足式机器人SLIP模型向上跳跃台阶的运动控制

由于存在地势起伏,台阶对足式机器人运动稳定性会带来较大挑战.弹簧负载倒立摆模型(SLIP)作为研究足式机器人的优良模板,能否完成向上跳跃台阶的动作与其腿部摆角,起跳位置和跳跃高度都有密切的关系.由于调整模型腿部摆角规律容易引发运动失效,故本文在算法中引入虚拟弹簧腿,根据虚拟弹簧腿的运行规律确定合理起跳位置,根据起跳位置来控制系统跳跃高度进而完成跳跃台阶的动作.最后利用仿真软件进行多组仿真,结果表明本文算法对起跳区间划分合理,对起跳高度控制精准,能够实现SLIP模型跳跃台阶前后的稳定运动.

Revealing the role of pyramidal slip in the high ductility of Mg-Li alloy

The high ductility of Mg-Li alloy has been mainly ascribed to a high activity of pyramidal<c+a>slip to accommodate plastic strain.In the present study,however,a quantitative analysis reveals that Li-addition can only slightly stimulate the activation of pyramidal<c+a>slip under compression along the normal direction of a hot-rolled Mg-4.5 wt.%Li plate,with a relative activity of approximately 18%.Although the limited activity of pyramidal<c+a>slip alone cannot accommodate a large plastic strain,it effectively reduces the number of{10.11}−{10.12}double twins,which are believed to be favorable sites for crack initiation.The evidently reduced activity of double twins leads to a lower cracking tendency,and therefore improves ductility.

Research on casing deformation prevention technology based on cementing slurry system optimization

The casing deformation prevention technology based on the optimization of cement slurry is proposed to reduce the casing deformation of shale oil and gas wells during hydraulic fracturing. In this paper, the fracture mechanism of hollow particles in cement sheath was firstly analyzed by discrete element method, and the effect of hollow particles in cement on casing deformation was investigated by laboratory experiment method. Finally, field test was carried out to verify the improvement effect of the casing deformation based on cement slurry modification. The results show that the formation displacement can be absorbed effectively by hollow particles inside the cement transferring the excessive deformation away from casing. The particles in the uncemented state provide deformation space during formation slipping. The casing with diameter of 139.7 mm could be passed through by bridge plug with the diameter of 99 mm when the mass ratio of particle/cement reaches 1:4. According to the field test feedback, the method based on optimization of cement slurry can effectively reduce the risk of casing deformation, and the recommended range of hollow microbeads content in the cement slurry is between 15% and 25%.

Effect of boundary slip on electroosmotic flow in a curved rectangular microchannel

The aim of this study is to numerically investigate the impact of boundary slip on electroosmotic flow(EOF) in curved rectangular microchannels. Navier slip boundary conditions were employed at the curved microchannel walls. The electric potential distribution was governed by the Poisson–Boltzmann equation, whereas the velocity distribution was determined by the Navier–Stokes equation. The finite-difference method was employed to solve these two equations. The detailed discussion focuses on the impact of the curvature ratio, electrokinetic width, aspect ratio and slip length on the velocity. The results indicate that the present problem is strongly dependent on these parameters. The results demonstrate that by varying the dimensionless slip length from 0.001 to 0.01 while maintaining a curvature ratio of 0.5 there is a twofold increase in the maximum velocity. Moreover, this increase becomes more pronounced at higher curvature ratios. In addition, the velocity difference between the inner and outer radial regions increases with increasing slip length. Therefore, the incorporation of the slip boundary condition results in an augmented velocity and a more non-uniform velocity distribution. The findings presented here offer valuable insights into the design and optimization of EOF performance in curved hydrophobic microchannels featuring rectangular cross-sections.

Coseismic deformation and fault slip distribution of the 2023 M_(W)7.8 and M_(W)7.6 earthquakes in Türkiye

