Study The Drop Of Temperature During Construction By Cooling Pipes Built-in Concrete Dams And Optimize Of Temperature Control Measures

In general, volume of concrete building of the hydraulic structures is very large, and because of constructing and structural command, it is often constructs in big one. While cement hardens, the heat of hydration in considerable quantities will take place in the cement of the concrete, make temperature inside concrete rise quickly in a few days after construction, after reaching the maximum temperature begins to drop. But because the concrete is a kind of material of a heat conduction with extremely bad performance, if let it distribute naturally, sometimes it will take a very last time just to a century, temperature of dam body can reach stabilizing temperature. According to benefited demand in time of the project, artificial cooling measure is needed to reduce temperature of dam. In addition, temperature change in dam may make concrete produce surface crack or deep layer, this is all unfavorable to structure function and prevention of seepage of structures, artificial cooling measure is needed to reduce temperature of dam too.Artificial cooling method of concrete dam have many kinds, in whom project adopt most in the practice is cooling pipe. According to the stage purpose of lowering the temperature, the whole operation course of cooling pipe can be divided into two issues, namely initial stage cooling and later stage cooling. It is after the concrete is congealed for the first time to cool in initial stage, even often begin at once when the concrete is construct, the purpose lies in cutting down concrete cement heat of hydration peak value, reduce the difference in temperature causes by the heat of hydration, thus reduce the stress of temperature caused by difference in temperature of heat of hydration, respond to the request that allow difference in temperature. Sometimes, later stage cooling begins after heat of hydration function has already been finished, purpose lie in make concrete temperature drop to steady temperature that joint grouting needed. Can be found out from the course of using of cooling pipe: the heat dissipation occurred on the concrete floor always combine together with in initial stage cooling, influence factors of cooling result are more that it lowers the temperature, it is strict to control the standard. This makes us be unable to adopt the traditional method, but must analyse the temperature of cooling pipe in initial stage with the aid of the FEM.Since U.S.A. adopted the cooling pipe for the first time in the thirties, with the extensive adoption of this kind of cooling way, through the efforts of the scholars of various countries, calculate the temperature about cooling function of the water pipe , have beenanalyzed with analytic and numerical solution in succession. In initial period, being influenced by computing technology, speed of computer operation, capacity of memory, always calculate cooling pipe temperature by 2-D FEM. In this respect, Zhu BoFang, Cai JianBo propose "Hybrid Element Method"; Cheng Lihong, Fu Zuoxin propose a kinetic multi-mesh method of FEM.In recent years, Our country make a large number of initiative work on study large volume concrete structure overall temperature field and temperature creep stress field with FEM. In analysing drop in temperature of cooling pipe adopt equivalent algorithm that proposed by Zhu Bofang, academician of Chinese Academy of Engineering.On this basis, Zhu Bofang, academician of Chinese Academy of Engineering, proposed "compound methods"; Professor Liu Guangting of Tsing-Hua University proposed "Sub-Structural FEM"; Professor Zhu Yueming, according to the equilibrium principle of thermal exchange between cooling pipe and concrete, proposed a new fully strict calculation approach; Professor Mai Jiaxuan of Tsing-Hua University proposed a combined method of theoretic and numerical solutions; professor Mei Puliang of Petroleum University proposed "the governing equations were expressed into the state equation dispersing a spatial domain by FEM" , regarding the element in which a cooling pipe exists as a sub-structure ,the other elements as common elements,and then were solved by the refined integral method ; Dr. Liu YongJun of the water conservancy bureau of Guangzhou proposed "adaptive precision method to calculate the cooling pipe temperature " etc., have made certain result.In cooling pipe temperature field emulation analyse, because each time that concrete constructs different to want; temperature of construction is different, the material parameter is different, we must subdivide the net. For comply with large volume concrete construction's development, it is necessary to explore a new simple and suitable way in control of engineer. Because of this point, Thesis propose with analyse transient state of module and Coupling field of analyse ANSYS, Simulation thermal exchange between cooling pipe with the concrete dam body.In chapter two, introduced the finite element method basic theories of temperature field briefly. The heat conduction differential controls