Method of adaptive PLL bandwidth adjustment without phase slipping

In a system based on the phase lock loop（PLL）, a trade-off must be made between the tracking precision and the dynamic performance if constant parameters are adopted. To overcome this drawback, a new method called no phase slipping adaptive bandwidth（NPS-AB） is proposed, which can adjust the loop bandwidth adaptively for different working conditions. As a result, both the tracking precision and the dynamic performance can be achieved concurrently. NPS-AB has two features to keep the loop stable： one is the capability of quick response to dynamics; the other is a series of additional constraints when the bandwidth is switched. Compared with other methods, there is no phase slipping during the adjustment process for NPS-AB. The phase integer ambiguity can be avoided and the phase value is kept valid. It is meaningful for carrier ranging systems. Simulation results show that NPS-AB can deal with sudden dynamics and keep the pseudo-range value stable in the entire dynamic process.

Grain-scale Stress and GND Density Distributions around Slip Traces and Phase Boundaries in a Titanium Alloy

For TA15 titanium alloy, slip is the dominant plastic deformation mechanism because of relatively high Al content. In order to reveal the grain-scale stress field and geometrically necessary dislocation（GND） density distribution around the slip traces and phase boundaries where the slip lines are blocked due to Burgers orientation relationship（OR） missing. We experimentally investigated tensile deformation on TA15 titanium alloy up to 2.0% strain at room temperature. The slip traces were observed and identified using high resolution scanning electron microscopy（SEM） and electron backscatter diffraction（EBSD） measurements. The grain-scale stress fields around the slip traces and phase boundaries were calculated by the cross-correlationbased method. Based on strain gradient theories, the density of GND was calculated and analyzed. The results indicate that the grain-scale stress is significantly concentrated at phase/grain boundaries and slip traces. Although there is an obvious GND accumulation in the vicinity of phase and subgrain boundaries, no GND density accumulation appears near the slip traces.

Velocity Slip and Interfacial Momentum Transfer in the Transient Section of Supersonic Gas-Droplet Two-Phase Flows

Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for super-sonic two-phase (gas-droplet) flow in the transient section inside and outside a Laval jet(L J). The initial velocity slipbetween gas and droplets causes an interfacial momentum transfer flux as high as (2.0-5.0) × 104 Pa. The relaxationtime corresponding to this transient process is in the range of 0.015-0.090 ms for the two-phase flow formed insidethe LJ and less than 0.5 ms outside the LJ. It demonstrates the unique performance of this system for application tofast chemical reactions using electrically active media with a lifetime in the order of 1 ms. Through the simulationsof the transient processes with initial Mach number Mg from 2.783 to 4.194 at different axial positions inside theLJ. it is found that Mg has the strongest effect on the process. The momentum flux increases as the Mach numberdecreases. Due to compression by the shock wave at the end of the L J, the flow pattern becomes two dimensionaland viscous outside the LJ. Laser Doppler velocimeter (LDV) measurements of droplet velocities outside the LJ arein reasonably good agreement with the results of the simulation.

Deformation of a two-phase medium due to a long buried strike-slip fault

The aim of the present paper is to obtain the two-dimensional deformation of a two-phase elastic medium consisting of half-spaces of different ri- gidities in welded contact due to a buried long strike-slip fault. The solution is valid for arbitrary values of the fault-depth and the dip angle. The effect of fault-depth on the displacement and stress fields for different values of dip angle has been studied numerically. It is found that the displacement field varies significantly for a buried fault from the corresponding displacement field for an interface-breaking fault. The contour maps showing the stress field for various dip angles for buried and interface-breaking fault have been plotted. It has been observed that the stress field varies significantly for a buried fault from the corresponding stress field for an interface-breaking fault.

Particle modulations to turbulence in two-phase round jets

The particle modulations to turbulence in round jets were experimentally studied by means of two-phase velocity measurements with Phase Doppler Anemometer （PDA）. Laden with very large particles, no significant attenuations of turbulence intensities were measured in the farfields, due to small two-phase slip velocities and particle Reynolds number. The gas-phase turbulence is enhanced by particles in the near-fields, but it is significantly attenuated by the small particles in the far-fields. The smaller particles have a more profound effect on the attenuation of turbulence intensities. The enhancements or attenuations of turbulence intensities in the far-fields depends on the energy production, transport and dissipation mechanisms between the two phases, which are determined by the particle prop- erties and two-phase velocity slips. The non-dimensional parameter CTI is introduced to represent the change of turbulence intensity.

