Formation of Tianwen-1 landing crater and mechanical properties of Martian soil near the landing site

After landing in the Utopia Planitia,Tianwen-1 formed the deepest landing crater on Mars,approximately 40 cm deep,exposing precious information about the mechanical properties of Martian soil.We established numerical models for the plume-surface interaction(PSI)and the crater formation based on Computational Fluid Dynamics(CFD)methods and the erosion model modified from Roberts’Theory.Comparative studies of cases were conducted with different nozzle heights and soil mechanical properties.The increase in cohesion and internal friction angle leads to a decrease in erosion rate and maximum crater depth,with the cohesion having a greater impact.The influence of the nozzle height is not clear,as it interacts with the position of the Shock Diamond to jointly control the erosion process.Furthermore,we categorized the evolution of landing craters into the dispersive and the concentrated erosion modes based on the morphological characteristics.Finally,we estimated the upper limits of the Martian soil’s mechanical properties near Tianwen-1 landing site,with the cohesion ranging from 2612 to 2042 Pa and internal friction angle from 25°to 41°.

Effects of retained dry material on the impact,overflow and landing dynamics

During long-term operation,the performance of obstacles would be changed due to the material accumulating upslope the obstacle.However,the effects of retained material on impact,overflow and landing dynamics of granular flow have not yet been elucidated.To address this gap,physical flume tests and discrete element simulations are conducted considering a range of normalized deposition height h0/H from 0 to 1,where h0 and H represent the deposition height and obstacle height,respectively.An analytical model is modified to evaluate the flow velocity and flow depth after interacting with the retained materials,which further serve to calculate the peak impact force on the obstacle.Notably,the computed impact forces successfully predict the experimental results when a≥25°.In addition,the results indicate that a higher h0/H leads to a lower dynamic impact force,a greater landing distance L,and a larger landing coefficient Cr,where Cr is the ratio of slope-parallel component of landing velocity to flow velocity just before landing.Compared to the existing overflow model,the measured landing distance L is underestimated by up to 30%,and therefore it is insufficient for obstacle design when there is retained material.Moreover,the recommended Cr in current design practice is found to be nonconservative for estimating the landing velocity of geophysical flow.This study provides insightful scientific basis for designing obstacles with deposition.

Stability Analysis of Nonlinear Models of Nose Landing Gear Shimmy

Shimmy can reduce the service life of the nose landing gear, affect ride comfort, and even cause fuselage damage leading to aircraft crashes. Taking a light aircraft as the research object, the torsional freedom of landing gear around strut axis and lateral deformation of tire are considered. Since the landing gear shimmy is a nonlinear system, a nonlinear mechanical model of the front landing gear shimmy is established. Sobol index method is proposed to analyze the influence of structural parameters on the stability region of the nose landing gear, and Routh-Huritz criterion is used to verify the reliability of the analysis results of Sobol index method. We analyse the effect of torsional stiffness of strut, caster length, rated initial tire inflation pressure, rake angle, and vertical force on the stability region of theront landing gear. And the research shows that the optimization of the torsional stiffness of the strut and the caster length of the nose landing gear should be emphasized, and the influence of vertical force on the stability region of the nose landing gear should be paid attention to.

TEST AND CONTROL SYSTEM DEVELOPMENT AND APPLICATION OF LANDING GEAR DROP TEST RIG

A control and test system of a landing gear drop test rig is developed considering the drop test specifica- tions for the ＂Seagull 300＂ multi-functional amphibious airplane. In order to realize the automation of drop test process, a servo system is proposed and programmable logic controller（PLC） technology is used. Several key technologies for measuring the horizontal load, the vertical load and the transient rotational speed are studied. According to the requirements of CCAR-23-R3, the drop test of landing gears of the ＂Seagull 300＂ airplane is accomplished. Test results show that the system has a high accuracy of data collection. The system is stable and reliable. The drop test satisfies the requirements of the drop test specifications and the results can be used as the certification of airworthiness for this kind of airplane.

