During the operation of large wind turbines, the blade vibration is a problem that needs to be avoided. Modern large-scale wind turbines use variable pitch technology to adapt to different working environments, but it can exacerbate blade vibration problems. In this paper, the influences of the rigid pitch motion on the coupled flapwise-edgewise bending vibration characteristics of a wind turbine blade are studied. The blade is simplified as a rotating cantilever beam with inherent rigid-flexible coupled vibration. Based on the Euler–Bernoulli beam theory and the Hamiltonian principle, the nonlinear dynamic equation of the coupled flapwise-edgewise bending vibration of the rotating pitching blade is established, where the harmonic pitch motion is considered and the unsteady aerodynamic forces based on the Greenberg empirical formula are employed. The control equations of static displacement and dynamic displacement are obtained by applying the modal superposition method and displacement decomposition. The nonlinear dynamic responses of blade with harmonic pitch motion are analyzed by employing direct numerical integration method. It is concluded that the system is sensitive to the parameter B. When it is a rational number, there is a multi-period response. When it is an irrational number, there is a quasi-periodic response. In the flapwise direction, there are two ranges of the resonance interval for the parameter B. One is from 0 to 1, and the other is from 10 to 12. But in the edgewise direction, it is from 10 to 12. The proposed method helps to understand the blade vibration characteristics during the pitch control process. It is effective for the blade vibration. Avoiding the dangerous values of the pitch control system, we can ensure the safe operation of the wind turbine.

Aiming at the existing stochastic degradation model has not formed an interactive linkage mechanism with the multi-sensor and multi-feature of the equipment, and the existing hybrid model generally adopts the linear stochastic degradation model for prediction, which results in the poor robustness of the constructed indexes and the low prediction accuracy of the model. A bearing life prediction method based on digital-model hybrid drive is proposed. Firstly, the correlation-trend moving average-monotonicity three-step feature screening method is proposed to extract features, screen the time domain features of the horizontal and vertical full-life vibration signals of the bearings, and avoid the use of ineffective features; we need to construct the composite degradation index of multi-sensors and multi-features, and construct the mean-square error of the composite bearing life prediction and the actual life of the bearings through the exponential Wiener model. The optimization objective function of the mean square error of the actual life is used to form a feedback closed loop between the optimization function and the stochastic degradation modeling to realize the reverse optimization to adjust the fusion coefficient of the previous step as well as the failure threshold, and to realize the prediction of the remaining life of the bearing. Open-source data verifies the superiority of the method proposed in this paper.

A dynamic pitch strategy is usually adopted to improve the aerodynamic performance of the blade of a wind turbine. The dynamic pitch motion will affect the linear vibration characteristics of the blade. However, these influences have not been studied in previous research. In this paper, the influences of the rigid pitch motion on the linear vibration characteristics of a wind turbine blade are studied. The blade is described as a rotating cantilever beam with an inherent coupled rigid-flexible vibration, where the rigid pitch motion introduces a parametrically excited vibration to the beam. Partial differential equations governing the nonlinear coupled pitch-bend vibration are proposed using the generalized Hamiltonian principle. Natural vibration characteristics of the inherent coupled rigid-flexible system are analyzed based on the combination of the assumed modes method and the multi-scales method. Effects of static pitch angle, rotating speed, and characteristics of harmonic pitch motion on flexible natural frequencies and mode shapes are discussed. It shows that the pitch amplitude has a dramatic influence on the natural frequencies of the blade, while the effects of pitch frequency and pith phase on natural frequencies are little.

为了提高分布式电动车自适应巡航控制(ACC)对复杂多变工况的适应能力,提出了一种具有紧急制动功能的多模式自适应巡航控制策略.针对复杂工况问题,在上层控制器中将ACC系统划分3种主模式和4种子工况;设计基于模糊PID的定速巡航模式以及基于模型预测控制(MPC)的多目标优化控制的跟随模式;在下层控制器中基于电机模型选取目标制动轮缸压力作为紧急制动压力.仿真结果表明:所设计的多模式切换策略有效提高了车辆跟车性与舒适性以及面对紧急工况时的安全性,验证了所设计的控制策略的有效性与可行性.

