Finite Element Method Calculations Research Articles

Rotor Design of Line-Start Synchronous Reluctance Machine With Round Bars

Within the field of industry applications, the induction machine (IM) is the most used motor type, due to its robustness and line-start ability. However, the need to constrain global warming demands new sustainable technologies with high efficiency. Therefore, line-start synchronous reluctance machines could be an opportunity to achieve a high efficiency for several industry applications, especially for constant-speed drives. This paper introduces a unique rotor design for line-start synchronous reluctance machines (LSSynRMs). Additionally, the influence of the rotor bar material/resistance and the stator resistance in comparison to common IMs for industrial applications is investigated. Finite element method calculations were used for the design and the efficiency enhancement was verified using experiments. Within the context of this analysis, a 4-kW-rated IM with an efficiency rating of IE3 was chosen as a benchmark motor. The new rotor-cage design decreases the motor losses at steady state by about 28%. This promising approach could be used to upgrade IMs in industry environments instead of replacing them. Nevertheless, a challenge in the design is a good balance between the steady-state performance and synchronization capability, which in turn limits the range of industrial applications for highly efficient LSSynRMs.

ITER Torus Diamond Window Unit: FEM Analyses and Impact on the Design

The ITER torus diamond window unit is part of the electron cyclotron (EC) upper launcher (UL) used to direct high power microwave beams generated by the gyrotrons into the plasma for heating and current drive (H&CD) applications. The UL consists of an assembly of ex-vessel waveguides (WGs) and an in-vessel port plug (PP). The diamond window units form vacuum and confinement boundaries between the torus volume and the transmission lines (TLs) which guide beams between 1 and 1.5 MW at 170 GHz from the gyrotrons to the launcher. There are eight window units attached to the assembly of the WGs, one unit for each WG. The design strategy of the unit is to have a very rigid outer frame able to withstand the potential external loads acting on the unit while thin copper cuffs brazed to the diamond disk allow indirect cooling of the disk to remove the EC power absorption during the beam transmission. The load combination given by the stringent ITER seismic level 2 (SL-2) event occurring during baking of the torus vessel is the design driver for the outer frame of the unit. In fact, the assembly of the WGs is connected from one side to the ceiling of the ITER port cell area by a support frame and to the UL PP from the other side. Movements of the torus vessel due to baking, seismic and plasma disruption events, result in forces and moments acting on the units. Furthermore, during a seismic event, the unit is subject to additional loads induced by the oscillation of the support frame attached to the ceiling. An outer frame surrounding the window unit is thus required to ensure the structural integrity and the confinement function of the unit. This paper shows how the design of the window unit was assessed and optimized by finite element method (FEM) analyses. A specific methodology was developed to carry out the analyses with respect to the seismic and baking loads. At Karlsruhe Institute of Technology (KIT), FABRY-PEROT resonators measure the loss tangent of the diamond disk and it is then used as input to the computational fluid dynamics and FEM analyses aiming to assess the design. The impact of the FEM analyses on the design of the window unit is discussed also together with the manufacturing aspects of the unit.

Optimal Design of Rotor Slot Geometry to Reduce Rotor Leakage Reactance and Increase Starting Performance for High-Speed Spindle Motors

This paper proposes optimal designs of three closed rotor slots geometries for reducing the rotor leakage reactance and increasing the starting performance of high-speed spindle motors. The optimal designs were developed using the response surface methodology and Finite Element Method (FEM). Three closed rotor slot geometries, namely closed, round, and oval were investigated through FEM calculation and validated by experimental measurement for improving starting performance parameters such as starting current, starting torque, magnetic flux linkage in starting condition, and efficiency. In this study, a starting performance analysis, including the alternative equivalent circuit method and flux linkage FEM analysis, was employed. The results show that among the three slot geometries, the optimal design of the circular closed rotor slot produces the lowest rotor leakage reactance and the highest magnetic flux linkage, starting torque, and efficiency. A comparison between the simulation and experimental results validated the accuracy of the proposed model with percentage error being approximately 8%.

