Three-dimensional Finite Element Method Simulations Research Articles

Modeling of the Interminiband Absorption Coefficient in InGaN Quantum Dot Superlattices

In this paper, a model to estimate minibands and theinterminiband absorption coefficient for a wurtzite (WZ) indium gallium nitride (InGaN) self-assembled quantum dot superlattice (QDSL) is developed. It considers a simplified cuboid shape for quantum dots (QDs). The semi-analytical investigation starts from evaluation through the three-dimensional (3D) finite element method (FEM) simulations of crystal mechanical deformation derived from heterostructure lattice mismatch under spontaneous and piezoelectric polarization effects. From these results, mean values in QDs and barrier regions of charge carriers’ electric potentials and effective masses for the conduction band (CB) and three valence sub-bands for each direction are evaluated. For the minibands’ investigation, the single-particle time-independent Schrödinger equation in effective mass approximation is decoupled in three directions and resolved using the one-dimensional (1D) Kronig–Penney model. The built-in electric field is also considered along the polar axis direction, obtaining Wannier–Stark ladders. Then, theinterminiband absorption coefficient in thermal equilibrium for transverse electric (TE) and magnetic (TM) incident light polarization is calculated using Fermi’s golden rule implementation based on a numerical integration into the first Brillouin zone. For more detailed results, an absorption coefficient component related to superlattice free excitons is also introduced. Finally, some simulation results, observations and comments are given.

Cause analysis on permanent deformation for asphalt pavements using field cores

Mechanical tests for asphalt mixtures generally use laboratory-produced specimens, which cannot truly represent material properties and construction conditions as they exist in the field. Therefore, field core samples have been increasingly selected for pavement performance testing. In this study, the field sampling and performance survey were firstly conducted on a highway with different pavement structures. Then, a three-dimensional finite element method (FEM) simulation was performed to compare the critical pavement responses related to permanent deformation (shear stress and pavement surface deflection) for different pavement structures. The advanced repeated load permanent deformation (ARLPD) and conventional repeated load permanent deformation (RLPD) tests were respectively employed to evaluate the rutting resistance on selected field cores. After mechanical tests, these specimens were further checked by the extraction and sieving tests. It is found from theoretical analysis that the maximum shear stress occurs at different locations (sublayers) for asphalt layers with different thicknesses. Consistent conclusions can be made from the ARLPD and RLPD tests results. Flow number index Fi shows the best ability to identify the field rutting resistance of asphalt pavements. A fair relationship is found between Fi measured from the ARLPD and RLPD tests. Compared with the control section with dense graded mixtures, heavy-duty long lasting pavement, porous permeable asphalt pavement, and asphalt rubber concrete pavement show superior rutting resistance while thin layer asphalt concrete pavement shows very poor anti-rutting performance at high temperatures. Finally, rutting causes and main factors for different pavement sections were respectively investigated. All these findings in this study are beneficial to accordingly improve the anti-rutting design for various pavement structures in future. The optimized pavement materials, structures, and techniques also have promising applicability prospects.

3-D FEM Simulation and Analysis on the Best Range of Lift-off Values in MFL Testing

Abstract In order to avoid oil and gas leakage or explosion due to corrosion defects or cracks in pipelines or tanks, it is very important to test the pipelines and tanks in service. In this study, a three-dimensional (3-D) finite element method (FEM) simulation model of the magnetic flux leakage (MFL) field was established. The MFL signals were simulated and analyzed in connection with different defects and lift-off values, considering the condition of the mechanical vibration and electromagnetic noise. The best range of lift-off values can be determined from the results of simulation and analysis. This is a very effective method for improving measurement accuracy in practical MFL testing. It also provides a reference for the optimization of testing mechanical structures in the MFL technique.

