When the power transformer is connected to the power grid, a surge of inrush current may occur as a result of residual flux. In order to mitigate this effect, measurement of residual flux is necessary. In this paper, a method for measuring the residual flux of ferromagnets was proposed, utilizing magnetic sensors and a finite element model. Residual flux originated from residual magnetization, which could be obtained from a matrix of spatial magnetic flux density measured by sensors and the conversion matrix calculated from the finite element model. By combining the residual magnetization with the background magnetic field, the residual flux could be determined. Experimental results confirmed the accuracy of the proposed method, which was particularly suited for measuring non-uniform residual flux, and also enabled determination of residual flux direction. In comparison to existing methods, this approach offered significant advantages.

The degaussing process is crucial for ensuring magnetic protection in ships. It involves the application of oscillating and attenuating magnetic fields to eliminate residual magnetism in the ship’s structure. However, this process can lead to the generation of distorted magnetic fields within the ship’s cabin, posing a potential threat to electronic equipment performance. Therefore, it is essential to have a comprehensive understanding of the dynamic magnetic field response in ship structures to develop effective degaussing systems. To address this need, this paper proposes an eddy current model for analyzing the dynamic magnetic field response in ferromagnetic metal structures. This model focuses on the role of eddy currents in shaping the magnetic field response and provides valuable insights into the underlying mechanisms. Using the proposed eddy current model, the effects of key system parameters such as thickness, conductivity, and the length-scale of the ship structure can be analytically investigated. This analysis helps in understanding how these parameters influence the dynamic magnetic field response and aids in the design and optimization of degaussing systems. The effectiveness and applicability of the proposed eddy current model are demonstrated through comprehensive investigations involving two simulation cases of varying complexity. The model accurately predicts the changing trends of the dynamic magnetic field response, as confirmed through finite element simulations. This validation highlights the model’s ability to reproduce simulation results accurately and its potential as a powerful tool for analyzing and optimizing dynamic magnetic field responses. In summary, the proposed eddy current model represents a significant advancement in the field. It provides a valuable theoretical framework for understanding and analyzing the dynamic magnetic field response in ferromagnetic metal structures. By offering insights into the underlying mechanisms and the influence of key parameters, this research contributes to the development of improved degaussing systems and enhances the overall magnetic protection capabilities of ships.

Magnetic field generated by ferromagnetic materials of underwater detectors varies with seawater pressure, which affects the accuracy of deep-sea resource exploration. Therefore, to precisely simulate the influence of deep-sea pressure on the magnetic field around the underwater detectors, a magneto-mechanical numerical model must be developed. In this paper, a magneto-mechanical coupling model of an oxygen tank was developed in COMSOL Multiphysics. Hysteresis curves of 37Mn-type steel were measured with Superconducting Quantum Interference Device, on which Jiles-Atherton parameters were identified. Initial magnetization of the oxygen tank was calculated according to the obtained conversion matrix and flux density matrix measured by sensors. Furthermore, the concept of equivalent mean field parameter was introduced to describe the magneto-mechanical coupling effect of ferromagnets by improving Jiles-Atherton theory, and three equivalent mean field parameters of 37Mn-type steel were obtained. The irreversibility of magnetization and relationship between the pressure and the spatial magnetic field were experimentally obtained and verified. With the escalation of inner pressure and the augmentation of the stress cycle number, reduction in the spatial magnetic field components occurred. The spatial magnetic field components demonstrated an approximate quadratic relationship with the pressure, while exhibiting an approximately linear association with the stress cycle number.

The initial workpiece diameter is one of the most fundamental process parameters in sheet metal forming, as it determines the resistance of the draw-in material flow. In the context of conventional deep drawing, its critical role has been clearly identified. In the context of electromagnetic sheet forming, however, its role has not yet been adequately addressed. This paper aims to clarify its role, by experimentally and numerically investigating the deformation behavior of circular sheet metal in electromagnetic forming. Various combinations of the initial diameter and discharge voltage were established to induce different deformation behaviors. It was found that adjusting the initial diameter can substantially change the forming height, shape, and thickness distribution by altering the draw-in, which suggests a great improvement in deformation controllability. In summary, this study demonstrates that the initial workpiece diameter could play critical role in deformation control in electromagnetic forming.

Under the DC field, live contamination is more likely to deposit on the surface of insulators due to the action of the external electric field. The deposition of dirt on the surface of Ultra High Voltage (UHV) insulators can lead to the occurrence of flashover phenomena, causing significant economic losses. Due to the particularity of UHV insulators, many traditional surface anti-pollution technologies designed for normal voltage insulators are not applicable to them. In order to prevent the harm of contamination accumulation affecting the safe operation of transmission lines, in this study, tetragonal BaTiO₃ was mixed into room-temperature vulcanized silicone rubber for the first time to prepare a composite coating with piezoelectric properties. This coating can use the piezoelectric effect to remove the contamination adhering to the surface of UHV insulators under a DC field. In this study, the piezoelectric properties of the prepared tetragonal BaTiO₃ were verified through material characterization. The results show that the introduction of piezoelectric fillers can significantly accelerate the dissipation of charges on the insulator surface under slight disturbances, which helps to reduce the accumulation of charged pollutants on the insulator surface. The anti-pollution performance under electric field conditions was verified through a simulation experimental device. Finally, through experiments in a real converter station environment, the anti-pollution effect of the insulator under actual working conditions was verified.

The time-varying magnetic field characteristics during the demagnetization process of complex ferromagnetic cavity structures were studied based on computational electromagnetic simulation. By establishing a simulation model of the complex ferromagnetic cavity structures and the magnetic field generation coil, the main factors affecting the time-varying magnetic field characteristics were analyzed and explained, including eddy current effects, hysteresis effects, material properties of the complex ferromagnetic cavity structure, and structural gap connections. The magnetic field amplitude at typical locations was investigated, and the temporal variation of the internal magnetic field was analyzed. Additionally, the evolution motion of eddy currents during the dynamic demagnetization process was simulated. It was found that the aforementioned factors significantly affect the internal magnetic field of the complex ferromagnetic cavity structures during the demagnetization process, and their influences intertwine, resulting in complex time-varying characteristics. Through theoretical analysis and numerical simulation, the mechanisms and rules of these influences were revealed. The research findings provide important references for optimizing the demagnetization process, improving demagnetization effectiveness, and developing equipment-level magnetic field protection criteria and design.