| In order to solve the problem of uneven distribution of water resources in China,many water diversion projects have been built in China.As an overhead trough,the aqueduct is not affected by the terrain and is widely used in water diversion projects,but the shortcomings are also obvious,and it is greatly affected by earthquakes and temperatures.Especially in the northwest region of China,the temperature is low in winter,and if you want to carry out water transportation,it is easy to freeze,and the temperature stress generated is relatively large.At present,there have been more and more research on water transmission in winter aqueducts,but the content of the research still needs to be studied and explored.Therefore,this paper takes a rectangular aqueduct project in Northwest China as the background to study the water temperature of the rectangular aqueduct in winter water transmission,the temperature field and temperature effect of the aqueduct when transporting water.Starting from the design and operation of the aqueduct,it is proposed to solve the problem of winter water transmission in the cold northwest region and provide a reference for the design and operation of the aqueduct.Based on the steady-state heat conduction theory,this paper uses Ansys Workbench software to establish two-dimensional and three-dimensional models of the aqueduct,and uses the differential equation of thermal conductivity,Newton’s cooling law and Manning’s formula to solve the problem to study the influence of the slope change of the rectangular aqueduct in winter on the water temperature,the water flow problem under the most unfavorable working conditions,the water temperature problem in the aqueduct during heat preservation,and the transient temperature field and temperature effect of the aqueduct under low temperature environment.By calculation,we know:(1)When the aqueduct transmits water according to the design flow,with the change of the slope of the aqueduct,the water temperature in the aqueduct will also change,and when the slope of the aqueduct is 1/1100,the outlet water temperature will appear at a minimum;(2)When the aqueduct is built according to the most unfavorable slope,under the condition that the external ambient temperature is the same,the larger the water transmission flow,the larger the corresponding flow rate,the shorter the time to flow through the aqueduct,the lower the heat loss,the higher the outlet water temperature,the smaller the flow is the opposite;And from the derivation of the change relationship between flow rate and water temperature,the corresponding critical flow value at a certain temperature is obtained.(3)Under the most unfavorable slope,when the aqueduct has the minimum water transmission flow,the aqueduct is first equipped with additional insulation plates around it.By comparing the insulation effects of polyurethane and polystyrene insulation boards of 2cm,5cm and 7cm,the water temperature calculation of the additional 5cm polyurethane insulation board to the aqueduct was selected,and it was found that the surrounding additional insulation board could not play a good thermal insulation effect compared with no insulation measures.Secondly,by covering the top of the aqueduct,it is found that compared with the absence of insulation measures,the total heat loss of the water body in the aqueduct decreases by 78%,and the water temperature at the lowest external ambient temperature is above 2 °C,which meets the insulation conditions of the aqueduct water transmission in winter.(4)The temperature change of 8 hours at night was selected as a typical working condition,and the temperature field change law of the aqueduct under the transient temperature field was studied.As the external ambient temperature decreases,the temperature distribution of the cross-section of the aqueduct gradually approaches from the outer surface to the inner surface.And the temperature change law of the web and the outer surface of the floor is consistent.(5)Under the action of temperature load,most of the tensile stresses at the outer edge of the entire floor and the bottom of the outer edge of the web have exceeded the design value of concrete tensile strength,and the outer edge of the floor is subjected to temperature tensile stress,and the distribution is relatively uniform.The bottom end of the outer edge of the web is subject to great temperature tensile stress,so appropriate temperature reinforcement should be configured in the design to ensure the safety of the structure.(6)Under the combination of self-weight,water pressure and temperature load of the structure,the stress in the X direction and Y direction of the aqueduct increased,the force condition at the bottom plate position was still external tension and internal compression,and the tensile stress at the middle span position of the outer edge of the bottom plate reached the maximum,but the tensile stress at both ends of the outer edge of the bottom plate decreased compared with the temperature load.The hand condition of the web position changes from external pulling internal pressure to internal pulling external pressure,especially at the inflection point between the inner edge of the web and the chamfer,the tensile stress reaches the maximum,so in the design,attention should be paid to the appropriate number of steel bars arranged at the middle position of the bottom plate span and the chamfer position of the web. |
