Flexural retrofit of a bridge subjected to overweight trucks using CFRP laminates

The reinforced concrete spans of a bridge subjected to extreme vehicular loads are investigated and retrofitted with carbon fiber reinforced polymer (CFRP) laminates. A finite element model of the bridge superstructure was created to determine the forces resulting from extreme loads. A moment–curvature analysis was subsequently carried out to investigate the flexural characteristics of the reinforced concrete sections prior to and after strengthening with CFRP laminates. The analytical modeling concluded that significant strength can be gained at the ultimate limit state, while relatively small increase in strength is observed at service load levels. The increase in flexural resistance at ultimate does provide an adequate margin of safety against further overloading. The analytical investigation and the retrofitting work are presented herein.     

Effects of post-synthesis treatments on the pore structure and stability of MCM-41 mesoporous silica

The effects of post-synthesis treatments on the structure and the stability of MCM-41 mesoporous material were investigated. It was found that, by adding ammonium salts and adjusting pH during the post-synthesis to alkalescently synthesized MCM-41, the regularity of the pore was improved dramatically and the stability of the mesostructure was retained; conversely, they were diminished by adding sodium salts. The results were studied by analyzing the samples using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Differential Thermal Analysis–Thermal Gravimetry (DTA–TG). The change of the electrostatic surrounding and the formation of hydrogen bonds caused by different ions were confirmed to be the main factors.     

On the behaviour of hygroscopic wheels: Part I – channel modelling

In this paper a detailed mathematical formulation is developed for the numerical modelling of the behaviour of a channel of a hygroscopic compact matrix. A comparison between the detailed version and a simplified one is performed considering a two-dimensional airflow between desiccant parallel plates. The distinct heat and mass transfer phenomena are strongly coupled, and some properties of the airflow and of the desiccant medium exhibit important changes during the sorption processes. Both physical models take into account the gas side and solid side resistances to heat and mass transfer. The wall domain is treated similarly in both models, by taking into account the simultaneous heat and mass transfer together with the water adsorption/desorption process. Two phases co-exist in equilibrium inside the desiccant porous medium, the equilibrium being characterized by sorption isotherms without hysteresis. The detailed model is based on the solution of the differential equations for the conservation of mass, energy and momentum, assuming that no momentum transport exists in the porous wall domain. In the simplified model, the airflow is treated as a bulk flow, the interaction with the wall being evaluated by using appropriated convective coefficients.Both models are compared in the simulation of a parallel plate channel during an adsorption process. The results show a good agreement for channel lengths greater than 0.1 m. In part II of the paper, the simplified model is adapted to the simulation of the three-dimensional problem in the channel of a hygroscopic rotor, and it is used to perform parametric studies.     

新型废水厌氧处理工艺——内循环厌氧反应器

介绍内循环(IC)厌氧反应器的发展、基本结构、运行机理。分析该反应器的工艺过程,指出该工艺具有处理效率高、抗冲击能力强等优点。针对IC反应器存在的缺陷,人们对该反应器进行技术改进:通过提高它的内循环的气量进行处理低浓度有机废水;增加外循环装置缩短IC反应器的启动周期。     

Evaluation of landscape and instream modeling to predict watershed nutrient yields

The project goal was to loosely couple the SWAT model and the QUAL2E model and compare their combined ability to predict total phosphorus (TP) and NO₃-N plus NO₂-N yields to the ability of the SWAT model with its completely coupled water quality components to predict TP and NO₃-N plus NO₂-N yields from War Eagle Creek watershed in Northwest Arkansas. Model predictions were compared using a statistical approach to identify significant differences between the two modeling methods. Results from two variations of the Pearson product-moment correlation (p < 0.05) indicated that correlation coefficients and regression slopes for the two data sets were not significantly different. This implies that neither modeling method was significantly better in predicting monthly TP and NO₃-N plus NO₂-N yields from the watershed. Additionally, no significant differences were present between predicted outputs of the SWAT model with instream components active compared with when instream components were inactive, indicating a need for further testing and refinement of the SWAT algorithms simulating instream processes. We can further infer that the instream processes available in SWAT may not be enhancing its predictive abilities as far as simulating instream components.     

