CN111581858B - Design method of heat preservation and heat insulation system for power transmission and transformation foundation - Google Patents
Design method of heat preservation and heat insulation system for power transmission and transformation foundation Download PDFInfo
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Abstract
The invention discloses a design method of a heat preservation and insulation system for a power transmission and transformation foundation, which adopts a numerical calculation means to study the influence rule of seasonal frozen soil in an actual engineering area on a temperature field and a mechanical field of a tower foundation, and provides economic, applicable and effective key design guidance parameters for the design of the power transmission and transformation foundation heat preservation system. And optimizing a heat preservation and heat insulation system and a design method of the power transmission and transformation foundation through numerical calculation of the material property or structural form of the power transmission tower foundation in the season frozen region. In actual engineering, the invention can be used for simulating the field engineering environment, and the heat-insulating foundation is designed by comprehensively considering environmental conditions, performance requirements, cost control and the like through numerical calculation, analysis and optimization.
Description
Technical Field
The invention relates to the technical field of geotechnical engineering in civil engineering, in particular to a heat preservation and heat insulation foundation for preventing frost heaving and thawing sinking of a foundation.
Background
When the air temperature is below 0 ℃, the soil layer contains solid water, the property of the soil layer is correspondingly changed along with the change of the temperature condition, and the soil layer has the phenomena of hot melting slump, thawing sinking, frost heaving and the like. Such soil layers are called frozen soil. Frozen soil can be classified into permafrost and seasonal frozen soil according to duration. By seasonal frozen soil is meant frozen soil that freezes in winter and melts in summer. Seasonal frozen soil is frozen or melted according to the change of seasons, so that uneven settlement of the foundation is likely to occur, and the stability of the foundation is seriously affected. When the temperature is reduced below 0 ℃, frozen soil is frozen, original water in the soil is frozen, the volume of the frozen water is expanded after the water is frozen, and at the moment, the foundation is raised; when the temperature rises, the frozen soil begins to melt, the tension generated by the expansion of the water volume disappears, and the foundation collapses. Due to the influence of heating conditions and building structures, uneven subsidence and frost heaving can periodically occur at the periphery of the building, which can bring adverse effects to the stability of the foundation, and meanwhile, the phenomena of wall cracking, step rising, ceiling lifting and the like can be possibly caused, and even the building can be inclined. Therefore, in designing the foundation of the transmission tower, importance must be attached to the influence of seasonal frozen soil on the foundation of the tower.
The regions in the middle and west of Gansu province belong to typical season frozen soil regions, most regions are in medium-deep season frozen soil regions, and the regions in China belong to Qinghai-Tibet plateau, northwest mountain strength frozen thawing regions and northwest loess plateau medium frozen thawing regions, and have the characteristics of long freezing period, large freezing depth, strong frozen thawing effect and the like. According to the power grid planning of China, a large number of construction tasks of power transmission and transformation projects still exist in the middle and western regions of Gansu provinces in the future. The construction of the engineering inevitably encounters the problems of freezing and thawing diseases of the foundation (uneven) frost heaving, frost heaving and the like under the repeated freezing and thawing actions of the seasonal freezing and thawing layer and the deterioration of the freezing and thawing damage of the concrete material. Therefore, how to effectively prevent and treat the problems of basic freeze thawing diseases and material freeze thawing damage for the construction of power transmission and transformation projects in the area is a problem to be solved by scientific research and engineering designers at present.
Ma Weidong and Li Cheng (2004) discuss some technical measures for the problem of frost heaving and thawing settlement in the engineering of roadbeds in frozen soil areas, including roadbeds of different forms and the use of hot bars and insulating materials in the engineering of roadbeds in frozen soil areas. Wei Donglin and Hua Guo (2017, publication No. CN 107973576A) are made of Portland cement, diatomite, foam particles, aluminum silicate fiber cotton, etc., and have heat-insulating building materials. Lv Zong (2019, publication No. CN 110453556A) discloses a foundation soil heat-preserving and anti-freezing treatment method. Hopefully (2018, publication number CN 208815556U) discloses an invention patent, and provides a heat-insulating building foundation structure capable of enhancing heat-insulating performance on the basis of bearing capacity. Jiang Haigong (2019, publication No. CN 208586629U) uses porous silicate materials for thermal insulation of building foundations.
