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详细分析了采用线性组合方法构造Gn连续过渡曲面时,基曲面以及重新参数化局部基曲面、调配因子和平衡因子等对过渡曲面的影响。提出基于辅助面的Gn连续过渡曲面的构造方法,即设计人员可根据设计要求和设计预期,以过渡切触线为边界来构造一张辅助面,该曲面在形状上和过渡曲面很贴近,然后在两基曲面的过渡切触线附近构造较小区域的重新参数化局部基曲面,由辅助面和一张重新参数化局部基曲面线性组合构造一张中间过渡面,再由中间过渡面和另一张重新参数化局部基曲面线性组合构造Gn连续过渡面,同时,选择较大值的平衡因子和调配因子λ1,以及较小的调配因子λ2,这样,所构造的过渡曲面和基曲面间Gn连续,且形状上和辅助面非常贴近,从而达到弱化基曲面或重新参数化局部基曲面对过渡曲面的影响,以及强化设计人员设计意图的目的。 相似文献
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<正> 三角B-B曲面具有许多类似于四边B(?)zier曲面的性质,如果将二者结合使用,则可以处理比较复杂的问题,有重要的实用意义。最近,刘鼎元教授给出了四边B(?)zier曲面片G1拼接的充分必要条件,并给出了G拼接的两个充分条件:简单连接条件和升阶连接条件。本文将升阶连接条件用于四边B(?)zier曲面和三角B-B曲面的G1拼接。结合使用简单连接条件,解决了在一般G1连续的四边B(?)zier曲面中嵌入G1连续的三角B-B曲面片的问题。 相似文献
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实际工程中的许多被控系统(如航天器,机器人,飞机等)几乎都处在一种变化的环境中,用精确的数学模型描述这类系统是不现实的。因此,研究考虑了这种不确定性的系统控制问题,在理论和应用中都有重要意义。 考虑用下述状态方程描述的不确定系统 (?)=(A0+△A(r,s))X+(B0+△B(r,s)u) (1)其中,X∈Rn,系统状态,n为系统阶数,u∈Rm,控制信号,A0,B0是适当维数的常值阵,r,s分别为p维和q维未知参数矢量,△A(r,s),△B(r,s)分别是与A0,B0同维的不确定矩阵。 相似文献
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基于遗传算法和空间推进方法的单壁扩张喷管优化设计研究 总被引:2,自引:0,他引:2
将单目标遗传算法和多目标遗传算法(包括NSGA-II和NCGA),与高效、高精度的空间推进流场数值模拟方法——SSPNS方法相结合,对二维超燃冲压发动机尾喷管即单壁扩张喷管(SERN)进行了气动优化设计研究。在巡航点(Ma=6.0)讨论了推力系数CT最大单目标模型,推力系数CT最大升力系数CL最大两目标模型,以及推力系数CT最大升力系数CL最大俯仰力矩系数Cm最小三目标模型,分别得到了喷管的最大推力设计和关于多个目标性能的Pareto最优前沿。结果表明,扩张壁初始扩张角θr,i和外罩长度Lc对CT影响较大;较小的Lc和较大的θr,i设计,将降低外罩内表面的负升力作用而使得SERN的CL较大;较长外罩和较小的θr,i,对应Pareto最优设计的CM较小。 相似文献
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剪切锁闭的本质及解除方法 总被引:1,自引:0,他引:1
C0连续的弯曲单元得到了广泛应用,一方面由于计算较厚结构(如夹层结构)的需要,一方面由于在构造C1连续单元时遇到困难。但C0连续单元有“剪切锁团”问题,即当计算薄的结构时,剪切应变能愈来愈大,结构过分刚硬,位移很小。 相似文献
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高性能无人机翼型的杂交优化设计 总被引:1,自引:0,他引:1
发展了用于高性能无人机翼型设计的杂交优化设计方法。针对“类全球鹰”翼型的算例表明,该方法能满足低速时高升力(CL)和跨声速巡航时高气动效率(CL/CD)两方面要求。优化翼型较初始翼型,其低速时的设计升力系数提高了19.80%,跨声速巡航时的设计升阻比提高了37.45%,并且在较大的速度区间内优化翼型都具有良好的综合性能。杂交优化设计方法可为高空长航时无人机的设计提供参考。 相似文献
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低压下V形火焰稳定器回流区流动特性研究 总被引:2,自引:0,他引:2
符号表 x、y、z:坐标方向、大小(mm) y0:零速度线纵向坐标 W:稳定器槽宽(mm) λ:微尺度(mm) P:压强(MPa) ρ:密度(kg/m3) V0:来流速度(m/s) Re:雷诺数 :x向平均速度(m/s) u、v:x、y向脉动速度(m/s)uv、u2:速度相关量(m2/s2)m:回流量(单位横向宽度)(kg/s)ψ:流函数,钝体后回流区和主流强烈的紊流交换对燃烧室的火焰稳定性和燃烧效率起着有利的作用。 相似文献
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为了改善固体推进剂中高氯酸铵(AP)热分解性能,降低其热分解温度,利用SEM,XRD,FT-IR对原位制备的g-C3N4/Fe2O3复合催化剂的形貌和结构进行了表征,通过差示扫描量热法(DSC)考察了催化剂对AP 热分解的催化效果。结果表明:g-C3N4/Fe2O3复合结构完整,Fe2O3颗粒紧密负载在g-C3N4上;加入不同质量分数的复合催化剂,AP的低温分解峰和高温分解峰都明显降低,且随着催化剂加入量的增加催化效果增强;加入复合催化剂质量分数5%时,高温分解峰和低温分解峰分别降低到348.1℃和281.7℃,表明g-C3N4/Fe2O3复合催化剂可有效降低AP的热分解温度,改善其热分解性能。 相似文献
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Plug-and-play technology is an important direction for future development of spacecraft and how to design controllers with less communication burden and satisfactory performance is of great importance for plug-and-play spacecraft. Considering attitude tracking of such spacecraft with unknown inertial parameters and unknown disturbances, an event-triggered adaptive backstepping controller is designed in this paper. Particularly, a switching threshold strategy is employed to design the event-triggering mechanism. By introducing a new linear time-varying model, a smooth function, an integrable auxiliary signal and a bound estimation approach, the impacts of the network-induced error and the disturbances are effectively compensated for and Zeno phenomenon is successfully avoided. It is shown that all signals of the closed-loop system are globally uniformly bounded and both the attitude tracking error and the angular velocity tracking error converge to zero. Compared with conventional control schemes, the proposed scheme significantly reduces the communication burden while providing stable and accurate response for attitude maneuvers. Simulation results are presented to illustrate the effectiveness of the proposed scheme. 相似文献
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为提高方位俯仰型船载天线伺服系统的船摇隔离度,稳定环是常采用的策略,但是选择传统的PID(Proportional Integral Derivative,比例积分微分)调节器往往不能获得满意的控制效果,针对该问题,提出了PID+积分+滞后校正环节作为稳定环调节器的具体实现形式。另外,通过对伺服系统内各环路带宽及响应速度的分析,将稳定环阶跃响应的上升时间作为参数调节依据。上述设计完成后,在实际系统中添加周期10s,幅值8°的正弦波信号模拟船摇扰动,此时添加稳定环后,方位轴的船摇隔离度提高了6dB,俯仰轴的船摇隔离度提高了13dB。这表明,采用PID+积分+滞后校正环节作为稳定环调节器的设计形式是正确且简单有效的。 相似文献
