Error Analysis of Space-Stable Inertial Navigation Systems

The error equations for a space-stable inertial navigation system are derived. This is done by directly perturbing the mechanization equations in the inertial frame and then transforming in open-loop fashion to the local-level frame. A rotating inertial platform and velocity and altitude damping are considered. The relations between errors in space-stable and local-level systems are noted. Numerical results are presented for certain random error sources.     

Altitude Damping of Space-Stable Inertial Navigation Systems

In order to stabilize the altitude calculation in an inertial navigation system, an altimeter is commonly used. In a conventional local-level mechanization, this is generally accomplished by correcting the vertical channel integrators with the difference between the inertial system and altimeter indication of vertical position. However, in a space-stable system the procedure is not as clear since a vertical channel is not physically present. Three altitude damping mechanizations for a space-stable inertial navigation system are proposed. The equivalent local-level mechanizations are then found by comparing error propagation equations in a common coordinate frame.     

Kalman Filter Design Considerations for Space-Stable Inertial Navigation Systems

Terrestrial inertial navigation is typically performed using an instrumented platform stabilized in a ?local-level? configuration for convenient generation of geographic navigation information. The local-level geographic reference must be maintained by torquing the system gyros, a requirement which may be incompatible with high-precision inertial sensors currently under development. Gyro torquing in a gimballed navigation system can be avoided by employing a ?space-stable? mechanization of the platform where an inertial, rather than geographic, reference is used for navigation calculations. The software design problems associated with this concept, especially those related to the application of Kalman filtering, are the principle focus of this paper. Although the space-stable configuration has been used extensively for spacecraft navigation and guidance, it has not been widely applied to terrestrial navigation, either for air or marine applications. The chief problem in this application is to perform navigation in local-level coordinates, using system outputs generated in an inertial reference frame. It can be demonstrated that, although the navigation system error dynamics are identical for the local-level and space-stable configurations, the dynamics of the sensor errors which drive these systems are quite different. These differences in sensor error propagation characteristics impose new requirements for the design of procedures to accomplish system calibration, alignment, and reset. This paper outlines a Kalman filtering approach which is applicable to all of the above procedures, and presents numerical results to demonstrate its effectiveness.     

Doppler Radar Error Equations for Damped Inertial Navigation System Analysis

The use of Doppler radar measurements to provide velocity damping for an aircraft inertial navigation system is considered. Three different Doppler antenna configurations are examined: two-axis stabilized, azimuth stabilized, and data stabilized antennas. A general reference velocity error equation is presented and appropriately evaluated for each of the Doppler configurations. Specific elements of the error equations are examined and physically interpreted for both local-level and space-stable inertial systems. Detailed examination of the interaction of Doppler radar and inertial navigation velocity error mechanisms is provided.     

A Comparison of Two Approaches to Pure-Inertial and Doppler-Inertial Error Analysis

Error equations for inertial navigation systems are derived using a perturbation (or true frame) approach and a psi angle (or computer frame) approach in a manner which shows the underlying as sumptions and allows direct comparison of the two methods. The comparison is general since the analysis is not associated with any particular mechanization. Different definitions of velocity errors and misalignment angles result from the two methods of error analysis, and, consequently, have significance in testing and analysis of pure-inertial systems, Doppler-inertial systems, and inertially aided weapon delivery systems. Examples and numerical results are presented for a local-level north-pointing mechanization.     

基于相对轨道要素的航天器相对运动碰撞分析

采用基于相对轨道要素的方法,建立了计算碰撺概率的数学模型.在二体圆轨道条件下,推导验证了与基于Clohessy-wiltshire(C-W)方程的碰撞模型的等价关系,并解决了C-W方程存在的若干问题.在航天器近距离相对运动构型设计中提出了基于相对轨道要素的碰撞分析方法,突出了相对轨道要素在构型设计以及碰撞分析中的作用....     

视觉辅助惯性定位定姿技术研究

在利用视觉系统辅助捷联惯性导航系统( SINS)进行定位定姿时,由于两者输出的位置表示方法不同,在信息融合时会存在匹配问题。以相对地理坐标系作为定位定姿系统的导航坐标系,重新对SINS进行了力学编排,分析了其误差传递特性,建立了相对地理坐标系下的状态方程模型,并利用Kalman滤波器实现了视觉辅助惯性定位定姿算法。仿真结果表明,方法避免了信息融合时位置匹配问题,同时降低了系统的计算量,满足了定位定姿系统的精度要求。     

