速度作用下非线性弹性地基上矩形薄板主共振

本文基于非线性弹性地基模型及弹性理论,建立了非线性弹性地基上矩形薄板在移动车辆荷载作用下的非线性动力方程,运用Galerkin方法及多尺度法求得该系统主共振的幅频响应方程,以行车速度为调谐参数,分析阻尼系数、车辆荷载、板厚及相位差等参数对非线性弹性地基上矩形薄板在移动车辆荷载作用下主共振幅频响应的影响。结果表明:非线性弹性地基上矩形薄板在行车速度作用下主共振系统的非线性特点不明显,振幅-速度响应曲线接近对称,改变阻尼系数、车辆荷载等参数时对共振区间影响不大。在正常取值范围内,随着阻尼系数值增大振幅-速度响应曲线峰值减小;随着车辆荷载、板厚及相位差的增大振幅-速度响应曲线峰值增大。     

Inspection equipment study for subway tunnel defects by grey-scale image processing

In recent years, much attention has been paid to Machine Vision-Based (MVB) technology for tunnel main defect (leakage and crack) inspection as an innovative technology. Based on the principle of MVB technology, various researchers have developed tunnel inspection equipment, but most of them need either a trailer or an external power supply, which cannot meet the demand of subway tunnel inspection in China. The limited inspection time, high demand for precision, rigid requirements of operational management and high cost of the equipment restrict the application of this method in China. MTI-100 (Moving Tunnel Inspection) was developed under these circumstances. To capture stable, high-quality images of the lining surface as the raw data of inspection, an image capture system is well designed based on CCD (Charge-coupled Device) camera scanning. Additionally, equipment optimization design of the mechanism and electricity requirements for the inspection accuracy of subway tunnel inspection is investigated. The maximal size and weight of equipment elements determined the convenience of inspection, which is primarily conditioned by these designs. The effects of lighting and vibration have been considered. A method to calculate the image shift caused by vibration is proposed. The software network is another core component of the equipment, which connects the image acquisition, image storage and defect recognition. The famous Otsu method is used for leakage recognition. A new algorithm based on the features of the local image grid is developed to recognize cracks. A comparative study shows its high accuracy for crack recognition. Finally, a simulative tunnel test and field inspection are undertaken to verify the performance of the non-destructive subway tunnel inspection equipment. Through these tests, the accuracy, stability, repeatability, labor intensity and efficiency of the equipment have been verified. A real project test certified that the developed MTI-100 is quite suitable for practical tunnel inspection.     

地震次生灾害作用下高坝风险分析研究

为开发我国西部地区丰富的水电资源,一批高坝大库已建或正在开工建设当中。西部地区是我国强震多发区,因此对高坝进行地震风险分析研究至关重要。坝址区多位于高山峡谷之中,在高烈度地震发生时,极易产生地震作用下的边坡滑动,滑坡入库将激起巨大涌浪,所产生的高水头冲击力作用于高坝上将会额外增大高坝风险。本文针对以上问题,对高坝在地震及地震所产生的滑坡次生灾害共同作用下的风险问题进行了研究,分析对比了高坝在不同作用组合条件下的风险,得出的结论可为高坝地震风险控制提供依据。     

Ni/Ni3Al拉伸力学性能的分子动力学模拟

采用分子动力学方法研究了Ni/Ni_3Al的拉伸力学性能。首先模拟了在室温、恒定应变速率环境下γ′强化相的含量对Ni/Ni_3Al拉伸力学性能的影响,重点研究了具有3种典型特征的γ′强化相含量的Ni/Ni_3Al微观组织演化。研究结果表明:相比于单晶Ni,γ′强化相可以提高Ni/Ni_3Al的抗拉强度。这是因为在塑性变形过程中,随着位错的不断增殖,位错密度逐渐增大,导致位错塞积,增大了位错运动的阻力,提高了抗拉强度。接着研究了温度对Ni/Ni_3Al拉伸力学性能的影响,发现Ni/10%Ni3Al(体积分数,下同)的抗拉强度随着温度的升高呈下降趋势。这是因为随着温度的升高,原子动能增大,导致原子热运动更剧烈,原子间的结合力更弱,脱离平衡位置的原子来不及回到平衡位置,fcc结构转变为大量的hcp结构和其他无序原子排列结构,导致晶格畸变,降低了抗拉强度。最后研究了应变速率对Ni/Ni_3Al的拉伸力学性能的影响,结果表明,抗拉强度对低应变速率不敏感,对高应变速率敏感。     

