Windloads on net covered structures.

摘要

Agricultural plastic nets are popular materials for constructing crop protection structures against natural or biological hazards such as hail, wind, or insects and birds. However, existing design standards do not provide a methodology for the calculation of wind loads on structures with permeable cladding. Computational Fluid Dynamics (CFD) simulations provide a cheap and easy to use alternative to full-scale or wind tunnel experiments for analysing the wind generated pressure distribution around net-covered structures. In these simulations, the permeable cladding is treated as a porous material. In this way, aerodynamic force coefficients are numerically estimated for structures covered with nets of various air permeability characteristics. In this paper, the aerodynamic coefficients of three typical designs used for supporting agricultural nets for various applications have been numerically calculated. In particular the following structures have been studied: (a) duo-pitch anti-hail canopy roof, (b) vaulted roof anti-insect house, and (c) flat roof shading house. The numerical results were compared against the provisions of the Eurocode-1-1-4 for the corresponding impermeable structures. The numerical results show that the numerically calculated aerodynamic coefficients are overestimated in the cases of the arched-roof and the flat-roof structures when an impermeable cover is considered. However, the numerical results corresponding to the net-covered structures may be closer to reality because the permeability of the net-covered roof suppresses the development of eddies and flow separation at the roof, which are the main reasons for the overestimated coefficients obtained by the numerical method in the case of impermeable covers. This can be examined by future experimental work investigating further wind loads on permeable structures.