Table of Content

10 December 2021, Volume 43 Issue 6

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A Special Issue of mechanics

An Experimental Investigation on the Slug Flow-induced Vibration of Flexible Riser

ZHU Hongjun, GAO Yue, ZHAO Honglei, HU Jie, LIU Wenli

2021, 43(6):  1-11.  DOI: 10.11885/j.issn.1674-5086.2020.10.16.02

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Experiments on hydrodynamic slug flow-induced vibration of flexible riser at different gas superficial velocities were carried out in the air-water test loop using the non-intrusive measurement with high-speed cameras. The vibration displacements were synchronously captured with the internal flow regimes. The dynamic characteristics of flexible riser are analyzed in terms of the amplitude response, modal weight, frequency variation as well as the slug flow characteristics. The results indicate that the amplitude is amplified, and the modal interaction is enhanced with increasing the gas superficial velocity. The fundamental mode dominates the vibration response despite the growth in the modal weight of higher ones. The flow instability of short slugs mainly contributes to the response when the gas superficial velocity is relatively small. In contrast, the response is closely related to the occurrence frequency of long slugs at larger gas superficial velocities. Additionally, both the slug length and migration velocity are enlarged with increasing the gas superficial velocity, while the liquid holdup is reduced.

An Experimental Study on Fracture Characteristic of Sandstone Subjected to Cyclic Wetting and Dryings

DONG Shiming, GAN Zhiqiang, HUA Wen

2021, 43(6):  12-21.  DOI: 10.11885/j.issn.1674-5086.2020.09.30.03

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Periodic water-rock interaction has a great influence on the physical and mechanical properties of rock materials, which has been recognized as one of the important factors affecting the safety and stability of geotechnical engineering structures. In this study, we conducted a series of fracture tests with central cracked Brizilian disk specimens on a typical sandstone after undergiong wetting-drying cycles to investigate the influence of cyclic wetting-drying on the mixed mode I~II fracture resistance and crack propagation. Meanwhile, the degradation mechanism of cyclic wetting and drying was discussed by observing the changing characteristics of the microstructure of sandstone after undergoing cyclic wetting and drying. Finally, the experimental results were compared with the theoretical values based on the fracture criteria. The results show that the pure mode I, pure mode II and mixed mode fracture toughness of sandstone decrease with increasing number of wetting-drying cycles. The deterioration trend of fracture toughness is similar, but the degradation degree is slightly different. The degradation effect of wetting-drying cycles is more significant for a large loading angle or a mode II dominant loading condition. In addition, there is a good agreement between the experimental results and the theoretical values based on the generalized maximum tangential strain and generalized maximum tangential stress criteria, which takes into account the T-stress near the crack tip. Moreover, the criterion provide a better prediction for pure mode II when compared with the criterion.

An Arcsinh-function Based on Cyclic Constitutive Model

ZHU Yilin, WANG Kai

2021, 43(6):  22-32.  DOI: 10.11885/j.issn.1674-5086.2020.10.11.01

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A novel kinematic hardening rule is proposed to improve the predictive capability for cyclic stress-strain hysteresis loops. In the proposed rule, the back stress is decomposed into long, middle and short-range components with each addressing an " A-F"evolution rule consisting of a linear hardening and a dynamic recovery term. For the long and middle-range components, the dynamic recovery coefficients are postulated to be evaluated with deformation to describe the transient Bauschinger effect and each contains a ratchetting coefficient accounting for ratchetting evolution. For the short-range component, the linear hardening and dynamic recovery terms are further divided into two parts respectively, with one part in each activating only when the reverse loading occurs to describe the lower plastic modulus at initial yielding stage during cyclic loading. Under the monotonic loading condition, the proposed rule is integrable and the integration form yields an Arcsinh-function. Besides, the material parameters for the proposed rule related to monotonic loading response, ratchetting behavior and stress-strain hysteresis loops can be determined separately. Finally, incorporating the proposed rule, a cyclic constitutive model is developed in the hypo-elastic finite deformation framework and the predictive capacity for ratchetting behavior and stress-strain hysteresis loops is validated.

