Field Finite Element Analysis Research Articles

Magnetic Circuit Design and Magnetic Field Finite Element Analysis of Converging Stepped Magnetofluid Seal with Small Clearance

The stepped magnetofluid seal is an effective method for improving the pressure ability of ordinary magnetofluid seals (OMS) with large clearance. At present, the research on stepped magnetofluid seal with less than 0.4 mm small clearance has not been carried out yet. The equivalent magnetic circuit design of converging stepped magnetofluid seal (CSMS) with small clearance has been carried out and verified by magnetic field finite element method based on the CSMS theory and magnetic circuit theory. The effects of the width of the axial seal position, the height of the radial seal position, the number of the pole tooth in the axial seal position, and the number of the pole tooth in the radial seal position on the theoretical pressure ability of the CSMS are investigated by numerical simulation. The calculation results are analyzed and discussed. The results show that the magnetic flux leakage at the junction of the permanent magnet and pole piece causes the higher pressure ability of the CSMS structure designed by the equivalent magnetic circuit method than that calculated by the magnetic field finite element method. When the width of the axial seal position is greater than the height of the radial seal position and the number of pole teeth in the axial seal position is less than the number of pole teeth in the radial seal position, the CSMS has the best effect. Compared with OMS with small clearance, CSMS has greater advantages.

Magnetic Field Finite Element Analysis of a Novel Diverging Stepped Magnetic Fluid Seal

In order to improve the anti pressure capability of magnetic fluid seal under the large gap condition, a novel diverging stepped magnetic fluid seal was designed and set the pole teeth on the stepped shaft. The magnetic field distribution in the gap of diverging stepped magnetic fluid seal were numerical simulations by the finite element method of magnetic field. The effects of axial pole teeth number, radial pole number, radial sealing gap height and axial sealing gap on the anti pressure capability of a novel diverging stepped magnetic fluid seal were studied. The results show that the anti pressure capabilities of magnetic fluid seal increase with the increase of axial pole teeth numbers. The anti pressure capabilities of magnetic fluid seal firstly decrease and then increase with the increase of radial pole teeth numbers. The anti pressure capability of magnetic fluid seal firstly decreases and then increase with the increase of radial sealing gap height. The anti pressure capabilities of magnetic fluid seal decrease with the increase of axial sealing gap width.

Vibration Behavior of Composite Slab with Precast Ribbed Panels due to Transient Impact

Excessive floor vibrations due to human activities such as heel-drop and jumping can induce annoyance to occupants and cause a serious serviceability problem. Both field tests and finite element analysis were conducted to study the vibration behavior of the composite slab with precast ribbed panels (CSPRP), a relatively new floor system compared with the cast-in-place reinforced concrete (RC) slab. In addition, both heel-drop and jumping impacts were employed to generate the acceleration response of the floor, from which two important vibration characteristics of natural frequencies and damping ratios are obtained. A comparison of the vibration behavior of CSPRPs with RC slabs indicates that the former exhibits more satisfactory perceptibility in terms of vibration. Appropriate coefficients (i.e. [Formula: see text] and [Formula: see text]) with the root-mean-square and peak accelerations subjected to heel-drop and jumping excitations are proposed for both CSPRPs and RC slabs. Lastly, an extensive parametric study considering different boundary conditions, floor types, and floor spans was carried out using the finite element method. It is recommended to use CSPRP under 3.3[Formula: see text]m span in order to keep the fundamental frequency above 3.0[Formula: see text]Hz.

Experimental modeling and application of push-pull electrostatic speakers.

