Transient Magnetic Field Research Articles

Finite-Element Analysis of Pulsed High-Field Magnets With Precise Thermal and Structural Calculations

The design of high-performance pulsed high-field magnets strongly depends on accurate thermal and structural analyses. In this article, a 2-D multi-physical simulation method for pulsed magnets based on the ANSYS is presented. The skin effect of the coil in a transient magnetic field and the magneto-resistance (MR) effect are considered using ANSYS-parameter design language (APDL). The induced voltage is calculated by the magnetic-penetration method to realize the transient field coupling between the coil and circuit. The MR effect is considered as an additional equivalent heat source. Contact pairs are used to simulate discontinuous boundary and axial compression. The simulated pulse waveform agrees well with the experimental results. Simulations show that the skin effect and MR will increase the maximum temperature by 40%. The contact state between layers in the axial direction is analyzed in detail, which increases the accuracy of stress calculation compared to the existing 1-D programs. The design accuracy of a 90 T magnet is improved effectively using the proposed method.

Magnetic Field Expulsion From a Conducting Projectile in a Pulsed Serial Augmented Railgun

The bore of a railgun is a harsh environment with high transient magnetic fields, temperature gradients, and forces. Most common payloads in railgun launch are made from conductive materials. In this article, we consider the effects of the transient magnetic field on a conducting payload during an electromagnetic launch by a serial augmented hexagonal railgun. The magnetic field distribution in the proximity of a solid aluminum payload was investigated by numerical calculations and experimentally by using a CMR-B-scalar sensor array.

Effect of Magnetic Field on Dilepton Production Rate in Relativistic Heavy Ion Collisions

It is believed that a transient strong magnetic field is generated in heavy-ion collision. The strength of this field perpendicular to the reaction plane and is estimated to be around eB=0.03GeV2 at RHIC and eB=0.3GeV2 at LHC. We study the effect of this magnetic field on dilepton yield using a modified quasi particle model. The results show a clear enhancement in dilepton yield and our result is in good agreement with the recently reported results.

Measurement of Transient Magnetic Field caused by ESD between Spherical Electrodes using a Shielded Loop Probe and Current Estimation of EM Radiation Model

Measurement of Transient Magnetic Field caused by ESD between Spherical Electrodes using a Shielded Loop Probe and Current Estimation of EM Radiation Model

Research on the Influence of Vibrations on the Dynamic Characteristics of AC Contactors Based on Energy Analysis

Aimed at the influence of the vibration environment on the performance degradation of AC contactors, the purpose of this study is to investigate the failure mechanism of AC contactors under vibration conditions. During the closing process of AC contactors, the impact energy of the iron core may change due to the vibration stress, which may have an uncertain effect on the parameters of the dynamic response characteristics of the contact, and affect the working performance and service life of AC contactors. In this paper, a double-E AC contactor is selected as the research object. Based on the calculation of the transient magnetic field of the electromagnetic mechanism, an energy distribution model of the AC contactor is established. Based on this, considering the influence of vibrations and the input electrical energy under different closing phase angles, the energy model of the iron core collision under simple harmonic oscillation is investigated. The steady-state vibration energy at different frequencies and accelerations is calculated, and its influence on the dynamic response parameters of the AC contactor is analyzed. Finally, the simulation model is verified by experimental data. The results show that the energy analysis model can effectively reflect and explain the uncertainty of the dynamic characteristics of AC contactors under vibrations, from the perspective of the mechanism.

A study of high transient voltage unit realization uncertainty

The problem of metrological support of high-voltage pulse generators with subnanosecond rise time, as well as pulse voltage dividers used in power engineering, aviation and rocket-space industries, has been solved. As a result of the modernization of the State primary special standard of transient electric and magnetic field strengths units with a pulse rise time in the range of 0.1–10.0 ns GET 148-2013, a mode of realization a unit of high transient electric voltage with a minimum pulse rise time of 100 ps was implemented. Uncertainties of high transient electric voltage unit realization obtained by numerical simulations using the Monte Carlo method, as well as in accordance with the Guide to the Expression of Uncertainty of Measurement (GUM), are estimated. Also, the error of a unit realization was estimated in accordance with GOST 8.381-2009 “GSI. Standards. Methods to Express Accuracy”.

