强震区碾压混凝土重力坝非线性地震响应分析

针对传统的线弹性模型不能准确模拟强震区碾压混凝土重力坝的地震响应问题,介绍了考虑坝体材料非线性的损伤模型和考虑接触非线性的缝接触模型,并将这两种模型应用于鲁地拉重力坝非线性地震响应分析中,以坝头部的裂缝贯穿为"破坏"准则,计算裂缝贯穿前坝体所能承受的最大地震作用。结果表明,在该准则下,材料非线性模型和接触非线性模型分别算出最大荷载作用为1.6倍设计地震和1.5倍设计地震,计算结果十分接近,均可用来评价碾压混凝土重力坝的极限抗震能力。     

渠道混凝土防渗体下土体特性变化试验研究

渠道衬砌结构的冻胀破坏在寒冷地区普遍存在,对其使用效果和寿命造成了很大影响,为了解季节性冻土区渠道防渗体冻胀发生的原因,以梯形渠道弧形混凝土防渗体为例,从渠道衬砌结构的防渗体下土体温度变化及防渗体冻胀位移量变化特点入手,通过在灌区选取典型渠道进行原型原位观测试验,监测不同时间点不同影响因素下渠道不同位置土壤深度处地温及冻胀位移量变化,分析土体各特性的变化机理。结果表明,不同土层深度处土壤含水率的大小为未冻层>临界层>冻土层;不同土壤深度处的温度变化基本相同;10cm厚的保温板的保温效果优于20cm厚保温板的保温效果。研究成果为解决灌区渠道衬砌的冻害及渗漏问题以及未来大中型灌区渠道施工过程中采取有效的防冻胀措施提供了参考依据。     

某大型泵站空箱隔墩不均匀沉降敏感度分析

鉴于泵站复杂的进出水流道及泵房结构受力特殊,裂缝普遍存在,直接影响建筑物安全有效服役。以某大型贯流泵站高程9.7m变频器层空箱处混凝土隔墩裂缝工程为例,采用回弹值测法、碳化深度检测、钢筋保护层厚度测定及混凝土钻芯取样测试裂缝区域混凝土病害程度,并采用计算机仿真分析,基于有限单元法,依托泵站运行期垂直位移观测数据,考虑温度变化分析了基础不均匀沉降引发裂缝敏感度。结果表明,在泵站空箱隔墩实际裂缝区域出现应力集中,其结果与实际混凝土开裂区域吻合,说明基础不均匀沉降影响了泵站裂缝发展。因此,泵站设计过程中应考虑基础不均匀沉降问题。     

混凝土热学特性对泄洪洞衬砌温度和温度应力影响研究

以溪洛渡水电站泄洪洞为例,采用大型通用有限元软件Ansys建模计算,模拟了衬砌混凝土的浇筑过程和温控措施,计算分析了混凝土最终绝热温升值和绝热温升速率对衬砌混凝土温度和温度应力场的影响,提出了在溪洛渡水电站泄洪洞衬砌混凝土的配合比设计中应尽量提高粉煤灰的掺量和采用低热水泥,以降低最终绝热温升值和早期绝热温升速率,从而防止与减少裂缝,可为溪洛渡水电站泄洪洞及类似工程衬砌混凝土设计和施工提供有价值的参考.     

烟气脱硫吸收塔反应过程的数值模拟及试验研究

以鼓泡式脱硫塔为例,采用双膜模型对烟气脱硫过程进行了数值模拟,并与试验结果进行了比较。结果表明:影响鼓泡式脱硫反应过程的主要因素有烟气中SO2含量、吸收液浓度、气体温度、pH值及喷管浸入深度等;在运行中应保持pH值>8和浸管深度>200mm,且吸收液浓度4.5%左右较为合适.同时,脱硫效率对入口烟气温度变化敏感,入口烟气温度越低,脱硫效率越高.通过对这些因素的分析,有助于脱硫装置的运行优化.     