Multiaxial Fatigue Failure of 2A12-T4 Aluminum Alloy at High Temperature

CUI Renhao, ZHANG Jianping, HE Yuanhua, YANG Bang

2021, 43(6):  33-41.  DOI: 10.11885/j.issn.1674-5086.2020.10.09.01

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The thermal-mechanical coupling state of structures under multiaxial fatigue loads and high temperature is very complex, and the failure prediction methods for structures under uniaxial loads are not applicable in this case. In order to study the high temperature multiaxial fatigue failure law of 2A12-T4 aluminum alloy at 175℃, the crack initiation and propagation under different loading cycles are recorded by intermittent loading, and the effect of specific loading path on crack initiation and propagation are studied. In the condition of φ=0, the direction of crack initiation is along the MSSA plane; when the φ=45°, the direction of crack initiation is near the MSSA plane, so the maximum shear stress play a major role in the process of crack initiation. Under the λ=0.5, φ=0 and λ=1.0, φ=0, the crack initiate and propagate along the MSSA, and there is no such a transition process from stage I to stage II during the main crack propagation; under λ=0.5, φ=45° and λ=1.0, φ=45°, there is an obvious transition process from stage I to stage II. A Comparison of the relation of crack initiation period and different fatigue life of four loading paths, reveals that the increase of shear stress proportion accelerate the crack initiation period, and the existence of phase difference blocked the crack initiation.

A Study on the Fracture Characteristics Analysis Based on the Generalized Maximum Tangential Strain Criterion

HUA Wen, PAN Xin, GAN Zhiqing, DONG Shiming

2021, 43(6):  42-53.  DOI: 10.11885/j.issn.1674-5086.2020.10.05.03

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The non-singular constant stress term (T-stress) around the crack tip remarkably affects the fracture characteristics of brittle or quasi-brittle materials, and it is also closely related to the shape and size of the plastic zone near the crack tip. In order to explore the influence of T-stress on the I~II mixed mode fracture characteristics of brittle or quasi-brittle materials, the generalized maximum tangential strain (GMTSN) criterion, which considers the effect of T-stress, has been proposed in our previous research. In this paper, the further study on the effects of T-stress, critical distance r₀ and Poisson's ratio ν on the crack propagation path and the fracture resistance for central cracked Brazilian disc (CCBD) specimens have been carried out according to the GMTSN criterion. Moreover, the GMTSN criterion is used to predict the test results obtained with CCBD specimens. The results indicate that the T-stress and Poisson's ratio have a remarkable influence on the mixed mode fracture resistance based on the GMTSN criterion. When compared with the traditional maximum tangential strain (MTSN) criterion, a negative T-stress in a CCBD specimen always decreases the absolute value of the fracture initiation angle; however, the value of critical stress intensity factor is increased for negative values of T-stress. Theoretical values based on the GMTSN criterion, which considers the effect of T-stress, are in very good agreement with the test results. Moreover, the GMTSN criterion provides a better prediction for pure mode II when compared with the generalized maximum tangential stress (GMTS) criterion.

Effect of Hydrogen Atom Permeation on Microcrack Propagation of Pipeline Steel

XU Taolong, HE Gongzhen, ZHANG Yi, FENG Wei, WANG Wei

2021, 43(6):  54-61.  DOI: 10.11885/j.issn.1674-5086.2020.09.30.01

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In the process of hydrogen-induced cracking of pipeline steel, hydrogen atoms enter the metal by adsorption and infiltration, and gather in micro-cracks and micro pores, and interact with defects, which greatly affects the mechanical properties of steel. In order to study the effect of hydrogen atom permeation on crack behavior of pipeline steel, molecular dynamics method is used in this paper, the ferrite-cementite microstructure of ferrite pipeline steel with defects was established firstly. Then, under uniaxial tensile load at 300 K, the effects of different hydrogen atom concentrations on crack propagation between ferrite and cementite layers were studied, and the mechanical properties curves were obtained, and the evolution characteristics of microstructure at different loading stages were observed. The results show that with the increase of hydrogen concentration, the peak stress of ferrite-cementite lamellar structure will decrease, and the higher the hydrogen concentration, the greater the decrease of peak stress. The introduction of hydrogen atoms will only change the speed of crack propagation, but will not change the direction of crack propagation. When the model enters plastic strain, a large number of dislocations and phase transitions are concentrated on the right side of the crack, which hinders the crack cracking on the right side, and the introduction of hydrogen atoms also hinders the transition from FCC phase and HCP phase to BCC phase. The research can provide theoretical reference for further exploring the micro evolution mechanism of hydrogen-induced cracking behavior of pipeline steel.

