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Cantilevers are one of the most utilized mechanical elements for acoustic sensing. In comparison to the edge clamped diaphragms of different shapes, a single edge clamped cantilever makes an acoustic sensor mechanically sensitive for detection of lower pressure. The aspect ratio of cantilevers is one of the most important parameters which affect sensitivity. Herein, we present a mathematical, finite element method and experimental analysis to determine the effect of the aspect ratio on the resonant frequency, response time, mechanical sensitivity, and capacitive sensitivity of a cantilever-based acoustic pressure sensor. Three cantilevers of different aspect ratios (0.67, 1, and 1.5) have been chosen for sound pressure application to detect capacitance change. The cantilever with the smallest aspect ratio (0.67) has the highest response time (206 ms), mechanical sensitivity, and capacitive sensitivity (22 fF), which reduce after increasing the aspect ratio. The resonant frequency of the cantilever was also analyzed by applying sweep in sound frequency. It was found to be minimum for the cantilever with the smallest aspect ratio (510 Hz) and increases with an increase in the aspect ratio. We have applied the garage fabrication process using low cost, recyclable, and easily available materials such as metal coated polymer sheets, mounting tapes and glass slides as alternative materials for expensive materials. [ABSTRACT FROM AUTHOR]

Transcranial magnetic stimulation (TMS) shows great research potential in human neuroscience. However, when it comes to stimulating deeper brain regions, traditional TMS is restricted by the balance between stimulation focalization and stimulation depth. Temporal interference (TI) stimulation offers a new thought to solve the problem. In this paper, we first discussed the principles of TI-TMS and then established the theoretical model of TI-TMS using the head-surrounded spatial array. Next, we specially designed the parametric characterized spatial array (PCS array) suitable for TI-TMS. The proposed PCS array contains eight special-shaped coils that constitute four sets of difference frequency stimulation pairs and are placed around the human head. Distribution characteristics of the temporally interfering electric fields (E-fields) including stimulation intensity, stimulation focalizations on 1D, 2D, and 3D levels, and attenuation ratios in X, Y, and Z directions were obtained using the finite element analysis method. Our results indicate that the proposed PCS array could form an obvious focusing area with strong stimulation at a stimulation depth of 5 cm below the human scalp while the superficial region is under weak stimulation, which effectively combines the advantages of TMS and TI stimulation. Compared to the traditional TMS systems, the TI-TMS with PCS array can realize selective and focalized stimulation in the deep brain and increase the average attenuation ratio of the induced temporally interfering E-fields by more than 1.93 times. A real human head model containing gray matter was also employed in this paper to verify our results. [ABSTRACT FROM AUTHOR]

The injection of the Direct Current (DC) bias component will lead to oversaturation of the transformer core and affect its safe operation. In this paper, the vector magnetic potential A and winding current I are used as the variables solved in the time-step finite element method to simulate the nonlinear transient magnetization characteristics of the transformer under DC bias, and the fixed-point reluctivity is introduced to deal with the nonlinear iterative problem. The field-circuit coupling relationship is established through the electromagnetic induction law, and the two-dimensional time-step finite element model of the transformer core is found. The dynamic J–A hysteresis model is used to deal with the hysteresis effect of iron cores. The fixed-point reluctivity of difference form is introduced to solve the problem of uneven transition and multi-value of magnetization curve with hysteresis in the iterative process. The determination scheme for the equivalent thickness of the core model and the initial iterative value are discussed. A laminated core transformer is made for experiments, and the accuracy and applicability of the model proposed in this paper are verified by comparing the calculation and experimental results. The influence of different voltages and different DC bias components on the electromagnetic characteristics of the transformer is analyzed. [ABSTRACT FROM AUTHOR]

In this paper, a pole-changing (PC) flux reversal permanent magnet (FRPM) motor is proposed for obtaining a wide speed range. According to the general air-gap field modulation theory, the permanent magnet (PM) magnetic field is modulated into a series of harmonics with different pole numbers by rotor teeth. By introducing an especial PM arrangement, two groups of working harmonics with different pole-pair numbers are generated in the proposed 12-7 PC-FRPM motor due to the modulation of rotor teeth. Based on the calculated slot pitch angles of these harmonics, two winding connections can be obtained for PC operation to achieve two operating modes. The electromagnetic performance of PC-FRPM motor before and after PC are analyzed using finite element analysis and verified by the experimental test results. [ABSTRACT FROM AUTHOR]

As the central component of the traveling wave tube (TWT), the thermal deformation of the electron gun is a critical concern. This paper presents a method for analyzing the electromagnetic characteristics of electron gun after thermal deformation. The method adopts multiple grid acceleration technology. Based on this method, a three-dimensional thermal stress analysis tool called the Thermal Stress Simulator (TSS) is developed. In addition, the TSS can be seamlessly coupled with the Thermal Simulator (TS) and the Electron Optical Simulator (EOS) previously developed by our team to realize the analysis of electromagnetic characteristics changes after thermal deformation and provide support for the reliable design of TWT. [ABSTRACT FROM AUTHOR]

The squeeze film damper (SFD) is a damping device that has been widely used in rotating machines. The SFD can effectively suppress rotor vibration and reduce transmitted forces. However, it would cause complex motions of the rotor system under specific operating conditions. This paper investigates the support structure of a high-pressure stage simulated rotor in an aircraft engine. A dynamic model of the SFD considering the effects of inertia and cavitation is established to investigate the influence of structural parameters on the stiffness and damping coefficient of the damper. Subsequently, a finite element model of the Jeffcott rotor–SFD system is developed to explore the effects of the structure parameters of the SFD on the critical speed, mode shapes, and other dynamic characteristics of the Jeffcott rotor–SFD system. Experimental tests are conducted to validate and refine the numerical calculations regarding the dynamic characteristics of the rotor–damper system. The results indicate that there is consistency between numerical simulations and experimental results. Within a certain range, enlarging the width of the damper can significantly increase the magnitude of the pressure distribution of the oil film. However, when the pressure amplitude increases to the saturation vapor pressure of the lubricating oil, the cavitation effect begins to manifest. As the width of the damper increases, both the stiffness coefficient and damping coefficient of the SFD are enhanced. Consequently, the vibration reduction effectiveness of the SFD is significantly improved. [ABSTRACT FROM AUTHOR]

