基于多坡度运动的岩羊垂直地反力特征

为了给具有优异攀爬性能的仿生四足机器人提供仿生蓝本,以岩羊为研究对象,利用内嵌压力板的可变坡度斜坡通道,测试其四肢垂直地反力在不同坡度上的变化规律.结果表明,岩羊在平地上行走时,前后肢左右两侧的垂直地反力峰值和垂直冲量完全对称,前肢对称指数分别为99.16%、99.62%,后肢对称指数分别为98.65%、99.42%.随着坡度的增加,岩羊调整四肢的垂直地反力分布以防止跛行,导致左右蹄的对称性指数出现波动.当岩羊在平地行走时,前肢比后肢承受更多的垂直地反力,后肢承受的垂直地反力随着坡度的增加逐渐增多.岩羊肢体左右侧的差异性指数随坡度的变化具有相似性,当坡度为0~35°时,岩羊肢体左右侧差异性指数的均值分别为1.298、1.3057、1.1744、1.22375、1.0175、0.8905、0.7778、0.7535.

跆拳道运动员后踢动作时下肢双侧生物力学差异性

探讨跆拳道后踢技术动作时下肢优势侧和非优势侧的运动生物力学特征,对影响后踢技术完成率的影响因素进行分析。采用VICON三维动作捕捉系统和KISTLER三维测力台同步采集12名武汉体育学院优秀跆拳道运动员完成后踢动作下肢的运动学和动力学数据,采用配对样本T检验分析后踢动作优势侧和非优势侧之间的差异。结果表明:进攻腿髋关节屈曲力矩峰值(P=0.000)、功率峰值(P=0.006)非优势侧大于优势侧,外展最大角速度(P=0.014)优势侧大于非优势侧;支撑腿髋关节屈曲最大角速度(P=0.001)、伸展功率峰值(P=0.037)优势侧大于非优势侧,屈曲力矩峰值(P=0.022)非优势侧大于优势侧。进攻腿膝关节屈曲最大角度(P=0.003)、伸展功率峰值(P=0.044)优势侧大于非优势侧;支撑腿膝关节屈曲最大角度(P=0.006)、角速度(P=0.018)优势侧大于非优势侧,伸展最大角速度(P=0.022)非优势侧大于优势侧。支撑腿踝关节跖屈最大角速度(P=0.005)、功率峰值(P=0.035)、力矩峰值(P=0.005)优势侧大于非优势侧。进攻腿击打速度(P=0.002)、电子护具力度值(P=0.015)优势侧大于非优势侧。可见在提膝阶段,优势侧提膝时间更短,优势侧踝关节跖屈和非优势侧屈髋产生的能量输出更多;在踢击阶段,优势侧伸髋和伸膝的功率峰值较大,能有效提高击打速度;优势侧击打速度和击打力度值大于非优势侧,选择优势侧踢击可以提高后踢技术得分成功率。

折板基础的有限元分析及简化计算

将作用于折板上的地反力换算成等效的均布荷载，根据构造措施和实际受力情况，可按周边固定的单元板进行计算．对折板基础进行有限元分析，并与弯矩分配法计算结果进行比较，说明有限元方法与弯矩分配法的计算结果基本吻合，同时能提供更详尽的数据，是分析折板基础的可靠方法．

基于智能可穿戴设备的Human Shaker结构动力测试方法

已建结构的动力测试是了解其实际动力性能、提升建模和计算分析精度、检测结构损伤情况的重要手段.提出了 Human Shaker(HS)的方法,利用人的行走、跳跃和摆动等运动实现对结构的激振,由智能可穿戴设备得到激振荷载和结构响应,并由此识别结构的模态参数.首先建立了由特征点加速度重构人致激振荷载的方法,以及利用可穿戴设备的HS应用步骤,进而以横向摆动为例通过实验确定了特征点位置及其对应的质量参与修正系数.最后将HS技术应用于某实际结构的动力测试和模态参数识别,结果表明,HS技术可以方便快捷地用于中小型结构的模态测试.

