共查询到20条相似文献,搜索用时 31 毫秒
1.
以氧化剂和燃料的混合比作为系统控制参数,研究同轴离心式喷嘴燃烧动力学过程。混合比增加和减少过程中,燃烧噪声和振荡燃烧状态间转变的混合比不同,说明系统出现了亚临界Hopf分叉现象,且在双稳定区内出现了燃烧噪声引发的振荡燃烧。利用临界慢化理论,分析3种表征参数:延迟为1自相关系数、方差和条件异方差(CH)对噪声引发不稳定的预警效果。结果表明:延迟为1自相关系数在噪声引发不稳定前出现明显的上升趋势且非随机现象,具有较可靠的指示作用。方差对噪声引发不稳定性的预示性较差。条件异方差在不稳定发生前振荡上升,可以作为辅助判断条件。基于Kendall秩相关系数趋势评估方法,提出一种在线预测噪声引发不稳定的判断准则,具有较好的适应性和可靠性。 相似文献
2.
3.
4.
5.
The improvement in SNR and detection range due to distributing an antenna array throughout the airframe and skin of an aircraft is examined. SNR formulas for three system configurations are presented and compared with that of a conventional, monostatic radar. Examples given in the paper show detection range increases as large as a factor of 4. Three additional potential advantages of the distributed array are an increase in spatial signal processing capability, an improvement in azimuthal resolution, and a potential reduction in transmitter power for fixed radar Performance so as to reduce the probability of intercept. 相似文献
6.
Luh J. Y. S. Shafran Joel S. Harvey C. Arthur 《IEEE transactions on aerospace and electronic systems》1968,(2):218-233
This paper considers the problem arising from the design of an autopilot for a large booster. The motion-controlling actuators of the booster have both position and rate limits. The problem is formulated as a bounded phase-coordinate problem and analyzed by the ``backing out of the target' procedure. A method of constructing the optimal control is presented. An example of an oscillatory system with two control inputs is given, and the optimal control is expressed as an explicit time function. 相似文献
7.
The estimation problem is defined, and a review of how the linear estimation approach of Kalman filtering is extrapolated to form an extended Kalman filter (EKF), applicable for state estimation in nonlinear systems is presented. A mechanization of an EKF variation known as an iterated EKF, offering improved tracking performance, is treated. A streamlined version of an iterated EKF that has a lesser computational burden (fewer operations per cycle or time step) than prior formulations is offered. A nonlinear filtering application example, to be used as a testbed for this new approach, is described, and the detailed modeling considerations as needed for exoatmospheric random-variable radar target tracking are discussed. The performance of the streamlined mechanization is illustrated in this radar target tracking example, and comparisons are made with the performance of an EKF without measurement iteration 相似文献
8.
Using the method of quasisolutions for inverse boundary-value problems of aerohydrodynamics, a problem of constructing an airfoil was solved by the specified velocity distribution along the sought airfoil contour when there is an irregularity in the flow such as a vorticity source. The cases of a source (sink) and vortex are obtained as particular ones. The airfoils are constructed numerically and analytically and conclusions are made about an influence of the irregularity position and type on the shape and aerodynamic characteristics of the airfoil. 相似文献
9.
裂纹叶片振动特性研究 总被引:3,自引:1,他引:2
建立应用传递矩阵法求解裂纹叶片振动特性的方法,以矩形截面裂纹悬臂梁为计算实例,分析了沿叶宽等深度扩展的横向裂纹位置、深度对其弯曲型振动特性的影响。选用方波函数模拟裂纹开合过程,理论分析了裂纹叶片的非线性振动特性。通过裂纹试件实验,对理论研究方法和结果做了验证。提出了叶片裂纹故障在线监测特征量的选择建议 相似文献
10.
The MOD is described as an urban transportation system which is based on a very small, two-passenger automotive rental vehicle using existing city roadways at the exclusion of the private passenger car. The proposed units of the MOD system have an empty weight of 300 pounds and have provisions for easy vertical parking. The MOD system is proposed as a self-supporting operation, run by private enterprise as a public utility. The urban transportation offered by the MOD system generates the set of institutional problems involved in proposals which exclude the private passenger car from the city. 相似文献
11.
