辐射井技术在利津黄河滩地地下水开发中的应用研究

辐射井是开发利用浅层地下水的有效井型,为了缓解利津县水资源供需矛盾,对利用辐射井技术开发黄河滩地浅层地下淡水进行了试验研究,具体阐述了在黄河下游滩地粉细砂、细砂含水层中辐射井的成井技术、竖井结构及深度、水平辐射管的布置、试验井的水质和出水量等。     

基于CFD的某仿古木塔风压分布研究

随着计算机技术的发展,CFD模拟分析成为研究复杂建筑体型风压分布的方法之一。本文采用计算流体力学软件FLUENT中的RNG k-ε湍流模型研究了某传统楼阁式仿古高层纯木佛塔具有代表性的4种风向角下的风压分布,并与现行《建筑结构荷载规范》(GB50009)中的相关风压体型系数进行了对比分析。研究结果表明,在0°风向下,该仿古木塔受到最大的风荷载作用;在0°和45。风向下,该结构各楼层层间墙面带和檐顶带的风压体型系数均与规范中的常数取值不同,而是随着楼层呈现出一定的变化。同时,给出了整个仿古木塔最大负风压的分布范围和大小。研究结论对该类结构风荷载的计算具有一定的参考价值。     

Thermal response of steel framing members in open car park fires

For open car park structures, adopting a performance-based structural fire design is often justified and allowed because the fire does not reach flashover. However, this design approach requires an accurate assessment of temperatures in structural members exposed to car fires. This paper describes a numerical study on the thermal exposure on steel framing members in open car park fires. Steel temperatures are computed by the coupling of computational fluid dynamics and finite element modeling, and by analytical models from the Eurocodes. In addition, the influence of galvanization on the steel temperature evolution is assessed. Results show that temperatures in unprotected beams and columns are influenced by the section geometry, car fire scenario, modeling approach, and use of galvanization. Galvanization slightly delays and reduces peak temperature. Regarding the different models, CFD-FEM (CFD: computational fluid dynamics, FEM: finite-element method) coupled models predict lower temperatures than the Hasemi model, because the latter conservatively assumes that the fire flame continuously touches the ceiling. Further, the Hasemi model cannot account for the effect of reduced emissivity from galvanization on the absorbed heat flux. Detailed temperature distributions obtained in the steel members can be used to complete efficient structural fire designs based on the member sections, structure layout, and use of galvanization.     

Effect of vehicular loading on suspension bridge dynamic properties

Since the 1970s, many researchers have attempted to use changes in natural frequencies as means for condition assessment of large civil engineering structures such as bridges, but have faced the challenge of decoupling frequency variations apparently caused by changing operational conditions. In the case of the Tamar Bridge in southwest England, the time series of natural frequencies exhibit diurnal variations resulting from a combination of thermal and vehicular loading, the effects of which would need to be compensated for in dynamics-based assessment. By examining monitored data for several years, the effects of traffic mass have been characterised and compared with other operational effects. While temperature changes appear to have a greater influence for lateral modes, traffic mass is a strong factor in all modes and the dominant factor for the vertical and torsional modes evaluated. Physics-based explanations for the variable effects of vehicle mass have been sought using a finite element model calibrated against experimental data. As a caution for performance prediction in structural dynamics, while acceptable reconciliation of natural frequencies from FE model and measurements was achievable, reconciling simulated effects of changing mass with observed behaviour has not been straightforward due to the complexity of the retrofitted suspension bridge structure studied.     

Application of singular spectrum analysis to structural monitoring and damage diagnosis of bridges

Singular spectrum analysis (SSA) is a novel technique and has proven to be a powerful tool for time series data analysis. Through singular value decomposition of Hankel matrix data, the time series of data can be decomposed into several simple, independent and identifiable components from singular values and singular vectors. It has already been widely applied to process climatic, meteorological, geophysical and economic data. In this paper, we demonstrate that the coupling degree of the 1st and 2nd singular values in SSA contains useful indications on the feature and composition of the analysed signal. The proposed method is successfully applied to the monitoring of structure, such as damage detection of the simulated dynamic system, experimental steel frame, bridge foundation scouring and pier settlement in the laboratory and on-site bridge monitoring during typhoon strike. The proposed algorithm is simple and suitable for structural health monitoring in the field.     