Influence of Corrosion Pit Size on Stress Concentration of High Strength Steel Wire

WU Mengxue, YIN Li, TANG Defa

2021, 43(6):  62-70.  DOI: 10.11885/j.issn.1674-5086.2020.10.22.01

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The mechanical properties of wires of cable-stayed bridges are extremely sensitive to corrosion. Corrosion pits on the surface of steel wires are caused by corrosion, which will lead to stress concentration and weaken local fatigue resistance of steel wires, and attract fatigue cracks to nucleate from here. This is usually the direct reason for the reduction of cable bearing capacity and service life of cable-stayed bridges. The influence of the length, width and depth of the pit on the stress concentration is discussed by means of numerical simulation. Firstly, a finite element model of a high-strength steel wire is established using finite element software ANSYS. Based on the different scale of pits, i.e. depth-width ratio and length-width ratio, the deep narrow and open pits are simulated. According to the data obtained by finite element calculation, the curve of the factors of pit size and stress concentration coefficient is fitted. According to the curve, the approximate calculation formula of stress concentration coefficient of semi-ellipsoid with different size ratio is established. Based on the stress distribution diagram of pits and the variation law of stress concentration coefficient with size ratio, the influences of length, width and depth of pits on stress concentration effect and stress distribution at pits are discussed, and the influences of three size factors on stress concentration effect are compared horizontally. The results show that the stress concentration coefficient of high-strength steel wire increases with the increase of the depth-width ratio or width-depth ratio of the corrosion pit, and decreases with its length. In addition, the variation of pit length has the most significant influence on the stress concentration coefficient of high-strength steel wire, followed by the pit depth and the pit width has the least influence.

A Study on Mechanical Response of Product Oil Pipeline under Landslide

JIANG Hongye, LAN Xubin, WANG Jinrong, HU Haiyang, WANG Tao

2021, 43(6):  71-83.  DOI: 10.11885/j.issn.1674-5086.2020.12.04.02

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In view of the potential hazards of pipeline crossing the landslide, a fully coupled soil-pipeline-oil model is established based on Smooth Particle Hydrodynamics and Finite Element coupling algorithm (SPH-FEM), considering material, geometry and contact nonlinearity, the action mechanism of soil-pipeline-oil is analyzed, and the influence of landslide displacement, buried depth and diameter-thickness ratio on pipeline physical behavior is discussed. According to the working conditions, the results show that, compared to a oil pipeline simplified to internal pressure (an empty pipeline with internal pressure), when considering the presence of product oil in the pipeline, all of them show typical damage behavior under the action of landslide. However, under the full pipeline transportation condition, the action of the product oil in the pipe changes from " anti-deformation" at the initial moment of landslide to " assisting deformation", and has a greater impact on the displacement and deformation of the pipe body. Compared with the simplified empty pipeline, its displacement increased by 10.63% (stress increased by 4.96%). With the displacement of landslide, the increase of landslide scale and the decrease of buried depth of pipeline (for the pipeline laid in the center of landslide), greater displacement and plastic deformation area will be generated. For the pipeline crossing the landslide area, the wall thickness can be appropriately increased to enhance the ultimate bearing capacity of the pipeline. The research results can provide theoretical guidance and technical support for pipeline safety operation and pipeline protection under landslide disaster.

Vulnerability Analysis of Large Plant-station Module for Land Transportation

LI Hu, WANG Chuanpin, LIU Tao, LAN Xubin, KUERBANAILI Tulafujiang, LIU Xinrui

2021, 43(6):  84-93.  DOI: 10.11885/j.issn.1674-5086.2020.05.04.01

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The land transportation of large plant-station module is an important link in the construction process.The integrity of its overall structure determines whether the field can be successfully put into operation.Based on this, in this paper, the mass element in ANSYS simulation software is used to establish the rigid coupling for a variety of conditions such as emergency braking in the process of transportation, so as to achieve the simplification of the module internal-member and analyze the deformation in the process of transportation.Furthermore, the module weight and acceleration were combined to give consideration to the results of structural failure and the accumulation of damage in transportation, and the probability curves of different damage states under different module weights were obtained.The results show that when the acceleration of emergency braking and accelerated turning is a 6 24 m/s² and a 6 3 m/s², respectively, the module deformation is dominated by the inertia force generated by the module weight, and with the increase of acceleration, the deformation of the upper beam is larger.The transport process maintains uniform speed (uniform acceleration and deceleration) and symmetrical binding constraints, which can avoid large deformation caused by the change of acceleration.Under different conditions, the damage probability curve of module has basically the same trend, and with the increase of module weight and acceleration, the probability of damage gradually increases. In addition, under the same conditions, accelerated turning is more likely to cause the damage of module.

