斜壁桶形基础水平承载力的三维有限元分析

利用有限元软件ABAQUS对桶形基础受水平荷载进行数值模拟,并与模型试验结果进行对比. 通过数值计算,分析饱和软黏土中单个斜壁桶形基础受水平荷载后的破坏模式. 通过变动参数,分别探讨研究了土体有效重度、土体不排水抗剪强度、桶体等效长度和宽度、荷载作用高度对饱和软黏土中单个斜壁桶形基础水平承载力的影响及相对敏感性.     

Sprint mechanical differences at maximal running speed: Effects of performance level

ABSTRACT

As the effect of performance level on sprinting mechanics has not been fully studied, we examined mechanical differences at maximal running speed (MRS) over a straight-line 35 m sprint amongst sprinters of different performance levels. Fifty male track and field sprinters, divided in Slow, Medium and Fast groups (MRS: 7.67 ± 0.27 m?s^?1, 8.44 ± 0.22 m?s^?1, and 9.37 ± 0.41 m?s^?1, respectively) were tested. A high-speed camera (250 Hz) recorded a full stride in the sagittal plane at 30–35 m. MRS was higher (p < 0.05) in Fast vs. Medium (+11.0%) and Slow (+22.1%) as well as in Medium vs. Slow (+10.0%). Twelve, eight and seven out of 21 variables significantly distinguished Fast from Slow, Fast from Medium and Medium from Slow sprinters, respectively. Propulsive phase was signi?cantly shorter in Fast vs. Medium (?17.5%) and Slow (?29.4%) as well as in Medium vs. Slow (?14.4%). Fast sprinters had significantly higher vertical and leg stiffness values than Medium (+44.1% and +18.1%, respectively) and Slow (+25.4% and +22.0%, respectively). MRS at 30–35 m increased with performance level during a 35-m sprint and was achieved through shorter contact time, longer step length, faster step rate, and higher vertical and leg stiffness.     

Adjusting athletes' body mass index to better reflect adiposity in epidemiological research

Abstract

The aim of the present study was to identify when body mass index (BMI) is unlikely to be a valid measure of adiposity in athletic populations and to propose a simple adjustment that will allow the BMI of athletes to reflect the adiposity normally associated with non-athletic populations. Using data from three previously published studies containing 236 athletes from seven sports and 293 age-matched controls, the association between adiposity (sum of 4 skinfold thicknesses, in millimetres) and BMI was explored using correlation, linear regression, and analysis of covariance (ANCOVA). As anticipated, there were strong positive correlations (r = 0.83 for both men and women) and slope parameters between adiposity and BMI in age-matched controls from Study 1 (all P < 0.001). The standard of sport participation reduced these associations. Of the correlations and linear-regression slope parameters between adiposity and BMI in the sports from Studies 2 and 3, although still positive in most groups, less than half of the correlations and slope parameters were statistically significant. When data from the three studies were combined, the ANCOVA identified that the BMI slope parameter of controls (5.81 mm · (kg · m^?2)^?1) was greater than the BMI slope parameter for sports (2.62 mm · (kg · m^?2)^?1) and middle-distance runners (0.94 mm · (kg · m^?2)^?1) (P < 0.001). Based on these contrasting associations, we calculated how the BMI of athletes can be adjusted to reflect the same adiposity associated with age-matched controls. This simple adjustment allows the BMI of athletes and non-athletes to be used with greater confidence when investigating the effect of BMI as a risk factor in epidemiological research.     

Validation of Weinbach's and Hanavan's Models for Computation of Physical Properties of the Forearm

Abstract

The purpose of the present study was to validate the Weinbach and the Hanavan models for the determinations of the forearm volume and center of mass. The study was conducted using 20 forearms from six male and four female cadavers. Results from the present investigation indicate that Weinbach's model is more accurate than Hanavan's model in estimating forearm volume and center of mass. The relative location of the center of mass and the center of volume was also investigated with the Weinbach model and these centers were found to coincide. The Hanavan model should be used only in the cases where the shape of the forearm closely resembles that of a truncated cone.     

