In order to study the dynamic behavior of stiffened cylindrical shells with composite material sandwiched by co-cured damping films under the clamped boundary condition,the specimens of stiffened cylindrical shell with composite material sandwiched by co-cured damping films were prepared,and the dynamic modal test platform was set up.The fundamental frequency,damping ratio and modal shapes of stiffened cylindrical shell specimens were solved,and the accuracy of finite element model was verified.The influence of geometric parameters on structural vibration characteristics was further discussed by the numerical simulation method.The results show that,the fundamental frequency,damping ratio and modal shape of the structure will change abruptly when the height of stiffeners changes,and there is a suitable height value before the abrupt change to make the whole structure consider both damping and stiffness requirements;when the thickness of composite materials is constant,the fundamental frequency of the whole structure decreases gradually and the damping ratio increases gradually with the increase of the damping thickness or damping layer number of single layer;for the stiffened cylindrical shell of single layer damping composite materials,the closer the damping layer is to the inner skin,the higher the stiffness is,and vice versa,the damping capacity is better.
Short-term power load forecasting plays an important role in power system dispatching. To improve forecasting accuracy, a short-term load forecasting model based on stacking ensemble learning was proposed. Firstly, add effective multi-feature variables, and establishes a Stacking ensemble learning model for the load data and feature, which was ensembles by Light Gradient Boosting Machine (abbr. LightGBM) and eXtreme Gradient Boosting (abbr. XGBoost) for prediction. Finally, the comparison and experimental results show that the forecasting error of the proposed model is less than that of the comparative model.
Quadrotors possess traits such as under-actuation, nonlinearity, and strong coupling. Quaternions are primarily used for attitude calculations in drones, with error quaternions seldom being employed directly in the control of specific quadcopter drones. This paper focuses on the low tracking accuracy and weak anti-interference ability of quadcopter drones in trajectory-tracking control. By establishing the quadcopter quaternion model, a controller based on quaternion error is designed through a combination of fractional-order PID control with S-plane control. Trajectory-tracking experiments demonstrate that, in comparison with fractional-order PID, this method exhibits strong wind disturbance resistance and high tracking accuracy.
The problems of leakage, frictional wear, and flow heat transfer caused by the hysteresis characteristics of brush seals are prominent, and existing models for solving the hysteresis characteristics of brush seals have convergence difficulties owing to the extreme degree of nonlinearity caused by additional contacts. In this study, numerical models based on the finite element software ABAQUS were proposed to address the hysteresis characteristics of brush seals with three different structures: basic, low-lag hysteresis, and low-wear high-pressure bearing. The models accounted for the contacts between: the brush, brush and the baffle, and brush and the rotor, while damping was introduced to improve the convergence of the models. The hysteresis of the three structures under differential pressure was investigated and compared with theoretical calculations and experimental test results. The hysteresis of the bristles was normalised by the contact force, the shift of the contact area, and the contact friction force when the hysteresis effect occurred in the brush seal. The results show that the basic model has the most obvious hysteresis characteristics in the presence of differential pressure. Although the low-lag hysteresis model and the low-wear high-pressure bearing model have the weakest hysteresis effect, the deformation variables of the last row of bristles of these two structures are larger than those of the basic model; therefore, the contact position is prone to fatigue fracture. Simultaneously, the hysteresis effect was verified by varying the contact area and contact friction force, and it was found that the larger the contact area and contact friction force, the larger the hysteresis.
In order to investigate the effect of tension–compression asymmetry of propellant mechanical properties on the structural integrity of a Nitrate Ester Plasticized Polyether (NEPE) propellant grain, the unified constitutive equations under tension and compression were established, a new method for grain structural integrity assessment was proposed and the structural integrity of the NEPE propellant grain under the combined axial and transverse overloads was evaluated. The results indicate that the mechanical state of the NEPE propellant grain is in the coexistence of tension and compression under the combined axial and transverse overloads, and the tension and compression regions in the propellant grain is independent of the propellant constitutive behavior. The tension–compression asymmetry of the propellant mechanical properties has a certain impact on its mechanical response. The maximum equivalent stress and strain considering the tension–compression asymmetry falls between that obtained through the tension and compression constitutive model, and is the same as damage coefficient. The safety factor of the NEPE propellant grain considering the tension–compression asymmetry of its mechanical properties is larger than that non-considering, and the traditional method of structural integrity assessment is conservative.
