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在卫星通信中,由于干扰信号强弱的变化很大,采用固定收敛因子的自适应算法是无法满足系统的性能要求,而采用目前常用的一些动态补偿性,又存在着算法复杂,计算量大,无法满足系统的实时性要求的问题。本文提出了一个可以应用于工程实际的方法,从而使在满足系统实时性要求的前提下,实现了收敛因子的动态调整。 相似文献
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本文对Lopes等人提出的利用变化系数和比值算子的结构检测算法进行了详细分析,指出在滤波窗口中存在多个结构特征或者线结构的宽度大于一个象素的情况下,原算法可能产生窗口结构检测的错误。文中针对这两个问题进行了相应的改进,提出了一种改进的结构检测算法。通过将改进后的算法应用于实际的SAR(合成孔径雷达)图像数据,验证了对原算法改进的有效性。 相似文献
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描述了具有最低旁瓣电平和使用粒子群优化算法(PSO)控制零陷的线性阵几何综合方法。PSO是一种最新开发的高性能优化算法,它能解决一般的N维线性和非线性优化问题。与遗传算法和模拟退火等其他进化算法相比,PSO算法更易于理解和实现,并且要求最少的数学预处理。针对以旁瓣抑制(SLL)和/或在特定方向放置零陷为目标的优化问题,首先提出了阵列几何综合的公式,然后运用PSO算法来解决单元的位置优化问题。最后给出了3个PSO算法应用的设计实例,且每个实例中的优化目标都易于实现。通过与使用二次规划方法(QPM)获得的结果相比较,验证了PSO算法结果的有效性。 相似文献
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研究了利用气动力进行星座保持的最优控制问题。首先得到了正则方程,然后针对最优控制问题提出了一种求解算法,利用此算法进行了仿真计算。结果表明,算法简单有效。 相似文献
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针对高超声速飞行器上升段飞行过程中强耦合、强非线性同时要求满足过程约束的特点,提出了一种结合级联控制方法和控制障碍函数的新型三维制导控制一体化算法。首先通过对速度子系统设计控制障碍函数约束算法来满足飞行器的过程约束要求,然后利用反步法、动态逆控制方法设计其余子系统的控制器,两者共同组成制导控制一体化控制器。考虑到飞行器在上升过程中容易遭遇阵风扰动的问题,设计非线性干扰观测器以增强算法的鲁棒性。最后通过李雅普诺夫函数证明了系统的稳定性,并且通过仿真验证了该新算法能够在满足高超声速飞行器上升段过程约束的同时,实现飞行器的三维跟踪控制。 相似文献
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多光谱图像中云层及阴影的检测与消除 总被引:2,自引:0,他引:2
云层及阴影的检测是遥感应用领域的一个非常重要的问题。目前这方面的资料比较少,尤其是在被动接收条件下。提出了一种云层及阴影检测的算法,该算法的主要依据是云层及阴影覆盖区域高平滑性的特征,算法主要包括图像变换、亮度校正、云层及阴影的检测、滤波四个步骤。相对于现存方法而言,优点在于整个算法适合主被动接收条件,算法的处理比较简单,算法实现过程中没有很苛刻的参数选择,算法的适用范围较广。仿真结果不仅验证了上面的分析,而且表明该算法去云层及阴影的效果比较理想。 相似文献
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纯方位目标定位精度不仅与所选择的节点数目有关,而且还与目标和节点间的相对位置有关,为了同时满足目标的定位精度尽量高和节点能量消耗尽量少这一要求,提出了一种改进的基于多目标蚁群优化算法的传感器节点组网策略。在此基础上,推导了基于当前统计模型的分散式纯方位跟踪算法并对纯方位机动目标实施跟踪。仿真结果表明:在选择相同数目节点的前提下,本文所提出的节点选择方法与传统的最近邻方法相比,跟踪精度不仅得到了提高,而且还节约了节点的能量消耗。 相似文献
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高分辨星载斜视合成孔径雷达回波信号中,多普勒中心频率随距离向的变化通常是十分显著的.这种变化导致系统需要更高的脉冲重复频率来实现方位向无混叠采样.然而,过高的脉冲重复频率将引起严重的距离模糊、极大的数据率,并将限制成像区域大小.本文推导了一种新的全零多普勒导引方法,并在此基础上提出了一种最小化多普勒中心频率随距离变化的姿态导引方法,从而能够最大限度地降低系统脉冲重复频率.根据星地空间几何关系和姿态导引原理,文中推导了实现全零多普勒导引的偏航角和俯仰角的解析表达式,并进一步给出了最小化多普勒中心频率随距离变化的姿态导引规律.最后通过计算机仿真,验证了该方法的有效性. 相似文献
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Sensitivities to the future growth of orbital debris and the resulting hazard to operational satellites due to collisional breakups of large derelict objects are being studied extensively. However, little work has been done to quantify the technical and operational tradeoffs between options for minimizing future derelict fragmentations that act as the primary source for future debris hazard growth. The two general categories of debris mitigation examined for prevention of collisions involving large derelict objects (rocket bodies and payloads) are active debris removal (ADR) and just-in-time collision avoidance (JCA). Timing, cost, and effectiveness are compared for ADR and JCA solutions highlighting the required enhancements in uncooperative element set accuracy, rapid ballistic launch, despin/grappling systems, removal technologies, and remote impulsive devices. The primary metrics are (1) the number of derelict objects moved/removed per the number of catastrophic collisions prevented and (2) cost per collision event prevented. A response strategy that contains five different activities, including selective JCA and ADR, is proposed as the best approach going forward. 相似文献
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深空大规模天线阵布局优化方法研究 总被引:1,自引:0,他引:1
由大量廉价的小型反射面天线组成阵列对航天器进行跟踪通信是未来深空测控网发展 的一条新思路。提出一种改进的遗传算法对大规模小天线阵列地理布局进行优化,提高天线 阵列的测控性能。首先分析了布局优化的约束条件,然后以最小化旁瓣电平为目标,建立了 优化模型。分析了Kogan梯度算法和常规遗传算法的局限性,最后给出了改进遗传算法的优 化流程。仿真结果表明,改进的遗传算法不但具有高的优化效率,还可应用于阵列布局的多 目标优化。