不同步行方向对女性膝关节运动学参数和步态的影响研究

本研究通过随机选取12名在校女性大学生(年龄:20.08±1.16岁),在红外捕捉系统和测力台上,进行正、反向步行各五次。对两种步行方向时的下肢膝关节运动学参数和步态指标,通过配对样本T检验的统计方法分析,取P<0.05为具有统计学差异,P<0.01为统计学差异具有极高显著性。结果发现,人在反向步行时的运动学参数和步态指标呈现不同变化。提示在保证安全的前提下,反向步行相对于正向步行可以减轻膝关节负荷,提高人体的平衡能力。

Nonlinear Behavior of Reinforced Concrete Slit Shear Walls under Seismic Actions *

A reinforced concrete slit shear wall is a new breed of earthquake resistant structure recently proposed by the authors. In this paper, the seismic responses of the slit shear walls under the shake of earthquake excitation have been dealt with. Based on a simplified structural model, which is shown to have a sufficient accuracy for the real slit shear wall structure, the analysis focuses on the influence of nonlinear behavior of the connecting beams between the slits on the dynamic performance of the whole slit shear wall structure. It has been found that the yielding of connecting beams in a slit shear wall can provide significant improvement in reducing the structural responses, and by choosing an appropriate strength value for the connecting beams, it is possible to optimize the seismic response of the slit shear wall.

Analysis of the Effects of Slope Geometry on the Dynamic Response of a Near-field Mountain from the Wenchuan Earthquake

Fourier spectra and acceleration response spectra of near-field acceleration records of the 2008 Wenchuan Earthquake have been calculated.Relative fundamental frequencies(or predominant periods) were characterized.Then,the natural frequencies of a range of slopes with different geometric characteristics,such as height,slope ratio,and pattern,were analyzed.The seismic responses of the slopes were compared,and the variability of seismic response with the above geometric elements was found.Results show that if slope height increases,and provided that other conditions are unchanged,the natural frequency of the first mode of a doublesurface slope will change as a power law.However,natural frequencies will diminish(based on a parabolic function) as the slope angle becomes large.Both the surface pattern and the number of surfaces on a slope can have a great impact on the seismic response of the slope.Moreover,within a certain range of slope heights or angles,either height or angle will also greatly influence the variability of the seismic response.The results of this research will be helpful to understanding seismic dynamic response features and explaining the ways that slope stability can be affected by earthquakes.

Reduction in ground reaction force variables with instructed barefoot running

Backgound:Barefoot(BF) running has recently increased in popularity with claims that it is more natural and may result in fewer injuries due to a reduction in impact loading.However,novice BF runners do not necessarily immediately switch to a forefoot strike pattern.This may increase mechanical parameters such as loading rate,which has heen associated with certain running-related injuries,specifically,tibial stress fractures.patellofemoral pain,and plantar iasciitis.The purpose of this study was to examine changes in loading parameters between typical shod running and instructed BF running with real-time force feedback.Methods:Forty-nine patients seeking treatment for a lower extremity injury ran on a force-sensing treadmill in their typical shod condition and then BF at the same speed.While BF they received verbal instruction and real-time feedback of vertical ground reaction forces.Results:While 92%of subjects(n = 45) demonstrated a rearfoot strike pattern when shod,only 2%(n = 1) did during the instructed BF run.Additionally,while BF 47%(n = 23) eliminated the vertical impact transient in all eight steps analyzed.All loading variables of interest were significantly reduced from the shod to instructed BF condition.These included maximum instantaneous and average vertical loading rates of the ground reaction force(p 【 0.0001),stiffness during initial loading(p 【 0.0001).and peak medial(p = 0.001) and lateral(p 【 0.0001) ground reaction forces and impulses in the vertical(p 【 0.0001).medial(p = 0.047),and lateral(p 【 0.0001) directions.Conclusion:As impact loading has been associated with certain running-related injuries,instruction and feedback on the proper forefoot strike pattern may help reduce the injury risk associated with transitioning to BF running.

Centrifuge modeling of dynamic behavior of pile-reinforced slopes during earthquakes

A series of centrifuge model tests of sandy slopes were conducted to study the dynamic behavior of pile-reinforced slopes subjected to various motions.Time histories of accelerations,bending moments and pile earth pressures were obtained during excitation of the adjusted El Centro earthquake and a cyclic motion.Under a realistic earthquake,the overall response of the pile-reinforced slope is lower than that of the non-reinforced slope.The histories of bending moments and dynamic earth pressures reach their maximums soon after shaking started and then remain roughly stable until the end of shaking.Maximum moments occur at the height of 3.5 m,which is the deeper section of the pile,indicating the interface between the active loading and passive resistance regions.The dynamic earth pressures above the slope base steadily increase with the increase of height of pile.For the model under cyclic input motion,response amplitudes at different locations in the slope are almost the same,indicating no significant response amplification.Both the bending moment and earth pressure increase gradually over a long period.