In order to analyze the simulation capability of the solenoid to the ship's magnetic field,an equivalent magnetic dipole array model is used to calculate the solenoid magnetic field.Based on the empirical setting of solenoid configuration parameters,combined with the measured data of the ship model magnetic field,the least squares method was used to invert the solenoid current based on the plane magnetic field vector inversion solenoid constant current,the planar magnetic field scalar inversion solenoid constant current,the planar magnetic field vector inversion solenoid time-varying current,and the planar magnetic field scalar inversion solenoid time-varying current and other four methods.The relative error of the solenoid magnetic field vector and scalar and the ship model magnetic field vector and scalar generated by the four inversion methods is calculated.The simulation capabilities of different inversion methods are compared and analyzed,and finally the current inversion method of solenoid simulating the ship's magnetic field is given.
针对非结构化复杂路面环境下无人战车在执行军事运输、抢险救灾等任务时通过性不足的问题,提出了一种轮腿式全液压驱动的 8 轮无人战车,该战车通过摆臂的协同控制调整其运行姿态,可适应不同的复杂地形.越障性能是衡量无人战车通过性的关键要素,建立无人战车的越障动力学模型和姿态规划模型,通过求取轮腿式无人战车不同越障高度与摆臂摆角的关系式,得到无人战车典型垂直墙障碍的越障性能.在理论分析的基础上,利用QT、Simulink、ADAMS建立综合仿真平台,进行了仿真验证.研究表明:轮腿式全液压驱动的 8 轮无人战车可完成高度为轮胎直径 1.176 倍的垂直墙越障,具有良好的地形适应能力,为 8 轮无人战车的实验测试提供了理论参考.
为了解决现存无人机(UAV)路径规划求解精度和求解速度难以平衡问题,基于蝙蝠算法(BA),提出了一种新型无人机路径规划算法.将粒子群算法(PSO)中的个体最优因素引入到BA的全局随机飞行搜索中,用于增加路径搜索的发散性.在BA局部搜索阶段,利用高斯分布与柯西分布融合的模型约束局部搜索和新解的产生.再将最优成功率策略动态调节的惯性权值引入算法,提出了新型无人机路径规划算法(OS-PSOBA).结合实际环境,搭建了模拟飞行环境模型,将OS-PSOBA与PSO、BA进行对比.仿真实验证明,OS-PSOBA与PSO和BA算法相比,OS-PSO-BA展示了算法的优越性,快速、有效地完成UAV路径规划任务.
针对磁悬浮系统具有的非线性、时滞性、强扰动等特性,提出一种基于线性扩张状态观测器的改进滑模控制方法.首先,建立电磁悬浮系统的数学模型,通过分析模型的动力学特性,将数学模型线性化;其次,为了改善一般滑模变结构控制的抖振问题,采用改进的滑模控制方法,通过引入边界可变幂fal函数代替Sign符号函数且关联滑模增益和超平面函数,抑制系统抖振引起的不稳定性;最后,引进LESO观测器主要将系统总扰动量反馈补偿给滑模控制器,既可以缓解滑模控制器对模型的依赖程度,又能进一步提高系统抗干扰性和鲁棒性.仿真结果表明:相比于传统算法,基于LESO的改进滑模控制减小超调、较快响应速度、大幅度增强系统抗干扰性能和鲁棒性,对于克服中低速电磁悬浮列车在不同工况和复杂环境下运行的工程实现难题具有理论指导意义.
为探究纤维、水胶和砂胶配比对珊瑚混凝土抗冲击性能的影响,采用LS-DYNA软件对高性能珊瑚混凝土的冲击响应过程进行了数值模拟研究,着重探讨了不同应变率下纤维掺量、砂胶比和水胶比对珊瑚混凝土破碎形态、抗压强度、弹性模量及韧性的影响规律.模拟结果表明:① 纤维掺量的增加能显著提高珊瑚混凝土的抗压强度,特别是在高加载速度下,其增强效果尤为明显,当纤维掺量从0.6%增加至1.2%时,在20m/s的加载速度下,DIF-fc 增长约22.2%.而纤维掺量对弹性模量和韧性的影响与应变率强相关.在较低加载速度下(v≤14 m/s),纤维掺量的增加会降低弹性模量和韧性;在较高加载速度下(v≥16 m/s),纤维掺量的增加会提高弹性模量和韧性.② 砂胶比含量的增加能显著提高珊瑚混凝土的抗压强度,然而会降低珊瑚混凝土的弹性模量,当砂胶比从 0.8 增加至 1.0 时,DIF-fc 整体增加了约0.2,DIF-E整体降低了约0.05.③ 水胶比含量的增加会提高珊瑚混凝土的弹性模量,当水胶比从0.22 增加到0.25 时,DIF-E整体增加了约0.1.水胶比对抗压强度和韧性的影响与应变率强相关.在较低加载速度下(约小于13 m/s),水胶比含量的增加会提高珊瑚混凝土的抗压强度和韧性;在较高加载速度下(约大于13 m/s),水胶比的增加会降低抗压强度和韧性.
