Zhenkun Lei - Academia.edu (original) (raw)

Papers by Zhenkun Lei

arXiv: Instrumentation and Detectors, 2016

In phase unwrapping, the locations and densities of residues are indicative of the severity of th... more In phase unwrapping, the locations and densities of residues are indicative of the severity of the unwrapping problem. The residues are used to detect and evade inconsistent phase areas. Gdeisat et al. proposed an algorithm to increase the number of residues in a wrapped-phase map to improve the results of phase unwrapping. But this method will take much time to make the Fourier transform, inverse Fourier transform, select and shift the spectral components, and there is no theoretical analysis on why the frequency shift can increase the number of residues. In view of the above problems, we proposed an algorithm to increase the number of residues in a wrapped-phase map, which only uses a simple multiply operation in spatial domain to realize frequency shift by taking advantage of the frequency shift property of Fourier transform. Besides that, we discuss the relationship between the number of residues and frequency shift. Finally, the experimental evaluation is conducted to prove the...

We propose an image encryption algorithm based on gradient decomposition and an improved logistic... more We propose an image encryption algorithm based on gradient decomposition and an improved logistic map. The original image is first decomposed into three subimages with different gradient sizes using the gradient decomposition. The pixel position of the three subimages is then changed by applying Arnold transformation, and the random sequence generated by the improved logistic map is used to perform the XOR operation on the three subimages. Subsequently, the row pixel values of the three subimages are converted into binary sequences, and then the binary sequences are shuffled with the random sequences generated by the improved logistic map. Finally, the three subimages are obtained as the R, G, and B components of the color image to generate the final encrypted image. For image decryption, the original image can be simply restored by joining the three subimages. The experimental results show that the improved logistic map has a larger key space and better randomness compared with the...

Optics and Lasers in Engineering

In order to completely eliminate, or greatly reduce the number of phase wraps in 2D wrapped phase... more In order to completely eliminate, or greatly reduce the number of phase wraps in 2D wrapped phase map, Gdeisat et al. proposed an algorithm, which uses shifting the spectrum towards the origin. But the spectrum can be shifted only by an integer number, meaning that the phase wraps reduction is often not optimal. In addition, Gdeisat's method will take much time to make the Fourier transform, inverse Fourier transform, select and shift the spectral components. In view of the above problems, we proposed an improved method for phase wraps elimination or reduction. First, the wrapped phase map is padded with zeros, the carrier frequency of the projected fringe is determined by high resolution, which can be used as the moving distance of the spectrum. And then realize frequency shift in spatial domain. So it not only can enable the spectrum to be shifted by a rational number when the carrier frequency is not an integer number, but also reduce the execution time. Finally, the experime...

Composites Science and Technology

European Journal of Mechanics - A/Solids

Journal of Physics: Conference Series

The stress concentration will appear at the edge of the hole of composite laminate after the open... more The stress concentration will appear at the edge of the hole of composite laminate after the openings, which will affect the buckling load and bearing capacity of the composite laminate. Generally, a local reinforcement near the hole is an effective method to alleviate the concentration near the hole and improve the bearing capacity of the structure. In addition, the curvilinear fiber laying scheme is tried to solve the stress concentration problem in this paper. Therefore, the finite element models of ordinary composite laminates with a circular opening, variable angle composite laminates with an open-hole and composite laminates with reinforcement near the circular hole were established by ABAQUS software, the buckling analysis and progressive damage analysis of the above models under shear load were carried out considering the Hashin damage failure criterion and Camanho stiffness degradation criterion. By comparing the buckling load and ultimate load of three different kinds of c...

Applied Optics

The fringe skeleton method is the most straightforward method to estimate phase terms in electron... more The fringe skeleton method is the most straightforward method to estimate phase terms in electronic speckle pattern interferometry (ESPI). It usually needs to binarize the fringe patterns. However, the massive inherent speckle noise and intensity inhomogeneity in ESPI fringe patterns make it difficult to binarize the ESPI fringe patterns. In this paper, we propose a binarization method for ESPI fringe patterns based on a modified M-net convolutional neural network. Our method regards the binarization of fringe patterns as a segmentation problem. The M-net is an excellent network for segmentation and has proven to be a useful tool for skeleton extraction in our previous work. Here we further modify the structure of the previous network a bit to suit our task. We train the network by pairs of ESPI fringe patterns and corresponding binary images. After training, we test our method on 20 computer-simulated and three groups of experimentally obtained ESPI fringe patterns. The results show that even for fringe patterns with high noise and intensity inhomogeneity, our method can obtain good binarization results without image preprocessing. We also compare the modified M-net with a classic segmentation network, the U-net, and a residual encoder-decoder network (RED-net). The RED-net was used for binarization of document images. The experimental results prove the effectiveness of our method.

Materials

The aim of this work was to study the buckling behavior and failure mode of the double-sided lase... more The aim of this work was to study the buckling behavior and failure mode of the double-sided laser-welded Al–Li alloy panel structure under the effect of axial compression via experimental and numerical simulation methods. In the test, multi-frequency fringe projection profilometry was used to monitor the out-of-plane displacement of the laser-welded panel structure during the axial compression load. In addition, the in-plane deformation was precisely monitored via strain gauge and strain rosette. The basic principles of fringe projection profilometry were introduced, and how to use fringe projection profilometry to obtain out-of-plane displacement was also presented. Numerical simulations were performed using the finite element method (FEM) to predict the failure load and buckling modes of the laser-welded panel structure under axial compression, and the obtained results were compared with those of the experiment. It was found that the fringe projection profilometry method for moni...

Optics & Laser Technology

Abstract The local high temperature of laser welding affects the mechanical damage properties of ... more Abstract The local high temperature of laser welding affects the mechanical damage properties of aluminum alloy. The full-field strain near the weld of the laser-welded aluminum alloy 6061 under uniaxial tension was obtained using digital image correlation. An iterative stress increment method for the isotropically hardened elasto-plastic damage coupling constitutive model is proposed herein based on the combination of a return mapping scheme and the nonlinear virtual field method. The elasto-plastic damage coupling constitutive parameters and its corresponding stress–strain relationship in each subzone around the weld are established. The results show that the plastic strain accumulating in the heat-affected zone is the fastest, where the damage initiation occurs earlier, and the damage evolution speed is faster than that other zones.

Materials Science and Engineering: A