However, the existing research results and engineering measures have small application range, and the influences of local climate conditions, geographical environments and other factors need to be fully considered in practical application (2, the basic design method of the power transmission and transformation circuit considering the seasonal freeze thawing effect needs to be perfected.
Citation literature:
li Xiaochen slope foundation study of high-voltage transmission tower in season frozen soil region [ D ]. Harbin: university of halbine industry, 2008.
Wang Lanmin, ma Wei, chen Zhenghan, etc. the key scientific problem research and hope in special soil engineering [ C ]. The second national society of rock-soil and engineering, university, has a sentence, wuhan, 2006.
She Yangsheng, cai Degou, yao Jianping, etc. the technology for controlling settlement deformation after special soil roadbed construction of high-speed railway [ C ]. The national society of science and technology: soft soil roadbed engineering society 2012.
Disclosure of Invention
The invention aims to solve the technical problems of providing a heat preservation and insulation system and a design method for a power transmission and transformation foundation, and adopting a numerical calculation means to study the influence rule of seasonal frozen soil in an actual engineering area on a temperature field and a mechanical field of a tower foundation, so as to provide economic, practical and effective key design guidance parameters for the design of the power transmission and transformation foundation heat preservation system.
In order to solve the technical problems, the invention utilizes large finite element numerical calculation software ANSYS to carry out detailed numerical calculation and analysis on the heat conductivity coefficient, the structural form, the surface temperature, the bottom soil temperature and the like of different heat protection and heat insulation materials, and obtains the deformation, stress, temperature numerical results, distribution cloud pictures and the like of the power transmission and transformation foundation under different working conditions. The method comprises the following steps:
first, the basic equation of the thermodynamic coupling model used by the simulation is:
the heat transfer process is a transient nonlinear problem, and the differential equation of heat conduction is:
wherein c is the specific heat capacity in J/(kg. Deg.C); k is the heat conductivity coefficient, and the unit is W/(m DEG C); t is the temperature in degrees Celsius; t is time, and the unit is s; x, Y and Z respectively represent the heat transfer direction.
From the thermal stress and thermal strain expressions, according to the elastomechanical equilibrium equation, a thermoelastomechanical equilibrium differential equation can be obtained, which is:
FX, FY and FZ are components of volume force of unit volume in X, Y and Z axes respectively;is Laplace operator; μ is poisson's ratio; e is the elastic modulus; delta T is the temperature difference between two moments; alpha is the thermal expansion coefficient; εX, εY, εZ are thermal strains.
e＝εX+εY+εZ
The method comprises the following specific steps
And S1, opening ANSYS software, defining and analyzing file names, and selecting file storage positions.
Step S2, defining a unit type. An analysis unit having a two-dimensional magnetic field-thermal field-electric field-structural field coupling function is selected.
And step S3, defining material properties. Parameters required for the simulation include thermal and mechanical parameters. Thermal parameters include specific heat capacity and thermal conductivity; the mechanical parameters include density, poisson's ratio, modulus of elasticity and coefficient of thermal expansion. In order to study the frost heaving effect of the soil body, the parameters are all physical parameters related to temperature, and specific numerical values are determined by combining an actual investigation report with an existing empirical formula.
And S4, establishing a geometric model. And comprehensively considering the actual engineering geological parameter report and the propagation influence rule of the stratum surface temperature below the earth surface, and selecting the calculation depth and the calculation width. CAD is used to build the model and to import ANSYS software.
And S5, meshing. The division is performed using a suitable grid cell size and grid cell density.
