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    REVISITING THE LOSS AND RECOVERY OF DISPLACEMENT ACCURACY IN FEM AS SEEN FROM MATRIX DISPLACEMENT METHOD 1)
    YUAN Si, YUAN Quan
    Mechanics in Engineering    2020, 42 (6): 689-694.   DOI: 10.6052/1000-0879-20-106
    Abstract58)      PDF(pc) (269KB)(55)       Save
    This paper is a revisit of Ref.[1], where it is shown that the errors from one-dimensional finite element (FE) results mostly come from the element fixed-end solutions. Based on this concept, the element energy projection (EEP) method for the super-convergence calculation is developed. Moreover, when the EEP technique is applied to the adaptive FE analysis to estimate and control the errors in FE solutions, the solutions satisfying the user pre-set error tolerances in the maximum norm can be obtained. Recent introspection leads to a realization that the essence in Ref.[1] has not been fully exploited: since the element fixed-end solutions are the major source of errors, then it is possible to calculate the errors a priori by using the EEP method, immediately generating a desirable mesh without the need for the FE analysis in advance. This paper gives a brief introduction to this novel idea and some initial numerical results are given to show the validity and effectiveness of the proposed technique.
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    INTERLAYER LEAKAGE FLOW IN THE SEALING TEST OF INSERT SEAL TOOL WITH HOLES 1)
    GAO Yonghua, LIU Huawei, SHI Shiying, LIU Quangang, LI Hua, LIU Lei, LI Mengchao
    Mechanics in Engineering    2020, 42 (6): 695-700.   DOI: 10.6052/1000-0879-20-187
    Abstract48)      PDF(pc) (4520KB)(44)       Save
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    GALERKIN APPROXIMATE SOLUTIONS OF A ROTATING CANTILEVER RAYLEIGH SHAFT 1)
    ZHANG Yuhuan, REN Yongsheng, ZHANG Jinfeng
    Mechanics in Engineering    2020, 42 (6): 701-707.   DOI: 10.6052/1000-0879-20-348
    Abstract37)      PDF(pc) (320KB)(42)       Save
    The whirling frequency and the critical speed of a rotating cantilever Rayleigh shaft are studied in this paper, based on the Rayleigh beam model, and the motion equation of the rotating cantilever Rayleigh shaft is derived, and discretized by the Galerkin method. During the Galerkin process, the modal shape functions of the non-rotating Euler-Bernoulli beam and the rotating Rayleigh beam with clamped-free boundary conditions are selected as the trial functions to obtain the whirling frequencies and the critical speeds. Both solutions are illustrated by numerical examples, the convergence of solutions is tested, and the results are compared with the classical solution obtained analytically. It is shown that using the modal shape of the non-rotating Euler-Bernoulli beam to obtain the approximation is usually far easier and faster than using the modal shape of the rotating Rayleigh beam. Therefore, it is preferred for the dynamic solution of the rotating cantilever shaft.
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    VERTICAL AND LATERAL DYNAMICS OF THREE-AXLE HEAVY-DUTY VEHICLE MODEL 1)
    LU Yongjie, YU Jing, ZHANG Hangxing, ZHANG Wei, LI Shaohua
    Mechanics in Engineering    2020, 42 (6): 708-716.   DOI: 10.6052/1000-0879-20-176
    Abstract39)      PDF(pc) (974KB)(28)       Save
    A vertical dynamics model for the three-axle heavy-duty vehicle is firstly established, and the road surface random excitation is generated using the filtered white noise method. Based on a magic formula tire model, a vehicle lateral dynamics model for the three-axle heavy-duty is established. Then a vertical-lateral coupling dynamics model for the three-axle heavy-duty vehicle is established. The vertical dynamical load of the tires is used to couple the vertical dynamics model to the lateral dynamics model. The dynamic coupling vertical-lateral model is implemented in Matlab/Simulink. The simulation results show that the independent vehicle vertical and lateral dynamics model can reflect the ride and handling stability of the vehicle to a certain extent. But the maximum values of the yaw rate, the side-slip angle, and the lateral acceleration of the coupling model are all smaller than those obtained with the independent lateral model. The coupling model for the three-axle heavy-duty vehicle can reflect the impact of the vehicle's vertical motion on the lateral motion. It can be used for the optimization of the vehicle performance under the complex working conditions.