A common problem of anisotropic materials is that the modulus of elasticity is not equal in tension and compression. Presently, research objects are mainly concentrated on beams with isotropic materials or laminated beams with orthotropic materials, and few are involved in composite sandwich beams with different moduli in tension and compression. Considering the shortcomings of the equivalent area method, we propose a developed theoretical analysis method for analyzing sandwich beams with different moduli in tension and compression based on the idea of layering. In this method, the sandwich beam is divided into four layers: upper panel, lower panel, tension zone of core, and compression zone of core. In addition, based on general weighted flexibility matrix material model and its simplified model, a finite element simulation model with high computational efficiency and good convergence is established. A comparison between the theoretical calculation results and the finite element results shows that the developed theoretical analysis method proposed in this paper has a higher accuracy than the equivalent area method, regardless of different types of loads or conditions with a large ratio of tensile to compressive elastic modulus. [ABSTRACT FROM AUTHOR]

This paper introduces a conceptual framework for finite element analysis of generalized Maxwell viscoelastic materials based on the initial stress approach. The proposed method facilitates the explicit and convenient determination of mechanical parameters for viscoelastic materials by directly utilizing relaxation test data. Each time step's viscoelastic relaxation stress is treated as the initial stress, and a recursive calculation formula for the material's initial stress is established, relying solely on the relaxation stress and strain from the previous time step. Based on this, the study outlines the computational steps for initial-stress-based finite element analysis of elastic materials. The proposed algorithm's accuracy and efficiency are validated through a classical one-dimensional axial rod example. Results demonstrate that the introduced initial stress-type finite element analysis maintains the stiffness matrix equal to the initial stiffness matrix throughout the calculation process, significantly enhancing the efficiency of finite element analysis for viscoelastic materials while reducing the computational resource required. The conceptual framework improves the efficiency and accuracy of analyzing the mechanical parameters of viscoelastic materials using relaxation test data. [ABSTRACT FROM AUTHOR]

In this paper, a winding loss calculation method used in the field of converter transformers is introduced into the realm of high-frequency transformers for the first time. In addition, the impact of winding structure on the calculation accuracy of the method is considered for the first time. Comparing the calculation results of this method with those of the formula method, based on the results of finite element simulation. The feasibility of using this method to calculate the winding loss of a high-frequency transformer is verified. First, the winding loss of rectangular wire commonly used in small-capacity high-frequency transformers is analyzed. Based on the finite element simulation results, the accuracy of the hybrid method is compared with the formula calculation method to demonstrate the feasibility of the hybrid method. Then, using the same method, the accuracy of the hybrid method in calculating the winding loss of the circular wire, which is also used in small-capacity high-frequency transformers, is compared with the formula method. The maximum number of continuous winding layers has been modified, and the outcomes for various layers are being computed. Finally, the cross-transposition winding structure is also calculated, demonstrating that the hybrid method is not only applicable to wires of various shapes but also compatible with different winding structures. The results show that the hybrid method has good calculation accuracy and applicability. It can provide more precise calculation results for the winding loss of high-frequency transformers with various winding shapes. [ABSTRACT FROM AUTHOR]

In this paper, finite element models of ultrasonic wave propagation in Cu–PMMA composites are established. The effects of second-phase particles, ultrasonic properties, and graded interfaces on the ultrasonic propagation behavior are investigated, and the contributions of particle-independent scattering, particle interactions, and matrix viscoelasticity to the ultrasonic attenuation are quantitatively evaluated. The results show that there is no obvious coupling between particle scattering and matrix viscoelasticity in Cu–PMMA composites, and the longitudinal wave speed has little effect with the variation of particle size, ultrasonic frequency, and graded interface, while the variation of the acoustic attenuation coefficient is related to the disorder of ultrasonic energy propagation direction. In the intra-layer uniform model, with the increase in Cu particle size and ultrasonic frequency, the scattering effect of Cu particles on the ultrasonic waves is enhanced, resulting in a significant increase in the acoustic attenuation coefficient. In the inter-layer graded multilayer model, there is a strong reverse energy propagation between the layers, causing the acoustic attenuation coefficient to increase significantly. [ABSTRACT FROM AUTHOR]

As a non-invasive neuromodulation technology, transcranial magnetic stimulation (TMS) shows great potential in the treatment of mental diseases. Using TMS to stimulate deep brain targets has significant scientific research value for the exploration of the causes of psychiatric diseases. However, the focalized induced electrical field (E-field) generated by traditional TMS coils or coil arrays is largely restricted to superficial cortical targets. To achieve focalized stimulation in the deep brain, a novel spatially symmetric array based on curved θ-type coils (the θ-SSA) is proposed in this paper. Four θ-type coils in the array are symmetrical to the YZ and XZ planes. Each θ-type coil is placed tangent to the human scalp and bent away from the human head to reduce the non-longitudinal component accumulation of the induced E-field and enhance the stimulation focalization. The finite-element method is used to obtain the 3D spatial distributions of the intracranial induced E-field generated by the proposed array. Results show that the θ-SSA can form an obvious focusing area in the deep brain 11 cm below the scalp. Under identical stimulation current excitation, the θ-SSA can increase the intracranial longitudinal attenuation ratio by 77% compared to the traditional TMS coil. In addition, when generating the same focusing area, the stimulation depth of the θ-SSA is 1.67 times deeper than that of the traditional TMS coil. Meanwhile, the proposed array can dynamically steer the intracranial stimulated area, and the spatial coordinates of the intracranial stimulation target point can be flexibly and continuously adjusted when changing the stimulation current parameters applied to the array. An anatomically realistic human head model with gray matter is employed in this paper to verify our method. [ABSTRACT FROM AUTHOR]

