Probabilistic Analysis of the Durability of Piles with Microcracks Under Chloride Attack

A probabilistic analysis approach for estimating the durability of piles with microcracks under chloride attack is presented. The chloride ingress model is obtained by considering the time-dependent diffusion process. The equivalent diffusion coefficient is derived to investigate the crack effect by introducing the crack effect factor. The fitting formula between the chloride diffusion coefficients and crack widths is established through experimental results, and the proposed equivalent diffusion coefficient is verified by comparison with the experimental results. The probabilistic evaluation of durability of piles with microcracks is performed, and then the parametric analysis is performed to study the effect of main parameters on the failure probability and durability life. The results indicate that the chloride concentration increases rapidly as the crack width increases at the same number of cracks. The durability life greatly reduces with increasing crack density of pile. The durability life predicted by probabilistic method is always less than those by deterministic method at the same condition. The deterministic approach may underestimate the threat of reinforcement corrosion induced by chloride attack, owing to the omission of probabilistic nature of main influencing parameters.

ОПРЕДЕЛЕНИЕ ПОЛОЖЕНИЯ ГРАНИЦЫ ОБЛАСТИ УСТОЙЧИВОЙ РАБОТЫ ОСЕВОГО МНОГОСТУПЕНЧАТОГО КОМПРЕССОРА ПРИ ВЫПОЛНЕНИИ РАСЧЕТНЫХ ИССЛЕДОВАНИЙ

The implementation of the high requirements for modern gas turbine engines depends on the perfection of their components. The reliability of the engine operation is largely determined by the compressor gas-dynamic stability margin. In this paper, a review and analysis of some of the most common approaches to determining the boundary of the compressor gas-dynamic stability region calculation are performed. Based on the analysis, it is shown that the diffuser factor and the equivalent diffuser coefficient are the most suitable for the practice of computational studies at the stage of designing and adjusting the compressor. However, different literary sources present different ranges of the limiting values of these criteria, corresponding to the boundary of gas-dynamic stability, which, in turn, can significantly affect the compressor stability margin. In this regard, it becomes necessary to determine the limiting values of the diffusivity criteria, which can be used both in the design of a compressor and in the construction of a model of a gas turbine engine using the proprietary description of blade machines. To analyze these criteria, we calculated a two-dimensional flow in an axial multistage compressor of a modern by-pass engine using the AxSym software package developed at the Department of Theory of Aircraft Engines of the National Aerospace University "KhAI". A comparison of the calculated data with the results of a physical experiment is carried out. The features of the change in the diffuser factor and the equivalent diffusion ratio depending on the compressor operating mode are established. Dependences which allow approximating the values of these criteria for different rotational speeds are proposed. Recommendations which specify the limiting values of the diffuser factor and the equivalent diffusion ratio for various compressor operating modes are presented.

On the Cryptanalysis of a Bit-Level Image Chaotic Encryption Algorithm

In this paper, the security analysis of a bit-level image chaotic encryption algorithm based on the 1D chaotic map is proposed. The original image chaotic encryption algorithm includes bit-level permutation encryption, diffusion encryption, and linear transform. Deciphering of it can be divided into two stages. First, bit-level permutation encryption, diffusion encryption, and linear transform can be simplified into bit-level equivalent permutation encryption and equivalent diffusion encryption, which is a key breakthrough point of cryptanalysis. Second, the chaotic sequence generated by this algorithm is independent of the plaintext image. Therefore, the equivalent diffusion key and the equivalent permutation key can be obtained by chosen-plaintext attack, respectively. Theoretical analysis and numerical simulation experiment results verify the effectiveness of the analytical method. Finally, some suggestions are proposed to promote the security of the original image chaotic encryption algorithm.

On the Security Analysis of a Hopfield Chaotic Neural Network-Based Image Encryption Algorithm

In this paper, the security analysis of a color image encryption algorithm based on Hopfield chaotic neural network is given. The original chaotic image encryption algorithm includes permutation encryption and diffusion encryption. The result of cryptanalysis shows that the chaotic sequences generated by this algorithm are independent of plaintext image, and there exist equivalent permutation key and equivalent diffusion key. Therefore, according to chosen-plaintext attack, the equivalent diffusion key and the equivalent permutation key can be obtained by choosing two special plaintext images and the corresponding ciphertext images, respectively, and the plaintext image is further recovered from the ciphertext image. Theoretical analysis and numerical simulation experiment results verify the effectiveness of the analytical method. Finally, some improved suggestions for the original encryption algorithm are proposed to promote the security.