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1

Experimental study of the nonlinear behaviour of deep-sea mooring polyester fibre ropes

Zhang He, Zeng Ji, Jin Bowen, Chou Chiate, Li Hangyu, Dong Hailei

Polish Maritime Research

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2023

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nr 3

153--162

EN

Mooring ropes are essential components of ships and offshore floating structures and they are subjected to cyclic axial loads. This study investigates the evolution of the full-cycle stiffness of fibre polyester ropes under long-term static and dynamic loading. First, the static stiffness characteristics of the ropes, including the rope elongation properties at different stages, shrinkage rates, and creep coefficients after an idle period, are examined under static loads; an empirical formula for static stiffness is established. Second, the dynamic stiffness characteristics of the ropes are investigated under cyclic loads that are typical of platform production operations. The stabilities of the structure under different tensions are compared; the effects of mean tension, tension amplitude, and load cycle on the dynamic stiffness of the ropes are analysed and an empirical formula is established to predict the dynamic stiffness during the engineering design phase. The results of this study can be helpful for the rational design of deep-sea taut-leg mooring systems because they present the evolution of the full-cycle stiffness characteristics of mooring ropes.

2

A mechanism reliability analysis method considering environmental influence and failure modes’ correlation : a case study of rifle automaton

Fang Yi-chuan, Wang Yong-juan, Sha Jin-long, Gu Tong-guang, Zhang He

Eksploatacja i Niezawodność

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2023

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Vol. 25, no. 2

art. no. 166145

EN

In order to overcome the challenge of quantifying the influence of environmental conditions and the coexistence of multiple failure modes involved in mechanism reliability modelling under different environments. In this paper, we propose a method for the analysis of mechanism reliability that takes into account the influence of environmental factors and failure modes’ correlation, quantifies the influence of environmental factors as the random distribution and degradation path of parameters, and derives the Copula description of failure mode correlation from the historical data of environmental experiments. On the basis of the discrete mechanism dynamics model, the output parameters of the characteristic points are calculated, and the failure rate of each failure mode is calculated based on the failure criterion and the performance margin theory. Additionally, the dynamic change pattern of the mechanism reliability is compared with the Kaplan-Meier estimation of the corresponding environmental test history data to assess the validity of the calculation results. The reliability modelling problem of a motion mechanism of an automatic rifle automaton in a high and low temperature environment is applied to the method, and the reliability calculation results are close to those of Kaplan-Meier estimation of the test history data, and all are within the upper and lower bounds given by the reliability boundary theory, demonstrating the method's validity.

3

Efects of high-temperature thermal treatment on the porosity of red sandstone: an NMR analysis

Zhang He, Sun Qiang, Jia Hailiang, Dong Zhihao, Luo Tao

Acta Geophysica

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2021

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Vol. 69, no. 1

113--124

EN

High temperatures afect the physical properties of red sandstone seriously, especially the pores. Understanding its mechanism is of great signifcance in coal mining following underground gasifcation, geothermal energy utilization, and the deep burial of nuclear waste. Nuclear magnetic resonance (NMR) was used to detect pore structure characteristics, and scanning electron microscopy (SEM) and polarizing light microscopy (PLM) were used to mechanism of change. The transverse relaxation time (T2) and signal strengths of red sandstone treated at various temperatures were observed by NMR, and then, the pore situation can be obtained, and fnally, the infuence of temperature on the pore structure of red sandstone can be obtained. Microscopic photographs of the pores of red sandstone were obtained by SEM and PLM to assist in explaining the process of microstructural change, especially the infuences of temperature on pore characteristics and grain morphology and distribution. The researches indicate that after the heat treatment of red sandstone at 25–1300 °C, the pore and strength characteristics change in well-defned stages. Before 500 °C, the pore diameters and distribution range increase, but the porosity and internal grain structure do not change signifcantly. At 500–1000 °C, red sandstone micropores contract, mesopores and macropores develop, and strength decreases. After 1000 °C, the grains that comprise sandstone melt and fll many of the pores, decreasing porosity. The proportion of micropores decreases, while mesopores and macropores increase. In addition, a large number of bubbly holes appear in and on the sandstone, presumably caused by gases such as CO2, and water vapor from dehydrating grains. The changes in pore and cementation states with temperature are the main factors afecting the tensile strength of red sandstone.

4

Analysis of the characteristics of magnetic properties change in the rock failure process

Zhang He, Sun Qiang, Zhenlong Ge

Acta Geophysica

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2020

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Vol. 68, no. 2

289--302

EN

It is difcult to observe changes in the internal structure of natural rocks when under certain pressure ranges. However, such rocks have specifc magnetic properties that are established during their formation process. Through studying changes in their magnetic properties while under pressure, which are readily observed and analyzed, as combined and contrasted with their associated structural changes, the relationship between the stress–strain and the magnetic feld intensity can be established. Based on the stress–strain and magnetic feld strength data obtained from the relevant literature, the process of rock and rock-like mechanical failure can be divided into three stages: elastic, plastic, and rupture. The performances of diferent rocks during these stages were analyzed, and there was an obvious transition point between any two adjacent stages. Thus, this study provides theoretical support to establish the relationship between structure and magnetic variations of rocks and rock-like bodies.