Analysis of an electricity-cooling cogeneration system for waste heat recovery of gaseous fuel engines

Waste heat recovery(WHR)is one of the most useful ways to improve the efficiency of internal combustion engines,and an electricity-cooling cogeneration system(ECCS)based on Rankin-absorption refrigeration combined cycle for the WHR of gaseous fuel engines is proposed in the paper.This system can avoid wasting the heat in condenser so that the efficiency of the whole WHR system improves,but the condensing temperature of Rankin cycle(RC)must increase in order to use absorption refrigeration system,which leads to the decrease of RC output power.Therefore,the relationship between the profit of absorption refrigeration system and the loss of RC in this combined system is the mainly studied content in the paper.Because the energy quality of cooling and electricity are different,cooling power in absorption refrigeration is converted to corresponding electrical power consumed by electric cooling system,which is defined as equivalent electrical power.With this method,the effects of some important operation parameters on the performance of the ECCS are researched,and the equivalent efficiency,exergy efficiency and primary energy rate are compared in the paper.     

An analytic study on the deflection of subway tunnel due to adjacent excavation of foundation pit

Predicting and estimating the response of subway tunnel to adjacent excavation of foundation pit is a research focus in the field of underground engineering. Based on the principle of two-stage method and incremental method, an analytic approach is suggested in this paper to solve this problem in an accurate and rapid way, and the upheavals of tunnel due to adjacent excavation are solved by analytic method. Besides, the presented method is used in the practical engineering case of Shenzhen Metro Line 11 and verified by numerical simulation and in situ measurement. Finally, a parametric analysis is performed to investigate the influence of different factors on tunnel’s deflection. Some useful conclusions have been drawn from the research as below: The deflection results of tunnel obtained from analytic method are nearly consistent with the results getting from numerical analysis and measured data, which verified the accuracy and rationality of presented method. The excavation size has a significant impact on both the displacement values and influenced range of tunnel. However, the relative distance only impacts the displacement values of tunnel, but not the influenced range of tunnel. It may provide certain reference to analyze the deflection of subway tunnel influenced by adjacent excavation.

     

闽江下游径流量和北港分流比变化及其对水龄的影响研究

利用闽江下游多年水文资料,分析了干流流量时空变化和北港分流比变化趋势,并借助EFDC模型研究水口水库下泄流量和北港分流比对闽江下游水体水龄的影响。分析表明:闽江干流径流量年际变化不均匀,北港分流比则经历了由小变大再变小的趋势。模拟的闽江水龄结果可知水龄与下泄流量成反比关系,北港分流比减小将增加北港水体交换时间,同时减少南港水体交换时间;水龄可以定量地描述污染物在北港河道的停留时间,为保障北港水源地水质安全,需要增大枯水期上游水口水库下泄流量和增大北港分流比。     

基于TEM图像的CNT溶液分散均匀性分形方法

针对传统评价方法的不足,提出了一种以分形理论为数学模型基础的碳纳米管长度分布及分布均匀性的定量评价方法.将碳纳米管溶液TEM图像进行处理,得到简化矩阵,以简化矩阵的第1个元素为原点,提取不同步长及该步长内所有元素的和,在双对数坐标中以拟合直线的斜率作为碳纳米管长度分布参数p1.以TEM图像的中心为圆心做圆,提取不同半径圆内的碳纳米管数量,在双对数坐标中以拟合直线斜率的倒数作为分散均匀性参数p2.将该方法应用于不同方法分散的碳纳米管分散均匀性的描述,结果验证了该方法能正确地评价碳纳米管的长度分布及其分布均匀性.     

