Research for Evaluation Method Based on Lamb Waves for Thickness of Ship Deck Beams
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COUSTIC METHODS
Research for Evaluation Method Based on Lamb Waves for Thickness of Ship Deck Beams Ze-Yu Donga, *, Hai-Tao Wanga, Xian-Ming Yangb, Xin Lia, Jun Xua, and Meng-Hao Jiangc a
College of Automation Engineer, Nanjing University of Aeronautics and Astronautics, Nanjing, China b Shandong Chuangke Automation Technology Co., Ltd., Yantai, China c Jiangxi Provincial Armed Police, Jiangxi, China *e-mail: [email protected] Received July 3, 2019; revised October 4, 2019; accepted October 18, 2019
Abstract—As the main force component of contemporary ships, the ship deck beam is of great significance and needs to be maintained regularly under the severe conditions of long-term complicated external loads form waves. The maintenance methods are usually related with the thickness of the beams. Due to the limited detecting methods, the thickness of beams cannot be evaluated accurately when maintaining. Therefore, in this paper, a detecting method based on active Lamb waves is proposed, which could evaluate the thickness of beams. On one hand, the two-dimension (2D) finite element simulation model of beams is established and the ability of three damage indexes of A0 mode signal at beams with different thickness is studied. On the other hand, experiments are carried out. To suppress measurement noise effectively, variational mode decomposition (VMD) is used to extract experimental signal feature parameters and the three damage indexes are also used to evaluate the thickness of beams. The experimental results show that the variation trend of the three damage indexes is consistent with the simulation results. Moreover, the damage index with the energy of the scatter signal based on the A0 mode has a better ability for the beams thickness. Thus, this method is proved to be feasible to evaluate beams with different thickness. Keywords: Lamb waves, damage index, ship deck beam, variational mode decomposition, thickness DOI: 10.1134/S1061830920070049
1. INTRODUCTION Under the heavy wave loads for long time, ships always face structural damage and deformation which is tiny and unobservable. Ship deck beam is the main load-bearing structure of ships. The withstand loads is related with the thickness of the beams [1, 2]. If the load exceeds the bearing capacity of ship deck beam, the deck and deck beam will be deformed and even cause a safety accident. Furthermore, maintenance personnel need to weld and construct some steel scaffold on ship deck at the process of maintenance in ship key structures. However, it is hard to bearing heavy load at ship maintenance owing to the thin ship deck. Therefore, the steel scaffold should be welded and constructed above ship deck beam. Considering the thickness of ship deck beam, the scaffold is different. If the beam cannot afford the scaffold which above it, it will might cause partial deck depression and scaffold collapse. Aiming to make ship more reliable during working and maintenance, the ship must be tested and trimmed regularly. To new ships, some signs are drawn on decks. However
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