Optimum Alignment of an Inertial Autonavigator 总被引:1,自引:0,他引:1
Jurenka Frank D. Leondes Cornelius T. 《IEEE transactions on aerospace and electronic systems》1967,(6):880-888
The performance of an inertial autonavigator can only be as good as the accuracy to which the system is initially aligned. Optical methods of alignment can be performed with high precision; however, this technique requires external equipment and is subject to some physical constraints, such as land-based operation. The general problem discussed here is the use of an automatic azimuth alignment technique known as gyrocompassing. In the use of the gyrocompassing technique to obtain azimuth alignment, accuracies are degraded considerably by two dominant error sources, the level axis controlling gyro drift rate and the imperfections of reference or independent velocity information. Consequently, an optimum performance controller is developed for driving the system in this mechanization and is based on a priori knowledge of the second-order statistics of the system error sources. The performance criteria will be to minimize the mean square azimuth error. 相似文献
12.
对带有上偏20°扰流板和不同偏角铰链襟翼的二维翼型气动性能进行了数值研究,并选择了分别适用于大型客机滚转控制和空中制动的襟翼辅助偏转方案。计算结果表明:(1)对于滚转控制,在将扰流板上偏的基础上进一步将铰链襟翼辅助上偏,既能产生更大的滚转力矩,又能避免不必要的阻力增加;(2)对于空中制动,在将扰流板上偏的基础上进一步将铰链襟翼辅助下偏,既能获得更好地减速效果,又能避免不必要的升力损失。 相似文献
13.
针对航空发动机燃烧室火焰筒结构声疲劳问题,建立了某型航空发动机燃烧室火焰筒有限元计算模型。采用耦合的边界元和有限元方法对该结构进行声激励载荷作用下的响应进行计算,获得该结构在不同声压级下的振动位移和应力响应结果,对燃烧室火焰筒结构疲劳故障分析和抗声疲劳结构设计具有一定参考价值。 相似文献
14.
15.
苗润才 《西安航空技术高等专科学校学报》2013,(4):3-6
论述大学办学特色和核心竞争力及其关系,说明办学特色是大学核心竞争力的重要体现,提出西安航空学院应以特色求生存、谋发展,构建鲜明的立足航空、服务航空、错位经营的办学特色,提升学校的核心竞争力。 相似文献
16.
The system worth or cost effectiveness concept covers the measure of a system in terms of total dollar value. System worth encompasses the elements of system effectiveness (a quantitative measure of a system's technical ability) as well as cost. One of the elements of system effectiveness is maintainability. Maintainability is an effective mechanism for the accomplishment of planned maintenance during the early design and development phases of a system. Planned maintenance is an element of integrated logistics support. The intent of this paper is to outline the basic elements associated with system worth, system effectiveness, and integrated logistics support, to outline the interrelation-ships of these concepts, and to cover the discipline of maintainability as an element of each concept. 相似文献
17.
We have developed a 2D semi-empirical model (Sittler and Guhathakurta 1999) of the corona and the interplanetary medium using
the time independent MHD equations and assuming azimuthal symmetry, utilizing the SOHO, Spartan and Ulysses observations.
The model uses as inputs (1) an empirically derived global electron density distribution using LASCO, Mark III and Spartan
white light observations and in situ observations of the Ulysses spacecraft, and (2) an empirical model of the coronal magnetic
field topology using SOHO/LASCO and EIT observations. The model requires an estimate of solar wind velocity as a function
of latitude at 1 AU and the radial component of the magnetic field at 1 AU, for which we use Ulysses plasma and magnetic field
data results respectively. The model makes estimates as a function of radial distance and latitude of various fluid parameters
of the plasma such as flow velocity V, temperature Teff, and heat flux Qeff which are derived from the equations of conservation of mass, momentum and energy, respectively, in the rotating frame of
the Sun. The term "effective" indicates possible wave contributions. The model can be used as a planning tool for such missions
as Solar Probe and provide an empirical framework for theoretical models of the solar corona and solar wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
18.
吴志军 《中国民航学院学报》1997,15(1):22-32
就话音频段数据通信中利用自适应滤波器和同态滤波器的方法消除回波干扰的基本原理进行了描述,介绍了采用DSP技术的滤波器的设计方法,并给出了硬件实现结构。 相似文献
19.
20.
Transition region explosive events are observed throughout the quiet Sun and represent an interesting local heating phenomenon. The coronal counterparts of these events, if they exist, were not observed in a sounding rocket campaign dedicated to this objective. The coronal instrument complement on the SOHO spacecraft provides an opportunity to extend this search for the coronal counterparts of the transition region explosive events, as well as to explore the correspondence of explosive events with large scale coronal structures, such as with coronal dark lanes. 相似文献