Modeling of the temperature field in the amorphous Ge2Sb2Te5 film induced by a picosecond laser with a body heat source

Three-dimensional body-heating finite element method simulation was carried out to study the temperature field of the amorphous Ge2Sb2Te5 film induced by picosecond laser pulse. In the model, the continuous medium heat conduction theory with semi-infinity heat conduction was employed together with the assumption of the Gaussian temporal and spatial profiles. The verification between the prediction and experiment showed that simulated results reasonably agreed with experimental observations. Based on the simulation, it showed that the maximum temperature appeared at the top surface center, and the variation of temperature field within the whole film followed the same trend. Characteristics of the temperature field between the thin and thick films were further compared. A relatively homogeneous temperature field along the thickness direction was obtained for the case of thin film where thermal equilibrium reaches quickly. The total absorbed energy by the Ge2Sb2Te5 film increased with the increase of film thickness, however, the predicted maximum temperature at the top surface center declines with the increment of film thickness, which is affected by thermal conduction.

Multi-objective Optimal Design of a Five-Phase Fault-Tolerant Axial Flux PM Motor

Electric motors used for traction purposes in electric vehicles (EVs) must meet several requirements, including high efficiency, high power density and faulttolerance. Among them, permanent magnet synchronous motors (PMSMs) highlight. Especially, five-phase axial flux permanent magnet (AFPM) synchronous motors are particularly suitable for in-wheel applications with enhanced fault-tolerant capabilities. This paper is devoted to optimally design an AFPM for in-wheel applications. The main geometric, electric and mechanical parameters of the designed AFPM are calculated by applying an iterative method based on a set of analytical equations, which is assisted by means of a reduced number of three-dimensional finite element method (3D-FEM) simulations to limit the computational burden. To optimally design the AFPM, a constrained multi-objective optimization process based on a genetic algorithm is applied, in which two objective functions are considered, i.e. the power density and the efficiency. Several fault-tolerance constraints are settled during the optimization process to ensure enhanced fault-tolerance in the resulting motor design. The accuracy of the best solution attained is validated by means of 3D-FEM simulations.

Experimental and numerical analysis of performance of two fluted mixer designs

In this paper, the effect of the Maddock mixer design on its performance in the single screw extrusion of High-density Polyethylene (HDPE) melt has been investigated experimentally on a special extrusion line equipped with a barrel having several glass windows as well as theoretically using a three-dimensional finite element method simulation. The red–green–blue spectral analysis has been used for the experimental quantification of the mixing efficiency, whereas a generalised Newtonian model (with Carreau–Yasuda viscosity function) and a viscoelastic modified White–Metzner model have been utilised in flow simulations. Based on the performed experimental work, it has been found that the mixer with no undercut wiping flight (‘Closed’ mixer) has a faster mixing/purging but a similar final mixing performance as the mixer with undercut wiping flight (‘Open’ mixer). It has also been revealed that the ‘Open’ mixer creates an unwanted dead zone (in the form of the stagnation layer of material rotating between the mixer and the barrel) at which the polymer melt degradation may take place. It has been found that based on the stress, residence time and pathline calculation, it is possible to predict the experimentally observed tendency of the ‘Closed’ mixer for a faster mixing/purging in comparison with the ‘Open’ mixer as well as the presence of a stagnation layer in the ‘Open’ mixer. The performed theoretical parametric study indicates that the gradual opening of the wiping gap causes the pressure driven flow to become more dominant than the drag flow in shearing as well as in the wiping gap independently of the utilised rheological model. On the other hand, the predicted particle trajectories inside the mixer were found to be shorter for the viscoelastic model, tending to occur mainly in the middle of the channel and thus leaving the mixer a little bit faster in comparison with the purely viscous calculations. Finally, it has been revealed that for the highest tested wiping flight opening, the viscoelastic modified White–Metzner model predicts back flow over the wiping flight, whereas the purely viscous Carreau–Yasuda does not, which can be explained by the elongational viscosity, considered in the viscoelastic modified White–Metzner model. This suggests that the modified White–Metzner model should be preferred more than the purely viscous Carreau–Yasuda model in the mixing element die design optimisation.

