Velocity estimation of moving targets with stepped-frequency radar based on Doppler frequency difference

By analyzing the signal model of stepped-frequency waveform, a novel method for velocity measurement is proposed. The method is based on Doppler frequency difference which is achieved by using Hough transform. As the estimated velocity is inversely proportional to the frequency step size instead of the carrier frequency of the transmitted signal as the pulse-Doppler （PD） processing, the new algorithm can achieve much wider unambiguous velocity range. Furthermore, non-coherent integration of the sub-pulses with different carrier frequencies can be implemented by Hough trans- form to improve the anti-noise performance. Besides, field experimental results show that the high range resolution profile （HRRP） of a bullet with high speed can be reconstructed correctly without distortion.

Influence of Different Velocities on Muzzle Flow Field

A two?dimensional axisymmetric numerical simulation was successfully carried out on the muzzle flow field of a 300 mm?caliber counter?mass propelling gun. Based on the FLUENT software,using the finite volume method(FVM)and the realizable k?ε turbulence model,we adopted the holistic movement of a partitioned mesh processing method coupled with the intermediate ballistic model and the six degree?of?freedom model(6?DOF). We compared the flow field characteristics at the velocity of 1 730.4,978.3,and 323.4 m/s. The results indicate that the pressure of the hypersonic initial flow field is much higher than that of the subsonic and supersonic initial flow fields. In the case of the subsonic(323.4 m/s)flow field,the tiny disturbance spreads throughout the whole domain. But in the cases of the supersonic(978.3 m/s) and the hypersonic(1 730.4 m/s) flow fields,it cannot spread to the upstream disturbance source,and the disturbance domain of the supersonic flow field is wider than that of the hypersonic. It is noted that the subsonic flow field has a rounded shock wave before the projectile. However,in the supersonic and hypersonic flow fields,a shear layer is formed which begins from the head of the projectile and extends outward from the side of the projectile. Then a multi?layer shock wave is formed composed of coronal shock waves,bottom shock waves,reflected shock waves,and Mach disk.

Novel method for radial velocity difference estimation of moving targets with wideband signals

For the frequency difference of arrival （FDOA） esti-mation in passive location, this paper transforms the frequency difference estimation into the radial velocity difference estimation, which is difficult to achieve a high accuracy due to the mismatch between the sampling period and the pulse repetition interval. The proposed algorithm firstly estimates the point-in-time that each pulse arrives at two receivers accurately. Secondly two time of arrival （TOA） sequences are subtracted. And final y the radial ve-locity difference of a target relative to two stations with the least square method is estimated. This algorithm only needs accurate estimation of the time delay between pulses and is not influenced by parameters such as frequency and modulation mode. It avoids transmitting a large amount of data between two stations in real time. Simulation results corroborate that the performance is bet-ter than the arithmetic average of the Cramer-Rao lower bound （CRLB） for monopulse under suitable conditions.

The time-dependent Ginzburg-Landau equation for the two-velocity difference model

A thermodynamic theory is formulated to describe the phase transition and critical phenomenon in traffic flow. Based on the two-velocity difference model, the time-dependent Ginzburg-Landau （TDGL） equation under certain condition is derived to describe the traffic flow near the critical point through the nonlinear analytical method. The corresponding two solutions, the uniform and the kink solutions, are given. The coexisting curve, spinodal line and critical point are obtained by the first and second derivatives of the thermodynamic potential. The modified Korteweg- de Vries （mKdV） equation around the critical point is derived by using the reductive perturbation method and its kink antikink solution is also obtained. The relation between the TDGL equation and the mKdV equation is shown. The simulation result is consistent with the nonlinear analytical result.

