Optimal Design and Experimental Study of Tightly Coupled SCR Mixers for Diesel Engines

Two types of tightly coupled Selective Catalytic Reduction(SCR)mixers were designed in this study,namely Mixer 1 integrated with an SCR catalyst and Mixer 2 arranged separately.Computational Fluid Dynamics(CFD)software was utilized to model the gas flow,spraying,and pyrolysis reaction of the aqueous urea solution in the tightly coupled SCR system.The parameters of gas flow velocity uniformity and ammonia distribution uniformity were simulated and calculated for both Mixer 1 and Mixer 2 in the tightly coupled SCR system to compare their advantages and disadvantages.The simulation results indicated that Mixer 1 exhibited a gas velocity uniformity of 0.972 and an ammonia distribution uniformity of 0.817,whereas Mixer 2 demonstrated a gas velocity uniformity of 0.988 and an ammonia distribution uniformity of 0.964.Mixer 2 performed better in the simulation analysis.Furthermore,a 3D-printed prototype of Mixer 2 was manufactured and installed on an engine test bench to investigate ammonia distribution uniformity and NOX conversion efficiency.The experimental investigations yielded the following findings:1)The ammonia distribution uniformity of Mixer 2 was measured as 0.976,which closely aligned with the simulation result of 0.964,with a deviation of 1.2%from the model calculations;2)As exhaust temperature increased,the ammonia distribution uniformity gradually improved,while an increase in exhaust flow rate resulted in a decrease in ammonia distribution uniformity;3)When utilizing Mixer 2,the NOX conversion efficiency reached 84.7%at an exhaust temperature of 200°C and 97.4%at 250°C.Within the exhaust temperature range of 300°C to 450°C,the NOX conversion efficiency remained above 98%.This study proposed two innovative mixer structures,conducted simulation analysis,and performed performance testing.The research outcomes indicated that the separately arranged Mixer 2 exhibited superior performance.The tightly coupled SCR systemequippedwith Mixer 2 achieved excellent levels of gas velocity uniformity,ammonia distribution uniformity,and NOX conversion efficiency.These findings can serve as valuable references for the design and development of ultra-low emission after-treatment systems for diesel engines in the field of diesel engine aftertreatment.

Integration of Multi-Constellation GNSS Precise Point Positioning and MEMS-Based Inertial Systems Using Tightly Coupled Mechanization

We develop a new integrated navigation system, which integrates multi-constellations GNSS precise point positioning (PPP), including GPS, GLONASS and Galileo, with low-cost micro-electro-mechanical sensor (MEMS) inertial system, for precise positioning applications. To integrate GNSS and the MEMS-based inertial system, the process and measurement models are developed. Tightly coupled mechanism is adopted, which is carried out in the GNSS raw measurements domain. Both un-differenced and between-satellite single-difference (BSSD) ionosphere-free linear combinations of pseudorange and carrier phase GNSS measurements are processed. Rigorous models are employed to correct GNSS errors and biases. The GNSS inter-system biases are considered as additional unknowns in the integrated error state vector. The developed stochastic model for inertial sensors errors and biases are defined based on first order Gaussian Markov process. Extended Kalman filter is developed to integrate GNSS and inertial measurements and estimate inertial measurements biases and errors. Two field experiments are executed, which represent different real-world scenarios in land-based navigation. The data are processed by using our developed Ryerson PPP GNSS/MEMS software. The results indicate that the proposed integrated system achieves decimeter to centimeter level positioning accuracy when the measurement updates from GNSS are available. During complete GNSS outages the developed integrated system continues to achieve decimeter level accuracy for up to 30 seconds while it achieves meter-level accuracy when a 60-second outage is introduced.

Bridging GPS outages of tightly-coupled GPS/SINS using GMDH neural network

A tightly coupled GPS （ global positioning system ）/SINS （ strap down inertial navigation system） based on a GMDH （ group method of data handling） neural network was presented to solve the problem of degraded accuracy for less than four visible GPS satellites with poor signal quality. Positions and velocities of the satellites were predicted by a GMDH neural network, and the pseudo ranges and pseudo range rates received by the GPS receiver were simulated to ensure the regular op eration of the GPS/SINS Kalman filter during outages. In the mathematical simulation a tightly cou pled navigation system with a proposed approach has better navigation accuracy during GPS outages, and the anti jamming ability is strengthened for the tightly coupled navigation system.