An Experimental Study on Fracture Characteristic of Sandstone Subjected to Cyclic Wetting and Dryings

XU Qiang, YUAN Weifeng

2021, 43(6):  94-101.  DOI: 10.11885/j.issn.1674-5086.2020.09.29.03

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When multi-walled carbon nanotubes (MWCNTs) are added into epoxy resin (EP), the randomly distributed MWCNTs will form a complex conductive network. The MWCNTs take different shapes in the EP resin, and they are either curved or straight, separated or intersected with each other, so the MWCNT/EP nanocomposites possess the characteristics of inductance, resistance and capacitance. In this study, an equivalent RLC internal circuit of the MWCNT/EP composite material was proposed, and the response of the 0.6 wt.% MWCNT/EP composite film to electromagnetic signals was tested. It is found that the MWCNT/EP composite film can resonate under the excitation of electromagnetic waves at a specific frequency, and the resonant frequency shifts with the strain of the film. Hence, the feasibility of using MWCNT/EP composite materials to fabricate wireless strain sensors is proven. Based on the experimental and theoretical analysis of the mechanical-electric characteristics of the MWCNT/EP composite film, the idea of developing a tag-type radio frequency strain sensor is proposed in this article.

A Numerical Study on Hydrodynamic Forces of Abnormal Shape Steel Cofferdams with High-low Blade

TANG Yu, YANG Song, HU Pan, JING Cong

2021, 43(6):  102-110.  DOI: 10.11885/j.issn.1674-5086.2020.10.12.01

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Cofferdams are often used in the construction of deep water piers of bridges. The hydrodynamic load acting on cofferdams is a key factor to control the structural design of cofferdams and to insure the safety and stability of their subsidence process. The existing design specifications consider the hydrodynamic forces on cofferdams roughly to some degree. In order to understand the characteristics of hydrodynamic load during the construction of a special shaped steel cofferdam with high-low blade for bridge pier, the flow field around cofferdam is simulated by computational fluid dynamics (CFD) method. A threedimensional fluid domain is constructed based on the cross-sectional terrain data of the river channel. The subsidence process of steel cofferdam is simulated by overlapping grid technique efficiently. Results show that there is a partial acceleration of flow on both sides of the cofferdam, and the distribution of this acceleration effect is asymmetrical. The flow velocity of the deep water side of the cofferdam is relatively greater, and below the cofferdam the flow velocity of the downstream side decreases gradually with the increasing river depth. The external surface pressure on cofferdams are mostly negative, compared to the positive pressure at the upstream face. With the increase in subsidence depth, the negative pressure in each area increases gradually. In the initial stage, the water flow is influenced by the cofferdam and the protection tube. As the cofferdam gradually sinks to the riverbed, the influence of the protection tube gradually disappeared. Along with the increasing subsidence depth, the turbulence intensity in each region of the flow field shows an overall trend of increasing at first and then decreasing. Finally the maximum turbulence intensity area stabilizes at the wake of the cofferdam. The coefficients of drag and lateral force do not change with the incoming flow speed, which depends on its dimensionless property. The drag and lateral force increase with the increasing of incoming flow velocity, as well as the increasing underwater penetration. However, under the influence of the three-dimensional flow effect, the lateral force shows a local minimum when the sunk depth is about 8 m.

Simulation Test of Mechanical Properties of B-type Sleeve Fillet Weld

CHENG Zhiqiang, HU Cong, DUAN Jinwei, Lü Zhiwei, YANG Tao

2021, 43(6):  111-118.  DOI: 10.11885/j.issn.1674-5086.2020.10.15.03

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The girth weld defects of X80 steel pipes are generally reinforced by B-type sleeves. In order to carry out the simulation test of the mechanical properties of the B-type sleeve fillet welds, and explore the influence of ultrasonic impact on the mechanical properties, a number of sets of X80 steel fractal fillet weld specimens are designed to simulate the tensile and bending of the reinforced pipe, and low-cycle fatigue conditions. Using universal testing machine and fatigue testing machine, the maximum tensile force, maximum bending load and tensile force-cycle number curve (analog S-N curve) of the specimen before and after ultrasonic impact treatment are measured. The test results show that ultrasonic impact treatment of fillet welds has basically no effect on the tensile strength, bending strength, and fatigue strength of the B-type sleeve structure; in the extreme case of complete cracking of the pipe girth weld, the ultimate bending moment that the B-type sleeve fillet weld can withstand is about 69% of the pipe base material. The test results can provide basic data for determining the applicable conditions of the B-type sleeve.

