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Local dynamic soil testing data on shear modulus reduction curves and equivalent damping ratios are basically unavailable.




 A theory for describing deformation behaviour of sands under cyclic loading is proposed on the basis of the assumption that the permanent deformation of sands after each cycle of loading is mainly determined by the effctive stress states at the peak and the valley of that cycle of loading and a loading history parameter named as effective number of cycles. A series of cyclic triaxialtests on a medium sand has been per formed in order to estabilish two sets of empirical relationships required in this theory.... A theory for describing deformation behaviour of sands under cyclic loading is proposed on the basis of the assumption that the permanent deformation of sands after each cycle of loading is mainly determined by the effctive stress states at the peak and the valley of that cycle of loading and a loading history parameter named as effective number of cycles. A series of cyclic triaxialtests on a medium sand has been per formed in order to estabilish two sets of empirical relationships required in this theory. The first one, giving the expressions for mean shear modulus and equivalent damping ratio, is derived from the model proposed by Hardin and Drnevich with a revision to consider the coaction of cyclic normal stress and cyclic shear stress. The second one gives the expression for increments of permanent volumetric strain and deviatorie strain, taking account of the influence of assymetry of stress levels at the peak and the valley of loading in each cycle. The theory may be used to predict the liquefaction potential and deformation of sands subjected to repeated loading under plane strain condition.  文中探讨了建立砂土动力应变关系的途径,并根据砂土的动力变形主要取决于每个荷载循环中动应力达到峰值和谷值时的有效应力状态的假设,提出一个计算动力变形的平均发展过程的理论。从这一理论出发,根据一种砂料的三轴反复荷载试验结果,建议了一组计算残余体应变和残余剪应变的经验公式,并对哈定和达尼维奇(Hardin and Drnevich)的动剪切横量公式进行了修改。这些公式可以用于计算低频动荷载作用下砂土的液化和变形。  In this paper, based on the detailed analysis of the dynamic cutting force of the helical tooth end milling cutters and its direction coefficients, a method of analysing the behaviour of regenarative chatter for helical tooth end milling cutters with waved cutting edges is proposed.The cutting tests are carried out to check the theoretical analysis on validity and they have proved to be in good agreement with the results calculated from the theoretical analysis. The results obtained are summarized as follows:... In this paper, based on the detailed analysis of the dynamic cutting force of the helical tooth end milling cutters and its direction coefficients, a method of analysing the behaviour of regenarative chatter for helical tooth end milling cutters with waved cutting edges is proposed.The cutting tests are carried out to check the theoretical analysis on validity and they have proved to be in good agreement with the results calculated from the theoretical analysis. The results obtained are summarized as follows: 1. The proposed theoretical formulae for the calculations of instantane ous and mean direction coefficients can be applied to up and down milling operations with helical tooth end milling cutters. By using these formulae the relations between the chatter and cutting conditions can be found, which enables us to select the optimum cutting conditions easily. 2. The equation which can be applied to the determination of the critical width of cut for helical tooth end milling cutters with waved cutting edges is given below: Where: Kd is the coefficient of chip thickness, b is the critical width of cut, D is the equivalent damping ratio, K is the equivalent static stiffness, Rm is the mean direction coefficient, Z is the number of teeth, ψ is the phase shift between the two vibration waves in successive cutting teeth, ξ is the ratio between the length of the chip and the lead of the waved cutting edges, ηi, η2, ……,ηz are the ratio between the partial length on the underside of the chip and the length of the chip respectively. 3. It is dear from the theoretical analysis and the experimental results th at the critical width of cut for the helical tooth end milling cutters with waved cutting edges is considerably larger than that of the conventional milling cutters. Practically, this method of analysis can also be applied to the determination of the chatter behaviour for the helical tooth end milling cutters with any kinds of grooves on the cutting edges and it may be expected o obtain the similar results mentioned above.  本文从理论上阐述了波形刃螺旋齿立铣刀再生自激振动的分析方法。在深入分析 了螺旋齿立铣刀的动态铣削力和方向系数的基础上，通过颤振稳定性的理论计算来说 明波形刃螺旋卤立铣刀比普通螺旋齿立铣刀具有更好的抑制再生自激振动的性能．最 后，用切削试验证明理论分析方法的正确性。  Referring to the adaptive scheme proposed by U.Hartmann et al.,this paperpresents a simplified model for parameterestimation and an extended Kalman filterparameterestimation algorithm.As a result,computation work is decressed to50% of the original.During the determination of feedback gains,the concepts ofequivalent inherent frequency and equivalent damping ratio specified by MILF8785C are utilized.Considering the influence of actuator dynamics and reasonablepoleassignment,we deduce approximate feedback... Referring to the adaptive scheme proposed by U.Hartmann et al.,this paperpresents a simplified model for parameterestimation and an extended Kalman filterparameterestimation algorithm.As a result,computation work is decressed to50% of the original.During the determination of feedback gains,the concepts ofequivalent inherent frequency and equivalent damping ratio specified by MILF8785C are utilized.Considering the influence of actuator dynamics and reasonablepoleassignment,we deduce approximate feedback gain formulas.A simplified andappropriate logic condition for the start of gain adaptation is recommended.Thusthe system stability and good flight handling quality are ensured.The estimation oftime varying parameters during the climbing maneuver with decreasing speed anddescending maneuver with increasing speed,the climbing or descending maneuverwith nearly invariant speed,is studeid in detail including the role of probesignals.The divergence phenomenon encountered in the conditions mentioned above isanalyzed and means for overcoming it are investigated.  本文参考 U.Hartmann 等人的方案,提出一种简化的参数估计模型和改进的卡尔曼滤波参数估计法,使运算量减少二分之一。在反馈增益的计算中,运用 MILF8785C 中的“当量固有频率”与“当量阻尼比”的概念,选择合理的极点分布,推导了考虑舵回路惯性影响的调参规律近似表达式。文中给出一种简易可行的启动自适应调参程序的逻辑条件,从而保证了系统的稳定性和良好的飞行品质。还深入研究了爬高减速、下滑增速及准等速爬高和下滑过程中时变参数的估计方法,加入探测信号对系统的影响,以及这些过程中出现发散现象的原因和克服的措施。   << 更多相关文摘 
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