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RHEOLOGICAL PARAMETER INVERSION AND ANALYSIS OF ROADWAY SURROUNDING ROCK BASED ON MODIFIED NISHIHARA MODEL1)
GAO Zilu, RONG Chuanxin, TANG Bin
Mechanics in Engineering    2020, 42 (1): 28-34.   DOI: 10.6052/1000-0879-19-376
Abstract28)      PDF(pc) (234KB)(24)       Save
When the stress reaches a certain level, the rock would undergo accelerated creep failure after the attenuation and stable creep processes, but the traditional Nishihara model could not reflect the accelerated creep stage effectively. In order to solve this problem, a non-linear rheological element is introduced and connected in series to the traditional Nishihara model to form a new six-element model, which could fully reflect the three stages of the rock creep. Based on the improved constitutive equation of the Nishihara model and the Laplace transformation, the variations of the radial displacement of the surrounding rock of the shield circular roadway are obtained. Based on the measured data of the convergence deformation of the surrounding rock of the roadway, the viscoelastic-plastic creep parameters of the rock are obtained by inversion. The comparison between the calculation results of the radial displacement of the surrounding rock and the measured data shows that when $t\leq 25$ d, the surrounding rock of the roadway is in the stage of the accelerated deformation, and the rate of change of the radial displacement is increased with time; the surrounding rock of the roadway enters the stage of the stable deformation when $t>25$ d, and the rate of change of the displacement of the radial surrounding rock is gradually stabilized with the passage of time.
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DYNAMIC CHARACTERISTICS OF VIBRATION ISOLATION SYSTEM WITH CUBIC STIFFNESS AND HYSTERESIS 1)
NIU Muqing,CHEN Liqun
Mechanics in Engineering    2019, 41 (5): 520-525.   DOI: 10.6052/1000-0879-19-246
Abstract165)   HTML18)    PDF(pc) (344KB)(65)       Save

The vibration isolation system with cubic stiffness and Bouc-Wen type hysteresis shows complex nonlinear dynamic characteristics. An undamped response model is established based on an anhysteretic restoring force. An approximate analytical solution is derived by the harmonic balance method (HBM) and the Taylor expansion. An analytical/numerical method is proposed to calculate the damped response of the vibration isolation system, based on the HBM and Levenberg-Marquardt algorithm. For the multi-value non-smooth function terms, the harmonic term coefficients are obtained by applying the fast Fourier Transform for the calculated time-domain response. The proposed methods are applied to a nonlinear vibration isolation system with horizontal wire ropes. It is verified that the vibration isolation system has a softening-hardening stiffness with cubic stiffness and Bouc-Wen type hysteresis. Both hysteretic damping and linear damping can effectively suppress the resonance, while with the hysteretic damping, better vibration isolation performance is shown at high frequencies.

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AUTONOMOUS NAVIGATION OF PROBE BY X-RAY PULSARS BASED ON FADING MEMORY FILTERING
HU Tengge, WU Di
Mechanics in Engineering    2019, 41 (4): 382-387.   DOI: 10.6052/1000-0879-19-086
Abstract144)   HTML4)    PDF(pc) (1386KB)(57)       Save

In view of the fact that the Extend Kalman Filter (EKF) is prone to be divergent in the autonomous navigation by X-ray pulsars, this paper proposes an algorithm utilizing the fading memory filter. Based on the study of the error pattern of the EKF with the increase of iterations, some possible reasons for the divergency are analyzed. The fading memory filter can be used to reduce the peak of error, while delaying the divergence

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THE CONDITIONS AND INFLUENCING FACTORS OF TRUCKS' ROLL-OVER DURING TURNING
YANG Yujie, QIU Xinming
Mechanics in Engineering    2019, 41 (4): 393-397.   DOI: 10.6052/1000-0879-19-073
Abstract211)   HTML18)    PDF(pc) (1550KB)(119)       Save

When driving on a bend, due to the high gravity center and the heavy load, large trucks or lorries are easy to roll-over if their speed is high. This paper proposes a simplified theoretical model of the roll-over process of a truck during its turning, based on the dynamics analysis. Two critical velocities are defined to evaluate the state of the truck: the tilting critical velocity and the roll-over critical velocity. For a truck of given parameters, the main factors that affect the roll-over process are analyzed, including the weight of the truck, the height of the gravity center, and the turning radius of the road. Finally, some qualitative driving suggestions are given about how to avoid roll-over of large trucks.

