大直径钢筋混凝土圆筒仓仓壁厚度的探讨

1问题分析《钢筋混凝土筒仓规范》GBJ77－85对直径小于或等于15m的圆筒仓仓壁厚度取值作了规定，而直径大于15m的情况未提及。本文以散装储库为例，探讨直径大于15m的圆筒仓仓壁厚度的合理取值。确定仓壁厚度需进行三种计算：强度计算、变形验算及裂缝宽度验算。根据规范GBJ77－85，圆筒仓的仓壁为－圆柱薄壳，强度计算时按无矩理论计算其薄膜内力。贮料侧压力作用下产生的环向拉力全部由环筋承担，与仓壁厚度无关；而仓顶荷载、仓壁自重、贮料摩擦力、风载、地震作用等共同作用下产生的竖向力由混凝土及竖向钢筋承担，由此确定的仓壁厚…     

尿素造粒塔温度应力计算方法探讨

为探讨尿素造粒塔的实际环向温度分布,对比了壳体结构在内外温差作用下温度应力的现有计算方法和<尿素造粒塔设计规范>计算方法;采用SAP 2000有限元程序对某造粒塔的温度应力进行了温差计算、理论计算和有限元分析,并与规范计算结果进行了比较.结果表明,直接使用长圆柱壳热弹理论计算的造粒塔温度应力值比实际值偏小,建议对规范计算结果进行修正.     

大直径浅圆仓缩尺模型试验研究

大直径浅圆仓在生产过程中,由于仓底的偏心卸料使筒仓仓壁产生不均受力,会给筒仓结构的使用带来安全隐患。通过对浅圆仓缩尺模型试验,模拟筒仓生产过程的卸料状况,并对筒仓仓壁及仓底廊道顶部进行压力测试,将测试结果与理论计算进行对比,从而得出偏心卸料与静载状态的超压系数,为大直径浅圆仓设计提供依据。     

大直径浅圆仓的实用内力计算及有限元分析

1 特殊大直径浅圆仓的内力计算 正是由于<钢筋混凝土筒仓设计规范>GB50077-2003在计算一些特殊大直径浅圆仓时候存在问题,设计人员需要为其建立正确模型才能保证设计的安全.由于该浅圆仓H＜D=0.1.故可近似认为墙后贮料相对于仓壁无限长,此时可将贮料作用与仓壁的压力近似认为是作用与挡土墙上的主动土压力,可以按照广义库伦理论计算主动土压力系数.     

聚乙烯超高压反应器计及温差应力时Rc值的探讨

本文采用Tresca屈服准则推导了聚乙烯超高压反应器在自增强处理时计及温差应力情况下的适宜弹塑性界面半径Rc的解析表达式。通过对实例的演算说明:按本文计算的Rc值,能进一步降低器应力壁的水平,实现内外壁等应力水平,提高疲劳强度。     

△t_壁≠△T_物(列管式换热器壁温差计算)

列管式换热器的管子与壳体的壁温差大小,将直接影响到换热器的结构。膨胀节是否需要?特别在压力较高的情况下,因膨胀节的结构困难,而要采用结构较复杂的浮头式换热器。我们在设计小品(一)中,介绍了是否需要膨胀节的计算,就需要求得正确的壁温差。壁温差的大小还影响到管板厚度的计算。如采用物料温差作壁温差,则势必增加管板厚度,因此将增加设备材料的消耗,加工工时和投资费用。     

固定式列管换热器管壁与壳壁温差对管板变形的影响

固定式列管换热器管板的变形受到多种因素的影响，其中有管程压力与壳程压力作用，管束支承效应，列管与壳体之间不同的热膨胀以及管板与壳体／管箱之间连接的相互作用等。本文通过数值计算分析了管壁与壳壁之间的温差热膨胀对管板变形的影响。     

预应力钢筋在选煤厂钢筋混凝土筒仓中贡献度的探讨

为了验证预应力钢筋在整个仓壁承载力计算过程中的贡献度,结合具体项目,对一个直径为25 m、容量为1.5万t的原煤仓进行详细计算,比较预应力混凝土仓壁在考虑预应力钢筋和不考虑预应力钢筋时的差别。计算表明,考虑预应力钢筋在仓壁强度验算中所起的作用时,所需环向普通钢筋质量为29 t,比不考虑预应力时节约钢筋7 t,节约比率接近1/5。     

薄管板换热器

管板是列管式换热器的主要另件,由于其受力情况复杂、有管内外压力、温差产生的力、法兰力矩的影响和管子的支撑力等,因此由于采用计算理论和假定不同,计算方法和结果也不一样,各国计算规范,如英国BS5500,BS1515,美国TEMA,西德AD,苏联PTM和法国的计算方法各不相同,我国新的压力容器设计规范是在BS基础上发展提高的,与前述规范亦有差异,这种差异的存在,是值得我们探讨研究的。     

GB50077-2017附录C仓壁贮料压力计算模型研究

针对GB50077—2017附录C仓壁贮料压力计算模型出现的工况横跳且侧压力不连续的问题,本文通过理论分析指出这些问题均是由侧压力求极值时产生,建议直接采用试算法获得侧压力的最大值及其所对应的破裂角。参数分析表明随着破裂角的不断增大,仓壁侧压力呈现出先增大后减少的趋势,侧压力最大值可直接取界限破裂角对应的侧压力值。传统浅仓计算方法的侧压力系数在各个高径比下均大于附录C侧压力模型的等效侧压力系数。     

