Behavior and dynamics of gecko＇s locomotion： The effects of moving directions on a vertical surface

The study of the movement behavior of geckos on a vertical surface, including the measurement and recording of the reaction forces as they move in different directions, plays an important role in understanding the mechanics of the animals’ locomotion. This study provides inspiration for the design of a control system for a bionics robot. The three-dimensional reaction forces of vertical surface-climbing geckos (Gekko gecko) were measured using a three-dimensional force-sensors-array. The behavior of gecko as it moved on a vertical surface was recorded with a high speed camera at 215 fps and the function of each foot of a gecko are discussed in this paper. The results showed that the gecko increased its velocity of movement mainly by increasing the stride frequency in the upward, downward and leftward direction and that the speed had no significant relationship to the attachment and detachment times. The feet above the center-of-mass play a key role in supporting the body, driving locomotion and balancing overturning etc. The movement behavior and foot function of geckos change correspondingly for different conditions, which results in safe and effective free vertical locomotion. This research will be helpful in designing gecko-like robots including the selection of gait planning and its control.     

Variation in spatial and temporal kinematics of level,vertical and inverted locomotion on a stinkbug Erthesina fullo

In the learning of locomotion behavior of a stink- bug Erthesina fullo, the seeked principle of its locomotion can be an important inspiration on the design of six-legged robot. To achieve this goal, in this paper, locomotion behavior of stink- bugs on glass and plastic foam are recorded. Hereby, variation in spatial and temporal kinematics of level, vertical and inverted locomotion is analyzed. Differential leg function and adhesive mechanism as well as the advantage of non-isometric legs of insects are presented. With increasing stride frequency, the speed of level, vertical and inverted locomotion can be higher without adjusting stride length. Variation in gait characteristics between level and vertical locomotion is very little, but lower speed and larger duty factor of inverted locomotion can be occurred while climbing on glass. On the surface of vertical and inverted plastic foam, stinkbugs cannot walk steady and agilely due to its adhesive mechanism.     

Dynamic stability of quadruped robot walking on slope with trot gait

The dynamic stability of a quadruped robot trotting on slope was analyzed.Compared with crawl gait, trot gait can improve walking speed of quadruped robots.When a quadruped robot trots, each leg is in the alternate state of swing phase or supporting phase, and two legs in the diagonal line are in the same phase.The feet in the supporting phase form a supporting region on the ground.When a quadruped robot walks on slope, the vertical distance from zero moment point ( ZMP) to the sup-porting diagonal line is defined as ZMP offset distance.Whether this distance is less than the maxi-mum offset distance or not, the stability of robot trotting on slope can be judged.The foot trajectory was planned with the sinusoidal function.Based on the kinematic analysis, the ZMP offset distance of quadruped robot under different slope angles, step length and step height was calculated, then the reasonable slope angle, step length and step height for quadruped robot trotting on slope to keep dy-namic stability can be determined.On the other hand, the posture angle of quadruped robot should be controlled within the desired range.Computer simulations were executed to verify the theoretical analysis.The study will provide reference for determining reasonable step parameters of the quadru-ped robot.     

Effect of Slope Plate Variable and Reheating on the Semi-Solid Structure of Ductile Cast Iron

Semi-solid metal casting and forming is a promising production method for a wide range of metal alloys, In spite of many applications for semi-solid processed light alloys, few works have reported on the semi-solid processing of iron and steel. In this research, an inclined plate was used to change the dendritic structure of iron to globular. The effects of the length and slope of the plate on the casting structure were examined. The results show that the process effectively changes the dendritic structure to globular. A sloped plate angle of 7.5° and length of 560 mm with a cooling rate of 67 K· s^-1 gave the optimum graphite nodu- larity and solid particle globularity. The results also show that the sloped plate more easily prevents inoculant fading since the total time processing is rather short. In addition the semi-solid ductile cast iron prepared using the inclined plate method was reheated to examine the effect of reheating conditions on the microstructure and coarsening kinetics of the alloy. The solid fractions at different reheating temperatures and holding times were used to find the optimum reheating temperature range.     