Application of High-speed Solenoid Valve to the Semi-active Control of Landing Gear

To select or develop an appropriate actuator is one of the key and difficult issues in the study of semi-active controlled landing gear. Performance of the actuator may directly affect the effectiveness of semi-active control. In this article, parallel high-speed solenoid valves are chosen to be the actuators for the semi-active controlled landing gear and being studied. A nonlinear high-speed solenoid valve model is developed with the consideration of magnetic saturation characteristics and verified by test. According to the design rule of keeping the peak load as small as possible while absorbing the specified shock energy, a fuzzy PD control rule is designed. By the rule controller parameters can be self-regulated. The simulation results indicate that the semi-active control based on high-speed solenoid valve can effectively improve the control performance and reduce impact load during landing.

GUIDANCE AND CONTROL FOR AUTOMATIC LANDING OF UAV

A scheme of guidance and control is presented to meet the requirements for automatic landing of unmanned aerial vehicles (UAVs) based on the airborne digital flight control system and radio tracker on ground station. An automatic landing system is realized for an unmanned aerial vehicle. The results of real time simulation and flight test are given to illustrate the effectiveness and availability of the scheme. Results meet all the requirements for automatic landing of the unmanned aerial vehicle.

DESIGN OF NEW PASSIVE ADAPTIVE SHOCK ABSORBER OF LANDING GEAR AND STUDY OF ITS LANDING PERFORMANCE

A new passive adaptive shock absorber of the landing gear with double-cavity and dual-damping is studied. Its mathematical model and the virtual prototype are established based on the dynamics simulation software ADAMS. The landing dynamic characteristics and the effect of the parameters on the proposed adaptive shock absorber are analyzed. The results show that the proposed adaptive shock absorber has the slightly better landing performance at the normal load case and much less overload at the crudely landing case than the shock absorber with single-cavity and variable orifice. It also can be concluded that the overload of the proposed adaptive shock absorber can be reduced through increasing the volumes of both cavities or decreasing the pressure of the high pressure cavity or increasing the pressure of the low pressure cavity.

云南省城市土地利用效率与土地生态安全耦合协调研究

为深入探究城市土地利用效率与土地生态安全之间的关系,探索出一条既能实现土地高效合理利用又能保护土地生态安全的可持续发展之路。以云南省为例,在构建城市土地利用效率及土地生态安全相应指标体系的基础上,综合运用SBM-Undesirable模型、综合指数法及耦合协调度模型测算云南省城市土地利用效率与土地生态安全水平及两者的耦合协调度及其时空变化特征。结果表明,(1)2006-2021年云南省城市土地利用效率呈现波动上升的变化趋势,研究期间均值为0.92,总体状况较好。(2)2006-2021年云南省城市土地生态安全水平总体呈现上升趋势,经历了“不安全-较不安全-临界安全-较安全”四个阶段,由2006年的0.18提升至2021年的0.77,土地生态安全水平显著提升。(3)2006-2021年,云南省城市土地利用效率与土地生态安全耦合协调度呈现波动上升的趋势,经历“轻度失调-初步协调-中级协调-良好协调-优质协调”5个阶段,空间格局上呈现西北、中部高,西南、东部地区较低的特征。总体来看,研究期间云南省大部分地区城市土地利用效率与土地生态安全处于协调阶段。

人工和天然草地对青年女性跳跃落地时下肢生物力学表现的影响

背景:研究发现运动者解剖结构、激素水平、神经肌肉功能等内部因素与前交叉韧带损伤风险密切相关,而运动场地材质等外部因素也成为影响非接触性前交叉韧带损伤发生的危险因素之一,但目前研究中对其关注度相对不足。目的:探讨人工草地和天然草地对青年女性跳跃落地时下肢生物力学表现影响。方法:根据测试需要将符合GB/T 20033.3-2006以及GB/T 19995.1-2005标准的人工草地和天然草地平整固定于2块三维测力台上。21名青年女性自愿受试者分别在人工草地和天然草地完成跳跃落地任务。受试者站立于台阶上随后向前跳跃,跳落至测力台后立即全力纵跳并再次落至测力台上,2次落地均要求双脚分别落至2块测力台上,整个跳跃动作流畅无停顿视为成功。同步采集下肢落地过程中运动学、动力学及肌电数据,比较分析二者差异。结果与结论:①动力学方面,在天然草地进行跳跃落地任务时初始触地时刻后向地面反作用力、纵向地面反作用力显著低于在人工草地时(P<0.05;P<0.01);峰值地面反作用力时刻二者亦显著低于在人工草地时(P<0.05;P<0.05),且表现出更高的膝关节屈曲力矩(P<0.01)。②肌电方面,在天然草地进行跳跃落地任务时初始触地时刻后100 ms内股内侧肌、股外侧肌、胫骨前肌肌电活动水平显著低于在人工草地时(P<0.05;P<0.01;P<0.05)。③结果说明,在人工草地进行跳跃落地任务时较天然草地时会出现使前交叉韧带张力升高的生物力学表现。