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LARGE-STRAIN CONSOLIDATION OF FOUNDATION WITH SAND DRAINS BASED ON HANSBO'S FLOW 1)
SHI Gang, WANG Yuxiao, LI Yonghui, LIU Zhongyu
Mechanics in Engineering    2019, 41 (4): 405-415.   DOI: 10.6052/1000-0879-19-084
Abstract60)      PDF(pc) (489KB)(35)       Save
Based on Gibson's theory for the large-strain consolidation, the governing equations for the void ratio and the excessive pore pressure for the large-strain consolidation of foundation with sand drains are derived by introducing the Hansbo's flow model with consideration of the sedimentary effect of the soil layer. By comparing with the existing research results, the reliability of the proposed method and the equivalence of the two description methods of the large deformation consolidation equation of the sand well foundation are verified. The numerical solutions of the equations are obtained by using the FlexPDE software, then the differences of the consolidation behaviors among the large-strain, the small-strain and the Barron's consolidation are investigated. And the effect of the parameters ($m$ and $I_1$) of the Hansbo's flow model on the consolidation behaviors is analyzed in detail. Finally, the consolidation behaviors of the axisymmetric consolidation, the radial consolidation and the 1D vertical consolidation are compared. The results show that the large-strain consolidation rate with the Hansbo's flow is smaller than that of any other consolidation models, and the average degree of the consolidation of the consolidation models with the Hansbo's flow tends to be the same with a comparatively long time. And the consolidation rate decreases with the increase of the parameters $m$ and $I_1$ and of the Hansbo's flow. Moreover, the difference of the average degree of the consolidation between the axisymmetric consolidation and the radial consolidation increases with the increase of the influence radius of the sand drains, and during the early stage of the consolidation, the consolidation rate of the 1D vertical consolidation is larger than those of the axisymmetric consolidation and the radial consolidation.
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STUDY ON INFLUENCING FACTORS OF FINE DYNAMIC MODEL OF CED400 HIGH SPEED PANTOGRAPH1)
YE Ziyou, LIU Longfei, WU Rongping, WU Mengzhen, XU Xianghong
Mechanics in Engineering    2019, 41 (3): 265-269.   DOI: 10.6052/1000-0879-19-087
Abstract258)      PDF(pc) (1160KB)(79)       Save
Fine dynamic modeling and vibration characteristics analysis of pantographs have great significance in structural optimization design and equipment performance improvement. For high speed pantograph with reliable structure and excellent performance, not only the overall dynamic characteristics, but also the local vibration characteristics become the key link. The fine dynamics modeling method of pantograph was studied and it was found that the proper mass distribution of the main components in pantograph and their connection setting characteristics are the important guarantee to obtain the natural vibration characteristics of the actual structure.
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DYNAMICAL CHARACTERISTICS ANALYSIS FOR UNILATERAL CONSTRAINED SIMPLY SUPPORTED BEAM WITH HARMONIC WAVE EXCITATION1)
ZHOU Yan, XIAO Shifu
Mechanics in Engineering    2019, 41 (3): 270-277.   DOI: 10.6052/1000-0879-18-468
Abstract232)      PDF(pc) (781KB)(93)       Save
In order to study the influence of the gap collision on the dynamic response of the system, the nonlinear discrete dynamics equations of the unilateral constrained simply supported beam system are derived by using the Rayleigh-Ritz function as the mode function of an ideal simply supported beam. The dynamic response characteristics of the system under the fundamental harmonic excitation and its influence on the applicability of the linear equivalent method of the resonant frequency are studied by numerical methods. It is shown that the local collision caused by the gap of the nonlinear dynamic system will lead to the system vibration energy transfer between the various modes of the system, which makes the linear equivalent method invalid. Even in nonlinear analysis, it is necessary to consider the modes in which the natural frequency of the system is much larger than the upper limit of the excitation band.