This paper introduces an improved Halpin–Tsai model to predict the mechanical, thermal, and electrical properties of silicon-carbide-reinforced polypropylene composites. The model considers the influence of porosity and corresponding silicon-carbide volume fractions and derives relationships between material property shape factors and the aspect ratio, silicon-carbide volume fraction, and porosity. The improved model's predictions exhibit errors of 4.00% for mechanical properties, 2.13% for thermal properties, and 2.24% for electrical properties when compared to finite element analysis. This study demonstrates that the improved Halpin–Tsai model can effectively predict the properties of silicon-carbide-reinforced polypropylene composites, aiding in the design and optimization of these materials. [ABSTRACT FROM AUTHOR]

This paper reports a novel piezoelectric quartz crystal pressure sensor with a double-ended tuning fork (DETF) resonator. The key design is the resonator beams with a continuously variable section shape. Different from the traditional DETF with straight beams or the one with variable sections with steps, this design can improve sensitivity effectively. Theoretical analysis indicates that the sensitivity will increase with a decrease in beam width. Resonant pressure sensors with three different DETFs are designed and analyzed by finite element analysis software. Simulation results show that the sensitivity of this design is 162.27 Hz/MPa. This sensor has a typical structure, which includes three parts: the diaphragm, DETF resonator, and back-cavity structure. Quartz MEMS processes have been used in fabrication. The three parts are bonded together by vacuum glass frit sealing process. Test results of this sensor show that the natural frequency is 44.709 kHz with a quality factor of 12 717. The sensitivity is 155.6 Hz/MPa in the pressure range of 0–20 MPa. The results indicate that this novel design has advantages in sensitivity and fabrication processes. It will be a benefit for a high-performance and low-cost pressure measurement. [ABSTRACT FROM AUTHOR]

The generation of acoustic vortex beams has attracted an increasing amount of research attention in recent years, offering a range of functions, including acoustic communication, particle manipulation, and biomedical ultrasound. However, incorporating more vortices and broadening the capacity of these beams and associated devices in three dimensions pose challenges. Traditional methods often necessitate complex transducer arrays and are constrained by conditions such as system complexity and the medium in which they operate. In this paper, a 3D printed acoustic lens capable of generating a double vortex pattern with an optional focusing profile in water was demonstrated. The performance of the proposed lens was evaluated through computational simulations using finite element analysis and experimental tests based on underwater measurements. The results indicate that by altering the positioning of the vortices' axes, it is possible to control both the intensity and the location of the pressurized zone. The proposed approach shows promise for enhancing the effectiveness and versatility of various applications by generating a larger number of vortices and freely tailoring the focal profile with a single lens, thereby expanding the practical uses of acoustic vortex technology. [ABSTRACT FROM AUTHOR]

This paper focuses on electromagnetic and loss analyses of an induction machine using the subdomain method. The proposed method derives an analytical solution for each subdomain using electromagnetic theory. On the basis of the derived analytical solution, electromagnetic performances are calculated and copper loss, iron loss, and rotor loss are derived. The validity of the proposed method was verified by comparing the analysis and loss analysis results with the finite element analysis results. In particular, the loss analysis results were input into an equivalent thermal analysis model, thermal analysis was performed, and the results were compared with those measured in the actual model. The reliability of the proposed method was verified through analysis and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, an electromagnetic analysis method is proposed to improve force characteristics by using spring permanent magnets (PMs) along the axial and circumferential directions of a linear oscillatory generator (LOG). For accurate electromagnetic analysis, a detailed analysis model of the LOG is developed, and the governing equations of each subdomain are derived based on Maxwell's equations and electromagnetic theory. Analytical solutions of the magnetic vector potential in each subdomain are derived using boundary conditions. The reliability of the proposed method is verified through a comparison with the results of a two-dimensional finite element analysis (FEA). In particular, the force characteristics depending on the spring PM is effectively derived by considering the three-dimensional (3D) circumferential and axial end effects. The proposed analysis method is used to determine the thickness of spring PM that transforms the detent force of the LOG with the spring PM into restoring force. The reliability of the proposed analysis method is verified through comparison with the results of a 3D FEA. [ABSTRACT FROM AUTHOR]

Nanocrystalline core is widely used in the design process of high-frequency transformers and inductors due to the attractive magnetic properties of nanocrystalline material. However, the flux density distribution is nonuniform in the core because the reluctance is closely related to its geometric shape. The nonuniformity of flux density distribution may cause huge calculation errors of core losses. In this paper, Finite Element Method (FEM) is used to justify taking into account nonuniform distribution of flux density during the process of core loss calculation. An improved loss separation equation considering nonuniform distribution of flux density is proposed, and the improved equation is verified through calculating and analyzing the losses of nanocrystalline cores with different wound thicknesses. Compared with the traditional loss separation equation, the accuracy is improved, and the average error of improved equation is confined in 10%. [ABSTRACT FROM AUTHOR]

The powder mixed electrical discharge machining (PMEDM) process was simulated via finite element analysis in the current study to assess heat behavior and material removal rate. The goal of this paper is to conduct a thorough experimental and thermal examination of electrical discharge machining (EDM) in order to forecast its cutting characteristics and subsequently optimize the output variables using a response surface methodology for simulations and choosing the most suitable set of process variables related to the PMEDM process. This study's objective is to design a 2D axisymmetrical transient thermal model that might also describe the physics of material removal in a single spark PMEDM operation on a Titanium Zirconium Molybdenum (TZM) superalloy. ANSYS (version 9.1) software is used to perform transient heat transfer simulations to determine the temperature profile with the amount of material removal at different current, pulse on and off times, gap voltages, and fraction of heat that enters the specimen. The PMEDM process produced craters with a lower diameter and depth, which increased the material removal rate and enhanced the surfacing quality. Compared to the conventional EDM process, the inclusion of powder raised the heat flux given to the work material by 10%–12%. It has been determined that with the single spark modeling technique, the temperature significantly dropped in both the radial and depth directions. The computational results are compared with experimental observations for similar machining conditions, and both results agree satisfactorily. [ABSTRACT FROM AUTHOR]