Local fracture toughness measurements in polycrystalline cubic zirconia using micro-cantilever bending tests

Local fracture toughness of a polycristalline ceramic was characterized with the micro-cantilever bending method. Beams were milled in single grains of cubic zirconia using a Focused Ion Beam (FIB) microscope. Grains with specific crystallographic orientations were chosen using Electron Backscatter Diffraction (EBSD) measurements to test specific plane families. Notched micro-cantilever beams were loaded up to fracture using a nano-indenter. For fracture toughness evaluation, three different methods were considered: an analytical solution, an isotropic Finite Element Method (FEM) calculation, and an anisotropic FEM model. These three methods gave similar toughness values. A good agreement was found with literature data measured on cubic zirconia single crystals at a macroscopic scale. In this work, no significant difference was noticed for fracture toughness between {100}, {110} and {111} crystallographic plane families. Such method could be used to characterize the local fracture properties of a sample showing extensive cracking such as irradiated nuclear fuel.

Wave Frequency Effects on Damage Imaging in Adhesive Joints Using Lamb Waves and RMS

Structural adhesive joints have numerous applications in many fields of industry. The gradual deterioration of adhesive material over time causes a possibility of unexpected failure and the need for non-destructive testing of existing joints. The Lamb wave propagation method is one of the most promising techniques for the damage identification of such connections. The aim of this study was experimental and numerical research on the effects of the wave frequency on damage identification in a single-lap adhesive joint of steel plates. The ultrasonic waves were excited at one point of an analyzed specimen and then measured in a certain area of the joint. The recorded wave velocity signals were processed by the way of a root mean square (RMS) calculation, giving the actual position and geometry of defects. In addition to the visual assessment of damage maps, a statistical analysis was conducted. The influence of an excitation frequency value on the obtained visualizations was considered experimentally and numerically in the wide range for a single defect. Supplementary finite element method (FEM) calculations were performed for three additional damage variants. The results revealed some limitations of the proposed method. The main conclusion was that the effectiveness of measurements strongly depends on the chosen wave frequency value.

Halo approach to evaluate the stress distribution in 3D discrete element method simulation: validation and application to flax/bio based epoxy composite

Discrete element method (DEM) is an interesting alternative to classical approaches as the finite element method (FEM) to simulate homogeneous and heterogeneous materials. Indeed, although DEM was initially developed to simulate granular systems in motion, it also enables to model a continuous medium with the help of a dense granular packing in which the cohesion is introduced between each pair of particles in contact using beam or spring elements. However, among other issues, the local stress field obtained using DEM is heterogeneous, even in the case where it is theoretically homogeneous. In the present contribution, we investigate the stress field distribution in 3D DEM mechanical simulation, and propose an approach we named Halo, to evaluate the level of stress distribution. The idea of the method is to evaluate the stress at the scale of every discrete element (DE) taking into account the contribution of its neighbors, inside the Halo of the DE. The effect of the number of DEs per Halo on the stress distribution is discussed in homogeneous and heterogeneous media. The approach results for homogeneous media are compared to FEM calculations and to the theoretical Hertz solution via a Brazilian test. For the homogeneous media, we use the unidirectional flax/bio based epoxy composite, for which macroscopic longitudinal Young’s modulus is experimentally quantified. Furthermore, comparisons with FEM are performed in this context. Results highlight a good agreement between both approaches in terms of stress fields including extremal values.

Cross-shaped nanostructures for the study of spin to charge inter-conversion using spin-orbit coupling in non-magnetic materials

Several spin–orbit effects allow performing spin to charge interconversion due to the spin Hall effects or the spin-momentum locking at Rashba interfaces and topological insulator surface states. Here, we focus on how these interconversions can be made electrically, using three different cross-shaped nanostructures. We apply the measurement configurations to the case of the spin Hall effect in Pt using CoFe electrodes to detect or inject spins. Both the direct and inverse spin Hall effects can be detected, with spin Hall signals up to two orders of magnitude higher than that of nonlocal measurements in metallic lateral spin valves, and with a much simpler fabrication protocol. We compare the respective signal amplitude of the three proposed geometries. Finally, we show that finite element method calculations allow extracting the spin Hall angle and the spin diffusion length of Pt from these measurements.

