Driving safety field(DSF) model has been proposed to represent comprehensive driving risk formed by interactions of driver-vehicle-road in mixed traffic environment. In this work, we establish an optimization model ba...Driving safety field(DSF) model has been proposed to represent comprehensive driving risk formed by interactions of driver-vehicle-road in mixed traffic environment. In this work, we establish an optimization model based on grey relation degree analysis to calibrate risk coefficients of DSF model. To solve the optimum solution, a genetic algorithm is employed. Finally, the DSF model is verified through a real-world driving experiment. Results show that the DSF model is consistent with driver's hazard perception and more sensitive than TTC. Moreover, the proposed DSF model offers a novel way for criticality assessment and decision-making of advanced driver assistance systems and intelligent connected vehicles.展开更多
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
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
为探究种植菌草的丘陵地区土壤间、土壤与移栽触土部件间相互作用的规律并获取其仿真参数,运用Hertz—Mindlin with JKR接触模型对特定的12%±1%和20%±1%的含水率土壤—移栽触土部件进行离散元参数标定。开展土壤堆积角物理试...为探究种植菌草的丘陵地区土壤间、土壤与移栽触土部件间相互作用的规律并获取其仿真参数,运用Hertz—Mindlin with JKR接触模型对特定的12%±1%和20%±1%的含水率土壤—移栽触土部件进行离散元参数标定。开展土壤堆积角物理试验、土球斜面滚动物理试验。以土壤颗粒间、土壤与移栽触土部件间的表面能、恢复系数、动摩擦系数、静摩擦系数为标定对象,设计旋转中心组合试验并以仿真的土壤堆积角、土球在65Mn板上滚动距离为响应值,采用Box—Behnken对试验数据回归分析,以实测的土壤堆积角、土球滚动距离为优化目标,采用两种典型含水率下土壤与触土材料(65Mn)的静摩擦系数为约束条件,得到两种典型含水率的土壤间、土壤与移栽触土部件的离散元参数:含水率分别为12%±1%、20%±1%时,土壤颗粒间表面能、恢复系数、动摩擦系数、静摩擦系数为11.042 J/m^(2)和11.851 J/m^(2)、0.412和0.574、0.093和0.129、0.994和1.009;土壤与触土部件表面能、恢复系数、动摩擦系数为5.046 J/m^(2)、8.026 J/m^(2),0.362、0.388和0.066、0.07。为验证优化后离散元参数的准确性,开展验证试验得:两种典型含水率土壤仿真、物理堆积角相对误差为0.96%、0.95%,仿真、物理滚动试验相对误差为0.52%、1%。结果表明,优化标定后的土壤模型参数能够仿真该地区真实的菌草土壤模型,可为菌草移栽械关键部件的设计与优化提供重要理论依据。展开更多
基金Projects(51475254,51625503)supported by the National Natural Science Foundation of ChinaProject(MCM20150302)supported by the Joint Project of Tsinghua and China Mobile,ChinaProject supported by the joint Project of Tsinghua and Daimler Greater China Ltd.,Beijing,China
文摘Driving safety field(DSF) model has been proposed to represent comprehensive driving risk formed by interactions of driver-vehicle-road in mixed traffic environment. In this work, we establish an optimization model based on grey relation degree analysis to calibrate risk coefficients of DSF model. To solve the optimum solution, a genetic algorithm is employed. Finally, the DSF model is verified through a real-world driving experiment. Results show that the DSF model is consistent with driver's hazard perception and more sensitive than TTC. Moreover, the proposed DSF model offers a novel way for criticality assessment and decision-making of advanced driver assistance systems and intelligent connected vehicles.
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。