径向基函数网络在优化机械加工参数中的应用

In machining processes, errors of rough in dimension, shape and location lead to changes in processing quantity, and the material of a workpiece may not be uniform. For these reasons, cutting force changes in machining, making the machining system deformable. Consequently errors in workpieces may occur. This is called the error reflection phenomenon. Generally, such errors can be reduced through repeated processing while using appropriate processing quantity in each processing based on operator's experience.According to the theory of error reflection, the error reflection coefficient indicates the extent to which errors of rough influence errors of workpieces. It is related to several factors such as machining condition, hardness of the workpiece, etc. This non-linear relation cannot be worked out using any formula. RBF neural network can approximate a non-linear function within any precision and be trained fast. In this paper, non-linear mapping ability of a fuzzy-neural network is utilized to approximate the non-linear relation. After training of the network with swatch collection obtained in experiments, an appropriate output can be obtained when an input is given. In this way, one can get the required number of processing and the processing quantity each time from the machining condition. Angular rigidity of a machining system,hardness of workpiece, etc., can be input in a form of fuzzy values. Feasibility in solving error reflection and optimizing machining parameters with a RBF neural network is verified by a simulation test with MATLAB.     

颗粒材料力学性质的离散元数值模拟

基于颗粒离散元法对二维颗粒体进行了双轴压缩数值模拟.将离散系统中的变形与连续体中相应的变形联系起来,应用于颗粒离散元方法中平均应力的计算,比较了不同颗粒形状、颗粒间摩擦系数对颗粒体的微观-宏观力学性能的影响,并分别考虑了不同摩擦系数下,颗粒颗粒间接触力的法向分量和切向分量对剪切应力的贡献.本文的计算结果表明颗粒的形状和表面性质对颗粒体的力学性能有显著的影响.     

Method to determine parameters in the rainstorm intensity formula

IntroductionTherainstormintensityformulaisanimportantandfundamentalformulainmodernmunicipaldrainagedesign,asthebasisincalculatingrainstormgroundrunoffandengineeringtheflowvolumeofaproject.Itdirectlyinfluencestheinvestmentbudgetandthereliabilityofamunicipaldrainagesystemtobebuilt.AccordingtoSpecificationsofDrainageDesignOutdoor(GBJ14-87)[1],thedesignflowvolumeofarainwaterpipesystemshouldbecalculatedbythelocalrainstormintensityformula.Thereliabilityofadrainagesystemhasdirectrelationtotherains…     

基于半参数回归分析法的隧洞变形量计算模型

通过补充随时间连续变化的系统误差分量来分析该误差对变形量计算的影响,运用非线性方法建立了隧洞变形量计算模型.基于实测数据,采用多种方法对隧洞变形监测过程和模型产生的厘米级系统误差进行了消除,提高了现场量测结果的精度.计算结果表明,阻尼最小二乘法、卡尔曼滤波法和半参数回归分析法三种误差消除方法都能满足工程需要,其中半参数回归分析法对隧洞变形的计算结果与实际最为接近,对工程设计具有指导意义.     

Uncertain educational returns in a developing economy

This paper estimates the distribution of educational returns by gender for India. While previous studies focus on mean returns, the variance of educational returns has important implications for policy-making and micro-level decision making with respect to education. If the variance of educational returns is large, it can leave large sections of the population with negative returns; if the variance of educational returns is gender specific, it can influence households’ decisions to educate girls versus boys. Our econometric results provide evidence that India's labor markets are characterized by significant uncertainty and that the uncertainty is systematically larger for women.     

无凸缘圆筒形件拉深成形质量的数值分析

利用有限元软件dynaform对无凸缘筒形件进行拉深成形过程的CAE分析。通过变化其拉深工艺参数来分析对工件质量的影响,从而为实际模具设计提出最优化的工艺参数。