An Automatized Frequency Analysis for Vine Plot Detection and Delineation in Remote Sensing

The availability of an automatic tool for vine plot detection, delineation, and characterization would be very useful for management purposes. An automatic and recursive process using frequency analysis (with Fourier transform and Gabor filters) has been developed to meet this need. This results in the determination of vine plot boundary determination and accurate estimation of interrow width and row orientation. To foster large-scale applications, tests and validation have been carried out on standard very high spatial resolution remotely sensed data. About 89% of vine plots are detected corresponding to more than 84% of vineyard area, and 64% of them have correct boundaries. Compared with precise on-screen measurements, vine row orientation and interrow width are estimated with an accuracy of 1$^{circ}$ and 3.3 cm, respectively.      

Discrete element modelling of drying shrinkage and cracking of soils

This paper is aimed at showing the efficiency of discrete element modelling for the prediction and understanding of drying shrinkage and associated cracking. The discrete element approach used is presented first. Cohesive forces between grains, as well as drying shrinkage deformation, are included in the formulation. A numerical model is then used to simulate drying shrinkage experiments conducted on a fine-grained soil. The numerical simulations agree well with the experimental measurements. When drying shrinkage is constrained at the boundaries, and when moisture gradients develop in the drying soil, the model is able to predict the time of the occurrence of cracking, as well as the crack pattern formed. Finite element simulations and the discrete element approach both predict similar behaviours before cracking occurs. The proposed discrete element approach is highly promising for studying the origins and causes of cracking in soils.     

Mechanical behaviour and failure of cohesive granular materials

We investigate the stress–strain behaviour and failure of a cohesive granular material both by experiments and numerical simulations. The material is an assembly of aluminium rods glued together by means of an epoxy resin. The behaviour of cohesive bonds (force–displacement relationship, failure conditions) is characterized by performing simple loading tests (tension/compression, shear…) on a couple of rods. Then, this local behaviour is introduced in a numerical code based on a discrete element method in order to perform numerical compression tests on large samples. The validation of this approach was the main goal of the present investigation that is essentially achieved by a direct comparison between the numerical results and similar experimental tests. As a basic application, we derive the macroscopic cohesion and friction characteristics of random cohesive materials by systematic numerical simulations in a biaxial geometry. Copyright © 2004 John Wiley & Sons, Ltd.