优选小波神经网络在周跳探测与修复中的应用

北斗导航定位过程中,传统的周跳探测与修复方法缺乏检验环节,无法保证修复结果的可靠性。为此,提出了一种级联式小波变换结合NARX神经网络多步循环预测修复的方法处理周跳问题。该方法通过构造载波相位双差模型检验量,探测周跳发生历元,采用NARX神经网络预测方法修复周跳,利用优选小波基函数进行周跳修复效果检验。实验证明,相较于经验模态分解和变分模态分解等模态分解法,优选小波神经网络周跳探测与修复方法可用于小周跳探测并判断出周跳正负性;构造的NARX神经网络周跳修复模型,解决了普通神经网络模型和传统多项式拟合法容易造成的二次奇异值问题。相较于长短期记忆(LSTM)和门控循环单元(GRU)深度学习神经网络模型,周跳预测精度分别提高了45.2%和55.9%。

实时周跳探测与修复的MGF周跳解算方法的改进

周跳的探测和修复是基于载波相位高精度定位的关键技术之一。基于改进的几何无关相位组合MGF方法具有直接分离不同频率上的周跳,对高频数据中较小的周跳实现有效探测,探测速度远快于TurboEdit法等优点。但MGF法无法探测4周以上的周跳,并对低采样率和低卫星高度角下的数据进行周跳探测时,会选取错误的周跳备选值作为周跳检验量从而造成周跳的误判。针对MGF法所存在的问题,通过联合相位减伪距法PRP法,构建新的周跳备选值判断方程,并对MGF法的周跳检验量进行二次历元间差分STMGF,组成PRP-STMGF周跳探测组合。PRP-STMGF周跳探测组合能够探测任意周的周跳,与TurboEdit法相比,修复时无需分离周跳,直接对PRP-STMGF法的周跳检验量进行四舍五入即可确定出正确的周跳值,且适用于低采样率和低卫星高度角下的实时周跳探测与修复。最后通过北斗双频实测数据进行实验验证,结果表明,PRP-STMGF周跳探测组合,避免了MGF法选取错误周跳备选值的问题,相较于TurboEdit法不仅低延时,准确率高,且适用于不同采样率和低卫星高度角下周跳探测与修复。

螺旋管内天然气冷凝流动传热数值模拟

针对螺旋管内天然气混合工质冷凝过程,在Lee模型的基础上,引入温度滑移因子,提出一种变温相变新模型,分别用新模型和Lee模型进行不同压力工况下的冷凝流动换热模拟。结果表明,新模型计算得到的温度沿流动方向下降很明显,反映了天然气温度滑移的影响,可以更好地反映出实际天然气冷凝过程中的物性变化,气液两相分布图中可明显观测到二次流扰动现象。为了同时考虑质量扩散热阻的影响,用Silver方法修正了新模型的模拟结果,修正后平均传热系数值与试验测定值的误差在10.7%~14%,预测精度优于Lee模型25%的误差精度。修正后的变温相变新模型适用于螺旋管内天然气混合工质的冷凝流动传热计算。

A NEW CRITERION FOR OCCURRENCE OF STICK-SLIP MOTION IN DRIVE MECHANISM

This paper, using Karnopp's model of friction force and phase plane method, studies the stick-slip motion of the flexible drive mechanism. It is explained that a sudden drop of friction force is the essential source of stick-slip motion when the sliding is impending. A new criterion for occurrence of stick-slip motion is established. The stick-slip region and the stable region in a parameter plane are separated by a critical parameter curve. Moreover, for the stick-slip motion of the flexible drive mechanism without viscous damping, a parameter expression is obtained. The results may be used in design of the flexible drive mechanism.

Efficient method of cycle slips detection for dual-frequency GPS data

An algorithm has been developed from various exiting techniques, that provides fully automatic cycle-slip detection at the data preprocessing stage. This algorithm, called pair linear combination, operates on undifferenced or double-differenced, dual frequency carrier phase data, and requires the sampling interval is short. Test results carried out in a variety of situations including static and kinematic modes, short and long baseline situation, and low and high data rates were presented.