Strain related relaxation of the GaAs-like Raman mode selection rules in hydrogenated GaAs1−xNx layers

The GaAs-like longitudinal-optical (LO) phonon frequency in hydrogenated GaAs1−xNx (x = 0.01) layers—with different H doses and similar low-energy irradiation conditions—was investigated by micro-Raman measurements in different scattering geometries and compared with those of epitaxial GaAs and as-grown GaAs1−xNx reference samples. A relaxation of the GaAs selection rules was observed, to be explained mainly on the basis of the biaxial strain affecting the layers. The evolution of the LO phonon frequency with increasing hydrogen dose was found to heavily depend on light polarization, thus suggesting that a linear relation between strain and the frequency of the GaAs-like LO phonon mode should be applied with some caution. Moreover, photoreflectance measurements in fully passivated samples of identical N concentration show that the blueshift of the GaAs-like LO frequency, characteristic of the hydrogenated structures, is dose-dependent and strictly related to the strain induced by the specific type of the dominant N-H complexes. A comparison of photoreflectance results with the finite element method calculations confirms that this dependence on the H dose is due to the gradual replacement of the N-2H complexes responsible for the electronic passivation of N with N-3H complexes, which are well known to induce an additional and sizeable lattice expansion.

Fracture Toughness Calculation Method Amendment of the Dissimilar Steel Welded Joint Based on 3D XFEM

The dissimilar steel welded joint is divided into three pieces, parent material–weldmetal–parent material, by the integrity identification of BS7910-2013. In reality, the undermatchedwelded joint geometry is dierent: parent material–heat aected zone (HAZ)–fusion line–weld metal.A combination of the CF62 (parent material) and E316L (welding rod) was the example undermatchedwelded joint, whose geometry was divided into four pieces to investigate the fracture toughness of thejoint by experiments and the extended finite element method (XFEM) calculation. The experimentalresults were used to change the fracture toughness of the undermatched welded joint, and the XFEMresults were used to amend the fracture toughness calculation method with a new definition of thecrack length. The research results show that the amendment of the undermatched welded jointgeometry expresses more accuracy of the fracture toughness of the joint. The XFEM models wereverified as valid by the experiment. The amendment of the fracture toughness calculation methodexpresses a better fit by the new definition of the crack length, in accordance with the crack routesimulated by the XFEM. The results after the amendment coincide with the reality in engineering.

Theoretical and practical backgrounds of monitoring system of ship power transmission systems\u2019 torsional vibration

Reliability of the marine propulsion system is closely correlated with the safety of navigation at sea. Typical ship’s powertrain has a lot of advantages (mainly efficiency) but is the source of high vibration level. What is more, rough sea conditions can be a source of additional ship vibration, especially for big container ships. Vibrations may have a dangerous influence on ship equipment’s strength and consequently on the ship’s safety. Torsional vibrations of the marine power transmission system are usually the most dangerous for the shaft line and the crankshaft. The power of propulsion system is quite often measured by commercial measuring device based on instantaneous angular speed (IAS). The angular speed measurements are performed using two optical sensors for reading the IAS, mounted at shaft line. The authors try to use existing apparatus for torsional vibrations’ continuous monitoring. Designing monitoring methodology consists several analytical methods. Simplified method of torsional vibration calculation is a first one. Simplified calculation method gives us a determination possibility of torsional vibrations in typical and emergency working conditions. Natural frequency value (resonance location) as well as vibration amplitudes can be estimated on the base of the method. The presented calculation method was verified by comparison with the detailed finite element method calculation and measurements on real ships. The second part of the monitoring system contains methodology of monitoring of piston engine’s crankshaft torsional vibrations by measurement of IAS at free and power output ends of the engine’s crankshaft. It is assumed that calculation of differential value between both ends shall give the picture of torsion angle magnitudes and phases of the peak values. Analysis method of recorded signals (e.g., recalculation of angular distance sampling into constants time function and frequency base by FFT analysis) is also developed. Description of the measurements of the crankshaft torsional vibration for marine engine with some simulated malfunction (a leak of fuel injection pump, and relayed on mounting of sets of injection valves with different nozzles characteristics—spraying nozzle angle) is presented. Presented results of experiment derive from test cycle carried out using laboratory stand of Gdynia Maritime University equipped with 3-cylinder self-ignition engine, powering electric generator. The planned monitoring system should have detecting possibility of torsional vibration changes (propulsion system malfunction), the ability to assess the degree of danger of failure and eventually determination of the risk of damage and the causes of propulsion system’s threat failure.