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STOCHASTIC VIBRATION CONTROL BASED ON PIEZOELECTRIC STACK INERTIAL ACTUATOR1)
LU Ke, HUAN Ronghua, ZHU Weiqiu, JIANG Wendong
Mechanics in Engineering    2019, 41 (3): 278-282.   DOI: 10.6052/1000-0879-19-013
Abstract271)      PDF(pc) (365KB)(69)       Save
This paper presents a stochastic vibration control strategy based on a piezoelectric stack inertial actuator and investigates the influence of the time delay on the control effectiveness. Firstly, the dynamic characteristics of the piezoelectric stack inertial actuator are analyzed, and the stochastic dynamic model of the main structure with an inertia actuator is established. Then, the LQG (linear quadratic Gaussian) control strategy is proposed and the influences of the system parameters (such as the inertia mass and the stiffness of the actuator) on the control effectiveness are discussed. Finally, the time delay is considered in designing the control strategy and a method of using the time delay is proposed to optimize the control strategy. The results show that the piezoelectric stack inertial actuator is very effective for the random vibration control, and the control effectiveness can be further optimized when the time delay $\tau=0.025$s.
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MECHANICAL ANALYSIS ON THE COLLAPSE ACCIDENT OF BUS SHELTER CEILINGS AFTER SNOWSTORM 1)
ZHANG Guimin, WANG Zhenshuo
Mechanics in Engineering    2019, 41 (3): 283-287.   DOI: 10.6052/1000-0879-19-024
Abstract267)      PDF(pc) (1946KB)(119)       Save
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THE APPLICATION OF MODIFIED CAMBRIDGE MODEL FOR THE WELLBORE STABILITY ANALYSIS OF DEEPWATER SHALLOW SEDIMENTS IN PETROLEUM DRILLING1)1)
Mechanics in Engineering    2019, 41 (3): 288-293.   DOI: 10.6052/1000-0879-18-480
Abstract247)      PDF(pc) (209KB)(45)       Save
Deepwater shallow sediments are weakly structured and unconsolidated. The deformation and failure is one of the key points in the study of deepwater shallow sediments. The modified Cambridge model was widely used in the studies of deepwater shallow sediments except for the borehole stability analysis, in which deepwater shallow sediments are still regarded as ideal elastic plastic materials. The formation is divided into three parts: the elastic zone, the flow zone and the plastic zone. In the elastic zone, the formation is linear elastic. In the flow zone, the modified Cambridge model is applied. In the plastic zone, the formation obeys the Mohr-Coulomb criterion. In this paper, the stress distribution of each region is solved, and on the basis of the solution, combined with the excess pore pressure, the borehole stability analysis model of deepwater shallow sediments is established. The calculation results agree with actual data, which verifies the proposed model.
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INFLUENCE OF SAMPLE PREPARATION TECHNOLOGY ON SHEAR BEHAVIOR OF INHERENT ANISOTROPIC SAND IN TRIAXIAL TESTS 1)
LUO Qiang, LI Xiaolei, MA Keshuan, WANG Zhongtao
Mechanics in Engineering    2019, 41 (3): 294-299.   DOI: 10.6052/1000-0879-18-505
Abstract183)      PDF(pc) (459KB)(50)       Save
Based on the capillary effect and using the freeze thawing method for the sand grain, a sample preparation is suggested to make the sand sample with an arbitrarily sedimentary direction in the range of 0°~90° for any grain composition. A series of triaxial compression shearing tests are performed under a medium confining pressure, the results show that the preparation method combined with the moist sampling and the freeze thawing has a significant influence on the shearing behavior of the sand. With the method, the developing speed of the relation between stress and strain will be decreased, and the ultimate shearing strength will be lowered, but with little influence on the residual shearing strength. Under other stress path conditions of the triaxial test, such as the triaxial tension, the reduced triaxial compression and the triaxial isostress compression, the sample preparation has little influence on the results. The suggested sample preparation method is applicable for the experimental study of the sand inherent anisotropy behavior.
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AUTOMATIC IDENTIFICATION OF MESOSCOPIC PARAMETERS OF DISCRETE ELEMENTS OF SAND MATERIAL 1)
CUI Yangyang, ZHANG Junhui, TONG An, WU Na
Mechanics in Engineering    2019, 41 (3): 300-307.   DOI: 10.6052/1000-0879-18-462
Abstract205)            Save
Accurate identification of mesoscopic parameters are the precondition to conduct the discrete element simulation reasonably. Based on the optimization theory, an automatic method for identifying mesoscopic parameters of sand material is proposed in this paper. The PFC software is used to simulate the biaxial compression test of a kind of standard sandy soil. By minimizing the error between the stress-strain curves obtained by conducting the PFC biaxial compression test and the laboratory test, mesoscopic parameters are identified automatically by using the mode search method. Numerical results show that the stress-strain curves obtained by the numerical simulation and the laboratory test agree very well with those based on the mesoscopic parameters obtained by using the proposed method in this paper, with high efficiency and accuracy.