The vehicle particle model was built to compare and analyze the effectiveness of three different collision avoidance methods. The results show that during vehicle high-speed emergency collision avoidance, lane change collision avoidance requires a smaller longitudinal distance than braking collision avoidance and is closer to that with a combination of lane change and braking collision avoidance. Based on the above, a double-layer control strategy is proposed to avoid collision when vehicles change lanes at high speed. The quintic polynomial is chosen as the reference path after comparing and analyzing three polynomial reference trajectories. The multiobjective optimized model predictive control is used to track the lateral displacement, and the optimization objective is to minimize the lateral position deviation, yaw rate tracking deviation, and control increment. The lower longitudinal speed tracking control strategy is to control the vehicle drive system and brake system to track the expected speed. Finally, the lane changing conditions and other speed conditions of the vehicle at 120 km/h are verified. The results show that the control strategy can track the longitudinal and lateral trajectories well and achieve effective lane change and collision avoidance.

针对特种车车内噪声声品质提升问题,利用极限梯度提升(XGBoost)算法建立声品质预测模型,模型预测值与实际主观评价值的平均相对误差为2.43%,分析得到客观参数对主观分数的影响权重;针对车内噪声非线性、非平稳性的特点,提出一种基于经验模态分解(Empirical Mode Decomposition,EMD)和滤波-x最小均方(Filtered-x Least Mean Square,FxLMS)算法相结合的主动控制方法,预测模型结果表明,主观分数提升 2.11,提升幅度为26.6%.此方法对特种车内噪声非线性、非平稳性具有良好的控制效果,能有效改善车内声品质.

The microstructure and mechanical properties of semi-continuous casting Mg-Gd-Y-Zr magnesium alloys with different Zn contents were studied in this paper. The results showed that an increase in Zn content resulted in gradual refinement of the grains and a gradual increase in the volume fraction of the second phase. At a Zn content of 0.7 wt%, the microstructure was mainly composed of the α-Mg matrix and the Mg5(GdY) and long-period stacking order (LPSO) phases. An increase in the Zn content lowered the volume fraction of the Mg5(GdY) phase and increased the volume fraction of the LPSO phase. At a Zn content of 3.3 wt%, the microstructure was mainly composed of the α-Mg matrix and the LPSO phase. Among these alloys, the alloy without Zn addition showed an optimal ultimate tensile strength and yield strength of 229 MPa and 185 MPa, respectively, while the alloy with 3.3 wt% Zn showed an excellent elongation after fracture of 4.5%. The tensile fracture analysis indicated that the cracks of the alloy without Zn mainly originated at the trigeminal junction of the grain boundary, the cracks of the 0.7 wt% Zn and 1.5 wt% Zn alloy mainly originated at the interface of the Mg/lamellar LPSO phase, and the cracks of the 3.3 wt% Zn alloy mainly originated at the bulk LPSO phase of the grain boundary and then propagated along the bulk LPSO phase.

The microstructures and mechanical properties of Mg-8.5Gd-4.5Y-0.3Zr (wt.%) alloys with and without Zn addition were investigated in this study, and the strengthening mechanisms of these two alloys were also discussed. The results show that the as -extruded alloys possesses a fine and uniform microstructure, while the as-extruded alloy with Zn addition has finer grains due to the dislocation motion inhibited by the long-period stacking ordered (LPSO) phase. Dynamic precipitation occurs during the extrusion process and unevenly distributes in both alloys, which is beneficial for the grain refinement. The yield strength and elongation of the peak-aged alloy with Zn addition are about 56 MPa and 2 times higher than that of the alloy without Zn addition; this higher elongation and yield strength can be mainly ascribed to the LPSO and g0 phases strengthening.(c) 2023 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

To improve the roll stability of semi-trailers, a robust model predictive controller (RMPC) is designed. To analysis the vehicle dynamic behaviour, a nonlinear seven-degree of freedom (7-DOF) vehicle model is defined. Based on the robust invariant set theory, and taking the uncertainty of the driver's driving behaviour into account, the maximal robust control invariant (RCI) set is calculated and its robustness is analysed. The N-step controllable sets of the vehicle are also solved. An anti-roll controller considering multiple constraints is designed based on the robust model predictive control theory. Simulation results show that the controller can keep the lateral load transfer rate within 0.7 and make the state variables converge. In addition, the controller can reduce the lateral acceleration by 50% in the step steering input test.

The purpose of this paper is to introduce a new nonlinear dynamical system with parameter sensitivity (it means that a little error of control parameter can cause dramatic difference of response). The mass, stiffness, damping, nonlinearity and external excitation of the system depend on a harmonically changing angle θ=Asin(BΩt+C), where Ω is the angular frequency of the external force; A, BΩ and C are the amplitude, angular frequency and initial phase of θ. The natural and damped frequencies of this system change periodically with θ, which bring complex properties to the system (especially at a large amplitude A). Direct numerical integration is employed to reveal the nonlinear dynamical properties of the system by taking two models. It shows that the system is sensitive to parameters A and B. Multi-periodic response occurs at a rational number B and quasi-periodic response appears at an irrational number B. Small error of parameter B can cause dramatic difference of the response. Both B-resonance and Ω-resonance need to be considered for this system, while there are many resonant intervals of B and Ω.

