An experimental investigation on jamming and critical orifice size in the discharge of a two-dimensional silo with curved hopper

During the silo discharging progress, if the orifice size is not large enough, the orifice of the silo would be jammed by granules due to the formation of an arch. The silo with a curved hopper can effectively prevent jamming because the contraction rate is constant. To clarify the critical orifice size of the curved hopper which does not affect the outpouring of cohesionless granules, the jamming at different orifice sizes was analyzed. It was found that the change in jamming probability is similar at different contraction rates. Moreover, the relationship between the structure of the arch and the critical orifice size was clarified. Later on, a prediction model for the critical orifice size of the curved hopper was proposed. Finally, the effectiveness of the model was verified by experiments. Overall, the results are useful for understanding the jamming during discharging and further providing guidelines for the appropriate design of curved hoppers.     

全液压凿岩台车专用防卡杆阀的设计与应用

根据全液压凿岩台车对防卡杆装置的要求,提出一种新型的防卡杆阀,详尽介绍了该阀的结构特点和动作机理,并给出了相关动作的传递函数及该阀的典型应用。     

基于LDPC-FFT-DSSS的通用宽带数据链上行链路NBJ抑制方案

针对现阶段通用宽带数据链窄带干扰(Narrow Band Jamming,NBJ)抑制中信噪比要求高的问题,该文提出了一种基于LDPC-FFT-DSSS的宽带数据链上行链路的NBJ抑制方案,分析了方案的实现过程,完成了不同条件下的窄带干扰抑制仿真。结果表明:该方案在较低信噪比条件下不仅对单音干扰有良好的抑制功效,更有效抑制了多音干扰,在现有通用宽带数据链的误码率条件下,当干信比为30dB时,该方案可以获得的信噪比增益至少为8dB。     

伪码体制引信的抗噪声调频干扰性能分析

在介绍伪码体制引信的工作原理和噪声调频干扰原理的基础上,详细推导了伪码调相引信和伪码调相与PAM复合引信在噪声调频干扰环境下的总信干比增益,并仿真实现了伪码体制引信的工作过程,得出的仿真总信干比增益与理论的推导值接近。理论和仿真结果及输出的相关值证明,一般而言,伪码体制引信具有较强的抗噪声调频干扰能力。     

对地面防空雷达网干扰能力的模糊综合评估研究

地面防空雷达网是防空系统的重要组成部分,对其实施有效干扰并对干扰效果进行评估,具有重要的现实意义。目前,结合具体的干扰方法对地面雷达网进行干扰效果定量评估的研究并不多,更多的是评估指标的选择确定和从微观的角度分析干扰效果。该文探讨了作战情况下,对地面防空雷达网进行干扰效果定量评估的方法,给出了一种模糊综合评估模型用于评估对地面防空雷达网的干扰能力,并指出该模型使用范围和条件。该文对研究评估对地面防空雷达网干扰能力具有一定的参考价值和指导意义。     

部分均匀环境中存在干扰时机载雷达广义似然比检测

针对部分均匀环境中存在干扰时的机载雷达检测问题,该文提出一步广义似然比(1S-GLRT)和两步GLRT(2S-GLRT)检测器。基于上述检测器,在小训练样本情况下进一步提出了降秩GLRT(RR-GLRT)和对角加载GLRT(DL-GLRT)。新检测器均能有效地抑制干扰并实现目标检测,在小训练样本情况下RR-GLRT和DL- GLRT比1S-GLRT和2S-GLRT具有更好的检测性能。1S-GLRT和2S-GLRT均具有恒虚警(CFAR)特性,RR- GLRT和DL-GLRT具有渐近CFAR特性。最后通过计算机仿真验证了所提多通道空时自适应检测器的有效性。     

基于调频率微调的ISAR抗干扰技术研究

逆合成孔径雷达的欺骗式干扰技术日趋成熟,而ISAR抗干扰技术则研究不足。在分析了ISAR有源欺骗式干扰的工作原理基础上,提出了基于线性调频信号调频率微调的ISAR抗干扰方法,使虚假目标回波的增益在Dechirp处理时因调频率失配而被抑制。但在该体制下调频率变化导致信号带宽变化,从而距离分辨率改变,为此提出先进行距离像插值再做ISAR成像。针对距离向插值导致的方位向多普勒模糊问题,采用了多普勒域平均处理提高了ISAR成像质量,以利于目标识别。利用仿真数据对该方法进行了验证,结果证明了该方法的有效性。      

A low-cost communication security scheme of UAV based on multi-round reverse auction model

In recent years, the security of wireless communication has received more and more attention. However, with the increasing requirements for security performance in the process of wireless communication, the cost of improving security also increases. Therefore, how to improve the security of wireless communication while reducing costs has become a serious challenge. Aiming at the security problems in the UAV-assisted wireless communication link based on the premise of low cost and high profit, this paper studies how to motivate non-offloading users to send jamming power to interfere with eavesdropping UAVs, so efficiently and economically to improve the security performance of wireless communication link. Firstly, the relationship between the security performance of the communication link and the interference power is revealed through the theoretical model. Then, we propose a scenario consisting of a legitimate UAV, a ground user group, and an eavesdrop UAV. In this scenario, we divide the ground users into offloading users and non-offloading users. At the same time, the cost functions for offloading users and utility functions for non-offloading users are defined, and non-offloading users are encouraged to help to offload users unload data safely to a legitimate UAV by obtaining rewards for offloading users. Considering the selfishness of users, a reverse auction algorithm based on multi-user groups is proposed to achieve the optimal mapping between non-offloading users and offloading users. Finally, the effectiveness of the proposed scheme is verified by a large number of simulations. The research results show that the scheme innovative designs a method for users to cooperate to interfere with eavesdroppers, which can reduce costs and improve utility while maximizing the improvement of wireless communication link security.     

能量收集型高斯窃听信道安全速率的优化

针对无线网络存在安全威胁和能量受限的问题,该文研究了基于ST(Save-then-Transmit)协议的能量收集型高斯窃听信道的安全通信。首先,对系统安全速率最大化进行研究;其次,为进一步提高系统安全速率,给出了协作抗干扰方案,并讨论了该方案提高安全速率的充分必要条件,且提出了该方案下安全速率的迭代优化算法;最后,给出了一种复杂度低的单辅助端的选择方案。仿真结果表明,第1种优化方案明显提高了系统的安全速率;第2种协作抗干扰方案可进一步提高系统的安全速率且收敛速度较快;当原能量收集型高斯窃听信道不能进行安全通信时,协作抗干扰方案可在一定条件下实现安全传输。     

Networked control of nonlinear systems under Denial-of-Service

We investigate the analysis and design of a control strategy for nonlinear systems under Denial-of-Service attacks. Based on an ISS-Lyapunov function analysis, we provide a characterization of the maximal percentage of time that feedback information can be lost without resulting in instability of the system. Motivated by the presence of a digital channel we consider event-based controllers for which a minimal inter-sampling time is explicitly characterized.