On February 6,2023,a devastating earthquake with a moment magnitude of M_(W)7.8 struck the town of Pazarcik in south-central Türkiye,followed by another powerful earthquake with a moment magnitude of M_(W)7.6 that struck the nearby city of Elbistan 9 h later.To study the characteristics of surface deformation caused by this event and the influence of fault rupture,this study calculated the static coseismic deformation of 56 stations and dynamic displacement waveforms of 15 stations using data from the Turkish national fixed global navigation satellite system(GNSS)network.A maximum static coseismic displacement of 0.38 m for the M_(W)7.8 Kahramanmaras earthquake was observed at station ANTE,36 km from the epicenter,and a maximum dynamic coseismic displacement of 4.4 m for the M_(W)7.6 Elbistan earthquake was observed at station EKZ1,5 km from the epicenter.The rupture-slip distributions of the two earthquakes were inverted using GNSS coseismic deformation as a constraint.The results showed that the Kahramanmaras earthquake rupture segment was distinct and exposed on the ground,resulting in significant rupture slip along the Amanos and Pazarcik fault segments of the East Anatolian Fault.The maximum slip in the Pazarcik fault segment was 10.7 m,and rupture occurred at depths of 0–15 km.In the Cardak fault region,the Elbistan earthquake caused significant ruptures at depths of 0–12 km,with the largest amount of slip reaching 11.6 m.The Coulomb stress change caused by the Kahramanmaras earthquake rupture along the Cardak fault segment was approximately 2 bars,and the area of increased Coulomb stress corresponded to the subsequent rupture region of the M_(W)7.6 earthquake.Thus,it is likely that the M_(W)7.8 earthquake triggered or promoted the M_(W)7.6 earthquake.Based on the cumulative stress impact of the M_(W)7.8 and M_(W)7.6 events,the southwestern segment of the East Anatolian Fault,specifically the Amanos fault segment,experienced a Coulomb rupture stress change exceeding 2 bars,warranting further attention to assess its future seismic hazard risk.

Experimental Determination of Deformation Induced Lattice Rotation by EBSD Technique for Slip System Analysis

A method was proposed to experimentally determine the deformation induced lattice rotation by electron backscatter diffraction （EBSD） technique, based on which the activated slip systems could be predicted. The method is to create a project file including the EBSD data of the sample before and after deformation, which allows the lattice rotation to be calculated and visualized using the commercial EBSD software. This method was applied to a polycrystalline Ni subjected to quasi-static compression. The lattice rotation of one grain was calculated and visualized and the activated slip systems were predicted. The comparison with the slip systems predicted by full-constraints （FC） Taylor model highlights the advantage of the present method.

Late Quaternary Slip-rates and Slip Partitioning on the Southeastern Xianshuihe Fault System, Eastern Tibetan Plateau

Quantitative analysis of the kinematics of the active faults distributed around the QinghaiTibetan Plateau is critical to understand current tectonic processes of the plateau. Chronological analysis, based on the comparison among regional climate and geomorphology, digital photogrammetry, offset landforms, and the tectonics were adopted in this study on the Xianshuihe fault in the eastern Tibetan plateau. Two or more offset-age data were obtained for each segment of the Xianshuihe and theYunongxi faults. The offset landforms, including river terrace, alluvial fan and glacial moraine, provide constraints for the late Quaternary slip rate of the Xianshuihe fault. The left-lateral strike slip rate of the Xianshuihe fault decreases from 17 mm/a on the northwest segment to 9.3 mm/a on the southeast segment. Regarding the Xianshuihe fault zone and its adjacent blocks as a regional tectonic system, vector analysis was used to quantitatively analyze the longitudinal kinematical transformation and transversal slip partitioning on the fault zone in terms of the kinematical parameters of the main faults within the zone. The results show that there is a distributed vertical uplift at a rate of 6.1 mm/yr caused by shortening across the Gongga Mountains region. Based on these results, we established a model of the slip partitioning for the southeastern segment of the Xianshuihe fault zone.

Influence of Tire Dynamics on Slip Ratio Estimation of Independent Driving Wheel System

The independent driving wheel system, which is composed of in-wheel permanent magnet synchronous motor（I-PMSM） and tire, is more convenient to estimate the slip ratio because the rotary speed of the rotor can be accurately measured. However, the ring speed of the tire ring doesn’t equal to the rotor speed considering the tire deformation. For this reason, a deformable tire and a detailed I-PMSM are modeled by using Matlab/Simulink. Moreover, the tire/road contact interface（a slippery road） is accurately described by the non-linear relaxation length-based model and the Magic Formula pragmatic model. Based on the relatively accurate model, the error of slip ratio estimated by the rotor rotary speed is analyzed in both time and frequency domains when a quarter car is started by the I-PMSM with a definite target torque input curve. In addition, the natural frequencies（NFs） of the driving wheel system with variable parameters are illustrated to present the relationship between the slip ratio estimation error and the NF. According to this relationship, a low-pass filter, whose cut-off frequency corresponds to the NF, is proposed to eliminate the error in the estimated slip ratio. The analysis, concerning the effect of the driving wheel parameters and road conditions on slip ratio estimation, shows that the peak estimation error can be reduced up to 75% when the LPF is adopted. The robustness and effectiveness of the LPF are therefore validated. This paper builds up the deformable tire model and the detailed I-PMSM models, and analyzes the effect of the driving wheel parameters and road conditions on slip ratio estimation.

