简易分析用的一种最小可分辨温差模型

通过最小可分辨温差(MRT)描述热成象装置的性能,MRT就是与空间频率相关的热分辨率。已成为热成象装置设计者研制了几种MRT模型。用这些模型求MRT需要知道一般使用者尚不知道的热成象装置的若干参数。本文介绍一种MRT模型,只要知道其典型的表列数据(空间分辨率、温度分辨率及视场)即可用它求得MRT。通过三种已知系统计算的MRT与测量值的比较,来检验这个模型。

变频空调负荷建模研究

变频空调的应用越来越广泛,其在电力负荷中所占比重越来越高。建立准确的变频空调负荷模型对于提高电力系统仿真的准确度具有重要意义。本文在详细分析变频空调运行原理和各组成元件特性的基础上,提出了变频空调的功率-温差模型,分别建立了变频空调的静特性模型和动特性负荷模型。通过实验室实测变频空调的运行特性,将变频空调负荷模型的响应与实测曲线进行了对比。结果表明,本文所提出的变频空调静特性和动特性模型能够准确地描述变频空调的负荷特性,具有较高的准确度。

层板推力室发汗冷却壁温特性的初步研究

对液体火箭发动机发汗冷却层板推力室的壁温特性进行了初步研究,通过建立一维固液耦合温差模型,利用有限体积法,计算得到沿推力室径向层板固体和冷却剂的温度分布,并对影响壁温特性的各种因素进行了计算分析,包括冷却剂流量、层板导热系数和冷却通道尺寸等.结果表明:冷却剂流量是控制层板结构温度的重要参数;层板应该采用一种导热系数适中的材料,过大或过小导热系数的材料都不利于推力室的整体性能;较大的冷却通道宽高比有利于层板向冷却剂导热;冷却通道内的换热效率与冷却剂流量和层板导热系数有关.

极端天气下计及气温影响的架空线路荷载风险建模方法

基于结构可靠性原理和线路设计基本理论,根据线路荷载一强度的随机特性与干涉理论,建立考虑气温影响的架空线路荷载风险分析模型,提出将极端天气下温差变化对线路的影响折算为等值荷载的方法,采用最小二乘法进行温差折算荷载建模。以一条实际运行的架空输电线路为例验证线路失效概率模型的有效性,研究结果表明,在分析极端天气下线路可靠性指标时计及气温变化的影响不可忽视。

Error Analysis of Adsorption Isotherm Models for Acid Dyes onto Bamboo Derived Activated Carbon

High surface area activated carbons were produced by thermal activation of waste bamboo scaffolding with phosphoric acid.Single component equilibrium dye adsorption was conducted on the carbons produced and compared with a commercially available carbon.Two acid dyes with different molecular sizes,namely Acid Yellow 117(AY117) and Acid Blue 25(AB25),were used to evaluate the adsorption capacity of the produced carbons.It was found that the dye with smaller molecular size,AB 25,was readily adsorbed onto the produced carbon,nearly three times higher than a commercially available carbon,while the larger size dye,AY117,showed little adsorption.The experimental data were analyzed using isotherm equations including Langmuir,Freundlich,Tempkin,Toth,Redlich-Peterson and Sips equations.The equilibrium data were then analyzed using five different non-linear error analysis methods.

Locating method of fire source for spontaneous combustion of sulfide ores

in order to achieve a more efficient way to accurately detect the position of the fire source of spontaneous combustion underground mine, a simple fire source locating method, based on infrared scanning system which can determine the point where the highest temperature on the surface of igniting ores occurs, was proposed. First, the differential equations that describe heat flow in ore body were presented and the relationship between the surface temperature distribution and the depth and intensity of inner fire source was established with a relatively simple heat transfer model. With the solution of equation, the expression of the relationship between the surface temperature distribution and the inner fire source was deduced and the mathematical-physical model of heat transfer process was set up. Then, with the model, visualization of fire source on the basis of MATLAB simulation platform was realized. The results show that： 1） within 10 m, when the detecting depth is less than 2 m, the temperature perturbation on ores surface can change rapidly, and then slowly; after 4 m, in contrast, it changes very little, and is even close to zero at 10 m; 2） When it is close to self-ignition duration and the detective depths are 2, 5 and 10 m, respectively, the maximum temperature differences are correspondingly 0.5, 0.04 and 0.005 ℃ in the scope of 1 m×1 m; under the same condition, the maximum temperature differences are 1.391, 0.136 and 0.018 ℃, respectively, in the scope of 2 m×2 m. Therefore, this system can be used to measure the temperature differences on the surface of ore body and determine the highest temperature point directly. Also, it is possible to determine the depth of fire source and its intensity by locating method of fire source indirectly.

