混凝土面板堆石坝面板应力变形仿真计算

【目的】基于混凝土面板与垫层之间接触面的数值计算模型,考虑温度荷载作用,研究面板堆石坝面板的应力变形特性。【方法】以接触摩擦单元理论为基础,采用接触单元模拟混凝土面板与垫层之间的接触面,进行了公伯峡混凝土面板堆石坝面板应力变形仿真计算,并将计算结果与观测数据进行对比分析。【结果】面板挠度呈现出中部大、两端小的分布规律,最大值为0.24 m,位于面板的中心位置,与观测结果基本一致;面板的顺坡向应力分布呈现出中部受压、两端受拉的变化趋势,顺坡向压应力最大值为7.9 MPa,出现在约1/2坝高处,拉应力最大值为1.3 MPa,出现在面板的底部与顶部;面板底面点与表面点的应力分布是一致的,在同一高程处,面板底面点的应力较表面点大;考虑温度荷载作用时,混凝土面板的顺坡向应力分布规律与不考虑温度荷载时基本一致,但拉应力值明显增大,并且与实际观测结果更为接近。【结论】基于接触摩擦计算模型,考虑温度荷载作用,可以获得更为准确的混凝土面板应力变形数值计算结果。     

Sharing Rate of Cooling Load of Radiant Terminal Device and Air Supply Terminal Device in Residential Buildings——From the Perspective of Thermal Comfort and Indoor Air Quality

Taking residential buildings as the study objects, for three different residential load types such as low load, medium load, and high load type, indoor thermal environments of different load sharing-rates are simulated, respectively. Indoor thermal comfort and indoor air quality of different load sharing-rates are also analyzed and evaluated. And the appropriate range of cooling load sharing-rates are given from the view of both occupants thermal comfort and occupants health. When ωc (the sensible heat load sharing rate of the radiant terminal device) <0.7, the human thermal index in work region can be controlled within the range of thermal comfort standard. From the point of avoiding local discomfort, ωc is suggested to take 04~1. As regard to indoor air quality, for the constant air volume mode, ωc is suggested to take 0.5~0.9 under low and middle load conditions, and ωc is suggested to take 0.35~0.6 under high load conditions. For the variable air volume mode, the smaller the value of ωc is, the better indoor air quality is.     

Voltage decoupling and load characteristics of high-speed motorized spindle

To study the impact of coupling circuits in high speed motorized spindle’s dynamic mathematical model on load characteristics of the spindle, according to invariance principle of control theory, external decoupling branches is introduced into the point where the difference between reference current and feedback current of the high speed motorized spindle is, to eliminate the impact of coupling voltage, and then the impact way of excitation current changes and torque current changes on the spindle’s flux, electromagnetic torque, and load characteristics are studied when the load varies. Meanwhile, the load characteristics are tested on the test platform of high speed motorized spindle. Theoretical analysis and experimental results show that the decoupling effect of high speed motorized spindle directly affects the stability of the spindle’s flux and the linear tracking ability of the torque current on load, which is reflected by the parallelism of mechanical characteristic curve under different frequencies, the pulse level of electromagnetic torque, the load capacity of the spindle, power factor, efficiency and other parameters. Therefore the spindle’s actual decoupling results and dynamic performance under the control mode can be judged and forecasted, according to the trends of mechanical characteristic curve, power factor curve and efficiency curve.     

First-order load with pulse-width modulation

For the limitation of the dynamic and time-varying characteristics of the load simulator, a novel design method for the first-order electrical load is presented. By adjusting the turn-on time of switches, the first-order load with the parameters in a certain range can be simulated. The simulation degree of the electrical load might be judged with the area percent of function distance in the load response. For the simulations on three loads with cut-off frequencies as 20,50,80 Hz, the PWM period is 1 ms. The duty cycles are 9.9%,39.4% and 69.1%. The simulation deviations are 1.48%,3.92% and 3.57%. The results show that the first-order electrical load designed with this method can simulate any first-order load with the parameters in a certain range .     

湖南农业大学住宅“负荷需要系数”选值的探讨

针对湖南农业大学住宅电气设计中计算的用电负荷值偏大问题，通过对教工住宅楼用电情况的调查与分析，探讨了住宅电气设计中“需要系数”的选值，住宅电气设计的“需要系数”值以选用０．３５为宜。     

均布载荷辗压重组木坯料的强度准则建立初探

采用横观各向同性假设，对均布载荷辗压方式下，重组木网状坯料的形成静力学强度准则进行了初步探讨。重组木的坯料要求将间伐材等沿径向与切向压溃，而纵向纤维不断。因此，必须准确地确定加压数值。本文以复合材料力学建立判据。其分析结果将高于传统木材力学的分析方法。     

