基于宏试验的水电机组健康状况在线监测方法

针对机组状态监测技术无法实时、有效地获取机组健康状况信息的问题,根据系统构成与行为关系模型及专家通过人工试验掌握机组健康状况的思路,提出了基于宏试验的机组健康状况在线监测方法。将机组正常运行中经历的工况当成试验,与人工试验统称为宏试验;在机组全状态监测的基础上,实时自动地识别宏试验、记录试验数据及计算试验性能指标;通过运行状态异常检测及性能降低与越限检测实时评估机组健康状况,实现机组健康状况在线监测。该方法已成功应用于葛洲坝电站,实际运行证明了该方法的实用性与有效性。

宏试验在水电机组状态监测数据分析中应用

采用宏试验的水电机组健康状况评估方法,是将机组正常运行工况当作试验,与人工试验相结合开展宏试验数据分析及状态评估工作,评价机组健康状态及性能指标。文章通过运行状态检测实时评估机组健康状况,实现机组健康状况在线监测,并进行了实例验证。

水工混凝土高温作用下宏、细观力学试验研究

为研究石梁河水库引水隧洞水工混凝土材料在高温热作用下压缩、拉伸力学特征,采用ACTS力学试验设备与细观测试装置,完成了水工混凝土压缩、拉伸宏、细观力学试验分析。试验表明,压缩力学状态下,温度热作用对混凝土应变影响弱于围压效应,同时热作用温度梯次递增,同一围压下试样承载应力水平也递增,但温度为175℃后增长效应减弱,提高围压,试样承载应力受温度热作用影响愈敏感。拉伸力学测试下,高温热作用会影响应变主导方向,尤以残余拉伸应变段最显著;同时各高温下,以175℃下试样承载应力最高。基于SEM扫描与核磁共振NMR细观分析,压缩力学裂隙来自颗粒结构破坏,而拉伸力学裂隙为颗粒间拉结破坏;拉伸力学下,不同温度区间内主导裂隙直径各异,而压缩力学下主导裂隙直径均为0.7μm。

排灌水引起砂土层沉降的宏细观试验分析

利用自行设计的砂土排灌水试验装置,分析地下水排灌引起的砂样宏观竖向变形及细观移动.通过试验测量了反复排水和回灌时砂样的竖向变形,采集了局部土颗粒图片并采用Geo DIP(geotechnical digital image processing)软件对颗粒位移及定向性进行了分析.结果表明:在砂样排灌水的初期阶段,砂样的结构发生了明显重组,砂样沉降不仅发生在排水时,而且回灌时砂样沉降继续增加,砂样产生了较大的、不可恢复的塑性和黏性变形;砂样结构达到相对稳定后,排水时产生的竖向变形变小,而回灌时砂样发生较大的回弹;土颗粒的长轴方向在第一次排水时转动不大,在第三次排水时转动较大,而在第六次排水时转动又变得不明显.试验结果可为控制地面沉降提供参考.

PE+SiO_(2)复合改性沥青储存稳定性多尺度研究

为了提高普通塑料(PE)改性沥青的热储存稳定性,提出在PE改性沥青中添加纳米二氧化硅(SiO_(2))粒子,以制备PE+SiO_(2)复合改性沥青,并基于宏、微观试验,结合图像处理和灰色关联熵等定量分析方法,揭示了不同类型PE+SiO_(2)复合改性沥青的储存稳定性、高低温性能、微观组分与结构形貌差异,得到了其特征官能团指数和改性剂分布指数与各项宏观性能之间的关联,确定了最佳PE类型和SiO_(2)掺量.结果表明:复合改性沥青中SiO_(2)和PE组分之间发生了物理交互连锁反应,使沥青高温稳定性和储存稳定性得以提升,且尤以线型低密度聚乙烯(LLDPE)型复合改性沥青的效果最优;SiO_(2)掺量为0.2%时,改性剂分散较好,荧光面积占比适中,软化点差最小,离析率最低,各项指标的关联较为均匀,为最佳掺量.研究成果可为高性能复合改性沥青的生产制备提供参考,为改性沥青多尺度特性的研究提供新视角.

Macro-micro investigation of granular materials in torsional shear test

A three-dimensional numerical torsion shear test is presented on hollow cylinder specimen which is performed on a spherical assemblage with fixed principal stress axes using the discrete element code PFC3D.Stack wall technique boundary conditions are employed and optimized to reasonably capture the microstructure evolution.Parametric studies are conducted in terms of the ratio κ,normal and shear stiffness of particles,wall stiffness and friction coefficients.Afterwards,in comparison with physical test,numerical results for a fixed principal stress angle(α=45°) are presented.The results show that the numerical test could capture the macro-micro mechanical behavior of the spherical particle assembly.The evolution of the coordination number demonstrates that particles in shear banding undergo remarkable decrease.The effects of localization on specimens illustrate that global stress and strain recorded from a hollow cylinder apparatus could not represent the localized response.The shearing band initiation and evolution from porosity and shear rate are visualized by contour lines in different shear strains.

A New Macro Model for Traffic Flow on a Highway with Ramps and Numerical Tests

In this paper, we present a new macro model for traffic flow on a highway with ramps based on the existing models. We use the new model to study the effects of on-off-ramp on the main road traffic during the morning rush period and the evening rush period. Numerical tests show that, during the two rush periods, these effects are often different and related to the status of the main road traffic. If the main road traffic flow is uniform, then ramps always produce stop-and-go traffic when the main road density is between two critical values, and ramps have little effect on the main road traffic when the main road density is less than the smaller critical value or greater than the larger critical value. If a small perturbation appears on the main road, ramp may lead to stop-and-go traffic, or relieve or even eliminate the stop-and-go traffic, under different circumstances. These results are consistent with real traffic, which shows that the new model is reasonable.

