Two-dimensional, steady-state temperature distributions in corners of arbitrary shape

A numerical method, which was originally developed to solve irrotational flow problems, is successfully applied to the steady-state thermal analysis of corners with arbitrary shapes. A unique feature of this method is the fact that the isotherm co-ordinates are found directly. The customary need for an extra computational procedure to establish isotherms when only the temperatures at discrete points in a solution domain are known is therefore eliminated. The method is used to illustrate temperature distributions in various corners. A computer program based on this method and written in BASIC is included.     

Two-dimensional steady-state temperature distributions and heat flows in square corners

The Schwartz-Christoffel transformation is applied to the case of symmetrical and asymmetrical square corners, with solid walls and isothermal surfaces. The steady-state patterns of temperature distribution and of heat flow lines are shown. The distribution of heat flow intensity along the inside surfaces is illustrated for a range of wall thickness ratios. The Finite Element Method is applied to obtain the components of the maximum intensity occurring at the point where the two inside surfaces meet, and the results are tabulated for a range of wall thickness ratios. The total rate of heat flow for various cases is compared with that obtained from an analytical expression derived by Carslaw and Jaeger. (Conduction of Heat in Solids, 2nd edn, p. 454). This is an approximate expression, asymptotically correct at points distant from the corner, but involving some error near to the corner. A simple graphical procedure is demonstrated, which now permits the total heat flow to be calculated at any distance from the inside corner. Additionally, a method is shown for finding the distance from the corner at which the analytical equation applies within a given error.     

Floc morphology and size distributions of cohesive sediment in steady-state flow

Fractal dimensions of particle populations of cohesive sediment were examined during deposition experiments in an annular flume at four conditions of steady-state flow (0.058, 0.123, 0.212 and 0.323Pa). Light microscopy and an image analysis system were used to determine area, longest axis and perimeter of suspended solids. Four fractal dimensions (D, D(1), D(2), D(k)) were calculated from the slopes of regression lines of the relevant variables on double log plots. The fractal dimension D, which relates the projected area (A) to the perimeter (P) of the particle (P proportional, variant A(D/2)), increased from 1.25+/-0.005 at a shear stress of 0.058Pa to a maximum of 1.36+/-0.003 at 0.121Pa then decreased to 1.34+/-0.001 at 0.323Pa. The change in D indicated that particle boundaries became more convoluted and the shape of larger particles was more irregular at higher levels of shear stress. At the highest shear stress, the observed decrease in D resulted from floc breakage due to increased particle collisions. The fractal dimension D(1), which relates the longest axis (l) to the perimeter of the particle (P proportional to l(D1)), increased from 1.00+/-0.006 at a shear stress of 0.058Pa to a maximum of 1.25+/-0.003 at 0.325Pa. The fractal dimension D(2), which relates the longest axis with the projected area of the particle (A proportional to l(D(2)), increased from 1.35+/-0.014 at a shear stress of 0.058Pa to a maximum of 1.81+/-0.005 at 0.323Pa. The observed increases in D(1) and D(2) indicate that particles became more elongated with increasing shear stress. Values of the fractal dimension D(k), resulting from the Korcak's empirical law for particle population, decreased from 3.68+/-0.002 at a shear stress of 0.058Pa to 1.33+/-0.001 at 0.323Pa and indicate that the particle size distribution changed from a population of similar sized particles at low shear to larger flocculated particles at higher levels of shear. The results show that small particle clusters (micro-flocs) are the formational units of larger flocs in the water column and the stability of larger flocs is a function of the shear stress at steady state.     

Validity of the two-node model for predicting steady-state skin temperature

The validity of the two-node model for predicting the skin temperature in the thermal steady state is studied by comparing the calculated and experimental results for various thermal conditions. For the experimental results of steady-state skin temperature, in addition to the authors’ original experimental data, literature data for mean skin temperature are collected, incorporating 56 conditions and 233 subjects in total. The results show that the two-node model (the 1986 edition) that is widely used for calculating SET* predicts effectively the steady-state skin temperature in the low-activity conditions. Additionally, the changes that were made to the two-node model by Gagge et al. and ASHRAE are summarized. It is shown theoretically and by experimental validations that, of these changes, the addition of the shivering model represents the most significant improvement in terms of predicting the skin temperature in the steady state.     

