Axially moving beams are often discussed with several classic boundary conditions, such as simply-supported ends, fixed ends, and free ends. Here, axially moving beams with generalized boundary conditions are discusse...Axially moving beams are often discussed with several classic boundary conditions, such as simply-supported ends, fixed ends, and free ends. Here, axially moving beams with generalized boundary conditions are discussed for the first time. The beam is supported by torsional springs and vertical springs at both ends. By modifying the stiffness of the springs, generalized boundaries can replace those classical boundaries. Dynamic stiffness matrices are, respectively, established for axially moving Timoshenko beams and Euler-Bernoulli (EB) beams with generalized boundaries. In order to verify the applicability of the EB model, the natural frequencies of the axially moving Timoshenko beam and EB beam are compared. Furthermore, the effects of constrained spring stiffness on the vibration frequencies of the axially moving beam are studied. Interestingly, it can be found that the critical speed of the axially moving beam does not change with the vertical spring stiffness. In addition, both the moving speed and elastic boundaries make the Timoshenko beam theory more needed. The validity of the dynamic stiffness method is demonstrated by using numerical simulation.展开更多
Shot boundary detection is the fundamental part in many real applications as video retrieval and so on. This paper tackles the problem of video segment obtaining in complex movie videos. Firstly, intermediate descript...Shot boundary detection is the fundamental part in many real applications as video retrieval and so on. This paper tackles the problem of video segment obtaining in complex movie videos. Firstly, intermediate descriptor is proposed to depict the variation of both abrupt and gradual change in shot boundaries, which is formed by distance vector on Local Binary Pattern(LBP), GIST(GIST) or their fusion. Instead of just using the adjacent frames distance, intermediate descriptor keeps the distances between current frame and consecutive frames. It comprehensively characterizes local temporal structure, which is especially important for gradual change. For the excellent ability for feature fusion in random forests, it is adopted here to verify the fusion effect of intermediate descriptor on LBP and GIST. The whole experiments are designed on the subset of TRECVid 2013 INS(INstance Search) task to verify the effectiveness of proposed intermediate descriptor and the fusion ability for random forest. Compared with static and adaptive thresholds approaches, the best performance can be achieved by post-fusion of intermediate descriptor on LBP and GIST.展开更多
Hole drilling or contour milling for the large and complex workpieces such as automobile panels and aircraft fuselages makes a high combined demand on machining accuracy,stiffness and workspace of machining equipment....Hole drilling or contour milling for the large and complex workpieces such as automobile panels and aircraft fuselages makes a high combined demand on machining accuracy,stiffness and workspace of machining equipment.Therefore,a 5-DOF(degrees of freedom)parallel kinematic machine(PKM)with redundant constraints is proposed.Based on the kinematics analysis of the parallel mechanism using intermediate variables,the kinematics problems of the PKM are solved through equivalent kinematics model.The structural stiffness matrix method is adopted to model the stiffness of the parallel mechanism of the PKM,where the stiffness of each joint and branch component is obtained by stiffness formula and finite element analysis.And the stiffness model of the parallel mechanism is improved by correction coefficient matrix,each element of which is constructed as a polynomial function of three independent end variables of the parallel mechanism.The terminal stiffness matrices obtained by simulation result are used to determine the coefficients of polynomial function by least square fitting to describe the correction coefficient over the workspace of the parallel mechanism quantitatively.The experiment results prove that the modification method can greatly improve the stiffness model of the parallel mechanism.To enhance the machining accuracy of the PKM,the proposed kinematics model and the improved stiffness model are utilized to optimize the working stiffness of parallel machine by searching the best relative position of parallel machine and workpiece.A plate workpiece taken as example is examined in the case study section,which demonstrates the effectiveness of optimization method.展开更多