IMPROVED LANDING-GEAR DESIGN FOR FLEXIBLE AIRPLANE

Landing dynamic simulation and landing-gear optimization design are used to improve the landing-gear design for a flexible airplane. Landing response is simulated by using velocity-squared damping, polytropic exponential air-compression spring, tire force power function characteristics, and an equivalent three-mass system.Optimization of landing-gear parameters is performed considering the maximum displacement of the landing-gear shock stroke, the maximum landing-gear force and the maximum deformation of the wingtip in the landing impact. Resutls show that landing-gear design parameters have an important influence on the structural flexibility of the airplane. And the landing performance of the landing-gear can be improved by the optimized metering pin type landing-gear.

近30年宁夏土地利用碳排放风险及影响因素

本文采用碳排放系数法和LMDI模型分解法,利用1990-2020年宁夏22个县区土地利用和能源消耗数据,分析了土地利用变化与碳排放风险及影响因素。结果表明,(1)1990-2020年宁夏建设用地、林地和水体面积显著增加,以建设用地面积增加最为突出,30年面积增加了15.77×10^(4)hm^(2);耕地和未利用土地面积先增加后减小、草地和面积不断减小,土地利用开发强度增大。(2)宁夏碳排放量呈显著增加趋势,净碳排放增加了4 669.25×10^(4)t,增幅448.69%。(3)宁夏土地利用碳排放风险逐步升高,空间上形成了沿黄县区碳排放风险高于中、南部县区的分布格局。(4)土地利用结构、土地碳排放强度、人均GDP和人口对碳排放的贡献率较大,促进了碳排放量的增加,而单位GDP用地强度对碳排放的贡献率最小,对碳排放起抑制作用。

粤北山区县土地利用变化及其对生态系统服务功能的影响研究——以广东省怀集县为例

经济和生态环境的可持续发展已经上升为国家现代化建设进程的一项重要内容。本文通过对粤北山区县怀集县2009-2018年间土地利用及其生态系统服务价值的变化进行分析,对当地可持续发展具有重要意义。研究表明,(1)怀集县的土地利用结构不平衡分布特征明显,土地利用类型结构总体表现为“多保一”的特点。(2)怀集县各地类都有向建设用地转移,而林地、耕地、草地和水域用地为主要土地类型大量转出流入到建设用地。(3)在研究期间,怀集县各项生态功能的生态价值均发生不同程度的变化,其中食物生产的生态价值经历了先增加后减少的过程,土壤形成与保护、水源涵养、气体调节、生物多样性保护、气候调节、原材料、废物处理以及娱乐文化的生态价值均在不断减少,主要是相对应的生态土地类型面积流入到建设用地,造成生态系统服务价值的下降。

兰州市耕地多功能时空演变分析

为充分了解兰州市各县区耕地利用状况,本文利用综合评价法及空间分析法对兰州市2008-2017年耕地多功能演变规律进行时空分析。结果表明,(1)从时序上来看,2008-2017年,兰州市耕地多功能主要以粮食生产功能及社会保障功能为主。(2)从空间上来看,各县区所发挥的耕地功能各不相同,其中永登县及榆中县为耕地总功能做出重要贡献。该研究结果可以为政府制定科学、合理的耕地多功能利用布局方案提供理论依据。

