Optical response of nanosatellite BLITS measured by the Graz 2 kHz SLR system

The nanosatellite BLITS (Ball Lens In The Space) is the first object designed as a passive, spherical retroreflector of the Luneburg type, dedicated for Satellite Laser Ranging (SLR). The optical response of BLITS has been measured by the Graz 2 kHz SLR station and compared with the response of the classical retroreflector arrays (RRA) of the Low Earth Orbiting satellites such as ERS-2 and Stella. This work demonstrates that the optical response of BLITS is flat and featureless, comparable with the signature of a point-source or a flat target, and suggests that this innovative design will deliver a higher normal point (NP) accuracy (2.55 mm) than any other SLR target currently in orbit. The high reflectivity of the glassy BLITS (about 60% of the return rate from the multi-reflector Stella) is found to be decreasing by about 30% per year, probably due to the solar irradiation. Detailed analysis of the reflective half-shell demonstrates that a high return rate of SLR measurements can be achieved regardless of the incident angle of the laser beam, thus making the spherical lens a perfect successor of the classical RRA panels mounted on active satellites such as CHAMP, GOCE and GRACE.     

基于接触有限元分析的斜齿轮齿廓修形与实验

研究了基于接触有限元分析的斜齿轮精确齿廓修形设计,并进行了振动对比验证实验.在AN-SYS环境下建立了精确的斜齿轮副接触有限元分析模型,并通过有限元接触分析,以直接提取的啮合线方向综合弹性变形作为齿廓修形设计的依据,精确确定了斜齿轮副的齿廓修形量及修形设计方案;根据所确定的齿廓修形设计方案,设计并建立了台架对比实验系统...     

New Neural Network Response Surface Methods for Reliability Analysis

This article presents two new kinds of artificial neural network (ANN) response surface methods (RSMs): the ANN RSM based on early stopping technique (ANNRSM-1), and the ANN RSM based on regularization theory (ANNRSM-2). The following improvements are made to the conventional ANN RSM (ANNRSM-0): 1) by monitoring the validation error during the training process, ANNRSM-1 determines the early stopping point and the training stopping point, and the weight vector at the early stopping point, which corresponds to the ANN model with the optimal generalization, is finally returned as the training result; 2) according to the regularization theory, ANNRSM-2 modifies the conventional training performance function by adding to it the sum of squares of the network weights, so the network weights are forced to have smaller values while the training error decreases. Tests show that the performance of ANN RSM becomes much better due to the above-mentioned improvements: first, ANNRSM-1 and ANNRSM-2 approximate to the limit state function (LSF) more accurately than ANNRSM-0; second, the estimated failure probabilities given by ANNRSM-1 and ANNRSM-2 have smaller errors than that obtained by ANNRSM-0; third, compared with ANNRSM-0, ANNRSM-1 and ANNRSM-2 require much fewer data samples to achieve stable failure probability results.     

压气机进气畸变诱导叶片振动数值研究

介绍了一种考察进气畸变对压气机叶片振动及结构强度影响的流固耦合分析方法。对压气机进行全周数值模拟分析进气总压畸变下转子流场的非定常响应;并结合有限元模型分析叶片模态及振动响应,通过气动模型与结构模型的不断信息迭代实现叶片振动过程的模拟。分析表明,周向总压畸变会引起叶片气动力在周向分布的不均匀及叶片应力波动,导致压气机叶片振动,对其结构稳定性产生重要影响。     

航空发动机状态变量模型的QPSO寻优混合求解法

针对航空发动机控制和故障诊断中的状态变量模型求解存在的系数矩阵精度不高的问题,结合阶跃响应法和拟合法的基础上,提出了一种基于量子粒子群寻优（QPSO）求取发动机状态变量模型的混合求解法。QPSO优化算法求解A,C矩阵使得状态变量模型和非线性模型在动态过程具有较好的吻合,阶跃响应法求取B,D矩阵保证了模型稳态响应一致。利用混合求解法建立了某型涡轴发动机在某一稳态工作点下的小偏离状态变量模型。仿真结果表明,这种方法不仅增强了状态变量模型的求解精度,相对于单纯的拟合法缩短了求解时间,精确的状态变量模型为进一步的故障诊断和控制系统设计提供了条件。     

