松花江哈尔滨段河道内生态需水研究

随着社会经济的发展,人与自然的冲突加剧,生态环境问题日益突出,水与生态系统研究成为普遍关注的热点。以松花江哈尔滨段为例,基于哈尔滨水文站1898～1987年实测逐日流量资料,运用次最小(大)值、频率排位法和四种适宜生态径流计算方法分别计算研究区河道逐月最小(大)生态需水量和适宜生态需水量,并采用Tennant法对计算结果进行评价和对比。结果表明,频率排位法更适合研究区最大(小)生态需水计算,四种逐月频率法计算的逐月适宜生态径流过程评价效果较理想,年内各月保证率均取50%的计算结果更适合适宜生态需水计算。     

超固结对防渗墙与高塑性粘土接触结构渗透性的影响

试验中概化了高塑性粘土保护层与混凝土防渗墙之间的接触冲刷过程,模拟了心墙与混凝土防渗墙连接部位过渡区粘土的应力状态和渗流状态,对比了超固结土体与普通土体的渗透性。结果表明,超固结土体在短时间内渗透性明显下降,下降的程度与土体所处的工作应力状态有关,且随时间增长,超固结土渗透性有逐渐恢复的趋势,为高塑性粘土经不同应力历史后的工作状态预测提供了依据。     

分段马斯京根法在黄河龙〖CD1〗潼河段洪水预报中应用

针对黄河龙潼区间河段长,洪水受支流影响大的问题,提出了用分段马斯京根法预报洪水过程的方法,确定了各分段节点初始流量,建立了对洪水分级进行参数率定的方案。实例验证表明,该方法适用性强,求解精度高。     

Influence of clays on the shrinkage and cracking tendency of SCC

The influence of different types of clay on the shrinkage and cracking tendency of fly ash modified self-consolidating concrete (SCCF) for the application of slipform paving were investigated in this study. The mortar phase of each mix was tested for autogenous shrinkage, total free shrinkage under drying and restrained shrinkage cracking. The mechanical properties (flexural strength, compressive strength, and modulus) were studied to supplement the results of the shrinkage and cracking tests. The plain SCCF mix was compared against the clay-modified SCCF mixes, as well as conventional SCC and slipform concrete (SFC) mixes. The results showed that the very early-age autogenous shrinkage of SCCF mortar was increased by the addition of clays due to adsorption effects. The effects of the clays on total shrinkage under long-term drying were found to depend mainly on the pozzolanic reactivity, but these effects were very slight at low dosages of about 1% by mass of binder. The early-age cracking tendency was aggravated by the clays composed of purified magnesium alumino silicate and metakaolin, but little influenced by the clay composed of kaolinite, illite and silica. Overall, the SCC mixture modified with both fly ash and a small amount of clay showed comparable shrinkage and early-age cracking performances as conventional SFC.     

Calculating transport of water from a conduit to the porous matrix by boundary distributed source method

This study presents the development of a suitable numerical method for porous media flow with free and moving boundary (Stefan) problems arising in systems with wetted and unwetted regions of porous media. A non-singular version of the method of fundamental solutions (MFS), termed the boundary distributed source method (BDS), is applied. Darcy flow and homogenous isotropic porous media is assumed. The solution is represented in terms of the fundamental solution of the Laplace equation in two-dimensional Cartesian coordinates. The desingularisation is achieved through boundary distributed sources of the fundamental solution and indirect calculation of the derivatives of the fundamental solution. Respectively, the artificial boundary, characteristic for the classical, singular MFS is not present. The novel BDS is compared with the MFS and the analytical solutions for several numerical examples with excellent agreement. A sensitivity study of the solution, regarding the discretization and the free parameters is performed. The main contributions of the study are the application of the BDS to free and moving boundary problems and the comparison of BDS with MFS for these types of problems. The developed model can be applied to various geohydrological problems.     

