Sliding mode control based guidance law with impact angle constraint

The terminal guidance problem for an unpowered lifting reentry vehicle against a sta- tionary target is considered. In addition to attacking the target with high accuracy, the vehicle is also expected to achieve a desired impact angle. In this paper, a sliding mode control （SMC）-based guidance law is developed to satisfy the terminal angle constraint. Firstly, a specific sliding mode function is designed, and the terminal requirements can be achieved by enforcing both the sliding mode function and its derivative to zero at the end of the flight. Then, a backstepping approach is used to ensure the finite-time reaching phase of the sliding mode and the analytic expression of the control effort can be obtained. The trajectories generated by this method only depend on the initial and terminal conditions of the terminal phase and the instantaneous states of the vehicle. In order to test the performance of the proposed guidance law in practical application, numerical simulations are carried out by taking all the aerodynamic parameters into consideration. The effec- tiveness of the proposed guidance law is verified by the simulation results in various scenarios.     

吊挂系统对波瓣混合排气系统气动热力性能影响

为了明确短舱中吊挂系统的堵塞效应对波瓣混合排气系统气动热力性能的影响,采用数值模拟的方法对包含吊挂的混合排气系统进行了定量研究。研究结果表明,受吊挂系统的影响,在波瓣混合排气系统混合段内,存在着一大尺度的回流区,其作用范围随吊挂长度的增加而增加。在性能参数方面,与未考虑吊挂系统时相比,考虑吊挂之后,虽然混合排气系统出口处热混合效率以及推力系数下降很小,最大降幅仅分别为0.017和0.01,但总压恢复系数却显著下降,最大降幅达到了0.03。此外,随着吊挂系统长度的变化,排气系统出口处的热混合效率、总压恢复系数以及推力系数变化幅度小于0.01,变化很小。     

Transient simulation of regression rate on thrust regulation process in hybrid rocket motor

The main goal of this paper is to study the characteristics of regression rate of solid grain during thrust regulation process. For this purpose, an unsteady numerical model of regression rate is established. Gas–solid coupling is considered between the solid grain surface and combustion gas.Dynamic mesh is used to simulate the regression process of the solid fuel surface. Based on this model, numerical simulations on a H2O2/HTPB(hydroxyl-terminated polybutadiene) hybrid motor have been performed in the flow control process. The simulation results show that under the step change of the oxidizer mass flow rate condition, the regression rate cannot reach a stable value instantly because the flow field requires a short time period to adjust. The regression rate increases with the linear gain of oxidizer mass flow rate, and has a higher slope than the relative inlet function of oxidizer flow rate. A shorter regulation time can cause a higher regression rate during regulation process. The results also show that transient calculation can better simulate the instantaneous regression rate in the operation process.     

翼型舵面偏转非定常流动数值模拟

针对NACA0012翼型舵面偏转问题,数值模拟了不同参数对翼型气动特性的影响。基于非结构动网格技术,采用ALE有限体积描述下的二维可压缩非定常N-S方程,计算通量采用Vanleer格式、时空二阶格式,利用Venkatakrishnan限制器抑制数值振荡。非定常计算结果表明,NACA0012翼型绕1/4弦点作周期性俯仰振动的升力系数和俯仰力矩系数结果与实验数据吻合良好,验证了数值方法的准确性;在翼型舵面表面有分离区产生,升力系数和俯仰力矩系数形成滞回环,在亚声速情况下,滞回环幅值较小,进入超声速阶段以后,幅值增大,随着翼型间缝隙宽度逐渐增加,翼型升力系数和俯仰力矩系数与无缝翼型相比逐渐降低。     

次流通道对双喉道气动矢量喷管的性能影响研究

为了进一步了解次流通道对双喉道气动矢量喷管(Dual Throat Nozzle,DTN)气动矢量性能的影响,基于二维DTN喷管构型进行了详细的数值模拟研究。结果表明:收扩的次流通道相对于平直的次流通道不会改善DTN喷管的推力矢量性能;随着次流流量增加,DTN的推力矢量角存在一个最大值,超过该值各推力矢量性能均会降低;次流通道宽度对DTN喷管推力矢量性能影响显著:(1)次流宽度不影响所能达到的最大推力矢量角;(2)小的次流宽度在进口总压较高的条件下具有更高的推力矢量角;(3)增大次流宽度能降低次流总压,但达到的矢量角会有所减小。     

某型机风挡加温系统控制规律的数值模拟

风挡电加温系统的控制规律是系统设计的重要部分。采用有限容积法模拟某型机风挡加温系统的控制规律,计算飞行包线下的温度和电加热功率的瞬时变化情况,分析在不同的天气条件下温度和加热功率瞬态变化的差异,得到实际情况下系统的工作规律。结果表明:由于玻璃具有热惯性,系统加温达到稳定状态后,基本上在较低的功率水平工作;外表面和导热膜的温度受外界环境影响较大,内表面的温度在加热过程中总体呈现增加趋势;设计时控制规律还可不断优化,以使系统具有更好的加热效率。该研究结果可为风挡加温系统的设计提供参考。     

一种基于因果关系的惯性制导工具误差系数分离方法

由于惯性测量系统误差模型的环境函数矩阵存在复共线性问题,所以无法采用最小二乘方法求解出误差系数.针对该问题,首先给出了几种传统的工具误差系数分离方法并进行了验证,但都无法准确估计结果.然后,提出了一种基于因果关系的惯性制导工具误差系数分离方法,引入相关系数对相互关联的系数进行重新整合,构造出新的误差模型.最后,进行了方...     

微小推力下小卫星的轨道递推与推力标定

针对采用微小推力进行轨道机动的小卫星,考虑复杂摄动力的基础设计了一种高精度轨道外推和推力在轨标定算法.首先,建立了考虑地球复杂摄动力和微小推力的小卫星轨道动力学模型;然后基于动力学模型,利用变步长龙格库塔算法,设计了对微小推力小卫星进行高精度轨道外推的方法.随后通过无迹卡尔曼滤波器(UKF),设计在轨标定算法,对存在误...     

印度将发射系列军事卫星

据国防科技信息网报道，印度国防部长的科学顾问、首席国防科学家萨拉斯沃特（V K Saraswat）称，印度计划发射一系列具备监视、成像、导航能力的国产军事卫星，以观察周边国家并为其巡航导弹制导提供帮助。他称由于保密原因，不能透露卫星数量。印度国防研发组织（DRDO）总干事称每年将发射1～2颗卫星。     

涡流阀式固体变推力集成原理样机设计与实验

针对涡流阀式变推力发动机,初步建立了设计方法,并设计了长尾管和环形燃气发生器组合的集成式原理样机,开展了考核试验.实验结果表明,设计的原理发动机实现了设计要求；涡流阀式变推力发动机具有存在旋流损失,可实现推力调节比大于压强调节比的工作特性；实验推力调节比达到9:1.