To ascertain the influence of the boundary friction on mechanical properties of disc-spring vibration isolators a load-displacement hysteresis curve formula of disc-spring vibration isolators is derived on the basis o...To ascertain the influence of the boundary friction on mechanical properties of disc-spring vibration isolators a load-displacement hysteresis curve formula of disc-spring vibration isolators is derived on the basis of the energy conservation law as well as considering the effect of the boundary friction.The formula is validated through the finite element analysis and static load tests.On this basis the effect of the boundary friction on the bearing capacity is researched. Then the dynamic performance of disc-spring vibration isolators is studied by dynamic tests.The experimental results indicate that the boundary friction can promise a larger damping with a ratio of 0.23 for disc-spring vibration isolators.Compared with the loading frequency the loading amplitude has a greater impact on the energy consumption dynamic stiffness and damping of vibration isolators.This research can provide valuable information for the design of disc-spring vibration isolators.展开更多
深部岩体节理往往存在不同程度的软弱充填物质,导致岩体力学性质更为复杂。开展恒定法向刚度CNS边界条件下,考虑高初始法向应力及不同节理粗糙系数JRC−充填度△组合模式的加锚充填节理岩体剪切试验,结合微观电镜扫描(scanning electron ...深部岩体节理往往存在不同程度的软弱充填物质,导致岩体力学性质更为复杂。开展恒定法向刚度CNS边界条件下,考虑高初始法向应力及不同节理粗糙系数JRC−充填度△组合模式的加锚充填节理岩体剪切试验,结合微观电镜扫描(scanning electron microscope,简称SEM)分析充填节理部分宏微观结构演变特征,推导CNS边界条件下峰值剪胀角相关计算方法。研究结果表明:当△<0.5,试件剪应力强度呈现应力硬化;当1.0<△≤1.5,剪应力强度由基本恒定演化为应力软化。当△小于临界充填度△_(cr),JRC成为峰值抗剪强度主要影响因素。△在节理法向变形中起到控制作用,随着△的增加,出现剪胀、先剪胀后剪缩、剪缩3种演化规律,JRC则影响着试件剪胀−剪缩变化程度。充填节理部分破坏模式随着△的增加主要经历3个阶段:粗糙点磨平、充填物质摩擦、充填物质磨碎。微观角度下由疏松多孔结构形式演化为散体碎屑状结构形式。受挤压破碎区与挤压应力集中区二者的相互演化机制影响,锚杆剪切变形模式逐渐由△=0的“近似”拉剪变形向△=1.5的拉弯变形模式演变。在此基础上,提出了一种CNS边界条件下加锚充填节理岩体峰值剪胀角的计算公式,并进行了试验验证及边界条件影响参数敏感性分析。展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.11772181 and11422214)the “Dawn” Program of Shanghai Education Commission(Nos.17SG38 and 2019-01-07-00-09-E00018)the Key Research Project of Shanghai Science and Technology Commission(No.18010500100)
文摘Axially moving beams are often discussed with several classic boundary conditions, such as simply-supported ends, fixed ends, and free ends. Here, axially moving beams with generalized boundary conditions are discussed for the first time. The beam is supported by torsional springs and vertical springs at both ends. By modifying the stiffness of the springs, generalized boundaries can replace those classical boundaries. Dynamic stiffness matrices are, respectively, established for axially moving Timoshenko beams and Euler-Bernoulli (EB) beams with generalized boundaries. In order to verify the applicability of the EB model, the natural frequencies of the axially moving Timoshenko beam and EB beam are compared. Furthermore, the effects of constrained spring stiffness on the vibration frequencies of the axially moving beam are studied. Interestingly, it can be found that the critical speed of the axially moving beam does not change with the vertical spring stiffness. In addition, both the moving speed and elastic boundaries make the Timoshenko beam theory more needed. The validity of the dynamic stiffness method is demonstrated by using numerical simulation.
基金Supported by the Young Teacher Support Plan by Heilongjiang Province and Harbin Engineering University in China(No.1155G17)partially by the Fundamental Research Funds for the Central Universities Grant to X.Xiang
文摘Shot boundary detection is the fundamental part in many real applications as video retrieval and so on. This paper tackles the problem of video segment obtaining in complex movie videos. Firstly, intermediate descriptor is proposed to depict the variation of both abrupt and gradual change in shot boundaries, which is formed by distance vector on Local Binary Pattern(LBP), GIST(GIST) or their fusion. Instead of just using the adjacent frames distance, intermediate descriptor keeps the distances between current frame and consecutive frames. It comprehensively characterizes local temporal structure, which is especially important for gradual change. For the excellent ability for feature fusion in random forests, it is adopted here to verify the fusion effect of intermediate descriptor on LBP and GIST. The whole experiments are designed on the subset of TRECVid 2013 INS(INstance Search) task to verify the effectiveness of proposed intermediate descriptor and the fusion ability for random forest. Compared with static and adaptive thresholds approaches, the best performance can be achieved by post-fusion of intermediate descriptor on LBP and GIST.
