Enhanced Feature Extraction Algorithms Using Oscillatory-Mode Pulsed Eddy Current Techniques for Aircraft Structure Inspection

A review of the existing literature shows that modern pulsed eddy current (PEC) technique for flaw detection in aircraft structure inspection is typically carried out in aperiodic mode. Аt the same time, the unstable characteristic points of the EC signal usually used as informative parameters can restrict the potential of this excitation mode due to significant measurement errors. This article considers an advanced PEC method of NDT based on the oscillatory mode. To obtain the conditions concerned with different modes of EC probe response oscillations, an equivalent scheme of the “testing object – EC probe” system was developed and analyzed. The frequency and attenuation coefficient of natural oscillations are proposed as the informative parameters of the probe signals. The obtained mathematical model of the probe signals allows for the dependence of proposed signal parameters on the characteristics of the testing object to be evaluated. Herein, we first develop algorithmic software for determining and analyzing the discrete amplitude and phase characteristics of PEC NDT signals based on the simulation results. The errors of the natural frequency oscillations and the attenuation coefficient determination as well as the optimal time for its determination are analyzed in order to minimize the possible errors. Next, the proposed informative parameters are experimentally investigated using a set of specimens. The obtained results confirm the possibility of the proposed methodology to enhance the inspection procedures related to the electrical conductivity and geometric parameters measurements as well as the detected defect sizing.

Weakly Nonlinear Double-Diffusive Oscillatory Magneto-Convection Under Gravity Modulation

An imposed time-periodic gravity field effect on double-diffusive magneto-convection for oscillatory mode has been investigated. The gravity field consisting of steady and periodic modes. A layer is confined with an electrically conducting fluid with Boussines q approximation and heated from below cooled from above. While using the perturbation technique we study nonlinear double-diffusive convection just above the critical state of the onset convection. The growth rate of the disturbances is confined with a critical Rayleigh number to investigate oscillatory convection. Analysis of finite- amplitude convection has been derived through the complex Ginzburg-Landau equation (CGLE). The convective heat and mass transfer obtained through CGLE at third-order under solvability conditions. This convective amplitude is required to estimate heat and mass transfer in terms of the Nusselt and Sherwood numbers. It is found that increasing the frequency of modulation causes diminishing heat and mass transfer. The effect of Prandtl number Pr, magnetic Prandtl number Pm, and amplitude δ enhances heat/mass transfer. It is found that an oscillatory mode of convection enhances the heat and mass transfer than the stationary mode. Further, streamlines, isotherms, and isohalines have their usual nature on double-diffusive magnetoconvection.

INVESTIGATION OF AN ELECTROMAGNETIC TWO-STROKE VIBRATING ACTIVATOR IN OSCILLATORY MODE

The article considers the results of the study of electromagnetic vibration exciter with sequentially included capacitor in the electrical circuit, consisting of mechanical and electrical subsystems. It is shown that by means of the Lagrangian-Maxwell equation the interconnection between mechanical and electric subsystems can be realized. The relations describing processes of establishment of amplitudes and phases of oscillations both in mechanical and in electric subsystems are deduced. The equations connecting the output (amplitude) of vibration of the vibrating exciter with its input (voltage) of the network are presented. As a result, the formulas allowing making corrections at the solution of the system describing operation of the electromagnetic vibrating exciter in two-stroke mode are presented.

The Complex Ginzburg Landau Model for an Oscillatory Convection in a Rotating Fluid Layer

A weakly nonlinear thermal instability is investigated under rotation speed modulation. Using the perturbation analysis, a nonlinear physical model is simplified to determine the convective amplitude for oscillatory mode. A non-autonomous complex Ginzburg-Landau equation for the finite amplitude of convection is derived based on a small perturbed parameter. The effect of rotation is found either to stabilize or destabilize the system. The Nusselt number is obtained numerically to present the results of heat transfer. It is found that modulation has a significant effect on heat transport for lower values of ωf while no effect for higher values. It is also found that modulation can be used alternately to control the heat transfer in the system. Further, oscillatory mode enhances heat transfer rather than stationary mode.