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    NONLINEAR STOCHASTIC OPTIMAL CONTROL OF ELECTROMECHANICAL SUSPENSION OF TORSIONAL TRACKED VEHICLE 1)
    YAN Jingxi, XIA Lei, SONG Huixin, HUAN Ronghua, ZHU Weiqiu
    Mechanics in Engineering    2020, 42 (6): 717-725.   DOI: 10.6052/1000-0879-20-232
    Abstract30)      PDF(pc) (403KB)(22)       Save
    When a tracked vehicle runs on a rough road surface, the vehicle body usually undergoes strong vibration, which significantly affects the working environment of the combat personnel and the shooting accuracy during the motion. Therefore, the vibration control of the vehicle body is much required. In this paper, a nonlinear stochastic optimal vibration control strategy for the electromechanical suspension of a torsional tracked vehicle with consideration of the actuator saturation is proposed. Firstly, the nonlinear stochastic dynamic model of the suspension system is built based on the space structure of the torsional bar and the nonlinear model of the air spring. Then, based on the stochastic dynamical programming principle, the dynamical programming equation of the electromechanical suspension system is established. The optimal bounded control strategy is formulated by solving the dynamical programming equation with consideration of the saturation of the actuator. Finally, the effectiveness of the proposed control strategy is evaluated by comparing the statistics of the responses of optimally controlled and uncontrolled systems. The influence of the time-delay on the control effectiveness is also discussed. Numerical results show that the proposed control strategy can effectively mitigate the nonlinear stochastic vibration of the electromechanical suspension, and the control strategy is found to be quite robust against the variations of the system parameters. To ensure the effectiveness of the control force, the time delay should be controlled within 0.15 second.
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    A FAST CALCULATION METHOD OF MANEUVERING LOAD IN AIRCRAFT SCHEME DESIGN STAGE
    ZHANG Jiangang, HE Kangle, JIN Xin
    Mechanics in Engineering    2020, 42 (6): 726-730.   DOI: 10.6052/1000-0879-20-254
    Abstract31)      PDF(pc) (279KB)(24)       Save
    A simple calculation method is proposed in this paper to quickly and accurately predict the design maneuver load of an aircraft in the preliminary design stage. Aerodynamic derivatives of the aircraft are calculated based on the static aeroelastic theory, and the maneuver simulation of aircraft is carried out with the aerodynamic derivatives, the control characteristics and the mass characteristics as the input. The time history of each motion parameter is obtained. Finally, the distributed load on the components is calculated by the vortex lattice method. The results of this paper are compared with those of traditional methods. It is shown that this method is accurate and reliable, and can meet the load requirements of the aircraft design in the preliminary design stage. This method can effectively overcome the shortcomings of the traditional method which needs a large number of data of aerodynamic characteristics and pressure distribution to be obtained in wind tunnel tests. With the method in this paper, calculations can be carried out with fewer input parameters, which can save time and speed up the development of the model.
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    THE SEISMIC PERFORMANCE OF MIXED REINFORCED CONCRETE COLUMNS 1)
    ZHAO Guangqi, MA Qianying, WANG Zuohu, LIU Du
    Mechanics in Engineering    2020, 42 (6): 731-739.   DOI: 10.6052/1000-0879-20-290
    Abstract35)      PDF(pc) (2531KB)(20)       Save
    To study the seismic characteristics of high-strength mixed-reinforced concrete columns, the seismic loading test is carried out for the same size concrete columns of different concrete types, different axial compression ratios, and with or without steel fiber or carbon fiber reinforced plastic (CFRP) reinforcement. The single variable method is used to compare and analyze the variations of the displacement ductility, the stiffness degradation and the energy dissipation capacity of concrete columns obtained in the experiments. It is found that the high-strength mixed reinforced concrete column shows typical ductile failure characteristics. Adding steel fibers or CFRP bars can effectively improve the bearing capacity and the deformation capacity of the column. When the concrete strength is greater, the bearing capacity is larger; when the CFRP reinforcement ratio is larger, the deformation capacity is larger; when the axial compression ratio is larger, the bearing capacity is larger.
