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中文摘要：
附加质量对于膜结构振动特性有明显影响,在其振动分析中不能忽略。利用真空箱测试薄膜在不同密度空气中的振动特性,研究了薄膜振动的附加质量影响因素和规律。真空箱采用钢板和钢化玻璃制作,利用真空泵调节真空箱内的气压可以改变箱内的空气密度。对比薄膜在不同密度空气中的振动频率,可以计算其附加质量。试验结果表明,薄膜自振频率随气体密度减小而增大,附加质量效应十分明显,且与模态振型相关。基于试验分析提出了附加质量分布的简化模型,即对于每阶模态,薄膜振动的附加质量分布相当于振型各区域上均匀分布有0.65倍该振型区域特征长度的空气,而振型区域特征长度,取该区域内切圆直径。利用该简化模型分析薄膜得到的振动频率与本文及已有试验结果符合良好,证明了该简化模型的有效性。
英文摘要：
The added mass has significant effect on the vibration of the membrane structures,which can not be ignored during their vibration analysis.The vibrations of a circular membrane in vacuum and in air were investigated to discover the influence factors of the added mass.The vacuum chamber was fabricated from steel plate and toughened glass.The air density can be changed through adjusting the air pressure with a vacuum pump.The membrane tension was uniformly applied through lifting up the edge of a circular membrane.The added mass could be obtained with analysis of the vibration frequency of the membrane in different air density.The analysis results showed that the frequency of the membrane increases as the air density decreases.The added mass is significant and depends on the mode shape.Finally,a simplified model of the added mass is proposed,i.e.the added mass equal to the uniformly distribution air over each region of the mode shape with height of 0.65l,in which l is the characteristic length taken as the diameter of the inscribed circle of the region.The vibration frequencies of the membrane considering the added mass with the simplified model are consistent with the test results,which validates the efficiency of the simplified model. The simplified model is further verified by a test on the natural frequency of a three-sided membrane carried out in a NASA laboratory.
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