Transient magnetic field formulation for solid source conductors

The formulation for the azimuthal component of the magnetic vector potential for axisymmetric magnetostatic applications is well known. However for transient magnetic fields with solid source conductors and eddy currents the formulation has to be revised. A variable transformation is introduced to remove the singularity from the numerical scheme. The numerical error cannot accumulate and is put instead to the postprocessing at every time step.

G-factors of some excited states in 49,50Cr

Magnetic moments of the first excited states in 50Cr and of the 7/2" and 19/2' states in 49Cr, have been measured by the transient field technique. The states were excited by the inverse reaction 40Ca + 12C and the recoil nuclei traversed a thick gadolinium foil. The observed rotations, of the 2+, 4+, 6+, 8+ states of the ground-state band in 50Cr, were found into the experimental error to be the same, suggesting similar g-factors for these states and thus supporting a high collectivity for the ground-state band, g-factors of the 7/2' and 19/2 states in 49Cr, were deduced by adopting both an overall parametrization of the transient magnetic field in Gd and by comparing the 49Cr rotations with rotations of states with known magnetic moments, as the 2+ ones of 50Cr and of 46Ti which was also populated in the same reaction. Both methods gave similar results and the g-factors adopted for the 19/2" and 7/2" states were + 0.78(17) and +0.35(7) respectively. These results are discussed in terms of cranked shell model calculations and are found to support a proton alignment in the f7/2 shell.

Simulations of magnetic fields produced by asteroid impact: Possible implications for planetary paleomagnetism

The origin and evolution of the Moon's magnetic field, specifically whether it has an endogenic or exogenic origin, has been a major question in lunar science. The lunar field today is a patchwork of magnetic anomalies carried as remnant magnetization in the rocks of the lunar crust. Recent publications suggest some magnetic anomalies may be associated with magnetized impact melt sheets of some large lunar basins cooling in the presence of an early lunar core dynamo or associated with portions of the impactor that formed the South Pole-Aitken Basin. By performing CTH simulations of asteroid impacts incorporating magnetic field generation and thermoremanence magnetization models, this paper helps explain the origin of lunar magnetic anomalies by showing: 1) transient magnetic fields produced by impact events will increase to substantial magnitude at the scale of large lunar basins and 2) magnetization of lunar rocks can occur during crater formation at nearly all scales. If occurring in pristine feldspathic lunar highlands rocks with relatively low thermoremanence susceptibility, the magnetic anomalies resulting from (1) and (2) produce magnetic fields observable in orbital magnetic field data only for large and relatively rare impact craters - large lunar basins greater than ~200 km diameter. If occurring in thick units with higher thermoremanence susceptibility, craters as small as 50–100 km may produce orbital anomalies. Craters at nearly all scales may leave behind remnant magnetic fields observable at the surface or in samples. This paper concludes magnetic fields produced by impacts may be an important contributor to the present state of the Moon's magnetic field.

Modelling of scanning pulsed eddy current testing of normal and slanted surface cracks

<p><span style="font-family: Arial; font-size: small;">Thanks to its wide bandwidth, pulsed eddy current (PEC) has attracted researchers of various backgrounds in the attempt to exploit its benefits in Non-destructive Testing (NDT). The ability of modelling PEC problems would be a precious tool in this attempt as it would help improve the understanding of the interaction between the transient magnetic field and the specimen, among others. In this work, a Finite Element Modelling (FEM) has been developed and experimental test data have been gathered for its validation. The investigated cases were simulated surface cracks of different sizes and angles. The study involved looking at time-domain PEC signals at different spatial distances from the cracks’ faces, which would particularly be useful for modelling scanning PEC probes. The obtained results show a good agreement between the FEM and experiment, demonstrating that the modelling technique can be used with confidence for solving similar problems.</span></p>

Simulation and optimisation design of the solenoid valve

This study first analyses the problems that the solenoid valve generates during operation. Then the electromagnetic valve was modelled and ANSYS finite element analysis simulation software was used to simulate the electromagnetic field and transient magnetic field of the solenoid valve. The magnetic induction intensity distribution diagram and magnetic field distribution diagram of the electromagnet were obtained. According to the simulation results of the solenoid valve, the magnetic flux leakage line is blocked after the magnetic isolation cover is added, the magnetic induction strength of the iron core and the valve head is increased, the leakage magnetic flux is reduced, and the structure is optimised.