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    CONSTITUTIVE MODEL OF UNLOADING STRESS PATH OF SILTY CLAY
    HU Jialiang, ZHOU Lelin
    Mechanics in Engineering    2020, 42 (6): 740-751.   DOI: 10.6052/1000-0879-20-196
    Abstract35)      PDF(pc) (3415KB)(23)       Save
    In this paper, for the silty clay in the foundation pit of Guicheng Station of Foshan Metro Line 3, different stress path consolidation undrained shear tests, the reduced triaxial compression test, reduced triaxial extension test, and triaxial extension test are carried out, respectively. By analyzing the mechanical properties of the soft clay under different stress paths in Foshan area and introducing normalization factors, a constitutive model for the stress path of the soft clay unloading in Foshan area is established, which can be used for the excavation of the foundation pits in silty soil in Foshan area.
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    INVERSION OF BOUNDARY CONDITIONS FOR ROCK UNIAXIAL COMPRESSION EXPERIMENTS 1)
    WU Jianing, XING Tongzhen, SONG Yimin
    Mechanics in Engineering    2020, 42 (6): 752-757.   DOI: 10.6052/1000-0879-20-218
    Abstract33)      PDF(pc) (664KB)(19)       Save
    Based on the finite element method and the measured data, the uniaxial compression boundary conditions and the elastic parameters of the specimen are obtained by inversion method. Firstly, the parameter inversion equations are derived. Secondly, the surface displacement field of a red sandstone specimen is obtained by the digital speckle correlation method. Finally, based on the grid node displacement calculated by the finite element method and the measured data, the boundary conditions, the elastic modulus and the Poisson's ratio of the specimen are obtained. It is shown that: (1) by using the method developed in this paper, the boundary conditions and the elastic parameters of materials are obtained by the inversion method. (2) the elastic modulus of the specimen is about 18~GPa, and the value is gradually stabilized in the later stage of loading; the Poisson's ratio gradually increases with the loading, and the value is between 0.14 and 0.34. (3) due to the heterogeneous nature of the rock material, a certain difference is observed in the direction and the magnitude of the external load of adjacent nodes in the horizontal direction.
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    SHEAR STIFFNESS AND DAMAGE MECHANICS MODEL OF FRP BAR BOLT IN PULL-OUT TEST 1)
    YANG Zhao, QIAO Chunsheng, CHEN Song
    Mechanics in Engineering    2020, 42 (6): 758-765.   DOI: 10.6052/1000-0879-20-229
    Abstract26)      PDF(pc) (4484KB)(19)       Save
    To study the variation of the interface shear stiffness of fiber reinforced plastic (FRP) bar bolt and grout, several groups of test data for the shear stiffness are analyzed and fitted into curves, and the curves of the interface shear stiffness of FRP bar anchor bolt against the shear displacement are in exponential variation. Combined with the damage mechanics theory, based on the equivalent strain assumption, the shear stress and shear displacement models with Weibull and power function distributions are established, respectively. It is shown that the model established based on the fitting law and the Weibull probability distribution is in good agreement with the experimental data. The degradation of the interface shear stiffness of FRP bar bolt and grout is closely related with the shear position, and based on this, the force transfer analysis of the bolt is carried out.
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    EXPERIMENTAL ANALYSIS OF ACTIVE STEERING HARDWARE-IN-LOOP BASED ON SLIDING MODE CONTROL 1)
    FAN Haoyang, LI Shaohua, WANG Guiyang
    Mechanics in Engineering    2020, 42 (5): 543-550.   DOI: 10.6052/1000-0879-19-478
    Abstract111)   HTML9)    PDF(pc) (5001KB)(87)       Save

    In order to improve the safety of heavy-duty vehicles in the steering process, this paper proposes an active front wheel steering control strategy based on the sliding mode variable structure control. With this strategy in mind, an active steering controller is designed. A simplified vehicle dynamics model with two degrees of freedom and a model for a three-axle commercial vehicle are established. The co-simulation platform is built with TruckSim and Simulink, and the hardware-in-loop experiment is carried out. Under different working conditions and at different speeds, the steering stability analysis of the vehicle with or without the active steering controller is carried out. Based on this, the sensitivity analysis of the active steering influencing factors of the sliding mode variable structure control is carried out. The experimental results show that this controller strategy has a good adaptability under different working conditions.

