大直径扩底桩竖向承载力影响因素分析

运用国际上通用的大型有限元软件ANSYS建立了桩-土作用的有限元模型,结合某工程实例,分析了大直径扩底桩竖向承载力的影响因素.通过把模拟结果与桩基静载荷试验对比,得出有限元结果与实测值接近;然后采用有限元方法模拟分析了不同扩底直径、扩底高度和桩长对大直径扩底桩竖向承载力的影响.结果显示,大直径扩底桩的竖向承载力随着扩底直径的增加而提高,当D/d大于2时,承载力的增长幅度开始变缓;承载力随着扩底高度的增加而提高,但是增长幅度比较缓和;承载力随着桩长的增加而提高,但桩长增大到一定程度时,承载力的增长幅度变得缓慢起来.     

Analysis of roof and pillar failure associated with weak floor at a limestone mine

A limestone mine in Ohio has had instability problems that have led to massive roof falls extending to the surface. This study focuses on the role that weak, moisture-sensitive floor has in the instability issues.Previous NIOSH research related to this subject did not include analysis for weak floor or weak bands and recommended that when such issues arise they should be investigated further using a more advanced analysis. Therefore, to further investigate the observed instability occurring on a large scale at the Ohio mine, FLAC3 D numerical models were employed to demonstrate the effect that a weak floor has on roof and pillar stability. This case study will provide important information to limestone mine operators regarding the impact of weak floor causing the potential for roof collapse, pillar failure, and subsequent subsidence of the ground surface.     

The importance of correct boundary conditions in the estimation of diffusion coefficients from mass sorption experiments

It is shown in this paper that the wrong choice of boundary conditions in the evaluation of diffusion coefficients in solids can lead to quite unreliable estimates. In particular the two frequent assumptions of immediate reequilibration at the interface or of a radiation--like boundary condition are shown to be completely inadequate if the process kinetics is different. To overcome these difficulties we describe a new method that estimates the unknown boundary conditions along with the diffusion coefficient. A numerical example is examined for comparison.     

基于改进MULTIMOORA方法的PCCP焊接工艺参数优选

焊接作为预应力钢筒混凝土管(prestressed concrete cylinder pipe, PCCP)钢筒加工的主要技术,焊接工艺控制参数直接影响焊缝质量,进而影响PCCP应用性能. 故确定PCCP钢筒最优焊接工艺参数尤为重要,基于现场采集数据和改进MULTIMOORA方法,以焊缝特征指标为评价依据,对螺旋焊接工艺进行综合优选. 首先获取并整理各指标数据,将各指标转化为多属性决策问题,通过评价指标数据,定义权重因子用来分配优先级,量化指标,根据优化原则对方案进行排序,过程采用OWA算子和熵权法消除主观评价值中极端值影响,得到指标综合权重,进行决策排序优选,最后利用占优理论对焊接控制工艺技术参数进行最终评价. 结果表明,PCCP钢筒最优焊接工艺参数为焊接电流340 A、电弧电压为24 V、焊接速度为10.81 mm/s,以期为PCCP钢筒焊接工艺提供技术参考.     

~(137)Cs示踪法研究黄土丘陵区坡面侵蚀空间变化特征

利用放射性同位素示踪技术,对黄土丘陵区不同坡长坡面土壤剖面中137Cs含量测定与分析,研究了坡面土壤侵蚀强度的空间变化特征.结果表明,坡长对坡面侵蚀强度的空间分布有重要影响,坡面侵蚀强度呈波动变化趋势.小流域全坡面水流汇集过程中,净泥沙流失强度随流程的增加先增加后减少.     