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EFFECT OF INTERGRANULAR FRICTION ON THE BOTTOM FORCE CHAIN OF TWO-DIMENSIONAL PARTICLE PILES WITH POINT DEFECTS1)
LIU Yuan, XU Tongtong, ZHAO Xianfeng
Mechanics in Engineering    2019, 41 (3): 308-313.   DOI: 10.6052/1000-0879-19-008
Abstract192)      PDF(pc) (2281KB)(49)       Save
The force chain plays a decisive role in the macroscopic and microscopic mechanical properties of granular matter. Based on the discrete element method (DEM), a two-dimensional regular particle system is established to study the influence of the friction coefficient between the particles on the contact force distribution at the bottom of the system under different loads and different defect sizes. The results show that in a defect-free particle system, the contact force distribution at the bottom of the system is affected by the friction coefficient and the point load. As the coefficient of friction increases, the bottom contact force turns from the bimodal form through the platform, gradually to a single peak form. In a system with point defects, the coefficient of friction and the size of the defect have an effect on the force distribution. With a fixed load, as the size of the defect increases, the peak value of the bottom contact force increases significantly; the average value of the force on the bottom is significantly weakened, and the force transmission to the boundary is enhanced. The presence of defects on the central axis of the system weakens the bottom intermediate region. When the defect size exceeds 2 layers, the variation curve of the bottom intermediate force against the friction coefficient changes from an increasing curve to a linearly decreasing curve.
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RESONANT FRACTURE OF LAYERED CYLINDRICAL PIEZOELECTRIC SENSORS LOADED WITH VISCOUS LIQUID1)
ZHAO Yue, CHEN Hongqian, JU Limei
Mechanics in Engineering    2019, 41 (2): 137-144.   DOI: 10.6052/1000-0879-18-384
Abstract184)      PDF(pc) (444KB)(50)       Save
The fracture behavior of a fluid-structure piezoelectric laminated column is studied under the condition of the axial shear vibration. The problem is solved by the variable separation method, the infinite trigonometric series, the Cauchy singular integral equation, the Bessel function and the Lobatto-Chebyshev collocation. The numerical results of the stress intensity factor (SIF) against the frequency are obtained, as well as the effects of the crack angle, the elastic modulus, the piezoelectric coefficient, the dielectric coefficient and the density on the first order resonance behavior of the stress intensity factor.
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EXPERIMENTAL STUDY OF SEISMIC PERFORMANCE OF SECTION STEEL-STEEL PLATE CONCRETE COMPOSITE WALL1)
WANG Lai, MA Jianglin, LI Xin, WANG Jinxin
Mechanics in Engineering    2019, 41 (2): 145-151.   DOI: 10.6052/1000-0879-18-434
Abstract157)      PDF(pc) (2361KB)(29)       Save
This paper proposes an innovative composite wall, named the section steel-steel plate concrete composite shear wall. The seismic behavior of the composite walls is examined and the results of the quasi-static cyclic tests on the walls designed and machined are presented. The failure mechanism, the hysteretic behavior, the stiffness degradation and the energy dissipating capacity are investigated under various axial load ratios and shear span ratios.The test results indicate that the specimens fail in a flexural mode, the steel tubes are torn on the front and the side, characterized by the local buckling of the boundary steel plates and the compressive crushing of the concrete at the wall base.For the composite walls, the plastic deformation ability and the energy dissipation capacity are improved with the increase of the axial load ratios, while the shear span ratio has less effect.
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MECHANICAL ANALYSIS OF SIMPLY SUPPORTED BEAM BASED ON CLASSICAL LAMINATED PLATE THEORY1)
CHEN Lingli, ZHAO Xiaoyu
Mechanics in Engineering    2019, 41 (2): 152-156.   DOI: 10.6052/1000-0879-18-337
Abstract338)      PDF(pc) (442KB)(62)       Save
Compared with the traditional metal materials, the composite materials have high specific strength, large modulus, good fatigue and corrosion resistance, and good thermal and electrical properties. In this paper, the composite materials are selected to carry out a layer-layer design for simply supported beams. Starting from the stress analysis of simply supported beams, the mathematical model of simply supported beams is established, according to the classical theory of composite material mechanics and the basic equation of elasticity. Then, the optimum design of the simply supported beam is carried out to determine the angle and the number of the layers of the simply supported beam, and the composite structure is constructed, the static analysis of the simply supported composite beam is carried out. Finally, the Tsai-Wu tensor criterion is used for the strength check.
