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.

Medial Longitudinal Arch Pad Influences Landing Control of the Lower Limbs during Single-Leg Jump-Landing

Background: Arch support has the effect of maintaining arch and correcting alignment, and it is broadly used for the prevention of sports impediment and treatment of athletes with lowered MLA and foot problems. The fact that the morphological change of MLA damages balance sense and postural control, it was reported that the insole supporting the arch of MLA improved postural balance. There are several studies regarding the effects of arch support;however, its effects on landing control have not been clarified. Therefore, in our research, we discussed the effect of MLA support for landing control, using lower limb dynamic alignment and the moment during landing as indexes. Methods: This study measured the landing motion to be evaluated was to jump from a platform with a height of 30 cm by taking-off with a single foot, and landing on a single foot on a floor reaction force gauge placed ahead and stay still for three seconds for the subjects were 13 healthy females. A soft 6 mm Boron sheet cut in the size of 9 × 3.5 cm, applied with double-sided tape (MLA pad) was used for arch support (hereafter referred to as “pad”). For the lower limb evaluation, an 8-camera with a three-dimensional behavioral analyzer (CORTEX, NAC product, sampling frequency: 120 Hz) and a floor reaction force gauge (AMTI product, sampling frequency: 1000 Hz) were used. Ten successful jump-landing tests for each limb were used for further analyses using Visual 3D software (Cmotion Inc., Kingston, Canada). Analysis objects were knee joint bending angle and valgus angle during landing;knee joint maximum bending angle;bending knee joint valgus angle, hip joint bending angle, adduction angle, ankle joint plantar flexion angle, varus angle at the time of knee joint maximum bending angle;and each joint moment. For statistical processing, the average value of three trials out of five trials was regarded as a representative value. Results: Regarding joint angles, significant differences were observed in maximum knee joint bending angle, knee joint bending angle during maximum valgus knee joint and ankle joint varus angle during knee joint maximum bending angle between before and after intervention. No significant differences were observed in other joint angles. Regarding joint moments, no significant difference was observed in each joint moment before and after the intervention. Significance: The decrease of knee joint valgus angle during landing by the use of MLA pad suggests the possibility of decreasing the risk of ACL injury. As the incidence of ACL injury in females is higher than that of males, and the evaluation for females had proceeded, it can be useful information for the prevention of ACL injury.

Reconstructing forest and grassland cover changes in China over the past millennium

Historical forest and grassland cover changes not only are critical indicators for quantifying ecological and environmental change processes but also serve as fundamental data for long-term climate change simulations and terrestrial ecosystem carbon emission assessments.However,because of limitations in historical data,quantitative estimations and spatially gridded reconstructions of these changes remain challenging,necessitating further methodological exploration.This study focused on China's present-day land area over the past millennium,objectively capturing the characteristics and drivers of forest and grassland cover changes.On this basis,using the forest transition theory and the space-for-time substitution method,we depicted the historical deforestation process as an inverted“S”curve and developed a model to reconstruct historical forest area changes based on the functional relationship between the forest area and population size dynamics.Subsequently,a gridded forest allocation model was established on the basis of deforestation tendencies.For the grassland cover,we implemented regionspecific methods,such as the cropland area deduction method and the habitat constraint method,to quantitatively reconstruct historical changes.Consequently,we obtained provincial forest and grassland area changes over the past millennium and mapped 10-km-resolution gridded data of forest and grassland cover.The results indicated the following.(1)The methods developed using population data as a proxy objectively reproduced the spatiotemporal evolution of forest and grassland cover in China over the past millennium.These feasible methods offer a novel pathway for the quantitative reconstruction of historical forest and grassland cover changes.(2)The data indicated that China's forest area generally decreased over the past millennium,characterized by a“decrease-then-increase”pattern.The forest area experienced three distinct phases:a slow decline(AD 1000–1650),a rapid decline(AD 1650–1960),and a gradual recovery(AD 1960–2000).The area decreased from 298 million hectares(Mha)in AD 1000 to 89 Mha in AD 1960 before increasing to 153 Mha in AD 2000.Spatially,deforestation began in the middlelower reaches of the Yellow River and gradually expanded to the middle-lower reaches of the Yangtze River,the southern coastal areas of China,southwest China,and northeast China,with the forest cover declining by 27%,40%,58%,55%,and 35%in these regions,respectively.(3)China's grassland area has shown a continuous decline over the past millennium with three phases:stable fluctuation(AD 1000–1600),slow decline(AD 1600–1900),and rapid decline(AD 1900–2000).The grassland area decreased from 305 Mha in AD 1000 to 277 Mha in AD 2000.Notably,zonal grassland areas in Northeast China,Inner Mongolia,Gan-Ning,Qinghai,Xinjiang,and Xizang decreased by 28 Mha over the millennium,whereas nonzonal secondary grassland areas in the hilly and mountainous areas of eastern and southern China increased by 0.3 Mha.