This study modeled the circular diaphragm of push-pull electrostatic speakers using electro-mechano-acoustical equivalent circuits to determine the frequency responses related to the average displacement and sound pressure of the diaphragm with respect to acoustic impedance effects. A laser vibrometer system was used to measure the displacement in the center of the circular diaphragms (60 mm and 65 mm in diameter) in optically transparent indium tin oxide (ITO) electrostatic speakers. The sound pressure levels (SPLs) were predicted using the average displacement of the diaphragm without resorting to sound field measurements or finite element analysis. The predicted SPL results were then compared to acoustic measurements. The results demonstrate that ITO plates are a practical tool for the measurement of displacement and the prediction of SPLs. When the proposed electrostatic speaker (65-mm-diameter diaphragm) design was applied to the over-ear electrostatic headphone, the SPL curve obtained from artificial ear measurements was similar to the preferred target curve of Harman International (Stamford, CT). This resulted in outstanding sound quality comparable to that of high-end commercial dynamic headphones.

How to get a correct estimate of the plastic zone size for shear-mode fatigue cracks?

It was found that standardly calculated sizes of plastic zones ahead of mode II and mode III cracks during fatigue experiments close to threshold loading were very large and the stresses in the specimen net cross section without stress concentration were close to the yield stress. This represents a theoretical contradiction, since at threshold loading the plastic zones should be very small. In order to clarify the situation, results from three approaches were compared: (i) linear-elastic fracture mechanics, (ii) nonlinear Hutchinson-Rice-Rosengren (HRR) stress field and (iii) elastic-plastic finite element analysis considering nonlinear material behaviour according to the cyclic stress-strain curve. It was explained that, unlike under mode I loading, the plastic zone size should not be calculated using the applied maximum stress intensity factor (SIF). Instead, the effective SIF range needs to be used for calculation of stress fields ahead of the crack tip and, consequently the plastic zone sizes. Using these values realistic plastic zone sizes were obtained (less than 50μm). It also implies that stress in the specimen net cross section should not be calculated directly. A large part of loading applied to the specimen in terms of force or torque is transferred by fracture surfaces.

Experimental and analytical evaluation of the redundancy of repurposed fracture-critical railroad-flatcars

Previous research focused on the development of guidelines to load rate highway bridges constructed out of repurposed railroad flatcars (RRFCs). Those guidelines were based on field testing and finite element analysis conducted on existing RRFC bridges both in the field and in the lab. However, load rating is only one of the issues related to RRFCs as the main components are often classified as fracture critical members (FCMs) since there are only two flatcars in the cross section in most instances. Classifying the individual RRFCs as FCMs requires a rigorous hands-on inspection as per the Code of Federal Regulations, which greatly increases the long-term costs associated with these structures. Hence, while they are attractive to many owners due to their low initial costs and considerable strength, long-term costs due to inspection have deterred some owners from utilizing this viable and renewable alternative for low-volume applications. This paper presents the results of laboratory testing and non-linear finite element analysis of a railroad flatcar bridge specimen constructed with a composite reinforced concrete deck. The results confirm that RRFCs have considerable reserve strength and adequate load redundancy in a severely faulted state and need not be classified as FCMs if certain requirements are met. The paper also presents recommendations for load redistribution factors between primary members of RRFCs obtained through the experimental and verified by numerical studies.

Development and Analysis of the Magnetic Circuit on Double-Radial Permanent Magnet and Salient-Pole Electromagnetic Hybrid Excitation Generator for Vehicles

With the improvement of vehicles electrical equipment, the existing silicon rectification generator and permanent magnet generator cannot meet the requirement of the electric power consumption of the modern vehicles electrical equipment. It is difficult to adjust the air gap magnetic field of the permanent magnet generator. Consequently, the output voltage is not stable. The silicon rectifying generator has the problems of low efficiency and high failure rate. In order to solve these problems, a new type of hybrid excitation generator is developed in this paper. The developed hybrid excitation generator has a double-radial permanent magnet, a salient-pole electromagnetic combined rotor, and a fractional slot winding stator, where each rotor pole corresponds to 4.5 stator teeth. The equivalent magnetic circuit diagram of permanent magnet rotor and magnetic rotor is established. Magnetic field finite element analysis (FEA) software is used to conduct the modeling and simulation analysis on double-radial permanent magnet magnetic field, salient-pole electro-magnetic magnetic field and hybrid magnetic field. The magnetic flux density mold value diagram and vector diagram are obtained. The diagrams are used to verify the feasibility of this design. The designed electromagnetic coupling regulator controller can ensure the stable voltage export by changing the magnitude and direction of the excitation current to adjust the size of the air gap magnetic field. Therefore, the problem of output voltage instability in the wide speed range and wide load range of the hybrid excitation generator is solved.

