Estimation of hydrodynamic loads acting on downstream fastening plates of low-pressure tubular structures

Abstract

In the article are presented the results of the state analysis of low-pointed tubular culverts widely used in land reclamation and fisheries construction, the lower pool of which is made in the form of an expanding socket with a central angle of 300 to 600 and checker-type energy absorbers. Field surveys have shown that only in the Moscow region such structures, built mainly in the 60-70s of the last century, makeup 76% of the total number of structures on water systems. The condition is from 70% to 85% of them, depending on the region unsatisfactory: the dampers are deformed and even shifted, the lining of the water break and the apron is destroyed, excessive erosion is observed in the discharge channel. The results of experimental studies of the averaged and pulsating pressure on the downstream attachment elements (the bottom of the water break in the flooded hydraulic jump zone and the initial sections of the apron), performed at Reynolds numbers (20...75) 103 on a model installation of a 3-point sluice-regulator, showed that a change in the angle of the bell and the energy parameter within 1.5...4.5 does not affect the nature of the longitudinal and transverse distribution diagrams of the average pressure in the bell and behind it. As a result, universal schemes of static loading by a vertical averaged load from a surface flow have been developed. In the discharge channel and on the slopes, the pressure fluctuation occurs mainly due to surface disturbance; therefore, a low-frequency component is traced on the autocorrelation functions, which also determines the spectrum's shape. It is proved that when constructing a quasi-static loading of plates by an instantaneous pulsating load for an expanding water break with triangular spreaders and checker-type dampers, it is possible to correctly use the longitudinal and transverse correlations corresponding to spatial turbulence and on the apron-homogeneous. The maximum amplitude of the pulsating load on plates of any size should be calculated with a transition coefficient equal to approximately 3.85 for apron plates and no more than 4.5 for water breakage. The results obtained make it possible to perform the entire complex of calculations to assess the stability of various elements of the downstream structures of the considered typology.