针对低分辨雷达人工目标识别效率较低的问题,提出了基于深度迁移学习的雷达自动目标识别方法.该方法利用雷达回波序列轮廓像构建空中目标数据集,使用深度卷积神经网络自动提取回波数据中的深层特征,并对雷达目标进行分类识别.为了解决深度学习对样本量的巨大需求,在分类模型训练时,引入迁移学习思想,将经ImageNet数据集预训练过的初始网络模型迁移到雷达目标识别任务中,再通过空中目标数据集对模型参数进行微调,实现小样本条件下对空中目标的粗分类.实测数据的结果表明:所提方法能够在小样本条件下较为准确地对空中目标的大小和架次进行分类识别,具有良好的识别性能.
为了验证TiZrNbVAl高熵合金弹体的可行性,开展了材料力学性能及弹体侵靶试验研究.对TiZrNbVAl高熵合金在应变率分别为10-3s-1、1 000 s-1、3 000 s-1和室温分别为、200℃、300℃条件下的力学性能进行了试验研究,获得了TiZrNbVAl高熵合金的准静态和动态力学性能,并对其冲击韧性、应变率效应及温度效应进行了分析,结果表明:TiZrNbVAl强度较好,抗冲击性能优异,在高温和动态加载条件下具有温度软化效应和应变率强化效应,并根据试验数据拟合得到了TiZrNbVAl高熵合金的Johnson-Cook模型参数.设计并开展了 125 mm火炮侵靶验证试验,TiZrNbVAl弹体以786 m/s速度穿透2 层Q345 钢板,头部侵蚀较为严重,但主体结构完整,验证了TiZrNbVAl高熵合金用于侵彻战斗部壳体的可行性.采用数值仿真模型对侵彻过程进行了模拟,弹体头部侵蚀仿真结果与试验结果较为吻合,验证了材料模型和数值仿真模型可靠性.研究结论和成果可为高熵合金侵彻弹体设计提供思路和依据.
为研究破片穿透防弹插板后对人体靶标的钝击与侵彻耦合杀伤机理,开展了钨合金破片侵彻有防护明胶靶标试验,获得了钨合金破片穿透NIJ Ⅲ级SiC/UHMWPE防弹插板后对明胶靶标造成的损伤特征、破坏规律及破片能量传递关系.建立破片侵彻有防护明胶的数值分析模型,获得破片的速度变化情况、防护后明胶靶标内压力、应力及应力波变化等终点效应特征量.试验及数值仿真结果表明:破片穿透防护所需动能随破片质量增加而减少,破片穿透防弹插板的能量传递率随质量增加而增大.破片速度由1 030m/s增加到1 157 m/s,钝击凹陷最大直径增加了约30%,钝击凹陷最大深度增加了约65%,而明胶靶标的瞬时空腔最大直径减少了约40%.破片侵彻过程中,越靠近破片侵彻位置明胶应力越大,等效应变场均呈环形分布.破片未击穿防弹插板时,应力波在明胶中以球面波形式传播,破片与明胶接触的过程中,存在持续的应力波输出,并与达到明胶边界的反射波叠加,影响明胶内部压力变化.
为增强聚能战斗部的后效毁伤能力,设计一种金属药型罩与PTFE/Al反应材料相结合的后效毁伤聚能战斗部,并通过数值仿真进行改进与分析;开展后效毁伤战斗部静爆试验,并结合数值仿真对含能毁伤元的成型、侵彻和后效作用过程进行研究.研究结果表明:通过加装挡环可以有效调整PTFE/Al在成型过程中的位置,使其位于惰性弹丸之后;相较于单一惰性药型罩聚能装药,在原有破甲能力基础上,破甲后的空气冲击波强度明显增强,后效毁伤能力提升显著;反应材料在靶板内的反应扩孔作用是削弱后效冲击波强度的主要原因,适当提高反应材料的反应阈值可增强后效冲击波强度;综合分析影响毁伤性能的因素,认为半Cu罩结构的毁伤效果更好.研究成果可为增强聚能战斗部后效毁伤能力的设计提供重要参考与数据支撑.