Double-difference tomography of P- and S-wave velocity structure beneath the western part of Java, Indonesia

West Java in the western part of the Sunda Arc has a relatively high seismicity due to subduction activity and faults.In this study,double-difference tomography was used to obtain the 3D velocity tomograms of P and S waves beneath the western part of Java.To infer the geometry of the structure beneath the study area,precise earthquake hypo・center determination was first performed before tomographic imaging.For this,earthquake waveform data were extracted from the regional Meteorological,Climatological,Geophysical Agency(BMKG)network of Indonesia from South Sumatra to Central Java.The P and S arrival times for about 1,000 events in the period April 2009 to July 2016 were selected,the key features being events of magnitude>3,azimuthal gap<210°and number of phases>8.A nonlinear method using the oct-tree sampling algorithm from the NonLinLoc program was employed to determine the earthquake hypocenters.The hypocenter locations were then relocated using double-difference tomography(tomoDD).A significant reduction of travel-time(root mean square basis)and a better clustering of earthquakes were achieved which correlated well with the geological structure in West Java.Double-difference tomography was found to give a clear velocity structure,especially beneath the volcanic arc area,i.e.,under Mt Anak Krakatau,Mt Salak and the mountains complex in the southern part of West Java.Low velocity anomalies for the P and S waves as well as the vp/vs ratio below the volcanoes indicated possible partial melting of the upper mantle which ascended from the subducted slab beneath the volcanic arc.

GROUP VELOCITY CONTROL SCHEME WITH LOW DISSIPATION

In order to prevent smearing the discontinuity, a modified term is added to the third order Upwind Compact Difference scheme to lower the dissipation error. Moreover, the dispersion error is controled to hold back the non physical oscillation by means of the group velocity control. The scheme is used to simulate the interactions of shock density stratified interface and the disturbed interface developing to vortex rollers. Numerical results are satisfactory.

Three-dimensional crustal P-wave velocity structure in the Yangbi and Eryuan earthquake regions, Yunnan, China

A magnitude 5.5 earthquakes occurred in Eryuan County,Dali Bai Autonomous Prefecture,Yunnan Province,China,on March 3.And a magnitude 5.0 earthquake occurred in the same place on April 17,2013,i.e.,45 days later.Then,on May 21,2021,multiple earthquakes,one with magnitude 6.4 and several at 5.0 or above,occurred in Yangbi County,Dali Bai Autonomous Prefecture,Yunnan Province,China.All of these occurred in the Weixi-QiaohouWeishan fault zone.In this study,1,874 seismic events in Yangbi and Eryuan counties were identified by automatic micro-seismic identification technology and the first arrivals were picked up manually.Following this,a total of 11,968 direct P-wave absolute arrivals and 73,987 high-quality Pwave relative arrivals were collected for joint inversion via the double difference tomography method.This was done to obtain the regional three-dimensional fine crustal P-wave velocity structure.The results show that the travel time residuals before and after inversion decreased from the initial–0.1–0.1 s to–0.06–0.06 s.The upper crust in the study area,which exhibited a low-velocity anomaly,corresponded to the basin region;this indicated that the low-velocity anomaly in the shallow part of the study area was affected by the basin.Results also showed some correlation between the distribution of the earthquakes and velocity structure,as there was a lowvelocity body Lv1 with a wide distribution at depths ranging from 15–20 km in the Yangbi and Eryuan earthquake regions.In addition,earthquakes occurred predominantly in the highlow velocity abnormal transition zone.The low-velocity body in the middle and lower crust may be prone to concentrating upper crustal stress,thus leading to the occurrence of earthquakes.

Modeling Tracer Flow Characteristics in Different Types of Pores: Visualization and Mathematical Modeling

Structure of porous media and fluid distribution in rocks can significantly affect the transport characteristics during the process of microscale tracer flow.To clarify the effect of micro heterogeneity on aqueous tracer transport,this paper demonstrates microscopic experiments at pore level and proposes an improved mathematical model for tracer transport.The visualization results show a faster tracer movement into movable water than it into bound water,and quicker occupancy in flowing pores than in storage pores caused by the difference of tracer velocity.Moreover,the proposed mathematical model includes the effects of bound water and flowing porosity by applying interstitial flow velocity expression.The new model also distinguishes flowing and storage pores,accounting for different tracer transport mechanisms(dispersion,diffusion and adsorption)in different types of pores.The resulting analytical solution better matches with tracer production data than the standard model.The residual sum of squares(RSS)from the new model is 0.0005,which is 100 times smaller than the RSS from the standard model.The sensitivity analysis indicates that the dispersion coefficient and flowing porosity shows a negative correlation with the tracer breakthrough time and the increasing slope,whereas the superficial velocity and bound water saturation show a positive correlation.

