A new method for array calibration of array gain and phase uncertainties, which severely degrade the performance of spatial spectrum estimation, is presented. The method is based on the idea of the instrumental sensor...A new method for array calibration of array gain and phase uncertainties, which severely degrade the performance of spatial spectrum estimation, is presented. The method is based on the idea of the instrumental sensors method （ISM）, two well-calibrated sensors are added into the original array. By applying the principle of estimation of signal parameters via rotational invariance techniques （ESPRIT）, the direction-of-arrivals （DOAs） and uncertainties can be estimated simultaneously through eigen-decomposition. Compared with the conventional ones, this new method has less computational complexity while has higher estimation precision, what＇s more, it can overcome the problem of ambiguity. Both theoretical analysis and computer simulations show the effectiveness of the proposed method.展开更多
In this paper, a novel calibration integral equation is derived for resolving double-sided, two-probe inverse heat conduction problem of surface heat flux estimation. In contrast to the conventional inverse heat condu...In this paper, a novel calibration integral equation is derived for resolving double-sided, two-probe inverse heat conduction problem of surface heat flux estimation. In contrast to the conventional inverse heat conduction techniques, this calibration approach does not require explicit input of the probe locations, thermophysical properties of the host material and temperature sensor parameters related to thermal contact resistance, sensor capacitance and conductive lead losses. All those parameters and properties are inherently contained in the calibration framework in terms of Volterra integral equation of the first kind. The Laplace transform technique is applied and the frequency domain manipulations of the heat equation are performed for deriving the calibration integral equation. Due to the ill-posed nature, regularization is required for the inverse heat conduction problem, a future-time method or singular value decomposition (SVD) can be used for stabilizing the ill-posed Volterra integral equation of the first kind.展开更多
为研究农业机械与水田壤土间的相互作用,需获取水田壤土的物理及接触参数。结合物理堆积试验,以休止角作为响应值,采用离散元法(DEM)并选取Hertz-Mindlin with JKR(Johnson-Kendall-Roberts)接触模型对长江中游地区水田壤土展开参数标...为研究农业机械与水田壤土间的相互作用,需获取水田壤土的物理及接触参数。结合物理堆积试验,以休止角作为响应值,采用离散元法(DEM)并选取Hertz-Mindlin with JKR(Johnson-Kendall-Roberts)接触模型对长江中游地区水田壤土展开参数标定研究。首先,通过物理堆积试验获取了壤土休止角(AoR)与含水率间的定量关系,由不同含水率土壤的堆积结果筛分出4种代表性堆积形态,由于水田壤土堆积体轮廓外形比较独特,因此仅对其左右两侧轮廓采用三次多项式进行局部拟合,计算其休止角。以长江中游地区水田壤土成因和预试验为依据来确定其离散元模型中9个参数的高低水平值,通过Plackett-Burman试验设计进行方差分析,发现壤土剪切模量、壤土间动摩擦因数、壤土与不锈钢间静摩擦因数和JKR表面能对AoR影响明显。然后,采用基于响应面法(RSM)原理的Box-Behnken试验设计(BBD)建立了AoR与4个显著性参数间的二次多项式回归模型。依据二次多项式回归模型对目标响应进行预测,得到最优参数组合。以此为基础对壤土AoR进行离散元仿真,AoR数值计算结果(45.4°)与试验结果(44.6°)相对误差为1.79%。最后,选取含水率分别为44.4%、48.7%的壤土进行堆积角仿真模拟,计算结果与堆积试验相对误差分别为2.8%、7.14%。研究表明:回归模型可以根据壤土含水率或AoR预测长江中游地区水田壤土的相关本征参数和接触参数。展开更多