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DESIGN OF LATERAL SOIL PRESSURE MODEL TEST SCHEME FOR ADJACENT COMPOSITE FOUNDATION1)
LI Mingyu, QIAN Yuben, GUO Yuancheng, WEI Yanqing, ZHAO Shiyong, CUI Xinlei
Mechanics in Engineering    2019, 41 (2): 157-163.   DOI: 10.6052/1000-0879-18-418
Abstract112)      PDF(pc) (460KB)(40)       Save
In order to study the influence of the rigid pile composite foundation on the lateral soil pressure of adjacent supporting structures, prior to the design of the indoor model test scheme, the models of the adjacent natural foundation and the composite foundation are built by the finite element software for the numerical simulation, and the soil pressure distribution on the static retaining wall side under different foundation forms is estimated. The comparison of the numerical simulation results of the two groups shows that the soil pressure distribution of the composite foundation is different from that of the natural foundation. When the soil stress between the piles under the composite foundation cushion is the same as that of the natural foundation soil, the additional effect of the natural foundation on the wall side soil pressure at the same position of the retaining wall is significantly greater than that of the composite foundation, but as the "load transfer effect", the influence of the composite foundation on the lateral earth pressure of the retaining wall is gradually transmitted to the deeper soil as the load increases. It can be clearly seen that compared with the natural foundation, the effect of the composite foundation on the lateral earth pressure of the retaining wall is relatively weaker in the shallow soil layer, but stronger in the deep soil layer, and the stress concentration at the pile end has a significant effect on the lateral soil pressure at the bottom of the retaining wall.
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INFLUENCE OF SEDIMENTARY DIRECTION ON SHEAR STRENGTH OF SATURATED DENSE SAND IN CONSOLIDATED DRAINED TRIAXIAL TEST1)
LUO Qiang, TANG Zhen, WANG Zhongtao, MA Keshuan, JIANG Gengmin, XIE Xiaokang
Mechanics in Engineering    2019, 41 (2): 164-170.   DOI: 10.6052/1000-0879-18-347
Abstract145)      PDF(pc) (724KB)(57)       Save
Based on the capillary effect of the sand, a test technology is suggested to prepare the dense sand sample with different sedimentary directions. A series of triaxial tests are performed to study the influence of the sedimentary direction on the strength and the volume change of the sand sample, meanwhile, a fitting formula is suggested for the relation between the ultimate strength and the sedimentary direction. Main study results show that the sedimentary direction has a great influence on the ultimate strength and the deformation characteristics of the sand for the direction in the range between 0°~90°, but it has little influence on the residual strength of the sand. When the sedimentary direction is close to the failure plane direction, which is suggested as 45°+ ϕ/2, the test sample is easier to reach the failure stage and the ultimate strength is low. The suggested fitting formula could reflect the relation between the sedimentary direction and the ultimate strength reasonably, in which the confined pressure has an influence on the relation. Meanwhile, the formula could be used to predict the most unfavorable sedimentary direction.
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EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF WATER-COOLED GRANITE UNDER HIGH TEMPERATURE1)
CHEN Yu, XU Nengxiong, QIN Yan, XIE Yuan
Mechanics in Engineering    2019, 41 (2): 171-177.   DOI: 10.6052/1000-0879-18-297
Abstract88)      PDF(pc) (3550KB)(34)       Save
With the uniaxial and triaxial compression tests of the water-cooled granite samples under high temperature, the mechanical properties of the water-cooled granite under high temperature within 800°C against the temperature change and the confining pressure are determined. The experimental results indicate that: (1)The threshold for the effect of high temperature heating and rapid cooling with water on the mechanical properties of the granite is 400°C. (2)Under the same temperature condition, the peak deviator stress and the peak strain increase with the increase of the confining pressure. The elastic modulus increases first and then decreases with the increase of the confining pressure. (3)In uniaxial tests, when the temperature is lower than 400°C, the rock samples will be in a form of composite failure. With the increase of the temperature, the damage morphology changes to a tensile failure. While in the triaxial test, the rock samples all have the shear failure.