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    HUMAN-LIKE CONTROL FOR SEMI-PASSIVE BIPEDAL ROBOT WALKING WITH VARIABLE LEG STIFFNESS 1)
    ZHANG Rui, ZHANG Qizhi, ZHOU Yali
    Mechanics in Engineering    2020, 42 (5): 551-557.   DOI: 10.6052/1000-0879-20-139
    Abstract62)      PDF(pc) (464KB)(67)       Save
    For the walking control of the semi-passive bipedal robot with variable stiffness, the human-like walking control strategy is adopted. By using the self-stabilizing characteristics of the bipedal spring loaded inverted pendulum model with variable stiffness, the rear leg stiffness is adjusted in the double support phase to keep the robot energy near the desired energy, and the position of the swinging leg touching down on the ground is adjusted in the single support phase to control the altitude and the forward velocity of the desired point. The simulation results show that the human-like control strategy can ensure a stable walking of the bipedal robot in the horizontal plane. The robot can achieve the passive periodic walking with zero-input when there is no disturbance. With the variable stiffness control of the leg, the total energy of the robot can be restored to a balance state, the robot can re-enter the steady-state walking, and the control system is robust to the external disturbance.
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    COMBINATION RESONANCES OF AN AXIALLY MOVING UNIDIRECTIONAL PLATE PARTIALLY IMMERSED IN FLUID WITH TIME-DEPENDENT AXIAL SPEED 1)
    LI Hongying, LI Xin, WANG Xueqi
    Mechanics in Engineering    2020, 42 (5): 558-564.   DOI: 10.6052/1000-0879-20-037
    Abstract60)      PDF(pc) (1079KB)(54)       Save
    This paper studies the dynamic characteristics of combination resonances of a plate partially immersed in fluid with a time-dependent axial speed. Based on the theory of von Kármán large deflection plate and taking into account of the effects of the fluid-structure interaction, the tension force and the time-dependent speed, the nonlinear dynamic equations of the plate partially immersed in fluid are established. By applying the Galerkin method to discretize the equations, the nonlinear dynamic equation set in modal coordinates is then obtained. The effects of parameters such as the average speed, the pulsating speed and the tension force on the nonlinear dynamic characteristics of the system are analyzed through the multiple scale method and the numerical method. It is revealed that when a combination resonance occurs, the system shows a complex dynamic behavior, the amplitude of the first order modal response is far larger than that of the second order, and the influence of the average speed and the pulsating speed on the frequency-response curve is quite remarkable.
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    DYNAMIC RESPONSE OF THE CATENARY RISER IN DEEP-SEA MINING SYSTEMS 1)
    KUAI Yanrong, WEI Mingzhu, WANG Xu, ZHOU Jifu
    Mechanics in Engineering    2020, 42 (5): 565-570.   DOI: 10.6052/1000-0879-20-085
    Abstract85)   HTML7)    PDF(pc) (817KB)(66)       Save

    With a finite element model, the dynamic response of the catenary riser of deep-sea mining systems under the action of the ocean current and the motion of the surface vessel is simulated. The results show that the maximum equivalent stress and the maximum displacement of the catenary riser change periodically with a phase difference of half a period between them. When the surface vessel moves to the highest position, the displacement of the catenary riser reaches the maximum. The maximum equivalent stress and the maximum displacement of the catenary riser increase with the increase of the displacement amplitude of the surface vessel and decrease with the increase of the period. In addition, the effect of the displacement and the period of the motion of the surface vessel on the equivalent stress of the catenary riser is greater than that on the displacement.

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    AEROELASTIC OPTIMIZATION DESIGN OF COMPOSITE WING WITH CONSIDERATION OF STRUCTURAL INSTABILITY
    LIU Xiaochen
    Mechanics in Engineering    2020, 42 (5): 571-575.   DOI: 10.6052/1000-0879-20-026
    Abstract63)      PDF(pc) (1468KB)(51)       Save
    Based on engineering mathematical solution and finite element analysis, the aeroelastic optimization technology is developed with consideration of both the wall stability constraints and the aeroelastic constraints. The aeroelastic comprehensive optimization design is carried out for a large aspect ratio composite wing. It is shown that if the stability constraints are not considered in the aeroelastic optimization of the wing, although a smaller structural weight can be achieved, the stability requirements are often not satisfied. Compared with the aeroelastic comprehensive optimization design method with consideration of the structural instability characteristics by the finite element, the optimization with the partition instability analysis of the wing structure by engineering mathematical solutions can control the variables more accurately, further reduce the structural weight and improve the structural instability factor while satisfying various performance requirements, especially, the stability constraints.