Macro and micro failure mechanism of surrounding rock of small span tunnel under different stress paths

According to the different stress paths,similar model test and PFC simulation test of tunnel surrounding rock are designed to compare the failure mechanisms at macroscopic and mesoscopic scales.The following conclusions are drawn.1)Excavation unloading will disturb the surrounding rock to form a certain excavation damaged zone.2)Under the loading path,the stress of surrounding rock failure is 1.500 MPa;under the unloading path with initial stress of 60% σ_(Zmax) and 100% σ_(Zmax),the failure stress is 1.583 and 1.833 MPa respectively in the model test.3)In terms of the failure mode of rocks under different stress paths,tensile fractures first appear in two sides of the vertical walls;thereafter,the spandrel and arch foot are loosened due to the stress concentration.The fractures gradually coalesce with those occurring in the vertical walls.4)In the process of excavation unloading,the proportion of shear cracks is 35.3%,and the rock is subject to strong shear effect.The final failure surface is approximately V-shaped.5)The tangential peak stress on the vertical walls at the free face is the lowest;the vertical walls at the free face show the poorest bearing capacity and are easily subjected to tensile failure.

Effect of heating-rate on failure temperature of pre-loaded magnesium alloy

The response and failure of magnesium alloy AZ31 specimens subjected to different pre-loaded-stress levels and heating rates were investigated with a Gleeble-1500 thermo-mechanical material testing system.It is found that the increases of either pre-loaded stresses or heating-rates decrease the failure temperatures of the specimens.The metallographs of the tested specimens were also observed.It is shown that the high heating-rate may cause stronger local thermal inconsistency,which remarkably increases the microdefects and reduces the macroscopic mechanical properties of the material.

新型碾压式导电混凝土功能材料力学性能试验与精细仿真分析

碾压式导电混凝土(electrically conductive roller-compacted concrete,ERCC)是一种新型功能性材料,可通过自身电热性能解决高寒地区路面跑道人工除雪去冰效率低、大坝工程结构温控难等问题.本文开展了ERCC材料设计、物理试验与数值仿真分析研究.利用扫描电子显微镜(scanning electron microscope,SEM)测试分析了表面活性剂对ERCC浆体流动性、炭黑分散效果的改善机理;针对碾压成型的大型ERCC钻芯取样试件,开展了力学性能的宏观试验与X射线断层扫描(X-ray computed tomography,XCT)的细观试验;进而在材料试验的基础上,通过耦合连续介质、非连续介质计算方法进行ERCC精细化数值仿真分析,建立了基于真实骨料的ERCC细观模型,解决了传统混凝土细观模拟中XCT模型计算成本过高、非连续介质计算效率低、传统球体/多面体骨料模型的精细化程度差等问题.结果表明:ERCC表面活性剂可明显改善炭黑分散效果,采用碾压施工工艺成型质量较好,抗压强度为22.85 MPa,劈拉强度为1.72 MPa,弹性模量为23.7 GPa,孔隙体积比为1.05‰;在砂浆、界面强度一定时,增大骨料体积比,可不同程度提高ERCC的力学性能;精细化仿真计算结果与多个实际工程混凝土材料特性统计规律相吻合,相比传统混凝土细观模拟方法具有更好的适用性.

Acute toxicity study of Aspidopterys obcordata aqueous extract in Sprague-Dawley rats

OBJECTIVE: To examine the acute toxicity of an aqueous extract of Aspidopterys obcordata(A. obcordata) in Sprague Dawley rats.METHODS: The rats were orally administered a dose of 5000 mg/kg body weight and observed continuously for 6 h and then daily for 14 days. Control rats were administered distilled water. The effect of the extract on general behavior, body weight, and food and water intake were measured.After 14 days, the rats were sacrificed and their organs(liver, heart, spleen, lungs, kidney, adrenal glands, ovaries, and testes) were removed for macroscopic examination. The body and organ weights in addition to hematology(e.g., hemoglobin and white blood cell counts) and clinical blood biochemistry(e.g., albumin and bilirubin) were also examined.RESULTS: There were no deaths recorded, and the rats treated with A. obcordata showed no signs of toxicity. All measured parameters in rats treated with A. obcordata were unaffected when compared with those in control rats. The acute toxicity(LD_(50))was estimated to be > 5000 mg/kg body weight.CONCLUSION: Our results demonstrate the safety of an acute oral administration of an aqueous extract of A. obcordata in rats and indicate that future subacute and long-term toxicity testing of A. obcordata is warranted.

Behavior of reinforced concrete structural walls with various opening locations: experiments and macro model

Two experimental tests of three-storied reinforced concrete structural walls having large openings were performed.Based on an original macro model,a multiple modified macro-model was proposed to develop a simple method to design a reinforced concrete structural wall with large openings and various opening locations.The interaction between reinforcement ties and concrete struts formed along the perimeter of openings was neglected in the original model.However,the strut-and-tie node was proposed to take account of such interaction in the proposed model.The predicted behavior of two specimens using such a proposed model was compared with the experimental results.It is shown that the behavior of structural walls with large openings could be modeled well using the proposed model.Moreover,the study indicates that the proposed model is applicable even in cases of multi-story structural walls having large openings and various opening locations.