Preparation of Ultra-High-Speed Casein Trade Mark Adhesive

In present trade mark adhesives for beer bottle labeling are mostly prepared based on starch, polyvinyl formal and their derivants ,but they can only be applied to the labeling speed of 20 000 bottle/h and their water proofness are not satisfactory, especially when the water temperature is 0℃ below. The application of metal foil requires that sealing and labeling must be finished at the same time, but different penetrating speed of water in metal foil and paper label causes different drying speed, and also, the labeling speed and need of iced beer are increasing now, so these changes result in more strict requirements for adhesive.     

Multi-factor sensitivity analysis of shallow unsaturated clay slope stability

An unsaturated clay slope, with various sloping angles and a thickness of 14 m, consists of backfill, slope soil and residual soil. Slide interfaces were determined by geophysical approaches and the original slope was reconstructed. Sub-slope masses were classified based on the varieties of sloping angle. A force recursive principle was proposed to calculate the stability coefficient of the sub-slope masses. The influencing factors such as sloping angle, water content, hydrostatic pressure, seismic force as well as train load were analyzed. The range and correlation of the above-mentioned factors were discussed and coupled wave equations were established to reflect the relationships between unit weight, cohesion, internal frictional angle, and water content, as well as between internal frictional angle and cohesion. The sensitivity analysis of slope stability was carried out and susceptive factors were determined when the factors were taken as independent and dependent variables respectively. The results show that sloping angle, water content and earthquake are the principal susceptive factors influencing slope stability. The impact of hydrostatic pressure on slope stability is similar to the seismic force in quantity. Train load plays a small role in slope stability and its influencing only reaches the roadbed and its neighboring slope segment. If the factors are taken as independent variables, the influencing extent of water content and cohesion on slope stability can be weakened and train load can be magnified.     

Interaction of aerodynamic roughness length and windflow conditions and its parameterization over vegetation surface

Surface aerodynamic roughness length is usually taken as a constant. In fact, it displays a remarkable dynamic change over underlying vegetation surfaces, because of the coupling of land surface roughness elements and windflow conditions. Current international research on this dynamic change and associated mechanisms is very limited. Using observations from different underlying surfaces (including forest, farmland and grassland) provided by a northern China coordinated observation test, the variation of aerodynamic roughness length, along with wind speed and friction velocity, is analyzed. We introduce two relationship fits, between aerodynamic roughness length and wind speed u, and dynamic variable u2/u*. Results show that aerodynamic roughness length has a clear dynamic change, and has complicated interactions with near-surface windflow. Further, the relationship fits between aerodynamic roughness length, u and u2/u*, are not only related to the roughness properties of the underlying vegetation surface (e.g. plant height), but also to plant dynamic response characteristics (e.g. flexibility). Aerodynamic roughness length decreases with increasing wind speed, because near-surface windflow conditions can change both plant roughness properties and airflow. However, the change of aerodynamic roughness length with friction velocity is complicated, and its sensitivities and transition points significantly depend on vegetation type. For underlying surfaces of forest and corn, with relatively substantial vegetative cover, roughness length correlates well with wind speed. For a surface with short vegetative cover, like natural lawn, the correlation is low. However, for all of the three vegetative surfaces, there is a close relation between roughness length and u2/u*, and their coefficients of fit from testing essentially represent the plant height and flexibility of different vegetation types. The test results also indicate that the parameterized relationships of roughness length over the underlying vegetation surface hold prospects for application.     