Application of Pore Evolution and Fracture Development Coupled Models in the Prediction of Reservoir "Sweet Spots" in Tight Sandstones

The Chang-63 reservoir in the Huaqing area has widely developed tight sandstone ＂thick sand layers, but not reservoirs characterized by rich in oil＂, and it is thus necessary to further study its oil and gas enrichment law. This study builds porosity and fracture development and evolution models in different deposition environments, through core observation, casting thin section, SEM, porosity and permeability analysis, burial history analysis, and ＂four-property-relationships＂ analysis.

Fully coupled fluid-solid productivity numerical simulation of multistage fractured horizontal well in tight oil reservoirs

A mathematical model, fully coupling multiple porous media deformation and fluid flow, was established based on the elastic theory of porous media and fluid-solid coupling mechanism in tight oil reservoirs. The finite element method was used to determine the numerical solution and the accuracy of the model was verified. On this basis, the model was used to simulate productivity of multistage fractured horizontal wells in tight oil reservoirs. The results show that during the production of tight oil wells, the reservoir region close to artificial fractures deteriorated in physical properties significantly, e.g. the aperture and conductivity of artificial fractures dropped by 52.12% and 89.02% respectively. The simulations of 3000-day production of a horizontal well in tight oil reservoir showed that the predicted productivity by the uncoupled model had an error of 38.30% from that by the fully-coupled model. Apparently, ignoring the influence of fluid-solid interaction effect led to serious deviations of the productivity prediction results. The productivity of horizontal well in tight oil reservoir was most sensitive to the start-up pressure gradient, and second most sensitive to the opening of artificial fractures. Enhancing the initial conductivity of artificial fractures was helpful to improve the productivity of tight oil wells. The influence of conductivity, spacing, number and length of artificial fractures should be considered comprehensively in fracturing design. Increasing the number of artificial fractures unilaterally could not achieve the expected increase in production.

Spatial-temporal coupling between high-quality source rocks and reservoirs for tight sandstone oil and gas accumulations in the Songliao Basin, China

The spatial-temporal relationship between high-quality source rocks and reservoirs is a key factor when evaluating the formation,occurrence,and prospectivity of tight oil and gas reservoirs.In this study,we analyze the fundamental oil and gas accumulation processes occurring in the Songliao Basin,contrasting tight oil sand reservoirs in the south with tight gas sand reservoirs in the north.This is done using geochemical data,constant-rate and conventional mercury injection experiments,and fluid inclusion analyses.Our results demonstrate that as far as fluid mobility is concerned,the expulsion center coincides with the overpressure zone,and its boundary limits the occurrence of tight oil and gas accumulations.In addition,the lower permeability limit of high-quality reservoirs,controlled by pore-throat structures,is 0.1×10^-3μm^2 in the fourth member of the Lower Cretaceous Quantou Formation(K1q^4)in the southern Songliao Basin,and 0.05×10^-3μm^2 in the Lower Cretaceous Shahezi Formation(K1sh)in the northern Songliao Basin.Furthermore,the results indicate that the formation of tight oil and gas reservoirs requires the densification of reservoirs prior to the main phase of hydrocarbon expulsion from the source rocks.Reservoir“sweet spots”develop at the intersection of high-quality source rocks(with high pore pressure)and reservoirs(with high permeability).

基于点线特征融合的实时视惯SLAM算法

为了在光照不足和低纹理场景中实现移动机器人的高精度实时定位和建图,提出了一种基于视觉点线特征以及IMU特征融合的实时SLAM算法。首先通过跳跃路由策略和自适应阈值策略改进了EDlines算法,提高了线特征提取的质量,从而提高了特征跟踪的有效性。然后将视觉惯性特征紧耦合建立约束,通过滑动窗口和边缘化模型进行非线性优化,实现了高精度高实时性的状态估计。实验证明,所提算法在线特征提取的有效性方面优于传统的线段提取算法,同时SLAM系统的定位精度和鲁棒性均得到有效提升。

