轻集料混凝土中轻集料上浮的试验研究

提出了一种新的评价轻集料上浮的试验方法,根据轻集料混凝土拌和物振动后的上下层混凝土的质量差异和上下层混凝土中轻集料的质量差异,计算轻集料混凝土匀质性系数kρ和轻集料的均布系数km,作为轻集料在混凝土拌和物中上浮的评价指标。试验采用不同的轻集料进行上浮性试验,并对振动后的上下层拌和物分别成型试件测定混凝土的强度比。结果表明,轻集料混凝土匀质性系数和轻集料均布系数均能很好地反映轻集料的上浮情况;对比同批混凝土7 d和28 d的强度比说明,轻集料的上浮对硬化混凝土早期强度影响不大,但对后期强度影响较大。

基于气动喷嘴的线面触觉再现分析与实验

针对气动喷嘴阵列喷气再现线面触觉问题,建立手指皮肤和喷嘴的流固耦合有限元模型。提出均布系数的概念表征线面载荷的均匀性和连续性。分析喷嘴直径、喷嘴间距和入口压力对线触觉的影响,确定气动喷嘴的设计标准。通过实验确定了能够再现逼真线面触觉的入口压力,并验证了分析得出的结论,为气动触觉广泛应用于虚拟装配、遥操作等领域打下良好的基础。

一类非均布荷载作用下厚壁圆筒平面问题的应力解析解

采用复变函数法给出了表面受有一类非均布径向压力作用下厚壁圆筒平面问题的应力解析解,发现随着非均布侧压系数的增大,圆筒内某些区域的切向应力和(或)径向应力会由压应力变为拉应力,并且切向拉应力远大于径向拉应力。在不存在拉应力区的前提下,反算出非均布侧压系数的范围,并给出了不同非均布侧压系数所对应的拉应力区。最后用数值方法验证了理论分析的正确性。

自走式果园多工位收获装备设计与试验

为解决现代化果园水果收获过程中人工劳动强度大、作业效率低、配套机械匮乏等问题,结合果树矮砧宽行密植模式和农艺种植要求,本研究设计了一种自走式果园多工位收获装备。首先介绍了自走式果园多工位收获装备的整机结构和工作原理,然后根据“两侧、两高度、六工位”采摘作业模式,对履带自走式底盘、扩展作业平台、果实自动输送装箱及转运系统的关键部件进行了参数分析、计算与结构设计。田间试验结果表明,所设计的自走式果园多工位收获装备可同步于六工位人工采收速度,苹果采收损伤率为4.67%,装箱均布系数为1.475,装箱速度为72.9个/min,能够满足果园采收作业要求。

CFD数值模拟技术在火电厂SCR脱硝系统中的应用研究

研究了脱硝SCR中CFD模拟技术,提出了CFD模拟起始位置选择问题、喷氨格栅前烟气均布系数、整流格栅处烟气垂直偏角、催化剂支撑梁处烟气垂直偏角、最下层催化剂烟气垂直偏角等存在的模拟技术问题,并根据实际设计及模拟经验,提出了对应的建议。通过提高设计质量和CFD模拟技术,达到精准喷氨、降低氨逃逸、提高催化剂使用寿命、降低燃煤机组运行风险的目的。

Mechanism of heterogeneous distribution of Cr-containing dispersoids in DC casting 7475 aluminum alloy

The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mechanism of the heterogeneous distribution of E(Al_(18)Mg_(3)Cr_(2))dispersoids in this DC ingot is revealed.The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392,respectively,and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy.After homogenization treatment at 470℃ for 24 h,Mg diffuses uniformly,but Cr hardly diffuses.Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously.The heat treatment at 250℃ for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.

Fuzzy logic controller design with unevenly-distributed membership function for high performance chamber cooling system

Fuzzy logic controller adopting unevenly-distributed membership function was presented with the purpose of enhancing performance of the temperature control precision and robustness for the chamber cooling system.Histogram equalization and noise detection were performed to modify the evenly-distributed membership functions of error and error change rate into unevenly-distributed membership functions.Then,the experimental results with evenly and unevenly distributed membership functions were compared under the same outside environment conditions.The experimental results show that the steady-state error is reduced around 40% and the noise disturbance is rejected successfully even though noise range is 60% of the control precision range.The control precision is improved by reducing the steady-state error and the robustness is enhanced by rejecting noise disturbance through the fuzzy logic controller with unevenly-distributed membership function.Moreover,the system energy efficiency and lifetime of electronic expansion valve(EEV) installed in chamber cooling system are improved by adopting the unevenly-distributed membership function.

Working models for the gravitational field of Phobos

Models for the gravitational field of Mars moon Phobos were developed using the latest shape model and assuming homogeneous density distribution.Three methods were applied in our study.Comparisons were made between these methods and all were shown to yield consistent results.Notably,the most accurate shape model of Phobos to date,complete up to degree and order 17 was used for the first time in our analysis.A set of spherical harmonic coefficients up to degree and order 17 were derived for the gravitational field of Phobos.Also considered was the gravitational field on the surface of Phobos.Typical characteristics as well as some pronounced surface features of this irregular-shaped small body could be conveniently identified.The results are readily applicable for such purposes as spacecraft orbit analysis and assessing the dynamical environment of Phobos.

Semiparametric estimation of average treatment effect through a random coefficient dummy endogenous variable model

This paper provides an estimation procedure for average treatment effect through a random coefficient dummy endogenous variable model. A leading example of the model is estimating the effect of a training program on earnings. The model is composed of two equations:an outcome equation and a decision equation.Given the linear restriction in outcome and decision equations,Chen(1999) provided a distribution-free estimation procedure under conditional symmetric error distributions. In this paper we extend Chen's estimator by relaxing the linear index into a nonparametric function,which greatly reduces the risk of model misspecification. A two-step approach is proposed:the first step uses a nonparametric regression estimator for the decision variable,and the second step uses an instrumental variables approach to estimate average treatment effect in the outcome equation. The proposed estimator is shown to be consistent and asymptotically normally distributed. Furthermore,we investigate the finite performance of our estimator by a Monte Carlo study and also use our estimator to study the return of college education in different periods of China. The estimates seem more reasonable than those of other commonly used estimators.