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
随着如今智能驾驶的快速发展,线控转向系统(steering-by-wire,SBW)作为其关键的组成部分,正成为汽车技术创新的核心领域之一。相较于传统机械转向系统,SBW通过电子化控制取代方向盘与执行机构间的机械连接,并借助控制器模拟路感反馈至...随着如今智能驾驶的快速发展,线控转向系统(steering-by-wire,SBW)作为其关键的组成部分,正成为汽车技术创新的核心领域之一。相较于传统机械转向系统,SBW通过电子化控制取代方向盘与执行机构间的机械连接,并借助控制器模拟路感反馈至驾驶员。为了模拟出适合驾驶员的路感,通过Matlab/Simulink和Carsim平台,构建了线控转向系统的车辆模型。然后通过计算轮胎上产生的回正力矩,同时加上电动助力转向系统(electric power steering system,EPS)中的助力力矩,得到最后的路感力矩。同时,为了实现路感电流的精确跟踪控制,引入了滑模变结构控制技术。为了缓解系统抖振问题,在滑模控制策略中整合了一种新型趋近律。仿真结果验证了滑模变结构控制在实现路感反馈功能上的优越性。展开更多
A small quasi-zero stiffness(QZS)vibration isolator is designed to be mounted on the roof of an agricultural vehicle for the working environment and vibration frequency of the inertial navigation system.By using the p...A small quasi-zero stiffness(QZS)vibration isolator is designed to be mounted on the roof of an agricultural vehicle for the working environment and vibration frequency of the inertial navigation system.By using the principle that the Euler beam has a negative stiffness in the critical state,the dynamic stiffness of the loaded QZS vibration isolator in the balance position tends to be close to zero by connecting a vertical spring in parallel.Firstly,the stiffness of the QZS vibration isolation system at the balance position is analyzed statically,and the material parameters and properties of the Euler beam are determined.Then,the dynamic equations are established,and the harmonic equilibrium method is used to solve the dynamic response under sinusoidal excitation to obtain the force transmissibility of the QZS vibration isolation system,and to make a comparison with that of the linear isolation system.Finally,the modal simulation,harmonic response simulation and random vibration simulation of the QZS vibration isolator are carried out through the finite element analysis,and the results show that the QZS vibration isolator has a lower initial isolation frequency and a larger isolation range,and the peak vibration isolation can reach about 11.58 dB.展开更多
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。
文摘随着如今智能驾驶的快速发展,线控转向系统(steering-by-wire,SBW)作为其关键的组成部分,正成为汽车技术创新的核心领域之一。相较于传统机械转向系统,SBW通过电子化控制取代方向盘与执行机构间的机械连接,并借助控制器模拟路感反馈至驾驶员。为了模拟出适合驾驶员的路感,通过Matlab/Simulink和Carsim平台,构建了线控转向系统的车辆模型。然后通过计算轮胎上产生的回正力矩,同时加上电动助力转向系统(electric power steering system,EPS)中的助力力矩,得到最后的路感力矩。同时,为了实现路感电流的精确跟踪控制,引入了滑模变结构控制技术。为了缓解系统抖振问题,在滑模控制策略中整合了一种新型趋近律。仿真结果验证了滑模变结构控制在实现路感反馈功能上的优越性。
文摘A small quasi-zero stiffness(QZS)vibration isolator is designed to be mounted on the roof of an agricultural vehicle for the working environment and vibration frequency of the inertial navigation system.By using the principle that the Euler beam has a negative stiffness in the critical state,the dynamic stiffness of the loaded QZS vibration isolator in the balance position tends to be close to zero by connecting a vertical spring in parallel.Firstly,the stiffness of the QZS vibration isolation system at the balance position is analyzed statically,and the material parameters and properties of the Euler beam are determined.Then,the dynamic equations are established,and the harmonic equilibrium method is used to solve the dynamic response under sinusoidal excitation to obtain the force transmissibility of the QZS vibration isolation system,and to make a comparison with that of the linear isolation system.Finally,the modal simulation,harmonic response simulation and random vibration simulation of the QZS vibration isolator are carried out through the finite element analysis,and the results show that the QZS vibration isolator has a lower initial isolation frequency and a larger isolation range,and the peak vibration isolation can reach about 11.58 dB.
