桥梁检测中基于非结构化网格的时差菲涅尔带反演方法研究

Research on Time-Difference and Fresnel Zone Inversion Method Based on Unstructured Grid in Bridge Inspection

层析技术是一种桥梁无损检测的新兴技术,但是传统层析反演使用矩形网格来剖分模型,并且需要大量的检波设备来确保精确度。为改善桥梁层析检测的效果,在反演中引入了菲涅尔带技术,增大反演射线的覆盖范围,改善了检波设备不足导致的射线稀疏问题;利用时差法,提高了初至数据的准确性,减小了初至拾取误差在小尺度测量中的影响。此外使用了三角网格对桥梁模型进行剖分,比起矩形网格能够更好地贴合边缘不规则的桥梁模型。模型试算和实际测量的结果表明:菲涅尔带方法可以较好地反演出速度异常区的位置、形状和大小;对有拾取误差的数据使用时差法处理后,反演结果接近于准确数据的反演结果;该算法提升了反演的准确性,可以有效运用于桥梁检测项目中。

Computerized tomographic technique is a emerging technique for nondestructive bridge inspection.In conventional tomographic inversion,rectangular grid is used to divide the model,and a large number of detection equipment is required to ensure the accuracy.To improve the effect of bridge tomographic inspection,the technique of Fresnel zone was introduced into the inversion to enlarge the coverage range of the inversion ray,which improved the ray sparseness caused by insufficient inspection equipment.By using the time difference method,the accuracy of first arrival data was improved and the influence of the first arrivals pick-up error in small-scale measurement was reduced.In addition,triangular mesh was used to divide the bridge model,which could fit the bridge model with irregular edges better than rectangular mesh.The results of model trial calculation and actual measurement showed that the Fresnel zone method could better deduce the position,shape and size of the velocity anomaly area.After using the time difference method to deal with the data with picking errors,the inversion results were close to the inversion results of accurate data.The algorithm improved the accuracy of inversion and could be effectively applied in bridge inspection projects.