Phase Behaviors in Bi-phase Simulation of Powder Segregation in Metal Injection Molding

Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe distinctly the flows of metallic powder and polymer binder. Viscous behaviors for the flows of each phase should hence be determined. The coefficient of interaction between the flows of two phases should also be evaluated. However, only viscosity of the mixed feedstock is measurable by capillary tests. Wall sticking is supposed in the traditional model for capillary tests, while the wall slip is important to be taken into account in MIM injection. Objective of the present paper is to introduce the slip effect in bi-phase simulation, and search the suitable way to determine the viscous behaviors for each phase with the consideration of wall slip in capillary tests. Analytical and numerical methods were proposed to realize such a specific purpose. The proposed method is based on the mass conservation between the capillary flows in mono-phase model for the mixed feedstock and in bi-phase model for the flows of two phases. Examples of the bi-phase simulation in MIM were realized with the software developed by research team. The results show evident segregation, which is valuable for improving the mould designs.

用于星间激光干涉测量的分频相位计辅助弱光锁相

弱光锁相是星间激光干涉测距的重要环节,通过锁相环跟踪外差干涉光信号相位.受散粒噪声、激光频率噪声等各类噪声限制,锁相环内部本地振荡器信号与外差信号间存在一定相位差,而锁相环的鉴相范围只有正负半个周期,若相位差某时刻超过鉴相范围,则本地振荡器在反馈调节下可能会进入错误的工作点,出现周跳,导致后续相位重构出错.本文提出了基于引力波探测背景的一种周跳诊断方法,在原锁相环基础上引入一个具有更大鉴相范围的辅助分频相位计,可以对锁相环是否出现周跳提供判断依据.结合已有的锁相环及噪声理论,建立了分频相位计的理论模型,以此数值模拟了分频相位计工作,模拟结果表明,分频相位计可以实现大范围鉴相,具有判断弱光锁相周跳的能力.

双频载波相位变化率与电离层残差法联合探测周跳

针对双频定位高精度数据处理过程中观测值含有周跳的问题,提出一种联合改进后的双频载波相位变化率与电离层残差的组合探测方法:首先在原始载波相位变化率法的基础上计算双频观测值的探测量,用以探测并修复大部分周跳;然后采用电离层残差作为检验量继续对双频观测值进行探测,实现对探测盲点下漏检周跳的修复。实验结果表明,该算法可以较全面、准确地探测出双频数据中存在的周跳,且探测过程较为迅速。

基于轮轨黏滑特性的地铁线路波磨趋势分析

针对地铁线路上普遍存在的波磨问题,依据实际运营情况,建立了车辆-轨道刚柔耦合数值模型,借助实测数据验证了模型的有效性.分析了直线和曲线轨道上的轮轨黏滑特性,并利用黏着系数总体离散率衡量了钢轨波磨的发生趋势,同时分析了黏滑振动的相位同步条件.结果表明:当不考虑轨面不平顺时,直线轨道轮轨界面具有发生横向黏滑振动的趋势,但振动强度相对较小;当存在短波不平顺时,直线轨道轮轨界面具有发生纵向黏滑振动的趋势,且振动强度相对较大;当存在长波不平顺时,直线轨道轮轨界面具有发生横向黏滑振动的趋势,但振动强度相对较小.对于直线无不平顺或存在长波不平顺情况,出现波磨或波磨进一步发展的原因与轮轨横向黏着系数达到饱和有关;而对于直线短波不平顺情况,波磨进一步发展的原因则与轮轨纵向黏着系数达到饱和有关.曲线轨道上内外侧轮轨均具有发生黏滑振动的趋势,且短波不平顺的存在会加剧黏滑振动强度.内侧轮轨界面纵横向黏着系数总体离散率大于外侧对应值,表明内轨更容易发生强度较大的黏滑振动,从而促使内轨波磨形成和发展.轨面固定缺陷会导致相同位置处产生同相位的钢轨磨耗,赋予同相位的周期黏滑振动,并沿着钢轨纵向发展,最终形成钢轨波磨.

一种“北斗”卫星导航系统三频周跳探测与修复方法

针对传统伪距-相位组合中伪距噪声过大的问题引入了多普勒观测值进行辅助,同时再联合无几何相位组合构成一种新的周跳探测与修复方法。在信号方面,选择B2a代替B2I,与B1I、B3I组成了“北斗”卫星导航系统(Beidou Navigation Satellite System, BDS)中定位性能更好的“北斗”三频观测组合。在选频方面,选用无几何相位系数[-1,1,0]、多普勒辅助伪距-相位系数[1,0,-1],[1,3,-4]组合进行周跳的探测。在修复方面,使用搜索法进行周跳的修复,并根据1-范数原则确保修复值的准确性。在1 s的采样率、电离层延迟稳定情况下,所提方法不仅能探测与修复出所有加入的1周在内的周跳,而且相比传统伪距-相位方法在小周跳探测方面性能更佳。