Velocity calibration for microseismic event location using surface data

Because surface-based monitoring of hydraulic fracturing is not restricted by borehole geometry or the difficulties in maintaining subsurface equipment, it is becoming an increasingly common part of microseismic monitoring. The ability to determine an accurate velocity model for the monitored area directly affects the accuracy of microseismic event locations. However, velocity model calibration for location with surface instruments is difficult for several reasons： well log measurements are often inaccurate or incomplete, yielding intractable models; ori- gin times of perforation shots are not always accurate; and the non-uniqueness of velocity models obtained by inver- sion becomes especially problematic when only perforation shots are used. In this paper, we propose a new approach to overcome these limitations. We establish an initial velocity model from well logging data, and then use the root mean square （RMS） error of double-difference arrival times as a proxy measure for the misfit between the well log velocity model and the true velocity structure of the medium. Double-difference RMS errors are reduced by using a very fast simulated annealing for model perturbance, and a sample set of double-difference RMS errors is then selec- ted to determine an empirical threshold. This threshold value is set near the minimum RMS of the selected samples, and an appropriate number of travel times within the threshold range are chosen. The corresponding velocity models are then used to relocate the perforation-shot. We use the velocity model with the smallest relative location errors as the basis for microseismic location. Numerical analysis with exact input velocity models shows that although large differences exist between the calculated and true velocity models, perforation shots can still be located to their actual positions with the proposed technique; the location inaccuracy of the perforation is 〈2 m. Further tests on field data demonstrate the validity of this technique.

基于程函面波成像的华北克拉通岩石圈三维高分辨率S波速度结构研究

利用“中国地震科学台阵探测”项目Ⅱ期和Ⅲ期的流动地震台站以及中国区域地震台网中的部分固定台站的观测资料,采用程函面波成像方法获得了华北克拉通及周边区域10—120 s周期的瑞雷面波相速度分布和高分辨率的三维S波速度结构,并基于该速度模型估算了岩石圈厚度分布。结果显示,华北克拉通内部岩石圈厚度除了存在“西厚东薄”的一级分布特征外,还存在一些更小尺度的差异,包括鄂尔多斯地块内部岩石圈“南厚北薄”、鄂尔多斯地块周缘断陷带岩石圈显著的不均匀减薄以及燕山构造带与其南侧华北平原之间的显著差异等。山西断陷带北部与南部地区上地幔浅部(<100 km)存在不同程度的低速异常,它们被中部的高速异常区所分隔。在150 km以下深度从太行山南缘向北至山西断陷北缘存在一条NNE向展布的显著低速异常带,表明上地幔浅部南北部的低速异常在深部相连。结合已有的其它成像结果,我们推测这些低速异常起源于更深处(>200 km),并与由太平洋俯冲板块的滞留脱水导致的上地幔热物质上涌和小尺度地幔对流等密切相关。燕山构造带与华北平原的岩石圈结构存在明显差异,前者遭受的岩石圈破坏改造程度明显弱于后者,张家口—渤海地震带位于这两种不同壳幔结构的过渡带,地震活动较强,我们认为深部结构和热作用的显著差异,以及青藏高原远场挤压效应的共同作用是导致该区地震活动较强的主要原因。

