S06 - Session P13 - Specifying wind speeds causing damage to net-house crops and quantifying effects on tidal damage

Authors: Maro Tamaki *

Net-houses used in the southwestern islands ofJapanare used mainly to avoid damage such as greenhouse collapse caused by strong winds. Greenhouses covered entirely with nets are widely used. Furthermore, nets cover areas under the film, on the sides, and on roof surfaces of common film-covered greenhouses. Typically, net gaps are 0.4n2.0 mm square mesh. The film is rolled up when a typhoon approaches and strikes the islands. Wind pressure therefore affects the net. The wind load on the greenhouse is lower with nets than with film because the nets are porous, reducing risks of a greenhouse collapse. Such a greenhouse would have a similar structure to that of a net house during a typhoon attack. However, air currents passing through net gaps have frequently caused wind damage to net-house crops. Wind damage, as used herein, refers to damage to leaves caused by wind pressure. To make more effective use of net-houses used for strong wind protection, greenhouses must be designed not only to prevent them from collapsing, but also to reduce wind damage to crops. For this study, the wind reduction rate of the net house and the air flow characteristics in the house were measured in field tests. Wind speeds sufficient to damage okra, hot pepper, and mango, all major crops grown in net-houses in the southwestern islands, were ascertained from wind tunnel experiments. Additionally, results confirmed that the wind damage reduction contributed to reduction of tidal damage to mango.