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Table of Content

    15 April 2018, Volume 40 Issue 2
    Review
    DRAG REDUCTION TECHNIQUE FOR LARGE TRANSPORT AIRCRAFT
    LIU Peiqing, ZHANG Wen, GUO Hao
    2018, 40(2):  129-139.  DOI: 10.6052/1000-0879-17-295
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    The techniques for the drag reduction of large transport aircraft are reviewed in this paper. The techniques intended to reduce the friction drag, the induced drag and the wave drag are reviewed specifically. Techniques like the suction control for delay boundary layer transition, the riblets for reducing turbulent friction drag, and the winglet are relatively mature for practical application. Distributed roughness, plasma actuators and the contour bump are most like to be used in the newly designed large transport aircraft. These newly developed techniques might be useful in further improving the drag characteristic of the next generation aircraft.

    Applied Research
    A THREE-VALUE-SEGMENTATION METHOD OF COAL CONTAINING INCLUSION BASED ON GRAY DISTRIBUTION OF COMPUTED TOMOGRAPHY IMAGE1)
    ZHONG Jiangcheng, ZHOU Hongwei, REN Weiguang, WANG Zihui, CHEN Ji
    2018, 40(2):  140-147.  DOI: 10.6052/1000-0879-18-003
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    The threshold segmentation of CT image of coal is the prerequisite for the reconstruction of 3D real structure. A porosity calculating method was proposed based on grey level distribution of CT images obtained under uniaxial compression. Combined with the gray scale histogram, CT images were experienced three-value-segmentation of fracture, coal matrix and inclusion by inverse process from experimental porosity. The three-value-segmentation results obtained by Otsu method, maximum entropy method and the improved gray histogram method show that maximum entropy method can not get a good segmentation between coal inclusion and coal matrix, and Otsu method can not effectively split crack and coal matrix for its low sensitivity to dramatic variation for gray value in small area of the image. However, the improved gray histogram method eliminates the disadvantages of the two methods mentioned above. The threshold of coal matrix and inclusion is obtained with higher reliability and accuracy based on the experimental results, and a better three-value-segmentation of image is obtained by the improved grey histogram method.
    LIMIT STATE DETERMINATION FOR A SUBWAY STATION STRUCTURE BY INCREMENTAL DYNAMIC ANALYSIS1)
    LIU Tong, YUAN Yong
    2018, 40(2):  148-154.  DOI: 10.6052/1000-0879-17-333
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    The seismic performance of the underground structures, is not well studied, while on the other hand, the seismic limit state determination is important for a performance-based design. In this paper, four limit states are defined in terms of the deformation and the waterproof performance of the structure while the maximum story drift angle (θmax) is selected as the characteristic indicator according to the feature of the subway station. Based on a multi-story subway station in Shanghai, a two-dimensional finite element model of the soil and the structure is established and the seismic limit state of the subway station is investigated using the incremental dynamic analysis (IDA). Finally, the relation curve between the seismic intensity measure PBA (peak acceleration at the base of subway station) and structural performance indictor θmax is established and the thresholds of θmax for this subway station are obtained in the four limit states.
    BIOT’S CONSOLIDATION ANALYSIS FOR CYLINDRICAL SOIL-SAMPLE BASED ON HANSBO’S FLOW1)
    LIU Zhongyu, ZHU Xinmu, XIA Yangyang, ZHENG Zhanlei, ZHANG Jiachao
    2018, 40(2):  155-160.  DOI: 10.6052/1000-0879-17-367
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    Some clay permeability tests show that the flow of the pore water in clays may depart from the Darcy law under the condition of the lower hydraulic gradient. In order to investigate the influence of the non-Darcy behavior of flow on the consolidation process, the Hansbo equation is introduced to describe the flow in cylindrical soil samples and the Biot consolidation equation under axisymmetric conditions is modified. The numerical analysis is performed by using the Crank--Nicolson finite difference method. The proposed method is validated by comparing the analytical solution of the axisymmetric Biot’s consolidation equation with the Darcy flow. Then the influence of the Hansbo’s flow parameters on the consolidation process of the cylindrical soil sample is investigated. The numerical results show that the Hansbo’s flow delays the consolidation process of the saturated clay compared with the Darcy flow. At the early stage of consolidation, the Mandel-Cryer effect becomes more significant with the increase of the Hansbo’s flow parameters. In other words, the peak value of the pore water pressure will increase, and the reaching of its peak will also be delayed. Similarly, the delaying phenomenon of the pore water pressure dissipation is also more obvious in the later stage of consolidation. However, the Hansbo’s flow has little effect on the displacement in the cylindrical soil.

