Airship skin strain measurement based on adaptive digital image correlation
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ORIGINAL PAPER
Airship skin strain measurement based on adaptive digital image correlation Jun-kai Ruan1 · Quan-bao Wang1
· Liu-yue Zhao1 · Deng-ping Duan1
Received: 27 February 2020 / Revised: 16 April 2020 / Accepted: 2 May 2020 © Shanghai Jiao Tong University 2020
Abstract Aiming at the non-uniform strain in the welding of airship skin, this paper studies the traditional digital image correlation algorithm, optimizes the shape and size of the subset, and presents an adaptive subset algorithm. Under the premise of ensuring a substantially constant subset area, the modified algorithm uses the initial u and v values to optimize the shape of the subset, find the optimal aspect ratio. Besides, the modified digital image correlation dynamically adjusts the shape of the subset according to the threshold value, making the algorithm better applicable to non-uniform deformation and large deformation. As the results show, in the simulation experiment, under the different strains such as 1000 µ2, 5000 µ2, and 9000 µ2, the standard error measured by the modified method is reduced to more than 50% compared with the traditional method. Meanwhile, during the real speckle experiment, the error in the modified digital image correlation algorithm was reduced from 9.3e−04 to 7.2e−04. Furthermore, the modified digital image correlation only costs 3% more time, has a little effect on computational efficiency. Therefore, the modified method can smooth the measured strain, and make the robustness and accuracy better during the airship skin measurement. Keywords Digital image correlation · Stratosphere airship · Adaptive subset algorithm · Non-uniform strain
1 Introduction The stratosphere airship is a lighter-than-air spacecraft that depends on buoyancy to stay in the atmosphere. Compared with aircraft and spacecraft, the stratosphere airship has great application value in remote sensing, positioning, real-time monitoring and intelligence collection [1, 2]. However, due to the ultraviolet radiation in the near space, the airship skin is liable to be damaged and has an impact on safety. Therefore, it is particularly important to measure the stress on the surface of the airship skin. Nevertheless, several common methods for measuring strain have some disadvantages. Resistance strain gauge will locally harden the skin surface and affect the measurement accuracy. Fiber grating has the problem of strain transmission. Meanwhile, a large number of cables can also cause wiring difficulties and weight problems [3]. To overcome these shortcomings, this article uses a digital image-related method for deformation measurement. It is a
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Quan-bao Wang [email protected] School of Aeronautics and Astronautics, Shanghai Jiaotong University, Dongchuan RD.800, Shanghai 200240, China
non-contact measurement method and has many advantages such as high accuracy, little environmental impact, simple operation, and full-field measurement [4–6]. In addition, the use of image processing algorithms can better perform subsequent smoothing and denoi
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