CALCULATION-EXPERIMENTAL SUBSTANTIATION OF VIBRATION STRENGTH OF NUCLEAR POWER PLANT PIPELINES BASED ON THE QUASI-STATIC APPROACH

In accordance with NP-096-15 [1], management of equipment and pipelines resources at the stages of design, operation and decommissioning should be based on the evaluation of the technical condition and residual life; identifi cation of the dominant (controlling) mechanisms of aging, degradation and damage of equipment and pipelines of nuclear power plants (NPP); the constant improvement of monitoring processes of aging, degradation and damage of equipment and pipelines of nuclear power plants. Despite the progress in computer development in recent decades, its capabilities are still insuffi cient to solve equations of hydrodynamics when high Re numbers are of practical interest (solution instability: arbitrarily small perturbation radically alters the stability of the solution of the Navier-Stokes equations). Challenges remain in the verifi cation of CFD codes. Due to the complex spatial confi guration of diff erent functional purpose piping systems of NPPs, as well as the specifi cs of the hydro-elastic interaction of the fl ow and tubing, calculation methods to evaluate the dynamic stress-strain state can be selected only based on the results of experimental measurements of vibration parameters of pipelines. The vibration parameters of the pipelines are the vibrational acceleration, velocity and displacement. Vibration of piping from the point of view of resource is classifi ed as high cycle fatigue, which, due to its specifi cs, requires adopting conservative approaches in substantiation of vibration strength of pipelines. As the pipelines are operating within the elastic deformation, the strength test with time-dependent load can in some cases be replaced with a quasistatic calculation. A numerical experiment illustrates the application of the quasistatic approach that gives satisfactory results. Substantiated application of the quasistatic approach is based on the analysis of the spectral density of the pipeline vibration at diff erent points of measurement and can be eff ectively used to assess vibrostresses, fracture toughness and substantiation of vibration strength of NPP pipelines.

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