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Table of Content

    08 August 2018, Volume 40 Issue 4
    Review
    INTERFERENCE OF SHOCK AND BOUNDARY LAYER IN SUPERSONIC FLOW
    LIU Peiqing, GUO Zhifei
    2018, 40(4):  357-361.  DOI: 10.6052/1000-0879-17-363
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    The compression boundary layer transition and separation caused by the interference of the shock and the boundary layer directly affect the drag, surface thermal protection and the flight performance of flying vehicles. This paper first reviews the past work on the interference between the shock wave and the boundary layer. And then, the effects of the forward shock, the oblique shock and the head shock on the laminar flow and the turbulent boundary layer of supersonic and transonic flows are studied and compared. The shock waves of different intensities have different effects on the boundary layer.A strong interference is more likely to cause the separation and the airfoil stall.

    Applied Research
    THE COLLISION MODEL OF THE BICYCLE ROLLING UP A STEP
    WANG Yuheng, QIU Xinming
    2018, 40(4):  362-366.  DOI: 10.6052/1000-0879-18-044
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    In colliding with a step, the front wheel of the bicycle may roll up the step or spring back to the ground. In the latter case, a rollover or a dumping accident may happen. In this study, a general collision model based on the coefficient of the restitution (COR) is built.The safe ranges of the wheel speed and the velocity direction are obtained. Besides, the influence of the step height is also discussed.
    BUCKLING ANALYSIS OF ELASTIC FILM BONDED ON SMP SUBSTRATE1)
    BAI Mengqi, MENG Xianhong
    2018, 40(4):  367-371.  DOI: 10.6052/1000-0879-18-063
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    The shape memory polymer (SMP) can restore its shape under certain conditions after its shape deformation. Therefore, as a soft substrate material, it is widely used in flexible electronic devices. For a two-layer structure made of the shape memory polymer (SMP) substrate and the elastic thin film, the elastic film on the surface can form wrinkling patterns when the SMP substrate contracts. Due to the shape memory characteristics of the SMP, the shape of the flexible electronic device is related to the time and the temperature. In this paper, the wavelength and the amplitude of the wrinkling patterns are analyzed, and the mechanical properties of the SMP at different temperatures are measured by experiments. With one-dimensional strain recovery function of the SMP and the buckling characteristics of the elastic film bonded to a soft substrate, the variations of the wave length and the amplitude of the wrinkling patterns against the time and the temperature are obtained, with good agreement with the experimental results.
    FLUTTER ANALYSIS OF MILLING WITH CONSIDERATION OF GYROSCOPIC EFFECT1)
    MA Bole, REN Yongsheng, ZHANG Yuhuan, MA jingmin
    2018, 40(4):  372-379.  DOI: 10.6052/1000-0879-18-073
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    The influence of the gyroscopic effect produced by the spindle rotation on the cutting chatter stability boundary is studied in this paper, based on a rotating model of the spindle, the tool holder and the tool. In the model, the Euler-Bernoulli cantilever beam theory is adopted to obtain the transfer function of the cutting system with consideration of the gyroscopic effect, as well as to determine the stability of the high speed cutting system.The results show that the gyroscopic effect affects the critical cutting depth of the high speed milling. With the consideration of the gyroscopic effect, when the tooth number of the tool increases, the critical cutting depth decreases. Meanwhile, the critical cutting depth decreases with the decrease of the stiffness of the system and the damping ratio of the system.
    TWO KINDS OF SCALE EFFECTS OF VIBRATION CHARACTERISTICS OF NANO-PLATE1)
    QIAN Chenfei, SHEN Huoming, ZHANG Bo, LIU Juan, ZHANG Yingrong
    2018, 40(4):  380-386.  DOI: 10.6052/1000-0879-18-022
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    In this paper, the lateral free vibration of nano plates is studied based on the nonlocal strain gradient theory. The expression of the nonlocal stress is obtained via the iterative method and the vibration governing equation of the nano-plate is derived based on the Hamilton variational principle. Under the simply supported boundary conditions, the expression of the natural frequency of the plate is obtained by using the double triangle series method. The influences of the nonlocal parameters, the material characteristic parameters and the geometrical dimensions on the natural frequencies of the nano plate are studied. Numerical results show that the nonlocal effect weakens the equivalent stiffness of the nano-plate and thus the natural frequency of the plate is reduced. The effect on the material characteristic parameter is just the opposite. The two kinds of effects have a significant bearing on the frequency of the vibration only in the nanoscale. The change of the geometrical size also has an important effect on the vibration frequency.
    AN ANALYSIS OF TRANSIENT HEAT CONDUCTION FOR FUNCTIONALLY GRADED SPHERES BASED ON STATE SPACE THEORY1)
    YAN Xiufeng, LIU Yihua, SHENG Hongyu, WU Zhigen
    2018, 40(4):  387-391.  DOI: 10.6052/1000-0879-18-086
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    Based on the state space theory, the spherically symmetric transient heat conduction is analyzed for functionally graded spheres. According to the heat conduction equation and the heat flux definition, the temperature field and the heat flux are taken as the state vector for the system. By dividing the sphere into spherical subshells and using the finite difference scheme in the time domain to discretize the governing equations, the state equation is established and a semi-analytical solution is obtained for the transient heat conduction problem of functionally graded spheres. The numerical examples show that the present solution is not only correct and efficient, but also can be applied to the transient heat conduction analysis for arbitrarily graded spheres.
