The accurate calculation and analysis of electromagnetic force waves are especially crucial for comprehensively predicting and weakening the electromagnetic vibration of electrical machines. In this ...study, a fast and accurate calculation method of radial electromagnetic force density of surface-mounted permanent magnet synchronous motor (PMSM) is presented, the radial electromagnetic force density including amplitude, frequency and order is obtained and the accuracy is verified. Comprehensively considering that the effects of the auxiliary slots on cogging torque and torque ripple, the weakening measure of radial electromagnetic force waves by inserting auxiliary slots is research, and the optimal determinations of the number and the structural parameters of auxiliary slots in PMSMs with different slot–pole combinations are summarised, and six PMSMs with 6-pole/36-slot (6p36s), 4p36s, 6p9s, 8p9s, 8p12s and 10p12s are analysed to verify the universality of the conclusions.
Zeroth-order spatial electromagnetic force wave has been regarded as one of the main sources for electromagnetic vibration and noise of integer slot multipole permanent magnet synchronous machine ...(PMSM) used in electric vehicles. In this study, the 48-slot-8-pole built-in permanent magnet synchronous motor for a vehicle was taken as an example. The main sources and characteristic parameters (frequency and amplitude) of the zeroth-order force wave of the integer slot multipole PMSM were presented. Based on this, a method of stator and rotor structure optimisation was proposed to effectively reduce magnitudes of vibration and noise for the machine by increasing the natural frequency and reducing the harmonic content and amplitude of electromagnetic force waves. The comparison of the noise reduced machine with the initial design was experimentally validated.
Computational fluid dynamics models with free surface tracking intended to simulate the melt pool produced by an electric arc usually model the electromagnetic force ignoring the deformation of the ...free surface. However, with an arc heat source, the electromagnetic force is known to be among the leading-order forces, especially at high currents. In addition, the free surface can undergo significant deformations, especially in the presence of metal transfer. In the present study, a generalization of the electromagnetic force model that accounts for the deformation of the free surface is therefore proposed. Test cases with a pulsed gas-metal arc that transfers one metal drop per pulse were investigated experimentally at three different travel speeds to provide validation data. The cases were simulated with both the proposed and the earlier model to assess the influence of the new developments. The results showed that, in the regions where both models determine the force, the discrepancy between the models’ results can reach up to an order of magnitude. Especially, the earlier model overestimates the electromagnetic force deep into the melt pool. On the other hand, it neglects it in the liquid metal that is located at an elevation above the original upper surface of the workpiece, while the proposed model showed that in this area the intensity of the electromagnetic force is the largest. These significant discrepancies result in non-negligible differences in the predicted melt pool thermal flow and geometry. Especially, the propose dextended model provides an improved prediction of the fingertip-shaped fusion boundary.
•A new design about stabilizing plate for the advanced tokamak is introduced in this article.•The electromagnetic analysis and electromagnetic-structural analysis are carried out. The results provide ...the theoretical feasibility for the design.•The contact resistance test is conducted. According to the experimental results, the total contact resistance of total stabilizing plates is less than 3.2 μΩ.
In tokamak devices, the stabilizing plates are installed in the vacuum vessel to mitigate the vertical instability of plasma. As the power and operating time of tokamak devices increase, the electromagnetic force generated by MD (Major Disruption) of plasma and thermal load will be greater than before. In order to maintain the performance of the stabilizing plate, a new concept about stabilizing plate for the advanced tokamak is introduced in this article. The new stabilizing plate is designed with a sturdy body and a composite cooling structure. Meanwhile, in order to reduce the contact resistance between stabilizing plates, an electrical connection structure is specially added for the stabilizing plate. Based on the electromagnetic analysis and thermal analysis, theoretical feasibility for the new stabilizing plate is provided. In order to verify the actual performance of the electrical connection structure, the contact resistance test is conducted. According to the experimental results, the total contact resistance of total stabilizing plates is less than 3.2 μΩ.
The reversal of current around an edge crack in a conductor induces an electromagnetic force that tends to open the crack in Mode I, potentially leading to fracture. In this study, we examine the ...influence of a uniform external magnetic field, applied perpendicular to the sample, on the fracture behavior of a metallic foil carrying an electric current. Experimental investigations were conducted by subjecting an 11 μm thick pre-notched aluminum foil to a series of electric current pulses in the presence of a low external magnetic field up to 0.4 T. Irrespective of the magnetic field, a sharp crack propagated from the notch tip once the nominal applied current density exceeded a critical value. However, the critical current density decreased linearly with the external magnetic field. Conjugate finite element analysis, employed to explore the interaction between the self-induced and the external magnetic fields, revealed a linear superposition of both magnetic fields. This coupling amplified the net crack opening stress, consistent with the observed experimental behavior. Furthermore, the transient stress intensity factor, KIE,t, evaluated for the critical combination of applied current density and external magnetic field demonstrated a reasonable match with the plane stress critical stress intensity factor, KIC, confirming the classic fracture condition of critical KIE,t ≥ KIC for crack propagation. This is the first study systematically highlighting the mechanisms governing crack propagation in thin conductors subjected to electric current and external magnetic fields simultaneously.