Low Stiffness and Gap Simulation Technology Based on Negative Stiffness Principle

XU Qinwei, WANG Fei

2021, 43(6):  119-125.  DOI: 10.11885/j.issn.1674-5086.2020.09.10.02

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In order to solve the problem of low stiffness of support system and the difficulty of nonlinear simulation of clearance in flutter related ground tests and wind tunnel tests, the simulation technology of low stiffness and clearance is studied. By analyzing the mechanical principle of the parallel support system with positive and negative stiffness, the stiffness expression of the system and the zero stiffness condition at the equilibrium position are obtained. According to this, a parallel system with positive and negative stiffness is designed, and relevant experiments are carried out. The experimental results show that the stiffness of the system is nonlinear, and it is in good agreement with the theoretical analysis results. On this basis, the possibility of using this system to simulate the airfoil clearance of aircraft is discussed, and a clearance simulation device based on positive and negative stiffness parallel mechanism is designed. The test results show that the gap simulation device can not only simulate the gap better, but also adjust the gap size by adjusting the relevant parameters. Through this research, a new low stiffness and stiffness nonlinear support system simulation technology is explored, which can be applied to all kinds of aircraft or flutter wind tunnel models. It has good engineering applicability and application value.

An Experimental Study on Nonlinear Vibration Characteristics of Large Deformed Bolted Beams

ZHANG Ke, ZHANG Yixiong, FENG Zhipeng, HUANG Xuan, CHEN Guo

2021, 43(6):  126-133.  DOI: 10.11885/j.issn.1674-5086.2020.09.27.01

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The operation accuracy of mechanical equipment such as flexible space manipulator, large-scale deployable antenna is significantly affected by the nonlinear vibration at the joints and the large deformations during its movement. This paper, taking the large-deformation beam with bolted joint structure as the research object, carries out experimental researches on its dynamic modeling and vibration characteristics, and verifies them through numerical calculation. An experimental bench with bolted flexible beams was built, and experimental tests of percussion and sinusoidal excitation were carried out. The experimental results show that the modal frequency of the bolted-connected flexible beam is lower than that of the continuous beam (without connection), and the damping is increased, which exhibits the nonlinear modal characteristics that the modal frequency decreases as the excitation energy increases. Changing the bolt connection position will significantly affect the structural modal frequency, and the influence law can be qualitatively reflected by solving the linear matrix eigenvalues.

A Comparative Analysis on Failure Criteria of X80 Pipeline Dent Defect

WU Ying, TIAN Zhongxu, LI Linya

2021, 43(6):  134-142.  DOI: 10.11885/j.issn.1674-5086.2020.10.22.06

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In order to improve the accuracy of safety evaluation of oil and gas pipeline dent defects, the ductile failure criteria of metal materials are applied to the damage evaluation of pipeline dents. Taking X80 dented pipeline as an example, the pipeline damage of three failure criteria under different working conditions was calculated by finite element method and a comparative study was made. It was found that the pipeline damage increases with the increased dent depth; when the dent depth is greater than 6% of the pipeline diameter, the growth rate of pipeline damage decreases. The damage calculated by Oyane ductile fracture criterion is the largest, the critical void expansion ratio criterion is the second, and the X-W damage failure criterion is the smallest. In addition, it was found that the Oyane ductile fracture criterion can better reflect the stress concentration in the dent area by studying the influence of the dent geometry defect on the damage amount. The results show that the Oyane ductile fracture criterion is more suitable for the evaluation of deep and different pipeline dent defects. It provides a reference for further research on the application of ductile failure criterion in pipeline dent evaluation.