Research on the Relationships Between Rainfall and Meteorological Yield in Irrigation District

Rainfall and grain yield are two closely related random variables to be worthy of studying. The meteorological yield explains the influences of weather changes on grain yield. Based on the data series from 1980 to 2006 in Jinghuiqu irrigation district of Shaanxi Province in China, the meteorological yield is achieved from grain yield. Then, the empirical mode decomposition method is applied to analyze fluctuating periods and local features of rainfall and meteorological yield. Meanwhile, the copula method is introduced into describe the joint probability distribution of rainfall and meteorological yield. The studied results show that rainfall and meteorological yield exist vary fluctuation periods with multi-time scales, including 2 to 4 years of short period level, 4 to 6 (or 7) years of middle period level and 19 (or 10 to 11) years of long period level. Using the frank copula method, the bivariate distribution and return period of rainfall and meteorological yield was successfully developed to reveal the encounter risk of their different magnitudes. Finally, similarly with rainfall and meteorological yield, the complex changes and fluctuation periods are also proven to be existed in their joint probability.     

基于一维运动波理论的坡面汇流和沟道汇流数学模型研究

一维运动波理论常用于坡面汇流和沟道汇流的模拟,根据坡面汇流和沟道汇流的特点,采用不同形式的运动波控制方程组来分别描述坡面汇流和沟道汇流过程。采用Mac Cormack格式开发了坡面汇流模型,采用线性离散和非线性离散的显式有限差分格式开发了沟道汇流模型,通过3个典型的算例对各模型进行了验证。验证结果表明,开发的沟道汇流模型是成功的;空间步长的尺度对数值解精度有较大影响,步长越小,数值解精度越高;在沟道汇流模型中,线性求解和迭代求解两种方法的计算结果基本一致。     

基于EMD和BP算法的降水数据插补

降水数据的插补可有效地改善数据系列的完整性。以西柳沟流域作为毛不拉孔兑的参证流域,采用EDM和BP算法对毛不拉孔兑缺失的降水量进行插补,并与已有的相关分析法、频率分析法及逐步回归分析法进行了比较。研究结果表明:EDM-BP模型综合利用了西柳沟降水序列EMD分量的有效信息,因而能较好地反映降水量的变化趋势,在数据拟合和预测方面达到较高的精度,适合毛不拉孔兑降水数据的插补,在其它水文数据插补延长中具有一定的推广应用价值。     

A general framework incorporating knowledge,risk perception and practices to eliminate pesticide residues in food: A Structural Equation Modelling analysis based on survey data of 986 Chinese farmers

Following a variety of incidents in China relating to food poisoning due to the presence of pesticide residues, it is crucial to correct for farmers’ unsafe and improper practices towards pesticide use. Although most studies have focused on the role of external stakeholders such as government extension agencies and pesticide retailers, the attention paid to farmers’ intrinsic motivations is limited. This paper applies Structural Equation Modelling to investigate psychological motivational concepts such as farmers’ knowledge and risk perception, their formation mechanisms and the underlying processes of these concepts that lead to farmers’ practices to eliminate pesticide residues, based on a representative survey conducted with 986 Chinese farmers from 20 counties selected from six provinces. We found both a direct and significant effect of farmers’ knowledge on pesticides residue on their safe pesticide practices and also an indirect effect, i.e. knowledge influences on risk perception which in turn enhances safe pesticide practices. It was also reported that government support strategies are more effective in promoting safe pesticide practices than government regulation.     

黄河下游河道11月至次年5月时期输沙和冲淤规律研究

利用1960—2010年黄河下游11月至次年5月时期实测水沙资料,系统地研究了黄河下游河道水沙运动和河床冲淤规律。分析了花园口、高村、艾山和利津等4站输沙率与各自上站的流量、含沙量和输沙率的关系,黄河下游河道冲淤量与小浪底站来水量、来沙量、含沙量和来沙系数之间的关系。结果表明:黄河下游河道的下站输沙率与上站输沙率有很好相关关系,该时期进入黄河下游河道的输沙量小于1.82亿t、或平均含沙量小于12.6kg/m3、或来沙系数小于0.014 kg·s/m6时,下游河道以冲刷为主,反之则以淤积为主;采用本文建立的下站输沙率与上站输沙率关系式计算的黄河下游各河段冲淤量具有较高的精度。利用本文建立的关系式可以方便地预测未来黄河下游河道该时期不同河段冲淤量,对快速判断黄河上中游水利工程建设对下游河道冲淤影响具有重要意义。