Comprehensive evaluation of high-steep slope stability and optimal high-steep slope design by 3D physical modeling

High-steep slope stability and its optimal excavation design in Shuichang open pit iron mine were analyzed based on a large 3D physical simulation technique. An optimal excavation scheme with a relatively steeper slope angle was successfully implemented at the northwest wall between Nos. 4 and 5 exploration lines of Shuichang Iron Mine, taking into account the 3D scale effect. The physico-mechanical properties of rock materials were obtained by laboratory tests conducted on sample cores from exploration drilling directly from the iron mine. A porous rock-like composite material was formed for the model, and the mechanical parameters of the material were assessed experimentally; specifically, the effect of water on the sample was quantitatively determined. We adopted an experimental setup using stiff modular applied static loading to carry out a visual excavation of the slope at a random depth. The setup was equipped with acoustic emission (AE) sensors, and the experiments were monitored by crack optical acquirement, ground penetrating radar, and close-field photogrammetry to investigate the mechanisms of rock-mass destabilization in the high-steep slope. For the complex study area, the model results indicated a clear correlation between the model's destabilization resulting from slope excavation and the collected monitoring information. During the model simulation, the overall angle of the slope increased by 1-6 degrees in different sections. Dramatically, the modeled excavation scheme saved over 80 million tons of rock from extraction, generating enormous economic and ecological benefits.     

Heat regulating strategy in numerical control end milling for hard metal machining

The trend in die/mold manufacturing at present is towards the hard machining at high speed to replace the electron discharge machining. Failure forms of the AlTiN-coated micro-grain carbide endmill when used for the machining of JIS SKD61 (HRC 53), a widely used material in die/mold manufacturing, are investigated. The endmill shows a characteristic that tool life decreases greatly due to the chipping when overload occurs or the rapid increase of wear when over-heat accumulation in cutting edges. As a consequence of the investigation, a strategy to regulate heat generation in the end milling process is proposed. This is accomplished by controlling the cutting arc length, i.e. the length of each flute engaging workpiece in a cutting cycle. Case studies on the slot end milling and comer rounding are conducted. The results show that the proposed strategy suggests the optimal tool path as well as the optimal pitch between successive tool paths under the cutting time criterion.     

Ecological and environmental explanation of microbiotic crusts on sand dune scales in the Gurbantonggut Desert, Xinjiang

Results obtained from the field investigation and the analysis in laboratory show that many species of microbiotic crusts of lichens, mosses and algae develop extensively in the Gurbantonggut Desert, Xinjiang. The formation, species and distribution are closely related to the environmental conditions at the different positions of sand dunes. The animalcule crusts develop mainly on the mobile or semi-mobile sand surface of dune tops, the alga crusts develop mainly at the upper to middle parts of dune slopes, the lichen crusts develop at middle and lower parts of dune slopes, and the moss crusts are mainly distributed at the lower part of dune slopes and the interdune lowlands. The species, thickness and developing degree of microbiotic crusts increase from the upper part to the middle and lower parts of dune slopes and the interdune lowlands, and an obvious contrast between the microbiotic crusts and the different species of plant communities forms. The development and differentiation of microbiotic crusts at the different positions of dunes are the ecological appearance and the natural selection of synthetic adaptability of the different microbiotic crust species to the local environmental conditions, and are closely related to the ecological conditions, such as the physiochemical properties of soils and stability of topsoil texture.     

基于对角步态下的液压4足机器人能耗研究

移动能耗是液压4足机器人的一项重要性能指标,因此,对不同步态参数下液压4足机器人的移动能耗分析研究具有重要意义. 文中对液压4足机器人进行运动学和动力学建模,利用运动学和动力学模型,根据机构的几何关系得到液压缸运动状态. 规划了摆线函数和三次曲线函数在对角步态下的足端轨迹,对比分析了两种足端轨迹的能量消耗,着重研究了不同步幅、步高、入地角度、周期大小、约束角度以及斜坡角度对移动能耗的影响. 研究结果表明,综合考虑系统的稳定性、冲击力以及速度要求,应选择相对较大的步幅、较大的周期以及较小的入地角度,在满足跨越障碍的情况下,应选择低步高,对整个周期能耗进行考虑,应选择约束入地角度.      