云南洱源地区地壳三维精细速度结构成像

云南洱源地区地处青藏高原东南缘的滇西北地区中部,区内地质构造复杂,多条断裂交会穿过,且地热活动活跃,显示出很强的断裂构造特征。地区内地震活动频繁,2013年以来在维西-乔后-巍山断裂西侧发生了多个5级以上地震。文中利用云南区域固定台网和滇西北密集台阵记录的2008年1月1日—2023年7月20日发生在洱源地区的地震走时数据,采用波速比模型一致性约束的双差层析成像方法,获得了云南洱源及其周边区域的地壳三维V_(P)、V_(S)和V_(P)/V_(S)模型及地震重定位结果。结果表明:1)在龙蟠-乔后断裂以东,维西-乔后-巍山断裂、红河断裂和鹤庆-洱源断裂交会处聚集了大量小地震,缺乏中强地震。从现有的层析成像结果分析认为浅层发生的部分小地震可能与地热流体无直接关系,而从浅层向深层逐渐变高的V_(P)/V_(S)值可能暗示深部存在流体,深部流体可能在循环流动过程中逐渐渗透到浅层岩石中,并与部分密集小地震的发生有关。2)2013年以来发生的4个5级以上地震均发生在维西-乔后-巍山断裂西侧,并呈NNW-SSE走向分布,表明川滇块体西边界断裂系统的地震危险性有所增大。3)2013年3月3日和4月17日发生的洱源地震序列主要位于低V_(P)、低V_(S)和低V_(P)/V_(S)值的异常体内。一般而言,如存在流体,则V_(S)比V_(P)下降得更快,从而导致高V_(P)/V_(S)值,而低V_(P)/V_(S)则表明低V_(S)并非由流体所致。因此,现有的成像证据表明地震序列所处区域并不存在流体,从而推断地震序列的发生与流体无直接关系。空间上与洱源地震序列接近的2017年3月27日M_(S)5.1漾濞地震序列也具有相同的速度结构特征,因此也可能与流体无直接联系。2016年5月18日发生的M_(S)5.1云龙地震序列的主震和部分余震主要位于高V_(P)、高V_(S)和V_(P)/V_(S)相对高值区内,高V_(S)表明并非因存在流体而导致出现相对高的V_(P)/V_(S)值,据此推测主震及周围的余震所处区域可能不存在流体,流体并未直接参与到地震序列的发生过程中。

间歇通风策略在西北地区夏季蛋鸡舍应用效果

在中国西北地区夏季蛋鸡养殖中,由于昼夜温差大,需对蛋鸡舍的通风换气量进行频繁调整以适应环境变化。在连续通风策略下,对风机运转数量的调整常导致舍内负压值的较大波动,并且难以实时准确地通过进风口来调控舍内负压水平,导致舍内温度波动大、热环境分布不均匀。为探究间歇通风策略在西北地区夏季蛋鸡舍的应用效果,该研究在两栋不同进风模式的商品代蛋鸡舍进行试验。通过对两栋鸡舍内温湿度、风速及内外压差的连续监测,对比间歇通风和连续通风策略下,侧墙小窗进风及纵向通风鸡舍内的热环境分布,并对风机的间歇调控策略进行分析。结果表明:间歇通风策略下,侧墙小窗进风和纵向通风鸡舍内的平均温度波动分别为0.6、0.7℃,水平方向最大温差分别为0.3、5.2℃;连续通风策略下,侧墙小窗进风和纵向通风鸡舍内的平均温度波动分别为1.2、1.0℃,水平方向最大温差分别为0.8、4.7℃。开启风机数量相同时,两栋鸡舍内外压差和风速均不随通风策略的改变而发生变化,侧墙小窗进风鸡舍风机相对山墙至风机排风端的内外压差由17 Pa增大至19 Pa,纵向通风鸡舍相对山墙处舍内外压差为11 Pa;侧墙小窗进风鸡舍平均进风风速和走道平均风速分别为3.30、0.49 m/s,与纵向通风鸡舍相比分别提高1.86、0.12 m/s。综合间歇和连续通风策略下两栋鸡舍内热环境情况,间歇通风策略应用于西北地区夏季蛋鸡舍可有效降低舍内温度波动并维持舍内外压差水平的稳定,间歇通风策略更适用于侧墙小窗进风式鸡舍,可提高舍内温度分布均匀性。