混凝土在1000℃以上高温作用下的变化

1引言进行灭火和火灾调查工作都应具有谨慎的态度和一定的技巧。即使经验丰富的消防队员和火灾调查人员,对在火灾现场遇到的许多现象也都难以解释。除了火灾原因各不相同之外,火灾现场的空气流通情况,可燃物的种类和数量以及建筑结构等因素都会使灭火和火灾调查工作变得更加复杂。混凝土是长期广泛使用的一种建筑材料。混凝土是将水泥(7%~14%,v/v)和水(15%~20%)搅拌成浆糊状,填充于骨料(砂子、碎石或卵石,66%~78%)的空隙之中而成的。水泥与水混合后,其中的硅酸钙、铝酸钙、铁酸钙等成分的硬化增强了混凝土的耐压强度和屈服强度,这也就是混凝…     

Effects of steady-state noise and temperature conditions on environmental perception and acceptability

The combined effects of noise and temperature on environmental perception and acceptability were studied on 18 lightly clothed subjects (0.6 clo), individually exposed for 2 h in a climatic chamber. Three homogeneous climatic conditions were chosen (air temperature at 18, 24 or 30 degrees C, air velocity =0.1 m/s). For each of them, three different noise levels were continuously maintained (35, 60, 75 dBA, recorded fan noise). The 18 subjects were divided into three groups and each group experienced only one single thermal condition, at each level of noise, during three different experimental sessions. Subjective answers about perception and comfort were obtained at t = 30 and 120 min. Main results indicate that acoustic perception decreases when thermal environment is far from thermoneutrality. Although the combined effects of noise and temperature did not influence the physiological data, our results show that whatever the ambient temperature, thermal unpleasantness is higher when noise level increases. Finally, equivalence between acoustic and thermal sensations is proposed for short-term exposure (1 degree C = 2.6 dBA) and for steady state (1 degrees C = 2.9 dBA). In conclusion, this study strongly suggests that interactions between environmental components do exist, right from perceptual level, and might explain some combined effects on cognitive performance.     

Estimation of complicated distributions using B-spline functions

The distributions of some of random variables are quite complicated and difficult to determine using ordinary statistical models. A method is presented in this paper which gives satisfactory estimation of the complicated distribution of a continuous random variable. There are two key steps in the method: one being that the probability density function (p.d.f.) of a random variable is approximated by a linear combination of B-splines and the other being that the best model is determined by entropy analysis. Extensive numerical experiments have made it clear that the proposed method is useful to determine the p.d.f. directly from a set of sample points without using any prior knowledge of the distribution form.     

Data-based mechanistic modelling of indoor temperature distributions based on energy input

Energy used for building heating, ventilating and air conditioning contributes to a great share in the total energy consumption worldwide. Better understanding and management of energy distribution in those processes is essential for the improvement of process quality and efficiency of energy use. This paper presents the data-based mechanistic modelling approach which has been developed to model the dynamic indoor temperature distribution in an imperfectly mixed ventilated airspace based on energy input to the system. The combination of classical heat balance differential equations and the data-based modelling techniques for continuous-time system has brought a robust dynamic model suitable for model-based controlling and yet providing a profound insight at the energy and temperature distributions in ventilated systems. The effect of changing heat input on the temperature distribution inside a ventilated structure was studied. Dynamic response of indoor temperature to varying energy input could be explained by a second order transfer function model with a high coefficient of determination (R² > 0.99), a low Young Identification Criterion (YIC < −2.3) and a low model standard error (SE < 0.028 °C). The physically meaningful model parameters as local heat load fraction γ and the coefficient of local temperature change h (°C J⁻¹) were revealed. This modelling approach is very useful for future design of model-based predictive controller for zonal control of indoor temperature by the direct adjustment of heat load into ventilated structures.     

神经网络BP算法在工程估价中的运用

先简要的介绍了神经网络和BP算法,提出了其优点和缺点,利用神经网络方法建立了数学模型,同时运用模拟软件对该数据进行分析,验证了该模型的可行性,得出神经网络在估价方面的应用存在很大的利用空间.     