Failure Analysis of Fatigue Cracking in the Tension Clamp of a Rail Fastening System

Fatigue cracking was recently discovered in the tension clamp (SKL15) of a rail fastening system during its service life. Here, the fatigue strengths of SKL15 and SKLB15 (used for replacement) tension clamps were assessed using field measurements and finite element analyses. The strain and displacement of these tension clamps were measured both in a laboratory and at the section of railway track where the original fatigue cracking occurred. Due to limited access to the exact crack initiation location, the strain gauge was instead installed nearby. Finite element analysis was conducted to obtain the stress conditions at the crack initiation location. Extremely high stresses were produced after the installation of tension clamps SKL15 and SKLB15, and this allowed small stress amplitudes for fatigue cracking. The fatigue strengths of the clamps were evaluated using Goodman and Gerber curves. The stress amplitude of the SKL15 was greater than the allowable stress amplitude, presenting the possibility of fatigue cracking.

Sensitivity Analysis and Optimal Design of a Stator Coreless Axial Flux Permanent Magnet Synchronous Generator

In this paper, the modified initial design procedure and economic optimization design of a stator coreless axial flux permanent magnet synchronous generator (AFPMSG) are presented to improve the design accuracy, efficiency, and economy. Static magnetic field finite-element analysis (FEA) is applied to the magnetic equivalent circuit (MEC) method to increase the accuracy of electromagnetic parameters and reduce the iteration times. The accuracy and efficiency of the initial design is improved by the combination of MEC method and static magnetic field FEA in the design procedure. For the economic optimization, the permanent magnetic (PM) material volume model, which affects the cost of the AFPMSG the most, is derived, and the influence degree of the main structure parameters, to the performance, is distinguished and sorted by sensitivity analysis. The hybrid genetic algorithm that combines the simulated annealing and father-offspring selection method is studied and adopted to search for the best optimization solution from the different influence degree and nonlinear interaction parameters. A 1 kW AFPMSG is designed and optimized via the proposed design procedure and optimization design. Finally, 3D finite-element models of the generator are simulated and compared to confirm the validity of the proposed improved design and the generator performance.

Long-term performance of fiber-grid-reinforced asphalt overlay pavements: A case study of Korean national highways

Abstract The objective of this study was to verify the effect of fiber grid reinforcement on the long-term performance of asphalt overlay pavements by performing field investigation, laboratory test, and finite element analysis. Crack, rutting, roughness, and other miscellaneous distresses of fiber-grid-reinforced overlay sections and ordinary overlay sections were compared. Pavement conditions of fiber grid overlay sections before and after the overlay were also compared. Cores were obtained from the fiber-grid-reinforced and ordinary sections to measure bonding shear strength between the intermediate and overlay layers. Fracture energy, displacement after yield, and shear stiffness of the cores were also obtained by analyzing the test results. Finite element analysis was performed by using the test results to validate the effect of the fiber grid reinforcement on the long-term performance of asphalt overlay pavements. Rutting and fatigue cracking were predicted for three cases: 1) fiber grid was not used; 2) glass fiber grid was used; and 3) carbon fiber grid was used. The cracking ratio of fiber-grid-reinforced sections was much smaller than that of ordinary sections. The results of field investigation, laboratory test, and finite element analysis showed that the fiber grid reinforcement improved the long-term performance of asphalt overlay pavements.