Study on Mechanical Parameters of Rocks and Regional Layer-Slip Systems in Hunan-Jiangxi Areas

In order to quantitatively study layerslip-dipslip, nappe-glide structure systems in the Hunan-Jiangxiareas, samples with divided layers of these classical cross sections in the studied area were selected, and various physicomechanical parameters were systematically determined. Furthermore, five regional layer-slip systems of the basement and the cover strata were scientifically divided in the Middle Yangzi area, and they have been synthetically compared with the determined parameters in the Lower Yangzi area. Overall, the parameter value of a sliplayer presenting relative plasticity, ductility and viscosity is higher than a non-slip layer presenting relative elasticity, brittleness and rigidity, except the value of the Poission’s ratio of the rock and the determined temperature of the inclusion, other parameters (such as the uniaxial pressure strength of the rock, the elastic module, the density and the elastic wave velocity) are all lower. On the basis of the study, the authors still further explain

Slip Compensation in Efficiency-Optimized Three-Phase Induction Motor Drive Systems

Energy efficiency optimization techniques of electrical drive systems improve the overall efficiency and reduce the hardness of mechanical characteristics of the drive system. It is therefore important to reduce the slip of induction motor to maintain its stable operation at different frequencies and loads. In this paper a slip compensator, based on fuzzy logic incremental controller has been developed to improve the steady state performance of efficiency-optimized three-phase induction motor drive system. The slip control is accomplished through a fuzzy controller with 9 rules, taking speed error and speed error variation as inputs, to produce the frequency. The proposed controller reduces the slip occurring at low frequencies and light loads to certain value, and also reduces the energy efficiency of the system.

Wall slip behavior of cemented paste backfill slurry during pipeline based on noncontact experimental detection

Wall slip is a microscopic phenomenon of cemented paste backfill(CPB)slurry near the pipe wall,which has an important influence on the form of slurry pipe transport flow and velocity distribution.Directly probing the wall slip characteristics using conventional experimental methods is difficult.Therefore,this paper established a noncontact experimental platform for monitoring the microscopic slip layer of CPB pipeline transport independently based on particle image velocimetry(PIV)and analyzed the effects of slurry temperature,pipe diameter,solid concentration,and slurry flow on the wall slip velocity of the CPB slurry,which refined the theory of the effect of wall slip characteristics on pipeline transport.The results showed that the CPB slurry had an extensive slip layer at the pipe wall with significant wall slip.High slurry temperature improved the degree of particle Brownian motion within the slurry and enhanced the wall slip effect.Increasing the pipe diameter was not conducive to the formation of the slurry slip layer and led to a transition in the CPB slurry flow pattern.The increase in the solid concentration raised the interlayer shear effect of CPB slurry flow and the slip velocity.The slip velocity value increased from 0.025 to 0.056 m·s^(-1)when the solid content improved from 55wt%to 65wt%.When slurry flow increased,the CPB slurry flocculation structure changed,which affected the slip velocity,and the best effect of slip layer resistance reduction was achieved when the transported flow rate was 1.01 m^(3)·h^(-1).The results had important theoretical significance for improving the stability and economy of the CPB slurry in the pipeline.

Underlying slip/twinning activities of Mg-xGd alloys investigated by modified lattice rotation analysis

The inconsistencies regarding the fundamental correlation between Gd content and slip(twinning)activities of Mg alloys appeal further investigations.However,the traditional slip dislocations analysis by TEM is time-consuming,and that by SEM/EBSD cannot recognize the partial slip modes.These urge a more efficient and comprehensive approach to easily distinguish all potential slip modes occurred concurrently in alloy matrix.Here we report a modified lattice rotation analysis that can distinguish all slip systems and provide statistical results for slip activities in Mg alloy matrix.Using this method,the high ductility of Mg-Gd alloy ascribed to the enhanced non-basal slips,cross-slip,and postponed twinning activities by Gd addition is quantitatively clarified.

Loading direction dependence of asymmetric response of pyramidal slip in rolled AZ31 magnesium alloy

Textured magnesium alloys usually exhibit anisotropic mechanical behavior due to the asymmetric activation of different twinning and slipping modes.This work focuses on the pyramidal slip responses of rolled AZ31 magnesium alloy under two loading conditions,compressive and tensile loading along the normal direction.Under the condition where the compressive loading direction is closely parallel to the c-axis of the unit cell,tensile twinning and basal slips are prohibited, dislocations then active and tend to accumulate at grain boundaries and form dislocation walls.Meanwhile,these dislocations exhibit zigzag morphologies,which result from the cross-slip from {10■1} first-order pyramidal plane to {11■2} second-order pyramidal plane,then back to {10■1} first-order pyramidal plane.Under the condition where tensile twins are prevalent,{10■1} first-order and {11■2} second-order pyramidal dislocations are favorable to be activated.Both types of dislocations behave climb-like dissociations onto the basal plane,forming zigzag dislocations.

