一种用于陀螺随机漂移预测的多尺度混合建模方法

针对陀螺随机漂移时间序列由于非平稳和非线性造成单一预测模型难以准确跟踪其变化趋势的问题,提出了一种基于集合经验模态分解(EEMD)和灰色极端学习机(GELM)的多尺度混合建模方法。首先,利用集合经验模态分解将随机漂移时间序列按照频率高低分解为多个本征模式分量和一个余量;然后针对不同类型时频特性分量选择合适激活函数和隐层神经元数目的GELM分别进行预测;最后,以等权相加的方式得到最终预测结果。将该方法用于某型激光陀螺随机漂移预测中,仿真结果表明:混合预测模型能够准确预测陀螺随机漂移,预测精度比残差GM(1,1)和GELM预测模型分别提高了33.43%和23.47%,可为激光陀螺的漂移补偿、故障预报和可靠性诊断提供依据。     

基于小波最小二乘支持向量机的加速度计温度建模和补偿

针对环境温度影响加速度计测量精度的问题,给出了温度对石英挠性加速度计零偏和标度因数的影响机理,提出采用小波最小二乘支持向量回归建立石英挠性加速度计零偏和标度因数的温度模型的方法。为了验证模型的有效性,进行了多个温度点下的参数标定试验,所获取的各温度点下的石英挠性加速度计零偏和标度因数作为小波最小二乘支持向量机模型的训练数据;将石英挠性加速度计固定在某一位置进行了升温试验,通过对比未进行温度补偿、最小二乘温度补偿和小波最小二乘支持向量回归温度补偿下石英挠性加速度计的输出,计算结果表明采用小波最小二乘支持向量机补偿后的石英挠性加速度计的测量精度最高。     

基于微粒群算法优化支持向量机的加速度计静态模型辨识

针对加速度计静态模型采用线性近似模型辨识存在较大误差的问题,利用支持向量回归在小样本、非线性及高维特征空间中具有很好的推广能力的优点,提出了一种利用支持向量回归进行加速度计静态模型辨识的方法.为了避免随机试凑法识别支持向量回归参数费时的问题,采用高效的并行搜索算法-微粒群算法进行支持向量回归参数优化.利用精密光学分度头对石英挠性加速度计进行了12位置静态翻滚试验,试验结果表明所提方法可以精确地对石英挠性加速度计静态模型进行辨识,其模型精度比最小二乘辨识法的模型精度提高一倍以上.     

一种基于多尺度和改进支持向量机的光纤陀螺温度漂移建模与补偿方法

为了提升光纤陀螺温度漂移模型建模的准确性及补偿的效果,提出了一种基于改进支持向量机的多尺度建模和回归方法。首先分析了造成光纤陀螺温度漂移的关键因素,给出了建模的属性参数和温度试验。然后根据经验模态分解得到的本征模态函数排列熵的变化趋势,得出了回归精度和熵之间的变化关系,进而提出了基于信号分解的多尺度回归方法。为了提高上述多尺度回归算法的适应性,在传统支持向量机的基础上,提出了基于组合核函数的支持向量机回归算法,以适应不同特性的回归数据集。为了进一步提高回归精度,基于降低回归数据复杂度的分段回归思想,在上述多尺度回归的基础上提出了双-多尺度回归,并验证了方法的有效性。最后,将提出的算法以实际的光纤陀螺温度漂移数据进行验证,结果表明,相比于传统的支持向量机和反向传播神经网络具有更好的回归精度,温度漂移模型也更加精确,以均方误差指标为例,回归精度提升了两个数量级。     

基于EEMD和SVR的多自由度结构状态趋势预测

由于工程结构的复杂性和引起结构损伤原因的不确定性,结构早期微弱和潜在的损伤难以识别和预测。为此提出了基于聚类经验模式分解(EEMD)和支持向量机回归(SVR)的结构健康状态趋势预测方法。首先对多自由度结构渐进损伤的加速度振动信号进行聚类经验模式分解(EEMD);再进行希尔伯特变换(HT)计算瞬时频率;然后用回归支持向量机对反映结构健康状态的瞬时频率进行趋势预测。详细分析了各种参数对回归和预测精度的影响,提出了这些参数的选用方法和一般原则。研究表明:该方法具有训练样本少的特点;在采用二阶多项式核函数、回归步长m=3~5、误差惩罚因子C=100、敏感因子ε=0.01时,可以准确地和高精度地预测结构状态趋势,预测精度达到0.24781%。     