This paper reports on the results of modeling the human colon and analyzes its effectiveness as a finite element analysis (FEA) tool for testing conventional and robotic colonoscope technologies. FEA has been used to model colon tissue before, but these analyses have been carried out on smaller tissue samples, such as to fit strain energy functions to mechanical testing data or to explore the inflation-extension response of a section of the colon. The full colon has not yet been modeled in this way, and this study aims to show the usefulness of such a tool for testing endoscopic devices for diagnostic and therapeutic purposes in the colon. Data from the literature and databases have been used to approximate the stress response of the tissues, and a critical analysis of the limitations of the approximations has been carried out. Characteristic colonoscope loops were created to analyze the mechanical response of the colon and provide comparable results to conventional colonoscopy. The results showed how stress would be propagated along the length of the colon and how neighboring structures can affect the stresses and strains experienced by the colon wall, demonstrating the need for and capabilities of a full FEA model of the colon to test endoscopic devices. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to analyze the nonlinear vibration of composite beams and the stability of the solution by using the reduced-order model and the incremental harmonic balance (IHB) method. Timoshenko beam theory is used to indicate the displacement of the beam element. Each nodal point has three degrees of freedom. Simplified homogenized beam theory is used to calculate the equivalent moduli of each ply of the composite beam. Element matrices are created using the weak form quadrature element method, and the equation of motion at the element is created using Lagrange's equation. A system matrix is created using the element matrix assemble rule of the finite element method. In order to reduce the calculation time, a reduced-order model is used. The nonlinear forced vibration equation is solved using the IHB method. The results calculated using the non-reduced-order model and the reduced-order model are compared, and the results are very close. Based on this, the reduced-order model is used to analyze the nonlinear vibrations of composite beams at the first resonance point, and stability tests are conducted for the calculated solutions using the multivariable Floquet theory. [ABSTRACT FROM AUTHOR]

MEMS electric energy utilization rate is the key parameter affecting firing performance. It has important relationship with its preparation technology, microscale and structure morphology. In order to improve the theory of energy exchange element design for MEMS pyrotechnics, reduce the design error of transducer parameters at microscale. To ensure the performance of MEMS pyrotechnics, in this paper, the influence of the central line of the thin film transducer element on the electrothermal conversion is simulated and analyzed. The electrothermal conversion and temperature characterization of different central lines in the transducer bridge area are calculated by the finite element method. The influence of the central line on the thermal efficiency under microscale is revealed. The corresponding data are obtained. [ABSTRACT FROM AUTHOR]

By applying the halbach arrangement, an integrated magnetic bearing structure can be designed that secures the space inside the rotor core as a space for inserting the magnetic bearing. In this case, since the bearing is present inside the rotor, the bearing magnetic flux for controlling the rotor position is affected by the magnetic field of the permanent magnet and the rotating magnetic field of the phase winding of the stator. At this time, in a specific combination of the number of pole slots, the arrangement of the windings of the stator facing the bearing teeth appears asymmetrically for each bearing phase. In this paper, for more linear control, the formula for the number of stator pole slots and the number of bearing teeth to eliminate structurally generated force asymmetry was presented, and the formula was verified by comparative analysis of the force waveform for each axis. The validity of the proposed model was verified using the finite element method. [ABSTRACT FROM AUTHOR]

A serious inrush current may occur when a power transformer is re-energized, which will cause many adverse effects on power equipment and the power grid. The corresponding potential hazards can be reduced if the existing residual flux density (Br) can be accurately measured. Combined with the field-circuit coupling analysis method, a novel method for measuring the Br based on the phase difference between the applied AC voltage and resulting transient current is proposed in this paper. When the same AC voltage is applied to the transformer winding, the Br affects the resulting transient current. The phase difference between the applied voltage and the resulting current can be calculated by the cross-correlation technique. Based on the finite element method (FEM), the empirical formula for the quantitative measurement of Br in the transformer core is determined. Finally, an experimental study is performed on the square core of single-phase transformers. The experimental results reveal that the proposed measurement method is with high accuracy. [ABSTRACT FROM AUTHOR]

Steel strands have been widely used in industrial fields as a reliable load-bearing component. Under the influence of environmental erosion and fatigue stress, different types of damage, such as corrosion and fracture, will occur in the in-service steel strands, which will cause unpredictable loss of personnel and property. Ultrasonic nondestructive testing technology has become an ideal testing method for long-distance metal structures in recent years due to the advantages of long detection distance and high efficiency. The detection effect of ultrasonic nondestructive testing technology largely depends on the propagation characteristics of the selected guided wave modes. However, due to the influence of the helical structure of the steel strands and the contact between the wires, the propagation characteristics of the guided waves in the steel strands are very complicated. In this paper, a method for analyzing the dispersion characteristics of steel strands based on the Floquet boundary conditions (Floquet BCs) is proposed. The essence of this method is the mutual transformation principle of wave solution and vibration solution. To adapt to the helical structure of steel strands, this paper proposes a helical coordinate system and twisted coordinate system and deduces the corresponding wavenumber conversion formula. The results of Floquet BCs are consistent with the semi-analytical finite element method and sweep frequency finite element modeling method, which proves the correctness of the Floquet BC method from both theoretical and experimental perspectives. This paper provides a new idea for analyzing the dispersion characteristics of complex waveguides such as steel strands. [ABSTRACT FROM AUTHOR]

In this paper, a new field-modulated permanent magnet (FMPM) machine with an improved rotor is proposed and analyzed. The proposed FMPM machine enjoys the advantages of high PM utilization and better heat dissipation. For a fair comparison, the proposed FMPM machine is designed with the same geometrical parameters based on the existing FMPM machine. The electromagnetic performances of existing FMPM (E-FMPM) machine and proposed FMPM (P-FMPM) are compared and analyzed by using finite element method, verifying that the proposed FMPM machine with an improved rotor can obtain high torque density and high PM utilization. [ABSTRACT FROM AUTHOR]

In this paper, based on the conventional flux-switching permanent magnet (PM) (FSPM) machine, a novel dual-three-phase dual-rotor FSPM machine with PMs of NS layout (NS-DRFSPM) is proposed. The stator of the proposed NS-DRFSPM machine is equipped with dual PMs and dual armature windings to operate in a variety of operating modes and to handle the case of PMs or armature windings failure. Firstly, the topological structure and eight fault operating states of the NS-DRFSPM machine are introduced, and the key design parameters of the NS-DRFSPM machine are optimized by genetic algorithm (GA) optimization and finite element analysis (FEA). Then, the operation principle of the NS-DRFSPM machine is analyzed in detail. Finally, the finite element method is used to analyze the performances of the NS-DRFSPM machine under eight fault operating states, which is mainly analyzed from two aspects: no-load performance and torque performance. The results show that the NS-DRFSPM machine has good electromagnetic performance under different fault conditions, including large back-electromotive force (EMF) amplitude, sinusoidal EMF waveform, high average torque, small torque ripple, and strong anti-saturation ability. [ABSTRACT FROM AUTHOR]