针对威胁环境下四旋翼无人机的低空突防问题,将其分解为轨迹规划与跟踪控制 2 个子问题进行统一研究.以无人机在最短时间内穿过威胁环境并到达指定位置为任务目标,假设战场环境中存在多个已知的雷达威胁、未知的动态障碍威胁,在考虑无人机平台性能的情况下,采用hp自适应Radau伪谱法离线求解出能规避雷达威胁的无人机最优参考轨迹,在此基础上,基于改进的模型预测控制方法设计轨迹跟踪控制器,实现对参考轨迹的在线跟踪与实时避障.最后利用仿真验证了所设计算法的有效性.
使用单一卷积神经网络去雾算法容易存在对比度偏低、细节信息丢失和去雾不完全等缺陷.为了解决上述问题,提出了一种增强型金字塔模型和图像超分辨率并联去雾网络结构.增强机制作用于特征金字塔图像重建过程,用以提升去雾图像信噪比.通道注意力将编码器提取的特征信息映射到解码器,赋予每个通道不同权重,以此提高去雾效率.超分辨率网络补充更多高频特征细节,提升去雾图像的清晰度.实验证明,增强型金字塔及超分辨率网络具有较强的去雾能力,性能优于其他方法,有效抑制单一的卷积神经网络输出图像分辨率下降问题.
为获取侵爆战斗部终点弹道参数对桥梁以及桥面目标损伤效应的影响规律,建立战斗部侵彻桥梁并起爆的整个过程非线性动力学仿真模型,分析不同侵彻速度与不同引爆延时下桥梁产生的裂纹、结构失效分布以及桥面冲击波的传播规律.研究结果表明:基于桥梁失效分布计算了桥梁损伤后的抗弯能力,侵彻速度为 800 m/s 时采取1.95～2.95 ms的延时引爆可以使箱梁抗弯能力达到最低;延时14.95 ms引爆可以使最大长度的桥墩混凝土崩落,承载能力最低.基于冲击波超压对目标的损伤判据,侵彻速度为800 m/s时采取0.95 ms左右的延时引爆可以在爆心半径3m范围内重伤或致死桥面人员,装甲车辆受到轻度或中等破坏.研究成果可为侵爆战斗部侵彻速度及引爆时间合理设置,为增大桥梁损伤程度提供参考.
针对复杂战场空间对抗环境下射频传感器的射频隐身问题,开展基于复杂电磁环境的主动射频隐身方法研究.通过自身平台电子侦察设备感知敌方电磁信号分布特征,主动构建对己有利、对敌不利的复杂电磁环境,在敌方威胁侦察接收机的子信道内形成时频交叠信号,影响敌方电子侦察设备的信号检测和分选聚类处理,增加敌方侦察设备的测量误差,不能形成稳定的辐射源,降低信号的被截获概率.通过仿真分析可以看出:将复杂电磁环境当作干扰扰动信号,干信比在6dB以上时,对侦察设备的频率、脉宽等参数测量和辐射源分选聚类影响较大.基于电磁态势感知结果主动构造的时频交叠的复杂电磁环境,可以根据作战任务和敌我双方电磁环境进行实时管控,实现主动射频隐身的优势.
采用单、双面焊方法对2mm厚5052 铝合金进行了搅拌摩擦焊试验,研究了接头的微观组织形貌、显微硬度、拉伸性能和断口形貌.结果表明:单、双面焊接头内部均存在"S"线,双面焊能够有效改善"S"线的分布情况,避免单面焊底部弱连接;单、双面焊焊缝截面横向硬度均呈"W"型,硬度沿厚度方向总体逐渐降低,单、双面焊沿厚度方向硬度最高分别为68.4 HV、84.2 HV,双面焊焊缝晶粒更加细化;单、双面焊平均抗拉强度分别为 198、210 MPa,双面焊接头力学性能优于单面焊;通过接头断口形貌分析,单、双面焊接头断裂方式均为韧性断裂与撕裂韧性断裂混合形式.
为高效对密封电池进行高精度空间定位与轮廓焊接,提出一种基于双阶段混合模型的高精度密封电池轮廓定位方法,并设计相关实验.该方法将图像分割网络与传统图像处理方法相结合,构成双阶段混合模型,从而实现端到端的密封电池空间定位与机械臂焊接,并具有较高的定位精度.在自己制作的电池数据集上进行模型训练,并在六轴机械臂上进行焊接实验.结果表明:相比于UNet网络,本文中提出的CA-UNet具有更快的训练和推理速度,以及相近的分割精度,使得双阶段混合模型可以很好地实现密封电池轮廓定位.
