα εφαρμογής των αναλυτικών μεθόδων σε διάφορες συνθήκες. Το αριθμητικό μέρος της εργασίας δεν είναι μια μελέτη πραγματικής αντιστήριξης, αλλά μια προσπάθεια παραμετρικής διερεύνησης του προβλήματος της κατανομής των εδαφικών πιέσεων επί πολλαπλά αγκυρωμένου εύκαμπτου πετάσματος. Προέκυψε το συμπέρασμα ότι οι αναλυτικές μεθοδολογίες προσεγγίζουν ικανοποιητικά τις κατανομές των εδαφικών ωθήσεων σε μη συνεκτικά εδάφη, ενώ δε συμβαίνει το ίδιο για συνεκτικά εδάφη. Προτείνεται, αναφορικά με τον υπολογισμό της συνολικής εδαφικής ώθησης, για χαλαρές άμμους η μέθοδος Twine–Roscoe, ενώ για μέσες και πυκνές άμμους η μέθοδος Peck και το κάτω όριο της μεθόδου NAVFAC. Για μαλακές αργίλους προτείνεται η μέθοδος Peck, ενώ για μέσης στιφρότητας αργίλους προτείνεται το άνω όριο της μεθόδου Peck που θεωρητικά αφορά στιφρές αργίλους. Τα πιο πάνω συμπεράσματα προέκυψαν από μεγάλο εύρος ωθήσεων μεταξύ της κατάστασης γεωστατικών τάσεων και της κατάστασης ενεργητικών ωθήσεων, για αντίστοιχα μεγάλο εύρος οριζόντιων μετατοπίσεων του πετάσματος.The present diploma thesis deals with the problem of the distribution of earth pressures on multi-tied flexible retaining walls. For the calculation of the aforementioned earth pressures, various researchers have proposed a variety of analytical semi-empirical methods. Aiming at evaluating these methods and for a realistic simulation of the problem of earth pressure distribution on a multi-tied wall, an appropriate numerical model was constructed and analyzed using the finite element method. A variety of cohesionless and cohesive soils was examined with the objective of evaluating the suitability of the analytical methods for a multitude of soil conditions. Therefore, the numerical part of this thesis is not an actual case study, but an attempt for a parametric study of the issue. It was concluded that the analytical methods approximate adequately the earth pressure distributions for cohesionless soils, whereas this specific conclusion is not applicable to cohesive soils. As for the calculation of the total earth pressure, the Twine-Roscoe method is proposed for loose sands. The method of Peck and the upper value of the NAVFAC method are proposed for medium and dense sands. For soft clays, the Peck method is considered more suitable, whereas for clays of medium stiffness, the upper limit of the Peck method theoretically applicable to stiff clays, is proposed. These conclusions were obtained from a wide range of pressures between the at-rest pressures and the active pressures, and for an accordingly large range of horizontal wall displacements.Κωνσταντίνος Α. Κιτσάκη

Simulation of extrusion of high density polyethylene tubes

The production of extruded polyethylene films rods, tubes and pipes is a typical industrial process that has been extensively investigated over many years. In this study the extrusion of High Density Polyethylene (HDPE) tubes was simulated by using the 3D finite element simulation software StarCCM+®. The simulation was applied in order to examine the influence of design and operational parameters on the characteristics and the soundness of the tube and for optimizing the overall quality of the product. Two alternative die configurations were studied; one with a four inputs head and the other with an eight inputs head. From the results obtained it is concluded that extrusion with the eight inputs head die design results in better overall pipe quality; this design was implemented successfully in an industrial production line

Simulation of extrusion of high density polyethylene tubes

The production of extruded polyethylene films rods, tubes and pipes is a typical industrial process that has been extensively investigated over many years. In this study the extrusion of High Density Polyethylene (HDPE) tubes was simulated by using the 3D finite element simulation software StarCCM+®. The simulation was applied in order to examine the influence of design and operational parameters on the characteristics and the soundness of the tube and for optimizing the overall quality of the product. Two alternative die configurations were studied; one with a four inputs head and the other with an eight inputs head. From the results obtained it is concluded that extrusion with the eight inputs head die design results in better overall pipe quality; this design was implemented successfully in an industrial production line

Scheduler Accelerator for TDMA Data Centers

Today's Data Centers networks depend on optical switching to overcome the scalability limitations of traditional architectures. All optical networks most often use slotted Time Division Multiple Access (TDMA) operation; their buffers are located at the optical network edges and their organization relies on effective scheduling of the TDMA frames to achieve efficient sharing of the network resources and a collision-free network operation. Scheduling decisions have to be taken in real time, a process that becomes computationally demanding as the network size increases. Accelerators provide a solution and the present paper proposes a scheduler accelerator to accommodate a data center network divided into points of delivery (pods) of racks and exploiting hybrid electro-optical top-of-rack (ToR) switches that access an all-optical inter-rack network. The scheduler accelerator is a parallel scalable architecture with application specific processing engines. Case studies of 2, 4, 8, 16 processors configuration are presented for the processing of all the transfer TDMA time slot requests for the cases of 512 and 1024 ToR network nodes. The architecture is realized on a Xilinx VC707 board to validate the results