元胞驻留视频群体状态预报方法

视频场景人群状态预报是防止公共场所安全事故的一种重要措施．为此提出了一种视频场景群体状态预报模型．该模型使用格内驻留元胞自动机(inner-grid parking cellular automata, IPCA)模型预报视频中群体状态．首先,通过光流法进行运动跟踪作为IPCA的输入特征对场景进行建模,并根据特征点的运动状态自适应地调整其在元胞格内的驻留时间以提高预报精度;其次,通过分析IPCA模型的预测结果判断群体微团间的相互作用得到视频帧的状态信息,从而达到对场景中人群状态进行预报的目的;最后,利用当前场景的状态信息对该场景的预报输出进行反馈校正,使模型能够及时地反映场景中群体状态的变化,该模型不依赖于具体的视频帧,以微团结构的碰撞作为异常检测依据．实验结果表明,与传统的检测方法相比,该预报模型能够提前预报视频场景中的异常状态,并具有较好的准确性．     

浅埋铁路隧道下穿高速公路施工方法比选

采用三维数值模拟方法,着重从开挖全过程结构体系转换和施工过程的空间效应的角度,分析比较了覆跨比小于1的浅埋铁路隧道下穿高速公路施工采用不同施工方法时的拱顶和地表沉降、衬砌变形和结构体系内力等关键参数的变化.计算结果表明,尽管双侧壁导坑法在开挖过程中断面较小,但由于分块多,前后掌子面滞后距离长,施工过程复杂,结构体系转换频繁,因而在地表沉降控制方面较中隔壁法并不具有明显的优势.而中隔壁法由于分块相对较少,各工序衔接紧密,拱顶沉降和地表沉降控制较好.其中CRD法由于采用了临时仰拱,对洞周收敛和中隔壁的变形较CD法具有更好的控制作用.基于施工全过程的不同开挖方法的三维数值分析比选研究对于选择恰当的施工方法并确保工程顺利实施具有重要意义.     

钢管混凝土柱与型钢梁装配式节点抗震试验

为了研究一种新型钢管混凝土柱与型钢梁装配式节点的抗震性能,对不同参数的节点进行低周往复循环加载试验.节点均经历弹性、塑性和极限破坏三个阶段,且为环板与钢梁翼缘的连接处破坏.对比分析表明：节点的轴压比越大,承载力越低;环板越宽,承载力越高;方形环板比圆形环板承载力更高;垫板对节点试件的承载力有提高作用.钢管混凝土柱与型钢梁装配式节点设计合理、传力明确、承载力高、构造简单、施工方便,是一种值得推广的组合装配式节点形式.     

Growth characteristics and kinetics of niobium carbide coating obtained on AISI 52100 by thermal-reactive diffusion technique

Niobium carbide coating was produced by thermal-reactive diffusion technique on AISI 52100 steel in salt bath at 1 123 K, 1 173 K, and 1 223 K for 1, 2, 4, and 6 hours. The salt consisted of borax, sodium fl uoride, boron carbide, and niobium pentoxide. The presence of NbC phase on the steel surface was confi rmed by X-ray diffraction analysis. Microscopic observation showed that niobium carbide coating formed on the substrate was smooth and compact. There was a distinct and fl at interface between the coating and substrate. The micro-hardness of niobium carbide coating was 2892±145HV. The thickness of coating ranged from 1.6 μm to 14μm. The forming kinetics of niobium carbide coating was revealed. Moreover, a contour diagram derived from experimental data was graphed for correct selection of process parameters. Some mathematical equations were built for predicting the coating thickness with predetermined processing temperature and time. The results showed that these mathematical equations are very practical as well as the kinetics equation.     

Synthesis of calcium silicate hydrate based on steel slag with various alkalinities

This study aimed to improve the hydraulic potential properties of the slag. Therefore, a method of dynamic hydrothermal synthesis was applied to synthesize calcium silicate hydrate. The phases and nanostructures were characterized by XRD, FTIR, TEM, and BET nitrogen adsorption. The infl uence of alkalinity of steel slag on its structures and properties was discussed. The experimental results show that, the main product is amorphous calcium silicate hydrate gel with fl occulent or fi brous pattern with a BET specifi c surface area up to 77 m2/g and pore volume of 0.34 mL/g. Compared with low alkalinity steel slag, calcium silicate hydrate synthesized from higher alkalinity steel slag is prone to transform to tobermorite structure.     

一种应用于噪声点分布密集环境下的噪声点识别算法

为了提高DBSCAN及其改进算法在噪声点分布密集环境下的噪声点识别率,通过结合PageRank算法思想及噪声数据分布密集的特点,构造簇间投票映射函数,提出了簇间投票噪声点识别算法-NoiseRank 。实验结果表明,在噪声点分布密集环境下,NoiseRank算法比DBSCAN算法具有更高的噪声点识别率。