Error evaluation of free-form surface based on distance function of measured point to surface

As free-form surface is widely used in engineering, it is urgently needed to develop advanced methodology of detecting and evaluating the profile error. To this end, the semantic of profile tolerance in ASME Y14.5.1M is reviewed and the mathematical definition of profile tolerance is discussed. Subsequently, a mathematical model for error evaluation is built. This mathematical model is augmented based on distance function by considering the second-order terms in the computation of the distance from point to surface. Then, a profile error evaluation algorithm, which combines Differential Evolution (DE) algorithm and Nelder–Mead (NM) algorithm, is developed to solve this model. The proposed model and optimization algorithm are validated with simulation results from a case study. Additionally, the model is superior to Least-squares (LS) model in simplicity, efficiency and robustness.     

Experimental studies on fragmentation of rock falls on impact with rock surfaces

Rock fall is a common natural hazard causing significant damage to infrastructure and loss of life. Rock fragmentation is frequently observed during rock fall events and several authors have raised issues related to the impact of fragments on the protection structure. However, this phenomenon is not accounted for when designing the protection barriers. The paper presents the results of 20 rockfall tests performed in a quarry in Italy to provide new insight into the fragmentation phenomenon, especially in the case of foliated materials. The results have shown that the impacting angle plays a key role in the fragmentation of foliated rocks whereas the effect of the impacting energy tends to be of second order. No threshold in impacting energy could be defined to explain what triggers the fragmentation. It has been noticed that the proportion of impacting energy dissipated during fragmentation is relatively constant and depends on the choice of the normal restitution coefficient.     

A study on sidewall displacement prediction and stability evaluations for large underground power station caverns

Based on an opening complex for a hydropower station in China, an equation considering four basic factors was fitted for prediction of displacement at the key point on the high sidewalls of the powerhouse, on the basis of a large number of numerical simulations. The basic factors include rock deformation modulus, overburden depth of caverns, height of the powerhouse and the lateral pressure coefficient of the initial stress. Quasi-three-dimensional stability analyses were carried out by using FLAC3D. With an equation, the elasto-plastic displacement and elastic displacement at a sidewall key point can be calculated quickly. The equation was applied to predict the displacements at key points on the sidewalls for caverns of nine projects. The computation results were compared with numerical modeling or back-analysis results. In addition, in order to consider the effects of cavern spacing, a new equation was proposed. Finally, three possible criteria for stability evaluation of the rock masses were considered. It is suggested that the rock stability is assessed by the ratio θ_c between the elasto-plastic displacement and the elastic displacement, which is commonly applicable. The stability of the surrounding rock for the above-mentioned nine underground projects was evaluated by the method. Long prestressed cables were considered to be needed to reinforce the sidewalls in order to ensure the stability of the caverns for some of the projects. For the actual design and construction of the five relevant projects, long prestressed cables were employed for reinforcement of high sidewalls. This showed that the evaluation criterion was valid.     

生物滞留池水文效应的模拟试验研究

为研究生物滞留池滞留雨水径流和缓解城市渍涝的能力,通过模拟试验监测了生物滞留单元的入流和出流过程,研究其对雨水径流总量的削减率、洪峰削减率和洪峰出现时间延迟等的水文效应。结果表明,生物滞留池对径流总量的削减率在12.83%～48.12%之间,对洪峰的削减率平均为70.85%,延迟洪峰出现时间约26.6min,对小流量的洪峰延迟时间最长(达31.7min)。     

Nitrates removal from polluted aquifers using (Sn or Cu)/Pd catalysts in a continuous reactor

The aim of this work is to study the catalytic removal of nitrates in natural water (not the water prepared in the laboratory by adding a nitrate salt to distilled water) from polluted aquifers, using a continuous stirred tank reactor. The catalysts studied are (Cu or Sn)/Pd supported on alumina. The activity and selectivity of these catalysts in different types of polluted waters are analyzed, optimizing the Pd–metal ratio and the reaction conditions. The deactivation of the catalysts, when using different types of water, is studied and discussed.     

Growth and characterization of silicon nitride films for optoelectronics applications

Silicon nitride (Si₃N₄) films have been deposited by thermal-CVD system and characterized by the ellipsometry, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive analysis of X-ray (EDAX). The present paper reports the effect of deposition temperature on the physical and optical properties of deposited Si₃N₄ films. The stress of the film has been observed to be tensile in nature and it is found to be decreased by increasing the deposition temperature through ellipsometric study. The increase in refractive index of the film has been observed with increasing deposition temperature. The Si–H, N–H and Si–N–Si stretching characteristic peaks of Si₃N₄ films have been observed with significant intensities by using FTIR spectroscopy. The peak positions of Si–N–Si stretching absorption band and the corresponding full width at half maxima (FWHM) have also been analyzed. The FWHM observed to be increasing on corresponding increase in the deposition temperature, which indicates the improvement in the deposited films quality. However, films deposited in the temperature range of 780–850 °C, have some amount of H contents. The total H concentration in the films decreases with corresponding increase in deposition temperature, which reveals that the densification of deposited films increases on increasing the deposition temperature. The SEM and EDAX have been used to carry the morphological and compositional analysis of the deposited films, respectively.     

水布垭水利枢纽工程泄洪消能防冲研究综述

水布垭水利枢纽坝址所在位置河谷狭窄,地形、地质条件复杂,泄洪落差与泄洪单宽流量均较大,河床基岩软弱,抗冲流速低,两岸又有巨大的滑坡体及右岸马崖高边坡,导流建筑物、泄水建筑物以及电站尾水出口的布置又相对比较集中,泄洪的安全问题属于水布垭水利枢纽的关键技术问题。为此,综合阐述了溢洪道结构布置和结构整体模型试验的研究成果以及防淘墙布置及其结构形式的研究成果,从而最终论证溢洪道及防淘墙结构布置形式在水布垭水利枢纽泄洪消能防冲系统中的可行性和合理性。     

Case-based reasoning in steel bridge engineering

The current inventory of the Ohio Department of Transportation (ODOT) contains about 12000 bridges. The great majority of the bridges rated by ODOT engineers are based on the working stress design (WSD) method. The new Federal Highway Administration guidelines require that all bridge ratings be done using the load factor design (LFD) method. Consequently, thousands of bridges have to be re-rated according to the LFD code. The WSD-based data files for existing bridges do not contain the detailed information about steel sections and cross frames needed for the LFD-based rating. In this research a case-based reasoning (CBR) system has been developed to assist the bridge engineer in converting the WSD-based ratings for existing bridges to new LFD-based ratings. A domain model has been created to represent the ODOT standard design cases of bridges.     

一种研究电压稳定的有载调压变压器模型

提出了用有载调压变压器模型分析电压稳定问题的方法。该法在建立模型后用它推导负荷动态特性并得出系统的电压稳定判据,即以主特征根的右特征向量中最大元素对应的节点为系统最薄弱点。最后通过一4机算例验证了所建模型及其稳定判据的正确性。     

大型水电项目业主人力资源需求预测研究

大型水电项目投入大、工期长、涉及参建的人员多,准确合理地预测项目业主的人力资源需求十分重要。本文通过定量和定性的分析,构建了大型水电项目人力资源需求预测模型,为项目业主人力资源需求预测提供了一种思路和方法。