连续速度场解析圆管辊拔减径

此文利用连续速度场解析了圆管辊拔减径问题的拔制力,并获得上界解析解.该解与圆管辊拔实验结果比较表明,两者吻合较好.因而,该解析解可在工程上计算圆管辊拔拔制力时推广应用.     

近断层强震速度脉冲效应及连续梁桥减隔震特性分析

应用非线性时程分析的方法 ,对于减、隔震连续桥梁在近场地震作用下的有效性和响应特性 ,作了深入的研究。通过有代表性的脉冲型近场强震记录时程分析 ,提出了用速度脉冲峰值及其周期之积来表示速度脉冲能量的方法 ,计算表明近场地震速度脉冲波能近似表征地震动破坏能力的大小 ,它和桥梁结构承受的地震响应大体成正比例关系。铅芯橡胶隔震支座在近场地震作用下仍然适用 ,但对于个别脉冲型强震记录效果不够明显 ,支座参数有必要进行优化。     

Prediction of near-field shear dispersion in an emergent canopy with heterogeneous morphology

The evaluation of longitudinal dispersion in aquatic canopies is necessary to predict the behavior of dissolved species and suspended particles in marsh and wetland systems. Here we consider the influence of canopy morphology on longitudinal dispersion, focusing on transport before constituents have mixed over depth. Velocity and longitudinal dispersion were measured in a model canopy with vertically varying canopy density. The vertical variation in canopy morphology generates vertical variation in the mean velocity profile, which in turn creates mean-shear dispersion. We develop and verify a model that predicts the mean-shear dispersion in the near field from morphological characteristics of the canopy, such as stem diameter and frontal area. Close to the source, longitudinal dispersion is dominated by velocity heterogeneity at the scale of individual stems. However, within a distance of approximately 1 m, the shear dispersion associated with velocity heterogeneity over depth increases and eclipses this smaller-scale process.     

改性天然植物胶对Cu~(2+)的吸附性能研究

以自制的重金属捕集剂MPC对Cu2+离子进行吸附实验,取得了良好的效果,并对吸附过程的动力学和热力学进行初步探讨。实验还表明,MPC可以实现洗脱再生和重复利用。MPC是由废弃植物渣皮中提取天然植物胶通过系列化学反应改性而成,实现了资源的综合利用,具有经济和环境的双重效益。     

Experimental study of recirculating flows generated by lateral shock waves in very large channels

Due to the lack of data on hydraulic-jump dynamics in very large channels, the present paper describes the main characteristics of the velocity field and turbulence in a large rectangular channel with a width of 4 m. Although a hydraulic jump is always treated as a wave that is transversal to the channel wall, in the case of this study it has a trapezoidal front shape, first starting from a point at the sidewalls and then developing downstream in an oblique manner, finally giving rise to a trapezoidal shape. The oblique wave front may be regarded as a lateral shockwave that arises from a perturbation at a certain point of the lateral wall and travels obliquely toward the centreline of the channel. The experimental work was carried out at the Coastal Engineering Laboratory of the Water Engineering and Chemistry Department of the Technical University of Bari (Italy). In addition to the hydraulic jump formation, a large recirculating flow zone starts to develop from the separating point of the lateral shock wave and a separate boundary layer occurs. Intensive measurements of the streamwise and spanwise flow velocity components along one-half width of the channel were taken using a bidimensional Acoustic Doppler Velocimeter (ADV). The water surface elevation was obtained by means of an ultrasonic profiler. Velocity vectors, transversal velocity profiles, turbulence intensities and Reynolds shear stresses were all investigated. The experimental results of the separated boundary layer were compared with numerical predictions and related work presented in literature and showed good agreement. The transversal velocity profiles indicated the presence of adverse pressure gradient zones and the law of the wall appears to govern the region around the separated boundary layer.     