Performance parameters of an ejector-absorption heat transformer

Ejector-absorption heat transformers (EAHTs) are attractive for increasing a solar-pond's temperature and for recovering low-level waste-heat. Thermodynamic analysis of the performance of an EAHT is complicated due to the associated complex differential equations and simulation programs. This paper proposes the use of artificial neural-networks (ANNs) as a new approach to determine the performance parameters, as functions of only the working temperatures of the EAHT, which is used to increase the solar pond's temperature under various working conditions. Thus, this study is helpful in predicting the performance of an EAHT where the temperatures are known. Scaled conjugate gradient (SCG) and Levenberg–Marquardt (LM) learning algorithms and a logistic sigmoid transfer-function were used in the network. The best approach was investigated for performance parameters with developed software using various algorithms. The best statistical coefficients of multiple determinations (R²-values) equal 0.99995, 0.99997 and 0.99995 for the coefficient of performance (COP), exergetic coefficient of performance (ECOP) and circulation ratio (F), respectively obtained by the LM algorithm with seven neurons. In the comparison of performances, results obtained via analytic equations and by means of the ANN, the COP, ECOP and F for all working situations differ by less than 1.05%, 0.7% and 3.07%, respectively. These accuracies are acceptable in the design of the EAHT. The ANN approach greatly reduces the time required by design engineers to find the optimum solution. Apart from reducing the time required, it is possible to find solutions that make solar-energy applications more viable and thus more attractive to potential users. Also, this approach has the advantages of high computational speed, low cost for feasibility, rapid turn-around, which is especially important during iterative design phases, and ease of design by operators with little technical experience.     

Estimating standard errors of accuracy assessment statistics under cluster sampling

Cluster sampling is a viable sampling design for collecting reference data for the purpose of conducting an accuracy assessment of land-cover classifications obtained from remotely sensed data. The formulas for estimating various accuracy parameters such as the overall proportion of pixels correctly classified, the kappa coefficient of agreement, and user's and producer's accuracy are the same under cluster sampling and simple random sampling, but the formulas for estimating standard errors differ between the two designs. If standard error formulas appropriate for cluster sampling are not employed in an accuracy assessment based on this design, the reported variability of map accuracy statistics is likely to be grossly misleading. The proper standard error formulas for common map accuracy statistics are derived for one-stage cluster sampling. The validity of these standard error formulas is verified by a small simulation study, and the standard errors computed according to the usual simple random sampling formulas are shown to underestimate the true cluster sampling standard errors by 20–70% if the intracluster correlation is moderate.     

Effect of heavy fuel oil/natural gas co-combustion on pollutant generation in retrofitted power plant

The purpose of this paper is to examine effect of co-combustion of heavy fuel oil and natural gas on the pollutant formation: CO₂, SO₂, SO₃, NO_X and soot. The analysis was carried out by means of numerical simulation on the case of retrofitted steam generator furnace of Thermal Power Plant Sisak (Croatia). Comprehensive mathematical model of the furnace with detailed 3D mesh was set up to include all relevant aerodynamic and thermo-chemical processes in the furnace. Dedicated model for SO₃ formation was developed earlier and used in this work. By increasing the natural gas contribution in overall fuel fired in the furnace, emissions of CO₂, SO₂, soot, NO_X and SO₃ decreased. Heat transferred to the furnace walls and temperature field in the furnace were also examined in order to establish regions of safe and efficient boiler operation for different operational regimes.     

海表面盐度卫星微波遥感研究进展

海表面盐度SSS(Sea Surface Salinity)是研究大洋环流和海洋对全球气候影响的重要参量、是决定海水基本性质的重要因素之一。卫星微波遥感可以满足盐度研究过程中大范围、连续观测的需要,国际上统一的认识是选择频率为1.413 GHz的L波段作为盐度遥感的首选波段。目前,国外发展的海面盐度微波遥感反演算法主要有两种:基于海表发射率估算海表盐度的算法和基于贝叶斯定理提出的反演算法。影响盐度反演精度的因素主要有太空辐射、电离层法拉第旋转、大气、海面粗糙度等。其中,海面粗糙度对盐度反演影响很大,海面粗糙度处理模型可以分为3大类:理论算法(间接发射率模型、直接发射率模型)、经验算法、半经验半理论算法(Hollinger 半经验模型、WISE半经验模型、Gabarró模型)。SMOS卫星和Aquarius/SAC\|D卫星的成功发射,将海表面盐度遥感的反演精度控制在0.2 psu以内,通过改进反演算法,有望得到更高的反演精度。