    ANALYTICAL SOLUTION OF THERMAL CONSOLIDATION OF SATURATED SOILS WITH TWO PARALLEL CYLINDRICAL HEAT SOURCES1)
    WU Zhangyan, ZHENG Rongyue, LIU Ganbin, XUE Chuancheng, ZHOU Min, HUANG Zehao
    2018, 40(4):  392-397.  DOI: 10.6052/1000-0879-17-421
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    Based on the stress equilibrium equation, the seepage continuity equation and the energy conservation equation, with consideration of the effect of the thermal expansion coefficients between the soil particles and the pore water, a three-dimensional thermo-mechanical governing equation for saturated soil with consideration of the thermohydraulic coupling is established.Using the Fourier transform and the Laplace transform to derive the governing equations and obtain the solution in the transform domain, then to obtain the analytic solution of the point heat source in the real domain, as well as the analytic solution of the temperature, the pore pressure and the displacement of the thermally consolidated soil with two parallel cylindrical heat sources The results show that the increase of the span ratio will lead to a weakening of the interaction between the two heat sources. The decrease of the thermal consolidation coefficient will lead to the increase of the pore pressure and the displacement peak.
    THE STRESS ANALYSIS OF HOLE WALL OF FLOWER SHAPE OBTAINED BY INCLINATION RECTIFICATION DIGGING AND ENGINEERING APPLICATION
    HU Chunlin, CHEN Weichao, ZHOU Wentao
    2018, 40(4):  398-401.  DOI: 10.6052/1000-0879-18-001
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    A method of the inclination rectification of digging hole of flower shape for rectifying the existing building inclination is proposed , and the approximate calculation formula for the maximum stress in the hole wall is obtained, and the applicability of this formula is verified by a comparison with the results obtained by the numerical method. The new method can make the inclination rectification much more controllable, accurate, and rapid and as compared with the traditional way, in addition, the back inclination is avoided. As the ratio of the large hole radius to the small flower shape hole radius is in the range of 1$\sim$6, the performance is good.
    THE INFLUENCE OF THE NEW TECHNOLOGY OF FIXED SURFACE PERFORATION ON CASING STRENGTH1)
    WANG Suling, SU Yibao, SUN Yan'an, SONG Wei
    2018, 40(4):  402-408.  DOI: 10.6052/1000-0879-18-058
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    The surface perforating process in unconventional reservoirs can effectively reduce the cracking pressure of hydraulic fractures and increase the drainage area near the well-bore. The influence of the technology on the casing strength is an important research issue. Based on the theory of the fluid - solid coupling , a stress-coupling model of the formation-cement-perforation casing is established. With the model being reduced to a bare casing to be compared with the API standards, the effectiveness of the model is tested, and it is found that the constraints of the strata under the casing pressure can withstand an increased internal pressure of 1.48$\sim$2.16 times. On this basis, the relations of the casing size, the perforation diameter and the perforation phase angle with the casing pressure bearing capacity are obtained. The results show that when the diameter of the casing is smaller, the thickness of the casing is thicker. Calculations show that the bearing capacity of the casing is higher when the azimuth angle of the spiral perforation is 45$^\circ$ and the angle between the fixed plane perforations is 30$^\circ$, the pressure bearing capacity of the casing is higher. With the same parameters, the perforating process of the fixed perforation is slightly lower than that of the casing caused by the spiral perforation.
    DYNAMIC MODEL AND MECHANICAL ANALYSIS OF THE ROTATING ARM OF THE DEEP SEA MINING MECHANISM1)
    ZHOU Zhijin, YANG Zhi, LIU Aijun
    2018, 40(4):  409-414.  DOI: 10.6052/1000-0879-18-043
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    In the movement of the multi joint swivel arm,the deep-sea mining mechanism is affected by the hydrodynamic force of the ocean, which in turns affects the driving torque of the arm and the driving force of the luffing mechanism. This paper analyzes the influence of the hydrodynamic force on the deep-sea mining mechanism, with a dynamic model of the mining arm in its capacity of adjusting the mining attitude. As an example of a mining mechanism of a specific arm size, we obtain the variation curve of the driving force of the joint driving torque and the variable amplitude mechanism oil cylinder against time, and the change curve of the joint driving torque based on the ADMAS model. By means of the dynamic numerical solution and the simulation analysis of the mining boom, the dynamic equation is verified.
    HEMODYNAMIC CHANGES OF THE LEFT CORONARY ARTERY DURING PERCUTANEOUS CORONARY WEI Chijun*, QIU Yue*, FAN Yubo†, PENG Liqing**, ZHENG Tinghui*,2)*
    WEI Chijun, QIU Yue, FAN Yubo, PENG Liqing, ZHENG Tinghui
    2018, 40(4):  415-421.  DOI: 10.6052/1000-0879-18-259
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    Percutaneous coronary intervention (PCI) is widely adopted to check and cure coronary heart disease. However, acute thrombus may occur during surgery. This study aims to numerically find out the underlying mechanism of the acute thrombus during surgery in terms of hemodynamics.Patient-specific 3D models of the coronary arteries (CA) were reconstructed based on the computed tomography scan images. And the hemodynamic parameters in the five stages of PCI guided operation were obtained under pulsatile physiological flow conditions. The results show that the intervention process resulted in changes of hemodynamics in the CAs, such as the eccentric blood flow in the CA, the increased time-averaged wall shear stress (Tawss) and the decreased oscillatory shear index (OSI). Also, the decrease in relative resistance time (RRT) for a particle and the slightly increase in transverse WSS (Transwss) were also observed, which indicates that the vascular endothelial cells are exposed to high WSS. The predispose to the thrombus formation due to the exposure to high Tawss and the eccentricity of blood flow may overweight the inhibition effect of low RRT and OSI.