GPS monitoring of a steel box girder viaduct

Structural performance monitoring of bridges has increased as major infrastructure ages and is required to sustain loads that are significantly greater than those predicted during design. Structural stiffness and/or mass distribution can change over the lifespan of a bridge structure. Resulting changes in profile or resonant frequency provide key indicators of change, and may identify structural defects. Field tests using GPS for monitoring relatively small deformations were carried out on a steel box girder viaduct bridge in the UK. The configuration consisted of five GPS receivers located at key locations on the viaduct and two reference GPS receivers. GPS data was collected at either 10 Hz or 20 Hz and post-processed using proprietary software, along with appropriate filtering and spectral analysis. Three main frequencies were clearly detected by the GPS in the vertical component. A previously reported frequency of approximately 0.56 Hz was identified along with two other frequencies. The peak vertical deflections lie in the range of ± 50 mm, while lateral and longitudinal deflections of much smaller magnitude – in the order of a few mm – are also measured. The use of GPS leads to readily obtained and useful engineering data for continued monitoring of structures.     

某鱼脊连续梁桥行车安全性分析

采用数值风洞方法,对大治河桥上车辆的行车安全进行了分析,给出合理的安全行车风速。大治河桥总体布置采用预应力混凝土鱼脊连续梁桥,鱼脊的设置对桥面上车辆的行驶安全性产生了一定的影响。首先,采用通用计算流体动力学软件FLUENT分析了鱼脊对行驶车辆受力的影响;其次,以车辆不发生侧滑为指标,给出了大治河桥在不同桥面特征下的安全行车风速标准;最后,根据现行标准给出了大治河桥在安全行车方面的管养要求。     

裂隙网络模型在地下水数值模拟中的应用研究进展

地下水在裂隙介质中的渗流和运移过程与在多孔介质中的过程存在机理上的差别,这与裂隙系统的尺度效应和非均质性有关,这也给数值模拟带来困难。采用裂隙网络模型可以对发生在不同尺度上的渗流和运移过程进行模拟,从而有效地解决以上存在的问题。构建裂隙网络模型的方法主要有体视学方法和随机模拟方法。按照假设条件和概念框架的不同,裂隙网络模型主要可分为连续体模型、离散裂隙模型和混合模型,在应用过程中可根据研究区的实际情况选择合适的模型。本文在对已有成果进行综合论述的基础上,指出其中存在的不足和需要改进之处,从而为以后的进一步研究指明方向。     

基于Holt指数平滑模型的地下水水质预测

地下水水质预测是地下水污染防治研究工作的重要组成部分。本文介绍了Holt指数平滑模型的基本原理及平滑参数的确定方法,在此基础上,以阿拉善腰坝绿洲地下水水质预测为实例对地下水HCO3-、Cl-、SO42-和TDS进行了预测,并与灰色模型预测结果进行了对比。结果表明2006年HCO3-、Cl-、SO42-和TDS浓度值将分别达到198．260、77．290、114．850和508mg／L。应查清地下水各种污染源及各污染源对地下水水质的影响程度,以便采取有效措施,遏制地下水水质进-步恶化。Holt指数平滑模型统-考虑了所有已有时间序列资料对预测值的影响,提高了预测精唐．适用于已有较长时间序列资料前提下的预测。     

伞-弹动力学及运动学在末敏弹目标识别中的应用

对于带有降落伞的灵巧弹来说,末敏器的目标识别算法是影响攻击精度的关键因素。利用伞一弹系统稳定下降阶段的9自由度动力学模型,分析了阵风小扰动作用下子弹姿态的运动特性;然后在末敏器的目标识别算法中融入了子弹姿态角的运动规律,用以消除子弹晃动所造成的目标识别误差。空投试验表明：融合了子弹运动学的目标识别算法有效可靠,可以提高灵巧子弹的命中精度。