吕梁地区不同地层结构黄土边坡坡脚开挖效应

黄土高原地区崩滑流地质灾害较为严重,与人类工程活动如灌溉和开挖等相关,尤其是坡脚开挖最容易导致坡体失稳形成滑坡崩塌地质灾害。在吕梁地区崩滑灾害野外调查的基础上,将该地区黄土边坡按地层结构概化为四种类型即单一黄土型(Q_3)、黄土-古土壤型(Q_2-S)、黄土-古土壤互层型(Q_3-S-Q_2)和黄土-古土壤-红黏土型(Q_3-S-Q_2-N_2),基于FLAC~(3D)有限差分软件,模拟分析了不同地层结构类型黄土边坡坡脚开挖效应。分析结果表明:四种不同地层结构类型黄土边坡在开挖进尺L≤20 m时,开挖角度对边坡稳定系数的影响不大;开挖进尺L≥30 m时,边坡稳定系数随开挖角度的增大显著降低,且在开挖进尺大、开挖角度较陡时边坡浅层产生贯通的最大剪应变增量带形成浅层滑坡,其中具有多层古土壤结构(Ⅲ型)的黄土边坡稳定性最好;开挖角度较缓时边坡位移以竖向回弹为主,开挖角度较陡时边坡水平与竖向位移均较大;坡型坡高相同的条件下,坡脚开挖导致不同地层结构类型的边坡变形破坏的破坏面形态基本一致,滑体厚度存在一定差异但区别不大。研究结果对黄土地区边坡科学合理开挖和灾害防治具有一定的指导意义。     

基于驾驶行为需求的长大纵坡界定

考虑到山区高速公路的设计中长大纵坡路段的设计,且现行路线设计规范中没有针对长大纵坡路段给出界定标准的问题.本文从驾驶需求出发,将车辆运行速度作为驾驶行为的宏观表现,对长大纵坡路段驾驶行为特性进行分析.采集20名大货车驾驶员在长大纵坡路段实车试验数据,分析得到驾驶员在长大纵坡路段运行速度与平均纵坡坡度和坡长之间的互动关系,建立了大货车运行速度预测模型.分析得到设计速度为60 km/h的山区高速公路在不同平均纵坡条件下最大坡长.      

灌丛分布与坡度的关系: 京津冀山地实例研究

以京津冀山地暖温带灌丛为研究对象, 基于网格化的坡度、气候和植被类型的数据, 利用分段线性回归模型, 分析灌丛的面积百分比与坡度之间的关系。结果显示, 网格内灌丛的百分比与坡度的关系之间存在一个拐点, 而不是单调的线性关系。在缓坡上, 灌丛的百分比随坡度增加而增加, 可能是因为坡地在一定程度上屏蔽了人类活动的干扰。在陡坡上出现两种格局: 除荆条酸枣以外的灌丛的百分比随坡度升高而降低, 主要体现陡坡对资源的限制作用; 荆条酸枣灌丛的百分比没有下降趋势, 可能是因为荆条酸枣灌丛在海拔分布上的差异导致。此外, 研究还发现, 当不考虑气候条件的空间差异时, 除荆条酸枣灌丛以外的类型均分布在15°附近; 在不同的气候条件下, 拐点的位置不同。     

Fabrication of high aspect ratio microfiber arrays that mimic gecko foot hairs

In nature, geckos have developed complex adhesion structures capable of smart adhesion, which is the ability to cling to different smooth and rough surfaces, even ceilings, and detach at will. The hierarchical structure of gecko foot hairs consists of microscale setae, branches and nanoscale spatulae, which contributes to their strong adhesion on different surfaces. In this paper, we propose a simple and low-cost method for fabricating two-level high aspect ratio microfiber arrays that mimic gecko foot hairs. SU-8 photoresist was used and single-level SU-8 microfiber arrays were obtained by a thick film photolithography process. Single-level polydimethyl-siloxane (PDMS) microfiber arrays were also obtained by a micromolding process and the master template for this process was fabricated using inductively coupled plasma (ICP) technology. Using the silicon mold with deep-hole arrays as a substrate, an SU-8 layer with microhole arrays was added to it using thick film photolithography and it formed a double stack mold from which the two-level hierarchical PDMS microfiber arrays were replicated. Water contact angle tests showed that the two-level hierarchical structures are extremely hydrophobic (about 148.5° compared with the Tokay gecko’s 160°).     

