Huu Kien Bui

The induction welding of a stringer on an aircraft fuselage skin with a lightning strike protection (LSP) on the underside of the skin is considered. The presence of LSP makes electromagnetic welding very difficult because it concentrates most of the power induced and is therefore more strongly heated than the stringer–skin interface. A new technic coupled with numerical approach that consists in inserting an electrically conductive material into the tooling in order to modify the magnetic field distribution and limit the power induced in the LSP is presented. A strongly coupled electrothermal 2-D finite element analysis (FEA) is developed to optimize the temperature profile. The 3-D FEA is then carried out in order to validate the optimum design.

In the field of marine renewable energies, the extraction of marine currents by the use of tidal current turbines has led to many studies. In contrast to offshore wind turbines, the mass minimization is not necessarily the most important criterion. In that case, Direct-Drive Electrically Excited Synchronous Generators (EESG) can be an interesting solution in a context where the permanent magnet market is more and more stressed. In the particular case of a tidal turbine, the electric generator operates at variable torque and speed all the time. Its sizing must therefore take into account the control strategy and check that all the constraints are respected during the working cycle, particularly the thermal one because its permanent regime is never reached. There is no solution today that can completely solve such a sizing problem. The paper presents a specific solution. In particular, we will see that the method presented allows an avoidance of an oversizing of the generator compared to conventional methods while finding the optimal control strategy. Thus, the design optimization of an EESG is conducted considering the variable torque and speed profiles related to marine currents. The analytical model used in the paper is presented at first. In a second step, the innovative and original method that allows solving at the same time the design optimization and the control strategy (dq stator currents and rotor current) are presented. It shows how it is possible to minimize both the lost energy during the working cycle and the mass while fulfilling all the constraints (especially the thermal constraint with its transient temperature response) and keeping a reduced computation time. The case of a 2 MW tidal wave turbine is chosen to illustrate this study. Finally, the optimal design selected is validated by a 2D magnetic Finite Element Analysis (FEA).

This work aims to compare quantitatively different nondestructive testing (NDT) techniques and data fusion features for the evaluation of adhesive bonding quality. Adhesively bonded composite-epoxy single-lap joints have been investigated with advanced ultrasonic nondestructive testing and induction thermography. Bonded structures with artificial debonding defects in three different case studies have been investigated: debonding with release film inclusion, debonding with brass film-large, debonding with brass film-small. After completing preprocessing of the data for data fusion, the feature matrices, depending on the interface reflection peak-to-peak amplitude and the principal component analysis, have been extracted from ultrasonic and thermography inspection results, respectively. The obtained feature matrices have been used as the source in basic (average, difference, weighted average, Hadamard product) and statistical (Dempster–Shafer rule of combination) data fusion algorithms. The defect detection performances of advanced nondestructive testing techniques, in addition to data fusion algorithms have been evaluated quantitatively by receiver operating characteristics. In conclusion, it is shown that data fusion can increase the detectability of artificial debonding in single-lap joints.

This paper presents a fast-numerical approach to optimize the localization of induced power in highly anisotropic composite materials with a large-scale factor. A one-dimensional hybrid multi-physical tool allows us to find the best ply sequence and the best strategy to constrain the induced currents to circulate in an interest area defined respecting specific temperature objectives. A three-dimensional multi-physical modeling is then used on a few selected candidates to refine results.

This paper aims to present a lightened 3D finite element model (FEM) for coupled electromagnetic thermal simulation of the induction thermography non-destructive testing (NDT) technique to reduce the computation time. The time harmonic electromagnetic problem is expressed in A – ϕ formulation and lightened by using the surface impedance boundary condition (SIBC) applied to both the massive induction coil surface and the surface of conductor workpiece including open cracks. The external circuit is taken into account by using the impressed voltage or the impressed current formulation. The thermal diffusion in the workpiece is solved by using surface electromagnetic power density as thermal source. The accuracy and the usefulness of the method for the design of the induction thermography NDT technique have been shown with acceptable deviation compared with a full FEM model. It is also observed that at high frequency, when the ratio between the local radius of the conductor and the skin depth is high, a very good accuracy can be obtained with the SIBC methods. At lower frequency, the effect of the curvature of the surface becomes significant. In this case, the use of the Mitzner’s impedance can help to correct the error. The SIBC can be used for both massive coil and workpieces with open cracks to alleviate 3D FEMs of the coupled electrothermal model. The implementation in matrix form of the coupled electrothermal formulation is given in details. The comparisons with reference analytical solution and full 3D FEM show the accuracy and performance of the method. In the test case presented, the computation time is 6.6 times lower than the classical model.

This paper presents a fast numerical approach to optimize the localization of induced power in highly anisotropic composite materials with a large scale factor. A one-dimensional hybrid multi-physic tool will allow to find the best ply sequence and the best strategy to constrain the induced currents to circulate in an interest area defined regarding to specific temperature objectives. A three-dimensional multi-physical modeling is then used on a few selected candidates to refine results.

This paper discusses the possible non-destructive testing (NDT) techniques for a novel bonding quality evaluation technique based on comparison of different inspection methodologies. The goal of this paper is to guide a way for bonding quality evaluation with high reliability by comparing different NDT techniques including ultrasonic, electromagnetic, and thermography. The advantages and limitations of each different NDT technique have been reported systematically. Two case studies have been investigated with two different NDT techniques, namely ultrasonic and induction thermography. The results suggested the limitations and advantages of NDT techniques. In order to compensate the limitations of each technique, data fusion of the selected techniques is proposed.

This paper presents an Abrupt Change Detection (ACD) algorithm based on Mathematical Morphology Gradient (MMG) for Non-Intrusive Load Monitoring (NILM). In the present research of MMG, it is focused on filtering the original signals rather than locating change points. Therefore, this paper considers this approach to detect abrupt changes. For the purpose of evaluating the performance of different algorithms, the True Positive Rate (TPR) and the F-score are employed in this paper. The simulation studies have been carried out on low-frequency signals and high-frequency signals from the Reference Energy Disaggregation Data Set (REDD) respectively. The MMG algorithm, which has the advantages of high accuracy and fast calculation speed, is superior for both two types of signals. In addition, it can provide not only the information of the position of a change but also the direction of a change. The results demonstrate that the MMG algorithm shows better performance than the CUmulative SUM (CUSUM), the Bayesian Information Criterion (BIC) and the Generalized Likelihood Ratio (GLR) algorithms.

Numerical simulations by means of finite elements are used to investigate the capacities of the induction thermography technique for the characterization of electrical conductivities of unidirectional Carbon Fiber Reinforced Polymer (CFRP) materials. A coupled electromagnetic-thermal model is presented using hexahedral elements to deal with thin region of fully anisotropic physical properties. Eddy-current problem is solved using the T – Ω formulation to deduce heat source density power. Transient thermal problem is solved with fixed time step. An error minimization-based method is presented to identify the electrical resistivity of unidirectional CFRP from induction thermography measurement.