Mechanism of the excitation of single pure mode L（0, 2） and its interaction with the defect in a hollow cylinder

Guided elastic waves have a great potential in pipe inspection as an efficient and low-cost nondestructive evaluation （NDE） technique, among which the wave of mode L（0, 2） receives a lot of attention because this mode is the fastest mode in a weakly dispersive region of frequency to minimize dispersion effects over a long distance and sensitive to the defects distributed circumferentially. Though many experimental and numerical researches have already been carried out about the excitation of L（0, 2） and its interaction with the defect in a hollow cylinder, its excitation mechanism has not been clarified yet. In this paper based on the transient response solution of the hollow cylinder, derived by the method of eigenfunction expansion, the theory about the exciting mechanism of mode L（0, 2） is advanced and the effects of the spatial distribution, vibration frequency and direction of the external force on the excitation are discussed. And the pure mode L（0, 2） is excited successfully under the parameters obtained through theoretical analysis. Furthermore, its interactions with some kinds of defects in hollow cylinders are simulated with the method of finite element analysis （FEA） and the results agree well with those obtained by other researchers.

Mechanism of the excitation of single pure mode L(0, 2) and its interaction with the defect in a hollow cylinder

Guided elastic waves have a great potential in pipe inspection as anefficient and low-cost nondestructive evaluation (NDE) technique,among which the wave of mode L(0,2) receives a lot of attentionbecause this mode is the fastest mode in a weakly dispersive regionof frequency to minimize dispersion effects over a long distanceand sensitive to the defects distributed circumferentially. Thoughmany experimental and numerical researches have already been carriedout about the excitation of L(0,2) and its interaction with thedefect in a hollow cylinder, its excitation mechanism has not beenclarified yet. In this paper based on the transient responsesolution of the hollow cylinder, derived by the method ofeigenfunction expansion, the theory about the exciting mechanism ofmode L(0,2) is advanced and the effects of the spatialdistribution, vibration frequency and direction of the externalforce on the excitation are discussed. And the pure mode L(0,2)is excited successfully under the parameters obtained throughtheoretical analysis. Furthermore, its interactions with some kindsof defects in hollow cylinders are simulated with the method offinite element analysis (FEA) and the results agree well with thoseobtained by other researchers.