基于离散元法的小麦植株切割过程仿真,对于小麦收获机械切割部件分析与优化具有重要的意义,而准确测量及标定小麦植株力学参数是仿真重要前提。本文基于Hertz-Mindlin with Bonding模型在自主研发的AgriDEM软件中建立小麦茎秆模型。搭...基于离散元法的小麦植株切割过程仿真,对于小麦收获机械切割部件分析与优化具有重要的意义,而准确测量及标定小麦植株力学参数是仿真重要前提。本文基于Hertz-Mindlin with Bonding模型在自主研发的AgriDEM软件中建立小麦茎秆模型。搭建单摆切割试验装置并进行了茎秆动态切割试验,探究了茎秆相关物理特性及切割参数对茎秆切断力的影响,同时,基于AgriDEM软件进行了茎秆单摆动态切割仿真并与实际试验进行对比,结果表明利用准静态粘接力学参数进行动态切割仿真时,茎秆切断力仿真误差随着切割速度增大而增大。为降低不同切割速度下仿真误差,提出了2种茎秆粘接力学参数标定方法。(1)以刚度和临界应力为试验因素的多变量中心组合优化标定方法,得到摆切线速度为1 m/s的情况下,法向刚度、切向刚度、临界法向应力和临界切向应力优化值分别为2.82×10^(11)N/m^(3)、1.32×10^(11)N/m^(3)、9.50×10^(6) Pa和6.46×10^(6) Pa。(2)以粘接半径放大因子为单变量的标定方法,得到摆切线速度为0.5、1.0、1.5、2.0、2.5、3.0 m/s时,粘接半径放大因子优化值分别为0.997、1.106、1.163、1.213、1.323、1.439,并得到切割速度与粘接半径放大因子标定值间的拟合方程。通过最大切割速度为1 m/s的往复式切割试验与仿真对比可知,采用刚度和临界应力组合优化标定方法,茎秆切断力仿真误差由22.55%降低到9.13%;采用粘接半径放大因子的方法,当粘接半径放大因子为1.068时,茎秆切断力仿真误差由22.55%降低至6.58%。证明了本文提出的两种参数标定方法可有效降低茎秆动态切割仿真误差,且利用有效切割速度中间值对应的粘接半径放大因子标定值开展往复式切割作业仿真是准确且可行的方法,研究结果为小麦切割作业过程仿真和关键切割部件优化设计提供参考。展开更多
文摘A new method for array calibration of array gain and phase uncertainties, which severely degrade the performance of spatial spectrum estimation, is presented. The method is based on the idea of the instrumental sensors method （ISM）, two well-calibrated sensors are added into the original array. By applying the principle of estimation of signal parameters via rotational invariance techniques （ESPRIT）, the direction-of-arrivals （DOAs） and uncertainties can be estimated simultaneously through eigen-decomposition. Compared with the conventional ones, this new method has less computational complexity while has higher estimation precision, what＇s more, it can overcome the problem of ambiguity. Both theoretical analysis and computer simulations show the effectiveness of the proposed method.
文摘In this paper, a novel calibration integral equation is derived for resolving double-sided, two-probe inverse heat conduction problem of surface heat flux estimation. In contrast to the conventional inverse heat conduction techniques, this calibration approach does not require explicit input of the probe locations, thermophysical properties of the host material and temperature sensor parameters related to thermal contact resistance, sensor capacitance and conductive lead losses. All those parameters and properties are inherently contained in the calibration framework in terms of Volterra integral equation of the first kind. The Laplace transform technique is applied and the frequency domain manipulations of the heat equation are performed for deriving the calibration integral equation. Due to the ill-posed nature, regularization is required for the inverse heat conduction problem, a future-time method or singular value decomposition (SVD) can be used for stabilizing the ill-posed Volterra integral equation of the first kind.
文摘为研究农业机械与水田壤土间的相互作用,需获取水田壤土的物理及接触参数。结合物理堆积试验,以休止角作为响应值,采用离散元法(DEM)并选取Hertz-Mindlin with JKR(Johnson-Kendall-Roberts)接触模型对长江中游地区水田壤土展开参数标定研究。首先,通过物理堆积试验获取了壤土休止角(AoR)与含水率间的定量关系,由不同含水率土壤的堆积结果筛分出4种代表性堆积形态,由于水田壤土堆积体轮廓外形比较独特,因此仅对其左右两侧轮廓采用三次多项式进行局部拟合,计算其休止角。以长江中游地区水田壤土成因和预试验为依据来确定其离散元模型中9个参数的高低水平值,通过Plackett-Burman试验设计进行方差分析,发现壤土剪切模量、壤土间动摩擦因数、壤土与不锈钢间静摩擦因数和JKR表面能对AoR影响明显。然后,采用基于响应面法(RSM)原理的Box-Behnken试验设计(BBD)建立了AoR与4个显著性参数间的二次多项式回归模型。依据二次多项式回归模型对目标响应进行预测,得到最优参数组合。以此为基础对壤土AoR进行离散元仿真,AoR数值计算结果(45.4°)与试验结果(44.6°)相对误差为1.79%。最后,选取含水率分别为44.4%、48.7%的壤土进行堆积角仿真模拟,计算结果与堆积试验相对误差分别为2.8%、7.14%。研究表明:回归模型可以根据壤土含水率或AoR预测长江中游地区水田壤土的相关本征参数和接触参数。