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ONE-DIMENSIONAL NONLINEAR CONSOLIDATION THEORY FOR SOFT GROUND WITH CONSIDERATION OF SECONDARY CONSOLIDATION1)
LIU Quan, DENG Yuebao, WANG Tianyuan, MAO WeiYun
Mechanics in Engineering    2019, 41 (2): 178-183.   DOI: 10.6052/1000-0879-18-420
Abstract219)      PDF(pc) (411KB)(49)       Save
Because the soft clay soil usually has a significant rheological effect, the deformation of the soft clay is divided into two parts, i.e., that caused by the effective stress change and that caused by the secondary consolidation. A new stress-strain relationship is thus derived. Based on the Davis's consolidation theory, a one-dimensional nonlinear consolidation equation with consideration of the secondary consolidation is established. The newly proposed equation is solved analytically and its reliability is verified by comparing with the numerical results. The influence of the secondary-consolidation on the settlement of the soft ground is studied. The results show that both the dissipation rate and the consolidation rate obtained by the present method are reduced as compared with those obtained by the traditional method, and the neglect of the secondary consolidation will underestimate the post-construction settlement of the soft clay foundation.
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THEORETICAL ANALYSIS OF THE DECREASE OF THE STRENGTH OF REINFORCED SOIL1)
LEI Shengyou, HUI Huiqing
Mechanics in Engineering    2019, 41 (2): 184-187,183.   DOI: 10.6052/1000-0879-18-370
Abstract163)      PDF(pc) (187KB)(40)       Save
The mathematical expression of the strength of the reinforced soil is theoretically deduced, and the influence of the soil cohesion and the soil-reinforcement interface parameters on the strength of reinforced soil is analyzed. It is shown that when the reinforced soil is subjected to the tensile load up to failure, the cohesive force is reduced to an extent as compared with the tensile force provided by the reinforcement, the strength of the reinforced soil will be less than that of the plain soil; when the reinforced soil is adhesively damaged, the strength of the reinforced soil is less than that of the plain soil when the cohesion are reduced to an extent as compared with the friction provided by the reinforcement. The degree of reduction of the strength of the reinforced soil is related closely to the degree of the interlayer formed by the reinforced material in the soil, the permeability of the soil-reinforcement interface, the spacing of the reinforcement and the indirect reinforcement range.
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THE MODIFIED TRIPLES ALGORITHM FOR FLUSH AIR DATA SENSING SYSTEM APPLIED TO THE VEHICLE WITH BLUNT FORE-BODIES1)
WANG Peng
Mechanics in Engineering    2019, 41 (2): 188-195.   DOI: 10.6052/1000-0879-18-330
Abstract128)      PDF(pc) (6403KB)(34)       Save
In view of the restrictive requirement of the pressure port configuration for the flush air data sensing (FADS) system based on the classical triple algorithm, a modified triple algorithm is developed and verified. Firstly, the classical triple algorithm and the modified triple algorithm are described. Secondly, the feasibility of the FADS system based on the modified triple algorithm including the pressure port configuration and the solving accuracy is evaluated. Finally, the advantages and the disadvantages of these two different methods are compared. The following results are obtained: (1)The solving accuracy becomes much less sensitive to the pressure port configuration for the FADS system based on the modified classical triple algorithm than that based on the classical triple algorithm. Therefore, much more pressure configurations can be used to predict the flight parameters and the restrictive requirement of the pressure port configuration is not necessary. (2)The solving accuracy differences between these two different methods is small, and the pressure port configuration still need to be verified.
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EXPERIMENT STUDY OF I TYPE CRACK BLUNT EXTENSION INDUCED BY WEAK PLANE1)
DONG Kangxing, WANG Suling, LI Jinbo, FANG Xinyao
Mechanics in Engineering    2018, 40 (6): 625-629.   DOI: 10.6052/1000-0879-18-194
Abstract448)      PDF(pc) (16211KB)(312)       Save
Shear failure of weak interface as natural cracks or bedding is the key factor for the formation of crack network. Based on the principle of a three-point bending test, this paper sets up the test bed of mode I crack extension weak plane. The digital image correlation method is used to obtain the specimen surface displacement and strain field changes when the crack extends through the weak plane. The experiment results show that: when the crack extended at the weak interface, the extension stopped transitory, the COD (crack opening displacement) increased rapidly, the crack blunted, the shear strain increased rapidly, the mode I crack transforms to a mixed mode I-II crack and the crack extended deflective.