Conventional surface mounted permanent magnet synchronous motor (SPMSM) at high speed has large iron loss in the stator and eddy current loss in the rotor. The higher the eddy current loss, the higher the rotor temperature. Therefore, a plan to reduce the loss must be devised. Also, weight at high speed is related to mechanical stiffness and electromagnetic vibration noise. Therefore, a plan to reduce the weight must be devised. In this paper, we propose to change the shape of the conventional 15 kW 110 000 rpm class into a slotless shape. A process of protocol change was proposed, and the sizing design of the rotor and stator was devised. The advantages of the proposed shape were verified through performance comparison through finite element analysis (FEA) and mechanical stiffness analysis. [ABSTRACT FROM AUTHOR]

Transcranial magnetic stimulation (TMS) has been widely used in scientific research and clinical application. In TMS, the stimulation coil generates a focusing induced electrical field in the intracranial target area to achieve neuromodulation. Since different disorders correspond to their specific target areas, in order to avoid non-target tissue being stimulated, the figure-of-eight (FOE) coil with good focusing performance is still the most commonly used magnetic coil. In this paper, the U-shaped coil with multi-parameters is introduced and optimized. The spatial distributions of the intracranial induced electrical field produced by the U-shaped coil are obtained using the finite-element method. Compared to the traditional FOE coil, the U-shaped coil not only has a great advantage in improving focalization but also is beneficial to obtain other improved characteristics. The mathematical relationship between the coil geometric parameters and the intracranial induced electrical field characteristics is analyzed under the constraint of fixed coil power loss. To further improve coil efficiency, the particle swarm optimization (PSO) is adopted to optimize the coil parameters. A real human head modeled as homogeneous and isotropic is occupied in this paper to verify our method, and a traditional FOE coil is used as the reference coil. We also checked the maximum induced charge density on the targeted plane generated by the optimized U-shaped coil to make sure that it will not cause induced neurologic damage. [ABSTRACT FROM AUTHOR]

The safety and reliability of the initiating explosive devices (IEDs) are critical for the weapon system. As the core components of IEDs, the method of resistance designing and the performance of conversion energy of energy conversion components (ECCs) are worth being studied. In this paper, the design method for the resistance of ECCs is established based on the finite element discrete method, and the currents of melting and electric explosion are presented for evaluating the performance of ECCs. The results show that the resistance of the ECCs is 1 ± 0.05 Ω with consistency. The ECCs were designed by the established design method of resistance and manufactured by the established machining method. The melting current of ECCs is 1.8 A, which is calculated by the infrared temperature measurement and finite element simulation. The electric explosion current of ECCs is 5 A, which was obtained by combining the snapshot obtained via the high-speed camera and finite element simulation. [ABSTRACT FROM AUTHOR]

In this paper, the influence of rectangular holes with different aspect ratios in a cylinder on shielding properties is investigated using the finite element method. The two indicators used to assess the shielding properties of the cylinder are its internal residual magnetic field and its outer-surface magnetic field map. The internal residual magnetic field (B) of a cylinder as a function of the aspect ratio of a rectangular hole and its area is simulated, and the conclusions are as follows: with increasing length of the hole, the value of B increases first and then decreases. A cylindrical shield with square holes (the hole aspect ratio is equal to 1) delivers the worst shielding performance. A cylinder with a smaller hole area has better shielding properties, resulting from a less flux leakage from the environmental magnetic field. The anisotropy of the shielding properties is evaluated, and the magnetic shielding in the radial direction is better than that in the axial direction. This research provides a theoretical guide for the application and optimization of magnetic shields. [ABSTRACT FROM AUTHOR]

A multi-resonance Cymbal hydrophone for detection of the open-circuit self-contained underwater breathing apparatus (scuba) diver was designed and fabricated in this work, which has the advantages of multi-resonant frequency, high sensitivity, and narrow bandwidth. By using standard hydrophones, the underwater acoustic signal of the open-circuit scuba diver in the pool was collected and the characteristics of the signal were analyzed: the signal was mainly distributed in high frequency and low frequency. According to this characteristic, a Cymbal hydrophone with multi-resonance frequencies was designed in the finite element method, and the resonant frequency, receiving sensitivity, and bandwidth of the hydrophone were calculated. The accuracy of the calculation was verified with the performance test of the prototypes fabricated in this work. Finally, the underwater acoustic signal of an open-circuit scuba diver in the pool was tested by the prototype to demonstrate that the multi-resonance Cymbal hydrophone developed in this paper can be used for open-circuit scuba diver detection. [ABSTRACT FROM AUTHOR]

Erosive damage of nitride coatings is predominantly attributed to coating delamination caused by crack initiation, propagation, and coalescence. For brittle nitride coating materials, inhibiting the crack initiation and propagation within the coating may enhance their erosion resistance. This paper focuses on TiAlN/TiAl multilayer coatings, and by increasing the thickness of the metallic sublayers, the initiation and propagation of cracks in ceramic/metal multilayer coatings are significantly suppressed. As the metallic sublayer thickness increases from 1 to 4 μm, the TiAlN/TiAl coating erosion rate decreases from 0.032 to 0.002 mg⋅g−1, resulting in an improvement in the erosion resistance of over ten times. Based on the failure mechanism of ceramic/metal multilayer coatings under sand erosion conditions and finite element analysis, there are two reasons for improving the erosion resistance of ceramic/metal multilayer coatings by increasing the toughness of the metal layer. On one hand, increasing the thickness of the ductile metal layer can effectively reduce the maximum tensile stress value on the coating surface and decrease the equivalent plastic deformation of the ductile metal layer, thereby improving the crack initiation suppression ability of the coating. On the other hand, increasing the TiAl layer thickness effectively suppresses the downward propagation of longitudinal cracks and the coalescence of transverse cracks in nitride coatings. This research proposes a new approach for enhancing the erosion resistance of nitride coatings. [ABSTRACT FROM AUTHOR]