混凝土导热系数与其饱和度及温度的关系

在已有混凝土导热系数影响因素研究成果的基础上,以普通混凝土、泡沫混凝土、植物纤维陶粒混凝土、棉花秸秆石膏混凝土四种不同混凝土为研究对象,采用QTM-500导热测试仪分别对四种混凝土不同饱和度时不同温度下(-30~20℃)的导热系数进行试验,并分析不同饱和度下各混凝土导热系数随温度(-30~20℃)的变化规律,最后采用压汞仪对四种混凝土的孔隙率、孔径分布等参数进行测试,从微观孔隙角度深入分析各混凝土导热系数随温度的变化规律。结果表明,各混凝土的导热系数与其饱和度呈显著的正相关性,干燥状态下,四种混凝土的导热系数随温度变化不显著;饱和状态下,各混凝土导热系数在一定温度范围内会发生突变,当超出温度敏感区域后,各混凝土的导热系数基本趋于稳定值;在试验温度范围内,混凝土导热系数变化规律与其孔隙参数有关。该研究结果可为寒冷地区大体积混凝土结构、建筑节能混凝土的导热系数试验及分析提供参考。     

开式循环吸收式热泵吸收器和再生器实验研究

针对基本配置的第二类开式循环吸收式热泵搭建系统实验台,以CaCl_2溶液为吸收剂,以湿空气模拟烟气,开展吸收和再生两个关键部件的实验研究。结果显示,设计条件下吸收过程的水回收率达到65.88%,出口冷却水温度高于50℃,可满足中温供暖的要求;气体入口处的切向进气孔对传质有强化作用,传质量比未设置切向进气孔的理论模拟值高2.74倍;变工况条件下,溶液喷淋量增加、冷却水流量增大及吸收器高度增加,传质效果均增强。再生过程中,溶液浓度及再生压力上升,再生温度上升;压力越低,溶液再生所需热负荷越小。     

Ⅰ型断裂尺寸效应及裂纹扩展阻力曲线的有限元分析

针对三点弯曲法在测定混凝土等材料断裂能时存在不同程度的尺寸效应现象,基于有限元软件ABAQUS,建立5种不同尺寸、几何相似的混凝土梁,采用线性内聚力模型模拟裂纹尖端微小内聚力区域的力学特性,分析单边带预制裂缝的三点弯曲梁的Ⅰ型断裂开裂过程,针对其尺寸效应和裂纹扩展阻力曲线开展研究。结果表明,随着试件尺寸的增大,试件断裂过程区的相对长度和名义强度减小,应力强度因子和峰值荷载及对应挠度值增大;小尺寸结构破坏模式的延性特性较显著,而大尺寸结构表现出更加显著的脆性特性;尺寸效应定律的线性形式能较好地反映名义强度和试件尺寸之间的关系;通过材料的裂纹扩展阻力曲线获得裂纹失稳扩展临界点所对应的宏观断裂能,其值与输入的数值模拟参数基本一致,采用裂纹扩展阻力曲线获取材料断裂能是可行的。     

大升程碾压混凝土翻升模板施工安全特性研究

针对碾压混凝土6.2m翻升模板施工工艺的安全问题,基于有限元原理,借助ADINA软件建立大模板整体结构三维有限元模型,模拟了碾压混凝土模板在各浇筑时间荷载工况下的形变和应力最大值,并以澜沧江乌弄龙水电站碾压混凝土工程组合大模板为例,获取现场浇筑中应变试验实测值与有限元模拟结果进行对比。结果表明,6.2m模板满足施工安全性要求,基于三维有限元仿真分析模板变形量和应力符合安全性要求并未超出设计容许值,结合现场试验实测数据也验证了有限元分析的准确性和有效性,可为其他大模板安全施工提供借鉴。     

基于曲管单元模型的海上热采管柱补偿器设计及应用

海上热采管柱一般使用热采封隔器,管柱在上下端固定的情况下管柱伸长势必会造成管柱破坏,因此隔热补偿器的设计与选型是影响海上热采井管柱结构安全的一项重要因素,而管柱伸长量是补偿器设计基础。为了解决三维直梁单元只适合小曲率的井的问题,准确模拟海上井身曲率较大的油井,采用曲管单元方法,建立了在重力效应、温度效应、螺旋弯曲效应、鼓胀效应、流体黏滞效应作用下计算注热管柱的伸缩量有限元模型,形成井下注热管柱伸缩变形计算有限元方法 ,为隔热补偿器设计提供关键数据。该方法应用于渤海某稠油油田,计算了某井在热采过程中各种效应的伸长量,并与实测数据进行对比。计算结果表明:在热采条件下,对管柱伸长影响因素最大的是温度效应,其次是重力作用和螺旋弯曲效应。此方法应用到渤海某稠油井热采补偿器设计,现场管柱抬升数据验证了热采管柱伸缩变形有限元方法的有效性和准确性。     

The effect of solar radiation on dynamic thermal performance of floor heating systems