增加着地时足外展角度可降低慢性踝关节不稳者内翻损伤的风险

背景:慢性踝关节不稳者在着地时易发生踝关节内翻扭伤,适度增大着地时足外展角度有助于减少踝关节内翻扭伤的发生,但尚无研究直接论证。目的:探讨着地时增加足外展角度对有无慢性踝关节不稳者着地过程中踝内翻角度、角度峰值时刻及角速度峰值的影响。方法:共招募了60名受试者,其中慢性踝关节不稳者30名,非慢性踝关节不稳者30名。使用模拟扭伤装置进行下落跳测试,该装置中的活动平台可向前翻转24°、向内侧翻转15°,从而模拟踝关节内翻扭伤时的足部位置。受试者需要在两种着地状态下进行下落跳测试,即自然着地和外展着地,后者的足外展角度更大,约为前者的150%以上。使用12摄像头三维红外动作捕捉系统记录运动学数据,采用双因素重复测量方差分析和Spearman相关分析进行数据分析。结果与结论:①下落跳时的内翻角度峰值(P<0.001,η^(2)p=0.270)、内翻角速度峰值(P=0.015,η^(2)p=0.098)和内翻角度峰值时刻(P<0.001,η^(2)p=0.260)均存在显著的状态主效应;内翻角速度峰值存在显著的组别主效应(P=0.029,η^(2)p=0.080);②慢性踝关节不稳组与非慢性踝关节不稳组受试者着地时的足外展角度与踝内翻角度峰值(P=0.021,r=-0.310;P=0.042,r=-0.278)、内翻角度峰值时刻(P=0.018,r=-0.312;P=0.021,r=-0.309)均存在显著的负相关关系;慢性踝关节不稳组受试者着地时的足外展角度与内翻角速度峰值(P=0.021,r=-0.312)之间也存在显著的负相关关系;③提示增加着地时的足外展角度可以减小慢性踝关节不稳及非慢性踝关节不稳人群着地过程中的内翻角度峰值、内翻角速度峰值,提前内翻角度峰值时刻,从而降低踝内翻扭伤的风险。

东北黑土区农村闲置宅基地空间分异及驱动因素——以吉林省梅河口市为例

在乡村振兴和国家粮食安全的大背景下,明晰黑土区农村闲置宅基地空间分异特征及驱动因素,有利于黑土区闲置宅基地的高效利用。本文从自然条件、区位条件、经济条件三个方面选取9个指标构建影响宅基地闲置率的指标体系,以梅河口市303个行政村宅基地为研究对象,利用地理探测器、空间自相关和逐步回归分析等方法,从村级小尺度微观研究黑土区农村闲置宅基地空间分异及驱动因素。结果表明,(1)农村闲置宅基地分布存在明显区域差异性和空间集聚性。(2)各指标因子在作用方向和作用强度上对农村宅基地闲置率影响各不相同。(3)研究区农村闲置宅基地的7大主导驱动因素是平均坡度、平均高程、到镇政府距离、到县城距离、到干道距离、到河流距离、人均耕地面积。(4)闲置宅基地的形成是各影响因子综合作用的结果。

黄土丘陵区县域耕地时空格局变化及驱动因素分析——以天水市武山县为例

以黄土丘陵区武山县为研究对象,基于土地利用数据,运用变化轨迹分析法、面积加权平均差椭圆和景观格局指数以及土地利用预测模型,探究1990-2018年武山县耕地格局变化特征,判断各要素对其变化的重要程度。结果显示,(1)3个研究时段武山县耕地面积总体呈减少趋势,耕地重心不同时段存在差异,耕地重心先向西南转移再向东南转移。(2)3个研究时段武山县耕地变化都具有减少补充的基本特征,2000年前速率缓慢,2000年后速率加快,耕地减少面积比补充面积多,耕地减少以城关镇和洛门镇为主。(3)3个研究时段武山县耕地图斑呈现出破碎化现象,破碎化程度加剧。(4)3个研究时段武山县耕地发生变化的主要原因可以归纳为政策影响、自然环境因子影响、空间距离要素的影响,而受地理空间要素影响较小。综上,武山县耕地在28年间变化明显,武山县需要贯彻耕地保护政策和可持续发展理念,合理利用耕地。

