The new multistage water adsorption model of Longmaxi Formation shale considering the spatial configuration relationship between organic matter and clay minerals

The water adsorption by shale significantly affects shale gas content and its seepage capacity.However,the mechanism of water adsorption by shale is still unclear due to its strong heterogeneity and complicated pore structure.The relationship between the adsorbed water content at different relative humidities(RHs)and shale compositions,as well as shale pore structure and the spatial configuration relationship between organic matter(OM)and clay minerals,was investigated to clarify the controlling factors and mechanisms of water adsorption by Longmaxi Formation shale from the Southern Sichuan Basin in China.Consequently,the water adsorption process could be generally divided into three different stages from 0%RH to 99%RH.Furthermore,the Johnston’s clay mine ral interlayer pore structure model(JCM),the Freundlich model(FM)and the Dubinin-Astakhov model(DAM)were tested to fit the three water adsorption stages from low RH to high RH,respectively.The fitting results of the JCM and FM at lower RHs were far from good,while the fitting results of DAM at higher RHs were acceptable.Accordingly,two revised models(LRHM and MRHM)considering the spatial configuration relationship between OM and clay minerals were proposed for the two stages with lower RHs,and performed better fitting results indicating the pronounced effect of the spatial configuration relationship between OM and clay minerals on the water adsorption process of Longmaxi Formation shale.The outcomes of this study will contribute to clarifying the water distribution characteristics in the pore network of shale samples with variable water contents.

Leader trajectory planning method considering constraints of formation controller

To ensure safe flight of multiple fixed-wing unmanned aerial vehicles(UAVs)formation,considering trajectory planning and formation control together,a leader trajectory planning method based on the sparse A*algorithm is introduced.Firstly,a formation controller based on prescribed performance theory is designed to control the transient and steady formation configuration,as well as the formation forming time,which not only can form the designated formation configuration but also can guarantee collision avoidance and terrain avoidance theoretically.Next,considering the constraints caused by formation controller on trajectory planning such as the safe distance,turn angle and step length,as well as the constraint of formation shape,a leader trajectory planning method based on sparse A^(*)algorithm is proposed.Simulation results show that the UAV formation can arrive at the destination safely with a short trajectory no matter keeping the formation or encountering formation transformation.

Trajectory Design and Optimization for LEO Satellites in Formation to Observe GEO Satellites’ Beams

This paper presents the methods and results for the trajectory design and optimization for the low earth orbit (LEO) satellites in formation to observe the geostationary orbit (GEO) satellites’ beams. The background of the trajectory design mission is the 9th China Trajectory Optimization Competition (CTOC9). The formation is designed according to the observation demands. The flying sequence is determined by a reference satellite using a proposed improved ephemeris matching method (IEMM). The formation is changed, maintained and transferred following the reference satellite employing a multi-impulse control method (MICM). Then the total observation value is computed by propagating the orbits of the satellites according to the sequence and transfer strategies. Based on the above methods, we have obtained a fourth prize in the CTOC9. The proposed methods are not only fit for this competition, but can also be used to fulfill the trajectory design missions for similar multi-object explorations.

Consensus and formation control of discrete-time multi-agent systems

Consensus problems for discrete-time multi-agent systems were focused on. In order to design effective consensus protocols, which were aimed at ensuring that the concerned states of agents converged to a common value, a new consensus protocol for general discrete-time multi-agent system was proposed based on Lyapunov stability theory. For discrete-time multi-agent systems with desired trajectory, trajectory tracking and formation control problems were studied. The main idea of trajectory tracking problems was to design trajectory controller such that each agent tracked desired trajectory. For a type of formation problem with fixed formation structure, the formation structure set was introduced. According to the formation structure set, each agent can track its individual desired trajectory. Finally, simulations were provided to demonstrate the effectiveness of the theoretical results. The mlmerical results show that the states of agents converge to zero with consensus protocol, which is said to achieve a consensus asymptotically. In addition, through designing appropriate trajectory controllers, the simulation results show that agents converge to the desired trajectory asymptotically and can form different formations.