Lightweight porous materials for electromagnetic interference (EMI) shielding applications are reviewed. EMI shielding refers to the capability of a material to protect from electromagnetic fields ...(EMFs) generated by electronic devices. Traditionally conducting metals are used in EMI shielding applications, which are slowly being replaced by conducting polymer based shields. This review is narrowly focused on understanding the approaches related to porous high EMI shielding composite materials that have very low density values. While metallic fillers can increase the EMI shielding capabilities of polymers, they also increase the weight, which can be offset by inducing the porosity in the matrix. Porosity is found to be effective in providing higher shielding effectiveness at low filler volume fraction due to concentrating the filler in the solid polymers. However, use of gas porosity results in composites with low mechanical properties. This problem can be alleviated to some extent by reinforcing polymer foams with lightweight conductivefillers such as carbon nanofibers (CNFs), carbon nanotubes (CNTs) and graphene. But the properties of pores such aspore size and distribution cannot be effectively controlled in such cases. Syntactic foams containing hollow particle fillers seem to be the best combination of EMI shielding capabilities and mechanical properties. These composites can be either filled with a second phase conducting filler, or hollow particles can be coated with a conducting layer, or hollow particles made of conducting materials can be used as fillers. The hollow particle wall thickness and volume fractions can be optimized to obtain the desired combination of properties in syntactic foams to enable their multifunctional applications.
The paper presents a detailed theoretical analysis of the electromagnetic forces in the arc plasma and the weld pool metal in Tungsten Inert Gas (TIG) welding at direct current (DC) and ...high-frequency pulse current (HFPC) modulation with a frequency of 10 kHz. The electromagnetic (Lorentz) force, acting on arc plasma and metal is presented via potential (magnetic pressure) and rotational (equivalent electromagnetic force) force components. This approach allows us to substantially simplify the analysis of the Lorentz force effect on the arc plasma and weld pool metal under different arc burning modes. It was shown that in HFPC TIG welding with a given frequency, the effect of modulated current on the arc plasma is inherently non-stationary, whereas the effect on the weld pool metal is determined by the time-averaged magnitude of electromagnetic force throughout the period of current modulation. The proposed approach serves as a basis for numerical analysis of the electromagnetic forces in arc plasma and weld pool metal during DC and HFPC modes of the welding process. We established that the application of HFPC modulation promotes a greater intensity of both the gas-dynamic processes in the welding arc, thereby significantly increasing the pressure on the weld pool surface, and convective heat transfer from the most heated central region near the weld pool surface towards the weld pool bottom. Both these factors lead to an increase of the arc penetrability in the case of the HFPC mode compared with the DC mode, all other conditions being equal.
•Only rotational part of the Lorentz force initiates vortical flow.•Square-wave pulse is used as a welding current wave form.•Non-stationary magnetic field diffusion equation is solved numerically.•In-house Wolfram Language code is used for FEM-analysis.•HFPC modulation increases the effective driving force in the weld pool.
Electromagnetic vibration is excited by the electromagnetic force waves generated by the air-gap magnetic field acting on the machine core. In this article, a fast and accurate calculation method of ...radial electromagnetic force density of surface-mounted permanent-magnet synchronous motors (SPMSMs) is proposed, and the radial force density including amplitude, frequency, and order is obtained. Comprehensively considering that the effect of the PM segmentation on electromagnetic force waves, cogging torque, and the no-load back electromotive force (back EMF), the optimal determination of the number of PM segmentation in different slot-pole combinations of SPMSMs is summarized, and six slot-pole combinations of SPMSMs with 6p36s, 4p36s, 6p9s, 8p9s, 8p12s, and 10p12s are calculated and analyzed to verify the universality of the conclusions, which lays a theoretical foundation for the weakening of the radial electromagnetic force.
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•A novel compliant mechanism based system to calibrate the spring constant of AFM cantilevers has been proposed.•The calibration system is mainly composed of a compliant suspension ...mechanism and an electromagnetic actuator.•An electromagnetic actuator is employed to provide calibration force and a capacitance sensor is utilized to monitor the displacement of the suspension mechanism.•The prototypes of the calibration system are established and experimental study is carried out.
Calibrating spring constant of atomic force microscope (AFM) cantilevers is necessary for the measurement of micro/nano newton forces, which are commonly-used in the characterization of micro/nano functional surfaces and materials, cell manipulation, and many more applications. This paper presents a novel compliant mechanism based system to calibrate the spring constant of AFM cantilevers. The calibration system is mainly composed of a compliant suspension mechanism and an electromagnetic force actuator, where two kinds of compliant structures of “L” shape flexures and “Archimedes” planar flexures are assembled in parallel to achieve compact devices, respectively. The characteristics of the suspension mechanism are investigated by analytical model and finite element analysis (FEA). Furthermore, a prototype of the calibration system is established and experimental tests are carried out to verify the performance. An electromagnetic force actuator is employed to provide calibration force. Meanwhile, a capacitance sensor is utilized to monitor the displacement of the suspension mechanism. The calibration results of AFM cantilevers reveal that the compliant mechanism based calibration system has a good performance and it can calibrate the spring constant of AFM cantilevers accurately and effectively.
To mitigate the occurrence of humping bead in high-speed gas metal arc welding, an external magnetic field is exerted into the weld pool to produce the forward electromagnetic force and to brake the ...backward flow molten jet. A thermal-magnetic coupling model is developed to analyze the distribution of the additional electromagnetic force in weld pool. The interaction of the external magnetic field in the arc region with the arc/liquid metal stream at the wire tip is taken into consideration, and the excitation current and the wire-magnet distance are optimized. The welding experiments on mild steel plates (Q235B) demonstrate that with help of the forward additional electromagnetic force, good weld bead quality without humping is obtained in high-speed gas metal arc welding.
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