Anticorrosion behavior of ultrafine-grained Al-26?wt% Si alloy fabricated by ECAP

Ultrafine-grained (UFG) Al-26 wt% Si alloy was obtained through multipass equal-channel angular pressing (EACP) procedure and subsequently tested in 3.5 wt% NaCl solution for the evaluation of electrochemical corrosion. The results show that the ECAPed alloy with increased number of pressing passes obtain lower mass-loss ratios, nobler E _corr and E _pit, lower I _corr values, and higher anode polarization. The improved corrosion resistance of the ECAPed alloy results from the homogeneous UFG structure with the breakage of brittle large primary silicon crystals, which contributes to a higher pitting resistance. The oxidation product with improved adhesion force and protection efficacy can be formed with greater ease on UFG alloys. It implies that grain refinement through severe-plastic-deformation can enhance anticorrosion behavior of hypereutectic Al–Si alloys, besides the well-known strengthening and toughening effects.     

Pattern Recognition Method for the Source Location of Acoustic Emission Generated During the Damage of Hydraulic Concrete

Abstract: To overcome the disadvantages of current acoustic emission (AE) source location methods, such as classical approaches based on times of arrival and artificial neural networks based on AE signal features, support vector machines (SVM)‐based models have been employed to recognise AE source regions in structures. However, in some circumstances, it seems that a more accurate positioning of AE sources is needed. This study concerns the spatial three‐dimensional (3D) positioning (i.e. coordinates) for damages in hydraulic concrete structures using the least squares SVM (LS‐SVM) regression with AE signal features. The data of artificial discrete AE sources were acquired from simulated AE events on a hydraulic concrete specimen. Various combinations of signal features were chosen to adequately excavate effective information and to obtain the multi‐output LS‐SVM regression model of the best performance. The training and testing results show that the proposed model can realise the accurate spatial 3D positioning of damages in hydraulic concrete structures in laboratory situations and reduce human factors (e.g. judgment of AE propagation velocity, etc.) in the AE source location process. Meanwhile, the work remaining in taking this idea to a practical implementation was discussed.     

防爆墙迎爆面反射压力系数计算方法研究

研究防爆墙迎爆面荷载计算方法有助于防爆墙的科学设计和合理使用。爆炸产生的反射冲击波压力是作用在防爆墙上的主要荷载,由入射压力和与相应的反射压力系数的乘积得到。论文针对墙体变形情况下作用于防爆墙上的反射压力系数的计算方法进行了研究,发现作用于墙体的反射压力系数和墙体变形没有直接关系。基于这一现象,将墙体变形和冲击波墙面反射解耦考虑,提出了反射压力系数的计算方法。论文对比了地面爆炸及近地表空中爆炸对墙体反射压力系数分布规律的差异,建议了近地表空中爆炸时墙体反射压力系数的计算方法。     

考虑激励随机过程性的桥面行车安全可靠度分析

探讨脉动风和路面粗糙度的随机过程性对行车安全可靠度的影响,研究同时考虑平均风的随机性和脉动风的随机过程性的行车安全概率评价方法。采用经典动力可靠度理论分析随机过程性的影响。研究结果表明：侧风环境下桥面行驶汽车的支撑力响应是弱非平稳过程,可以采用经典动力可靠度理论研究行车安全可靠度。车速高时,随机过程性的影响较大;以桑塔纳为代表的小汽车受随机过程性的影响程度比箱式货车的大;随机过程性的影响程度还与动力可靠度曲线和平均风速概率密度函数的风速范围有关。     

基于小波多尺度的索塔锚固区变形特征提取

苏通大桥索塔锚固区高频度的监测数据显示,在造成数据失真的各种噪声中,温度对类似索塔的高耸构筑物的影响尤其明显,会使其产生“背日葵”现象,为了查清温度导致的索塔变形情况,准确评估索塔的安全性,结合实时的气象资料和工况,分时段的采用小波多尺度去噪方法逐层分离出温度产生的索塔偏离度,提取出因实际工况产生的索塔锚固区变形特征。为锚固区传力机理以及施工控制提供了可靠的计算分析依据,对高耸构筑物受力分析具有很好的工程应用前景。