And S6, applying boundary conditions and loads. And selecting a plurality of working conditions according to actual engineering conditions, and applying thermal and mechanical boundary conditions and loads to the model.
And S7, setting a solving option and a convergence criterion, and solving. Transient analysis is selected as an analysis type, gradual change control is selected as a load step, and iterative calculation is performed in a fixed time step.
And S8, post-processing. And after the operation is finished, thermal and mechanical numerical results, a distribution cloud picture and the like under different working conditions are obtained. And analyzing the change conditions of the temperature field and the mechanical field of the model under different working conditions. And obtaining the influence rules of multiple parameters such as structural form, load condition, thermal conductivity coefficient of the thermal protection material and the like under different working conditions through parameter analysis.
Compared with the prior art, the invention has obvious advantages and beneficial effects. By means of the technical scheme, the heat preservation and insulation system and the design method for the power transmission and transformation foundation have certain technical progress and practicality and have wide industrial utilization value, and the heat preservation and insulation system and the design method have at least the following advantages:
(1) The invention carries out simulation numerical calculation by means of the large-scale application software ANSYS, can simulate the field engineering environment, and is practical, economical and wide in adaptability.
(2) According to the invention, thermodynamic coupling calculation of the power transmission tower foundation in the season freezing region under different working conditions is realized, and the numerical results of the temperature, displacement and stress change around the foundation and the distribution cloud picture are obtained.
(3) According to the invention, the influence of the material property or the structural form of the power transmission tower foundation in the season freezing region on the heat protection of the power transmission tower under different environmental conditions can be calculated, and then the design optimization of the heat preservation and heat insulation system of the power transmission and transformation foundation is carried out.
Drawings
Fig. 1 is a schematic structural view of a power transmission tower foundation in three different forms of thermal protection structures.
Fig. 2 shows the temperature of the center line of the mold in the form of different heat protection structures as a function of depth.
FIG. 3 is a cloud of temperature profiles for different conditions.
Fig. 4 is a block diagram of a thermal insulation foundation of a power transmission tower.
In the figure: 1-heat preservation and insulation layer, 2-backfill soil and 3-bearing platform.
Detailed Description
The preferred embodiments of the present invention will be described in further detail
Example 1
As shown in FIG. 1, three power transmission tower foundations with different heat protection structure forms are selected according to the thicknesses of heat protection materials at the upper end and the lower end of a bearing platform for calculation and analysis, and the thicknesses of the surface layer and the bottom are respectively 1.5m-0.5m, 0.5m-1.5m and 2m-0m. The limit condition working condition in the research problem is selected for research, namely the surface temperature is-30 ℃, the bottom soil temperature is 20 ℃, and the heat preservation coefficient of the heat protection material is 0.08W/(m.DEG C).
Fig. 2 shows the temperature of the center line of the mold in the form of different heat protection structures as a function of depth. FIG. 3 is a temperature distribution cloud for this condition. The result shows that when the heat protection structure is 2m-0m, the temperature of the midpoint of the bottom end of the bearing platform is higher, and the heat protection structure has better heat protection effect.
