Three-dimensional Finite Element Method Simulations Research Articles

Coupled mechanical stress and multi-dimensional CFD analysis for high temperature proton exchange membrane fuel cells (HT-PEMFCs)

We use a combined finite element method (FEM)/computational fluid dynamics (CFD) methodology to numerically investigate the effects of gas diffusion layer (GDL) compression/intrusion on the performance of a phosphoric acid-doped polybenzimidazole (PBI) membrane-based high temperature proton exchange membrane fuel cell (HT-PEMFC). Three-dimensional (3-D) FEM simulations are conducted under various displacement clamping conditions to analyze cell deformation characteristics. Then, a multi-dimensional HT-PEMFC CFD model is applied to the deformed cell geometries to study transport and electrochemical processes during HT-PEMFC operations. Our numerical simulation results reveal that the maximum stresses in the deformed GDLs always occur near the edge of the ribs. The combined effects of GDL compression/intrusion considerably increase spatial non-uniformity in the species and current density distributions, and reduce cell performance.

Disturbance Characteristics of Vertical Channel Phase Change Random Access Memory Array

A novel vertical channel phase change random access memory (VPCRAM) was proposed for reducing leakage current and increasing chip density of phase change random access memory (PCRAM). Since VPCRAM cells are integrated into the vertical channel structure, disturbance characteristics between each cell should be important issues for array design. In this work, the dependence of device parameter on electrical disturbance characteristics and thermal disturbance characteristics has been investigated by three-dimensional device simulation and finite element method simulation respectively. Electrical disturbance characteristics are determined by both channel potential coupling and junction leakage current between adjacent cells. The effects of substrate doping concentration and Si wall have been investigated. Thermal distribution has also been investigated with finite element method simulation. The oxide layer on the gate has large effect on thermal transfer within phase change materials due to the small thermal conductivity.

Light-trapping plasmonic nanovoid arrays

We consider the suitability of metallic nanovoid arrays for confining incident light and enhancing absorption in an adjacent absorbing material, such as an organic semiconductor. Such nanostructures can facilitate strong coupling of incident light into plasmonic modes localized at the surface of the metal. We investigate this system both experimentally and by performing numerical calculations. To fabricate the samples, we employ a novel imprinting technique to obtain large-area, highly ordered metallic nanovoid arrays. Strong overall absorption enhancements are measured for nanostructured samples compared to planar samples for interfaces between silver and a common organic semiconductor, phenyl-C${}_{61}$-butyric acid methyl ester. Full-wave, three-dimensional finite element method simulations are employed to investigate the nature of this light trapping, and very good agreement is observed between experimental and simulated absorption spectra. The simulations reveal highly localized surface modes and indicate that the majority of the additional absorption occurs within the organic semiconductor.

A 320 Gb/s-Throughput Capable 2$\,\times\,$2 Silicon-Plasmonic Router Architecture for Optical Interconnects

We demonstrate a 2 × 2 silicon-plasmonic router architecture with 320 Gb/s throughput capabilities for optical interconnect applications. The proposed router platform relies on a novel dual-ring Dielectric-Loaded Surface Plasmon Polariton (DLSPP) 2 × 2 switch heterointegrated on a Silicon-on-Insulator (SOI) photonic motherboard that is responsible for traffic multiplexing and header processing functionalities. We present experimental results of a Poly-methyl-methacrylate (PMMA)-loaded dual-resonator DLSPP waveguide structure that uses two racetrack resonators of 5.5 μm radius and 4 μ m-long straight sections and operates as a passive add/drop filtering element. We derive its frequency-domain transfer function, confirm its add/drop experimental spectral response, and proceed to a circuit-level model for dual-ring DLSPP designs supporting 2 × 2 thermo-optic switch operation. The validity of our circuit-level modeled 2 × 2 thermo-optic switch is verified by means of respective full vectorial three-dimensional Finite Element Method (3D-FEM) simulations. The router setup is completed by means of two 4 × 1 SOI multiplexing circuits, each one employing four cascaded second order micro-ring configurations with 100 GHz spaced resonances. Successful interconnection between the DLSPP switching matrix and the SOI circuitry is performed through a butt-coupling design that, as shown via 3D-FEM analysis, allows for small coupling losses of as low as 2.6 dB. The final router architecture is evaluated through a co-operative simulation environment, demonstrating successful 2 × 2 routing for two incoming 4-wavelength Non-Return-to-Zero (NRZ) optical packet streams with 40 Gb/s line-rates.

