一种多频多系统周跳探测与修复方法

为满足多频多系统精密单点定位（PPP）数据预处理的实际需求,提出了一种周跳探测与修复方法。针对多频多系统PPP数据处理中各卫星的信号数量不同,利用最小二乘模糊度降相关平差（LAMBDA）原理构建模糊度组合。通过仅使用相位观测值估计的倾斜电子总量（STEC）探测不敏感周跳和漏判周跳。对于周跳修复,将伪距和载波相位的观测值在历元间作差求得周跳的浮点解和协方差阵,然后应用LAMBDA算法搜索周跳整数解并进行修复。通过静态、动态以及磁暴环境下周跳探测和修复实验,验证了所提方法的有效性,多频条件下周跳修复的正确率达到100%。     

综合电离层残差和超宽巷探测和修复北斗周跳

周跳的探测与修复对于GNSS高精度定位来说至关重要。随着精密单点定位应用日益广泛,高效、可靠的非差数据周跳探测与修复方法必不可少。为了提高非差数据周跳探测的可靠性,根据北斗多频载波相位观测值的组合特性提出了一种新的非差数据周跳探测方法。该方法联合电离层残差法与Moulborne-Wuebbena超宽巷模糊度观测值(M-W)联合建立方程组,解算每个频率观测值的周跳,从而实现周跳的探测和修复。实验数据处理结果表明,这种组合方法可以探测不同的周跳,包括50周大小的大周跳、1大小周的小周跳、同时产生的两个频率的周跳以及连续周跳,并能够准确进行修复。本方法适用于静态定位与动态定位,为快速准确地探测与修复非差数据的周跳提供了新的思路。     

北斗/INS紧组合的惯性辅助三频周跳探测和修复

传统的使用伪距和相位组合进行周跳探测的方法受限于伪距精度,在多路径效应严重和载体高动态下不可靠。针对该问题,构建北斗/INS紧组合模型,利用惯性辅助北斗三频信号线性组合构造了周跳探测量,兼顾错探率和漏探率,确定探测阈值系数为2.576 8。基于卫星高度角采用正弦函数模型确定载波噪声,分析了载波噪声和卫地距误差对周跳探测和修复的影响。在此基础上选择组合量(0,-1,1),(1,3,-4),(-3,4,0)联合进行周跳探测和修复。使用车载组合导航实测数据验证周跳探测模型的效果。实验结果表明,对于模拟的密集小周跳,所有卫星错探率低于1.75%,漏探率低于0.11%,除低高度角卫星C05,所有卫星修复错误率低于0.35%。对于北斗信号中断的场景,在75 s部分中断内或18 s完全中断内都能够正确修复所有卫星的所有类型周跳。     

一种小卫星高精度自主定轨/定姿一体化新方法

基于传统小卫星对轨道和姿态参数确定采用分别计算的复杂模式,提出了一种利用地磁场和天文信息同时确定卫星轨道和姿态参数的新方法。首先通过分析小卫星轨道动力学J2模型和卫星姿态动力学模型,建立系统状态方程。其次将三轴磁强计与地磁场模型参考值的矢量作差,分析微分差值与状态变量的数学关系,建立定位/定姿观测方程。利用星敏感器提供的高精度姿态信息,建立定姿观测方程,同时利用星敏感器间接敏感地平观测折射恒星,建立定位观测方程。最后提出基于信息融合的先进滤波算法,并通过对多种导航模式进行数值仿真及结果分析,论证所设计一体化方法提高了系统定轨/定姿的精度和可靠性。     

北斗三频观测值强电离层条件下的周跳探测与修复

采用伪距相位组合和无几何相位组合作为周跳探测量,分析了无几何相位组合的漏探率和误探率,并给出了该组合的适用条件。针对强电离层条件下误探率较高的缺点,提出了采用RBF(Radial basis function)神经网络模型对一阶电离层延迟变化量进行预测,并根据预测残差判断周跳是否发生,采用电离层延迟改正的相位组合周跳估值进行周跳修复。利用电离层活跃期间的北斗三频观测数据验证所提出的算法,实验结果表明:该模型即使在大磁暴发生期间也能够准确地探测出所有周跳并正确修复,不存在不敏感周跳组合,同时误探率在0.3%以下。     