Air ventilation impacts of the “wall effect” resulting from the alignment of high-rise buildings

The objective of this study is to investigate the air ventilation impacts of the so called “wall effect” caused by the alignment of high-rise buildings in complex building clusters. The research method employs the numerical algorithm of computational fluid dynamics (CFD – FLUENT) to simulate the steady-state wind field in a typical Hong Kong urban setting and investigate pollutant dispersion inside the street canyon utilizing a pollutant transport model. The model settings of validation study were accomplished by comparing the simulation wind field around a single building block to wind tunnel data. The results revealed that our model simulation is fairly close to the wind tunnel measurements. In this paper, a typical dense building distribution in Hong Kong with 2 incident wind directions (0° and 22.5°) is studied. Two performance indicators are used to quantify the air ventilation impacts, namely the velocity ratio (VR) and the retention time (T_r) of pollutants at the street level. The results indicated that the velocity ratio at 2 m above ground was reduced 40% and retention time of pollutants increased 80% inside the street canyon when high-rise buildings with 4 times height of the street canyon were aligned as a “wall” upstream. While this reduction of air ventilation was anticipated, the magnitude is significant and this result clearly has important implications for building and urban planning.     

近场地震速度脉冲效应及模拟模型的研究

从近场地震速度脉冲的形成机理分析入手 ,对近场地震动的时程曲线和反应谱进行探讨 ,说明了具有前方向性速度脉冲效应的幅值要大的多 ,对反应谱的长周期段影响显著 ,使反应谱变胖 ,引起谱峰值向长周期处漂移 ,蕴含了巨大的地震能量 ,因此 ,对结构抗震提出了更高的要求。在以上研究的基础上 ,对典型的简化脉冲模拟模型参数进行讨论 ,提出了更为合理的参数取值 ,最后 ,从时程曲线、反应谱和结构地震反应 3个方面 ,对模拟脉冲和实际记录的差异进行对比 ,验证了推荐参数的合理性。     

Predicting the ejection velocities of fragments from explosions cylindrical pressure vessels: Uncertainty and sensitivity analysis

The purpose of this study was a refinement of knowledge on predicting the ejection velocities of fragments generated by explosions of cylindrical horizontal pressure vessels. A procedure is proposed for assessing these velocities by means of the stochastic simulation. The procedure is used to quantify uncertainties related to the ejection velocities and to carry out a simulation-based sensitivity analysis. The main finding is that the currently available information on phenomena related to the vessel fragmentation is sparse and, therefore, predicting ejection velocities will require a substantial amount of subjective judgement. It was found that ejection velocities are functions of a relatively large number of random input variables, many of which must be modelled subjectively. The study revealed also the need to choose subjectively between several alternative mathematical models used to specify input variables that influence the ejection velocities. The most critical choice must be made between several models used for an assessment of the energy liberated during vessel explosions. Results of the sensitivity analysis indicate that the ejection velocities are influenced mainly by input variables used to express energies involved in the prediction problem. Increased sensitivity to filling ratio of a two-phase pressure vessel was also detected. Results of the study can be used for an improvement of estimation of fragment impact probabilities and design of protective barriers that are built close to the pressure vessels posing explosion hazard.     

Comments on “turbulent velocity profile in fully-developed open channel flows”

In a recent paper published in this journal, Bonakdari et al. (Environ Fluid Mech 8:1–17, 2008) presented a new formulation of the vertical velocity profile in the central portion of steady fully developed turbulent open-channel flows which is based on an analysis of the Navier–Stokes equations. The predicted mean streamwise velocity profiles presented by the authors represent dip phenomenon (maximum velocity below the free surface). The discusser would like to point out some contradictions and an error in the main demonstration. This error appears in the right-hand side term of the main Eq. 22 (Environ Fluid Mech 8:1–17, 2008) in the parameter α. Our corrected demonstration shows that α is equal to and not to as obtained by the authors (Environ Fluid Mech 8:1–17, 2008). The values of α used by the authors are under-estimated by 1, this difference has a significant effect on velocities and therefore will involve a difference between measured and predicted velocity profiles. Finally, the assumption of at the free surface is in contradiction with predicted velocity profiles.