This paper presents a numerical investigation of transient heat transfer in floor heating systems using a three-dimensional explicit finite difference model. The study focused on the influence of the cover layer and incident solar radiation on floor temperature distribution and on energy consumption. Complete and partial (area) carpets were considered as well as hardwood cover layers over concrete or gypcrete thermal storage. Experimental and simulation results for an outdoor testroom reveal that solar beam radiation can cause a local floor surface temperature in the illuminated area 8°C higher than that in the shaded area. Partial carpet cover further increases floor surface temperature differences up to 15°C when solar radiation is absorbed. Solar radiation stored in the floor thermal mass was found to reduce heating energy consumption significantly (30% or more). Increase of thermal mass thickness from 5 cm to 10 cm did not lead to higher energy savings with conventional proportional-integral control. Advanced control algorithms need to be developed to maximize energy savings while maintaining good thermal comfort.     

聚氨酯保温、保湿材料在高寒地区坝工混凝土工程中的应用

为了保证高寒地区坝工混凝土建筑物的质量与安全,防止混凝土产生温度裂缝及混凝土干缩裂缝,通常在混凝土表面覆盖必要的保温保湿材料进行防护。新疆冲乎尔水利枢纽采用在大坝及泄流底孔混凝土表面喷涂聚氨酯材料起到了良好的防护效果。     

冷辐射板吸收太阳辐射的特性研究

为计算辐射空调系统中冷辐射板吸收太阳辐射能的大小及比例,在分析室内太阳光线传播的基础上,提出采用一种线性方程的方法.结果表明,以本文房间为例,冷辐射板吸收的太阳辐射能的大小以及比例在夏至日表现为正午最小,冷辐射板所吸收的太阳辐射能理论上最大能达到32 W/m2,吸收系数在0.13～0.28之间变化.冷辐射板所吸收的太阳...     

Study on shallow solar pond applications at Tehran

In this study, a theoretical model which is validated experimentally is used to predict the performance of a shallow solar pond in Tehran. The theoretical and experimental results show good agreement. The maximum hourly water temperature of the shallow solar pond is found to lag behind the maximum hourly ambient temperature and solar radiation by 1–2 and 3.5 h, respectively.The maximum monthly daily-average water temperature follows the trend of the monthly daily-average solar radiation but leads the monthly daily-average ambient temperature in one month. The shallow solar pond, with 10-cm water depth, cannot be used as a thermal source in winter but can be used for many thermal applications in summer. With 5-cm water depth, the shallow solar pond can be used as a thermal source for low heat applications in most of the winter but can be used, even for moderate applications, where high temperature up to 95°C is obtained in summer. Using a reflector makes the 10-cm depth shallow solar pond useful for low heat applications and the 5-cm depth useful for moderate heat applications in most of the winter. Using a double cover top glazing is found to have no effect on improving the system performance.     

Effect of absorption of solar radiation in glass-cover(s) on heat transfer coefficients in upward heat flow in single and double glazed flat-plate collectors

Absorption of solar radiation in the glass cover(s) of a flat plate solar collector increases the temperature of cover(s) and hence changes the values of convective and radiative heat transfer coefficients. The governing equations for the case of single as well as double glazed collector have been solved for inner and outer surface temperatures of glass cover(s) with/without including the effect of absorption of solar radiation in the glass cover(s), with appropriate boundary conditions. The effects of absorption of solar radiation on inner and outer surface temperatures and consequently on convective and radiative heat transfer coefficients have been studied over a wide range of the independent variables. The values of glass cover temperatures obtained from numerical solutions of heat balance equations with and without including the effect of absorption of solar radiation in the glass cover(s) are compared. For a single glazed collector the increase in glass cover temperature due to absorption of solar radiation could be as high as 6°. The increase in temperatures of first and second glass covers of a double glazed collector could be as high as 14° and 11°, respectively. The effect on the convective heat transfer coefficient between the absorber plate and the first glass cover is substantial. The difference in the values of the convective heat transfer coefficients between the absorber plate and the first glass cover (h_cp1) of a double glazed collector for the two cases: (i) including the effect of absorption and (ii) neglecting the effect of absorption in glass cover, could be as high as 49%. Correlations for computing the temperatures of inner and outer surfaces of the glass cover(s) of single and double glazed flat plate collectors are developed. The relations developed enable incorporation of the effect of absorption of solar radiation in glass cover(s) in the relations for inner and outer surface temperatures in a simple manner. By making use of the relations developed for inner and outer surface temperatures of glass cover(s) the convective and radiative heat transfer coefficients can be calculated so close to those obtained by making use of surface temperatures of glass cover(s) obtained by numerical solutions of heat balance equations that numerical solutions of heat balance equations are not required.     