Increasing Detection Resolution of Wire Rope Metallic Cross-Sectional Area Damage Based on Magnetic Aggregation Structure

Wire rope is a chain structure, and the strength of the weakest link is the strength of the entire wire rope. The axial resolution of loss of metallic cross-sectional area (LMA) detection using the induction coil is related to the length of the detection probe, which is usually greater than or equal to the length of the probe. Improving the axial resolution is an important technical indicator of the LMA. In this article, through theoretical analysis based on the principle of magnetic aggregation and 3-D transient magnetic field simulation, a particular kind of magnetic aggregation structure used for winding coil is proposed and optimized. Simulation and experimental results show that for wire rope LMA detection adding the proposed magnetic aggregation structure, the defect signals’ signal-to-noise ratio (SNR) is improved and the axial resolution of the LMA is increased to 20 mm. At the same time, the cross-sectional area loss can be quantitatively evaluated by the magnetic flux peak-to-peak value. The difference between the maximum and minimum values of the derivative of the magnetic flux signal can be used to evaluate the defect length.

Design of Heading Fault-Tolerant System for Underwater Vehicles Based on Double-Criterion Fault Detection Method

This paper proposes a heading fault tolerance scheme for operation-level underwater robots subject to external interference. The scheme is based on a double-criterion fault detection method using a redundant structure of a dual electronic compass. First, two subexpansion Kalman filters are set up to fuse data with an inertial attitude measurement system. Then, fault detection can effectively identify the fault sensor and fault source. Finally, a fault-tolerant algorithm is used to isolate and alarm the faulty sensor. The program can effectively detect the constant magnetic field interference, change the magnetic field interference and small transient magnetic field interference, and conduct fault tolerance control in time to ensure the heading accuracy of the system. Test verification shows that the system is practical and effective.

Fabrication and mechanical behaviors of iron–nickel foam reinforced magnetorheological elastomer

Magnetorheological elastomers (MREs) have excellent magnetic-control mechanical properties, which ensures its great engineering application value in the field of vibration control. In this paper, the iron–nickel foam (INF) reinforced MREs with excellent magnetorheological (MR) properties were developed. The soft magnetic properties and three-dimensional (3D) foam structure of INF ensure an effective enhancement on the magnetic-control mechanical properties of MRE. The static and dynamic mechanical properties of the MRE were tested based on a parallel plate rheometer. Among them, static compression tests were carried out to study the static mechanical properties of MREs. The test results showed that INF reinforced MREs have excellent magneto-induced compression modulus. The effects of magnetic field, shear strain, and frequency on the dynamic mechanical properties of MREs have studied by the dynamic oscillatory shear tests. The test results revealed that the MRE has excellent MR properties under small strain. In addition, several successive tests were conducted to evaluate the response behavior under transient magnetic field and hysteresis properties of MREs under periodic magnetic field, and no obvious hysteresis in the repeated test curves have been observed. The INF reinforced MRE studied in this paper has potential application prospects in the field of micro-vibration control.

Gyrotropic slab waveguide coupled silica microfiber-based magnetic field sensor

Intensive transient magnetic field measurement is highly necessary in modern electric power systems. In this paper, a novel compact microfiber-based magnetic field sensor for real-time detection of intense magnetic field is presented. The sensor consists of a silica microfiber with an attached gyrotropic slab waveguide. By the exploration of the magnetic-optic Kerr effect of the gyrotropic slab, the variations of its refractive index under an external magnetic field leads to the coupling spectrum of the sensor shifting. Using this probe, static magnetic fields with strengths up to 2 T and square waveform signals with rise times of 5 ms were successfully measured.

Simulation and Measurements of Transient Fields From Conductive Plates of Shielded Room for SQUID-Based Ultralow Field Magnetic Resonance Imaging

In order to enhance the signal-to-noise ratio (SNR) of ultralow field magnetic resonance imaging (MRI) measurements, a prepolarization ( B p) coil is usually introduced to generate a magnetic field with magnitude in the order of tens of mT or even stronger to prepolarize the sample before MRI sequences. The macromagnetization M of the sample is now directly determined by the B p strength, thus the SNR is effectively improved. However, the rapid turn-off of B p current induces eddy currents in the conductive shielded room and the surrounding conductors, which in turn causes unwanted transient magnetic fields in the imaging area. In this paper, according to the relative position of the B p coil and the shielded room, two physical models of the conductive shielded room are described to simulate the transient fields at the sample position: the B p coil plane parallel to the ceiling and floor of the shielded room, and the coil plane perpendicular to the walls. The simulation is in good agreement with the experimental results. This paper will help us design the structure of the conductive shielded room as well as develop the eddy current cancellation technique.