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    NUMERICAL STUDY OF THE PHENOMENON THAT A FERRY BOAT DRIFTS ATHWART AT THE DESERTED CROSSING
    YU Yongfei, CHEN Chen, SI Tiedong, HU Ting, WEI Jiawang
    Mechanics in Engineering    2020, 42 (5): 576-579.   DOI: 10.6052/1000-0879-20-108
    Abstract106)      PDF(pc) (1258KB)(272)       Save
    In order to study the phenomenon that a ferry boat drifts athwart at the deserted crossing, a numerical simulation is carried out for the motion of a boat under the water flow action. Conclusions are as follows: The boat can keep a balance both along and across the water. But it is an unstable balance along the water, it will be lost because of an external disturbance, and the boat can not restore to its homing position again. While the boat is in a stable balance across the water, it can restore to the homing position again even if the boat loses the balance under an external disturbance.
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    RESEARCH OF STEPPING PRESSURE AND CONTROL OF NEAR FIELD ROOF OF TASHAN COAL MINE BASED ON NUMERICAL SIMULATION 1)
    LI Jinbo, WANG Suling, DONG Kangxing, ZHAO Xinyu, XIE Wenqi, ZHANG Ziheng
    Mechanics in Engineering    2020, 42 (5): 580-587.   DOI: 10.6052/1000-0879-20-075
    Abstract64)      PDF(pc) (5908KB)(41)       Save
    The hard roof of coal seam is directionally weakened by hydraulic fracturing technology, which can effectively control the stepping pressure distance and reduce the risk of accidents. Based on the cohesion model and the secondary development technology of the finite element platform, a numerical calculation model of coal seam mining before and after fracturing is established, the roof collapse law and its influencing factors are analyzed, and the fracture spacing design is optimized. The results show that the stepping pressure span has a positive correlation with the roof thickness and strength, and a negative correlation with the buried depth. Prefabricated fractures in tensile stress concentration areas can promote the crack initiation and propagation. Geological parameters of each rock layer should be carefully determined, as well as the location of stress concentration areas, to design the fracture spacing for controlling the stepping distance economically and effectively.
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    AN IMPROVED IRS METHOD FOR STRUCTURE MODEL CONDENSATION 1)
    YANG Qiuwei, ZHANG Jinxin, LI Cuihong
    Mechanics in Engineering    2020, 42 (5): 588-593.   DOI: 10.6052/1000-0879-20-163
    Abstract69)      PDF(pc) (294KB)(58)       Save
    The model condensation method is widely used in the static and dynamic analysis of structures. With the model reduction, the calculation scale of structural static and dynamic equations can be effectively reduced, with the calculation time and cost saved, and to obtain a reduced finite element model matching the experimental measurement freedoms. A new IRS (improved reduced system) method is proposed in this paper by considering the second-order inertia, to effectively improve the calculation accuracy. Compared with the IIRS (iterated IRS), the proposed second-order IRS method can be used to build a more accurate reduced model with smaller calculation amount. Taking a truss structure and a frame structure as examples, the proposed second-order IRS method is verified, and the calculation results are compared with the exact solution, the Guyan condensation solution, the IRS solution and the IIRS solution. It is shown that the proposed method enjoys the best calculation accuracy, with a good engineering application prospect.