Three-dimensional finite element method simulation study of fusion screw geometry

In this paper, a detailed three-dimensional finite element method (3D FEM) study of the mixing performance of the Fusion screw geometry by using two different rheological models is presented. Special criteria characterising the mixing performance in dependence of the barrier undercut separating the waving channels are developed. A great mixing performance is achieved when a right balance in both dispersive and distributive parts of the mixing process is found. An optimal undercut of the barrier was found to be about 2 mm. Both rheological models were successfully used to validate data of the real experiment with an error less than 15%.

The Effect of Notch Tip Position on the Charpy Impact Energy for Bainitic and Martensitic Functionally Graded Steels

Functionally graded steels (FGS) are a group of functionally graded materials with elastic-plastic properties that are recently produced from austenitic stainless steel and carbon ferritic steel via electroslag remelting process. FGSs provide a possible solution to improve the properties of composites including martensitic and bainitic brittle phases. In the present work, keeping into account the relationship between the impact energy and the notch tip plastic zone size, an analytical model has been developed to predict the Charpy impact energy of bainitic and martensitic FGSs. The Charpy impact energy of the FGSs is compared with that of a specimen made of the homogeneous material corresponding to the layer that includes the notch tip. Moreover, three-dimensional finite element method (FEM) simulation of the process has been carried out via ABAQUS software. The material properties of the layers have been obtained considering the Holloman law for the plastic region. Meanwhile, an exponential variations of the material parameters along the specimen width have been considered. The results of the model show a sound agreement with previous results taken from the literature and the FEM results.

The finite element method with continuity constraints for stair-step grids in geoscience

This work investigates the enforcement of continuity constraints on stair-step grids which are specialized grids for simulations in geosciences. They are rectilinear in horizontal directions but locally discontinuous (i.e., nonconforming) in the vertical direction. Furthermore, they allow for (partly) collapsed elements in order to model pinched-out layers. A robust and efficient algorithm for enforcing continuity is proposed which is tailored to the special properties of stair-step grids. A number of two- and three-dimensional finite element method (FEM) simulations on stair-step grids are conducted. Thereby, the Lagrange multiplier and penalty method with different ansatz spaces are studied for pointwise and averaged constraints. A particulary useful choice is the penalty method with continuous constraints and penalty parameters that depend on the element size.

Numerical investigation of a nano-scale electro-plasmonic switch based on metal-insulator-metal stub filter

We present a nano-scale electro-plasmonic scheme operating at 1550 nm based on plasmonic Metal-Insulator-Metal waveguide and stub filter configuration. The linear dependency of the transmission spectra of the stub filter to the length of the stubs allows designing a switch that works as normally ON or OFF switch by selecting the length of the stubs 300 or 410 nm, respectively. In our proposed waveguide-based structure, the core is an electro-optic material known as 4-dimethyl-amino-Nmethyl-4-stilbazolium tosylate with the refractive index 2.2 while the metal cladding is silver. Three-dimensional Finite Element Method simulations demonstrated that by applying a 10 V voltage to the silver cladding, a red-shift in the transmission spectra of the filter leads to turn the switch OFF or ON with calculated extinction ratio \(-13.83\) and 11.81 dB, respectively. The calculation of the capacitance implies that the switching rise-time of the switch is less than 20 fs and the bandwidth is far beyond the 18 GHz. At the maximum dimension \(460\,\hbox {nm}\times 450\,\hbox {nm}\), the subwavelength size of the switch promises the potential for future compact integrated plasmonic circuitry. For the verification of three dimensional simulation results, we have tried it, using two-dimensional transmission line method for modeling the stub filter, which demonstrates a reasonable accuracy in comparison with three-dimensional finite element method.