Analysis of Surface Geometry Changes after Hybrid Milling and Burnishing by Ceramic Ball.

The production of modern machines requires parts with much greater geometric accuracy and surface geometry (SG) precision than several years ago. These requirements are met by so-called hybrid technologies that must simultaneously be inexpensive to implement. The integration of treatment procedures (usually in one operation) is geared towards achieving a synergistic effect. Combining different treatments from various technologies produces synergy, i.e., benefits greater than the optimization of each individual process done separately. This paper presents experimental results and numerical experiment data on surface plastic deformation. The hybrid technology used in the study was a combination of milling and finishing with plastic burnishing using a ceramic ball. These processes were integrated on a multi-axis CNC machining center. The plastic deformations of real surfaces were determined in simulations. The paper also discusses the structure of the model and how to use it to conduct a finite element method (FEM) computer simulation. The aim of the study was to determine how to use the potential developed model of hybrid treatment to predict the surface performance expressed by the amplitude, volume, and functional parameters of the surface geometry, with the EN-ISO 25178-2 profile.

Seismic numerical investigation on historical centres compounds: a new modelling technique of structural units

Historical centres are often constituted of a series of masonry building compounds very vulnerable to earthquakes, whose static non-linear behaviour is not predicted by building codes. This paper propose a simplified modelling approach to predict the seismic response of structural units into masonry building compounds. This approach is based on the equivalent frame method modelling, a technique easy to be implemented within finite element method calculation programs. The modelling technique has been applied to investigate constructions representative of Southern Italy building aggregates erected during the past decades. Firstly, the whole aggregates have been modelled and analysed in order to evaluate the seismic behaviour of structural units having intermediate, heading and corner positions. Later on, the seismic response of these structural units has been assessed by modelling the single units as isolated structures with appropriate boundary conditions to consider, in a simplified way, their position in the aggregate and, therefore, the influence of other constructions. Finally, comparison of the achieved results has been carried out in order to confirm the effectiveness of the proposed analysis approach.

Numerical investigations on the electromagnetic enhancement effect to tip-enhanced Raman scattering and fluorescence processes

In the present work, we theoretically study the electromagnetic (EM) enhancement of the Raman and fluorescence signals for a molecule placed in a nanocavity formed by a metallic tip and substrate that mimics a tip-enhanced Raman scattering (TERS) setup using three-dimensional finite element method calculations. The influence of tip size and tip-molecule distance on the EM enhancements of the incident field as well as the radiative and non-radiative decay rates of the molecule are systematically investigated. Simulation results show that the maximum EM enhancement to the incident light as provided by the localized surface plasmon resonance in the nanocavity can reach ∼285 for the configuration considered in the present work. Meanwhile, it was found that, at the classical limit, decreasing the apex radius or the tip-molecule distance can both reduce the spatial distribution (as characterized by the full width at half maximum) of the Raman enhancement in a linear fashion. Moreover, simulation results show that the nonlocal dielectric response of the tip and the substrate plays a key role to the fluorescence quantum yield of the molecule. However, it was found that the strong EM excitation enhancement is the dominating factor for the tip enhanced fluorescence (TEF) effect and stronger fluorescence enhancement has been found when increasing the apex radius or reducing the tip-molecule distance with an incident wavelength of 532 nm. The best TERS and TEF enhancements were found to be ∼ and ∼, respectively, with the tip-molecule distance around 1 nm.