基于载噪比加权融合的异步伪卫星室内定位方法

异步伪卫星室内定位系统的钟漂会引起较大的伪距观测值误差,同时多径和室内信号传播效应会加剧时钟同步误差。针对此问题,提出了一种利用伪距双差测量值和伪卫星信号载噪比的室内融合定位方法。载噪比观测量不受时钟同步误差的影响,将伪距和载噪比在观测值域进行组合,以增加观测方程的稳定性。使用无迹卡尔曼滤波对坐标参数进行解算,进一步削弱线性化误差。利用自主研制的伪卫星系统实测数据对算法性能进行了评估,并与传统伪距双差和加权质心定位方法进行了对比,实验结果表明:融合算法的定位精度优于传统两种方法,在伪卫星几何分布较好的情况下,东方向、北方向的定位精度分别达到0.131 m、0.036 m,在伪卫星几何分布较差的情况下,东方向、北方向的定位精度分别为0.764 m、0.362 m。所提出的算法对接收机采样时间不同步和多径误差具有较好的抑制作用,且表现出良好的鲁棒性,适用于深度室内场景。     

INS辅助周跳修复以实现精密单点定位瞬时重新收敛

GNSS接收机信号极易受外界环境遮挡而完全中断,使得接收机所输出的相位观测值产生周跳,这将引起精密单点定位(PPP)模糊度参数的重新初始化,并需要十几分钟甚至更长时间的重新收敛,限制了PPP的推广应用。针对以上问题,以星间单差PPP/INS紧组合为研究基础,借助INS短期导航精度高的优势,提出一种INS辅助的周跳修复新方法。该新方法使用星间单差相位新息与星间单差电离层残差作为周跳修复量;为提高周跳修复可靠性,新方法对周跳修复量进行了质量控制并设置了多重修复准则。两组车载组合导航实验表明:与不修复相比,周跳修复后可实现PPP瞬时重新收敛,定位精度提升至20 cm以内;但需注意,周跳修复成功率会随着GNSS信号中断时间的延长而降低。     

北斗站间单差载波相位差分定位方法

针对传统基于站间-星间双差载波相位差分存在放大观测量随机误差,使得卫星间存在耦合,导致参考星变换时产生整周跳跃的问题,提出一种基于站间单差模型的精密定位算法,通过站间单差消除大气延迟、卫星端等偏差,保持了卫星间观测量的独立性,并结合双钟差模型以保持载波相位的整周特性。通过北斗实测车载实验进行了验证,测试结果表明,基于改进的单差模型定位精度达到厘米级,模糊度固定率达到90%以上。     

一种Galileo五频周跳探测与修复新方法

提出联合四组无几何相位组合和一组无几何伪距相位组合探测Galileo五频周跳,针对上述组合修复周跳过程中遇到的法方程病态性问题,提出一种基于条件数最小原则优选组合系数的策略.首先,按照波长较长、电离层延迟放大系数和周跳探测量标准差较小的标准选出部分适合的周跳探测组合,这些组合均满足有良好的周跳探测性能,之后依据条件数最...     

联合多普勒的载波相位精密测速方法

针对传统载波相位时间差分测速方法未考虑观测噪声以及周跳因素影响测速可靠性的问题,提出一种联合多普勒的载波相位精密测速方法。首先通过多普勒观测量辅助消除周跳干扰,之后利用无周跳的载波相位时间差分作为观测量,并利用Kalman滤波抑制观测噪声对速度测量的影响。静态和动态的测试结果表明,所提方法能有效消除周跳干扰,抑制高频噪声影响,静态测速精度达1 mm/s,动态测速精度优于2 cm/s,提高了测速精度和可靠性。     

A damage directional constitutive model for Mullins effect with permanent set and induced anisotropy

A stress softening, commonly known as the Mullins effect, is observed usually in filled rubberlike materials after the first load. Experimental observations have shown that the Mullins effect induces a permanent set and some anisotropy. In order to account for these two features, a strain energy density is proposed, which is based on material directions and coupled with a theory for network alteration. The constitutive law is based on a macromolecular approach, and the network alteration theory is motivated physically. The model has been compared to experimental data successfully.     

Identification of Parameters of Short-Time Creep of Plexiglas By Means of Studying Decaying Flexural Vibrations of Test Samples

A technique for identification of hereditary properties under conditions of short-time creep of Plexiglas is developed. The technique is based on experimental determination of shifting of the center of decaying flexural vibrations of vertically aligned test samples after their preliminary maintaining in a static bent state. Mathematically, the technique is based on using the finite element method and integral equations of the theory of hereditary viscoelasticity with the Koltunov–Rzhanitsyn hereditary kernel. An object function is constructed for identification of rheological parameters of this kernel. The minimum of this function is found by the direct search method, which does not require the function gradient to be known. The hereditary kernel of Plexiglas averaged on the basis of data for several test samples is obtained as a function of time.     

