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采用基于Favre平均的三维N-S方程和k-ε湍流模型对固体火箭发动机二次喷射推力矢量喷管复杂干扰内流场进行数值模拟。空间上采用三阶精度差分格式进行求解,时间上采用隐式Jacobi点迭代方法进行迭代推进,直至流场收敛。数值模拟得到矢量喷管二次射流的激波系结构,以及复杂的主/次流干扰流动图像。二次喷射流场包含复杂的涡系结构和波系结构,还存在着边界层与激波的相互干扰、自由剪切层、激波、膨胀波和大尺寸分离。数值模拟还表明,高温燃气射流导致喷射孔附近喷管壁面处的温度相当高,需采取相应的热防护措施。 相似文献
126.
研究了网络延时对路由器主动队列管理机制的影响,分析了几种典型主动队列管理算法在大延时网络中的性能。在介绍了基于内模补偿的DC-AQM算法的优缺点之后,根据PID控制器延时补偿的Ziegler-Nichols设定方法,提出了ZNDC(Ziegler-Nichols delay compensation)AQM算法并进行了仿真实验验证,实验结果表明算法达到了预期的目标。 相似文献
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In this paper, a condition-based maintenance model for a multi-unit production system is proposed and analyzed using Markov renewal theory. The units of the system are subject to gradual deterioration, and the gradual deterioration process of each unit is described by a three-state continuous time homogeneous Markov chain with two working states and a failure state. The production rate of the system is influenced by the deterioration process and the demand is constant. The states of the units are observable through regular inspections and the decision to perform maintenance depends on the number of units in each state. The objective is to obtain the steady-state characteristics and the formula for the long-run average cost for the controlled system. The optimal policy is obtained using a dynamic programming algorithm. The result is validated using a semi-Markov decision process formulation and the policy iteration algorithm. Moreover, an analytical expression is obtained for the calculation of the mean time to initiate maintenance using the first passage time theory. 相似文献
128.
正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)是现代移动通信中一项重要的物理层通信技术,并且OFDM系统要求子载波间严格正交。然而,在实际系统中,振荡器和滤波器等器件的非理想特性会导致同相正交(In-phase and Quadrature-phase,IQ)不平衡,从而破坏子载波的正交性,严重影响OFDM系统的性能。通过研究IQ不平衡对OFDM系统的影响,提出了一种并联深度神经网络架构下的IQ不平衡补偿算法。该算法利用了深度神经网络不依赖于模型的特点,直接从接收到的频域信号恢复原输入信号的二进制序列,并利用干扰信号来自镜像子载波的先验知识来初始化模型驱动的神经网络,加快其网络优化的收敛速度。仿真结果表明,该算法能有效地补偿IQ不平衡失真,并且在幅度和相位失真的补偿上,其性能都优于传统的基于导频的最小二乘补偿算法,证明了深度学习方法解决物理层问题的优越性。 相似文献
129.
《防务技术》2020,16(2):432-438
The airborne missile launch mechanism often subjects to significant deformations induced by the large ejection force during high-speed actuations in missile ejection process, leading to a substantial deviation of separation parameters from designed values that threats safety of the carrier. This study proposes a novel variable topology design for launch mechanism, achieved via a Prismatic-Revolute-Revolute pair (PR-R) motion formed by the structural gap with a specific direction. It enables launch mechanism variability during missile ejection process and optimizes the ejection force given by the front and back ejection arms, and greatly optimizes the separation parameters during missile ejection. The kinetics simulation analysis is conducted under working conditions of the original ejection mechanism and the novel mechanism with variable topology design, respectively. The results show that the novel variable topology design is more befitting for the launch process in terms of system safety and controllability, effectively improving the separation posture, restraining the flexible effect of the mechanism, and fulfilling the effectiveness of the design value of multi-rigid body. 相似文献
130.
《防务技术》2020,16(2):401-407
The measurement and control of high temperature play very important roles in national defense, military, scientific experiments, industrial and agricultural production. Photoelectric pyrometer is one of the important radiation thermometers for non-contact temperature measurement. It has an important application in the field of high temperature measurement, and its performance directly affects the accuracy of temperature measurement. By improving the design of the detection optical system of the photoelectric pyrometer, the imaging performance of the photoelectric pyrometer can be improved effectively, and the temperature measurement accuracy can be improved. In this paper, the temperature measurement principle of photoelectric pyrometer, the working principle of the detection optical system and the composition of the system are introduced. The optical components that affect the imaging of the optical system of the photoelectric pyrometer are analyzed. The optical pyrometer detection optical system is simulated by ZEMAX software, based on the analysis results, the Modulation Transfer Function (MTF) and the spot Diagram are used as the main evaluation criteria to optimize the design of the objective lens of the photoelectric pyrometer detection optical system. The imaging performance of the photoelectric pyrometer detection optical system and the accuracy of temperature measurement of the photoelectric pyrometer are improved by optimization design of the detection optical system. 相似文献