激光陀螺捷联惯导系统参数稳定性与外场自标定

惯导系统参数稳定性是决定系统精度的重要因素。基于激光陀螺捷联惯导系统参数稳定性统计分析,建立了适合激光陀螺捷联惯导系统外场自标定的加速度计组件误差参数模型。以惯性组合转动后重新调平的水平姿态修正量以及静态下重力测量误差为观测量,不依赖外界方向姿态转角等基准信息,实现了加速度计组件主要误差参数在外场条件下的自标定,并给出了标定参数的修正方法。实验表明,常温下加速度计组件的标定参数发生明显变化,采用外场标定方法可对其进行修正,相应的水平姿态最大误差由65″减小到10″。该方法标定精度好,标定时间短,操作简便,且对基座不稳造成的瞬时姿态小扰动影响有抑制能力。     

钢-混凝土混合框架结构多尺度分析及其建模方法

多尺度计算是保证计算精度的同时最大限度降低计算代价的有效途径,在众多学科领域和工程问题中都得到了应用.在结构有限元多尺度分析领域,要解决的一个关键问题是如何实现局部微观模型与宏观结构模型之间的共同工作.为实现精细有限元模型在植入宏观结构模型时不同尺度模型界面的变形协调,提出有限元微观模型与宏观模型的界面连接方法,给出了轴向、横向和转角的约束方程.通过编制用户子程序,使该方法在有限元软件中得以实现,并通过简单的圆柱筒算例,对界面连接的合理性进行了验证.最后基于多尺度建模方法和复杂混合结构节点的精细模型,给出了钢-混凝土混合框架结构多尺度弹塑性时程分析的应用实例,结果表明多尺度计算可较好模拟节点的复杂边界条件.本文建议的界面连接方法可有效实现不同尺度模型界面的变形协调,为工程结构进行多尺度提供了条件.     

石英挠性加速度计温度建模和补偿

为降低环境温度对石英挠性加速度计测量精度的影响,从工程应用角度设计了加速度计温度建模试验环境和试验方法.为加速度计设计独立的温控装置,验证了加速度计温度特性具有重复性的基础上,在多个温度点下采用四位置翻滚试验对加速度计进行标定,利用线性拟合方法建立了加速度计零偏和标度因数的温度模型.应用该模型对加速度计进行温度补偿后,可使加速度计的测量稳定性精度提高5.55倍.将所建温度模型应用于捷联式惯性导航系统中,可有效提高系统的导航精度.     

Multi-scale modeling of grouted sand behavior

The mechanical properties of sand: stiffness, cohesion and, to a less extent, friction angle can be increased through the process of grouting. A constitutive model adapted for cohesive-frictional materials from a homogenization technique which allowed us to integrate constitutive relations at the grain level has been developed to obtain constitutive equations for the equivalent continuous granular medium. A representative volume was obtained by mobilizing particle contacts in all orientations. Thus, the stress–strain relationship could be derived as an average of the behavior of these local contact planes. The local behavior was assumed to obey a stress-dependent elastic law and Mohr–Coulomb’s plastic law. The influence of the cement grout was modeled by means of adhesive forces between grains in contact, which were added to the contact forces created by an external load. The intensity of these adhesive forces is a function of nature and amount of grout present inside the material and can be reduced due to a damage mechanism at the grain contact during loading. In this paper, we present several examples of simulation which show that the model can reproduce with sufficient accuracy the mechanical improvement induced by grouting as well as the damage of the grain cementation during loading.     

Multi-scale modeling of hemodynamics in the cardiovascular system

The human cardiovascular system is a closedloop and complex vascular network with multi-scaled heterogeneous hemodynamic phenomena. Here, we give a selective review of recent progress in macro-hemodynamic modeling, with a focus on geometrical multi-scale modeling of the vascular network, micro-hemodynamic modeling of microcirculation, as well as blood cellular, subcellular,endothelial biomechanics, and their interaction with arterial vessel mechanics. We describe in detail the methodology of hemodynamic modeling and its potential applications in cardiovascular research and clinical practice. In addition,we present major topics for future study: recent progress of patient-specifi hemodynamic modeling in clinical applications, micro-hemodynamic modeling in capillaries and blood cells, and the importance and potential of the multi-scale hemodynamic modeling.     

Multi-scale modeling of tensile behavior of carbon nanotube-reinforced composites

A multi-scale representative volume element (RVE) for modeling the tensile behavior of carbon nanotube-reinforced composites is proposed. The RVE integrates nanomechanics and continuum mechanics, thus bridging the length scales from the nano- through the mesoscale. A progressive fracture model based on the modified Morse interatomic potential is used for simulating the behavior of the isolated carbon nanotubes and the FE method for modeling the matrix and building the RVE. Between the nanotube and the matrix a perfect bonding is assumed until the interfacial shear stress exceeds the corresponding strength. Then, nanotube/matrix debonding is simulated by prohibiting load transfer in the debonded region. Using the RVE, a unidirectional nanotube/polymer composite was modeled and the results were compared with corresponding rule-of-mixtures predictions. A significant enhancement in the stiffness of the polymer owing to the adding of the nanotubes is predicted. The effect of interfacial shear strength on the tensile behavior of the nanocomposite was also studied. Stiffness is found to be unaffected while tensile strength to significantly decrease with decreasing the interfacial shear strength.     

