基于小波变换和模态曲率差的起重机金属结构损伤识别

属于焊接结构的起重机金属结构受交变载荷的影响,随着使用年限的增加,不可避免地会产生裂纹和腐蚀等损伤,从而引发突发性重大断裂事故。为此,基于结构的振动特性及小波变换理论来研究起重机金属结构的早期损伤识别问题,通过改变局部弹性模量模拟不同损伤工况,分析了起重机主梁在不同损伤工况下的动态响应特性。结果表明,小波变换可明显放大不易察觉的损伤突变,模态曲率差具有较好的损伤识别能力,可为起重机金属结构损伤识别提供新的思路。

Damage identification of the crane metal structures based on the wavelet transformation and modal curvature difference

The given paper is devoted to the trace and identification of the damage of a 41 t double girder gantry crane in terms of the structural dynamics parameters and the position of the damage,in addition to the quantitative assessment of the damage extent via the wavelet transformation,so as to get rid of any crane safety accidents. And,for the said purpose,we have established a parametric model of the gantry crane structure to have an inspection from the 2 aspects of strength and stiffness to determine the reliability and accuracy of the model via the ANSYS APDL language. At the same time,we have also simulated the damages under the 13 damage conditions,including the different damage positions and degrees via the APDL parameterization commands,so as to modify and simulate the elastic modulus values of the local elements of the main girder,and then perform their modal analysis. The results of the above said analyses tend to indicate that the damage location could not be identified from the modal shape diagram. And,when the modal shape diagrams have been magnified locally,it can be found that some positions turn to be abnormally protruding into the figure. And,then,the db5 wavelet can be used to detect the singularity of the data,whereas some points have been found wrong with the exact failures being identified. To improve the accuracy of the damage identification further,we have turned up to the central difference method and 2 damage indicators for help,that is,the modal curvature and the modal curvature difference. And,consequently,through comparisons of identification effects of the above said two indicators,different degrees and locations of damage can have been made identified accurately through tracing and examination of the modal curvature difference. At the same time,the modal curvature difference and the damage degree have also been made fitted,which prove that the fitted curve can help to identify the damage degree of the structure under a single-damage condition. And,last of all,the research results we have gained can be expected to provide a novel idea for the damage identification of the crane metal structure.