双钢板混凝土组合剪力墙抗震性能研究综述

双钢板混凝土组合剪力墙由于具有延性好、承载力高、高强度及刚度大等优点,组合剪力墙是目前比较理想的抗侧力构件,近些年来得到了广泛的应用和发展。文中在总结国内外研究的基础上,介绍了对不同截面形式双钢板混凝土组合剪力墙的承载力计算、受力性能影响因素及试验研究,指出目前有关双钢板组合剪力墙研究领域存在的问题和尚未研究的方面,为双钢板混凝土组合剪力墙的进一步试验研究及设计提供建议和参考。     

An experimental study of the relationship between the matric potential,unfrozen water,and segregated ice of saturated freezing soil

Bulletin of Engineering Geology and the Environment - Frost heave damage is caused by the in situ freezing of pore water and segregated ice due to moisture migration. Previous studies have shown...     

唐巴公路嘉陵江大桥加固工程变形监测分析

结合嘉陵江大桥加固工程的建设实际,在旧桥不减载的情况下,采用全站仪对大桥拱轴线进行监测。采用三角高程测量法计算观测点的高程坐标;再根据各观测点的高程值计算各点的挠度,比较挠度的实际迭加值和设计的理论迭加值,二者的差异在许可范围内,从而确认该方法切实可行。该监测分析方法可为同类工程提供参考。     

An efficient integrated approach for global sensitivity analysis of hydrological model parameters

Efficient sensitivity analysis, particularly for the global sensitivity analysis (GSA) to identify the most important or sensitive parameters, is crucial for understanding complex hydrological models, e.g., distributed hydrological models. In this paper, we propose an efficient integrated approach that integrates a qualitative screening method (the Morris method) with a quantitative analysis method based on the statistical emulator (variance-based method with the response surface method, named the RSMSobol' method) to reduce the computational burden of GSA for time-consuming models. Using the Huaihe River Basin of China as a case study, the proposed approach is used to analyze the parameter sensitivity of distributed time-variant gain model (DTVGM). First, the Morris screening method is used to qualitatively identify the parameter sensitivity. Subsequently, the statistical emulator using the multivariate adaptive regression spline (MARS) method is chosen as an appropriate surrogate model to quantify the sensitivity indices of the DTVGM. The results reveal that the soil moisture parameter WM is the most sensitive of all the responses of interest. The parameters Kaw and g₁ are relatively important for the water balance coefficient (WB) and Nash–Sutcliffe coefficient (NS), while the routing parameter RoughRss is very sensitive for the Nash–Sutcliffe coefficient (NS) and correlation coefficient (RC) response of interest. The results also demonstrate that the proposed approach is much faster than the brute-force approach and is an effective and efficient method due to its low CPU cost and adequate degree of accuracy.     

Study on combustion mode transition of hydrogen fueled dual-mode scramjet engine based on thermodynamic cycle analysis

Hydrogen fueled scramjet is a candidate for use as the engine of the aerospace plane for its high specific impulse. To further improve the engine performance, analysis of combustion mode transition for a hydrogen fueled scramjet engine was investigated in this study. In order to identify the differences between Scram- and Ram-mode cycles in propulsive and economic performances for selection and optimization of operation modes, a thermodynamic cycle analysis was made with a dual-mode scramjet engine. It was found through comparative analysis that the specific impulse of the Ram-mode cycle was superior to that of the Scram-mode cycle in meeting the specific thrust requirement. From the viewpoint of performance optimization, the combustion mode transition in a dual-mode scramjet engine should occur in the range of Mach number 6–7. It was therefore concluded that a dual-mode scramjet engine should be operated as much at the Ram-mode cycle as possible when the flight Mach number is less than 6, and the combustion mode transition between Ram-mode cycle and Scram-mode cycle should take place in the range of flight Mach number 6–7.