Modeling of the Absorption of the Electromagnetic Wave Energy in the Human Head Induced by Cell Phone

In this paper, we present the Projection Based Interpolation (PBI) technique for construction of continuous approximation of MRI scan data of the human head. We utilize the result of the PBI algorithm to perform three-dimensional (3D) Finite Element Method (FEM) simulations of the heating of the human head induced by cell phone. In particular, we utilize the Pennes equation to describe the bioheat transfer with the right hand side representing the heat generated by cell phone. We utilize our own non-stationary time dependent multi-thread parallel direct solver for the solution of this computational problem. From our numerical results it follows that 15 minutes (1000 seconds) exposure to the cell phone radiation implies up to 2 degrees Celsius increase of the temperature of the brain in the range close to the cell phone.

Room temperature ultraviolet GaN metal-coated nanorod laser

This study demonstrates a room-temperature ultraviolet GaN/Al nanorod (NR) metal laser with an optimized sidewall. A wet-chemical etching process with potassium hydroxide was used to control the GaN NR sidewall angle and polish the NR surface. The lasing action was observed near a wavelength of 365 nm with a low threshold power density of 5.2 mJ/cm2. The high-quality factor (Q) surface plasmon lasing modes were characterized with experiments and three-dimensional finite-element method simulations. We also studied the optical modes in GaN metal-coated NR with and without an Al layer and verified the metal layer is necessary for high-Q resonant modes.

Acoustic waveguiding by pliable conduits with axial cross sections as linear waveguides in two-dimensional sonic crystals

Pliable conduits composed of periodically arranged concentric aluminum tori in air, with their axial cross sections acting as linear waveguides in two-dimensional sonic crystals, are numerically shown to guide acoustic waves in three dimensions in a flexible manner. Waveguide band structures are obtained by exploiting axial symmetry in a super-cell approach through two-dimensional finite-element simulations under the periodic boundary conditions. One isolated band having a bandwidth of 19.66% or 10.10% is observed for each guide, whose cross section is either in square or triangular geometry, respectively. Corresponding mode profiles indicate efficient guiding, as the acoustic energy is mainly concentrated in the hollow-core region of the guides. Transmittance spectra calculated through finite-element simulations are in agreement with the computed guiding bands. Transmittance along the waveguides with square and triangular axial cross sections around mid-band frequencies of their guiding bands varies slightly from -6.05 and -6.65 dB to -5.98 and -8.86 dB, respectively, as the guide length is increased from 10 to 200 periods. Efficient guiding across the smooth bends over circular arcs up to 90 deg is also demonstrated through three-dimensional finite-element method simulations.

Electromagnetically induced transparency with hybrid silicon-plasmonic traveling-wave resonators

Spectral filtering and electromagnetically induced transparency (EIT) with hybrid silicon-plasmonic traveling-wave resonators are theoretically investigated. The rigorous three-dimensional vector finite element method simulations are complemented with temporal coupled mode theory. We show that ring and disk resonators with sub-micron radii can efficiently filter the lightwave with minimal insertion loss and high quality factors (Q). It is shown that disk resonators feature reduced radiation losses and are thus advantageous. They exhibit unloaded quality factors as high as 1000 in the telecom spectral range, resulting in all-pass filtering components with sharp resonances. By cascading two slightly detuned resonators and providing an additional route for resonator interaction (i.e., a second bus waveguide), a response reminiscent of EIT is observed. The EIT transmission peak can be shaped by means of resonator detuning and interelement separation. Importantly, the respective Q can become higher than that of the single-resonator structure. Thus, the possibility of exploiting this peak in switching applications relying on the thermo-optic effect is, finally, assessed.