Joint inversion of gravity and multiple components of tensor gravity data

Geological structures often exhibit smooth characteristics away from sharp discontinuities. One aim of geophysical inversion is to recover information about the smooth structures as well as about the sharp discontinuities. Because no specific operator can provide a perfect sparse representation of complicated geological models, hyper-parameter regularization inversion based on the iterative split Bregman method was used to recover the features of both smooth and sharp geological structures. A novel preconditioned matrix was proposed, which counteracted the natural decay of the sensitivity matrix and its inverse matrix was calculated easily. Application of the algorithm to synthetic data produces density models that are good representations of the designed models. The results show that the algorithm proposed is feasible and effective.

Back analysis of general slope under earthquake forces using upper bound theorem

Long time monitoring is acquired to obtain the displacement data for displacement-based geotechnical material back analysis, and these data are hard to be measured under some special condition, such as earthquake. For a simple homogeneous slope, the position of a critical failure surface is determined by value of c/tan ~b. Utilizing upper bound theorem of limit analysis, the external work rate and internal energy for normal slope under earthquake forces are given, and the formula for minimum safety factor is derived. On this basis, the equation of slip surface and the surface depth of a given position are solved. In this way, the strength parameter can be analyzed by known slip surface depth. For practical use, the surface depth for a given slope under varying strength parameter is presented. Finally, two examples are given to show its simplicity and effectiveness.

Property Identification of Anomalous Seismic Bodies by GMES Techniques, A Case History

What are the anomalous seismic reflection bodies at depths of over 6000m？Are they reefs or igneous rock？This is a difficult problem for seismic techniques,but the GMES technique can handle it .The GMES technique is a joint exploration technique combining gravity,magnetic,electrical,and seismic techniques.The specific procedure is to conduct a 2D interface-constrained CEMP inversion using 2D seismic and log data followed by a property parameter inversion of the anomalous bodics using gravity and seismic data by the stripping technique.We then estimate the physical properties ofthe anomalous bodies,such as density,susceptibility,resistivity,velocity,and etc.to deduce the geological features of the bodies and provide a basis for drilling decisions.The work in the TZ area reported in this paper shows the applicability of the technique.

Fundamental Characteristics of Reduction System for Seismic Response using Friction Force

A new device of reduction for seismic response using friction force was developed. In this paper, fundamental characteristics of reduction system for seismic response using this device were investigated by excitation experiment using artificial seismic waves. The peak acceleration amplitude on this system has decreased to about 50-90% over the input waves. Although a spectral peak around the frequency of 0.5Hz that is the natural period of this system was identified, the value of a spectral peak was decreased using bearings with the high friction force. This device is useful for reduction of seismic response.

A Guide to the Influence of Ground Reaction on Ship Stability

Grounded ship faces up exceptionally different stability forces unlike in her normal operating condition. This critical situation must be corrected as soon as can minimize hull stress, the risk of pollution and stability failure. Re-floating the ship need full understanding of the impact of ground reaction （R） on the ship buoyancy and stability. Re-floating the ship has different phases and there are several immediate actions that should be taken by ship＇s crew; one of these phases is re-calculation of ship stability conditions. In this paper, a guide to understanding the effect of the ground reaction （R）, determines the amount of ground pressure and its location. With consideration of the seabed form whether symmetric of asymmetric. Calculating the magnitude of the ground reaction （R） using different applicable methods, explaining the effect of using weight to re-float the ship by her own means, focusing on GM calculation after grounding.

Combined back-analysis method of ground stress based on refined geological modeling

A new back-analysis method of ground stress is proposed with comprehensive consideration of influence of topography, geology and nonlinear physical mechanical properties of rock on ground stress. This method based on non-uniform rational B-spline (NURBS) technology provides the means to build a refined three-dimensional finite element model with more accurate meshing under complex terrain and geological conditions. Meanwhile, this method is a back-analysis of ground stress with combination of multivariable linear regression model and neural network (ANN) model. Firstly, the regression model is used to fit approximately boundary loads. Regarding the regressed loads as mean value, some sets of boundary loads with the same interval are constructed according to the principle of orthogonal design, to calculate the corresponding ground stress at the observation positions using finite element method. The results (boundary loads and the corresponding ground stress) are added to the samples for ANN training. And on this basis, an ANN model is established to implement higher precise back-analysis of initial ground stress. A practical application case shows that the relative error between the inversed ground stress and observed value is mostly less than 10 %, which can meet the need of engineering design and construction requirements.