Modeling quaternion errors in SDINS: computer frame approach

We propose new equivalent tilt error models which are applicable to the analysis of the terrestrial strapdown inertial navigation systems (SDINS), based on the quaternions. The currently available equivalent tilt error models, like the conventional Φ model of the gimbaled inertial navigation systems (GINS), are derived only by the true frame approach. The true frame approach has a computational disadvantage that it produces an error model where the attitude error equation is coupled with its position and velocity error equations. The motivation of this work is to solve this problem. As a result, two kinds of error models are derived. Among them, one is derived by the computer frame approach for practical onboard implementations. Thus, like the conventional GINS Ψ model, its attitude error equation is decoupled from the position and velocity error equations. The other is derived in order to show the relationship between the true frame approach and the computer frame approach which are applied to the quaternion-based SDINS. Thus, like the GINS δΘ model, it can be used to transform the error variables into each other which are calculated by the two different approaches     

机床定位精度对磁流变抛光的影响分析

根据KDMRF-1000磁流变抛光机床的结构形式,建立机床坐标系.对机床进行运动求解,得到磁流变抛光机床后置处理算法模型.在此模型的基础上,分析了机床各轴定位精度对磁流变抛光加工的影响,进行仿真分析,得到了误差的影响规律和对机床的定位精度要求.     

Advanced Development of ESG Strapdown Navigation Systems

The fundamental problem of inertial navigation, double integration of acceleration to obtain position, is defined and discussed. Mechanizations of both space-stable and local-vertical platform systems are exhibited. The synthesis problem for an electrically suspended gyro (ESG) strapdown system is defined and discussed: readout, readout errors due to vehicle motion, synchronization of readout with system computer, alignment, correction and calibration for mass unbalance drift, and digital mechanization. Alignment, calibration, and acceleration measurement are also discussed. Sources of error involved in the electronic gimbaling including those peculiar to strapdown configuration are discussed and compared to mechanically gimbaled systems. Advanced developments required in the component and systems areas are listed, and it is shown that such development will lead to reduced complexity, higher accuracy, and increased reliability and utility for inertial systems.     

螺旋桨滑流对发动机进气道气动性能的影响

针对螺旋桨/短舱/进气道一体化构型,采用多重参考系(MRF)法和滑移网格非定常法进行了数值模拟研究,实现了螺旋桨/短舱/进气道一体化内外流耦合流场仿真,研究了不同工况下螺旋桨滑流对进气道气动性能的影响,并与无桨构型的进气道性能进行了对比,最后通过数值分析解释了螺旋桨桨盘后总压上升的原因。结果表明:多重参考系法和滑移网格非定常法对进气道出口的时均参数的计算结果吻合较好,多重参考系法可用于螺旋桨及进气道的气动性能参数计算;螺旋桨做功使进气道总压恢复系数增高,螺旋桨转速越大,总压恢复系数的增量就越大,且螺旋桨滑流使进气道出口畸变指数明显增大;通过数值分析推导的桨盘前后总压关系公式与仿真结果的误差均在3%以内。      

富氢燃气旋转爆轰波传播特性实验研究

为研究富氢燃气旋转爆轰波传播特性,利用氢气与氧气预燃烧产生的富氢燃气作为燃料,空气为氧化剂,开展了旋转爆轰实验研究。对富氢燃气旋转爆轰压力变化、时频特性及传播速度等参数进行了分析,研究了不同传播模态下富氢燃气旋转爆轰波传播特性。研究表明：本文实验条件下,富氢燃气与空气旋转爆轰的传播模态主要受当量比影响,当量比高于1.06时呈现单波模态,随着当量比减小,旋转爆轰波呈现单波-双波过渡模态,即同一工况下,单波模态和双波模态交替出现,当量比减小到0.68左右时,基本呈现复杂的双波模态;在270 g/s的空气流量下,当量比增大,旋转爆轰波在环形燃烧室内的传播速度随之提高,但当量比到达临界点以后,传播速度提高不明显;在相同当量比下,当空气流量增大到370 g/s 时,旋转爆轰波的传播速度会进一步提高;空气流量越大,临界点对应的当量比越低,其中270 g/s空气流量对应临界当量比为1.32,370 g/s空气流量对应临界当量比1.16;达到临界当量比以后,传播速度受当量比和空气流量影响不大。     

Real Time Satellite Position Determination for TDMA Systems

A real time satellite position determination method using a single reference station is presented. The satellite position is determined from these three parameters: the distance between the reference station and the satellite that can be obtained by a single-hop measurement, the elevation angle, and the azimuth angle obtained from the antenna encoder. The error of the transmit frame delay is determined from the position equations, together with other possible errors. The accuracy is about ± 42 symbols for a 90 Mbit/s timedivision multiple access (TDMA) system using an encoder with a ± 0.001 ? resolution.     