Influencing Factors of Cultivated Land Fragmentation on Planting Decision of Daylily

Based on questionnaire survey data of daylily planting farmers in the paper,from the perspective of farmers own conditions(including age,gender,education level,and annual household income),climate perception ability,policy perception ability,and land fragmentation situation,consistency analysis,variance analysis,regression analysis and other methods were used to analyze the impact of land use on farmers decision-making changes in planting daylily.The results showed that the age of the household head,annual household income,policy perception ability,and average cultivated land area per block had a significant impact on the planting area of daylily,and the degree of impact increased in order.This study can provide theoretical basis and practical guidance for farmers decision-making and land use methods in planting daylily.

Survey and Recommendations for Land Use of Agricultural Machinery Service Organization Facilities in Guizhou Province

With the advancement of agricultural modernization, agricultural machinery service organizations, as an important part of the rural operating entities, show an increasing trend year by year, and need new facilities land in the process of development and growth. Based on the written survey of 597 agricultural machinery service organizations in Guizhou Province, the demand and demand gap of various facilities land use in agricultural machinery service organizations were analyzed and compared. In addition, based on the field survey and policy background, the main practices and experiences of agricultural machinery service organizations in Guizhou Province in the approval and use of facility land were sorted out, and the problems and causes of large gap in facility agricultural land, lack of standards and difficulty in policy implementation were analyzed. Finally, it recommended that the site selection of agricultural machinery service organization facilities needs to be standardized, the land demand needs to be coordinated, the land scale needs to be scientifically demonstrated, and financial support should be sought to promote Guizhou agricultural machinery service organization to become bigger, better and stronger.

Land use/cover change and ecological network in Gansu Province,China during 2000-2020 and their simulations in 2050

Land use/cover change(LUCC)constitutes the spatial and temporal patterns of ecological security,and the construction of ecological networks is an effective way to ensure ecological security.Exploring the spatial and temporal change characteristics of ecological network and analyzing the integrated relationship between LUCC and ecological security are crucial for ensuring regional ecological security.Gansu is one of the provinces with fragile ecological environment in China,and rapid changes in land use patterns in recent decades have threatened ecological security.Therefore,taking Gansu Province as the study area,this study simulated its land use pattern in 2050 using patch-generating land use simulation(PLUS)model based on the LUCC trend from 2000 to 2020 and integrated the LUCC into morphological spatial pattern analysis(MSPA)to identify ecological sources and extract the ecological corridors to construct ecological network using circuit theory.The results revealed that,according to the prediction results in 2050,the areas of cultivated land,forest land,grassland,water body,construction land,and unused land would be 63,447.52,39,510.80,148,115.18,4605.21,8368.89,and 161,752.40 km^(2),respectively.The number of ecological sources in Gansu Province would increase to 80,with a total area of 99,927.18 km^(2).The number of ecological corridors would increase to 191,with an estimated total length of 6120.66 km.Both ecological sources and ecological corridors showed a sparse distribution in the northwest and dense distribution in the southeast of the province at the spatial scale.The number of ecological pinch points would reach 312 and the total area would expect to increase to 842.84 km^(2),with the most pronounced increase in the Longdong region.Compared with 2020,the number and area of ecological barriers in 2050 would decrease significantly by 63 and 370.71 km^(2),respectively.In general,based on the prediction results,the connectivity of ecological network of Gansu Province would increase in 2050.To achieve the predicted ecological network in 2050,emphasis should be placed on the protection of cultivated land and ecological land,the establishment of ecological sources in desert areas,the reinforcement of the protection for existing ecological sources,and the construction of ecological corridors to enhance the stability of ecological network.This study provides valuable theoretical support and references for the future construction of ecological networks and regional land resource management decision-making.

Assessment of ecological geological vulnerability in Mu Us Sandy Land based on GIS and suggestions of ecological protection and restoration