超深层裂缝性致密砂岩气藏多尺度耦合流动数值模拟

塔里木盆地克拉苏气田白垩系气藏是罕见的超深层裂缝性致密砂岩气藏,该类气藏的储渗空间具有显著的多尺度特征,基质与多尺度裂缝、断层介质的渗透率级差相差5~6个数量级,常规渗流理论难以准确描述其流动规律和开发机理。为此,基于单裂缝流动物理实验结果及流体力学理论,结合多尺度裂缝几何信息,应用均化理论和体积平均尺度升级方法,将多尺度介质划分为5个流动系统,建立了考虑介质间的非稳态窜流多尺度耦合流动数学模型,并应用有限体积法对耦合流动模型进行了数值求解和数值试井分析。研究结果表明:(1)不同尺度裂缝中具有不同的流动特征,随缝宽增加流速加快,流动模态发生变化;(2)多尺度耦合流动模型与双重介质模型结果存在较大差异,导数曲线具有不同趋势特征;(3)应用所建立的多尺度耦合流动模型成功解释了气藏实际试井数据,模型能够反映实际地层中的流动过程。结论认为,超深层裂缝性致密砂岩气藏多尺度耦合流动模型揭示了多尺度裂缝以及致密基质间逐级动用、协同供气的开发机理,可为类似气藏制订合理开发技术政策及气藏提高采收率提供理论和技术支撑。

基于微观流固耦合的超深层致密砂岩气藏应力敏感性分析

超深层致密砂岩气藏具有强应力敏感性,目前常用的研究方法包括压力脉冲实验法和实时在线CT扫描法两种,压力脉冲实验法不能揭示产生应力敏感性的微观机理,而实时在线CT扫描法也无法模拟深部地层高压、高应力的条件。为解决应力敏感性实验研究的不足,基于离散单元法与管道网络模型建立了微观流固耦合算法,编制了模拟器,并对模拟器力学计算和流固耦合模块的正确性进行了验证,分析了应力大小、加载方向和孔隙压力对岩心渗透率的影响,最后从微观上揭示了超深层致密砂岩气藏的应力敏感性机理。研究结果表明:①应力通过增加与之垂直方向上喉道两侧的法向压力,减小喉道的水力半径,进而降低储层的渗透率;②较高的孔隙压力能够阻碍岩石颗粒在应力作用下的移动,从而减缓了孔隙和喉道的变形,使模型保持较高的渗透率;③致密砂岩气藏的渗透率受到应力和地层压力的共同控制,并且具有各向异性,在垂直于最小主应力方向上形成渗透率较大的优势通道;④异常高压阻碍了地应力的压实作用,有利于保护储层孔隙,使地层有较好的储集性能和较高的渗透率。结论认为,根据离散元法结合孔隙网络模型建立的流固耦合方法可为理解超深层致密砂岩应力敏感性提供理论参考,并为超深层致密砂岩气藏的科学高效开发提供指导。

3D打印技术在机载超宽带共形天线中的应用研究

为提高共形相控阵天线的设计制造效率,在平面紧耦合天线的基础上,设计了与飞机襟翼曲面共形的紧耦合超宽带相控阵天线。按照共形天线的安装要求,提出了混合3D打印技术,即采用熔融堆积成型技术及微滴喷射成型技术实现襟翼流线型曲面模型的打印,并完成了紧耦合天线辐射层的打印,验证了3D打印技术在共形天线上的应用。加上馈电结构后对单元电压驻波比(voltage standing wave ratio, VSWR)和方向图进行了测试,结果表明所设计的天线在0.4~2.0 GHz范围内,VSWR、单元方向图和阵列方向图符合设计技术指标,为后续共形天线设计和加工提供了技术基础。

一种高功率微波宽带紧耦合偶极子阵列天线

提出了一种新型高功率微波宽带紧耦合偶极子阵列天线。在常规的紧耦合偶极子阵列天线的基础上,该阵列天线通过采用全金属结构设计、天线匹配层和密封层一体化设计以及调节天线结构的手段,获得了宽带高功率性能。仿真结果显示,在0.8~4.0 GHz的范围内,天线未扫描时的驻波比小于2;在16 mm×32 mm单元尺寸内和1个大气压的SF6气体中,功率容量达到0.12 MW;以该单元天线组成10×10阵列,100个单元总尺寸仅为160 mm×320 mm,在1个大气压的SF6气体中,功率容量可以达到12 MW,另外,该天线可实现45°的宽角扫描。该阵列天线的提出为实现高功率微波宽带天线的宽频带、大角度扫描、紧凑化、小型化以及低剖面化提供了参考。

抛罩分离仿真研究进展

抛罩分离仿真是航空航天研发过程中的重要一环,其关键在于对分离安全性的分析。回顾以往对抛罩分离安全性的仿真研究,发现现有的分析方法和模拟方法都基于生成的仿真分离轨迹进行。而随着时代和需求的发展,罩体本身的材料结构和抛罩的环境都发生了变化。在原有刚体分离轨迹的基础上,针对柔性整流罩的分析已经成为了仿真整流罩分离的主要研究方向。在对现有研究进行总结后,认为现有抛罩仿真的主要难点和关键技术集中在耦合模型、动网格以及CSD模型的简化上,对这3种技术做出了具体分析与展望。最后对抛罩分离仿真的发展给出了几点结论和建议。