料仓内粉体静态应力分布特性

料仓内的粉体静态应力分布是指导料仓设计和运行的重要参数之一。本文在三维有机玻璃料仓中，对料仓应力分布进行试验研究，利用应力传感器对料仓壁面及粉体内部水平、竖直应力进行研究，获得料仓中粉体内部应力的分布规律，并基于拱效应对料仓中的应力分布进行理论研究。结果表明：料仓内部水平应力与距出口及料仓中心的距离基本无关，壁面处的水平应力在筒锥结合处达到最大值且随加料高度的增加大幅度增加。料仓内部垂直应力的最大值出现在筒锥结合处近筒段的料仓中心位置。同一平面，从料仓中心至仓壁，垂直应力呈逐渐减小的趋势。随加料高度的增加，垂直应力均逐渐增加。在壁面处，侧压力系数随着距出口高度的增加出现先增大后减小的趋势，在筒锥结合处大于1。     

U形圆管中超临界压力RP-3航空煤油换热数值研究

基于航空发动机空-油换热器的冷却换热问题,开展了竖直U形圆管内超临界压力RP-3航空煤油换热的数值研究。探究了进口竖直段、弯管段、出口竖直段的换热特征和换热机理,阐述了运行压力和热质比对换热的影响机制。结果表明：进口竖直段呈现均匀换热的特征。弯管段离心力作用致使流体温度出现异常分层,周向密度不均匀,横向不平衡动能诱发强二次流问题,最大二次流速度达到0.45 m·s^-1。固体热传导过程也受到影响,出现固体温度异常分层。两者综合作用下导致管壁温度和热通量的周向差别。出口竖直段的周向换热差别依然存在,二次流被削弱。提高运行压力或降低热质比,管截面热物性变化趋缓,周向换热差别减弱。     

中心降料管的料仓中垂直应力分布实验研究

The distribution of vertical stress for both active and passive state in the silo with a central inner downcomer is reported in this paper.Experimental measurement of the axial distribution of vertical stress for both active and passive state in the silo are in good agreement with that predicted by theoretical analysis.The mean axial stress is reduced due to the presence of the inner downcomer in the silo.     

Simulation of Temperature Distribution in Stored Wheat without Aeration

A neural-deterministic simulation model applied for calculating distributions of temperatures and moisture content in a bed of wheat stored in a steel silo without aeration is presented in the article. The model consists of differential equations of heat and moisture transfer, initial and boundary conditions, and three artificial neural networks used during simulated ambient air conditions. Experiments and computer simulations were carried out in order to determine temperature fields in wheat grain stored in a steel silo for two months. The computer simulations were carried using MATLAB and FEMLAB software. The difference between measured and simulated temperature in grain near the silo wall at a height of 2.5 m from the bottom was less than 3.0°C. On the basis of the analysis performed it was concluded that the temperature distributions obtained with the model were consistent with the measured results obtained for grain stored in a steel silo without aeration.     

Simulation of Temperature Distribution in Stored Wheat without Aeration

A neural-deterministic simulation model applied for calculating distributions of temperatures and moisture content in a bed of wheat stored in a steel silo without aeration is presented in the article. The model consists of differential equations of heat and moisture transfer, initial and boundary conditions, and three artificial neural networks used during simulated ambient air conditions. Experiments and computer simulations were carried out in order to determine temperature fields in wheat grain stored in a steel silo for two months. The computer simulations were carried using MATLAB and FEMLAB software. The difference between measured and simulated temperature in grain near the silo wall at a height of 2.5 m from the bottom was less than 3.0°C. On the basis of the analysis performed it was concluded that the temperature distributions obtained with the model were consistent with the measured results obtained for grain stored in a steel silo without aeration.     

Temperature and Time Consolidation Effect on the Bulk Flow Properties and Arching Tendency of a Detergent Powder

Time consolidation flow properties of a commercial detergent powder were measured at different elevated temperatures with the Brookfield powder flow tester (PFT). A substantial increase of powder cohesion was observed at higher temperature and after time consolidation. The Jenike method for silo design was applied to correlate the powder time consolidation flow properties at elevated temperature to the critical outlet slot to attain an arch-free silo. The dependence of the critical diameter on temperature and time consolidation was successfully described by the model.     

基于离散元的中心椎体筒仓偏心卸料侧压力分析

利用EDEM建立中心锥体筒仓缩尺试验模型,通过EDEM软件模拟得出中心锥体筒仓仓壁及锥体侧压力,对比EDEM模拟值、试验值和相关的Janssen公式值.验证EDEM软件模拟的合理性.然后进行中心锥体筒仓单孔卸料模拟,提取部分与试验传感器位置的仓壁及锥体侧压力,得出侧压力超压系数,与试验值进行对比.     

Maturation of fresh cement paste within 1- to 10-m-large formworks

The objective of this research was to examine the maturation of early-aged cement paste through the survey of the evolutions of the total lateral pressure exerted by cement paste against formworks and of the pore water pressure. The experimental device was specially developed for this purpose. Three types of cement paste mixtures with a water/cement (W/C) ratio of 0.30, 0.36 and 0.45, respectively, have been tested. In addition, temperature and setting kinetics were also examined. The results have shown that the kinetics of the pore water pressure and the total lateral pressure were strongly affected by the W/C ratio, the vibration and the level of stress, to which the fresh cement paste is subjected. The confrontation of these results with the theory currently available as regards setting of cement makes it possible to identify the physicomechanical phenomena, which occur within formworks.