利用极限梯度提升(XGBoost)算法建立特种车车内声品质预测模型.首先,进行车内噪声的采集试验并进行试验数据挑选,将其处理成68个可以进行主观评价试验的有效声音样本,然后计算声音样本的客观参数,并分析各参数随工况的变化趋势.以客观参数作为声品质预测模型输入,主观评价预测值为输出,得出预测值与实际主观评价值的平均相对误差为2.43％,相关性系数为0.943,表明根据XGBoost预测模型所得结果与主观评价一致.最后通过分析声品质客观参数的特点得到客观参数对主观分数的影响权重.

Aiming at the problem of body instability caused by actuator failure in a distributed electric vehicle drive system, a fault-tolerant control strategy of longitudinal and lateral force cooperative reconstruction with active steering control was proposed, and a layered control structure was adopted based on the vehicle model. In the upper controller, the resultant force and torque are calculated according to the vehicle parameter state and MPC algorithm; the lower controller is the cooperative reconfiguration allocation layer, and the minimum tire load rate, longitudinal and lateral force constraints and front wheel angle control are considered. Finally, offline simulation experiments and hardware-in-the-loop experiments are completed to verify the effectiveness and real-time performance of the designed strategy. The results show that the designed strategy can significantly improve the driving stability and safety of the vehicle when the actuator fails.

Although maize is one of the main crops in the Northeast region, yield is still considered low when compared to other regions. One of the main solutions to increasing yield is the selection of cultivars adapted to the conditions of the Northeast region. Thus, the present study aims to use the Bayesian segmented regression model to evaluate the adaptability and stability of maize. The experiment was set up in a randomized block design with two repetitions, where 25 maize hybrids were evaluated in different states. Initially, the analysis of variance was performed. Then, the Bayesian approach of the segmented regression method was used to select the hybrids regarding adaptability and stability. There was a difference between the genotypes indicated using the a priori distribution and those indicated by the minimally informative a priori distribution. Hybrids 20A55HX, 2B433HX, 2B512HX, and P2830H were considered ideal for the Northeast region.

In emergency situations, it is difficult to meet the requirements of safe driving only by relying on the braking system, and the probability of accidents can be reduced by employing an emergency lane-changing mode. To improve the adaptability of the distributed electric vehicle adaptive cruise control (ACC) strategy to complicated and volatile conditions, a multimode ACC strategy with emergency lane-changing function is proposed. Firstly, the ACC is divided into four modes aimed at the problem of complex conditions, and a switching strategy is designed to control the switching of them. Simultaneously, the car-following mode is divided in greater detail based on time to collision (TTC), and the acceleration weighted average algorithm is adopted for accuracy and output continuity during switching. Then, the ACC is established with a hierarchical control framework, in which a PID-based cruise mode and a multi-objective optimized car-following mode based on model predictive control (MPC) are devised. The target brake wheel cylinder pressure is selected as the emergency brake pressure in takeover mode. In addition to the MPC-based system, the emergency lane-changing mode incorporates a yaw moment controller in the upper-level controller to improve body stability during emergency lane changing in the upper-level controller. In the lower-level controller, the upper-level output is converted into driving torque, wheel cylinder pressure, and front wheel angle to control vehicle travel and generate additional yaw moment. Finally, the results indicate that the presented multimode switching strategy can adapt to complex and instable transportation environments. In the cruise control scenario, the host vehicle can rapidly reach cruising speed within 5 s. In the car-following scenario, the host vehicle can stably follow the preceding vehicle with an acceleration of −5–3.5 m/s2 and a jerk of −2–2 m/s3 throughout the entire process, maintaining a safe distance from the preceding vehicle. In emergency lane-changing scenarios, vehicles with body stability control can better follow the lane-changing trajectory, and tracking accuracy is improved by 65%. Simultaneously, parameters such as front wheel angle, yaw rate, sideslip rate, and lateral acceleration remain within the normal range. In mixed switching scenarios, each mode can be correctly switched according to diverse operating conditions, and obstacle avoidance can be accomplished through horizontal and vertical strategies, which also verify the effectiveness and rationality of the control strategy proposed.