Underwater noise pollution from pile driving is now attracting increasing attention. However, most of the current numerical and semi-analytical models for predicting the noise are still expensive and time-consuming, and the near-field noise and far-field noise have to be obtained from different models. This paper proposes an efficient semi-analytical solution for predicting underwater noise in both near field and far field with only one model, whose computational efficiency is orders of magnitude higher than that of the finite element model. It is the first time that the Baranov–Novak thin-layer model for soil-pile interaction has been extended to the subject of underwater noise prediction during pile installation, taking into account pile-fluid-soil interaction. The solutions are obtained using the Laplace transform and the variable separation method. By comparing the prediction results with the five reported research cases, it is shown that the error of the proposed model is within reasonable limits for both near-field and far-field noise predictions. [ABSTRACT FROM AUTHOR]

Acoustic-based leakage detection and location in a spacecraft has attracted many researchers' interest. Due to the fact that wave propagation through the stiffened structure is too complicated to be comprehensively understood, current leakage detection technologies have low-quality performance. Using numerical simulations, this paper parametrically investigates wave propagation across stiffened structure under different configurations. First, wave propagation through the stiffened structures with different stiffener heights is analyzed, showing that acoustic propagation features are different from Reusser's model. Second, the stiffened structures with different widths are analyzed; meanwhile, the two cases of too large and too small stiffened ratios were compared. Acoustic wave propagation paths become complicated due to acoustic mode conversions. Third, different configurations of structure types are addressed. When the stiffener's height–width ratio was large, the acoustic wave first reached the bottom of the stiffened block and then traveled up to the top of the stiffened block. When the stiffener's height–width ratio was small, the acoustic wave reached the incident side at the bottom of the stiffened block and then propagated separately. [ABSTRACT FROM AUTHOR]

This paper proposes using Finite Element Analysis (FEA) simulations to optimize the design structure for low-frequency Magnetically Shielded Rooms (MSRs). In constructing a multi-layer MSR, the different characteristics of the material and laminated structure will bring different levels of magnetic Shielding Effectiveness (SE). The theoretical SE of an MSR can be determined quickly. By using the method used in this paper, the ideal laminated material structure can be found without increasing the MSR construction cost. According to the simulation results and the actual MSR measurement results we built, the optimized MSR design structure can improve the SE by 13 dB. In the area where the external measurement magnetic field is 37 820 nT, the magnetic field in the MSR is as low as 28 nT, and the SE of the MSR is higher than 57.3 dB. The method proposed by this research can provide the theoretical basis for optimal design structure and the FEA simulation method for engineering practice, which can effectively improve the SE of shielded rooms and save the construction cost. The FEA simulations used in this paper can be obtained from the following URL: https://github.com/YuukiAsuna/-Finite-element-simulation-of-material-lamination-sequence. [ABSTRACT FROM AUTHOR]

In this paper, it is shown that the static magnetic signature of a propulsor belonging to a ghost ship, whose hull is made of fiberglass, can be calculated by regarding it as a composite ferromagnetic medium. The calculation of the magnetic signature in the static regime is carried out using finite-element method simulations and according to a simple analytical model based on the concepts of volume averaged magnetization arising from a source magnetic field, volume averaged permeability, surface magnetic charges, and the demagnetization tensor applied to a composite magnetic medium. Using targeted simulations, it is demonstrated that the magnetostatic field of demagnetizing nature forming inside the propulsor almost cancels the contribution of the volume averaged magnetization. From the interplay between the numerical simulations and the analytical model, the elements of the demagnetization tensor in the region filled by the propulsor are locally calculated, and their role in determining the localization effects of the magnetic signature is discussed. By replacing the original ferromagnetic materials with weakly ferromagnetic ones, it is shown that, in the underwater region outside the propulsor, the magnetic signature drop is 64%. This analysis suggests an experimental way to use a simple passive method to minimize the magnetic signature of a propulsor as an alternative to more complex and time-consuming methods, such as the deperming and degaussing methods, widely employed to reduce the magnetic signature of ships and underwater objects in military applications. [ABSTRACT FROM AUTHOR]

With the rapid advancement of next-generation communication technology, traditional Quad Flat No-leads (QFN) packaging is facing challenges to meet functional requirements. Due to its high integration and excellent thermal performance, the Multi-chips Module combined with Quad Flat No-leads (MCM-QFN) packaging is gaining popularity. However, the structural complexity of MCM-QFN packaging and the thermal coupling effect between multiple dies make it challenging to analyze the steady-state thermal distribution of MCM-QFN packaging, which is necessary for assessing the reliability and optimizing the layout design of the multi-chips module. By analyzing the heat dissipation path from each die to the ambient, this paper proposes an analytical thermal resistance network model for calculating each mean die temperature of MCM-QFN packaging. The thermal coupling effect among the multi-chips, the thermal spreading resistance between critical layers, and the boundary conditions and cooling conditions are all considered. All thermal resistances in the model are expressed analytically, and the mean temperature of each chip can be calculated within 0.1 s using MATLAB programming. To validate the accuracy of the proposed model, finite element method (FEM) simulations are conducted to provide a reference for the mean temperature of each chip under four sets of thermal conditions. The data comparison demonstrates that the analytical model is fast and accurate in calculating each mean die temperature of MCM-QFN packaging, with a maximum error of 3.72%, and the calculation speed increased by about 600× compared to that of FEM simulation. Furthermore, the analytical model is able to offer a direction for optimizing the layout design and material selection of MCM-QFN packaging. [ABSTRACT FROM AUTHOR]