Numerical Model of Fluid Induced Vibration Force of Reactor Internals

FENG Zhipeng, HUANG Xuan, LIU Shuai, SHEN Pingchuan, CAI Fengchun

2021, 43(6):  143-151.  DOI: 10.11885/j.issn.1674-5086.2020.09.09.05

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Aiming at difficulty in obtaining fluid exciting force in the flow induced vibration analysis and evaluation of reactor internals, the numerical model of three-dimensional flow field analysis of typical reactor internals is studied based on computational fluid dynamics (CFD). Firstly, according to the structural characteristics and operating parameters of reactor internals, the key components and physical boundaries of the actual structure are extracted and simplified, so as to reduce the calculation scale reasonably and retain the flow field characteristics. Secondly, considering the computational resources and efficiency, the hybrid grid generation method of structural grid and unstructured grid and the partition grid size strategy are adopted. In order to capture the characteristics of the flow field, porous media is used to simulate the core section with complex flow field but not paying attention to its details, and then a three-dimensional flow field analysis model suitable for engineering is established. Three turbulence models with good prediction results are compared. The three-dimensional streamline and pressure distribution characteristics of reactor internals, the time history and PSD characteristics of pressure fluctuation at typical monitoring points, the prediction of fluid excitation forces of reactor internals by three turbulence models, and the characteristics of fluid exciting force acting on the surface of the core barrel are obtained. The results show that LES model can predict the fluid induced vibration forces of reactor internals, and has a certain conservatism. The fluid induced vibration forces acting on reactor internals conform to the wide-band and randomness. It can provide key parameters and input loads for flow induced vibration analysis and evaluation of reactor internals.

Flow Field and Noise Characteristics of Hydrogen Cooler Circuit Regulating Valve During Opening and Closing Process

ZHANG Yu, HE Chao, YUAN Shaobo

2021, 43(6):  152-161.  DOI: 10.11885/j.issn.1674-5086.2020.09.09.04

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In order to study the flow and hydraulic noise characteristics of the regulating valve installed in a conventional island hydrogen cooler circuit during opening and closing process, computational fluid dynamics method is used to capture the flow details in the flow field. The hexahedral and tetrahedral mixed grids are used to discrete the flow field of pipeline and regulating valve. The pressure and velocity quantities are obtained by solving the continuity and N-S equations, the pressure-based solver and SIMPLE scheme are adopted. The standard k-ε turbulence model is applied to close the N-S equation. The opening and closing of valve is realized by parallel user defined function and dynamic mesh technology. The noise characteristics are acquired by an acoustic analog model. The results show, the internal flow field has credible periodicity. The kind of flow indicated noise of regulating valve is typical broadband noise, and the internal noise level is about 8% higher than the downstream area of the regulating valve during the dynamic process. In addition, the overall noise level of the regulating valve elevates with the decrease of the opening, meanwhile, the difference of noise intensity between inside and outside regulating valve increases gradually.

Fast Analysis of Aircraft Flutter Based on Fictitious Mass Method

WANG Fei, RAN Yuguo, LI Qiuyan

2021, 43(6):  162-168.  DOI: 10.11885/j.issn.1674-5086.2020.09.10.01

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Aiming at the difficulties in flutter design due to uncertainties of structural parameters for the initial stage of aircraft design project, the research on the aircraft flutter rapid analysis method in the planning stage is carried out. The fictitious mass method is applied to create a uniform mode shape that can cover the changes of local structural parameters. Then the fictitious mass is removed from the mass matrix to avoid affecting the dynamic characteristics of the original structure. The mass matrix, damping matrix, stiffness matrix and aerodynamic matrix under different parameters will be generalized with this mode shape. The flutter equation in the fictitious mass modal space is established, which is solved by the g method, and the flutter velocity of the aircraft with different parameters is obtained. In this paper, a fast analysis method of aircraft flutter is established, which can effectively reduce the work load of modal analysis and improve the efficiency of aircraft scheme phase analysis when carrying out sensitivity analysis in the face of a large number of parameters. Through the comparative analysis of examples, it can be seen that the calculation accuracy of this method is basically consistent with the traditional method, which meets the engineering needs.

