基于有限元的原木横切面应力波振动特性的研究

Stress wave vibration characterization of cross section of log using finite element method

为获得原木横切面应力波的振动特性,并验证利用有限元法在原木中建模的正确性,对健康樟子松和空洞樟子松圆盘试件横切面分别进行了有限元计算模态分析和试验模态分析。在有限元计算模态分析时,建立了健康樟子松与空洞樟子松圆盘试件横切面的有限元模型,然后加载求解,得到了健康樟子松与空洞樟子松圆盘试件的前5阶固有频率与模态振型;在试验模态分析时,分别采集了健康樟子松与空洞樟子松圆盘试件横切面的应力波信号,并对其进行小波包去噪处理和快速傅里叶变换,得到了健康樟子松与空洞樟子松圆盘试件的前5阶固有频率。将计算模态与试验模态前5阶固有频率相互对应并进行误差分析,结果表明,计算模态与试验模态固有频率的相对误差小于10%,具有高度吻合性,验证了樟子松圆盘试件有限元模型的正确性。由计算模态振型图可知,木材出现空洞缺陷时,空洞附近的形变量较大,这为利用有限元模型进行木质结构的优化设计提供了依据。

In order to examine the vibration characteristics of the stress wave on the cross section of the log,the finite element modal analysis was utilized.The experimental validations were carried out on the cross sections of the healthy and hollow Pinus sylvestris disc specimen.In the finite element calculation,the cross section of the P.sylvestris log disc specimen was discretized to the reasonable finite element mesh divisions,then the boundary conditions were assumed and loads were applied,and finally the problem was solved using the finite element method.The first five order of natural frequencies and the modal deformation quantity of the healthy and the hollow P.sylvestris log disc specimen were obtained.In the experimental validation process,the stress wave signals of the cross sections of the P.sylvestris logs were collected respectively,and then the collected stress wave signals were denoised by the wavelet packet,and the fast Fourier transformation(FFT)of the processed stress wave signals was carried out,finally the first five order natural frequencies of the P.sylvestris disc log specimen were obtained.The first five natural frequencies of the finite element calculated results and the experimental validation results were compared.The comparison results showed that the relative errors between the finite element calculated and experimental natural frequencies were within 10%,which verified that the developed finite element model can be used to predict the stress wave vibration characteristics of the cross section of the P.sylvestris logs with an acceptable accuracy.From the calculated modal deformation quantity diagram,it was found that,when there were holes in the wood,the deformation quantity of the cavity was higher in the vicinity of the cavity.This finding can provide the theoretical foundation for the optimization design of wood structure using the finite element modal.