A method for the analysis of the geometric characteristics of protection screens.

摘要

The installation of insect-proof screens in ventilation openings in greenhouses is a technique to exclude insects which has become more widespread in recent years. This method of protecting crops received a considerable support from both economic and environmental points of view, allowing the number of phytosanitary treatments to be reduced. The major limitation of this method concerns the screens' resistance to air flow, determined by the porosity of the screen. The present work aims to elaborate a method of analysis which allows the geometric characterisation of these screens. The methodology consists of analysing digital images taken by a microscope. These images show the screens in two dimensions, allowing us to distinguish between the regions which correspond to either fibres or pores. As each pore of the insect-proof screen is outlined by four intersecting monofilament threads, it can be defined as a quadrilateral. The analysis is based on the coordinates of the vertices of each quadrilateral of the sample. For this purpose a computer programme has been developed which solves the problem of identifying the vertices, and from the coordinates it calculates all the measurements required to make a geometrical characterisation of the screen. Furthermore, this work analyses the aerodynamic characteristics of several insect-proof screens, carrying out tests in a wind tunnel designed and built for this purpose. The analysis of these data has provided simple ratios of the permeability and inertial factor as a single function of porosity..