| As the main force-bearing component of contemporary ships,the ship deck beam needs to be maintained regularly due to running under the long-term complicated external loads form waves.For different types of ship deck beam,it is necessary to determine the thickness and position of the beam accurately during the maintenance.Although the traditional detection method can complete the detection task,its efficiency is too low to detect the huge ship deck.Ultrasonic guided wave detection technology has the advantages of high detection efficiency and long propagation distance,which can make up for the shortcomings of traditional detection technology.In this paper,Lamb waves detection technology is used to inspect the ship deck beam.A method for evaluating the thickness of the beam based on damage indexes is proposed,and a localization method for the position of deck beams based on probabilistic imaging is also studied.The main work of this paper can be summarized as follows:In theoretical analysis,the propagation law of Lamb waves in marine CCSA-steel materials is analyzed and the dispersion curves is also drawn with the propagation law in the paper.The method of the Lamb waves excitation and sensing is analyzed with the model of piezoelectric element,and the appropriate excitation frequency and detection mode of Lamb waves excitation signal is selected for the detection of the deck beam.At the same time,the paper describes the basic principles of the method for evaluating the thickness of deck beams based on damage indexes and the method of positioning deck beams based in probabilistic imaging in some detail.In simulation research,the ship deck beam model is established by ANSYS which is a finite element simulation software.The propagation characteristics of Lamb waves in the ship deck and the influence of the deck beam on Lamb propagation are analyzed based on the finite element model.Four different kinds of damage indexes are compared for the evaluation abilities of the ship deck beam with different thickness.Moreover,the influence of different types of ship anti-slip coatings on the propagation speed of Lamb waves is described and the beam is imaged and positioned by probabilistic imaging with baseline-free signals.In experimental verification,a ship deck beam detection system based on wireless sensor network is designed and the performances of internal components and whole system are tested,which are described in this paper.For the noise interference in the original signals,the variational modal decomposition method is used in signal procession which could reduce the impact of measurement noise.The ship deck beam detection system is used to evaluate the beam with different thickness.Besides,the influence of different anti-slip coating on the deck is tested by the detection system,and the experiments are carried out on the positioning of the ship deck beam.According to the finite element simulation and experimental results,the method for evaluating the thickness of the beam based on damage indexes and the localization method for the position of deck beams based on probabilistic imaging are verified to the effective evaluation and positional performance.The results in this paper provide a good theoretical and experimental basis for the application of the ship maintenance work and the detection of deck beam. |
