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Numerical and experimental investigation of the flow over a car prototype for the Shell Eco Marathon
No full textThe Eco-Marathon is a challenge organized by Shell in which student teams compete in designing energy-efficient vehicles. The event spark debate about the future of mobility and inspire engineers to push the boundaries of fuel efficiency. The aim of the present work consists of the numerical and experimental investigation of the aerodynamic performance of a Shell Eco Marathon prototype designed by a group of students of the University of Cassino, Italy. The car design has been provided by means of detailed 3D CFD modelling with Comsol Multiphysics®. The numerical tool has been validated against experiments conducted at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino. In particular, a scale model of the car has been investigated in an open chamber wind tunnel by means of the Particle Image Velocimetry (PIV) technique, for different free stream velocities within the range 11 - 23 m/s. Measurements have been associated to a proper uncertainty analysis. The experimental data has been compared to numerical results obtained employing different turbulence models and the validated numerical tool has been applied to the simulation of the full-scale car model, allowing to analyse the wake flow structures, and estimate the overall drag coefficient
Wound healing rate in oriental beech trees following logging damage
No full textBeech is the most important commercial species in the Caspian forests of Iran. Selective cutting and harvesting methods may adversely impact the quality of the residual trees, as the injuries make the trees prone to future disease, insect infestations or timber defects. Although attempts to better understand how wounds affect the residual trees have been made in many different contexts, there are still few investigations on uneven-aged forests. In this study the key objectives were to determine and model the healing rate for different wound parameters (width, length, and area of wound); to analyse the relationship between wound healing rate (WHR), tree diameter growth and tree height growth; to analyse the WHR in relation to wound position on the stem; and to analyse the relationship between WHR, width and area of wound in DBH classes and social classes, with the aim of enabling the prognosis of logging wounds. Wounded beech trees were examined immediately after selective logging and after a 5-year period. The WHR was 31.2 ±7.7 cm2 year-1. The wound width healing rate (18.4 ±3.4 mm·year-1) was significantly higher than the wound length healing rate (4.5 ±1.6 mm·year-1). Only 12% of wounds were completely closed after a 5-year period, and 15 years are necessary for the complete closure of 80% of total wounds. The ratio of wound area to stem area at wound height (RWS) showed a more pronounced effect on diameter than on height. Regression analysis showed that WHR was correlated negatively with wound area and width and positively with tree diameter growth, but no significant relationship was found between height growth and WHR parameters. The WHR was significantly higher at an upper position than at a lower one, and statistical tests showed that the tree vertical layering classes had a significant effect on WHR. Finally, it was shown that WHRs in upper-storey trees are significantly higher than in the middle and lower storeys.6s