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In tracking a target through clutter, the selection of incorrect measurements for track updating causes track divergence and eventual loss of track. The plot-to-track association algorithm is modeled as a Markov process and the tracking error is modeled as a diffusion process in order to study the mechanism of track loss analytically, without recourse to Monte Carlo simulations, for nearest-neighbor association in two space dimensions. The time evolution of the error distribution is examined, and the connection of the approach with diffusion theory is discussed. Explicit results showing the dependence of various performance parameters, such as mean time to lose track and track half-life, on the clutter spatial density are presented. The results indicate the existence of a critical density region in which the tracking performance degrades rapidly with increasing clutter density. An optimal gain adaptation procedure that significantly improves the tracking performance in the critical region is proposed 相似文献
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Performance analysis of GPS carrier phase observable 总被引:3,自引:0,他引:3
The accuracy analysis of Global Positioning System (GPS) carrier phase observable measured by a digital GPS receiver is presented. A digital phase-locked loop (DPLL) is modeled to extract the carrier phase of the received signal after a pseudorandom noise (PRN) code synchronization system despreads the received PRN coded signal. Based on phase noise characteristics of the input signal, the following performance of the first, second, and third-order DPLLs is analyzed mathematically: (1) loop stability and transient process; (2) steady-state probability density function (pdf), mean and variance of phase tracking error; (3) carrier phase acquisition performance; and (4) mean time to the first cycle-slipping. The theoretical analysis is verified by Monte Carlo computer simulations. The analysis of the dependency of the phase input noise and receiver design parameters provides with an important reference in designing the carrier phase synchronization system for high accuracy GPS positioning 相似文献
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In tracking optical beams from a source, a pointing error signal is derived from photodetecting the field in the receiver focal plane. This error signal is then used in some manner to control a gimballed system that continually points the receiver optics toward the source. When the source field undergoes turbulent transmission, the optical beam is attenuated and scattered, and the field is randomly defocused at the receiver. In this case the pointing error of the tracking system will evolve as a random vector process in time, statistically related to the random scattering, the photodetection process, and the dynamics of the gimballing system. Such vector processes have probability densities that satisfy well-known differential equations. These equations are derived in terms of accepted scattering models and tracking systems, assuming quadranttype error detectors are used in the focal plane. Approximate solutions are obtained and analyzed for typical operating conditions, and the manner in which the degree of scattering degrades the entire pointing operation is shown. 相似文献
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Marola G. Santerini D. Prati G. 《IEEE transactions on aerospace and electronic systems》1989,25(3):325-334
The system under consideration is a cooperative spatial tracking system between two stations for laser beam communications, using a quadrant photodetector at each station. After determining the equilibrium points of the cooperative system for the case of periodical relative motion, the authors concentrate on the stability of the transient behavior around the equilibrium points for the case of uniform angular relative motion. This case corresponds to an assumption that the steady-state motion is slow with respect to transient phenomena, and is applicable to currently foreseen intersatellite and deep-space optical communications. The analysis is aimed at determining the combined effect of the basic system parameters, such as propagation delay time, tracking loop gains, DC servomotors time constant, and point-ahead velocity error, on the stability and the transient behavior of the overall tracking system. The stability conditions and the transient response around the steady-state trajectory provide a tool for evaluating the consistency of the design parameters for a given propagation delay 相似文献
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本文从旋转变频磁控管式频率捷变雷达的本振频率跟踪原理出发,分析了产生本振频率跟踪误差的主要因素。文中着重讨论了本振频率冷跟踪误差问题。同时也提出了热跟踪后本振频率跟踪误差项。分析前者,可以决定热跟踪电路应予修正的频率范围,而后者则是跟踪本振最终的误差。以上分析对如何采取措施提高系统的跟踪精度是有参考作用的。 相似文献