基于Kriging形函数的线性时变结构模态参数辨识

近年来,对航空航天飞行器随时间变化的动力学特性研究需求越来越迫切。仅输出参数化时域的时变时间序列模型以其结构简约、精度高且跟踪能力强而成为研究热点,尤其是泛函向量时变自回归(FS-VTAR)模型已经得到了广泛应用。然而传统的FS-VTAR模型在保证其辨识优势的同时却需要针对不同时变结构选择合适的基函数形式及较高的基函数阶数,该过程相当复杂且耗时。本文借鉴无网格法中移动最小二乘(MLS)法构造形函数的思想,提出一种基于Kriging形函数的线性时变结构模态参数辨识方法。该方法首先引入自适应于辨识信号的Kriging形函数;再把时变系数在形函数上线性展开,利用最小二乘(LS)法得到形函数的展开系数;最后把时变模型特征方程转换为广义特征值问题提取出模态参数。利用时变刚度系统非平稳振动信号验证该方法,结果表明:基于Kriging形函数的FS-VTAR模型相比于传统的FS-VTAR模型能有效地避免基函数形式的选择和较高的基函数阶数,且精度相当;相比于移动最小二乘法能有效地解决其数值条件问题且具有更高的模态参数辨识精度。     

孔壁通透率对平面附壁射流的影响

本文研究了不同壁面通透率对平面附壁射流动态特性的影响。实验结果表明孔壁减弱、甚至消除了流场中的低频摆动现象。随着孔壁通透率的增加,射流时均附壁点向下游逐渐移动,射流和壁面之间的回流区长度逐渐增大,而射流内侧剪切层内的涡旋与壁面之间的相互作用减小,壁面压强脉动强度变小,附壁射流的动态特性逐渐向自由射流转化。当孔壁通透率为40％左右时,射流与二维平面自由射流类似。距离射流出口不同位置上的壁面脉动压强之间的互谱表明,当孔壁通透率增大以后,射流内侧剪切层中的旋涡向下游传播距离变得更长,传播速度加快,这说明低孔壁通透率情况下的附壁射流中存在的低频摆动现象阻碍了剪切层高频旋涡向下游的发展。     

Nonlinear relative position control of precise formation flying using polynomial eigenstructure assignment

A nonlinear relative position control algorithm is designed for spacecraft precise formation flying. Taking into account the effect of J₂ gravitational perturbations and atmospheric drag, the relative motion dynamic equation of the formation flying is developed in a quasi-linear parameter-varying (QLPV) form without approximation. Base on this QLPV model, polynomial eigenstructure assignment (PEA) is applied to design the controller. The resulting PEA controller is a function of system state and parameters, and produces a closed-loop system with invariant performance over a wide range of conditions. Numerical simulation results show that the performance can fulfill precise formation flying requirements.     

拉压、扭转载荷下铸铝合金的亿周疲劳性能研究

应用超声疲劳试验机对铸铝合金2-AS5U3G-Y35在扭转和拉压循环载荷下进行了超高周疲劳性能测试.介绍了超声扭转疲劳试验装置的设计.应用35 Hz常规疲劳试验机和20 kHz的超声疲劳试验机完成应力比R=-1的拉压、扭转疲劳试验,进而研究不同载荷条件、加载频率对铸铝合金超高周疲劳性能的影响.S-N曲线显示,铝合金在105～1010疲劳周次间仍发生疲劳断裂,不存在疲劳极限.断口分析表明,在超高周循环拉压载荷下,疲劳裂纹常萌生于试样次表面材料内部缩孔.与循环拉压载荷下的疲劳断裂机理不同,在循环扭转载荷下疲劳裂纹主要萌生于试样表面,疲劳断裂面为一种典型的沿试样轴向45°的螺旋面,即沿最大主应力平面断裂.扭转疲劳断面清晰的剪切条带表明扭转疲劳断裂实质上是剪切断裂.     

照射系统故障树的建造及BITE检测点的设置

遵循ＧＪＢ７６８．１提供的方法。以某型雷达为例，探索建造照射系统故障树的方法，阐明取顶事件的角度，故障定义，建树假设等问题，并对其ＢＩＴＥ检测点的设置作了评述。     

片梭织机卷取辊涂布金刚砂的研制

介绍了片梭织机卷取辊涂布金刚砂的制造工艺，并对制造工艺进行了讨论。     

A biophysical model for estimating the frequency of radiation-induced mutations resulting from chromosomal translocations.

Gene mutations can be induced by radiation as a result of chromosomal translocations. A biophysical model is developed to estimate the frequency of this type of mutation induced by low-LET radiation. Mutations resulting from translocations are assumed to be formed by misrejoining of two DNA double strand breaks (DSB), one within the gene and one on a different chromosome. The chromosome containing the gene is assumed to occupy a spherical territory and does not overlap spatially with other chromosomes. Misrejoining between two DSB can occur only if the two DSB are closer than an interaction distance at the time of their induction. Applying the model to mutations of the hprt gene induced in G0 human lymphocyte cells by low-LET radiation, it is calculated that mutations resulting from translocations account for about 14% of the total mutations. The value of the interaction distance is determined to be 0.6 micrometers by comparing with the observed frequency of translocations in the X-chromosome.     

数据结构课程教学改革实践与探索

数据结构课程教学的突出难点是知识的抽象性和动态性,传统的以教师为主体的教学模式和单一的教学方法难以克服教学中存在的问题:概念抽象、算法繁多、理论知识与实际应用脱节。实践表明以学生为主体的现代教学模式,及基于此模式下的多种教学方法应用的课程教学改革,能提高学生的学习兴趣和主动性,有利于提高学生的编程能力和解决实际问题的能力。