Path planning for UAVs formation reconfiguration based on Dubins trajectory

Multiple UAVs are usually deployed to provide robustness through redundancy and to accomplish surveillance,search,attack and rescue missions.Formation reconfiguration was inevitable during the flight when the mission was adjusted or the environment varied.Taking the typical formation reconfiguration from a triangular penetrating formation to a circular tracking formation for example,a path planning method based on Dubins trajectory and particle swarm optimization(PSO)algorithm is presented in this paper.The mathematic model of multiple UAVs formation reconfiguration was built firstly.According to the kinematic model of aerial vehicles,a process of dimensionality reduction was carried out to simplify the model based on Dubins trajectory.The PSO algorithm was adopted to resolve the optimization problem of formation reconfiguration path planning.Finally,the simulation and vehicles flight experiment are executed.Results show that the path planning method based on the Dubins trajectory and the PSO algorithm can generate feasible paths for vehicles on time,to guarantee the rapidity and effectiveness of formation reconfigurations.Furthermore,from the simulation results,the method is universal and could be extended easily to the path planning problem for different kinds of formation reconfigurations.

Complex genesis of multiperiod fractures in the Middle Triassic Leikoupo Formation in the Pengzhou gas field, western Sichuan Basin, China

The cumulative expression of multistage deformation is complex multiperiod fractures,which are commonly seen in tectonic zones.The Middle Triassic Leikoupo Formation in the western Sichuan Basin Depression,China,is a typical marine carbonate reservoir with natural fractures caused mainly by tectonic movements.According to outcrops,drill cores,image logging,and fluid inclusions,the fracture characteristics,types of natural fractures,and interactions of fractures are determined.In total,419 natural fractures in 493.2 m of cores from 7 wells are investigated,which are mainly shear and tensile fractures with a small number of weathering generated fractures.Meanwhile,the results of the stable isotope analysis of δ13C and δ18O,as well as the flow fluid inclusion data,reveal four tectonic periods of fractures with different occurrences.Based on the history of regional tectonic evolution,indicating one period of weathering fractures ascribable to stratal uplift and three periods of structural fractures related to the sequential tectonic movements of the Longmenshan fault belt.By analyzing the interaction relationships of fractures,three types of fracture interaction relationships are observed:cutting,restraining,and overlapping.The four stages fractures are chronologically assigned to(1)the early Indosinian N-S trending compression,(2)the late Indosinian NW-SE compression,(3)the middle Yanshanian NE-SE compression,and(4)the early Himalayan E-W compression.The influence of natural fractures on gas migration and well production in marine carbonates is discussed,and indicates that tectonic fractures could provide seepage channels for gas migration and accumulation from near or distant hydrocarbon source rocks into the Middle Triassic Leikoupo Formation.This study utilizes a pragmatic approach for understanding the fracture genesis mechanism in oil and gas field with multiperiod fractures.

Recent advances of bismuth-based electrocatalysts for CO_(2)reduction:Strategies,mechanism and applications

Electrocatalytic CO_(2)reduction reaction(CO_(2)RR),driven by clean electric energy such as solar and wind,can not only alleviate environmental greenhouse effect stemming from excessive CO_(2)emissions,but also realize the storage of renewable energy,for it guarantees the production of value-added chemicals and fuels.Among CO_(2)RR products,formic acid shows great advantages in low energy consumption and high added-value,and thus producing formic acid is generally considered as a profitable line for CO_(2)RR.Bismuth-based electrocatalysts exhibit high formic acid selectivity in CO_(2)RR.Herein,we review the recent progress in bismuth-based electrocatalysts for CO_(2)RR,including material synthesis,performance optimization/validation,and electrolyzers.The effects of morphologies,structure,and composition of bismuth-based electrocatalysts on CO_(2)RR performance are highlighted.Simultaneously,in situ spectroscopic characterization and DFT calculations for reaction mechanism of CO_(2)RR on Bi-based catalysts are emphasized.The applications and optimization of electrolyzers with high current density for CO_(2)RR are summarized.Finally,conclusions and future directions in this field are prospected.