浅谈无定向导线计算程序设计

根据红外线测距仪的普及以及全站仪的广泛使用,在导线测量取代传统的三角测量的同时,归纳出平面控制测量方法,并利用当今飞速发展的微型机用高级计算机语言开发了一个切实可行的测量计算应用程序,该程序短小,计算精度高,使用方便,在处理大量的测量数据时能节省大量的时间,同时亦能避免一些人为的计算错误,为测量电算化开拓了一条新的思路。     

预应力混凝土变截面连续刚构桥箱梁体积计算

南平西城大桥是大跨度预应力混凝土变截面连续刚构桥,其连续刚构采用挂篮悬臂浇现法施工,在各箱梁节段施工时需要求得待浇筑混凝土梁段的自重,首先必须得到待浇筑混凝土梁段的体积,即必须先求得各节段混凝土箱梁的体积,但根据设计资料并未提供这些数据,因此必须自己进行计算求解,在此我们采用MIDAS/Civil软件自带的截面特性值计算器进行计算出该截面的相关截面特征值(截面面积),再采用数值积分进行求解体积,对计算所得体积和施工结果皆表明本文的处理方法是正确的。     

Inference of discontinuity trace length distributions using statistical graphical models

The characterization of discontinuities within rock masses is often accomplished using stochastic discontinuity network models, in which the stochastic nature of the discontinuity network is represented by means of statistical distributions. We present a flexible methodology for maximum likelihood inference of the distribution of discontinuity trace lengths based on observations at rock outcrops. The inference problem is formulated using statistical graphical models and target distributions with several Gaussian mixture components. We use the Expectation–Maximization algorithm to exploit the relations of conditional independence between variables in the maximum likelihood estimation problem. Initial results using artificially generated discontinuity traces show that the method has good inference capabilities, and inferred trace length distributions closely reproduce those used for generation. In addition, the convergence of the algorithm is shown to be fast.     

篦冷机余风喷雾增湿降温系统使用

1 概述江苏巨龙水泥集团有限公司拥有一条原年设计能力100万t水泥干法生产线,经过多年的技术改造,目前,日产熟料已稳定在3500t,年产水泥130万t。由于产量增加,篦冷机余风量有所增加,余风温度较高(250～350℃),粉尘比电阻大,电除尘效率底,排放浓度超标。另外电收尘内分布板、阴极丝、阳极板等易在高温状态下产生侵蚀变形、磨损加剧。入内检查有明显的过高温痕迹,有的地方被熟料颗     

劲性钢筋轻骨料混凝土梁抗弯刚度计算

以实验为基础,通过理论分析,着重探讨了劲性钢筋轻骨料混凝土受弯构件(梁)在受力过程中内在变化规律以及影响刚度的诸因素,从而建立了刚度计算公式,为工程计算提供了依据。     

The computation of heat flows through multi-layer slabs

To model the transient thermal behaviour of buildings it is necessary to calculate time-dependent heat flows through multi-layer slabs representing walls, floors and roofs. A numerical method is presented which calculates these from a knowledge of past temperatures on each side of the slab at specified time intervals. Response factors are found using Laplace transforms. The number of response factors is minimized using previously calculated heat fluxes. An estimate of the error introduced by taking only a finite number of response factors is given and a correction term derived. The method is compared with the more standard z-transform method.     

混凝土柱吊装的一种验算方法

本文通过对实际工程中混凝土柱吊施工验算方法的分析,阐述了吊装验算三个主要内容的计算公式,并在实际工作中给予了验证。     

The computation and reporting of dissolved gas levels

Provisional standards are proposed for the computation and reporting of dissolved gas levels in freshwater and seawater. Total gas pressure should be reported in terms of excess pressure (ΔP). while component gases such as nitrogen, argon, oxygen and water vapor should be reported in terms of partial or excess pressure. Barometric pressure, dissolved oxygen, water temperature and salinity must also be reported.     

应用结构计算分析软件应注意的几个问题

从正确使用程序、分析判断计算结果、人工调整计算结果等方面,分析了进行结构计算和设计时应用结构计算分析软件应注意的问题。     

The impact of population on the reduction of steady-state disparities across Spanish regions

Despite the abundant literature on convergence across the Spanish regions, most of the empirical research has used cross-section regressions or panel data techniques with fixed effects, resulting in biased estimates. Furthermore, many of these studies have not explicitly accounted for the effect of population changes in the convergence process. This paper attempts to overcome these limitations by applying a dynamic panel data model using the generalized method of moments system estimates for the seventeen regions of Spain during the 1955–2008 period. The main conclusion that stems from our analysis is that the deep reduction in steady-state disparities across Spain’s regions can be largely attributed to the differences in their population growth rates, which were mainly due to migration flows. In contrast, investment in physical capital, although it promoted convergence, played a minor role, while technology was a strong factor for divergence.