A Study on Wear and Fatigue of High-speed Railway Wheels

ZHU Zhenyu, WANG Qingyuan, DAI Guangze, ZHU Yilin

2021, 43(6):  169-182.  DOI: 10.11885/j.issn.1674-5086.2020.10.23.04

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During the last two decades, high-speed railway has been developing rapidly. However, as the key walking part of high-speed railway, wheels with characteristics of open service environment and the increase of vehicle speed and axle load, have suffered more severe and complex damage. Starting from the wheel/rail contact problem, main damage behaviors of highspeed railway wheels, such as wear and fatigue, are summarized. It is found that thermal elastic instability beneath wheels tread caused by mechanical heat exchange between wheels and rails, is the fundamental reason of wear. However, unlike slow damage process of wear, repeated changes of stress magnitude and direction caused by material composition and mechanical loading during service lead to fatigue initiation and propagation, and forms of wheel fatigue are more various and destructive. Based on the analysis of thermal elasticity and internal texture of surface/sub-surface materials by using the plastic rheology theory, wheel characteristic responses of microstructure related to wear and fatigue degradations are revealed, which provides a theoretical support for wheels molding design and service safety assessment.

The Vibration Test and Response Analysis of Wind Power Generation Stator

LI Yuan, CAO Guohao, MA Wufu, LIANG Chen, HU Xin

2021, 43(6):  183-190.  DOI: 10.11885/j.issn.1674-5086.2020.10.29.02

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In order to solve the vibration and noise problems of large-scale wind power generator, this paper takes a certain type of direct-drive wind power generator as the research subject. The axial acceleration of the wind power generator stator is tested by acceleration sensor when the generator is running, effective model of the wind power generator stator is established using finite element software. The natural frequency, mode shape and resonance frequency of the wind power generator stator can be obtained by modal analysis and response analysis, and the finite element simulation results and test results are analyzed. The measured results show that the axial acceleration of the wind power generator stator at 6 o'clock position is much greater than the axial acceleration at 9 o'clock position, and the axial acceleration reaches its maximum when the wind power generator rotates at 9.5 r/min. The simulation results show that the resonant frequency of the wind power generator stator is 23 Hz, which is three times the rotational frequency corresponding to the maximum axial acceleration. Under this frequency, the displacement ratio of the wind power generator stator at 6 o'clock position and 9 o'clock position is close to the measured acceleration ratio. The research can provide references for the actual operation, vibration test and simulation of wind turbines.

Study on Accident Consequence of Skid Mounted Natural Gas Treatment Plant Based on Domino

LIU Mingming, ZHANG Hongjie, ZHU Lin, LI Wenqian, ZHENG Zilong

2021, 43(6):  191-200.  DOI: 10.11885/j.issn.1674-5086.2020.05.12.07

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In view of the serious accident consequences caused by the tightness of skid mounted equipment, starting from skid mounted treatment plant, first calculate the failure probability of each skid mounted equipment in the treatment plant according to RBI formula, take the equipment with the largest failure probability as the failure equipment for explosion simulation, then calculate the failure probability of surrounding equipment according to probit method, and get the initial event Therefore, the consequence of the accident (one accident); the second explosion simulation is carried out for the equipment with failure probability of 100%, and then the failure probability of the surrounding equipment is calculated according to the improved probit method to get the consequence of the second accident; finally, the consequence severity of the first accident and the second accident is compared. The results show that the maximum impact radius of the primary accident is 49.5 m, the maximum impact radius of the secondary accident is expanded to 161.2 m, and there are three possibilities of accidents; the probability of personal injury in the operation area after the primary accident and the secondary accident of the equipment is 100%, and the relevant departments should strengthen the protection of the operation area.

The Leakage Function of Gravity Displacement in the Narrow Safety Density Window

WANG Cunxin, XU Jiaxin, LI Yong, LI Gao, XIAO Dong

2021, 43(6):  201-208.  DOI: 10.11885/j.issn.1674-5086.2020.10.31.01

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Due to gravity displacement, overflow and lost circulation occur simultaneously in fractured formations. This not only causes complicated downhole conditions and increases the difficulty of drilling pressure control, but also damage the reservoir, which will cause adverse effect on production. This paper establishes a gravity displacement model. And based on gravity displacement model, a leakage function of the gravity displacement in the narrow safety density window of high pressure gas layer has been formed. Then an experiment has been designed to testify leakage function by using the test device development of wellbore-formation coupling flow. The experimental results show that the calculated results of the leakage function are consistent with the experimental data. When drilling in fracture development formation, whether it is underbalanced drilling, balanced drilling, or overbalanced drilling, gravity displacement can't be avoided. However, when we maintain the wellbore pressure close to equilibrium (slightly exceeding), the gravity displacement phenomenon can be significantly reduced. Results of this study have important guiding significance for the mechanism of complex material exchange laws and wellbore safety control of the bottom hole when encountering fractured formations during drilling operations.