    SPECTRAL ENTROPY AND CUMULATIVE SPECTRAL ENTROPY OF HAUSDORFF DERIVATIVE DIFFUSION MODEL1)
    QIN Yanan, LIANG Yingjie, CHEN Wen
    2018, 40(2):  161-166.  DOI: 10.6052/1000-0879-17-383
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    The cumulative spectral entropy in space is derived based on the spectral entropy of the Hausdorff derivative diffusion model for describing the spatial and temporal complexity of the anomalous diffusion process. The individual, the total spectral and the cumulative spectral entropies are investigated by varying the diffusion coefficient and the diffusion time. It is shown that the spectral and the cumulative spectral entropies increase with the decrease of the order of the time Hausdorff derivative α or the space Hausdorff derivative β and are characterized by a heavy tail. With the decrease of the diffusion time or the diffusion coefficient, the normal diffusion ( α = 1,β = 1) sees a faster decay of the individual spectral entropy than the anomalous diffusion, and the corresponding spectral density becomes narrower. Thus, the spectral and the cumulative spectral entropies of the Hausdorff derivative diffusion model can reflect the heterogeneous structure of complex media and the uncertainty of the underlying diffusion process.
    INVESTIGATIONS ON THE MECHANICAL CHARACTERISTICS OF NANOBEAMS BASED ON THE NONLOCAL STRAIN GRADIENT THEORY1)
    ZHANG Yingrong, SHEN Huoming, ZHANG Bo
    2018, 40(2):  167-172.  DOI: 10.6052/1000-0879-17-361
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    A size-dependent mechanical model of nanobeam is built within the framework of the nonlocal strain gradient theory. The present model considers the nonlocal effects of the strain field and first gradient strain field, as well as the high-order shear deformation effect. Governing equations and boundary conditions are derived simultaneously by using Hamilton’s principle. The Navier-type solutions are developed for nanobeams with simply-supported boundary conditions. Parametric studies are performed to exhibit the static bending, free vibration and linear buckling behaviors of nanobeams with different groups of geometrical and material parameters. It is found that the non-local effect produces a softening effect on the stiffness of the beam while the strain gradient effect produces a hardening effect, the stiffness of nanobeams is significantly dependent on the ratio between the nonlocal parameter and strain gradient parameter. In addition, the stiffness-hardening or stiffness-softing effects become increasingly significant as the thickness is close to the material characteristic and can be negligible when the thickness is sufficient large.
    FREQUENCY-SHAPING LQR CONTROL OF WHOLE-SPACECRAFT VIBRATION ISOLATION PLATFORM BASED ON MR DAMPER1)
    WANG Lei, PAN Zhongwen, CHEN Zhaobo
    2018, 40(2):  173-179.  DOI: 10.6052/1000-0879-17-362
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    To improve the interface vibration environment of the satellite and the rocket,a magnetorheological six-pole vibration isolation platform is designed. The dynamic model of the satellite vibration isolation platform is established by using the Newton-Euler method. The dynamic model of the satellite and the vibration isolation platform is built by using the fixed interface modal synthesis method. In order to study the specific frequency band attenuation, the frequency-shaping LQR (linear quadratic regulator) method which extends the system state variables by direct decomposition is used to design the semi-active control system of magnetorheological damper. The simulation results show that the frequency-shaping LQR method is better than the traditional control method, and the control effect is not deteriorated in other frequency bands. The effectiveness of the algorithm is verified.
    FATIGUE LIFE ANALYSIS OF BONDED OFFSHORE LOADING HOSE UNDER ENVIRONMENTAL LOADS1)
    SHI Wenbin, GAO Qiang, AN Chen, DUAN Menglan, SU Yangxuan
    2018, 40(2):  180-187.  DOI: 10.6052/1000-0879-17-238
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    The bonded floating hose is a key equipment for the floating production storage and offloading unit (FPSO). The hose has a very complex structure, floating on the sea surface, subjected to wind, wave and current load. First of all, ABAQUS is used to build a finite element model, and a case under the bending moment and the internal pressure is analyzed. Secondly, the modified horizontal Morison equation and the wind load are used to describe the complex load condition. The above static analysis results are used by the FE-Safe fatigue analysis software as the input. The load spectrum is acquired by multiplying the node stress results with the corresponding load ratio. Then the life distribution contour of the hose is obtained. The calculated minimum fatigue life meets the engineering requirements. Finally, the effect of the internal pressure on the fatigue life is considered. The results show that the certain internal pressure can improve the fatigue performance of the hose.
    ENERGY-BASED PROGRESSIVE COLLAPSE RESISTANCE ANALYSIS OF STEEL FRAME STRUCTURES WITH SEMI-RIGID CONNECTIONS1)
    WANG Ning, WANG Lai, FENG Jianlong, ZHOU Nannan
    2018, 40(2):  188-193.  DOI: 10.6052/1000-0879-17-356
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    In order to study the anti-progressive collapse capacity of steel frame structures with semi-rigid connections, the resistance-displacement curve of the steel frame structures under the progressive collapse condition is obtained based on an energy method, as well as the resistance expression at each stage. The performance of the steel frame structure is analyzed based on a beam mechanism in the small deformation state and a catenary mechanism in the large deformation state to prevent the occurrence of the progressive collapse. The reliability of the theoretical formula is verified by comparing with the experimental results of the existing experiments, and a good agreement is observed. It is shown that the progressive collapse resistance expression of the steel frame structures with semi-rigid connections is simple and the results are reliable, and it can be used in the rapid analysis of the progressive collapse resistance of steel frame structures in the related design.