Design Method of a Foldable Ventricular Assist Device for Minimally Invasive Implantation

To date, ventricular assist devices (VADs) have become accepted as a therapeutic solution for end-stage heart failure patients when a donor heart is not available. Newer generation VADs allow for a significant reduction in size and an improvement in reliability. However, the invasive implantation still limits this technology to critically ill patients. Recently, expandable/deployable devices have been investigated as a potential solution for minimally invasive insertion. Such a device can be inserted percutaneously via peripheral vessels in a collapsed form and operated in an expanded form at the desired location. A common structure of such foldable pumps comprises a memory alloy skeleton covered by flexible polyurethane material. The material properties allow elastic deformation to achieve the folded position and withstand the hydrodynamic forces during operation; however, determining the optimal geometry for such a structure is a complex challenge. The numerical finite element method (FEM) is widely used and provides accurate structural analysis, but computation time is considerably high during the initial design stage where various geometries need to be examined. This article details a simplified two-dimensional analytical method to estimate the mechanical stress and deformation of memory alloy skeletons. The method was applied in design examples including two popular types of blade skeletons of a foldable VAD. Furthermore, three force distributions were simulated to evaluate the strength of the structures under different loading conditions experienced during pump operation. The results were verified with FEM simulations. The proposed two-dimensional method gives a close stress and deformation estimation compared with three-dimensional FEM simulations. The results confirm the feasibility of such a simplified analytical approach to reveal priorities for structural optimization before time-consuming FEM simulations, providing an effective tool in the initial structural design stage of foldable minimally invasive VADs.

An explanation of the crystallization of amorphous Ge2Sb2Te5 films induced by a short Gaussian laser pulse

Three-dimensional finite element method simulation and experimental investigation were employed to study the fast crystallization mechanism of Ge2Sb2Te5 phase-change alloy films induced by a short Gaussian laser pulse. A crystallization mechanism was proposed which took into account the roles of heating and cooling rates on crystallization of the phase-change materials. Microstructure characteristics of crystallization, primarily attributed to inherent material properties and temperature field, were discussed. The present study not only unveils the crystallization mechanism induced by laser radiance but also distinguishes the roles of the ultrahigh heating/cooling rate for the phase transition.

Fabrication, Characterization, and Functionalization of Dual Carbon Electrodes as Probes for Scanning Electrochemical Microscopy (SECM)

Dual carbon electrodes (DCEs) are quickly, easily, and cheaply fabricated by depositing pyrolytic carbon into a quartz theta nanopipet. The size of DCEs can be controlled by adjusting the pulling parameters used to make the nanopipet. When operated in generation/collection (G/C) mode, the small separation between the electrodes leads to reasonable collection efficiencies of ca. 30%. A three-dimensional finite element method (FEM) simulation is developed to predict the current response of these electrodes as a means of estimating the probe geometry. Voltammetric measurements at individual electrodes combined with generation/collection measurements provide a reasonable guide to the electrode size. DCEs are employed in a scanning electrochemical microscopy (SECM) configuration, and their use for both approach curves and imaging is considered. G/C approach curve measurements are shown to be particularly sensitive to the nature of the substrate, with insulating surfaces leading to enhanced collection efficiencies, whereas conducting surfaces lead to a decrease of collection efficiency. As a proof-of-concept, DCEs are further used to locally generate an artificial electron acceptor and to follow the flux of this species and its reduced form during photosynthesis at isolated thylakoid membranes. In addition, 2-dimensional images of a single thylakoid membrane are reported and analyzed to demonstrate the high sensitivity of G/C measurements to localized surface processes. It is finally shown that individual nanometer-size electrodes can be functionalized through the selective deposition of platinum on one of the two electrodes in a DCE while leaving the other one unmodified. This provides an indication of the future versatility of this type of probe for nanoscale measurements and imaging.