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    DEFLECTION OF FOUR TYPES OF CANTILEVER BEAMS WITH VARIABLE CROSS SECTION UNDER LATERAL TRIANGULAR DISTRIBUTED LOADS 1)
    LIAO Han, JIANG Lüfeng, LI Hengda, YANG Xingchang, LI Yinghui
    Mechanics in Engineering    2020, 42 (5): 594-597.   DOI: 10.6052/1000-0879-20-015
    Abstract107)      PDF(pc) (209KB)(85)       Save
    The deflection of cylindrical, conical, parabolic and hyperbolic cantilever beams with reversed sections under laterally triangular distributed loads is studied. Firstly, from the distribution of moment of inertia along the length direction of four types of rotating cantilever beams, the deflection curve equation under any lateral triangular distributed load is obtained. Based on the deflection curve equation under the linear load, the deflection at the lower end of the lateral triangular distributed load is obtained. Under the assumption of equal length and equal volume, the minimum deflection among the four types of cantilever beams is found by comparing the end deflection values. It is shown that among the four types of cantilever beams under lateral triangular distributed load, the characteristic parameters are within a specific range, and the deflection of the cantilever beam with hyperbolic bus is the smallest.
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    THE MECHANISM OF THE INTERACTION BETWEEN NANOPARTICLE AND LIPIDS MONOLAYER OF PULMONARY SURFACTANT 1)
    JIAO Fengxuan, SANG Jianbing, LIU Zhaoyang, LI Yang
    Mechanics in Engineering    2020, 42 (4): 424-429.   DOI: 10.6052/1000-0879-20-034
    Abstract79)   HTML3)    PDF(pc) (7510KB)(37)       Save

    The inhaled nanoparticles (NPs) are first met by the biological barrier inside the alveolus known as the lung surfactant (LS). They can reach deep into the lung and interfere with the biophysical properties of the lung components. The interaction mechanisms of the gold nanoparticles (AuNPs) with the LS monolayer and the consequences of the interactions on the lung function are not well understood. Coarse-grained molecular dynamics simulations are carried out to study the interaction between the AuNPs and the LS monolayers at the nanoscale. It is observed that the presence of the AuNPs deforms the monolayer structure, changes the biophysical properties of the LS monolayer, and the results also indicate that the AuNPs with different shapes have different effects on the LS monolayer. These findings could help to identify the possible consequence of the airborne NPs inhalation.

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    EFFECTIVENESS OF THE PROPELLENT CROSS-FEED TECHNOLOGY FOR LAUNCH VEHICLE
    XIAO Zhiwen, WU Di
    Mechanics in Engineering    2020, 42 (4): 413-417.   DOI: 10.6052/1000-0879-19-483
    Abstract98)   HTML4)    PDF(pc) (349KB)(60)       Save

    This paper presents a simple method to estimate and optimize the maximum launch capability of low Earth orbit (LEO) with different launch modes and trajectories, combined with trajectory optimization. The numerical calculation is carried out for the CZ-7 rocket, to analyze the specific effect and the characteristics of the optimal launch trajectory when launching with the cross-feed technology. The results show that the maximum launch capability of the LEO can be increased by 3 t (about 20%) and the maximum axial acceleration during the launch can be reduced by nearly 50% if for the CZ-7, the propellant cross-feed technology is applied in the launching process. With the help of the propellant cross-feed technology, the launch capability of such lift launch vehicle can be greatly improved.

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    DROP FORMATION FROM A CAPILLARY TUBE IN THE PRESENCE OF SURFACTANT 1)
    CHEN Yazhou, ZHOU Zhiqiang, PENG Jie
    Mechanics in Engineering    2020, 42 (4): 405-412.   DOI: 10.6052/1000-0879-19-484
    Abstract119)   HTML11)    PDF(pc) (590KB)(77)       Save

    In this study, the growth of an incompressible Newtonian drop from a vertical circular capillary tube in the presence of surfactant is analyzed. The flow is assumed to be axisymmetric and can be reduced to a spatially one-dimensional system by using the Taylor expansion and the lubrication approximation. The finite difference method combined with a coordinate transform is adopted for the numerical simulation. The results show that the existence of the surfactant will promote the breakup process of the drop, and prolong the limit length. Furthermore, the surfactant concentration has a more critical influence on the interface shapes than the surfactant activity.

