Resonance failure sensitivity analysis of straight-tapered assembled pipes conveying nonuniform axial fluid by active learning Kriging method

Purpose The purpose of this paper is to study the resonance failure sensitivity analysis of straight-tapered assembled pipe conveying nonuniform axial fluid by an active learning Kriging (ALK) method. Design/methodology/approach In this study, first, the motion equation of straight-tapered assembled pipe conveying nonuniform fluid is built. Second, the Galerkin method is used for calculating the natural frequency of assembled pipe conveying nonuniform fluid. Third, the ALK method based on expected risk function (ERF) is used to calculate the resonance failure probability and moment independent global sensitivity analysis. Findings The findings of this paper highlight that the eigenfrequency and critical velocity of uniform fluid-conveying pipe are less than the reality and the error is biggest in first-order natural frequency. The importance ranking of input variables affecting the resonance failure can be obtained. The importance ranking is different for a different velocity and mode number. By reducing the uncertainty of variables with a high index, the resonance failure probability can be reduced maximally. Research limitations/implications There are no experiments on the eigenfrequency and critical velocity. There is no experiments about natural frequency and critical velocity of straight tapered assembled pipe to verify the theory in this paper. Originality/value The originality of this paper lies as follows: the motion equation of straight-tapered pipe conveying nonuniform fluid is first obtained. The eigenfrequency of nonuniform fluid and uniform fluid inside the assembled pipe are compared. The resonance reliability analysis of straight-tapered assembled pipe is first proposed. From the results, it is observed that the resonance failure probability can be reduced efficiently.

A Two-Dimensional Model of Particle Motion in Ureteral Peristaltic Flow

Physiological fluids in human or animals are, in general, propelled by the continuous periodic muscular contraction or expansion (or both) of the ducts through which the fluids pass, a phenomenon known as peristalsis. Peristaltic mechanisms may be involved in the swallowing of food through the esophagus, vasomotion of small blood vessels, spermatic flows in the ductus efferentes, embryo transport in the uterus, and transport of urine through the ureters, among others [1]. Peristaltic fluid flow can be accompanied by solid particles. In this work the Basset-Boussinesq-Oseen (BBO) equation will be employed to analyze particle motion in peristaltic fluid flow, this model considers motion of a small spherical particle suspended in a nonuniform fluid flow and diverse forces are considered. In ureteral peristaltic flow, fluid being transported is essentially Newtonian and incompressible. Ureteral peristaltic flow is sometimes accompanied by particles such as stones or bacteria. In the present study, the geometrical form of the peristaltic wave will be taken to be sinusoidal. The governing equations are Navier-Stokes for the fluid and momentum for the particle (BBO equation). A regular perturbation series in which the variables are expanded in a power series of the wavenumber (ε = πRw/λ) is used to solve the fluid problem. One-way coupling between the fluid and particles is assumed.

Frequencies in the Vibration Induced by the Rotor Stator Interaction in a Centrifugal Pump Turbine

The highest vibration levels in large pump turbines are, in general, originated in the rotor stator interaction (RSI). This vibration has specific characteristics that can be clearly observed in the frequency domain: harmonics of the moving blade passing frequency and a particular relationship among their amplitudes. It is valuable for the design and condition monitoring to count on these characteristics. A CFD model is an appropriate tool to determine the force and its characteristics. However, it is time consuming and needs highly qualified human resources while usually these results are needed immediately and in situ. Then, it is useful to determine these characteristics in a simple, quick, and accurate method. At present, the most suitable method indicates a large amount of possible harmonics to appear, without indicating the relative importance of them. This paper carries out a theoretical analysis to predict and explain in a qualitative way these frequencies and amplitudes. The theoretical analysis incorporates the number of blades, the number of guide vanes, the RSI nonuniform fluid force, and the sequence of interaction. This analysis is compared with the method currently in use, and both methods are applied to a practical case. The theoretical analysis gives a resulting force over the pump turbine, which corresponds well to the measured behavior of a pump turbine in terms of its frequencies and the relationship between their amplitudes. A corrective action is proposed as a result of the analysis and after it is carried out in one of the units, the vibration levels are reduced. The vibration induced by the RSI is predicted considering the sequence of interaction and different amplitudes in the interactions between the same moving blade and different stationary blades, giving a different and original interpretation about the source of the vibration characteristics. A successful corrective action is proposed as a consequence of this new interpretation.