防風網編織形式對減風效果之風洞試驗研究

Abstract

Windbreak Net is an extremely important facility of prevention of wind damage; however, windbreak net's function varies with different types; hence, the research's main purpose was to compare the differences of shelter effect with diverse windbreak net weaving types. The research adopted three types of windbreak nets of higher market share in Taiwan: plain weave, knitted weave, which had two different mesh shapes, and ribbed weave, which had two varied weaving methods. The wind tunnel test was conducted with these five sets of windbreak net, and relative wind velocity, wind velocity reduction coefficient, protection index, and economic benefit were used respectively to do comparison and make analysis to explore the influence of weaving type, mesh number and shape on wind velocity reduction effect.The test results showed that when all windbreaks had the same ventilation rate, the windbreak net of plain weave had the best shelter effect, the secondary was ribbed weave, and the worst was knitted weave; however, if both the shading and anti-insect functions were required, the windbreak net of knitted weave type was relatively more ideal to choose; yet if taking economic benefit into consideration, the windbreak net of ribbed weave was the cheapest. As for the mesh shape, triangle had better shelter effect than rectangle, and in this research case, mesh number had no significant difference in wind velocity reduction.防風網是風害防治極為重要之設施，然而防風網之功能因其形式不同而異；因此，本試驗主要目的即在於比較防風網編織形式對減風功效之差異，研究中採用國內市占率較高之平織、針織及羅紋織三種形式防風網，其中針織有兩種不同網目形狀，而羅紋織則有兩種不同編織方式，將此五組防風網，進行風洞試驗，分別以相對風速、減風係數、保護指數及經濟效益比較分析，探討編織形式、網目數量及形狀對減風效果之影響。經試驗結果顯示，當透風率相同時，在減風功效方面，以平織形式之防風網最佳，羅紋織次之、針織最差；然而若需兼具遮陽及防蟲功效，則應選用針織形式之防風網較為理想；但若考量經濟效益，則又以羅紋織防風網最為價廉。至於網目形狀以三角形比矩形有較佳之減風功效，而網目數量在本試驗個案中，對於減風並無明顯差異