基于多传感器的紧耦合三维室内定位与建图

即时定位与地图构建(SLAM)因其可以解决未知环境中的定位与地图构建问题,广泛应用于移动机器人领域。本文使用雷达、相机、IMU和轮式里程计提出了一种名为3D-MultiFus的SLAM方法。其中雷达-IMU-里程计子系统(Ls)快速构建全局地图的几何结构,通过最小化点到平面误差估计系统位置状态。相机-IMU-轮式里程计子系统(Vs)可剔除被遮挡或深度不连续的特征点,以最小化帧间地图光度误差进一步估计位姿状态,并可实现子图中点云地图的着色渲染。IMU与里程计融合后的数据、雷达系统点到平面误差和相机系统中光度误差以基于误差状态的迭代卡尔曼方式(ESIKF)实现数据紧耦合,从而在保证精度和鲁棒性的同时,实现快速定位与建图。为了验证本文算法的定位与建图精度,布置了室内运动实验场景并将3D-MultiFus算法与相关算法比较。仿真和实验结果表明,3D-MultiFus算法完成一次数据处理需185 ms,在运行效率上优于其他算法。在复杂的室内场景下,长时间运行定位首末位置误差仅0.0856 m,3D-MultiFus移动机器人的全局地图精度得到了较大的提升,所构建的全局地图具有较好的一致性。证明了所提出算法能够在室内场景中稳健可靠的工作。

基于多类别特征点匹配的紧耦合激光惯性里程计

针对现有的激光SLAM在室外动态场景建图时,LiDAR数据存在运动畸变、地面采样数据稀疏造成激光里程计精度低的问题,提出了一种基于多类别特征点匹配的IMU紧耦合里程计方法。首先,从原始点云数据入手,通过IMU数据对每一帧LiDAR数据进行线性插值校正畸变点云,以提高LiDAR数据的质量;其次,对畸变校正后的点云进行2D网格投影,根据每个网格与其相邻网格的最小高度平均值大小,利用双阈值将网格中点云划分为地面点和非地面点,再根据局部特征的线性度、平面度、曲率等,将非地面点进一步划分得到多类别特征点;再次,对多类别特征点匹配的IMU紧耦合进行建模,考虑到原本的LiDAR观测误差无法提供高精度的重力矢量估计,引入IMU状态估计,构建里程计误差函数,使得重力矢量估计得到进一步约束,抑制了重力矢量方向上的漂移,有效提升了激光里程计的精度;最后,基于LeGO-LOAM框架设计了基于多类别特征点匹配的IMU紧耦合激光里程计,并完成了验证系统的搭建。实验结果表明,该方法能有效抑制重力矢量方向上的漂移,提高激光里程计的精度。

工程材料专业复合教学模式创新设计及实践效果

为了实现复合材料与工程专业人才培养质量的提升,构建以目标为导向、学生通过实质参与进行有效学习的格局,提出基于对分课堂与项目式教学的紧耦合关系构建复合型教学模式。以《程序设计基础》课程为对象,以“航空复合材料库存管理系统”为主线构建项目式对分课堂教学模式,从实施策略和实施路径进行了理论分析与实践探索。实践效果表明:项目式对分课堂实施过程明确,有较强的可操作性,对教师与学生双方的能力都有一定的提升,符合应用型本科院校课程教学特点,是一种互利共生的教学模式。

Indoor positioning based on tightly coupling of PDR and one single Wi-Fi FTM AP

The indoor positioning system is now an important technique as part of the Internet-of-Things(IoT)ecosystem.Among indoor positioning techniques,multiple Wi-Fi Access Points(APs)-based positioning systems have been researched a lot.There is a lack of research focusing on the scene where only one Wi-Fi AP is available.This work proposes a hybrid indoor positioning system that takes advantage of the Fine-Timing Measurements(FTM)technique that is part of the IEEE 802.11mc standard,introduced back in 2016.The system uses one single Wi-Fi FTM AP and takes advantage of the built-in inertial sensors of the smartphone to estimate the device’s position.We explore both Loosely Coupled(LC)and Tightly Coupled(TC)integration schemes for the sensors’data fusion.Experimental results show that the proposed methods can achieve an average positioning accuracy of about 1 m without knowing the initial position.Compared with the LC integration method,the median error accuracy of the proposed TC fusion algorithm has improved by more than 52%and 67%,respectively,in the two experiments we set up.