文摘Hole drilling or contour milling for the large and complex workpieces such as automobile panels and aircraft fuselages makes a high combined demand on machining accuracy,stiffness and workspace of machining equipment.Therefore,a 5-DOF(degrees of freedom)parallel kinematic machine(PKM)with redundant constraints is proposed.Based on the kinematics analysis of the parallel mechanism using intermediate variables,the kinematics problems of the PKM are solved through equivalent kinematics model.The structural stiffness matrix method is adopted to model the stiffness of the parallel mechanism of the PKM,where the stiffness of each joint and branch component is obtained by stiffness formula and finite element analysis.And the stiffness model of the parallel mechanism is improved by correction coefficient matrix,each element of which is constructed as a polynomial function of three independent end variables of the parallel mechanism.The terminal stiffness matrices obtained by simulation result are used to determine the coefficients of polynomial function by least square fitting to describe the correction coefficient over the workspace of the parallel mechanism quantitatively.The experiment results prove that the modification method can greatly improve the stiffness model of the parallel mechanism.To enhance the machining accuracy of the PKM,the proposed kinematics model and the improved stiffness model are utilized to optimize the working stiffness of parallel machine by searching the best relative position of parallel machine and workpiece.A plate workpiece taken as example is examined in the case study section,which demonstrates the effectiveness of optimization method.
基金Transformation Program of Science and Technology Achievements of Jiangsu Province(No.BA2008030)
文摘To ascertain the influence of the boundary friction on mechanical properties of disc-spring vibration isolators a load-displacement hysteresis curve formula of disc-spring vibration isolators is derived on the basis of the energy conservation law as well as considering the effect of the boundary friction.The formula is validated through the finite element analysis and static load tests.On this basis the effect of the boundary friction on the bearing capacity is researched. Then the dynamic performance of disc-spring vibration isolators is studied by dynamic tests.The experimental results indicate that the boundary friction can promise a larger damping with a ratio of 0.23 for disc-spring vibration isolators.Compared with the loading frequency the loading amplitude has a greater impact on the energy consumption dynamic stiffness and damping of vibration isolators.This research can provide valuable information for the design of disc-spring vibration isolators.
文摘深部岩体节理往往存在不同程度的软弱充填物质,导致岩体力学性质更为复杂。开展恒定法向刚度CNS边界条件下,考虑高初始法向应力及不同节理粗糙系数JRC−充填度△组合模式的加锚充填节理岩体剪切试验,结合微观电镜扫描(scanning electron microscope,简称SEM)分析充填节理部分宏微观结构演变特征,推导CNS边界条件下峰值剪胀角相关计算方法。研究结果表明:当△<0.5,试件剪应力强度呈现应力硬化;当1.0<△≤1.5,剪应力强度由基本恒定演化为应力软化。当△小于临界充填度△_(cr),JRC成为峰值抗剪强度主要影响因素。△在节理法向变形中起到控制作用,随着△的增加,出现剪胀、先剪胀后剪缩、剪缩3种演化规律,JRC则影响着试件剪胀−剪缩变化程度。充填节理部分破坏模式随着△的增加主要经历3个阶段:粗糙点磨平、充填物质摩擦、充填物质磨碎。微观角度下由疏松多孔结构形式演化为散体碎屑状结构形式。受挤压破碎区与挤压应力集中区二者的相互演化机制影响,锚杆剪切变形模式逐渐由△=0的“近似”拉剪变形向△=1.5的拉弯变形模式演变。在此基础上,提出了一种CNS边界条件下加锚充填节理岩体峰值剪胀角的计算公式,并进行了试验验证及边界条件影响参数敏感性分析。