激光陀螺捷联系统高精度加速度计非线性模型参数标定

为克服激光陀螺捷联系统内减振变形引入的加速度计测量误差,建立以陀螺敏感轴为约束的IMU机体坐标系。针对零偏稳定性优于5×10?6g的高精度加速度计非线性项误差不可忽视的特点,提出加速度计非线性测量模型。基于角位置精度为5″的三轴转台,采取最小二乘分步辨识的思想,借助线性化方法,首先正交多位置转台转动辨识出加速度计的二次项系数,再倾斜转台多位置辨识出加速度计的交叉耦合项系数。实验结果表明,转台正交位置时,基于非线性模型的加速度计重力值测量误差的标准差减小至线性模型的9.38%,且3次实验得出的由模型二次项系数引入的测量误差的最大标准差为8.53×10?7g;转台倾斜位置时,基于非线性模型的加速度计重力值测量误差的标准差减小至线性模型的31.41%,且3次实验得出的由模型交叉耦合项系数引入的测量误差的最大标准差为1.14×10?6g,从而实现高精度加速度计的精确标定。     

Multi-scale constitutive modeling of the small deformations of semi-crystalline polymers

A multi-scale constitutive model for the small deformations of semi-crystalline polymers such as high density Polyethylene is presented. Each macroscopic material point is supposed to be the center of a representative volume element which is an aggregate of randomly oriented composite inclusions. Each inclusion consists of a stack of parallel crystalline lamellae with their adjacent amorphous layers.Micro-mechanically based constitutive equations are developed for each phase. A viscoplastic model is used for the crystalline lamellae. A new nonlinear viscoelastic model for the amorphous phase behavior is proposed. The model takes into account the fact that the presence of crystallites confines the amorphous phase in extremely thin layers where the concentration of chain entanglements is very high. This gives rise to a stress contribution due to elastic distortion of the chains. It is shown that the introduction of chains’ elastic distortion can explain the viscoelastic behavior of crystalline polymers. The stress contribution from elastic stretching of the tie molecules linking the neighboring lamellae is also taken into account.Next, a constitutive model for a single inclusion considered as a laminated composite is proposed. The macroscopic stress-strain behavior for the whole RVE is found via a Sachs homogenization scheme (uniform stress throughout the material is assumed).Computational algorithms are developed based on fully implicit time-discretization schemes.     

力反馈式加速度计动态特性分析及重要参数选择

力反馈式微机械加速度计闭环系统的静电反馈力可以等效成一个与反馈电压成正比的负反馈力和一个与其平方成正比的负刚度,这使得加速度输入不同时,可以等效成不同参数的线性系统.首先,通过系统的等效开环数学模型的分析,提出静电反馈力的负刚度给整个系统带来的影响;然后在保证系统稳定性和其它性能的同时,以满足整个量程内的动态性能指标为目的,提出校正方案以及机械刚度的取值;接着对校验方案以及所选取参数进行了稳定性仿真和动态特性仿真;最后通过不同刚度和校正参数的两个加速度计的对比实验证明:适当提高系统机械刚度并合理选择校正参数能够在几乎不影响系统阈值的情况下提高系统的动态特性和稳定性.     

Multi-scale plasticity modeling: Coupled discrete dislocation and continuum crystal plasticity

A hierarchical multi-scale model that couples a region of material described by discrete dislocation plasticity to a surrounding region described by conventional crystal plasticity is presented. The coupled model is aimed at capturing non-classical plasticity effects such as the long-range stresses associated with a density of geometrically necessary dislocations and source limited plasticity, while also accounting for plastic flow and the associated energy dissipation at much larger scales where such non-classical effects are absent. The key to the model is the treatment of the interface between the discrete and continuum regions, where continuity of tractions and displacements is maintained in an average sense and the flow of net Burgers vector is managed via “passing” of discrete dislocations. The formulation is used to analyze two plane strain problems: (i) tension of a block and (ii) crack growth under mode I loading with various sizes of the discrete dislocation plasticity region surrounding the crack tip. The computed crack growth resistance curves are nearly independent of the size of the discrete dislocation plasticity region for region sizes ranging from to . The multi-scale model can reduce the computational time for the mode I crack analysis by a factor of 14 with little or no loss of fidelity in the crack growth predictions.