Study of side impact of manifold thin-walled tubular structures

66 σ.Η εργασία στοχεύει στη διερεύνηση της πλευρικής κατάρρευσης συστοιχιών κυλινδρικών μεταλλικών σωλήνων. Η βασική διάταξη / συστοιχία (ίδια διάταξη – διαφορετικές διαστάσεις) είναι η 2x2 (τέσσερις σωλήνες ανά δύο κάθετα διασταυρούμενοι). Για αυτή τη διάταξη διερευνήθηκε η επίδραση διαφορετικών διαστάσεων σωλήνων. Επιπλέον, επιλέχθηκε σωλήνας συγκεκριμένων διαστάσεων ώστε να διερευνηθεί περαιτέρω η συμπεριφορά σε αντίστοιχη (πλευρική) καταπόνηση όλων των δυνατών συνδυασμών διάταξης / συστοιχίας (ίδιες διαστάσεις – διαφορετική διάταξη) από έναν έως τέσσερις σωλήνες. Παράλληλα επιχειρήθηκε η μοντελοποίηση με τη μέθοδο των πεπερασμένων στοιχείων (κώδικας LS-DYNA) όλων των παραπάνω περιπτώσεων πλευρικής καταπόνησης προκειμένου να διερευνηθεί η δυνατότητα πρόβλεψης της συμπεριφοράς των συγκεκριμένων διατάξεων.This study aims at exploring the lateral collapse of tubular structures. The main structure is 2x2 (4 tubes; 2 tubes mounted perpendicular to the length of the other 2 tubes). The combination effect of tubes of different sizes has been examined for this structure. Moreover tubes of a specific size have been chosen in order to examine further the behavior after side impact. In this case structures from 1-4 tubes have been tested. At the same time modeling with LS-Dyna code has been used for all the above cases of lateral compression in order to predict the way these structures collapse.Φωτεινή Α. Πασχαλίδο

Do tomorrow’s diversified cropping systems need ley pastures?

International audienc

Role of ley pastures in tomorrow’s cropping systems. A review

International audienceAbstractDiversification of cropping systems has been proposed as a major mechanism to move towards sustainable cropping systems. To date, a diversification option that has received little attention is introduction of ley pastures into cropping systems, but the use of ley pastures is challenged by most future-oriented scenarios aiming to feed the world sustainably. In these scenarios, ruminant livestock feed only on permanent pastures, while cropping systems focus completely on production of crop-based human food. Diversification of cropping systems with ley pastures is thus compromised by knowledge gaps and future-oriented policy options. Here, we review ecosystem services provided by introducing ley pastures into cropping systems to increase sustainability of agriculture, discuss types of ley pastures and their management liable to promote these services, and raise future challenges related to introducing ley pastures into cropping systems. We conclude that (1) ley pastures provide a large set of input (soil conservation, nutrient provision and recycling, soil water retention, biological control of pests) and output (water purification, climate regulation, habitat provision for biodiversity conservation, forage production) ecosystem services of primary importance to cropping systems and society, respectively, as long as their spatial and temporal insertion within cropping systems is well-managed; otherwise, disservices may be produced. (2) To benefit from ecosystem services provided by ley pastures in cropping systems while limiting their disservices, it appears necessary to define a safe operating space for ley pastures in cropping systems. Moving towards this space requires changing plant breeding programs towards multiservice ley pastures, producing knowledge about emerging ways of introducing ley pastures into cropping systems (e.g., living mulch, green manure) and better quantifying the bundles of ecosystem services provided by ley pastures in cropping systems