A. R. Alexiev

Bio: A. R. Alexiev is an academic researcher from Bulgarian Academy of Sciences. The author has contributed to research in topics: Finite element method & Longitudinal wave. The author has an hindex of 1, co-authored 2 publications receiving 7 citations.

Numerical Simulation of Ultrasonic Torsional Guided Wave Propagation for Pipes with Defects

Abstract: Long-range ultrasonic guided waves are widely used for the detection of defect founded in the long distance pipeline. Numerical simulation of guided wave propagation is considered for an experimental pipe with various forms of defects. The pipe is subjected to the propagation of the torsional guided wave . Numerical models are constructed for a sample pipe without defect and two sample pipes with two different types of defects: a notch and a notch with a hole. The desired T(0, 1) guided wave is simulated by a special excitation pressure function applied to one end of the pipe, which spreads via shearing motion parallel to the circumferential direction. Finite element software ANSYS is used to build 3D solid and finite element models of the sample pipes and perform full transient analysis. The simulation results allow obtaining information on the amplitude and the transit time of the impulse reflected from the defect and from the end of the pipe. The results also include the investigation of influence of the length and depth of the notch on the stress-strain state of the pipe.

Interaction of Low-Frequency Guided Waves with Discontinuities

Abstract: Modern methods of ultrasonic nondestructive testing allow one to detect defects in pipes with the help of guided ultrasonic waves. This chapter studies the propagation of longitudinal and torsional ultrasonic low-frequency guided waves in a pipe with discontinuities and defects. The defects considered for investigations include notches, holes, and their combination. Solid and finite element numerical models are developed for a sample pipe without defect, and for sample pipes with various types of defects. In order to simulate the propagation of ultrasonic guided waves in an isotropic medium, an excitation load is applied to one end of the pipe. For longitudinal guided waves simulation, the load vector is directed along the length of the pipe, and for torsional guided waves simulation, the load vector is directed tangentially to the circumference of the pipe. The results of the simulations allow us to estimate the amplitude and transit time of the impulse reflected from the defect and to analyze how various defects influence the stress–strain state of the pipeline.

Detection, Localisation and Assessment of Defects in Pipes Using Guided Wave Techniques: A Review.

Abstract: This paper aims to provide an overview of the experimental and simulation works focused on the detection, localisation and assessment of various defects in pipes by applying fast-screening guided ultrasonic wave techniques that have been used in the oil and gas industries over the past 20 years. Major emphasis is placed on limitations, capabilities, defect detection in coated buried pipes under pressure and corrosion monitoring using different commercial guided wave (GW) systems, approaches to simulation techniques such as the finite element method (FEM), wave mode selection, excitation and collection, GW attenuation, signal processing and different types of GW transducers. The effects of defect parameters on reflection coefficients are also discussed in terms of different simulation studies and experimental verifications.

Forced vibration analysis of composite-geometrically exact elliptical cone helices via mixed FEM

Abstract: In this pioneering study, the cross-sectional warping included transient response and normal/shear stress components of composite elliptical and elliptical cone helices over exact axis geometry are...

Research of non-destructive testing for aluminium sheaths of HV cables using ultrasonic-guided waves

Abstract: The method of fast non-destructive testing for aluminium sheaths of high-voltage (HV) cables using ultrasonic-guided waves is proposed. The dispersion curve is calculated by solving the dispersion equation from the simplified model of aluminium sheaths of HV cables; thus, the appropriate wave mode and excitation frequency can be chosen. Three defects including crack, perforation, and sag have been set up. Then, the simulation experiments have been carried out for aluminium sheaths of HV cables based on the theoretical analysis and finite element simulation. The results show that cracks with the loss ratio of the sectional area over 4.25% can be detected by the T (0, 1) mode whose frequency is 32 kHz; the amplitude of the flaw echo increases along with the loss ratio of the crack. Theoretical analysis, finite element simulation, and experiments prove the feasibility of aluminium sheaths using ultrasonic-guided waves, providing a new method for the defect testing.