模态密度瞬态测试法中指数窗的应用

Application of Response Window to Modal Density Testing by Impact

由于低阻尼结构的模态频率响应曲线宽度很窄,而频谱分析仪谱线间隔有限,在其谱线间隔相对于模态导纳半功率点带宽较小时,采用结构速度导纳实部平均值测量结构模态密度的误差很大。因此分析得到准确测量模态密度的保守条件是测试仪谱线宽度小于单个模态的半功率点带宽,并在瞬态测试法的谱线间隔不能够满足这个要求时,应用指数窗增加等效阻尼,虚拟地增大模态导纳半功率点带宽,使谱线间隔条件得到满足,准确测得低阻尼板的模态密度。

Low damping structure’s transfer function is very narrow. When the spectrum interval of spectrum analysis apparatus is narrower than the half power bandwidth of a single modal, the error of the modal density testing based on the mobility theory is great. The necessary spectrum interval, which guarantees testing accuracy, is deduced out. An exponent window is used to increase the apparent damping of the tested structure. The half power bandwidth of the structure’s mobility function is apparently broadened, so the testing condition is satisfied. At last an experiment is made on a low damping plate for verification.