The June 2022 Khost earthquake in southeastern Afghanistan:A complicated shallow slip event revealed with InSAR

On June 22,2022,the Mw6.2 earthquake in southeastern Afghanistan caused a severe disaster.We used the Sentinel-1A ascending and descending track images of the European Space Agency and interferometric synthetic aperture radar(In SAR)to obtain the coseismic surface deformation field of the earthquake,which showed that the earthquake caused complex ruptures of multiple faults and various types.Using the dislocation model of the elastic half-space,we determined the focal parameters and slip distribution on the fault plane of this event.The results reveal that:(1)the seismogenic fault of this event is an unknown fault on the northeastern edge of the Katawaz microblock;(2)The slip on the fault plane is mainly in the range of 0—8 km along the dip,with maximum slips about 2 m at a depth of 2 km,which projected on the surface is 69.44°E,32.96°N.This event suggests that,similar to the Chaman,Ghazaband and other large faults,the faults inside the microblock also play an important role in adjusting for the collision stress between India and Europe.

On the strengthening and slip activity of Mg-3Al-1Zn alloy with pre-induced{1012¯}twins

{1012¯}twins were introduced into the magnesium(Mg)plate AZ31 via pre-rolling along its transverse direction.The plates,both with and without the pre-induced{1012¯}twins,were subjected to uniaxial tension along different directions.Using crystal plasticity modeling,we found that the strengthening effect of the pre-induced{1012¯}twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries,rather than the orientation hardening due to the twinning reorientation(although the latter did make its contribution in some specific loading directions).Besides,the pre-existing{1012¯}twins were found,by both experiments and simulation,to promote the activity of prismatic and pyramidal<c+a>in the parent matrix of the material.Further analysis showed that the enhanced non-basal slip activity is related to the{1012¯}twin boundaries’low micro Hall-Petch slope ratios of non-basal slips to basal slip.With the critical resolved shear stress(CRSS)obtained from crystal plasticity modeling and the orientation data from EBSD,a probability-based slip transfer model was proposed.The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at{1012¯}twin boundaries than that at grain boundaries,which agrees with the experimental observation that the strain localization was primarily associated with the latter.The present findings are helpful scientifically,in deepening our understanding of how the pre-induced{1012¯}twins affect the strength and slip activity of Mg alloys,and technologically,in guiding the design of the pre-strain protocol of Mg alloys.

Tensioner Vibration and Belt Slipping Behavior Investigation for Damped Serpentine Belt Drive Systems

A nonlinear rotational motion model for n-pulley damped serpentine belt drive systems （SBDSs） was developed.The effects of the belt deflection along the contact arc of pulleys on the belt span tensions were considered.The methods for calculating the tensioner arm vibration and belt slipping on pulleys were introduced.The effects of belt damping on rotational vibration of tensioner arm and belt slipping on pulleys were studied.Numerical solutions for a 3-pulley SBDS indicate that the belt slipping at the steady states should be controlled to avoid belt slipping at transient states.The slip factors tend to decrease when the belt damping increases,and the possibility of the belt slipping can be controlled through adjusting the wrap angles of pulleys and the preload of the tensioner when the design parameters of SBDS remain constant.

Yield Vertices for Symmetric Slip on {110}<111> and Asymmetric Slip on {112}<111> Systems

The single crystal yield surfaces (SCYS) of bcc metals for symmetric slip on {110} (111) and asymmetric slip on {112} (111) systems have been analyzed and deduced. The complete SCYS have been derived when their critical resolved shear stresses (CRSS) are specified in a particular case (such as for Mo metal). The results showed that there are 600 stress states that can be classified into 35 groups according to the crystal symmetry. Each group activates eight, six or five {110} (111) and {112} (111) slip systems depending on crystallographically nonequivalent slip systems groups. Among all these stress states, three groups activate eight systems, there are 24 stress states; four groups activate six systems, there are 48 ones; the remaining twenty-eight groups activate five systems, there are 528 ones. In this case, the fraction of vertices for which there is slip ambiguity (more than five active systems) is reduced considerably compared with pure {110} (111) slip.

