GPS/INS 组合导航系统降阶滤波器设计

本文研究了某型号飞机上ＧＰＳ／平台惯性组合导航系统中降阶卡尔曼滤波器的设计方法；提出一种降阶滤器结构，并讨论了模型误差的伪随机噪声补偿方法。采用蒙特—卡洛分析法对降阶滤波器的实际误差进行了数字仿真，结果表明，本文提出的这种降阶滤波器能保证组合系统的导航精度，而且具有实际使用价值     

Numerical simulation of thermally and chemically nonequilibrium flows and heat transfer in underexpanded induction plasmatron jets

The results of numerical simulation are presented for thermally and chemically nonequilibrium air plasma flows in a plasmatron discharge channel and underexpanded dissociated and partially ionized air jets flowing past a cylindrical model with a blunt leading edge and cooled copper surface under the experimental conditions realized in a VGU-4 100 kW induction plasmatron (Institute for Problems in Mechanics of the Russian Academy of Sciences) (see, for example, [1, 2]). The nonequilibrium excitation of the vibrational degrees of freedom of the molecules in the modal approximation and the difference between the electron and translational heavy-particle temperatures are taken into account in the calculations. The calculated data on the heat transfer and pressure at the stagnation point are compared with the results obtained within the framework of the thermally equilibrium model. Comparison with the experimental data obtained in the Institute for Problem in Mechanics of the Russian Academy of Sciences (Laboratory for interaction between plasma and radiation and materials) and kindly provided for comparison purposes gives satisfactory agreement.     

A Reduced Order Cyclic Method for Computation of Limit Cycles

A reduced order cyclic method was developed to compute limit-cycle oscillations for large, nonlinear, multidisciplinary systems of equations. Method efficacy was demonstrated for two simplified models: a typical-section airfoil with nonlinear structural coupling and a nonlinear panel in high-speed flow. The cyclic method was verified to maintain second-order temporal accuracy, yield converged limit cycles in about 10 Newton iterates, and provide precise estimates of cycle frequency. This method was projected onto a low-order space using a set of variables governing the amplitudes of empirically derived modes, which were computed with the proper orthogonal decomposition. In this reduced order form, the cyclic Jacobian was greatly compressed, allowing accurate limit cycle solutions to be very efficiently computed.The U.S. Governments right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

On the Investigation of Some Parameter Identification and Experimental Modal Filtering Issues for Nonlinear Reduced Order Models

This paper discusses modal filtering of experimental data and the corresponding identification of linear and nonlinear parameters in reduced order space. Specifically, several experimental configurations will be discussed in order to provide insight into such identification issues as spatial discretization, observability, and the linear independence of the assumed filter or basis. The two experiments considered herein represent different measurement configurations of the same clamped–clamped beam. First, asymmetric inertial loading via asymmetric sensor location was considered, while the second scenario presents a symmetric sensor configuration. Several important conclusions can be drawn from the two experimental scenarios. First, by asymmetrically loading the beam, a corresponding asymmetric beam mode was excited yet not observable. In the second scenario, the symmetric distribution of sensors minimized the impact of the respective asymmetric mode. The resulting spatial information allowed for the proper filtering of the remnants of the asymmetric mode. Nonlinear parameters in modal space as well as the underlying linear parameters were successfully identified simultaneously in both experimental scenarios, although the usefulness of the asymmetrically loaded beam was limited. Finally, successful comparisons were made between the identified reduced order model and experimental response at the beam quarter point using the symmetric case and the beam midpoint using both experimental scenarios.     

Data-based hybrid reduced order modeling for vortex-induced nonlinear fluid–structure interaction at low Reynolds numbers

Fluid–structure interaction (FSI) phenomena are of significant importance in several engineering fields. Recently developed active flow control devices regulate the FSI in order to control the dynamic response of the structure that is involved. As a first step to use active control, computationally efficient reduced-order models are required. The reduced-order models must be able to predict the nonlinear structural dynamic response given an incoming flow condition. This paper presents a computationally efficient method for the construction of a hybrid reduced-order model for FSI problems based on data obtained through high-fidelity numerical simulations. The model splits the force and the structural dynamic response into two separate blocks and uses model reduction techniques to account for the flow field information. The current model is tested on a vibrating rigid cylinder submerged in a flow at low Reynolds number regime.     

Approximate inertial manifolds of exponential order for semilinear parabolic equations subjected to additive white noise

A class of semilinear nonautonomous parabolic equations subjected to additive white noise is considered. The existence of a family of randomN-dimensional approximate inertial manifolds (AIMs) whose neighborhoods of thickness of order exp(- _N+1 ) attract exponentially in the mean all the trajectories is proved forN large enough. Here _N+1 is the (N+1)th eigenvalue of the corresponding linear problem, and and are positive constants. We also construct a sequence of AIMs which converges to the exact inertial manifold, when a spectral gap condition is satisfied. These results remain true for deterministic autonomous and nonautonomous cases.     

基于边界元方法的气动弹性降阶模型及仿真

传统气动弹性的时域计算耗费了大量时间,为了提高计算效率,本文发展了基于边界元方法的降阶模型技术。首先基于边界元方法建立非定常流场的求解模型,结合特征值分析技术建立了非定常气动力的低阶模型;然后,利用边界元方法建立了气动网格和结构网格之间的信息转换矩阵;最后将非定常气动力降阶模型和结构动力学方程联合,建立了气动弹性系统的低阶状态空间模型。将所发展的降阶模型方法应用于NACA0012翼型的非定常气动力求解中,结果表明降阶模型可以在保证原系统计算精度的同时提高了计算效率;将降阶模型技术应用到三维机翼的气动弹性响应计算中,在系统阶数仅为12阶的情况下可以得到与原系统一致的极限环响应,说明降阶模型技术在求解气动弹性问题中的巨大优势。     

基于气动力降阶模型的跨音速气动弹性稳定性分析

基于离散型输入输出差分模型,运用非定常CFD方法训练信号,然后运用最小二乘方法进行参数辨识,得到降阶的非定常气动力模型,再将该离散差分模型转换为连续时间域内的状态方程.耦合气动状态方程和结构状态方程,得到耦合系统的气动弹性状态方程.求解不同动压下状态矩阵的特征值,根据根轨迹图分析系统的稳定性特性.分析结果与直接耦合CFD/CSD方法结果相吻合,可以计算跨音速非线性气动弹性问题.其计算效率比直接耦合CFD/CSD方法提高1~2个数量级.针对Isogai wing在跨音速出现的S型颤振边界进行了较为细致的分析,阐述了该现象是由于系统诱发颤振的分支随着速度(来流动压)的提高而发生转移所导致的.