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    LIMIT CYCLE FLUTTER CHARACTERISTICS RELATED TO CONTROL SURFACE OF LARGE AIRCRAFT 1)
    LÜ Jihang, LUO Linyin
    Mechanics in Engineering    2020, 42 (4): 418-423.   DOI: 10.6052/1000-0879-20-009
    Abstract82)      PDF(pc) (312KB)(66)       Save
    The freeplay of the control surfaces is a cause of the structural nonlinearity, which will easily lead to the limit cycle flutter. According to the design requirements, considering the center freeplay of the control surface, rational function approximations of the unsteady aerodynamics in the frequency-domain are constructed based on the Minimum-State Approximation Formula, with the nonlinear stiffness caused by the center freeplay being described by the subsection function. Then the nonlinear response characteristics and the behaviors of the limit cycle flutter due to the freeplay on the control surface are studied. Results show that due to the influence of the central freeplay in the nonlinear system, the limit cycle oscillation is produced below the linear flutter speed, and the limit cycle amplitude increases with the increase of the flight speed or the center gap.
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    FREE VIBRATION ANALYSIS OF CARBON NANOTUBES BASED ON THE MESHLESS METHOD 1)
    LI Lin, SHI Feng, XIANG Song, ZHAO Weiping, WANG Yanbing
    Mechanics in Engineering    2020, 42 (4): 430-434.   DOI: 10.6052/1000-0879-20-014
    Abstract77)      PDF(pc) (410KB)(47)       Save
    Free vibration of carbon nanotubes is analyzed by the meshless method. Several numerical examples are used to verify the convergence of the present method. The natural frequencies of the carbon nanotubes of different length-to-diameter ratios are calculated and compared with the available results in published literature. The results show that the present method enjoys a high accuracy, and the meshless method based on the thin-plate spline radial basis function can successfully be used to analyze the free vibration of carbon nanotubes.
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    THE IMPACT MECHANICAL PROPERTIES OF COAL CONTAINING GAS 1)
    YANG Dan, LIU Yang
    Mechanics in Engineering    2020, 42 (4): 435-441.   DOI: 10.6052/1000-0879-20-101
    Abstract91)      PDF(pc) (2698KB)(58)       Save
    In order to obtain the impact mechanical properties of coal containing gas, the mechanical properties of coal samples with adsorption gas pressures of 0 MPa, 2 MPa, 4 MPa and 6 MPa are determined by the uniaxial compression test method. The results show that the compressive strength, the elastic modulus and the impact energy index of coal samples decrease linearly and the peak strain increases linearly with the increase of the adsorbed gas pressure. With the increase of the adsorbed gas pressure, the failure type of the coal body changes from brittleness to ductility, and the portion of the separation failure portion is enhanced. The adsorbed gas accelerates the process of instability and failure of the coal body, and makes the coal and rock gas dynamic disaster change from the rock burst dominated type to the coal and gas outburst dominated type.
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    DYNAMIC ANALYSIS OF A LOADED SHOULDER-POLE DURING WALKING
    Liu Rongmei
    Mechanics in Engineering    2020, 42 (4): 442-446.   DOI: 10.6052/1000-0879-20-022
    Abstract138)      PDF(pc) (412KB)(104)       Save
    A dynamic model and the related equations for a loaded shoulder-pole during walking are established. Three frequencies are involved, i.e. the vibration frequency of the load simplified as a pendulum, the walking frequency and the vertical vibrant frequency of the loaded shoulder-pole. Numerical calculation results indicate that in order to make the walking comfortable, the above three frequencies should be coordinated. When the walking frequency is 70%,$\sim$80% of the vertical vibrant frequency of the loaded shoulder-pole, the vertical additional dynamic reaction force on the shoulder is about 30% of the weight of the load and is in the same direction with the vertical moment of the shoulder. When the vibration frequency of the load simplified as a pendulum is 25%,$\sim$30% of the walking frequency, the swing of the loads and the horizontal additional dynamic reaction force on the shoulder are relatively small.
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    WIND TUNNEL TEST AND STABILITY STUDY OF ICED QUAD BUNDLE CONDUCTOR 1)
    MIN Guangyun, LIU Xiaohui, Yan Bo, SUN Ceshi, CAI Mengqi
    Mechanics in Engineering    2020, 42 (4): 447-454.   DOI: 10.6052/1000-0879-20-006
    Abstract116)      PDF(pc) (1477KB)(39)       Save
    The aerodynamic coefficients of the iced quad bundle conductor and a single conductor are obtained under four different conditions through wind tunnel test. The equivalent aerodynamic coefficients of the central axis of the quad bundle conductor are obtained by the equivalent method and compared with those of a single conductor under the same conditions. Based on the Den Hartog's galloping mechanism and the Nigol's torsional mechanism, the stable and unstable regions of the equivalent coefficients of the iced quad bundle conductor are determined. The results of this paper can be used in the research of the galloping and the simulation of the galloping of the iced conductor.