Near-field imaging of surface-plasmon vortex-modes around a single elliptical nanohole in a gold film

We present scanning near-field images of surface plasmon modes around a single elliptical nanohole in 88 nm thick Au film. We find that rotating surface plasmon vortex modes carrying extrinsic orbital angular momentum can be induced under linearly polarized illumination. The vortex modes are obtained only when the incident polarization direction differs from one of the ellipse axes. Such a direct observation of the vortex modes is possible thanks to the ability of the SNOM technique to obtain information on both the amplitude and the phase of the near-field. The presence of the vortex mode is determined by the rotational symmetry breaking of the system. Finite element method calculations show that such a vorticity originates from the presence of nodal points where the phase of the field is undefined, leading to a circulation of the energy flow. The configuration producing vortex modes corresponds to a nonzero total topological charge (+1).

Synthesis and Characterization of Elongated-Shaped Silver Nanoparticles as a Biocompatible Anisotropic SERS Probe for Intracellular Imaging: Theoretical Modeling and Experimental Verification.

Progress in the field of biocompatible SERS nanoparticles has promising prospects for biomedical applications. In this work, we have developed a biocompatible Raman probe by combining anisotropic silver nanoparticles with the dye rhodamine 6G followed by subsequent coating with bovine serum albumin. This nanosystem presents strong SERS capabilities in the near infrared (NIR) with a very high (2.7 × 107) analytical enhancement factor. Theoretical calculations reveal the effects of the electromagnetic and chemical mechanisms in the observed SERS effect for this nanosystem. Finite element method (FEM) calculations showed a considerable near field enhancement in NIR. Using density functional quantum chemical calculations, the chemical enhancement mechanism of rhodamine 6G by interaction with the nanoparticles was probed, allowing us to calculate spectra that closely reproduce the experimental results. The nanosystem was tested in cell culture experiments, showing cell internalization and also proving to be completely biocompatible, as no cell death was observed. Using a NIR laser, SERS signals could be detected even from inside cells, proving the applicability of this nanosystem as a biocompatible SERS probe.

The impact of partly liquefied SF<inf>6</inf> on the dielectric performance of SF<inf>6</inf>-insulated switchgear

When gas insulated switchgear (GIS) is operated at temperatures below the condensation temperature of the SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> used as the insulating medium, liquid droplets or puddles can form and influence the electric field distribution. For the surface conditions and electric field strengths and distributions relevant for GIS, the instability of liquid droplets represents the worst case. Finite element method calculations were carried out to model the interaction between the electric field and unstable liquid droplets, both for water (in air) and liquid SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . The model accurately reproduced experimental data available for water in the literature. The model was then used to assess how critical the presence of liquid SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> droplets is for the dielectric performance of GIS. It was found that SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> droplets are much less critical than small (0.5 mm) metallic particles, the presence of which is assumed and taken into account in the design of GIS. Water droplets, on the other hand, can lead to high field enhancement and a corresponding reduction in the breakdown electric field strength.