太阳辐射对混凝土结构温度应力的影响

根据太阳辐射和气温的日变化规律,采用二维有限元方法建立了混凝土浇筑模型,仿真分析了大体积混凝土结构施工期和运行期的温度场和温度应力分布情况。结果表明,考虑太阳辐射和气温变化后,混凝土温度和应力均有明显增加,从而导致混凝土开裂的几率增大,因此在实际施工计算混凝土温度场和温度应力时应考虑太阳辐射的影响。     

On the ocean heat budget and ocean thermal energy conversion

Ocean water covers a vast portion of the Earth's surface and is also the world's largest solar energy collector. It plays an important role in maintaining the global energy balance as well as in preventing the Earth's surface from continually heating up because of solar radiation. The ocean also plays an important role in driving the atmospheric processes. The heat exchange processes across the ocean surface are represented in an ocean thermal energy budget, which is important because the ocean stores and releases thermal energy. The solar energy absorbed by the ocean heats up the surface water, despite the loss of heat energy from the surface due to back‐radiation, evaporation, conduction, and convection, and the seasonal change in the surface water temperature is less in the tropics. The cold water from the higher latitudes is carried by ocean currents along the ocean bottom from the poles towards the equator, displacing the lower‐density water above and creating a thermal structure with a large reservoir of warm water at the ocean surface and a large reservoir of cold water at the bottom, with a temperature difference of 22°C to 25°C between them. The available thermal energy, which is the almost constant temperature water at the beginning and end of the thermocline, in some areas of the oceans, is suitable to drive ocean thermal energy conversion (OTEC) plants. These plants are basically heat engines that use the temperature difference between the surface and deep ocean water to drive turbines to generate electricity. A detailed heat energy budget of the ocean is presented in the paper taking into consideration all the major heat inputs and outputs. The basic OTEC systems are also presented and analyzed in this paper. Copyright © 2011 John Wiley & Sons, Ltd.     

A theoretical study on area compensation for non-directly-south-facing solar collectors

Solar energy integrated with the building is an important approach for the synchronous development of solar energy and architecture. The energy gain of the solar collector integrated with the pitched roof has been greatly influenced by the roof azimuth and tilted angle. Investment cost of the collectors is mainly decided by the size of the collector area. Accordingly, it is significant for solar building design to economically determinate the area compensation of the solar collector at different azimuth and tilted angles. Take Kunming and Beijing as examples, area compensation for the flat-plate tube-fin solar collector used in southern regions and the evacuated tube collector with cylindrical absorbers used in northern regions in China have been theoretically calculated. The results to some extent show that the daily horizontal solar radiation, ambient temperature, the azimuth and tilted angle of the collector integrated into the roof have an influence on the area compensation. The azimuth angle and tilted angle of the roof are the main factors that influence the A/A₀, which is defined as the collector area ratio of the non-south-facing collectors to the south-facing ones with the optimal tilted angle. Comparative studies found that the range of A/A₀ for the evacuated tube collector used in the northern regions is close to that for the flat-plate tube-fin solar collector used in the southern regions. When the pitched roof tilted angle β ∈ [25°, 45°] and the azimuth angle ∣γ∣ ⩽ 30°, the collectors can intercept a lot of solar radiant-energy. Considering the economic situations of the ordinary consumers in China, the optimal area compensation A/A₀ ⩽ 1.30 is recommended in this paper.     

Effect of off-south orientation on optimum conditions for maximum solar energy absorbed by flat plate collector augmented by plane reflector

A complete analysis of the off-south oriented, simple flat plate collector, augmented by flat sheet specular reflector, is developed. The enhancement of heat flux absorbed by solar collector due to the use of reflector is calculated as a funciton of solar altitude and azimuth angles, off-south orientation angle of collector and relative sizes and tilt angles of both collector. The shading effect due to the presence of the reflector is considered in the analysis. The collector and reflector variables are optimized for maximum solar energy flux absorbed by the collector during a pre-specified period of time. The Hooke and Jeeves optimization technique has been used in the analysis.     

The effect of surface coatings on the solar radiation equilibrium skin temperature of an earth satellite

The skin temperature of an earth satellite is governed mainly by equilibrium between absorbed solar radiation and re-emitted infrared radiation. A polished metal surface will reflect a large portion of the incident solar radiation but will give a relatively high skin temperature because its infrared emissivity is low. A coating of white nonmetallic material will give a lower skin temperature, even though it absorbs a greater portion of the incident solar radiation, because its infrared emissivity is much greater.