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A steering law of control moment gyros for spacecraft attitude control by using one-step ahead singularity index is addressed in this paper. In some recent studies, the null motion approaches or singularity robustness steering laws have been extensively investigated to avoid singular configurations for a control momentum gyro (CMG) cluster. As a novel approach different from them, the proposed approach is based on optimization technique by minimizing the one-step ahead singularity index. Modified approaches are also presented in this paper. The proposed one-step prediction method ultimately gives an optimized solution of gimbal rates with advanced ability to avoid a singularity. A singularity index for reliable computation of a gradient vector is also introduced. Finally, performance of the proposed algorithm is demonstrated by numerical simulations. 相似文献
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本文章旨在介绍一个航天器工程设计工具———“VISPERS”。它对提升我国航天器设计水平有一定价值。与其他软件相比,该软件与其他软件相比有许多特色。首先,它可以在航天器初步设计阶段进行声振,、振动,、冲击分析,并直接输出部件级或系统级试验规范曲线。第二,使用方便,、快捷,、直观。,例如:可以一键预报动力学环境结果,也就是当用户点击航天器/运载火箭某个位置,这个位置的动务学载荷、试验规范就马上显示。比如,它可以一键预报动力学环境结果。也就是用户点击到航天器/运载火箭某个位置,这个位置的动力学载荷,试验规范就马上显示。第三,它可以提供其他动力学环境分析(如:火工品冲击,疲劳寿命分析)(比如:火工品冲击,疲劳寿命分析)。第四,各类数据库和专家系统干预或参加运算,把不确定性降到最小,使预报结果可信。因为声振,振动,冲击环境预报工作由航天器结构复杂和可靠性要求高而带来的不确定性很多,该软件针对这一难题,通过各类数据库和专家系统干预或参加运算,把不确定性降到最小。第五,引入由知识内涵编制的专家系统。这是该软件最大的特点。本文将对以上这些特色一一介绍。最后,提供一个火工品冲击损伤可能性的例子,说明该专家系统的工作应用价值。 相似文献
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“单二”组合检测技术的唯一性研究 总被引:3,自引:0,他引:3
本文针对曲面构形刚体,利用动态景物图象序列的“单二”组合技术,建立了运动方程。但是,同时产生了增根。为了从瞬间三维运动参数的多组解中确定唯一的真解,在考虑到噪声的影响后,导出了判决函数d(f,R)及其判决规则。仿真实验结果表明,利用d(t,R)0,可以有效地确定唯一的瞬间旋转矩阵R_。和三维平移矢量t(与真解t_。同向),从而证实了理论分析的工确性,解决了“单二”组合检测技术的多解问题。 相似文献
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Coulomb formations refer to swarms of closely flying spacecraft, in which the net electric charge of each vehicle is controlled. Active charge control is central to this concept and enables a propulsion system with highly desirable characteristics, albeit with limited controllability. Numerous Coulomb formation equilibria have been derived, but to maintain and maneuver these configurations, some inertial thrust is required to supplement the nearly propellant-less charge control. In this work, invariant manifold theory is applied to two-craft Coulomb equilibria, which are admitted in a linearized two-body gravity model. The manifolds associated with these systems are analyzed for the first time, and are then utilized as part of a general procedure for formulating optimal reconfigurations. Specifically, uncontrolled flows along the manifolds are sought which provide near continuous transfers from one equilibrium to another. Control is then introduced to match continuity, while minimizing inertial thrusting. This methodology aims to exploit uncontrolled motions and charge control to realize the shape-changing ability of these formations, without large inertial control efforts. Some variations in formulating and parameterizing the optimal transfers are discussed, and analytical expressions are derived to aid in establishing control parameter limits, under certain assumptions. Numerical results are provided, as demonstrative examples of the optimization procedure, using relatively simple control approximations. Finally, Particle Swarm Optimization, a novel stochastic method, is used with considerable success to solve the numerically difficult parameter optimization problems. 相似文献
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This paper presents a systems approach to optimization of the size and orbital life of photovoltaic systems via minimizing the nighttime energy demand while maximizing the daytime energy consumption. The Day-Night Management of Load (DANMOE) strategy calls for sizing the system to a pre-selected day/night average load power ratio and operating the spacecraft in orbit within the day and night capacity capability, rather than the conventional single orbital average power capability. Examples for the Space Station and the telecommunication satellites show that the reduction in their specific masses can be substantial using any of the photovoltaic system technologies. The DANMOE scheme may also be used effectively to extend the life of batteries on currently orbiting satellites, and hence prolong their lifetime. The paper also discusses other benefits at the spacecraft level and the method of implementing the DANMOE approach. 相似文献