Influence of Warping on Bearing Capacity of Steel I-Beam with Non-Fork Support

The European Standard 3 does not provide a direct answer about how to verify the bearing capacity of a beam with non-fork support. For a pinned beam it assumes, that there is no constraint on lateral bending and warping or full restraint. But in the most of design cases the constrainment is somewhere between them. There are some guidelines in scientific literature and computer programs that enhance the calculation of the value of a Critical Moment (which governs the Lateral-Torsional Buckling and as a result – the Bearing Capacity of Bending) for a flexible support. But there is no official information about which of method is the best for a certain case. To confine the variables only an influence of warping on a Lateral-Torsional Buckling was taken into the consideration. It was created by adding an endplate on one or both ends of a beam. Few approaches to calculate the Critical Moment were compared. A beam based on cross section of IS-300/150/10.7/7.1 with the length of 5.0m were taken into the consideration. The first method is the General Formula from pre-code of the European Standard 3 (1992) with the additional equations for calculating the stiffness of endplates according to Lindner (1994). The second approach bases on the General Formula, but with modification of C1 factor derived by Lopez, Yong and Serna (2006). The third method uses very similar equation to the G. F., but with other value of C1 factor. It was derived by Lindner (1994). Those approximated formulas were compared with Finite Element Method calculation. It was conducted using three different computer programs. In the first one, ABAQUS CAE, the spatial shell model of a beam was created. An influence of a type of a discretisation on results was validated. Secondly, LTBeamN, the dedicated program for calculating the value of Critical Moment written by CTICM, was used. Thirdly, computing was made using the RFEM – an application for civil engineers which allows to create models of beams with seven degrees of freedom in each node. The results show that an endplate’s influence on a value of a Critical Moment is significant. Even the thinnest plates can noticeably increase the bearing capacity of a cross-section. But over the certain value of plate’s thickness there is no further growth of the Critical Moment value. The results from equations based on the General Formula and calculations with the FEM are approximate for endplates below 4.0cm of thickness. It is very important to take few approaches to discretise the model of beam with endplates using ABAQUS, because there could be a major difference between them in outcomes.

Tunable plasmonic resonances in Si-Au slanted columnar heterostructure thin films

We report on fabrication of spatially-coherent columnar plasmonic nanostructure superlattice-type thin films with high porosity and strong optical anisotropy using glancing angle deposition. Subsequent and repeated depositions of silicon and gold lead to nanometer-dimension subcolumns with controlled lengths. We perform generalized spectroscopic ellipsometry measurements and finite element method computations to elucidate the strongly anisotropic optical properties of the highly-porous Si-Au slanted columnar heterostructures. The occurrence of a strongly localized plasmonic mode with displacement pattern reminiscent of a dark quadrupole mode is observed in the vicinity of the gold subcolumns. We demonstrate tuning of this quadrupole-like mode frequency within the near-infrared spectral range by varying the geometry of Si-Au slanted columnar heterostructures. In addition, coupled-plasmon-like and inter-band transition-like modes occur in the visible and ultra-violet spectral regions, respectively. We elucidate an example for the potential use of Si-Au slanted columnar heterostructures as a highly porous plasmonic sensor with optical read out sensitivity to few parts-per-million solvent levels in water.

Eddy Current Linear Speed Sensor

Novel eddy current speed sensor with axisymmetric coils and solid iron rod as moving part is presented. The analysis is performed for both dc and ac coil currents and for variable iron rod translational speed. The coil inductance and induced voltage results using the analytical method and finite-element method calculation are compared with the measured values. Two different coil configurations are used for simulations and measurement.

Dynamic testing of asphalt mixes

In the presented research, conventional cyclic tension–compression complex modulus tests and dynamic tests were performed on an asphalt mix (AM) specimen. For the tension–compression tests, the complex modulus was calculated from the measurements of the axial strain and axial stress. For the dynamic tests, an automated impact hammer equipped with a load cell and an accelerometer were used to determine the frequency response functions (FRFs) at five different temperatures. A back-analysis using finite element method (FEM) calculations and a very simple modelling of the material behaviour was proposed to determine the complex modulus of the specimen at each tested temperature. Complex modulus results from dynamic and cyclic tests were compared and are in good agreement. The norm of the complex modulus obtained from dynamic test is slightly higher and no significant difference is seen for the phase angle. Part of the differences observed may be explained by the nonlinearity of AM (strain amplitude is about 500 times smaller for dynamic tests).