面向海流扰动和通信时延的欠驱动AUV编队跟踪控制

由欠驱动自主水下航行器(Autonomous Underwater Vehicle,AUV)编队组成的水下探测阵列具有响应快、机动性好、智能化程度高的特点。针对无速度信息传输的多AUV在海流和时延复合扰动下的编队控制问题,提出一种虚拟轨迹、轨迹预测、自适应反演滑模控制技术相结合的编队控制方法。使用领航者的位置信息和期望队形得到跟随者的参考轨迹,并引入虚拟轨迹使其与跟随者参考轨迹有限时间重合,从而得到跟随者的期望位置和速度。在此基础上,使用最小二乘法拟合轨迹曲线进行时延补偿,并通过自适应反演滑模控制技术完成海流干扰下的编队轨迹跟踪。理论分析和仿真结果表明,新方法具有可行性和有效性。

基于知识的目标关系分析挖掘技术

在战场目标价值分析和打击目标排序分析过程中,为了构建敌方作战目标体系,需要分析战场目标间的关联关系。轨迹和部署数据中隐藏大量信息,提出了一种从轨迹和部署数据中挖掘出感兴趣的目标关系类型信息的方法,所提方法对轨迹部署数据进行时空聚类,从聚类结果提取目标;对聚类目标使用频繁项挖掘算法分析挖掘满足一定支持度的有关联关系的目标,再根据构建的关系类型知识库或关系规则,分析目标间的具体关系类型。所提方法能对积累的目标历史轨迹部署数据分析挖掘出目标间的关联关系,挖掘出目标潜在的关系类型可为后续构建目标体系提供关系数据。

雪峰弧构造带钻孔轨迹控制关键技术研究

随着近年来矿产资源勘查要求的提高,岩心钻孔的深度及地层复杂性也不断加大,为能精准的钻遇靶区矿体以实现地质目的,对钻孔轨迹控制的要求越来越高。雪峰弧构造带部分工作区地层倾角大、软硬交替频繁、地层破碎,实际施工中地层造斜情况严重,随着孔深增加导致终孔轨迹与靶区矿体偏差较大,影响矿产资源勘查的精度和质量。通过对该工作区地层造斜情况的深入分析,在ZK1001钻孔绳索取心钻进施工中采用初级定向孔技术和满眼钻具工艺,大幅度提高了钻孔孔身质量,较好地实现钻孔轨迹控制。并通过试验不同的岩心钻具组合,提出了满眼钻具组合的优化意见和建议,为工作区岩心钻孔轨迹控制提供技术参考。

双无人机对地快速移动目标跟踪的构型设计与控制方法

为实现对地面快速移动目标的探测跟踪,基于无人机侦察载荷的误差模型,设计了双无人机编队跟踪目标的构型与跟踪控制律。面向持续跟踪的典型应用场景,设计了基于Leader-Follower的双机编队构型,并基于相机误差模型建立了双无人机探测叠加区域的误差分布模型,以此确定了目标与无人机编队的位置关系。之后,基于无人机与目标的视觉关系定义长机的矢量前置角和与目标之间的距离为跟踪误差,设计了基于李雅普诺夫方法的跟踪控制律,并证明跟踪控制的渐近稳定性。设计了僚机相对于长机的编队控制律,以保持双机平行编队的构型。仿真结果表明,目标机动运动时,双无人机系统能够在较短时间内收敛,实现对目标的持续稳定跟踪。

基于APSO的微纳卫星编队轨迹规划方法

针对微纳卫星编队在指定时间内由初始构型到指定构型的路径规划问题,提出了一种基于自适应惯性权重粒子群优化(adaptive-inertial-weightedparticleswarmoptimization,APSO)算法的轨迹规划方法。首先,通过Radau伪谱法将轨迹规划的连续最优控制问题离散化为参数优化的非线性规划(nonlinear programming, NLP)问题;其次,采用APSO算法对NLP问题求解,避免了复杂梯度求解困难的问题,同时降低了计算量;最后,通过仿真实验表明,所提方法可在更短时间内求得满足约束条件的最优轨迹,以完成在线轨迹规划任务。

