| With the increasing capacity of the unit of the hydropower station,the HD value of the spiral case has also increased dramatically and the spiral case has become increasingly huge.This has reduced the cost of the turbine,but it has also caused a series of problems.For example,the selection of the embedding type for the spiral case of the giant hydropower station;the spiral case and the stay ring may produce significant deformation around the centerline of the unit under the effect of unbalanced hydraulic thrust;the cushion layer material of the spiral case with cushion layer may lose its elasticity due to aging.There would be a large gap between concrete and steel spiral case,which may cause problems such as hydropower house vibration.On account of the aforementioned problems,by means of the finite element method(FEM)using ANSYS,this dissertation is restricted to the discussion based on some engineering examples.The main research contents are as follows:(1)This dissertation compares the different simulation methods of the inlet boundary conditions of spiral case.Considering the influence of the upstream penstock of spiral case on the calculation accuracy,the complexity of the calculation model and the increase in the calculation workload,there is some suggestions for the spiral case calculation model in the future.Establishing the model of the exposed penstock and the range of the inlet section of the spiral case is taken to the first stiffening ring in the upstream penstock.Axial rigid restraints are applied at the stiffening rings and the exposed penstock outside the excavated surface of the hydropower house is exposed to the actual internal water pressure that may be assumed according to the specifications.(2)Studying the effect of the anti-thrust ring setting on the mechanical characteristics of spiral case with cushion layer and complete bearing spiral case,it was found that no anti-thrust ring is required for the complete bearing spiral case regardless of whether the upstream penstock is provided with expansion joint.For the spiral case with cushion layer,when expansion joint is provided,the anti-thrust effect of the anti-thrust ring is more obvious,and it is necessary to improve the safety margin of the channel structure.When there is no expansion joint,the upstream penstock or stiffening ring can replace the anti-thrust effect of the anti-thrust ring,it could be considered cancelling the anti-thrust ring.(3)The influence of the anti-thrust ring on the dynamic characteristics of the spiral case with cushion layer is studied.When the cushion layer material is not aged,the anti-thrust ring has no obvious influence on the natural vibration characteristics of the structure.When the cushion layer material is aged,the vibration mode of the hydropower house is mainly represented by the vibration of the steel spiral case and the fundamental frequency is significantly reduced.Setting the anti-thrust ring can effectively improve the natural vibration frequency of the steel spiral case and it is conducive to the anti vibration of spiral case and hydropower house.Under the effect of the pulsation pressure in the spiral case,the anti-thrust ring can play a certain role in anti-thrust effect,improving the mechanical characteristics of the stay ring.At the same time,it also increases the vibration speed and vibration acceleration of the concrete structure,but it has little impact.(4)Considering the advantages of preload filling spiral case and spiral case with cushion layer,the mechanical characteristics of the spiral case with a thin cushion layer are studied.From the aspects of the concrete surrounding the spiral case,the unbalanced forces experienced by the channel structure,the stress of the steel spiral case and the stay ring,and the uneven deformation of the stay ring and the generator pier,the thin cushion layers with different thicknesses and certain residual deformations are analyzed and compared.Finally,this dissertation proposes reasonable thin cushion layer parameters. |
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