equation; Consider the water pipe cools the concrete equivalent heat-conduction equation of the result; the initial condition and border condition of the heat-conduction equation; The parameter value of adiabatic temperature rise; External temperature and water temperature of reservoir; the Euler equation derive of variational method; solve the extreme value question by FEM.In chapter three, brief introduce ANSYS software at first; the thermal analysis moduleof ANSYS, Control differential equation of ANSYS thermal analysis, thermal transmission way in ANSYS thermal analysis; Classification of ANSYS thermal analysis, The border condition and initial condition of ANSYS thermal analysis; the principle, the solving course, transmission means of the data, realizing the course of thermal coupling in ANSYS thermal module.On this basis, From the unity of differential equation and finite element equation, unity of the computing technology, unity of initial condition and border condition, unity of coupling field coupling mechanism, Prove with coupling thermal analyse simulation concrete dam cooling pipe feasibility on theory.Though ANSYS has very strong functions, apply to the construction time of concrete dam directly there are much difficulty in coupling temperature field emulation, Must combine rationally its relevant functions, can analyse actually. So in the end of this thesis, have introduced corresponding emulation and analysis step and realized the merger about the function is used in the course in detail.In chapter four, emulate by ANSYS software on 11# block in one RCC dam with cooling temperature field during construction time, and has done analysis to it, Have verified ANSYS is used in the feasibility with artificial temperature field in construction time of concrete dam of the large volume. Utilize result of calculation, sensitiveness analyse of factor influenced dam cool effect, have got the general choice principle in such factors: interval of cooling pipe, diameter and material of pipe, flow of cooling pipe, cooling water temperature, length of the cooling pipe, cooling pipe duration, etc.In chapter five, have made a brief instruction to the temperature control principle of the large volume concrete, and study the question of thermal and quality transfer with porous molecule of diffuse theory. Through calculating results, in the course of concrete construction, moisture evaporation can commute temperature rise of concrete in part or in whole caused by solar radiation. It is obvious, confirm high temperature, atmospheric relative humidity, wind speed, solar radiation environmental terms factor to concrete construction course influence that temperature being changed, make corresponding temperature at the control measure, must consider concrete moisture to mix and stir material evaporate this factor synthetically.Form the foundation permits temperature difference, difference temperature from up to down layer, supreme temperature control of dam, etc. have introduced the current temperature control standard. On this basis, thesis proposed it is necessary to treat the temperature-controled question from the whole course of concrete dam construction, namely the maintenance period after initial design, material are prepared, the material istransported, the material constructs and constructs will carry on temperature control. From choosing and using the cement rationally, guarantee and strive to improve the concrete and resist the ability of splitting, rational parting pattern, arrange the concrete operational procedure and construction speed rationally, warm control measure before the concrete producing machine, temperature-controled measure while transporting and constructing, control dam maximum temperature measure, cooling pipe, surface protect respect introduce possible temperature control measure in detail.In the course of actual construction of the concrete dam, there are many kinds of temperature-controled measures adopted; the operation expenses of each kind of measure are not the same. How to optimization assembly various kinds of temperature-controled measures, not only met the demand for temperature control, can reduce the temperature at the same time cause the stress condition unlikely deterioration, but also reduce the comprehensive expenses of the temperature-controled measure, enable dam to pondage as soon as possible, will dive into operation and bring into benefit early, it is essential for speediness high-quality constructing of the dam. For this reason, thesis established the mathematics model of the control measure of temperature optimizes in chapter six. The optimization design of the temperature control measure of concrete dam is to regard the whole dam as the research object, under guaranteeing time limit for a project and such prerequisites as the construction technology condition, through the calculation of temperature field, control the peak value of temperature and the gradient while construction, adopt many kinds of feasible temperature control measures, try to get the temperature-controled measure of the lowest all-inclusive cost as the optimum goal.