混凝土面板堆石坝水下面板裂缝成因数值分析

混凝土面板堆石坝的水下面板裂缝形成发展,影响了面板的工作性态。为揭示水下面板裂缝的成因,依据监测资料研究了运行期不利温度工况及施工质量对面板裂缝的影响,提出以空隙率的概率分布函数表征施工质量的方法,采用质量保证率模拟堆石区的施工缺陷区域,确定了运行期堆石坝面板裂缝分析的流程。以某混凝土面板堆石坝为例,通过结构计算研究了面板裂缝开裂区域的应力情况及变化趋势。结果表明:温度因子对深水区裂缝产生及发展影响不大。在水荷载作用下,当施工质量缺陷区堆石料质量保证率为90%时,计算的裂缝应力符合裂缝的检查情况,验证了该模拟方法的合理性。研究成果对面板堆石坝的安全运行具有工程意义,也对同种坝型运行期水下裂缝的成因和判断具有参考价值。     

模型桥墩局部冲刷瞬时地形数据自动获取装备研制

模型试验中冲刷地形测绘装备相对落后,致使桥墩周围局部冲刷瞬时地形数据无法实时获取,冲刷动态发展过程及机理的模型试验研究工作难以开展。研制了一种模型桥墩局部冲刷瞬时地形数据等值线自动绘制装备,并利用室内水工模型试验优化了各组成的性能指标,量化了绘制装备的设计参数,分析了监测系统在模型应用中的测绘精度及在工程原型中的适用性。模型试验研究表明,该装备结构简单,操作方便,加工制作成本较低,精度及灵敏性较高,能够快速获取动态过程中局部冲刷瞬时地形等值线,适用于局部冲刷发展影响流场特性研究中的水下地形快速测绘,也可按放大比尺制作成型后应用于涉水建筑物周围水下地形监测。     

Exact probabilistic testability measures for multi-output circuits

The computation of probabilistic testability measures has become increasingly important and some methods have been proposed, although the exact solution of the problem is NP-hard. An exact analytical method for singleoutput combinational circuits is extended to deal with multi-output circuits. Such circuits are reduced to singleoutput ones by introducing a dummy gate, the X-gate, and applying to the resulting graph the analysis based on supergates.     

海水中VLF传播特性分析

本文以电磁波反射定律与折射定律为基础,建立了电磁波在两种介质分界面处的传播模型,研究了甚低频电磁波在导电媒质中的传播特性,推导了甚低频波在海面及海水中传播的电场表达式,分析了导电媒质对不同频率的电磁波所产生的影响,分析结果表明,甚低频电磁波在海水中的穿透深度较大,能够满足水下通信要求。     

Surface characterization of 6H-SiC (0001) substrates in indentation and abrasive machining

Surface characterization of 6H-SiC (0001) substrates in indentation and abrasive machining was carried out to investigate microfracture, residual damage, and surface roughness associated with material removal and surface generation. Brittle versus plastic deformation was studied using Vickers indention and nano-indentation. To characterize the abrasive machining response, the 6H-SiC (0001) substrates were ground using diamond wheels with grit sizes of 25, 15 and 7 μm, and then polished with diamond suspensions of 3 and 0.05 μm. It is found that in indentation, there was a scale effect for brittle versus plastic deformation in 6H-SiC substrates. Also, in grinding, the scales of fracture and surface roughness of the substrates decreased with a decrease in diamond grit size. However, in polishing, a reduction in grit size of diamond suspensions gave no significant improvement in surface roughness. Furthermore, the results showed that fracture-free 6H-SiC (0001) surfaces were generated in polishing with the existence of the residual crystal defects, which were associated with the origin of defects in single crystal growth.     

Particular behavior of spindle thermal deformation by thermal bending

Thermally induced errors reduce the accuracy in precision machining, and a great deal of research has been presented on compensation for these errors in machine tools. However, during the transition period after commencing or stopping spindle rotation, thermal deformation behavior is very complex. In particular, the y-directional movement of the vertical machining center cannot be explained by thermal expansion alone because of the relationship between deformation and temperature. Thermal bending that is generated from the thermal gradient in the structure causes this movement. In the research described in this paper, a theoretical explanation and an experimental verification is given for the particular behavior of spindle thermal deformation. As it is not easy to map the relationship of the compensation model, separation of the steady from the non-steady state in the mapping process is strongly recommended.     

刀盘结构对水下切粒水室流场分布的影响

对于特殊材料的水下切粒加工,采用立式爪形刀盘的独特结构。运用有限元分析软件fluent,对水下切粒水室进行数值模拟,对比分析立式爪形刀盘与传统刀盘的水室流场分布,探究不同的刀盘结构以及刀盘位置的变化对于切粒水室流场分布的影响。     

高温水冷后循环加卸载条件下花岗岩的渗透性

针对水下隧道火灾喷水灭火降温过程中围岩的渗透性问题,对高温水冷后循环加卸载条件下花岗岩的渗透性开展了试验研究.以高温(25、400和900 ℃)水冷后的花岗岩试样为研究对象,通过轴向压应力循环加卸载过程中气体渗透性试验,研究花岗岩渗透率变化规律.结果表明:轴向压应力循环加卸载试验过程中,花岗岩试样的卸载模量随着高温水冷处理温度升高而减小,随着轴向压应力增大,卸载模量总体呈上升趋势,气体渗透率随温度升高而增大;花岗岩BET比表面积与BJH孔体积在900 ℃高温水冷后明显减小.     

水下设备安装过程及其影响因素分析

为了提高水下设备安装精度与工作效率,基于海上工作经验及查阅国内外相关文献,对水下设备的安装过程进行了研究,其总体过程大致分为5个阶段,即装船固定、提升操作、穿越飞溅区、深水下放、落地坐放;分析了影响水下设备安装过程的主要因素,其中水深主要影响吊放系统和设备在水下的横向偏移;波浪载荷主要应用船舶的动态响应,在设备经历穿越飞溅区阶段时对设备及缆绳造成损伤的风险较大;水下设备自身参数主要影响安装方式和安装船舶的选用。     

特高压带电作业绝缘工器具试验电压优化及安全裕度

针对1 000 kV特高压交流输电线路带电作业绝缘工器具的试验电压偏严格,造成工器具非正常损坏的问题,深入分析了1 000 kV交流输电线路带电作业工况下的工频及操作过电压水平,同时开展了1 000 kV特高压带电作业绝缘工器具试验的电压选取及其安全裕度研究。综合分析后提出了较为合理的试验电压以及安全裕度范围,并对提出的修订值进行了工频耐压验证试验、绝缘材料电气性能验证试验以及带电作业安全性试验验证等,充分分析并证明了其合理性。