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    THE DURABILITY OF GLASS FIBER REINFORCED COMPOSITE REBARS IN SALT LAKE HIGH AND COLD AREA 1)
    LI Shuangying, ZHAO Jianchang
    Mechanics in Engineering    2020, 42 (4): 455-462.   DOI: 10.6052/1000-0879-20-087
    Abstract58)      PDF(pc) (1627KB)(40)       Save
    The durability tests of glass fiber (GFRP) and GFRP-reinforced steel rebars are carried out under the action of multiple environmental factors in Salt Lake Area. The environmental types and the action time influence the ultimate tensile strength, the elastic modulus and the ultimate strain. It is shown that the tensile strength of the GFRP rebars and the GFRP steel rebars decreases gradually with the increase of the corrosion cycles, the freeze-thaw cycles and the dry-wet cycles in Salt Lake, and the brine under the coupling of multiple factors, but the tensile strength reduction of the GFRP rebars is small, the ultimate tensile strength reduction of GFRP steel rebars is not significant, especially when the GFRP steel rebars is put in Salt Lake for more than 90 days. With the brine and more than 150 cycles of freeze-thaw, the yield strength of the GFRP bars is almost non-existent and close to the ultimate tensile strength, and the elastic modulus of the GFRP bars decreases and then increases with the increase of age, however, the elastic modulus of the GFRP rebars decreases gradually, which is not very large in comparison with the GFRP rebars under various coupling factors, and the ultimate tensile strength and the elastic modulus of the GFRP rebars under various coupling factors are smaller than those under a single factor, and the relationship with the corrosivity is: Salt Lake Brine + dry-wet cycle + freeze-thaw coupling > Salt Lake Brine + dry-wet cycle > freeze-thaw > Salt Lake Brine.
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    SHEAR TEST AND FINITE ELEMENT SIMULATION OF POLYURETHANE POLYMER GROUTING MATERIALS 1)
    WANG Daolu, WANG Chaojie, SHI Mingsheng, ZHAO Peng, FAN Bingsen, LI Yang
    Mechanics in Engineering    2020, 42 (4): 463-469.   DOI: 10.6052/1000-0879-19-463
    Abstract70)      PDF(pc) (4538KB)(34)       Save
    The shear mechanical properties of polymer are investigated in this paper by torsion experiment. The failure characteristics of the cell at the fracture surface are observed under scanning electron microscope (SEM). Furthermore, based on the finite element analysis, the deformation and mechanical properties and the distribution of shear stress are analyzed. It is shown that the density has a significant effect on the shear strength and the shear modulus of the polymer material, which can be significantly improved with the increase of the density of the polymer. The cell distribution of the polymer follows the minimum energy principle. A higher density of the polymer means smaller surface area and surface energy, which would make the system more stable. The face centered cube building model can simulate the shear deformation behavior of the fitted material well, and the higher the density, the better the fitting effect.
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    OPTIMIZATION OF FUSELAGE OPENING ZONE OF CIVIL AIRCRAFT
    YIN Kaijun, SU Yanfei, ZHANG Yinli
    Mechanics in Engineering    2020, 42 (3): 289-293.   DOI: 10.6052/1000-0879-19-342
    Abstract147)   HTML3)    PDF(pc) (1761KB)(88)       Save

    The cabin door openings are usually arranged in the fuselage for civil aircraft, resulting in fuselage stiffness discontinuity. In view of the structural stiffness and the transmission of the load, the paper studies the opening structure of the fuselage: clarifying the factors affecting the stiffness of the opening structure and optimizing the opening angle and the size of the reinforcing structure. The above research shows the direction and the method of the design and the reinforcement of the opening structure in the preliminary design stage of the opening structure of the aircraft fuselage.

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