基于空间位置关系的轨迹数据高效降维和查询算法

由于新型信息技术的快速发展,社会处于数字化、信息化转型的关键时期,各行业对于以数据库技术为基础的信息系统的需求也日益凸显.基于位置的服务依赖于海量实时生成的轨迹数据,在处理亿万级随时间连续变化的轨迹数据时,降维算法和查询技术一直是研究的关键,通过降低轨迹数据的规模,减少查询操作时处理数据的时间,能有效提升查询的性能,而能否实现高质量、高效率查询对于数据库而言至关重要.提出了面向轨迹数据的均匀网格编码,并在进一步优化后提出非均匀网格降维算法,将轨迹数据的坐标转化为1维字符串存储,对不符合要求的网格进行合并处理;通过空间位置映射充分保留轨迹数据间复杂的相互关系,并采用范围查询与最近邻查询对降维后的数据进行性能测试.实验使用不同城市真实轨迹数据与模拟生成轨迹数据作为数据集,将提出的均匀网格算法、非均匀网格算法与3种基准方法进行对比.实验证明,优化后的非均匀网格算法降维后数据的空间位置关系相似度可高达82.50%,范围查询时间较其他查询时间提升了至少73.86%,最近邻查询时间提升了至少52.26%,与其他基准方法相比取得了更好的效果.

航天器编队飞行相对运动轨迹优化方法综述

针对航天器编队飞行过程中存在的轨迹优化问题,首先系统综述其多种相对运动动力学模型,分类比较模型的特点,并考虑航天器运动环境和不同求解方法阐述编队轨迹优化问题。在建立数学优化模型的基础上描述该问题的一般形式,提出了航天器编队飞行相对运动轨迹优化问题的难点。综述航天器编队飞行构建或重构任务中轨迹优化问题的求解方法,总结分析其优缺点,并介绍常用的数学求解工具。最后,提出值得深入研究的关键技术需求和航天器编队飞行未来发展的重要方向。

基于MPC延时补偿器的农机多机器人编队行驶轨迹跟踪方法

[目的/意义]农机装备尺寸大、行驶慢等特点,在路面归库作业过程中容易造成严重道路拥堵。因此,在多机协同过程中,编队行驶被认为是未来道路上行驶的主要方式。然而,目前农机自动驾驶技术停留在单机阶段,多农机之间的协同仍是制约中国农业规模化自主生产的主要瓶颈。为解决多车编队协同控制中通信延时的问题及其补偿策略,本研究基于一种模型预测控制器(Model Predictive Control,MPC)延时补偿器的农机多机编队行驶的轨迹跟踪方法。[方法]以车联网技术为基础,聚焦多农机编队协同控制领域,针对控制器局域网总线(Controller Area Network,CAN)通信存在的延时问题而产生的横向控制精度差,基于线性二次调节器(Linear Quadratic Regulator,LQR)与MPC算法,设计了一种带有延时补偿的模型预测控制器,用于对通信延时进行补偿控制。最后对所提算法利用Carsim和Simulink软件进行联合仿真。[结果和讨论]Carsim与MATLAB/Simulink可以有效兼容,实现软件与外部求解器的联合仿真。当延时步长d=5时,应用延时补偿,MPC反应速度更快,表现更为平滑;速度误差曲线响应更快,且能够逐渐稳定至零误差,没有出现振荡现象;1号车在较短时间内有效地变更车道,与头车保持在同一车道上。在更长的延时步长d=10情况下,未应用延时补偿的控制器表现出更显著的性能下降。即使在较高的延时条件下,应用延时补偿的MPC速度误差和纵向加速度仍然能够快速响应并逐渐稳定至零误差,避免了振荡现象。1号车的轨迹表明,延时补偿机制效果在极端延时条件下有所下降。[结论]本研究所设计的编队算法能够使得多车完成多车变道形成队列并保持一定距离和一定速度。通信延时补偿控制算法使得带有加入延时的车辆能较好完成编队任务,实现稳定的横纵向控制,验证了本研究带有延时补偿的模型预测控制器的可行性。