结冰对飞机动态响应特性的影响

结冰条件下运输类飞机的适航审定是确保飞行安全的重要保障.建立了飞机本体非线性动力学模型和不同状态的结冰模型,计算了结冰前后飞机对驾驶员控制输入指令的响应特性,并探讨了结冰对飞机爬升性能的影响.仿真结果表明,结冰会导致舵面操纵效率下降,从而引起动态响应特性的恶化,而且飞机出现不对称结冰时将严重偏离正常状态、危及飞行安全,...     

刚柔耦合状态下索杆式伸展臂多体动力学研究

索杆式伸展臂在展开过程中,其斜拉索存在大运动和大变形问题,运用传统分析方法进行仿真分析难度较大.文章基于非线性弹性理论的绝对节点坐标方法,描述了斜拉索的空间运动和变形,研究了横向框架在贮存段、消旋段、提升段和套筒外的动力学特性,实现了索-刚体组成耦合系统的多体动力学数值仿真.     

一种冷热交变环境下太阳帆应力保持方法

针对冷热交变环境导致太阳帆内部应力剧烈变化的问题,基于形状记忆合金(SMA)弹簧提出了太阳帆的张拉方案和薄膜应力保持恒定的方法,该方法利用形状记忆合金在高低温下的刚度非线性特性,有效补偿薄膜和支撑杆之间的间隙变化,以使薄膜内部应力基本保持恒定。针对六边形构型太阳帆开展了数值仿真,首先建立了太阳帆的热分析模型和力学分析模型,获取了高低温工况下的温度场。然后通过热致变形分析得到薄膜与支撑杆在高低温工况下的间隙变化,据此确定形状记忆合金弹簧的参数。最后对太阳帆在高低温工况下的薄膜内部应力进行了验证。     

Research on nonlinear model predictive control for turboshaft engines based on double engines torques matching

In order to reach a compromise between fast response control and torques matching control in double turboshaft engines, research on nonlinear model predictive control for turboshaft engines based on double engines torques matching is conducted. Meanwhile, a Nonlinear Model Predictive Control (NMPC) method is proposed, which combines the control index of the power turbine speed with torques matching of double engines creatively. In addition to the control index, the difference of output torques between each engine is also incorporated in the objective function as a penalty term to ensure constant speed control and short torques matching time. Simulation results demonstrate that relative to unilateral torques matching, the settling time of the bidirectional matching method can be reduced by nearly 30.8%. Nevertheless, compared with the bidirectional torques matching method under the cascade PID controller, the NMPC method can decrease the overshoot of the power turbine speed by 65% and reduce the matching time by 15.5% synchronously. Besides fast response control of turboshaft engines, fast torques matching control of double engines is accomplished as well.     

A double integral method for quantitative evaluation of influence on thin-walled casing response caused by bearing uncertainties

Bearings in a gas turbine engine are the key connecting components transmitting force and motion between rotors and thin-walled flexible casing. The bearing stiffness and damping of squeeze film damper (SFD) nearby bearings are easily affected by many factors, such as assembly process, load condition and temperature variation, resulting in uncertainties. The uncertainties may influence the response of the measuring point on the casing. Hence, it is difficult to carry out the fault diagnosis, whole machine balancing and other related works. In this paper, a double integral quantitative evaluation method is proposed to simultaneously analyze the influence of two uncertain dynamic coefficients on the response amplitude and phase of casing measuring points. Meanwhile, the coupling influence of stiffness and damping accompanied by dramatic changes with rotational speeds are essentially discussed. As an example, a typical engine bearing-casing system with complex dynamic characteristics is analyzed. The impact of uncertain dynamic coefficients on the unbalance response is quantitatively evaluated.