基于伪距相位组合法的三频周跳探测

【目的】载波因具有波长短的优势而被广泛应用于卫星高精度定位中,但载波数据在接收过程中易受干扰,易发生周跳,从而对定位精度产生影响。为消除周跳带来的误差,就要进行周跳探测,以确定其发生位置。【方法】采用三频伪距相位组合(0,1,-1)和单频伪距相位组合对周跳进行探测。【结果】通过对采样率1 s的数据进行试验验证,结果显示,三频伪距相位法实现全频率周跳的高精度实时探测,单频伪距相位解决了三频法中存在不敏感组合周跳和无法判断是哪个频率发生周跳的问题。【结论】结果表明,该方法可快速准确地判断出周跳发生位置及大小,是一种良好的周跳探测及修复方法。

风沙环境下高速列车气动特性分析

基于SST k-ω湍流模型和Euler-Lagrange离散相模型,建立了风沙环境下高速列车空气动力学计算模型,研究了不同沙粒浓度、不同风速及不同车速条件下的列车空气动力学性能。计算结果表明:风沙环境下,列车头车迎风侧主要受正压力影响,背风侧主要受负压力影响,最大正压力区域由鼻尖逐渐向迎风侧偏移;由于横风的影响,随着沙粒浓度的增强,头车迎风侧沙粒质量浓度增大,背风侧沙粒质量浓度变化较小;对于固定的车速和风速,头车气动力系数随沙粒浓度的增强而增大,且与沙粒浓度近似呈线性关系;沙粒浓度固定时,头车气动力系数随风速的增大而增大,随着车速的提升,头车气动力系数反而下降;风沙环境下,头车侧力系数、头车侧滚力矩系数可近似拟合为沙粒浓度、侧偏角及合成风速的二次多项式;头车升力系数可近似拟合为沙粒浓度、侧偏角及合成风速的三次多项式。

用相位减伪距法与电离层残差法进行周跳探测分析

在GPS测量中,对接收的数据进行预处理时,会发现数据产生周跳的现象,所以周跳的探测与修复是处理数据的必要环节。在处理周跳时主要采用的方法是先用高次差法进行大周跳数据过滤,然后在探测小周跳数据时,分别用相位减伪距法和电离层残差法进行探测,得出这2种方法中电离层残差法可以更好地对小周跳进行探测。但是如果2个载波的组合是某一特殊值,则很难用这种方法进行探测,这时需要采用多种方法组合探测。

小波去噪与北斗三频信号周跳探测与修复

传统的三频伪距相位组合方法易受到伪距观测噪声的影响,难以检测不敏感的小周跳.三个频率的载波相位观测数据组成的无几何距离组合(GF)方法具有检测敏感小周跳的能力,但存在病态方程组的问题.鉴于此,提出了一种利用小波去噪的无几何伪距相位组合与GF组合建立组合模型的方法,即利用小波变换对伪距观测值进行去噪,通过选择最优组合系数,构建优化的组合模型.该方法通过小波去噪保证了源数据的质量,采用无几何伪距相位组合与GF组合模型提高了周跳检测和修复的准确性,同时病态方程组问题得到解决.最后利用最小二乘方法结合正交三角(QR)分解算法,以及用空间搜索和L1范数最小原理固定周跳的最优整数并修复周跳,采集北斗卫星导航系统(BDS)三频测量数据用于实验验证.实验结果表明:小波变换去噪的优化组合模型可以检测和修复各种周跳,尤其是对不敏感的小周跳.

同频异位式复合冲击器的研究开发与现场试验

为了提高PDC钻头在硬地层中的破岩效率,增加切削齿吃深,同时消除井底钻头的“黏滑”现象,研制出同频异位式复合冲击器。该复合冲击器具有轴向冲击和扭向冲击2种功能,且2种冲击频率相同、但相位不同。基于同频异位式复合冲击器的结构特点和工作原理,确定了轴扭冲击相位角θ2为20°,建立了PDC切削齿轴向冲击力和扭向冲击力的数学模型,明确工具扭冲系统与轴冲系统消耗水力能量比值的合适范围为2.0~3.0。现场试验结果表明,带有复合冲击器钻进时,井底钻柱扭矩平稳,与邻井扭力冲击器+PDC钻头的钻具组合相比,其进尺和机械钻速分别提高111.36%和46.83%,节省1趟钻,且出井PDC钻头复合片磨损轻微。该工具使用效果良好,可为复杂难钻地层提速增效提供一种有效手段。