Modeling and Optimal Design of 3 Degrees of Freedom Helmholtz Resonator in Hydraulic System

Three degrees of freedom (3-DOF) Helmholtz resonator which consists of three cylindrical necks and cavities connected in series (neck-cavity-neck-cavity-neck-cavity) is suitable to reduce flow pulsation in hydraulic system. A novel lumped parameter model (LPM) of 3-DOF Helmholtz resonator in hydraulic system is developed which considers the viscous friction loss of hydraulic fluid in the necks. Applying the Newton’s second law of motion to the equivalent mechanical model of the resonator, closed-form expression of transmission loss and resonance frequency is presented. Based on the LPM, an optimal design method which employs rotate vector optimization method (RVOM) is proposed. The purpose of the optimal design is to search the resonator’s unknown parameters so that its resonance frequencies can coincide with the pump-induced flow pulsation harmonics respectively. The optimal design method is realized to design 3-DOF Helmholtz resonator for a certain type of aviation piston pump hydraulic system. The optimization result shows the feasibility of this method, and the simulation under optimum parameters reveals that the LPM can get the same precision as transfer matrix method (TMM).     

火星气囊气体发生器充气过程稳压仿真研究

文章对低温和常温环境下的气囊稳压充气过程的参数进行了仿真计算。主要分析计算了气囊内外壁的对流换热、囊内气体与囊壁间辐射以及水蒸气液化等传热方式的传热量。同时,计算了在不同环境温度下,气囊内气体温度、充气质量以及充气质量流率随时间的变化关系。分析结果可以为工程研制提供参考和数据支持。     

Aerodynamic Modeling and Parameter Estimation from QAR Data of an Airplane Approaching a High-altitude Airport

Aerodynamic modeling and parameter estimation from quick accesses recorder (QAR) data is an important technical way to analyze the effects of highland weather conditions upon aerodynamic characteristics of airplane. It is also an essential content of flight accident analysis. The related techniques are developed in the present paper, including the geometric method for angle of attack and sideslip angle estimation, the extended Kalman filter associated with modified Bryson-Frazier smoother (EKF-MBF) method for aerodynamic coefficient identification, the radial basis function (RBF) neural network method for aerodynamic modeling, and the Delta method for stability/control derivative estimation. As an application example, the QAR data of a civil airplane approaching a high-altitude airport are processed and the aerodynamic coefficient and derivative estimates are obtained. The estimation results are reasonable, which shows that the developed techniques are feasible. The causes for the distribution of aerodynamic derivative estimates are analyzed. Accordingly, several measures to improve estimation accuracy are put forward.     

A Prediction Method for△f0F2min of a Single Station From Interplanetary Parameters Based on Statistical Study

Using 86 CME-interplanetary shock events,the correlation between the peak values of （a） the solar wind parameters(B_z,E_y,P_dyn) and the geomagnetic indices（SYM-H,ASY-H,Kp）, （b） the coupling functions（Borovsky,Akasofu,Newell） and the geomagnetic indices,（c） the solar wind parameters/coupling functions/geomagnetic indices and the ionospheric parameter(Δf₀F_2min), are investigated.The statistical results show that in group（a）,B_{z min} and SYM-H_min have the best correlation,that in group（b）,the best correlation is between the peak values of Akasofu function (A_min) and SYM-H_min,and that in group（c）,the best correlation is between K_pmax andΔf₀F_2min. Based on the statistical results,a method for predicting f₀F₂ of a single station is attempted to be set up.The input is modified B_{z min} and the outputs are SYM-H_min andΔf₀F_2min.Then 25 CME-IPS events that caused geomagnetic storms in 1998 and 2009 are used to check the prediction method. The results show that our method can be used to predict SYM-H_min andΔf₀F_2min.     

各向异性Chaboche黏塑性本构方程隐式应力积分算法

针对各向异性Chaboche黏塑性本构方程,利用有效参数控制法推导了该方程的隐式积分算法,该算法把所有未知量都用同一个控制参数表示,并形成控制方程,从而把本构方程应力积分的问题转化成一个非线性控制方程的求解问题.该积分算法程序,与通用有限元软件Marc结合,通过单个单元对单向拉伸、循环、松弛的响应的实验数据进行了数值模拟,通过与显式算法对比,该隐式算法的稳定性和收敛性有所提高.构件的对比分析也表明隐式算法比显式算法具有较高的效率.      