Development of an Internal Bone Remodelling Theory and Applications to Some Problems in Orthopaedic Biomechanics*

Bone tissue is a porous, heterogeneous and anisotropic material, which adapts its mechanical properties depending of the local stress level. This evolutive behaviour of the bone is normally known as bone remodelling. In this work, a bone-remodelling theory, based on the principles of continuum damage mechanics, is presented. The corresponding mathematical formulation has been implemented in a finite element code in order to predict the bone response after implantation of a prosthesis or fixation. Although the present model is not based on experimental verification, the model predicts important qualitative experimental results, being still necessary to test against experimental/clinical work. The main aim of this paper has been, therefore, the qualitative study of the long-term bone evolution, especially of the human femur when different types of implants are employed. A comparative analysis between two widely used hip prostheses (the Exeter and the SHP), has been performed. We have also studied the treatment of proximal femoral fractures by means of extramedullary and intramedullary implants.     

A comparison of two formulations of the fin efficiency for straight fins

A formulation of the fin efficiency based on Newton’s law of cooling is compared with a formulation based on a ratio of heat transferred from the fin surface to the surrounding fluid to the heat conducted through the base.The first formulation requires that the solution of the nonlinear fin equations for constant heat transfer coefficient and constant thermal conductivity is known,whilst the second formulation of the fin efficiency requires only that a first integral of the model equation is known.This paper shows the first formulation of the fin efficiency contains approximation errors as only power series and approximate solutions to the nonlinear fin equations have been determined.The second formulation of the fin efficiency is exact when the first integrals can be determined.     

Bounds and estimates for elastic constants of random polycrystals of laminates

In order to obtain formulas providing estimates for elastic constants of random polycrystals of laminates, some known rigorous bounds of Peselnick, Meister, and Watt are first simplified. Then, some new self-consistent estimates are formulated based on the resulting analytical structure of these bounds. A numerical study is made, assuming first that the internal structure (i.e., the laminated grain structure) is not known, and then that it is known. The purpose of this aspect of the study is to attempt to quantify the differences in the predictions of properties of the same system being modelled when such internal structure of the composite medium and spatial correlation information is and is not available.     

Mesh deformation based on artificial neural networks

In the article a new mesh deformation algorithm based on artificial neural networks is introduced. This method is a point-to-point method, meaning that it does not use connectivity information for calculation of the mesh deformation. Two already known point-to-point methods, based on interpolation techniques, are also presented. In contrast to the two known interpolation methods, the new method does not require a summation over all boundary nodes for one displacement calculation. The consequence of this fact is a shorter computational time of mesh deformation, which is proven by different deformation tests. The quality of the deformed meshes with all three deformation methods was also compared. Finally, the generated and the deformed three-dimensional meshes were used in the computational fluid dynamics numerical analysis of a Francis water turbine. A comparison of the analysis results was made to prove the applicability of the new method in every day computation.     

A comparison of different approaches to detect the transitions from regular to chaotic motions in SMA oscillator

Meccanica - It is well known that dynamical systems that include devices based on shape memory alloys (SMA) can exhibit a wide spectrum of responses: periodic, quasi-periodic and chaotic motions....     

A new method for computing the uniaxial modulus of articular cartilages using modified inhomogeneous triphasic model

It is well known that subtle changes in structure and tissue composition of articular cartilage can lead to its degeneration. The present paper puts forward a modified layered inhomogeneous triphasic model with four parameters based on the inhomogeneous triphasic model proposed by Narmoneva et al. Incorporating a piecewise fitting optimization criterion, the new model was used to obtain the uniaxial modulus Ha, and predict swelling pattern for the articular cartilage based on ultrasound-measured swelling strain data. The results show that the new method can be used to provide more accurate estimation on the uniaxial modulus than the inhomogeneous triphasic model with three parameters and the homogeneous mode, and predict effectively the swell- ing strains of highly nonuniform distribution of degenerated articular cartilages. This study can provide supplementary information for exploring mechanical and material properties of the cartilage, and thus be helpful for the diagnosis of osteoarthritis-related diseases.     

计算特征向量摄动量的混合基展开法

在结构修改和模型校正中，模态展开法是计算特征向量摄动量的常用方法之一，但当高阶模态被截断时，它会带来很大的截断误差。本文利用已知的有限阶模态，构造了Ｎ维欧氏空间的一个新基－混合基，并将特征向量的摄动量在新基上展开来计算特征向量的一、二阶 摄动量。该方法使得不管截模态个数的多少，其精度总与全模态展开法相同，且计算量都远少于全模记展开法；与改进的部分民开法相比，本方法不要求所截留的模态边连续的低阶模态