Uniform Strike-Slip Rate along the Xianshuihe-Xiaojiang Fault System and Its Implications for Active Tectonics in Southeastern Tibet

Recent studies on the Xianshuihe-Xiaojiang fault system suggest that the Late Quaternary strike-slip rate is approximately uniform along the entire length of the fault zone, about 15±2 mm/a. This approximately uniform strike slip rate strongly supports the clockwise rotation model of the southeastern Tibetan crust. By approximating the geometry of the arc-shaped Xianshuihe-Xiaojiang fault system as a portion of a small circle on a spherical Earth, the 15±2 mm/a strike slip rate corresponds to clockwise rotation of the Southeastern Tibetan Block at the （5.2±0.7）×10^-7 deg/a angular velocity around the pole （21°N, 88°E） relative to the Northeast Tibetan Block. The approximately uniform strike slip rate along the Xianshuihe-Xiaojiang fault system also implies that the Longmeushan thrust zone is not active, or at least its activity has been very weak since the Late Quaternary. Moreover, the total offset along the Xiaushuihe-Xiaojiang fault system suggests that the lateral extrusion of the Southeastern Tibetan Block relative to Northeastern Tibetan Block is about 160 km and 200-240 km relative to the Tarim-North China block. This amount of lateral extrusion of the Tibetan crust should have accommodated about 13-24% convergence between India and Eurasia based on mass balance calculations. Assuming that the slip rate of 15±2 mm/a is constant throughout the entire history of the Xianshuihe-Xiaojiang fault system, 11±1.5 Ma is needed for the Xianshuihe-Xiaojiang fault system to attain the 160 km of total offset. This implies that left-slip faulting on the Xianshuihe-Xiaojiang fault system might start at 11±1.5 Ma.

Prophylactic fixation of the unaffected contralateral side in children with slipped capital femoral epiphysis seems favorable:A systematic review

BACKGROUND Slipped capital femoral epiphysis(SCFE)occurs in adolescents and has an incidence of around 10 per 100000 children.Children presenting with a unilateral SCFE are 2335 times more likely to develop a contralateral SCFE than the general population.Prognostic factors that have been suggested to increase the risk of contralateral slip include a younger patient,an underlying endocrine disorder,growth hormone use and a higher radiographic posterior sloping angle.However,there is still much debate on the advantages and disadvantages of prophylactic fixation of the unaffected side in an otherwise healthy patient.AIM To investigate the risk rate of contralateral SCFE and assess the(dis)advantages of prophylactic fixation of the contralateral hip.METHODS A systematic literature search was performed in the Embase,Medline,Web of Science Core Collection and Cochrane databases.Search terms included‘slipped capital femoral epiphysis,’‘fixation,’‘contralateral,’and derivatives.The eligibility of the acquired articles was independently assessed by the authors and additional relevant articles were included through cross-referencing.Publications were considered eligible for inclusion if they presented data about otherwise healthy children with primarily unilateral SCFE and the outcomes of prophylactically pinning their unaffected side,or about the rates of contralateral slips and complications thereof.The study quality of the included articles was assessed independently by the authors by means of the methodological index for non-randomized studies criteria.RESULTS Of 293 identified unique publications,we included 26 studies with a total of 12897 patients.1762 patients(14%)developed a subsequent symptomatic contralateral slip.In addition,38%of patients developed a subsequent slip on the contralateral side without experiencing clinical symptoms.The most outspoken advantage of prophylactic fixation of the contralateral hip in the literature is prevention of an(asymptomatic)slip,thus reducing the increased risk of avascular necrosis(AVN),cam morphology and osteoarthritis.Disadvantages include an increased risk of infection,AVN,peri-implant fractures,loss of fixation as well as migration of hardware and morphologic changes as a consequence of growth guidance.These risks,however,appeared to only occur incidentally and were usually mild compared to the risks involved with an actual SCFE.CONCLUSION The advantages of prophylactic pinning of the unaffected side in otherwise healthy patients with unilateral SCFE seem to outweigh the disadvantages.The final decision for treatment remains to be patient-tailored.

Development of an Efficient Tapered Slip-Form System Applying BIM Technology

Slip-form system constitutes the latest technology for the erection of elevated concrete pylons. This paper investigates the design of slip-form system applying BIM technology for the efficient development of the slip-form system. The considered pylon has a height of 10 m and presents the rectangular hollow section generally adopted in cable-supported bridges. The slip-form was thus designed to accommodate the tapered cross-section and changing thickness considering the continuous placing of concrete. In addition, the safety of the system was examined with regard to the various loads applied on the slip form along the construction. The design results could be verified visually through BIM and the applicability of the designed slip-form was validated in advance through virtual assembly and construction.