2022年东台地震序列区域速度结构和精确定位

2022年江苏东台接连发生数十次小地震,其中,震级最大的M_(S)3.0地震导致震中附近震感明显。为探究该地区近期地震相对活跃的原因,文中收集了2008—2022年的地震走时资料,利用双差层析成像方法对苏北盆地的速度结构和地震位置进行了联合反演,获得了震中区P波三维速度结构和地震精确定位结果,并结合断裂分布、震源机制解和当地工业活动等资料,对地震序列可能的发震机制和发震构造进行了探讨。结果显示:1)重定位后,地震序列总体呈近SN向带状展布,发震优势深度在11~16km,与已探明的断裂带缺乏明显联系。结合震源机制结果推测,序列下方可能存在NNE-SSW向隐伏构造。2)震中区下方速度分布具有明显的非均匀性特征,15km深度处存在纺锤状P波高速异常体,地震序列的震源位置表现出从该异常体向远处扩散的发震特点。3)震中区附近现存多处工业活动,其中五烈—时堰—溱东作业点、地震序列和深部高速异常三者的位置存在一定的关联性,且作业时间和发震时间相近。由此推断,此次地震序列的发生与深部非均匀速度结构有关,震中附近的工业活动可能改变了区域应力状态,导致了能量的释放。

2019年四川威远东两次M_(S)>5.0地震序列活动特征及震源区体波速度结构

自2015年以来,四川威远及邻区的地震活动强度显著增强,其中2019年9月8日和12月18日在威远东发生了M_(S)5.4和M_(S)5.2地震,刷新了威远地区有记录以来历史地震震级上限.本文利用2019年8月至2020年3月期间威远及邻区25个流动台和17个固定台记录到的5638次M_(L)≥1.2地震Pg和Sg波到时以及连续波形资料,采用双差层析成像方法获得了威远东这两次地震序列的重定位结果和震源区浅层地壳高分辨率三维体波速度结构.重定位结果显示震源区地震震源深度主要集中在3~4 km.基于两次M_(S)>5.0地震震后10天余震序列空间展布,本文推测两次地震的发震构造均为NNE走向且倾向SE(倾角40°左右)的盲冲断层.三维体波速度结构反演结果揭示:震源区V_(P)异常变化较V_(S)异常变化显著,V_(P)/V_(S)比背景值普遍低4%~10%.在深度小于5 km的浅层内,地震多分布在V_(P)低速异常和V_(S)弱高速异常以及二者的高低速异常过渡带内;在5~7 km深度范围,地震基本上都发生在V_(P)低速异常区.上述速度结构特征揭示震源区附近可能发育着富含气体的孔隙和裂缝且存在流体活动.此外,2019年11月7日以后的地震活动具有明显的流体扩散驱动地震迁移特征,沿两次地震发震断层走向和倾向的流体扩散系数分别为1.5 m~2·s^(-1)和0.1 m~2·s^(-1).两次地震的发生机理很可能是流体扩散引起的孔隙压力上升.

适应波达时刻不确定性及较低采样率的新能源送出线路就地暂态量主保护判据

不对称接地故障占所有线路故障的90%以上,接地距离保护在应对此类故障方面发挥了不可替代的作用。随着新能源高比例渗透,各种传统单端工频量保护性能显著下降已成为共识。基于故障分量线模和零模波速差的保护判据理论上仅需利用到故障初始行波到达时刻信息,是一种原理简单可靠的单端量快速保护判据,已经在直流电网中成功实践。但在尝试将这类保护应用于交流电网时发现,受波头前陡较缓而难以精确定位波到时刻、依赖高采样率等诸多不利因素影响,存在过大的模糊判别区,除了特长线路外,对绝大部分线路几乎没有应用可行性。波到时刻的精准辨识是一个复杂的非线性问题,利用人工智能的方法进行辨识是一条可行的解决思路,对此,该文提出一种新的单端暂态量主保护判据。首先,分析波达时刻与波形关系,并指出这种关系能够采用机器学习来映射;其次,引入高斯过程回归(Gaussian process regression,GPR),在对初始行波数据进行预处理得到样本集后,输入GPR预测模型进行训练;然后,依据模型评估指标得到最优训练模型以输出高可信性的线-零模波达时差,据此实现了基于行波模量传输时间差的保护判据;最后,在利用PSCAD仿真验证所提保护判据有效性和普适性的基础上,进一步利用现场实测数据对判据进行测试,验证其实用性。该文工作为新能源交流系统下单端暂态量保护的性能提升提供新的解决思路。