Aerodynamic characteristics of a long-span cable-stayed bridge under construction

Aerodynamic characteristics or parameters such as pressure distributions, static force coefficients, and aerodynamic admittance of a long-span cable-stayed bridge girder during the erection stage have been investigated through field measurements. Buffeting response of the bridge girder at the longest single-cantilever stage was estimated via the field measurements and finite element analysis. Results of this study suggest that the drag- and lift-force coefficients, estimated from the field measurements, increase with an increase in the angle of attack. The Sears function and Davenport’s approximation function were found to overestimate corresponding aerodynamic admittances in the low frequency region. In the high frequency region, the Sears function tends to underestimate the lift force and moment aerodynamic admittances. Davenport’s approximation function were found to be smaller compared to those drag force aerodynamic admittance obtained via the field measurements. Lastly, the buffeting response of the bridge obtained via the finite element analysis and field measurements were found to agree well within a given range of wind speed.

A New Architectural Perspective on Wind Damage in a Natural Forest

Wind damage is a significant driver of forest structure, ecology and carbon cycling in both temperate and tropical regions, but most of the literature on wind damage focusses on conifer plantations. Previous studies in broadleaf forests have been limited by a lack of data on tree architecture, a problem that is potentially overcome by terrestrial laser scanning. Here we apply novel approaches to estimate the critical wind speeds at which trees will break in a temperate, deciduous forest plot in Wytham Woods, UK, using a combination of field data and finite element analysis. Ash trees (Fraxinus excelsior) tend to have lower critical wind speeds than sycamores (Acer pseudoplatanus), while English oak (Quercus robur) are the most mechanically robust. This difference in critical wind speed is driven by tree size and architecture, rather than material properties. We observe a trade-off between critical wind speed and growth rate, both within and across species. Our estimates of critical wind speeds from field data are lower in summer than in winter, emphasizing the importance of the spring and autumn transition periods. Of the three species we studied, those with lower critical wind speeds drop their leaves earlier in autumn, suggesting that the timing of leaf shedding may be under selection pressure to minimize risk of tree damage from winter storms. These results are tentative, but also intriguing and intuitive.

Magnetic field finite element analysis of concentric biaxial stepped ferrofluid seals

Magnetic field finite element analysis of concentric biaxial stepped ferrofluid seals

Overheated pipe due to scale: Field failure investigation and finite element analysis

Through a field failure investigation and finite element analysis, a study on overheated pipe due to scale was performed. The field failure samples were collected from primary reformer convection tube made of material based on ASTM A 335 grad P91 modified specification. The type of the object was a fin tube coil. The tube shows rupture with the shape of fish mouth accompanied by bulging. The analysis performed using finite element mimics the actual field conditions. It was discovered that long term overheating due to scale both at the outside and in the inside of the tube hinders the smooth heat transfer process. This consequently leads to poor heat transfer and violates the original design philosophy. Metallurgical evaluation proves this verdict. Furthermore, the finite element analysis also supports the conclusion.

On characterizing spatially variable soil Young’s modulus using spatial average

The purpose of this study is to investigate whether the effective Young’s modulus (Eeff) for a spatial variable soil mass can be strongly correlated to any spatial average. The spatially variable Young’s modulus of the soil mass is modeled as a stationary lognormal random field, and the Eeff of the soil mass is simulated by random field finite element analysis. Spatial averages are calculated from the input random field. If a strong correlation exists, it is possible to replace a random field analysis by a simpler random variable analysis. Two classes of problems are considered: a soil cube subjected to displacement-controlled compression and a footing problem. For the soil cube problem, Eeff is found to be strongly correlated to a suitable spatial average. However, for the footing problem, only the statistics (mean and standard deviation) of Eeff can be well approximated by a suitable spatial average, but the correlation is not strong. It is possible that the two classes of problems behave differently because the finite elements in the soil cube are mobilized uniformly, whereas those in the footing problem are mobilized non-uniformly. This leads to a weighted spatial average model that applies a different weight on the log modulus of each finite element over the domain being averaged.