Focal Mechanism Solutions and Stress Field Inversion of Moderately Strong Earthquakes in the Northern Tianshan Area

Using the focal mechanism solutions of 24 moderately strong earthquakes in the northern Tianshan area,we carried out system cluster and stress field inversion analysis.The result indicates that,the focal mechanism solutions of moderately strong earthquakes are mainly dip-slip reverse faulting in the northern Tianshan area.The principal rupture planes of earthquakes are NW-oriented.It is basically consistent with the strike of earthquake structure in its adjacent area.The direction of the principal compression stress P axis is nearly NS,and its inclination angle is small;while the inclination angle of the principal extensional stress T axis is large.It shows that the regional stress field is mainly controlled by the near-NS horizontal compressive stress.The direction of the maximum principal stress shows a gradation process of NNE-NS-NW from east to west.

Is changing footstrike pattern beneficial to runners?

Some researchers, running instructors, and coaches have suggested that the "optimal" footstrike pattern to improve performance and reduce running injuries is to land using a mid-or forefoot strike. Thus, it has been recommended that runners who use a rearfoot strike would benefit by changing their footstrike although there is little scientific evidence for suggesting such a change. The rearfoot strike is clearly more prevalent. The major reasons often given for changing to a mid-or forefoot strike are(1) it is more economical;(2) there is a reduction in the impact peak and loading rate of the vertical component of the ground reaction force; and(3) there is a reduction in the risk of a running-related injuries. In this paper,we critique these 3 suggestions and provide alternate explanations that may provide contradictory evidence for altering one's footstrike pattern.We have concluded, based on examining the research literature, that changing to a mid-or forefoot strike does not improve running economy, does not eliminate an impact at the foot-ground contact, and does not reduce the risk of running-related injuries.

Distribution of acceleration and empirical formula for calculating maximum acceleration of rockfill dams

To find the distribution patterns of dynamic amplification coefficients for dams subjected to earthquake, 3D seismic responses of concrete-faced rockfill dams with different heights and different shapes of river valley were analyzed by using the equivalent-linear model. Statistical analysis was also made to the seismic coefficient, and an empirical formula for calculating the maximum acceleration was provided. The results indicate that under the condition of the same dam height and the same base acceleration excitations, with the increase of the river valley width, the position of the maximum acceleration on the axis of the top of the dam moves from the center to the riversides symmetrically. For the narrow valleys, the maximum acceleration occurs in the middle of the axis at the top of the dam; for wide valleys the maximum acceleration appears near the riversides. The result negates the application of 2D dynamical computation for wide valleys, and shows that for the seismic response of high concrete-faced rockfill dams, the seismic coefficient along the axis should be given, except for that along the dam height. Seismic stability analysis of rockfill dams using pseudo-static method can be modified according to the formula.

3D joint inversion of surface and borehole gravity data using zeroth-order minimum entropy regularization

Surface and borehole gravity data contain complementary information.Thus,the joint inversion of these two data types can help retrieve the real spatial distributions of density bodies.When a sharp boundary exists between an anomalous density body and its surrounding rock,the interface recovered by smooth inversion with Tikhonov regularization is not clear,leading to difficulties in the subsequent geological interpretation.In this work,we develop a joint inversion of surface and borehole gravity data using zeroth-order minimum entropy regularization.The method takes advantage of the complementary information from surface and borehole gravity data to enhance the imaging resolution of density bodies.It also produces a focused imaging of bodies through the zeroth-order minimum entropy regularization without requiring a preselection of a proper focusing parameter.We apply the developed joint inversion approach to three diff erent synthetic data sets.Inversion results show that the focusing inversion with the zeroth-order minimum entropy regularization provides a good description of the true spatial extent of anomalous density bodies.Meanwhile,the joint focusing inversion reconstructs a more reliable density model with a relatively high resolution when a density body is passed through by one or more boreholes.

Inversion of the Volumetric Strain of Aquifer According to the Tidal Effect of Groundwater in North China

The change of the confined aquifer level reflects the pore pressure change,and the pore pressure change of the aquifer is closely related to the aquifer pressure. This paper uses the tidal response of the well water level data in the North China region to calculate the tidal factor of each well and extract the effective water trend information. Then,the volumetric strain of an existing confined aquifer well in the North China region is inverted,and the contour maps are plotted on a half-year scale from 2009 to 2012. Results show that it can reflect the state of stress and strain in deep crust to a certain extent in the North China region.