This study uses a spectral method to study wave scattering by the local defect in the structural waveguide. The force response is decomposed into some subproblems by combining with standard finite element method with lower computational cost. Dynamic reduction method is used for both the narrowband and wideband analyses of wave scattering by defects or some standard structural features. Numerical study of plate mode scattering by defects indicates that the mode conversions complicate the resultant signal, and a set of modes with different frequencies is necessary to properly estimate the defect type and severity. If the wideband wave modes are generated, some signal processing, such as time-frequency analysis, should be used for mode identification or defect localization. Numerical study can also be extended to more complex structures, and some conclusions from the presented investigations are also suitable to those cases.
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