Evaluation of top-down cracking potential for asphalt pavements with 4.75 mm nominal maximum aggregate size mixture layer using full-scale field tests and finite element analysis

This study primarily focused on evaluating top-down cracking resistance for pavement structures with 4.75 mm nominal maximum aggregate size asphalt mixtures (i.e. SP-4.75) that will help determine more effective application of these mixes for layered flexible pavement system. Crack evaluation and pavement surface response measurements were conducted using full-scale field test sections. In addition, a three-dimensional (3-D) viscoelastic finite-element (FE) pavement model was developed to further validate the results of field tests using analytical solution. The results indicated that the pavement structure with SP-4.75 mixture at the top becomes more prone to top-down cracking when a thin layer with unmodified asphalt binder is applied. It was found that both layer thickness and binder type are key parameters to control top-down cracking potential. Also, the comparative observations between analytical and experimental results confirm that the FE model developed was able to provide accurate, reliable, and realistic prediction for change in pavement surface strain responses due to different conditions of SP-4.75 layer application. It was concluded that adequate thickness and binder type should be considered for proper application of SP-4.75 mixture as a surface course of layered flexible pavement system to effectively resist top-down cracking.

Impact of Mechanical Stress on Characteristics of Interior Permanent Magnet Synchronous Motors

In this paper, we investigate the impact of mechanical stress on characteristics of interior permanent magnet synchronous motors from both results of measurement and calculation. First, the basic experiments by using stator cores with/without shrink fitting of housings are carried out. The measured iron loss is compared with the calculated results obtained by combined stress and electromagnetic field finite-element analysis. Next, the measured torque and iron loss of the motor under load conditions are compared with the analysis that considers the mechanical stress caused by both the stator shrink fitting and the rotor centrifugal force. The measured and calculated results are found to be in good agreement. From these results, it is clarified that the mechanical stress causes not only an increase in the stator iron loss, but also an increase in the rotor-iron loss, and a decrease in the reluctance torque of interior permanent magnet synchronous motors.

Dynamic assessment of a FRP suspension footbridge through field testing and finite element modelling

The use of advanced fibre composite materials in bridge engineering offers alternative solutions to structural problems compared to traditional construction materials. Advanced composite or fibre reinforced polymer (FRP) materials have high strength to weight ratios, which can be especially beneficial where dead load or material handling considerations govern a design. However, the reduced weight and stiffness of FRP footbridges results in generally poorer dynamic performance, and vibration serviceability is likely to govern their design to avoid the footbridge being too lively. This study investigates the dynamic behaviour of the 51.3 m span Wilcott FRP suspension footbridge. The assessment is performed through a combination of field testing and finite element analysis, and the measured performance of the bridge is being used to calibrate the model through an updating procedure. The resulting updated model allowed detailed interpretation of the results. It showed that non-structural members such as the parapets can influence the dynamic behaviour of slender, lightweight footbridges, and consequently their contribution must be included during the dynamic assessment of a structure. The test data showed that the FRP footbridge is prone to pedestrian induced vibrations, although the measured response levels were lower than limits specified in relevant standards.

Toroidal Field Electromagnetic Launcher

A conventional electromagnetic launcher is incapable of driving large mass for the inherent technical drawback. This paper presents a novel electromagnetic launcher based on toroidal magnetic field induction acceleration. The fundamental model and launch mechanism of the electromagnetic acceleration force from toroidal magnetic field interaction are first proposed and analyzed. The essential theory with systematic formulism for toroidal magnetic field, circuit, and dynamics is established. Circumventing necessary initial speed, huge propulsion could be obtained by projectile from the improved effective electromagnetic force and larger radial cross-sectional area with significant eddy current. The four-stage transient launch process of the toroidal field electromagnetic launcher is simulated through electromagnetic field finite-element analysis. The simulation results demonstrate that the toroidal field electromagnetic launcher is a potential candidate for massive emission and supervelocity launch.

Analysis of the Settlement of Roadbed-Culvert Transitional Section in the High Salinity Regions

In this paper, the construction treatment technology for the transition section connecting road and culvert founded on the high salt saturated fine sand is carried out, in which an actual project of a new local railway from XieTieshan to North Hobson in China is the background. Meanwhile,the field monitoring and finite element analysis of the settlement law of the transition section are carried out under different load conditions. The results are of referential significance to the settlement law and design of roadbed-culvert transitional section in high salinity regions.