基于极限平衡法和FLAC3D软件的高陡边坡稳定性分析

某露天矿山设计终了边坡高度278～350m,坡角42～48°,属于典型高陡边坡。开采过程中出现了出现裂缝、下挫等现象。为了确保该矿山的安全生产,结合其地质资料及边坡的现状,本次选取了6个典型剖面,采用极限平衡法和FLAC~(3D)数值模拟软件,对该露天边坡进行稳定性分析,为后续边坡安全管理提供建议。     

三维软硬互层边坡的破坏模式与稳定性研究

采用FLAC3D强度折减法,研究在岩层倾角、岩层与边坡走向夹角变化时三维软硬互层边坡的稳定性状况,并对其破坏模式进行辨识与归纳分析.结果表明:边坡破坏模式的判别应综合考虑岩层的倾角大小、岩层走向与边坡走向的夹角大小及坡面上的剪出条件;当岩层与边坡走向夹角β<90°时,随着岩层倾角α的增大,边坡的破坏模式变化趋势为由蠕滑-压致拉裂、塑流-拉裂、滑移-拉裂向滑移-弯曲、弯曲-拉裂转变;当β>90°时,边坡的破坏模式趋势为塑流-拉裂、滑移-弯曲、弯曲-拉裂;边坡稳定性系数随走向夹角的增大先增加后减小,β=90°时最大,且α越大,稳定性系数峰值越大;顺向时随着岩层倾角的增大,边坡的破坏模式变化趋势为蠕滑-压致拉裂、滑移-拉裂、滑移-弯曲、弯曲-拉裂,稳定性系数变化先减小后增大,存在一最不利岩层倾角,其对应的稳定性系数最小;反向坡的破坏模式变化趋势为蠕滑-压致拉裂和弯曲-拉裂,稳定性系数逐渐增加.     

不同减小运动学和动力学数据误差的方法对下蹲跳运动仿真结果的影响

探究不同方法处理运动学和动力学数据对运动仿真计算结果的影响,进而减小数据误差以提高运动仿真计算结果的准确性。采集1名普通男性在校大学生的一次下蹲跳(CMJ)测试的运动学和地面反作用力(GRF)数据,分别使用直接计算方法(DK)和逆向运动学方法(IK)计算关节运动学数据;对原始GRF数据(RF)分别进行10 Hz(SF)和50 Hz(HF)的Butterworth 4阶低通滤波处理。应用Open Sim 3. 3软件结合不同方式处理的运动学和GRF数据进行CMJ运动仿真,计算CMJ过程中下肢肌肉-肌腱长度变化和下肢各关节力矩。采用复相关系数(CMC)和平均绝对变化值(MAV)来评价结果的相似性。结果显示:(1)DK和IK计算的CMJ过程的关节角度曲线相似度高,CMC值为0. 93～1. 00,但两种方法计算的髋关节内收外展角及旋转角结果间差异较大,MAV值分别为4. 40°和4. 81°;(2)DK计算的下肢环节长度最大变化量达48 mm,IK计算的下肢环节长度在CMJ过程中保持不变;(3)两种方法计算的肌肉-肌腱长度相似度与各关节角度结果相关;(4)RF、SF和HF计算所得的下肢关节力矩结果相似,但落地缓冲阶段结果差异较大。所得结论如下:(1)使用IK方法处理运动学数据更有利于减小运动学数据误差,提高运动仿真结果的准确性;(2)不同截断频率低通滤波GRF数据对关节力矩计算结果的准确性有影响。建议根据运动特征,选择不同的截断频率处理GRF数据。     

含胶结物砂质边坡稳定性的新分析方法

砂质边坡失稳问题在沿海建设过程中经常发生,常规的土坡稳定性分析方法在合理确定砂质边坡坡顶裂隙的水平位置和破坏时边坡破坏倾角存在明显不足.对于含弱胶结物的砂质边坡(无侧限抗压强度qu<30 kPa),假定破坏面平行于边坡坡面,建立极限平衡方程;对于含中等胶结物的砂质边坡(无侧限抗压强度30 kPa相似文献