Eco-geological vulnerability assessment is a significant research topic within the field of eco-geology,but it remains poorly studied.The Mu Us Sandy Land,located in the central part of the farming-pastoral ecotone in northern China,plays a critical role in maintaining the ecological security pattern in this region.However,this sandy land also faces severe sandy desertification and ecological degradation.This study conducted a regional eco-geological vulnerability assessment of the Mu Us Sandy Land using a comprehensive index evaluation method based on eco-geological theories and survey results.To construct an appropriate index system for the eco-geological vulnerability assessment of the Mu Us Sandy Land,the study considered the sandy land’s unique characteristics and identified 15 factors of five categories,namely geology,meteorology,soil,topography,and vegetation.The paper calculated the comprehensive weights of all the indices using the analytic hierarchy process(AHP)and the entropy weight method(EWM).Furthermore,it established the eco-geological vulnerability index(EGVI)and obtained the assessment results.The results showed that the eco-geological vulnerability of the Mu Us Sandy Land gradually intensifies from east to west,manifested as vulnerable eco-geological conditions overall.Specifically,extremely vulnerable zones are found in the northwestern and southeastern parts of the study area,highly vulnerable zones in the western and southern parts,moderately vulnerable zones in the central part,and slightly and potentially vulnerable zones in the eastern and southern parts.Areas with high spatial autocorrelations include the northern Uxin Banner-Otog Banner-Angsu Town area,the surrounding areas of Hongdunjie Town in the southeastern part of the study area,the Hongshiqiao Township-Xiaohaotu Township area,Otog Front Banner,and Bainijing Town,which should be prioritized in the ecological conservation and restoration.Additionally,the paper proposed suggestions for the ecological conservation and restoration of county-level administrative areas in the study area.Overall,the findings provide a valuable reference for the ecological conservation and restoration of the Mu Us Sandy Land and other desert areas in arid and semi-arid regions.

基于Landsat数据的江苏省土地利用变化分析

随着人类社会生活的不断演变,土地利用模式和土地使用形态随之发生根本性变化。文章以江苏省为例,通过土地利用动态度、土地利用转移矩阵等方法,深入研究江苏省土地利用特征的时空变化情况。研究发现,江苏省耕地、未利用土地面积减少趋势明显,大部分转向建设用地和坑塘、滩地等用途,草地面积明显增加。这表明江苏省在加速城市化步伐的过程中,同步增强了对生态文明建设的重视。文章为江苏省国土空间规划、可持续发展路径的探索以及经济生态的协调发展贡献了多元化的思考维度。

基于谷歌地球引擎和Landsat影像的广西壮族自治区土地覆盖变化及驱动因素研究

基于GEE和随机森林分类算法研究广西壮族自治区在1995—2022年27 a间的土地覆被变化,采用地理探测器对不同土地覆被类型的时空变化及其主要驱动因素进行分析研究。结果表明:1)土地覆被类型分类结果具有较好的分类精度,整体精度在87%~92%。2)1995—2022年,广西壮族自治区的林地和建设用地面积持续增加,增幅分别达75.94%和132.67%。林地面积从85382.72 km^(2)增加到150224.55 km^(2),建设用地面积从2038.73 km^(2)增加到4743.46 km^(2);与此同时,草地及稀疏灌草混交地面积减少了82.46%(66990.97 km^(2));其他土地覆被类型变化则相对稳定。3)通过地理探测器模型的分析结果显示,人为因素是影响土地利用/覆被(LULC)变化的主要驱动因素,经济的快速发展、城市人口的增加和工业扩张是建设用地和林地扩张以及植被减少的主要原因。研究结果对于广西壮族自治区的生态环境管理和土地可持续利用规划具有参考价值。

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.

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.

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.

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.

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%.

Guidance and Control Techniques of Carrier-Based Aircraft for Automatic Carrier Landing

We summarize the guidance and control techniques of automatic carrier landing for carrier-based aircraft.First,we analyze the carrier landing operations of the manned fixed-wing aircraft,unmanned fixed-wing aircraft and helicopters.Second,we look into the navigation and guidance system and the flight control methods for current different aircraft.Finally,we draw several conclusions of the development prospects for aircraft carrier landing,including the precision landing control techniques,precision approach and landing guidance techniques,and adaptive,reconfigurable and intelligent flight control techniques.

基于Landsat影像的城市土地利用动态监测

土地是自然界不可或缺的资源,土地利用反映了人地关系。随着人口数量的持续增加和社会工业化、城市化的持续推进,如何科学地开发利用宝贵的土地资源越来越受到人们的重视。本文通过2013年和2023年的Landsat影像数据,结合遥感与GIS,对10年间合肥市土地资源进行监测与分析,结果表明,经过10年的城市发展,合肥市耕地面积减少了65707.92 hm 2,建设用地增长了39181.05 hm 2,林地减少了1728.27 hm 2,水域增加了28255.14 hm 2。

Autonomous Landing of Small Unmanned Aerial Rotorcraft Based on Monocular Vision in GPS-denied Area

Focusing on the low-precision attitude of a current small unmanned aerial rotorcraft at the landing stage, the present paper proposes a new attitude control method for the GPS-denied scenario based on the monocular vision. Primarily, a robust landmark detection technique is developed which leverages the well-documented merits of supporting vector machines (SVMs) to enable landmark detection. Then an algorithm of nonlinear optimization based on Newton iteration method for the attitude and position of camera is put forward to reduce the projection error and get an optimized solution. By introducing the wavelet analysis into the adaptive Kalman filter, the high frequency noise of vision is filtered out successfully. At last, automatic landing tests are performed to verify the method's feasibility and effectiveness. © 2014 Chinese Association of Automation.