Numerical study of thermal stresses in high-temperature proton exchange membrane fuel cell (HT-PEMFC)

The purpose of this work is to numerically examine the thermal stress distributions in a high-temperature proton exchange membrane fuel cell (HT-PEMFC) based on a phosphoric acid doped polybenzimidazole (PBI) membrane. A fluid structure interaction (FSI) method is adopted to simulate the expansion/compression that arises in various components of a membrane electrode assembly (MEA) during the HT-PEMFC assembly processes, as well as during cell operations. First, three-dimensional (3-D) finite element method (FEM) simulations are conducted to predict the cell deformation during cell clamping. Then, a nonisothermal computational fluid dynamic (CFD)-based HT-PEMFC model developed in a previous study [1] is applied to the deformed cell geometry to estimate the key species and temperature distributions inside the cell. Finally, the temperature distributions obtained from these CFD simulations are employed as the input load for 3-D FEM simulations. The present numerical study provides a fundamental understanding of the stress–temperature interaction during HT-PEMFC operations and demonstrates that the coupled FEM/CFD HT-PEMFC model presented in this paper can be used as a useful tool for optimizing HT-PEMFC clamping and operating conditions.

基于MEMS工艺的高增益低副瓣太赫兹波纹喇叭天线设计

本文提出了一种基于微电子机械系统(MEMS)工艺的高增益低副瓣太赫兹波纹喇叭天线设计方法。利用三维全波有限元电磁仿真软件Ansys HFSS，对角锥喇叭的波纹开槽尺寸和条数进行参数分析和优化设计，获得了在275 GHz至580 GHz的有效带宽内(回波损耗小于10 dB)增益超过8 dB和副瓣电平小于-13 dB的太赫兹波纹喇叭天线。结果表明波纹开槽可有效提高太赫兹喇叭天线增益并压低副瓣，同时也说明MEMS工艺可有效用于太赫兹功能器件设计。 A novel high gain and low side-lobe terahertz (THz) corrugated horn antenna based on Micro-electro-me- chanical-systems (MEMS) technology is proposed. Properties of the antenna for different corrugated groove sizes and numbers are investigated and optimized by using three-dimensional (3D) electromagnetic full-wave finite element method (FEM) simulation software package Ansys High Frequency Structure Simulator (HFSS). The gain and side-lobe of the THz antenna can be designed greater than 8 dB and less than -13 dB, respectively in the band wide for 10 dB return loss from 275 GHz to 580 GHz. The results show that the corrugated groove can effectively improve the gain and depress the side-lobe of the horn antenna at the THz frequency range. Meantime, the THz functional devices could be effectively fabricated using MEMS technology.

Validation of 3-D finite element analysis for predicting the density distribution of roll compacted pharmaceutical powder

This study compares the density results from three-dimensional FEM simulations of a roll compaction process to those measured experimentally. Unlike previous studies, the experiments were performed with an air-powered piston feeder configuration that applied a known, uniform stress on the powder. All model boundary conditions were based on experimentally-measured values. To further improve model accuracy, the simulations also utilized density-dependent stress–strain constitutive parameters to describe the powder mechanical behaviors. Results show that the FEM model results agree well with the corresponding experimental data. Important experimental trends are successfully captured by the simulations, including the ribbon width-wise density distribution and the observation that the average ribbon density was independent of the inlet stress when the system was operated at conditions that allowed the roll gap to ‘float’. Further, as a result of cantilevered roll shaft supports, the experimental rolls were not perfectly parallel so the ribbon width-wise density distribution was slightly asymmetrical against the roll half-width. Incorporating non-parallel roll configurations in the FEM simulations resulted in an asymmetrical ribbon density distribution similar to the experimental observations. Finite element method (FEM) simulations of a roll compaction process were performed using experimentally measured data as model inputs. The FEM-predicted density distribution results are compared to those measured experimentally at conditions that closely match the simulation boundary conditions. Excellent agreement between FEM and experimental data is observed. ► Density results from FEM simulations are validated against experimental measurements. ► An air-powered piston that applies a known, uniform stress on the powder is used. ► All model boundary conditions were based on experimentally-measured values. ► The simulations also utilized density-dependent stress–strain constitutive parameters. ► FEM model density results agree well with the corresponding experimental data.