“三生空间”视角下贵溪市土地利用转型的生态系统服务价值效应

本文基于贵溪市2010-2018年土地利用现状数据为基础,在“三生空间”视角下,使用土地利用转移矩阵表达了贵溪市土地利用转型过程,并通过生态系统服务贡献值从正负两方面量化土地类型转变造成的生态系统服务价值效应。结果表明,2010-2018年,贵溪市生态用地面积减少,生产和生活用地不断增加,其中林地生态用地减少最多,共计2 330.73 hm^(2),农业生产用地增加最多,面积为1 183.35 hm^(2)。贵溪市生态系统服务价值存在明显差异,整体上是“南北高,中部低”的空间分布。2010-2018年,从生态系统服务价值总体层面,贵溪市呈下降趋势。由于城市化和工业化的快速推进,生活用地和生产用地正在侵占大量生态用地,对生态系统服务价值产生负效应影响。对生态系统服务有正效应影响的主要土地利用转换类型是农业生产用地向各种生态用地的转换,“退耕还林还草”的实施是主要原因。贵溪市生态系统服务价值从2014年开始下降幅度得到缓解,但总体上生态系统服务价值负效应大于正效应。分析2010-2018年贵溪市土地利用转型及其生态系统服务价值效应对贵溪市国土空间规划和“生态文明建设”具有指导意义。

考虑基础-土相互作用的采空区输电铁塔承载特性研究

采空区地表沉降后,输电铁塔基础可能发生沉降、倾斜,影响杆件变形及轴力分布,导致杆件失效。以某采空区750 kV输电铁塔为研究对象,建立了输电铁塔、基础与土相互作用的有限元模型,对不同基础型式、不同沉降位置的塔腿杆件轴力分布及变形影响规律进行了分析,同时分析了铁塔基础的受力特性。结果表明,当考虑相互作用影响时,杆件轴力和节点位移随沉降值呈非线性变化;相较于独立基础,不同沉降位置对大板基础的塔腿主材、斜材轴力的影响更大;当基础处于沉降位置时,防护大板能有效减小基础所受应力。

Hierarchical Optimization of Landing Performance for Lander with Adaptive Landing Gear

A parameterized dynamics analysis model of legged lander with adaptive landing gear was established. Based on the analysis model, the landing performances under various landing conditions were analyzed by the optimized Latin hypercube experimental design method. In order to improve the landing performances, a hierarchical optimization method was proposed considering the uncertainty of landing conditions. The optimization problem was divided into a higher level(hereafter the "leader") and several lower levels(hereafter the "follower"). The followers took condition?ing factors as design variables to find out the worst landing conditions, while the leader took bu er parameters as design variables to better the landing performance under worst conditions. First of all, sensitivity analysis of landing conditioning factors was carried out according to the results of experimental design. After the sensitive factors were screened out, the response surface models were established to reflect the complicated relationships between sensi?tive conditioning factors, bu er parameters and landing performance indexes. Finally, the response surface model was used for hierarchical optimization iteration to improve the computational e ciency. After selecting the optimum bu er parameters from the solution set, the dynamic model with the optimum parameters was simulated again under the same landing conditions as the simulation before. After optimization, nozzle performance against damage is improved by 5.24%, the acceleration overload is reduced by 5.74%, and the primary strut improves its performance by 21.10%.

长白山山脉耕地土壤属性与改良利用的调查研究

本研究以长白山山脉,尤其位于火山口土壤中具备火山灰的耕地为研究对象,从土壤pH、有机质、大量元素氮磷钾、微量元素铜锌铁锰等多个项目进行土壤属性的检测。结果表明,耕地土壤PH值的加权平均值为5.50,呈弱酸性,有机质含量加权平均值为3.74%,全氮的加权平均值为0.2077%,土壤有效磷的加权平均值为44 mg/kg,土壤速效钾的加权平均值为82.79mg/kg,土壤有效铜的加权平均值为2.49 mg/kg,土壤有效铁的加权平均值为30.18 mg/kg,土壤有效锰的加权平均值为28.68mg/kg,土壤有效锌的加权平均值为2.05 mg/kg。调查区域内整体耕地地力大量元素丰富,微量元素除铁外均贫瘠,需采用具有针对性的改良利用方法。