Analysis Of Hydraulic Characteristics And Structural Performance Of Grid Type Underflow Energy Dissipation Based On Fluid-structure Interaction

With the continuous development and utilization of water resources,the difficulty of pivot project layout faces a great challenge.In the case where the outlet of the spillway building has to face the mountain or intersect the downstream channel diagonally,the topographic conditions do not easily meet the linear bottom flow dissipation pool length requirements.For bottom-flow dissipation,when the downstream water depth is insufficient,it is usually possible to make a forced water jump at the outlet of the spillway building by reducing the height of the retaining tank or increasing the tailing can.In order to reduce the project investment,can be set up by adding auxiliary energy dissipation worker to improve the effect of energy dissipation or smooth the downstream flow pattern.The common auxiliary energy dissipation workers are dissipation pier,arch network,hanging fence,Γ-shaped grille and so on.Therefore,the study relies on an actual project,using the fluid-solid coupling finite element method,by adjusting the position and opening rate of the Γ-shaped grating in the dissipation pool,analyzing the effect of different grating thickness(0.35 m,0.25 m,0.15m)on the hydraulic characteristics,and further analyzing the influence of the grating structure stress,strain and displacement response,the results show that:Hydraulic characteristics:(1)The degree of turbulence on the surface of the water flow in front of the grille gradually decreases as the thickness of the grille decreases,while the turbulence on the surface of the water burst at the horizontal grille and the water flow behind the grille gradually increases.(2)the bottom of the flow velocity in the grille after the drop gradually decreases,the average pressure of the cross-section at the bottom plate of the force pool and the opposite flow velocity,while the average pressure of the longitudinal section before and after the grille,the average pressure of the grille before the increase in the average pressure of the grille after the decrease in the average pressure of the grille.(3)Due to the reduction of the cross-sectional area of the water flow,the flow velocity increases suddenly in front of the grid hole,and the flow velocity decreases at the grid hole with the thickness of 0.35 m and 0.25m;however,the flow velocity increases instead of decreasing at the bottom hole with the thickness of 0.15 m,and the average pressure gradually decreases to a certain value and then gradually increases.(4)As the grille thickness decreases,the energy dissipation effect is also gradually weakened;at the same time,according to the standard specification,we can get the cavitation number of the water flow before the grille is greater than 0.30,and it is not easy for the cavitation water flow and cavitation damage to occur in the dissipation pool.Structural performance:(1)the grille thickness of 0.35 m,the grille can be placed in the middle and rear of the force pool,the grille thickness is reduced to 0.25 m,the grille can only be placed in the rear of the force pool;grille thickness of 0.35 m,the opening rate can be adjusted to 34% and 40%;grille thickness of 0.35 m,the opening rate of 34% of the grille placed in the middle and rear of the force pool or the grille opening rate of the middle of the force pool The opening rate is adjusted to 40% to meet the structural stress requirements.(2)The grille thickness decreases,the tensile and compressive strains in all three directions show a gradual increase trend,and all meet the structural strain requirements.(3)When the thickness of the grating is 0.35 m,the maximum displacement of the grating is the front part of the horizontal grating;when the thickness of the grating is0.25 m and 0.15 m,the maximum displacement of the grating is shifted to the middle of the straight grating(decreasing from the middle to the surrounding),i.e.,both meet the requirements of structural displacement response.In short,when the grille thickness is 0.35 m,the grille opening rate of 34% is placed in the middle and rear of the force sink or the grille opening rate in the middle of the force sink is adjusted to 40%,and the grille thickness continues to decrease to 0.25 m and 0.15 m,which can meet the structural stress,strain and displacement response requirements by increasing the opening rate and shifting the grille position backward.