Estimating extreme temperature differences in steel box girder using long-term measurement data

The extreme temperature differences in fiat steel box girder of a cable-stayed bridge were studied.Firstly,by using the long-term measurement data collected by the structural health monitoring system installed on the Runyang Cable-stayed Bridge,the daily variations as well as seasonal ones of measured temperature differences in the box girder cross-section area were summarized.The probability distribution models of temperature differences were further established and the extreme temperature differences were estimated with a return period of 100 years.Finally,the temperature difference models in cross-section area were proposed for bridge thermal design.The results show that horizontal temperature differences in top plate and vertical temperature differences between top plate and bottom plate are considerable.All the positive and negative temperature differences can be described by the weighted sum of two Weibull distributions.The maximum positive and negative horizontal temperature differences in top plate are 10.30 ℃ and -13.80 ℃,respectively.And the maximum positive and negative vertical temperature differences between top plate and bottom plate are 17.30 ℃ and-3.70 ℃,respectively.For bridge thermal design,there are two vertical temperature difference models between top plate and bottom plate,and six horizontal temperature difference models in top plate.

A neural network method for estimating weighted mean temperature over China and adjacent areas

To improve the applicability of the global pressure and temperature 2 wet(GPT2w)model in estimating the weighted mean temperature in China and adjacent areas,the error compensation technology based on the neural network was proposed,and a total of 374800 meteorological profiles measured from 2006 to 2015 of 100 radiosonde stations distributed in China and adjacent areas were used to establish an enhanced empirical model for estimating the weighted mean temperature in this region.The data from 2016 to 2018 of the remaining 92 stations in this region was used to test the performance of the proposed model.Results show that the proposed model is about 14.9%better than the GPT2w model and about 7.6%better than the Bevis model with measured surface temperature in accuracy.The performance of the proposed model is significantly improved compared with the GPT2w model not only at different height ranges,but also in different months throughout the year.Moreover,the accuracy of the weighted mean temperature estimation is greatly improved in the northwestern region of China where the radiosonde stations are very rarely distributed.The proposed model shows a great application potential in the nationwide real-time ground-based global navigation satellite system(GNSS)water vapor remote sensing.

A new group contribution-based method for estimation of flash point temperature of alkanes

Flash point is a primary property used to determine the fire and explosion hazards of a liquid. New group contribution-based models were presented for estimation of the flash point of alkanes by the use of multiple linear regression(MLR)and artificial neural network(ANN). This simple linear model shows a low average relative deviation(AARD) of 2.8% for a data set including 50(40 for training set and 10 for validation set) flash points. Furthermore, the predictive ability of the model was evaluated using LOO cross validation. The results demonstrate ANN model is clearly superior both in fitness and in prediction performance.ANN model has only the average absolute deviation of 2.9 K and the average relative deviation of 0.72%.

混凝土单箱多室箱梁温度梯度地域差异性

为确定不同地区混凝土单箱多室箱梁日照温差代表值,在西藏山南、陕西铜川与广西来宾分别建立了室外日照温度场试验模型,同时安装了大量温度传感器与气象采集器,通过现场实测数据总结了山南、铜川和来宾气象差异性;通过长期箱梁测试温度与逐时气象数据的逐步回归,提出了山南、铜川和来宾箱梁温差计算公式;调研了西藏6个地级市、陕西10个地级市和广西14个地级市1955—2016年的气象数据,并将气象日值数据分解为逐时气象数据用于温差计算,基于超阈值分布模型得到了3个地区重现期为50年的温度作用代表值,并绘制了温度作用分布地图。研究结果表明:箱梁模型实测的向阳侧边腹板竖向温差、中腹板竖向温差、顶板横向温差与底板横向温差从高到低依次为山南、铜川和来宾,说明受地理位置影响,中国不同地区的箱梁竖向温差和横向温差具有差异性;混凝土箱梁顶板向阳侧横向温差均高于底板,山南、铜川和来宾箱梁顶板向阳侧横向温差比底板分别高30.7%、23.2%和11.1%;西藏、陕西和广西的中腹板竖向温差地域差异性最大可达10.5℃,顶板横向温差地域差异性最大可达20.3℃,说明混凝土桥梁的日照作用具有明显的地域差异性。

基于实测数据的悬索桥钢箱梁温度场特性研究

为明确大跨度悬索桥扁平钢箱梁温度和温度梯度特征,以南溪长江大桥正交异性钢箱梁为研究对象,基于健康监测系统中温度传感器的长期实测数据,采用分段函数描述环境温度和日照辐射共同作用下钢箱梁日温度变化曲线。在此基础上,采用高斯混合模型描述钢箱梁年温度多峰概率分布,并引入赤池信息判别准则(AIC)和贝叶斯信息判别准则(BIC)确定最优高斯分量数。统计钢箱梁一年日温差极值并进行参数评估,得到钢箱梁年温差极值分布模型。对年温差极值分布函数进行外推,得到设计基准期温差的极值分布函数并计算温差标准值。引入相关系数分析法对各温差组进行相关性分析,剔除实际不存在的温差模型。研究结果表明:相比正弦函数,分段函数能更准确地描述太阳辐射作用下箱梁截面日温度变化特征;当高斯分量数为3时,混合高斯模型拟合钢箱梁年温度概率分布最优;外推设计基准期模型能够较好地计算设计基准期温差标准值;通过相关性分析剔除了4组不存在的温差模式;得到顶板和腹板各8组温差模式;最后与《公路桥涵设计通用规范》(JTG D60—2015)中钢混结构竖向正温差设计值进行对比,一、二级温度梯度与设计规范分别相差4.2℃和2.3℃。