基于改进一致性理论的无人机编队航迹在线规划

针对无人机编队在飞行过程中任务发生变化的情形,提出了基于改进一致性理论的无人机编队航迹在线规划方法。首先,针对一致性算法进行改进,引入人工势场法,提出了考虑机间距离和相对速度的防碰撞策略;基于无人机相对位置和状态量,提出了考虑无人机转弯半径和速度的转弯策略。其次,基于编队拆分思想和RRT*算法,提出了基于拆分编队思想的在线航迹规划方法。仿真结果表明:防碰撞策略能使无人机之间在编队成形前保持安全距离,不发生碰撞;转弯策略能使编队在转弯过程中保持队形;编队重组的在线航迹规划方法能满足执行新增任务的情形。

引入控制量变化率约束的双层协同轨迹规划器

针对亚音速飞行器编队飞行轨迹规划约束复杂、求解困难的问题,提出了一种引入控制量变化率约束的双层亚音速飞行器协同轨迹规划器。首先,引入控制量变化率约束以保证轨迹可行性,为了避免增加新的状态方程而增加计算量,采用拉格朗日插值多项式计算控制变量变化率,将其作为求解最优控制问题伪谱法的约束条件。然后,使用顶层单飞行器规划器在不考虑多飞行器协同约束的条件下使用较少配点的伪谱法快速求解每个飞行器的粗略轨迹结果,求解结果使用拉格朗日插值作为底层多飞行器规划器的初值。底层多飞行器规划器使用更多的配点以确保求解的精度,在考虑多飞行器协同约束条件下进行伪谱法求解,以解决伪谱法初值敏感问题并提高优化效率。最后仿真结果表明了所提方法的有效性,与引入虚拟控制量而增加状态方程方法相比,此方法计算量更小,求解效率更优,满足协同轨迹规划的要求。

川中资阳—东峰场区块须家河五段储层“四性”关系及应用

川中资阳—东峰场区块须家河五段(以下简称须五段)储层具有低孔、低渗且非均质性强的特点,为了建立可靠的测井解释模型以及确定有效储层下限,应用砂岩测井、录井、岩心及试气等资料,以岩心归位及测井曲线标准化为依据,开展储层“四性”关系研究,结果表明:岩性、物性、电性、含气性相关性较好,自然伽马随粒度减小而增大;电阻率曲线可以识别含钙砂岩;声波时差与孔隙度相关性好;含气性与物性呈正相关。在“四性”关系研究的基础上建立了孔隙度、渗透率及含水饱和度解释模型,并确定了储层判别标准。以上研究成果在生产中取得良好的应用效果,储层测井、试气和实验结果符合“四性”关系图版。通过测井解释模型计算的物性参数与岩心实验测试结果吻合;产气剖面测试结果与储层判别标准匹配。“四性”关系研究为测试方案设计提供了有效的技术支撑。

中国传统村落与乡村旅游重点村的空间关系及形成机理研究

传统村落作为特殊的乡村地理单元,拥有丰富的资源禀赋,但由于经济落后,大多数未能得到较好的发展。乡村振兴背景下,乡村旅游成为重要的发展业态,国家政策导向下全国乡村旅游重点村得以提出,如何发掘传统村落与乡村旅游的内在关联和逻辑,成为亟待解决的重要问题。以六批传统村落和四批乡村旅游重点村为研究对象,剖析二者之间的空间关系,为实现传统村落的有序开发与活化利用提供依据。结果表明:(1)传统村落和乡村旅游重点村总体上呈胡焕庸线东侧分布多、胡焕庸线西侧分布少的空间格局;(2)乡村旅游重点村密度高—传统村落密度高的聚类区域分布在浙皖闽赣聚集区、黔桂湘渝聚集区和晋冀豫聚集区;高—低类区域分布在京津冀地区和苏皖交界处;低—高类区域分布在湘黔桂交界处和云南部分地区;低—低类区域分布在东北地区和西部地区;(3)传统村落和乡村旅游重点村的空间关系受社会经济环境、历史文化环境和政府政策环境等因素影响。