Sub-Line Transient Magnetic Fields Calculation Approach for Fault detection, classification and location of High Voltage Transmission Line

Sub-Line Transient Magnetic Fields Calculation Approach for Fault detection, classification and location of High Voltage Transmission Line

A regularised-adaptive Proper Generalised Decomposition implementation for coupled magneto-mechanical problems with application to MRI scanners

Latest developments in high-strength Magnetic Resonance Imaging (MRI) scanners with in-built high resolution, have dramatically enhanced the ability of clinicians to diagnose tumours and rare illnesses. However, their high-strength transient magnetic fields induce unwanted eddy currents in shielding components, which result in fast vibrations, noise, imaging artefacts and, ultimately, heat dissipation, boiling off the helium used to super-cool the magnets. Optimum MRI scanner design requires the capturing of complex electro-magneto-mechanical interactions with high fidelity computational tools. During production cycles, this is known to be extremely expensive due to the large number of configurations that need to be tested. There is an urgent need for the development of new cost-effective methods whereby previously performed computations can be assimilated as training solutions of a surrogate digital twin model to allow for real-time simulations. In this paper, a Reduced Order Modelling technique based on the Proper Generalised Decomposition method is presented for the first time in the context of MRI scanning design, with two distinct novelties. First, the paper derives from scratch the offline higher dimensional parametrised solution process of the coupled electro-magneto-mechanical problem at hand and, second, a regularised adaptive methodology is proposed for the circumvention of numerical singularities associated with the ill-conditioning of the discrete system in the vicinity of resonant modes. A series of numerical examples are presented in order to illustrate, motivate and demonstrate the validity and flexibility of the considered approach.

Numerical investigation of influence of different underexcited operations on temperature distribution in the large turbine generator end domain with copper screen

Overheating of the complex end parts has become one of the main problems affecting safe and stable turbine generator operation under the underexcited operation. In order to study the temperature distribution in the large turbine generator end domain with copper screen under the different underexcited operations, a 330 MW turbine generator is studied. Three-dimensional fluid-thermal coupling model for the end domain of turbine generator is established. Three-dimensional transient magnetic field of the large turbine generator end domain with copper screen is calculated with 0.85 pf underexcited operation and 0.9 pf underexcited operation. Loss values of the end metal parts from the three-dimensional transient magnetic field are applied to end domain as heat source with 0.85 pf underexcited operation and 0.9 pf underexcited operation. Outlet-pressure values and fan inlet velocity from flow network calculations are applied to the end domain as boundary conditions in the fluid and thermal coupling analysis. The three-dimensional fluid and thermal fields in the turbine generator end domain are calculated with 0.85 pf underexcited operation and 0.9 pf underexcited operation. Distribution of the radial fluid velocity component around the stator winding is determined. Temperature distribution of the end metal parts in the large turbine generator end domain with copper screen is studied with 0.85 pf underexcited operation and 0.9 pf underexcited operation. Temperature calculation results of the copper screen are compared with measured values. Calculation results are in good agreement with measured values.

Electromagnetic analysis of composite structures subjected to transient magnetic fields

When carbon composites are exposed to a transient electromagnetic field, a rapid temperature increase can be observed due to joule heating from magnetic induction. The electromagnetic induction heating and heat transfer in the composite are anisotropic and concentrated upon the carbon fiber orientation and distribution. In addition, the strength and frequency of transient electromagnetic fields have great influence on the final quality of the composite. A computational model has been developed by solving coupled Maxwell’s and heat transfer equations. The analysis accounts for the three-dimensional transient electromagnetic field and electrical conductivity of the composite material. This paper will illustrate the derived formulation and numerical solution based on finite element methods. The developed code is validated with a 2D closed-form solution. Numerical simulations of a cylinder and a flat laminated plate are conducted to illustrate the computational capability. The induction heating for composite manufacture is also discussed for current Army’s applications.