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GALLOPING BEHAVIORS OF SECTOR-SHAPE ICED EIGHT BUNDLE CONDUCTORS1)
CAI Mengqi, XU Qian , ZHOU Linshu , LIU Xiaohui , YAN Bo
Mechanics in Engineering    2018, 40 (6): 630-638.   DOI: 10.6052/1000-0879-18-061
Abstract206)      PDF(pc) (11770KB)(318)       Save
The sector-shape iced eight UHV (ultra-high voltage) bundled conductors are in a condition more similar to the heavy ice conditions than that of the crescent-shape ice. Test models of sector-shape cross section iced eight bundled conductors are prepared. The aerodynamic coefficients of the sector-shape iced conductor models varying with the wind attack angle are obtained by the wind tunnel test. Based on the wind tunnel test results of sector-shaped iced eight bundle conductors, the numerical methods are used to study the effects of critical parameters on the galloping of eight sector-shaped iced conductors. The effects of the wind velocity, the span length and the initial wind attack angle on the galloping of sector-shaped iced eight bundled iced conductors are investigated. The result shows that the sector-shaped iced eight conductors can reflect the galloping characteristics of eight bundle conductors under heavy ice conditions.
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REBOUNDING OF GALILEAN CANNON FROM A RIGID WALL1)
LIU Lizhi, WANG Bingxiang, ZHENG Yuxuan, YU Tongxi, ZHOU Fenghua
Mechanics in Engineering    2018, 40 (6): 639-646.   DOI: 10.6052/1000-0879-18-203
Abstract236)      PDF(pc) (9530KB)(358)       Save
The Galilean Cannon involves a chain of different size balls rebounding on a rigid wall. Three mechanical models are used to analyze the rebound process: (1) The rebounding is treated as a series of separated one-to-one "elastic" impacts; (2) The rebounding is treated as a one-dimensional multi-body impact, using the Hertzian contact model to describe the rigid body interactions; and (3) The rebounding process is simulated using a 3-D FEM software. Each model reveals a disintegration phenomenon of the ball-chain after impact. It is shown that the rebound speed of the smallest ball in the far end of the chain can be several times larger than the incident speed. The increase of the rebounded speed is more significant when a spacing is assigned between the balls so that the multi-impacts occur as "separated" impact events. Also the differences among the three analytical models are discussed. Experiments are conducted with agreeable results as compared with the theoretical analysis.
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A p-TYPE SUPERCONVERGENT RECOVERY METHOD FOR FE ELASTIC STABILITY ANALYSIS OF EULER BEAMS1)
YE Kangsheng, YIN Zhenwei
Mechanics in Engineering    2018, 40 (6): 647-652.   DOI: 10.6052/1000-0879-18-198
Abstract328)      PDF(pc) (3964KB)(325)       Save
This paper extends the p-type superconvergent recovery method to the finite element elastic stability analysis of Euler beams. Based on the superconvergence properties of the buckling loads and the nodal displacements in the buckling modes in regular FE solutions, a linear ordinary differential boundary value problem (BVP) is set up, which approximately governs the buckling mode in each element. This linear BVP within an element is solved with a higher order element, and a more accurate buckling mode is recovered. Then by substituting the recovered buckling mode into the Rayleigh quotient in analytic form, the buckling load is recovered. This method is simple and clear. It can improve the accuracy and the convergence rate of the buckling loads and the buckling modes significantly with a small amount of computation. Numerical examples demonstrate that this method is reliable and efficient and is worth further extending to other skeletal structures.