介绍了本轮新高考改革的主要内容,对新高考改革对高校机械专业生源质量、人才培养方案的影响进行分析,从高校机械专业人才培养方案、课程设置、教学过程等方面进行相应的有针对性的改革和探索.

Autonomous driving technology in urban environments is a very important avenue of research. Notably, the question of how to plan safe lane-changing trajectories is a challenge in multi-vehicle traffic environments. In our research, three kinds of polynomial lane changing mathematical models were analyzed and compared. It was found that the fifth polynomial is the most suitable for lane changing trajectories; it is defined as a generalized lane-changing trajectory cluster, whereby the minimum lane change time is determined by the vehicle lateral stability threshold. Here, a collision avoidance algorithm is proposed to eliminate unsafe trajectories. Finally, the TOPSIS algorithm is used to solve the multi-objective optimization problem, and the optimal lane-changing expected trajectory is obtained from the safe trajectory cluster. The simulation results showed improvements in lane-changing efficiency of 6.67% and no collisions in the overtaking condition. In general, the proposed method of identifying the optimal lane changing trajectory can achieve safe, efficient and stable lane changing.

针对十字路口交通环境中,大量车辆由于红灯造成延误和非必要燃油消耗的问题,提出了一种交通信号和车队轨迹协同优化策略,建立了两层优化模型优化信号配时和车队轨迹.其中,上层基于动态规划方法,以总体车辆延误值最小为目标,优化信号配时和周期;下层基于最优控制理论,以燃油经济性为目标,优化车队中头车轨迹并划分队列.最后搭建Vissim/Matlab联合仿真验证所设计策略,结果表明,3种车流输入下延误值分别优化下降32.8％、48.8％和44.2％,燃油消耗分别下降20.2％、21.9％和24.1％,验证了协同优化策略的有效性.

This study aimed to investigate the tensile properties and microstructure of Al-Cu alloy casting with a dimension of ∅500 mm × 700 mm and a 5mm-thick wall at room temperature and 200°C. The results indicated that the strength and elongation of Al-Cu alloy casting at room temperature were excellent, exceeding 425 MPa and 8%, respectively. Such a good performance was attributed to the tiny equiaxed grains. However, the occurrence of acicular θ phase distributed around the α-Al matrix grains was disadvantageous to strength and especially to elongation. Moreover, no dynamic recrystallization was observed in the tensile tests at 200°C. Besides, numerous dimples were found in the fracture morphology, which were beneficial to the elongation.

In this paper, the influence of boundary relaxation on the free vibration characteristics of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) imperfect beams is studied based on the first-order shear theory. An analysis model of the imperfect FG-CNTRC beams with arbitrary boundary conditions is presented using the boundary spring technique. The relaxation degree of the boundary is evaluated by introducing relaxation parameters, which are simulated by adjusting the stiffness of springs. The governing equations are derived using the Rayleigh–Ritz method and solved to obtain the frequencies of the beams with geometric imperfections and relaxed boundaries. The results reveal that boundary relaxation and geometric imperfections have a coupling influence on the vibration behavior of FG-CNTRC beams. The influence of boundary relaxation on frequency is highly dependent on the amplitude and modes of the geometric imperfection, but not sensitive to the geometric imperfection location. Boundary restraint enhancement reduces the influence of relaxation on the beam vibration. The influences of CNTs distribution pattern and volume fraction of on the vibration characteristics of the beams with relaxed boundaries are also discussed.

Autonomous urban driving navigation is still an open problem and has ample room for improvement in unknown complex environments. This paper proposes an end-to-end autonomous driving approach that combines Conditional Imitation Learning (CIL), Mask R-CNN with DDPG. In the first stage, data acquisition is first performed by using CARLA, a high-fidelity simulation software. Data collected by CARLA is used to train the Mask R-CNN network, which is used for object detection and segmentation. The segmented images are transformed into the backbone of CIL to perform supervised Imitation Learning (IL). DDPG means using Reinforcement Learning for further training in the second stage, which shares the learned weights from the pre-trained CIL model. The combination of the two methods is an innovative way of considering. The benefit is that it is possible to speed up training considerably and obtain super-high levels of performance beyond humans. We conduct experiments on the CARLA driving benchmark of urban driving. In the final experiments, our algorithm outperforms the original MP by 30%, CIL by 33%, and CIRL by 10% in the most difficult tasks, dynamic navigation tasks, and in new environments and new weather, demonstrating that the two-stage framework proposed in this paper shows remarkable generalization capability in unknown environments on navigation tasks.