基于三相Biot速度应力波动方程的水合物储层波场数值模拟

天然气水合物储层可以看作由骨架、水合物和孔隙水构成的三相孔隙介质。以三相Biot一阶速度应力波动方程作为声波在水合物储层传播的控制方程,用有限差分法(FDTD)进行数值模拟。波场快照可以清楚展现3个纵波和两个横波,与Biot理论相符。根据实测速度优化控制方程参数,使数值速度与实测速度相符。结果表明:孔隙度对水合物剪应力分量影响最显著,对水合物、孔隙水和骨架速度分量的影响次之,所以储层中孔隙度最适合用水合物剪应力分量来分析。骨架速度分量和应力分量受饱和度的影响较小,水合物剪应力分量受饱和度的影响最大,所以分析储层中水合物饱和度的最佳选择是水合物剪应力分量。

基于时差法的低功耗超声波三维海流测量系统

声学时差海流计具有高精度、高采样率、无盲区和不受海洋散射条件限制的优点,目前国内尚无时差海流计系统样机以及核心部件(四声道双晶换能器)的报道。为了实现对海洋矢量流速的长期精确测量,设计并研制了基于时差法的低功耗超声波三维海流测量系统,构建了四声轴三维矢量流速测量模型,通过有限元仿真设计并制备了小体积异形异构V形双晶换能器。系统采用低功耗STM32L431和MSP4306288为主控芯片,由TDC-GP22高精度时间测量模块、换能器驱动电路、低功耗放大滤波电路、SD卡存储模块等组成测量电路,通过测量换能器4个声轴上的超声波飞行时间差,得到海水的三维矢量流速。系统采用低功耗硬件系统设计,配合软件低功耗管理降低系统功耗。经实际测试,所研制的三维海流测量系统具有测量准确、低功耗、存储方便等优点。

超声速差法平面叶栅流场试验和数值研究

针对平面叶栅狭小通道中流场非接触测量难题,提出一种基于超声速差原理的二维流场测量方法。设计一种2×4超声波斜、平口换能器组合阵列,研制一套多通道超声法测量和气流速度场重建系统。开展平面叶栅流场测量试验,成功获取了3种不同进口速度条件下流道二维速度场。利用COMSOL Multiphysics中CFD模块同步开展叶栅流场数值模拟,并与试验结果对比。结果表明:超声测量与数值模拟结果较为接近,速度大小和偏转角误差均在5%以内,较好地反映叶栅通道的流动特点。提出的超声测量技术有望进一步用于高马赫数流场研究。

Origin软件在声速的测量实验数据处理中的应用

以大学物理实验中声速的测量为例,利用了Origin软件对实验测量所得的数据进行了线性拟合,并和传统的逐差法计算结果进行了比较,两种方法所得出的声速大小几乎吻合。结果表明,在实验教学中引入Origin软件对实验数据进行处理,操作更为方便快捷,并且能够有效提高实验效率和实验准确率,避免人为因素带来的误差。

矿山微震震源定位精度分析

定量研究初至拾取精度和速度模型对矿山微震震源定位精度的影响直接关系到矿山开采质量评估和矿山风险预警。由于矿山微地震监测主要接收岩石破裂激发的P波,故往往采用基于P波到时的同型波时差法进行震源定位,基于数值模拟方法研究了速度模型和初至拾取精度对同型波时差法矿山微震震源定位精度的影响。结果表明:反演速度模型偏离准确速度模型的误差逐渐增大时,震源定位精度表现出降低的趋势;初至拾取精度降低时,震源定位的精度随之降低;当速度模型误差和初至拾取误差分别控制在200 m/s和10 ms以内时,同型波时差法在矿山微震震源定位中的误差整体控制在20 m以内,可以满足矿山微震质量控制和风险预警的要求。