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ANALYSIS OF MECHANICAL CHARACTERISTICS OF FROZEN CLAY AND MODIFIED S-M CREEP MODEL1)
GUO Mengyuan, YAO Zhaoming, LI Mengjie, CHEN Junhao
Mechanics in Engineering    2018, 40 (6): 653-660.   DOI: 10.6052/1000-0879-18-107
Abstract219)      PDF(pc) (2893KB)(222)       Save
To describe the mechanical characteristics of the mine soil layer constructed by the artificial freezing method, the uniaxial compressive strength test and the uniaxial compression creep test are carried out by using the remolded soil samples of a certain mine, and the stress-strain curves and the creep curves of the remolded frozen clay at different temperatures and loading grades are obtained. Experimental results show that the uniaxial strength of the soil is higher at a lower frozen temperature; The creep deformation of the soil increases with the increase of the stress level at the same frozen temperature; The isochronous stress-strain curve of the uniaxial compression creep deviates with respect to the strain axis with time. The soil sample experiences two stages of the initial creep and the stable creep, with a tendency to enter the accelerated creep stage in a higher stress level. By modifying the meaning of the parameters in the Singh-Mitchell model and with consideration of the influence of temperature, the improved S-M creep explicit model of the artificial frozen clay is obtained. Then the parameters of the S-M creep explicit model are optimized by using the particle swarm algorithm. Compared with the modified S-M explicit model, the calculated values are in good agreement with the experimental data, which indicates that the modified S-M creep explicit model can well simulate the creep characteristics of the deep frozen clay. The modified S-M creep explicit model provides a new method for the creep calculation of the artificial frozen soil.
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MECHANICAL MODEL OF COLUMN BASE CONNECTION IN ANCIENT TIMBER STRUCTURES1)
WANG Ziang, GUO Rui, QIAN Xingjian, YANG Ruixin, DAI Jianbo, HE Jiayong
Mechanics in Engineering    2018, 40 (6): 661-665.   DOI: 10.6052/1000-0879-18-141
Abstract549)      PDF(pc) (423KB)(272)       Save
According to the investigation of earthquake damage over the years, the slippage of the column foot is a typical damage of the column base connection part of ancient timber structures in Sichuan areas. In order to predict the slippage of the column foot and determine the degree of earthquake damage of ancient timber structures, the column base connection is chosen as the research object. The connecting part is simplified into horizontal and rotating springs, then the dynamic equations of structures are established accordingly. In the solution process, the irregular seismic excitation is simplified, and the peak excitation is used as the constant input. The equivalent stiffness and the correction coefficient are introduced to modify the equation and the solution results, and finally the expressions of the slip distance of the column foot, the maximum slip distance and the maximum inclination angle of the column are obtained.
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MODEL ESTABLISHMENT AND LOAD TRANSFER OF SEMI ARTICULATED FLEXIBLE DRILLING TOOL1)
LUO Min, DONG Xiaona, XU Tingting, LI Qiaozhen
Mechanics in Engineering    2018, 40 (6): 666-670.   DOI: 10.6052/1000-0879-17-444
Abstract215)      PDF(pc) (4913KB)(260)       Save
The load transfer law of the semi articulated flexible drilling tool directly affects the drilling in ultra short radius horizontal wells. In this paper, firstly, the element stiffness equation is deduced and the bending moment transfer rule of the semi articulated flexible drill is obtained. Then, combining the theoretical analysis and the numerical simulation, the semi articulated flexible drill rod model is verified. Finally, the semi articulated flexible drill mechanical model is established in the build section and the load transfer under different borehole curvature radius conditions is discussed. The analysis results show that with the same well depth, with the increase of the radius of curvature, the bottom hole torque value increases, when the semi articulated flexible drill rod is not locked, the semi articulated flexible drill rod does not transfer the bending moment and increase the large fluctuate torque at the bottom hole . The research results provide a theoretical basis for the design of flexible drilling tools.
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STUDY ON AMPLIFICATION FACTOR OF FLEXURAL BUCKLING CRITICAL LOAD OF AXIAL COMPRESSION BARS1)
WANG Duxin, LIU Zhanke
Mechanics in Engineering    2018, 40 (6): 671-675.   DOI: 10.6052/1000-0879-17-437
Abstract303)      PDF(pc) (709KB)(359)       Save
In order to establish the calculation theory of flexural buckling critical loads for axial compression members under normal conditions, First of all, the total potential energy equation for bending buckling of bars was derived, then the critical loads for four kinds of end constraint conditions were obtained by employing Rayleigh-Ritz method and based on the principle of potential energy stationary value theory, and the formula of critical load amplification coefficient was given by comparing the Euler's critical load, which was able to consider the influence of slenderness ratio, compression deformation, shear deformation and cross-sectional shape coefficients, and the formula was derived in this paper can be used to calculate the critical loads for compression bars in possession of smaller slenderness ratio. The analysis of the critical loads between the circular-section and the biaxial symmetric I-section axial compression members show that the slenderness ratio of the member is the dominant factor affecting the amplification coefficient.
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