北墙不同外倾角对日光温室表面风压与体型系数的影响

为探明日光温室北墙外倾角的改变对其屋面风压系数和风荷载体型系数的影响,该研究基于计算流体力学原理,采用数值模拟方法,考虑北风和西北风2种风向,研究了不同北墙外倾角下日光温室表面风压分布规律,并给出不同北墙外倾角情况下的细化分区风荷载体型系数。结果显示：1）风压分布规律为：北风和西北风时日光温室前屋面和后屋面上半部风压系数为负,屋脊处和东、西边缘风吸力集中;随北墙外倾角减小,前屋面上部和后屋面风压系数绝对值明显减小,前屋面下部风压系数无显著变化。2）风荷载体型系数规律：北风时,以北墙外倾角90°（即竖直）为参照,外倾角减至30°可使前屋面上部体型系数的绝对值减小16%～26%,可使前屋面下部体型系数的绝对值增大6%～57%,可使后屋面体型系数绝对值减至0左右;西北风时,前屋面上部和后屋面体型系数绝对值均为西端大、东端小,前屋面下部体型系数绝对值为中间大两端小,屋面风荷载体型系数随北墙外倾角的变化不显著。因此,北墙外倾角的变化导致日光温室屋面风荷载分布发生变化较大,对日光温室结构的抗风性能影响较大,建议日光温室屋面风荷载计算应考虑北墙外倾角的影响,抗风设计时可合理选择北墙外倾角以减小屋面风荷载,边榀骨架结构和围护结构的边缘处需加强。     

渭河流域极端降雨变化趋势及其对水沙情势的影响

为探究渭河流域极端降雨变化趋势及其对水沙情势的影响,采用非参数趋势检验、突变检验和连续小波变换诊断了渭河流域1960—2019年的极端降雨指数及径流输沙序列的变异特征,通过双累积曲线法和相关分析法定量评估了流域极端降雨对水沙变化的影响。结果表明:各极端降雨指数呈阶段性波动变化,总体上PRCPTOT,RX5day和RX1day呈不显著下降趋势,R95pTOT,SDII和FSPTOT呈不显著上升趋势。各极端降雨指数均存在以4～6 a,11～12 a,28～29 a为周期的变化特征。径流与输沙量均呈显著减少趋势,分别在1993年、1999年发生突变,其中径流存在5 a和12 a的周期。各极端降雨指数均与径流、输沙量正相关,相比之下,输沙量与各极端降雨指数之间的相关系数偏低。极端降雨变化对径流与输沙量的减少具有重要影响。其中,PRCPTOT对径流减少的影响最大(29.65%),其次是RX5day(25.68%)和FSPTOT(25.95%)。PRCPTOT对输沙量减少的影响也是最大的(10.02%),其次是RX5day(7.12%)。综上,渭河流域水沙情势的变化受极端降雨的显著影响。     

不同草本植被过滤带对径流中氮磷的生态阻控效果

为明确在不同条件下植被过滤带对地表径流氮、磷的阻控规律,分别构建百慕大、马尼拉、高羊茅、玉龙草等4种植被过滤带和裸地对照组过滤带,通过模拟3种污染物浓度和3种水力负荷强度的径流,探讨不同草本植被过滤带对表流和渗流中的氮、磷的阻控效果。结果表明,与对照组相比,植被过滤带显著提高土壤系统对径流以及来水中的氮、磷等污染物的拦截能力,在3种水力负荷强度下,百慕大、马尼拉、高羊茅、玉龙草和裸地对照组的平均径流拦截率分别为56.10%,54.28%,63.16%,60.53%和39.10%,4种植被的径流拦截率均显著高于对照组(p＜0.05);4种植被覆盖均显著降低表渗流量比,提高土壤的入渗能力;水力负荷强度的提高降低植被过滤带对NH₄⁺—N和TP的去除效率,但植被过滤带去除率降低的幅度小于对照组;在一定范围内,渗流中TN、NO₃^-—N和TP的去除率随着来水中氮、磷浓度增加而提高;在一定的水力负荷下,根冠比越低的植被削减径流的能力越强。     

近70年长江干流寸滩站以上流域水沙关系变化及其驱动因素

以长江干流寸滩水文站以上流域为研究对象,基于1953-2018年的实测水沙资料,采用线性回归、Mann-Kendall趋势检验和水沙关系曲线分析径流、输沙的时间趋势及其关系变化,并采用双累积曲线法分析水沙变化的驱动因素。结果表明:寸滩站以上流域多年平均径流量为3425亿m^3,多年平均输沙量为3.61亿t;多年平均月径流量为294.8亿m^3,多年平均月输沙量为3013万t,且主要分布在6-10月,分别占年径流泥沙总量的70%和95%以上。趋势分析显示,流域年降雨量和径流量变化趋势不明显,年输沙量呈极显著减小趋势;月径流量在1-4月显著增加,其他月份变化不显著,而各月输沙量均呈显著减少趋势。水沙关系曲线均可用幂函数拟合,拟合参数受时间尺度影响,统计检验显示悬移质输沙量实测值与水沙关系曲线的估算值差异不显著。双累积曲线分析发现水利工程建设和水土保持等人类活动是寸滩水文站输沙减少的主要原因,其作用占69%~93%,其中2000年以来人类活动的贡献超过90%。