The prediction of reverberant sound fields generated by a directional source is of great interest because practical sound sources are not omnidirectional, especially at high frequencies. For an arbitrary directional source described by cylindrical and spherical harmonics, this paper developed a modal expansion method for calculating the reverberant sound field generated by such a source in both two-dimensional and three-dimensional rectangular enclosures with finite impedance walls. The key is to express the modal source density using the cylindrical or spherical harmonic expansion coefficients of the directional source. A method based on the fast Fourier transform is proposed to enable the fast computation of the summation of enclosure modes when walls are lightly damped or rigid. This makes it possible to obtain accurate reverberant sound fields even in a large room and/or at high frequencies with a relatively low computational load. Numerical results with several typical directional sources are presented. The efficiency and the accuracy of the proposed method are validated by the comparison to the results obtained using the finite element method. [ABSTRACT FROM AUTHOR]

The correlation of guided wave propagation characteristics with structural prestress is of paramount importance to the structural health monitoring of gas pipelines. A variable section structure and inhomogeneous prestress are common conditions in the pipeline. However, most of the existing guided wave finite element models focus on the structure size and stress distribution under two-dimensional conditions, and it is difficult to analyze the three-dimensional structure with non-uniform stress and variable cross section. In this paper, an acoustoelastic theory combined with a semi-analytical finite element based on the three-dimensional mapping method is proposed to investigate guided wave propagation. It provides a generalized tool to study guided waves in waveguides with a variable cross section under inhomogeneous prestress. Then it is applied to two cases, a hollow cylinder with a variable cross section subjected to axial force and radial force, to demonstrate the capability of the method. Dispersive solutions are obtained in terms of the three-dimensional dispersion surface and the change in phase velocity in a variable cross section. The results show that there is a propagation mode, which is insensitive to the change in the section but sensitive to the change in prestress. The effectiveness of the proposed method is verified by comparing with the experimental results. This study provides a good application prospect for the structural design and performance analysis of variable cross section waveguides. [ABSTRACT FROM AUTHOR]

With the rapid development of microelectronic interconnection technology, the reliability requirements of electronic products are becoming higher and higher. Among them, temperature has the greatest impact on electronic devices. Due to the different coefficients of thermal expansion (CTE) between the many materials of a chip, the inside of a solder joint is subjected to cyclic temperature action. Under the effect of cyclic temperature, the solder joints are subject to internal fracture resulting in the failure of the solder joint. Therefore, it is necessary to find a more reliable material for the solder joint. In this paper, the advantages and disadvantages of pure silver material and low silver material are compared by finite element simulation analysis of nano-silver pure silver material and SAC305 low silver material, and the fatigue life prediction of nano-silveris predicted by a life prediction model. Then, using the Electric Power Research Institute estimation method to estimate the fatigue life of solder joints, the results are compared with those calculated by the finite element method. [ABSTRACT FROM AUTHOR]

In this paper, a new optimization design strategy is explored to achieve a rapid design of lightweight structures for unmanned aerial vehicles (UAVs) using honeycomb sandwich panels. Based on the existing performance equivalent method of honeycomb core material, an effective mechanical property homogenization model of honeycomb material is proposed and applied to finite element analysis. A finite element model is established to analyze the mechanical response of honeycomb sandwich panels under different bending loads, and the rationality of the model is verified by mechanical tests. The error between the simulation results and the experimental results is about 10%. Based on the variable density method and rational approximation of material properties interpolation method, a topology optimization model with the minimum structural flexibility as the objective is constructed. By comparing with the experiment-based design scheme, it is found that the optimized design scheme has a more reasonable structure and better performance. The optimized design can effectively reduce the structural weight and improve the load transfer path while ensuring structural stiffness. In this way, the influence of stress concentration and large deformation on the structure is avoided, which is of great significance for the design of UAV structures. [ABSTRACT FROM AUTHOR]

The expressions of the axial and transverse acoustic radiation forces of a rigid sphere arbitrarily positioned in a zero-order Mathieu beam are derived in this paper. The expansion coefficients of the off-axis zero-order Mathieu beam are obtained using the addition theorem of the Bessel functions, and numerical experiments are conducted to verify the theory. The three-dimensional acoustic radiation forces on a rigid sphere are studied when the beam is set at different ellipticity parameters, half-cone angles, and offsets of the incident wave relative to the particle center. Simulation results show that the axial acoustic radiation forces of the rigid sphere are always positive, but the transverse forces vary with the positions of the particle and the beam parameters. Also, by changing the frequency, half-cone angle, and offset of the zero-order Mathieu beam, the value and direction of the transverse forces can be adjusted, which has applications in controlling the rigid sphere to be close to or away from the beam axis. Furthermore, the finite element model is set up to verify the theoretical model, and the results obtained by the two methods are in good agreement. This work may contribute to a better understanding of the underlying mechanisms of the particle manipulation with different acoustic beams. [ABSTRACT FROM AUTHOR]

This paper presents a noise propagation approach based on the Gaussian beam tracing (GBT) method that accounts for multiple reflections over three-dimensional terrain topology and atmospheric refraction due to horizontal and vertical variability in wind velocity. A semi-empirical formulation is derived to reduce truncation error in the beam summation for receivers on the terrain surfaces. The reliability of the present GBT approach is assessed with an acoustic solver based on the finite element method (FEM) solutions of the convected wave equation. The predicted wavefields with the two methods are compared for different source-receiver geometries, urban settings, and wind conditions. When the beam summation is performed without the empirical formulation, the maximum difference is more than 40 dB; it drops below 8 dB with the empirical formulation. In the presence of wind, the direct and reflected waves can have different ray paths than those in a quiescent atmosphere, which results in less apparent diffraction patterns. A 17-fold reduction in computation time is achieved compared to the FEM solver. The results suggest that the present GBT acoustic propagation model can be applied to high-frequency noise propagation in urban environments with acceptable accuracy and better computational efficiency than full-wave solutions. [ABSTRACT FROM AUTHOR]

This paper investigates the vibration bandgap properties of two-dimensional (2D) periodic composite beam frame structures with component defects. Combined with the topological characteristics of the structure, a generalized position coordinate system is proposed, and an assembly method of the stiffness matrix for the virtual full component model is presented. Then the spectral equations of motion of the whole 2D periodic composite beam frame structures and the ones with component defects are established. Compared with the frequency-domain solutions calculated using the finite element method, the accuracy and the feasibility of the spectral element method (SEM) solutions are verified. It can be shown that the SEM is suitable for analyzing the vibration bandgap properties, and the influence of different component defects and their combination on the bandgap characteristics of 2D periodic frame structures is studied. The results show that forbidden gap splitting will occur in the main bandgap of the structure, but the degree of influence varies. The results also show that the influence of component defects on unsymmetrical or irregular positions of the vibration bandgaps of periodic frame structures is greater than the one in symmetrical or regular positions. [ABSTRACT FROM AUTHOR]