一种基于迭代的多音干扰消除方案

针对正交频分复用技术(OFDM)系统的多音干扰,本文提出先通过增加频域分辨率进行多音干扰识别,再基于迭代运算逐个对多个单音干扰进行参数估计、重构和消除的方案。其中,在多音干扰识别阶段,使用Zoom FFT技术以提高频域分辨率并简化计算复杂度。然而,Zoom FFT后的降采样序列点数不一定满足2的整数次幂,对于单音干扰参数估计,此时可采用经典的基于离散傅里叶变换(DFT)的最大似然参数估计(DFT-MLE),但当采样点数太大时,DFT运算将带来很大的实现复杂度。本文在基于DFT-MLE算法基础上给出一种基于快速傅里叶变换(FFT)的单音参数估计法FFT-MLE,不仅简化了运算复杂度,而且相比DFT-MLE其估计性能有更好的鲁棒性。最后的仿真结果说明了该多音干扰消除方案的有效性。     

一种多分量chirp信号阵列检测新方法

提出了一种多分量chirp信号检测与参数估计的新方法。该方法利用天线阵列的空间特性,通过阵列平均在分数阶傅里叶域中引入加权函数来降低噪声、抑制不同源信号之间的相互干扰。和单阵元方法相比,文中方法大大提高了多分量chirp信号检测和参数估计的性能,仿真结果证明了方法的有效性。     

直升机滑油散热器动态性能分析

滑油散热器的动态特性是直升机滑油冷却系统设计的基础,使用模块化集总参数法建立了直升机滑油散热器的动态仿真模型,采用Laplace变换建立动态传递函数,结合动态仿真模拟曲线的比较以及传递函数的分析,对热侧和冷侧入口温度阶跃变化时的热侧出口温度动态响应性能进行分析,得到了影响动态性能的重要影响参数——芯体蓄热时间常数τw以及热侧温度随流动时间τ变化的时间常数hτ,从而可通过改变这两个重要影响参数来有效改变散热器以及系统的动态延迟时间.通过散热器动态实验测量,验证了模型的正确性.研究成果可有效改进散热器以及系统的动态性能,以及指导散热器与系统的优化耦合设计.     

Fast Online Approximation for Hard Support Vector Regression and Its Application to Analytical Redundancy for Aeroengines

The hard support vector regression attracts little attention owing to the overfitting phenomenon. Recently, a fast offline method has been proposed to approximately train the hard support vector regression with the generation performance comparable to the soft support vector regression. Based on this achievement, this article advances a fast online approximation called the hard support vector regression (FOAHSVR for short). By adopting the greedy stagewise and iterative strategies, it is capable of online estimating parameters of complicated systems. In order to verify the effectiveness of the FOAHSVR, an FOAHSVR-based analytical redundancy for aeroengines is developed. Experiments on the sensor failure and drift evidence the viability and feasibility of the analytical redundancy for aeroengines together with its base-FOAHSVR. In addition, the FOAHSVR is anticipated to find applications in other scientific-technical fields.     

用参数辨识法进行直升机悬停性能拓展

准确计算直升机在不同飞行状态的有效气动参数对于确定直升机飞行性能具有重要意义。然而,由于复杂的旋翼空气动力现象以及直升机状态和环境条件的变化,准确预估气动参数有较大难度。为此,采用无量纲分析法建立直升机悬停状态的数学模型,首先对参数重组,确定了几个悬停状态重要参数,包括气动参数和直升机状态参数;然后,以直-9×型直升机为例,结合实际试飞数据,提出了用最小二乘法对该模型进行参数辨识的方法;最后,通过相关性分析,确定了辨识方法的可行性,并将辨识结果有效地用于直升机悬停性能拓展。结果表明,这种利用参数辨识进行性能拓展的方法是可行的,由于辨识结果是利用实际试飞数据确定的,拓展结果具有较高的可信度。这种数据处理方法可有效减少试飞周期,节约试验成本。