Finally, it should be noted that: the foregoing description is only a preferred embodiment of the present invention, and the present invention is not limited thereto, but it is to be understood that modifications and equivalents of some of the technical features described in the foregoing embodiments may be made by those skilled in the art, although the present invention has been described in detail with reference to the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (1)
1. The design method of the heat preservation and heat insulation system for the power transmission and transformation foundation is characterized in that large finite element numerical calculation software ANSYS is utilized to carry out detailed numerical calculation and analysis on the heat conductivity coefficient, the structural form of the heat protection and heat insulation material, the surface temperature and the bottom soil temperature of different heat protection and heat insulation materials, and deformation, stress and temperature numerical results and distribution cloud patterns of the power transmission and transformation foundation under different working conditions are obtained;
the method comprises the following steps:
first, the basic equation of the thermodynamic coupling model used in simulation is as follows:
the heat transfer process is a transient nonlinear problem, and the differential equation of heat conduction is:
wherein c is the specific heat capacity in J/(kg. Deg.C); k is the heat conductivity coefficient, and the unit is W/(m DEG C); t is the temperature in degrees Celsius; t is time, and the unit is s; x, Y and Z respectively represent the heat transfer direction;
from the thermal stress and thermal strain expressions, according to the elastomechanical equilibrium equation, a thermoelastomechanical equilibrium differential equation can be obtained, which is:
FX, FY and FZ are components of volume force of unit volume in X, Y and Z axes respectively; 2 is Laplace operator; μ is poisson's ratio; e is the elastic modulus; delta T is the temperature difference between two moments; alpha is the thermal expansion coefficient; εX, εY, εZ are thermal strains;
e＝εX+εY+εZ
the method comprises the following specific steps
Step S1, opening ANSYS software, defining and analyzing file names, and selecting file storage positions;
step S2, defining a unit type, and selecting an analysis unit with a coupling function between a two-dimensional magnetic field, a thermal field, an electric field and a structural field;
step S3, defining material properties, wherein parameters required by the simulation comprise thermal parameters and mechanical parameters; thermal parameters include specific heat capacity and thermal conductivity; mechanical parameters include density, poisson's ratio, modulus of elasticity and coefficient of thermal expansion; for researching the frost heaving effect of the soil body, the above parameters are all physical parameters related to temperature;
s4, establishing a geometric model, comprehensively considering an actual engineering geological parameter report and a propagation influence rule of the stratum surface temperature to the position below the earth surface, and selecting a calculation depth and a calculation width; establishing a model by adopting CAD and importing ANSYS software;
step S5, grid division is carried out by adopting proper grid cell size and grid cell density;
s6, applying boundary conditions and loads, selecting a plurality of working conditions according to actual engineering conditions, and applying thermal and mechanical boundary conditions and loads to the model;
step S7, setting solving options and convergence criteria, and solving; transient analysis is selected as an analysis type, gradual change control is selected as a load step, and iterative calculation is performed in a fixed time step;
step S8, post-processing; after the operation is completed, thermal and mechanical numerical results and distribution cloud pictures under different working conditions are obtained; and analyzing the change conditions of the temperature field and the mechanical field of the model under different working conditions, and obtaining the influence rules of multiple parameters such as structural form, load condition and thermal conductivity coefficient of the thermal protection material under different working conditions through parameter analysis.
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| UA115760C2 (en) * | 2017-09-25 | 2017-12-11 | Андрій Васильович Єрьомін | METHOD OF COMPLEX THERMODODERIZATION OF BUILDINGS AND BUILDINGS BY YERMYN |
| CN110205983A (en) * | 2019-05-20 | 2019-09-06 | 松花江水力发电有限公司丰满大坝重建工程建设局 | Severe cold area dam thermal-insulating leakage-resistant is anti-icing to pull out protection system and its construction method |
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| RU2602538C1 (en) * | 2015-09-03 | 2016-11-20 | Общество с ограниченной ответственностью "Газпром добыча Ямбург" | Method for reduction of action of forces of frost boil and increasing stability of pile foundations in permafrost zone |
| UA115760C2 (en) * | 2017-09-25 | 2017-12-11 | Андрій Васильович Єрьомін | METHOD OF COMPLEX THERMODODERIZATION OF BUILDINGS AND BUILDINGS BY YERMYN |
| CN110205983A (en) * | 2019-05-20 | 2019-09-06 | 松花江水力发电有限公司丰满大坝重建工程建设局 | Severe cold area dam thermal-insulating leakage-resistant is anti-icing to pull out protection system and its construction method |
| CN110702729A (en) * | 2019-09-19 | 2020-01-17 | 中国石油大学(华东) | Device and method for testing heat insulation performance of vacuum heat insulation sleeve under simulated frozen soil environment |
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