A Maxwell coil is a gradient magnetic field source with high uniformity, and it is widely used in the experiment of magnetic effect in space gravitational wave detection, magnetic resonance molecular imaging, and other precision magnetic measurement experiments. In this paper, taking the square Maxwell coil as a research object, the influences of four kinds of assembly errors on the uniformity of magnetic field gradient (UOMFG) are systematically analyzed and the results are verified by simulation using the finite element method. We obtained variation rules of UOMFG changing with the four assembly errors and summarized three useful conclusions. These rules and conclusions are instructive in the design, processing, and assembly of the square Maxwell coil and are beneficial for the optimal utilization of the working area in the precision magnetic measurement experiments. [ABSTRACT FROM AUTHOR]

To solve the problem that finite element analysis and calculation need to be repeated during model updates, which leads to tedious and inefficient correction work, ABAQUS (a powerful finite element software for engineering simulation) is used to develop a user-friendly graphical user interface platform for automatic completion of this update for cable-stayed bridges. In this paper, a method for establishing the benchmark finite element model of cable-stayed bridges based on ABAQUS and influence matrix (IM)-hunter prey optimization (HPO) is proposed. The method is based on the secondary development of ABAQUS to realize the modules of sensitivity analysis, influence matrix, and optimization. According to the sensitivity analysis module, the influence of the change in the finite element model parameters on the static response of a cable-stayed bridge is studied, and the cable area is used as the parameter to be corrected. The influence matrix module is used to obtain the IM of the cable area to girder displacement and cable force under a static load. The objective function is constructed by combining the measured displacement and cable force data using the optimization module, and the global optimal solution of the parameters to be corrected in the objective function is found by HPO. Finally, the solution is sent to the finite element model for correction, and the corrected displacement and cable force data are compared with the measured data. The results show that the modified calculation results obtained by this method are in good agreement with the measured results. The modified finite element model can be used as presented. [ABSTRACT FROM AUTHOR]

Geological tectonic movement plays a controlling role in the distribution pattern of coalbed methane (CBM) resources. The traditional CBM resource estimation methods use the measured CBM as the overall CBM content and do not consider the influence of geological structure on the nonuniform distribution of CBM resources. In this paper, the geological structure of the Guojiahe coalfield in the northern Yonglong mining area, China, was used as the research background. Based on the precise three-dimensional (3D) seismic interpretation results of the coal seam geological structure and the tested CBM contents at sampling points, a fuzzy comprehensive evaluation method was used to classify the tectonic complexity of the study area, and the CBM contents of different tectonic locations in the tested coal seams and the results determined by the finite element method were analyzed. On this basis, a quantitative relationship between the tectonic complexity index and the amount of CBM resources was established, and finally, a CBM-enrichment prediction model and a CBM resource estimation method for areas with different tectonic complexities were proposed. The agreement between the amount of CBM resources obtained by the estimation method and the actual exploration result is 85.2%; therefore, the proposed method has a theoretical guidance and engineering application value for the exploration and precise development of CBM resources. [ABSTRACT FROM AUTHOR]

Variable flux memory machines (VFMMs) with series hybrid magnets using both low coercive force (LCF) and high coercive force (HCF) permanent magnets (PMs) have been recognized as a viable candidate for wide-speed-range industrial applications due to the advantages of high torque density and wide speed range. Nevertheless, the adverse effects of LCF PM on the HCF PM in series-type VFMM under different magnetization states (MSs) are still unreported. In this paper, the flux barrier effect (FBE) of the LCF PM existing in series hybrid magnet VFMM is first revealed, and its causes are discussed as well as analyzed in depth on the basis of the equivalent magnetic circuit method and finite-element (FE) analyses. A topology of VFMM with dual-layer PMs is further developed to alleviate the FBE induced from LCF PMs. It can be found that the FBE can be effectively suppressed by employing the dual-layer (DL) PM arrangement and additional leakage flux paths. A prototype of the proposed design is built, and the theoretical and FE results are experimentally verified. [ABSTRACT FROM AUTHOR]

Although the finite element method (FEM) is highly reliable, it is time-consuming and expensive, for example, substantial computing costs are incurred for coupled analysis while considering the mechanical and electromagnetic properties. Therefore, in this paper, a high-speed permanent magnet generator's electromagnetic and stress characteristics have been mathematically derived, and the optimal point is selected based on NSGA-II. The objective functions are power density and efficiency, with the constraints being the current density, slot fill factor, core saturation, voltage limit, and rotor safety factor. The method presented in this study was verified via FEM analysis and experimental results of the optimal model. [ABSTRACT FROM AUTHOR]

Electrically driven magnetization switch has attracted much attention in the new spintronic memory, especially for spin–orbit torque (SOT)-based magnetic random access memory (MRAM). However, the published models are facing limitations with the continuous shrinkage of the feature size down to nanoscale. Also, the thermal effect caused by switching operation is non-negligible. Therefore, an effective model is needed to represent the switching dynamic of the device concerning the influences of the nanoscale and the thermal effect. In the paper, a compact model of three-terminal SOT-driven switching is established. The influence of the voltage-controlled magnetic anisotropy (VCMA) and spin transfer torque (STT) effect induced by bias voltage on the field-free SOT-driven switching is considered by numerically solving the LLG equations. Furthermore, a 3D model of the SOT-MTJ device is established by finite element method to trace the thermoelectric behavior inside the device. The thermoelectric behavior is integrated into the compact model to show the influence of the temperature on the switching behavior, highlighting the importance of the thermal effect for the realistic modelling of SOT-driven switching. Finally, a novel voltage pulse scheme is proposed, which can effectively shorten the switching time and improve the reliability of the device. The established model could provide strategies and guidelines for next-generation memory design and application. [ABSTRACT FROM AUTHOR]