Circles with a suspended aid: reducing pommel reaction forces

The aim of this study was to investigate the influence of a suspended aid on the reaction forces during a basic skill on pommel horse. Twenty gymnasts performed three sets of 10 circles with and without a suspended aid on a pommel horse under which two force plates were set. The results confirmed that the suspended aid could reduce the magnitude of the pommel reaction forces during circles while maintaining the general loading pattern. On the left hand, the average and peak forces were attenuated to 0.59 body weight (BW) and 0.85 BW from 0.76 BW and 1.13 BW, respectively. The right hand experienced slightly larger forces with no-aid trials, but the asymmetry between the hands decreased with the aid. Despite a relatively large variability, all gymnasts experienced smaller impact peak forces with the aid. A suspended aid is most commonly used for a beginner gymnast as an introduction to pommel horse exercises. However, this study confirmed that it can also be useful for all levels of gymnasts who would like to practice pommel horse exercises with reduced pommel reaction forces for a purpose such as a progression for learning a new skill, control of training volume, or rehabilitation.     

Numerical Modeling of Response and Damage of Masonry Walls to Blast Loading

To model the damage process of masonry walls under blast loading, a dynamic continuum damage material model is constructed for brick and mortar separately. The degradation of both the stiffness and strength are governed by a damage variable. By using the proposed material model, damage and fragmentation of a typical masonry wall under blast loading at different scaled distances is calculated. The hazard level of the masonry wall to blast loading is evaluated by analyzing the numerical results.     

ON THE HYDRAULIC FAILURE PROBABILITY OF FLOOD CONTROL DAMS

防洪堤坝不仅在河道洪水超过设计泄洪能力时才会发生防洪事故，水力因素的不确定性也会引起洪灾损失。但在大多数水文分析计算及防洪规划设计中，是不考虑这种水力风险的。本文应用风险理论探讨了这种水力风险的大小及其估算方法，为完善现有的防洪理论提供依据，应用结果表明，在防洪标准较低的河道，可以不考虑这种水力风险；而在防洪标准较高的河道，则必须重视这种水力风险，另外还要考虑洪水荷载的偏态分布特征．     

学生课余体育锻炼应注意的几个问题

学生课余体育锻炼是学生体育课学习锻炼之外的自主学习行为,没有体育教师的参与和指导,锻炼活动还不够科学系统,锻炼环境、体育器材保障、医务救护监督等各方面条件也有所限制。本文就学生在课余体育锻炼如何做到科学合理,从而保证锻炼顺利进行并取得良好的锻炼效果做了探讨。     

飞机结构静强度与疲劳试验双向加载技术研究

选取橡胶块胶板式、聚氨酯密封胶灌注式和双组分PU密封胶灌注式三种加载块与飞机结构模拟件粘接后,采用MTS810液压伺服疲劳试验机通过施加拉-压双向载荷的静强度和疲劳寿命试验方法完成了可行性研究,然后在某型飞机减速板进行了双向加载试验的考核验证,从而发展了一种施加拉-压双向载荷的试验方法。该方法能够满足复杂飞机结构静强度和疲劳试验中施加拉-压双向载荷的技术要求。试验结果表明,与传统加载所采用的胶布带相比,三种形式加载块的静强度、疲劳性能和加载速率均有明显提高。     

小直径薄壁管直接拉伸方法研究

大学材料性能实验教学通常以棒料单向拉伸为主要内容,而未能兼顾各种型材在服役状态下的几何属性对材料属性的影响。研究小直径薄壁管直接拉伸实验技术和方法,并将其引入实验教学,使学生通过实验自主地分析塞头装配、试样类型及加载速率对拉伸结果的影响,取得了良好的实践教学效果,对管形状态下材料力学性能的准确获取与促进管材塑性成形理论研究具有重要学术意义。     

Dynamic analysis of a high-speed train operating on a curved track with failed fasteners

A high-speed train-track coupling dynamic model is used to investigate the dynamic behavior of a high-speed train operating on a curved track with failed fasteners. The model considers a high-speed train consisting of eight vehicles coupled with a ballasted track. The vehicle is modeled as a multi-body system, and the rail is modeled with a Timoshenko beam resting on the discrete sleepers. The vehicle model considers the effect of the end connections of the neighboring vehicles on the dynamic behavior. The track model takes into account the lateral, vertical, and torsional deformations of the rails and the effect of the discrete sleeper support on the coupling dynamics of the vehicles and the track. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. The train model couples with the track model by using a Hertzian contact model for the wheel/rail normal force calculation, and the nonlinear creep theory by Shen et al. (1984) is used for wheel/rail tangent force calculation. In the analysis, a curved track of 7000-m radius with failed fasteners is selected, and the effects of train operational speed and the number of failed fasteners on the dynamic behaviors of the train and the track are investigated in detail. Furthermore, the wheel/rail forces and derailment coefficient and the wheelset loading reduction are analyzed when the high-speed train passes over the curved track with the different number of continuously failed fasteners at different operational speeds. Through the detailed numerical analysis, it is found that the high-speed train can operate normally on the curved track of 7000-m radius at the speeds of 200 km/h to 350 km/h.     

Optimal controller for uncertain stochastic polynomial systems

This paper presents the optimal quadratic-Gaussian controller for uncertain stochastic polynomial systems with linear control input and a quadratic criterion over linear observations. The optimal closed-form controller equations are obtained using the separation principle, whose applicability to the considered problem is substantiated. As intermediate results, the paper gives closed-form solutions of the optimal regulator and controller problems for stochastic polynomial systems with linear control input and a quadratic criterion. Performance of the obtained optimal controller is verified in the illustrative example against the conventional quadratic-Gaussian controller that is optimal for stochastic polynomial systems with known parameters. Simulation graphs demonstrating overall performance and computational accuracy of the designed optimal controller are included.     

皮带煤仓转载工程施工体会

本文介绍了开滦钱家营矿业分公司八采区皮带煤仓转载工程的卸载硐室、煤仓、给煤机硐室的施工工艺,采用合理、先进的施工方案,实现了安全、优质、高效。     

An LMI approach to robust H∞ filtering for uncertain systems with time-varying distributed delays

In this paper, the problem of robust H_∞ filtering for uncertain systems with time-varying distributed delays is considered. The uncertainties under discussion are time varying but norm bounded. Based on the Lyapunov stability theory, sufficient condition for the existence of full order H_∞ filters is proposed by linear matrix inequality (LMI) approach such that the filtering error system is asymptotically sable and satisfies a prescribed attenuation level of noise. A numerical example is given to demonstrate the availability of the proposed method.