复杂环境下GPS+BDS-3 PPP/INS紧组合算法性能分析

针对城市复杂环境下精密单点定位(PPP)连续高精度定位受限的问题,本文基于北斗三号全球卫星导航系统(BDS-3)与全球定位系统(GPS)双系统,利用PPP与惯性导航系统(INS)紧组合算法来改善城市复杂环境下定位性能。通过构建GPS+BDS-3双系统PPP/INS紧组合滤波模型,分别对GPS PPP、GPS+BDS-3 PPP、GPS PPP/INS紧组合、GPS+BDS-3PPP/INS紧组合4种方案在城区开阔、复杂环境下的定位、测速、定姿性能进行了分析和评估。实验结果表明,开阔环境下PPP/INS紧组合相比PPP定位精度略有提升;而在复杂环境下PPP/INS紧组合可显著解决PPP定位结果连续性和有效性较差的问题;引入BDS-3后,PPP/INS紧组合导航性能进一步提升,GPS+BDS-3 PPP/INS紧组合相比GPS PPP/INS紧组合,在东、北、天方向上,开阔环境下定位精度分别提升18.5%、32.7%、43.2%,复杂环境下定位精度分别提升35.9%、49.1%、56.5%。

西湖凹陷古近系致密砂岩气“三元耦合控藏”特征

针对西湖凹陷古近系致密砂岩气成藏机制与成藏模式尚不明确等问题,综合分析了烃源岩的特征与生排烃期次,研究异常高压的成因与分布特点,以及大型储集体的展布与物性特征,建立了致密砂岩气的成藏模式。研究结果表明:烃源岩、异常高压和致密储层“三元耦合控藏”是西湖凹陷致密砂岩气藏成藏关键因素,其中古近系煤系烃源岩条件优越,生气高峰期与储层致密形成时间一致,生烃增压同时提供了富厚的物质基础;异常高压改善储层物性,同时利于致密砂岩气的长距离运移和聚集;大规模的砂岩储集体发育,致密砂岩气在异常高压作用下汇聚成藏。西湖凹陷致密砂岩气藏呈现出“自源侧向-垂向”的成藏模式,共发育“原生型”和“改造型”2类致密砂岩气藏,具有良好的勘探前景。

基于热-应力耦合的LNG储罐泄漏状态下外罐壁受力分析

为分析LNG全容罐在内罐泄漏状态下的外罐壁液密性,采用大型通用有限元分析软件对外罐在正常使用、夏季高中低液位及局部冷点泄漏状态下的结构响应进行了非线性有限元分析,并验证分析了热角保护结构的可靠性。研究结果表明:正常使用阶段外罐壁向内轻微收缩,外罐壁外侧根部出现轻微受拉损伤。泄漏阶段外罐壁收缩明显增大,外罐壁内侧出现大范围受拉损伤,钢筋应力水平显著增加,但外罐壁液密性指标满足要求。热角保护结构在内罐泄漏状态下可有效保证外罐壁底部不直接接触低温液体。

GPS/BDS/INS tightly coupled integration accuracy improvement using an improved adaptive interacting multiple model with classified measurement update

An Extended Kalman Filter（EKF） is commonly used to fuse raw Global Navigation Satellite System（GNSS） measurements and Inertial Navigation System（INS） derived measurements. However, the Conventional EKF（CEKF） suffers the problem for which the uncertainty of the statistical properties to dynamic and measurement models will degrade the performance.In this research, an Adaptive Interacting Multiple Model（AIMM） filter is developed to enhance performance. The soft-switching property of Interacting Multiple Model（IMM） algorithm allows the adaptation between two levels of process noise, namely lower and upper bounds of the process noise. In particular, the Sage adaptive filtering is applied to adapt the measurement covariance on line. In addition, a classified measurement update strategy is utilized, which updates the pseudorange and Doppler observations sequentially. A field experiment was conducted to validate the proposed algorithm, the pseudorange and Doppler observations from Global Positioning System（GPS） and Bei Dou Navigation Satellite System（BDS） were post-processed in differential mode.The results indicate that decimeter-level positioning accuracy is achievable with AIMM for GPS/INS and GPS/BDS/INS configurations, and the position accuracy is improved by 35.8%, 34.3% and 33.9% for north, east and height components, respectively, compared to the CEKF counterpartfor GPS/BDS/INS. Degraded performance for BDS/INS is obtained due to the lower precision of BDS pseudorange observations.