三维网格动态细化技术在切削仿真中的应用

为解决切削加工有限元仿真模型求解速度与精度难以平衡的问题,提出了一种适用于三维有限元模型的网格动态细化算法。该算法的主要功能包括网格细化区域判断、网格细化以及新旧网格物理场传递。采用Python语言对Abaqus软件进行二次开发,将该算法应用于Ti2AlNb钛合金车削加工仿真之中,并最终通过实验验证了仿真模型的准确性。与采用局部网格细化的仿真模型计算结果对比,采用网格动态细化技术的仿真模型求解切削力误差增加了7.3%,求解最大应力误差增加0.2%,求解速度提升174.2%。实现了在保证仿真计算精度的基础上,有效提高运算速度。     

基于模糊RBF网络的自适应变结构制导律设计

针对空中高速、大机动目标的拦截问题,传统的滑模变结构制导律虽然对外界干扰和参数摄动具有较好的鲁棒性,但是存在视线角速率抖振及参数不易确定等缺点.对此,在变结构控制理论的基础上,提出了三维自适应变结构制导律,将目标加速度视为外界干扰,设计了一种快速趋近律,并利用模糊RBF网络的高效自学习能力对变结构项的增益进行了在线自适应调节.仿真结果表明,该制导律能够有效削弱系统抖振,提高制导精度,并对拦截大机动目标具有很强的自适应性.     

Adaptive sensitive frequency band selection for VMD to identify defective components of an axial piston pump

The underlying study investigates single valued neutrosophic entropy based adaptive sensitive frequency band selection for variational mode decomposition(VMD) for the purpose of identifying defective components in an axial pump. The proposed methodology is applied in the following steps. First, VMD is applied for decomposing vibration signals into various frequency bands, called as modes. After computing energy of each VMD, the lower(minimum) and upper(maximum) bounds from these energy readings ...     

蜂窝状薄壁管拉伸时的收缩分析

为研究蜂窝材料拓扑结构与其整体力学性能的关系，从非平面Vertex模型的势能形式出发，结合蜂窝薄壁管拉伸时的轴对称特征，通过变分法得到了管拉伸时母线满足的控制方程，证实了边界效应是蜂窝状薄壁管受拉时产生收缩的原因，并结合控制方程的若干特解，考察了非平面Vertex模型中材料参数对管弯曲程度的影响。结果表明，非平面Vertex模型中表征夹角势强度的参数决定了材料的整体抗弯性，而距离管端最近的3层元胞是管拉伸时的主要收缩区。最后进一步探讨了蜂窝薄壁管曲率与收缩幅度之间的非线性关系，揭示了构型曲率是蜂窝材料泊松比的影响因素之一。     

A novel variable structure multi-model approach based on error-ambiguity decomposition

Model Set Adaptation (MSA) plays a key role in the Variable Structure Multi-Model tracking approach (VSMM). In this paper, the Error-Ambiguity Decomposition (EAD) principle is adopted to derive the EAD-MSA criterion that is optimal in the sense of minimizing the square error between the estimate and the truth. Consequently, the EAD Variable Structure first-order General Pseudo Bayesian (EAD-VSGPB1) algorithm and the EAD Variable Structure Interacting Multiple Model (EAD-VSIMM) algorithm are constructed. The proposed algorithms are tested in two groups of maneuvering target tracking scenarios under different modes and observation error conditions. The simulation results demonstrate the effectiveness of the EAD-VSMM approach and show that, compared to some existing multi-model algorithms, the proposed EAD-VSMM algorithms achieve more robust and accurate tracking results.     

Joint parameter and state estimation for stochastic uncertain system with multivariate skew t noises

Due to the pulse interference, measurement outliers and artificial modeling errors, the multivariate skew t noise widely exists in the real environment. However, to date, little attention has been paid to the state estimation for systems in which the process noise and the measurement noise are both modeled as the heavy-tailed and skew non-Gaussian noise. In this paper, the multivariate skew t distribution is utilized to model the heavy-tailed and skew non-Gaussian noise. Then a probabilistic gra...     

Feedback structure based entropy approach for multiple-model estimation

The variable-structure multiple-model（VSMM）approach,one of the multiple-model（MM）methods,is a popular and effective approach in handling problems with mode uncertainties.The model sequence set adaptation（MSA）is the key to design a better VSMM.However,MSA methods in the literature have big room to improve both theoretically and practically.To this end,we propose a feedback structure based entropy approach that could fnd the model sequence sets with the smallest size under certain conditions.The fltered data are fed back in real time and can be used by the minimum entropy（ME）based VSMM algorithms,i.e.,MEVSMM.Firstly,the full Markov chains are used to achieve optimal solutions.Secondly,the myopic method together with particle flter（PF）and the challenge match algorithm are also used to achieve sub-optimal solutions,a trade-off between practicability and optimality.The numerical results show that the proposed algorithm provides not only refned model sets but also a good robustness margin and very high accuracy.     

飞机简化模型水上迫降入水的数值研究

在飞机水上迫降过程中,其尾部吸力对姿态角的变化具有重要影响.基于Fluent软件,利用动网格技术、用户自定义函数(UDF)、六自由度(6DOF)模型、流体体积(VOF)模型,首先对二维圆柱、三维椭圆抛物体垂直入水以及三维平板水平划水进行数值模拟,并与试验结果对比验证模拟方法的可靠性;然后对NACA TN 2929简化飞机模型进行水上迫降数值模拟.研究发现:尾部吸力使飞机俯仰姿态角发生剧烈变化,入水初期尾部吸力产生的抬头力矩使飞机姿态角快速增加,当姿态角达到最大时,尾部吸力产生的抬头力矩很小,在重力作用下飞机姿态角快速减小.本文所采用的三维数值模拟方法能够较好地模拟飞机水上迫降过程中的吸力和姿态角变化.     

Variational Bayesian labeled multi-Bernoulli filter with unknown sensor noise statistics

It is difficult to build accurate model for measurement noise covariance in complex back-grounds. For the scenarios of unknown sensor noise variances, an adaptive multi-target tracking algorithm based on labeled random finite set and variational Bayesian (VB) approximation is pro-posed. The variational approximation technique is introduced to the labeled multi-Bernoulli (LMB) filter to jointly estimate the states of targets and sensor noise variances. Simulation results show that the proposed method can give unbiased estimation of cardinality and has better performance than the VB probability hypothesis density (VB-PHD) filter and the VB cardinality balanced multi-target multi-Bernoulli (VB-CBMeMBer) filter in harsh situations. The simulations also confirm the robustness of the proposed method against the time-varying noise variances. The computational complexity of proposed method is higher than the VB-PHD and VB-CBMeMBer in extreme cases, while the mean execution times of the three methods are close when targets are well separated.     

Influence of blade negative twist on aerodynamic performance of cycloidal propeller

In order to improve the analysis accuracy of the influence of shape parameters on the aerodynamic performance of cycloidal propeller, a set of CFD methods suitable for the simulation of the cycloidal propeller flow field based on the dynamic overset mesh and Unsteady Reynolds time average method equation were established. The characteristics of the spanwise lift distribution and surface pressure distribution in case of different negative twist were provided. The influence of the negative twist on the aerodynamic performance of cycloidal propeller was emphasized. The results showed that, the change of negative twist caused the change of azimuth for cycloidal propeller lift. The larger the absolute value of negative twist, the lower the figure of merit of the cycloidal propeller; the smaller the negative twist, the more gentle the instantaneous aerodynamic fluctuation; the influence mechanism of negative twist on the aerodynamic performance of cycloidal propeller was generated from changing the non-uniform distribution of the cycloidal propeller''s effective angle of