Stochastic analysis of two dimensional nonlinear panels with structural damping under random excitation

Stochastic behavior of panels in supersonic flow is investigated to assess the significance of including the damping caused by the strains resulting from axial extension of the panel. The governing equations of motion are based on the Von Karman's large deflection equation and are considered with Kelvin's model of structural damping. The panel under study is two dimensional and simply supported for which the first order piston theory is used to account for the unsteady aerodynamic loading. Transformation of the governing partial differential equation to a set of ordinary differential equations is performed through the Galerkin averaging technique. The statistical response moment equations are generated for two modes using the Fokker–Planck equation with a Gaussian closure scheme. The response moments history and their steady state values are considered. Comparison with previous studies shows that the new nonlinear damping term developed through modeling has a significant effect on the response moments. This is verified through analysis of the effects of external pressure and in-plane force spectral density, air-to-structure mass ratio and structural damping ratio on the mean square value of modal amplitudes.     

Ground Testing of Inertial Navigators to Improve Dynamic Performance

A ground testing method has been devised to evaluate the dynamic errors of an inertial navigation system. A trimmed stationary inertial system in the navigation mode can be subjected to programmed platform orm drift rates, and generate position outputs which are compared with those of a perfect navigator. The linearized error equations for this testing mode are derived and the resulting position error propagation is analyzed using Kalman filtering in order to identify the error sources. A simulated platform with a fixed set of error sources is analyzed to evaluate this testing concept. An example is presented to show that the gyro and accelerometer scale factor and misalignment error coefficients can be estimated.     

粘弹减摆器几何耦合模型及对直升机悬停空中共振的影响.

针对具有几何耦合的非线性粘弹减摆器，在旋转坐标系下建立了其在平衡位置附近的小扰动微分方程，然后通过多桨叶坐标转换的方法将方程变换到不转坐标系中，并与直升机悬停时的线化小扰动方程结合起来进行特征值分析；减摆器静态位移和几何耦合对直升机空中共振稳定性的影响进行了分析。结果表明，粘弹减摆器会提高直升机空中共振稳定性；增大减摆器的静态位移会降低其有效阻尼；对于所考虑的旋翼系统来说，几何耦合可能会减小减摆器的静态位移，从而提高摆振后通型模态的阻尼。     

失衡旋翼的直升机自激振动分析模型

直升机使用中很可能出现旋翼各片桨叶特性不一致的情况,为了研究失衡旋翼对直升机自激振动的影响,建立了适用于地面、悬停及前飞状态的旋翼/机体耦合动稳定性分析模型。采用当量铰旋翼模型,计入动力入流的影响,分别在旋转坐标系和固定坐标系中建立了桨叶及机体的动力学方程。以减摆器失效对直升机地面共振的影响为例,对桨叶及机体的时域响应进行了非线性数值仿真,用Floquet传递矩阵法计算了摆振后退型模态频率及阻尼,并用时域分析进行了检验。结果表明,其中一个减摆器失效后,各片桨叶摆振运动特性相差很大,系统的摆振后退型模态阻尼下降幅度高达60%以上。     

Spectral Analysis of Optimal and Suboptimal Gyro Monitoring Filters

Gyro monitoring filters are used to estimate and correct gyro drift rates of local-level inertial navigation systems. Conventional gyro monitoring filters are usually designed based on a simplified model of gyro drift rate. Furthermore, the effectiveness of these filters-and of many filters of the "Kalman" type-is often measured in terms of the root mean square (rms) criterion in contrast to the spectral content criterion typical of classical Wiener filtering theory. This paper has two objectives: to propose a gyro monitoring filter which is based on a more detailed model of gyro drift rate; and to propose a method of filter performance evaluation which uses as criterion a measure of the spectral content of the error process. The proposed gyro monitoring filter is shown to have improved spectral contents resulting in superior navigation performance for the gyro error models used in the calculations (comparable to commercial-grade aircraft gyros).     

弧齿锥齿轮和准双曲面齿轮非线性动力学研究

通过引入理想传动的概念,首次给出了弧齿锥齿轮和准双曲面齿轮啮合力和阻尼力的表示方法,同时也给出了多对齿啮合条件下啮合力和阻尼力产生的扭矩在不同啮合区域内的表示方法,并在此基础上,建立了弧齿锥齿轮和准双曲面齿轮非线性系统动力学方程。      

错频对叶片的气动弹性稳定性影响

采用求解动网格下的非定常可压缩Navier-Stokes方程模拟了振荡叶片下的气动弹性问题,研究了叶片的频率错频对叶片气动弹性稳定性的影响.通过数值模拟平面叶栅的气动弹性第10标准算例,验证了气动弹性的数值模拟方法,计算了不同叶片间相位角和折合频率下的气动阻尼系数,研究了叶片振动频率改变对叶片气动弹性稳定性的影响.计算结果说明:频率错频是提高气动弹性稳定性的有效方法,其主要作用是减小叶片间振动的耦合效应和叶片间相位角的影响,并且随着错频量增大叶片稳定性增强;通过模拟三维环形叶栅的气动弹性第4标准算例,计算了气动阻尼系数随错频量变化的规律,验证了错频量和气动弹性稳定性增强的规律.