Numerical simulation for flow behaviour on micro- and nanomoulding

Three-dimensional finite element method simulation was performed to clarify the mechanism on surface replication in microinjection moulding and thermal nanoimprinting. In particular, the filling flow behaviour into micro- and nanosurface features was discussed in comparison with the experimental results. The simulation results and the experimental results of injection moulding show possibility of the generation of air traps in the filling stage and it is considered that those air traps have a strong relation with replication shape and replication rate. The simulation results of thermal imprinting revealed the penetration behaviour of polymer melt into nanosurface features and showed that the aspect ratio of the surface features and imprinting pressure and temperature influenced flow behaviour in thermal imprinting.

Three-dimensional finite element method simulation and optimization of shrink fitting process for a large marine crankshaft

Shrink fit is an important method used to connect mechanical parts but less studied by three-dimensional finite element method. Through a finite element method study, here we have simulated the crankshaft shrink fitting process by focusing on four main aspects: the optimization of heating method before shrink fit, the contact behavior on the interface in shrink fit process, and the structural distortion after shrink fit, as well as the evaluation of the bonding strength. Our results have demonstrated: (1) an extended bore with a satisfied radius can be obtained by imposing temperature gradient around the bore during the heating process. (2) In the beginning of the shrink fit, the journal tends to be absorbed into the shrink fit bore until the interfaces are fully contacted. The journal is then squeezed in radius and extended in axial as the heat transfer becomes stable through the interface. (3) The upper crankweb bends upward when heated, while downward after shrink fitted. The shrink fit distortion leads to the journal’ offset and rotation in an individual shrink fit process, and the stacking offset of each journal aggregates the distortion in an integrated crankshaft as compared with the expected shape in an ideal state. (4) The interfacial bonding strength reaches a relative constant in a time that much shorter than expected. The final distribution of the contact pressure on the interface is not uniform but the maximum transmitted torque evaluated by finite element method agrees with that obtained via the proposed analytical method. In terms of these simulated results, a series of practical measurements have been performed with an aim of efficiently enhancing the bonding strength and preventing the shrink fit distortion.

Electrode artifacts in low resistance organic spin valves

Artifacts can originate from the inherent shortcomings of the cross bar configuration, when the resistance of the device is small compared to that of one of the electrodes. This is particularly relevant to the field of organic spintronics, in which at least one recent work overlooked this effect. We use a simplified one-dimensional resistor model and a full three-dimensional finite element method simulation to show that an increase in the resistance of one electrode appears as a decrease of the measured resistance. We found that the model agrees qualitatively but not quantitatively with observation.

X-ray diffraction study of the composition and strain fields in buried SiGe islands

We report on studies of strain and composition of two-dimensionally ordered SiGe islands grown by molecular beam epitaxy using high resolution x-ray diffraction. To ensure a small size distribution of the islands, pit-patterned \(4''\) (001) Si wafers were used as substrates. The Si wafers were patterned by optical lithography and reactive ion etching. The pits for island growth are ordered in regular 2D arrays with periods ranging from 500 to 1000 nm along two orthogonal 〈110〉 directions. After the growth of a Si buffer layer, 5 to 9 monolayers of Ge are deposited, leading to the formation of islands with either dome- or barn shape, depending on the number of monolayers deposited. The Si capping of the islands is performed at low temperatures (300○C) to avoid intermixing and thus strain relaxation. Information on the surface morphology obtained by atomic force microscopy (AFM) was used to set up models for three-dimensional Finite Element Method (FEM) simulations of the islands including the patterned Si substrate. In the model, special attention was given to the non uniform distribution of the Ge content within the islands. The FEM results served as an input for calculating the diffracted x-ray intensities using kinematical scattering theory. Reciprocal space maps around the vicinity of symmetric (004) and asymmetric (113) and (224) Bragg peaks were recorded in coplanar geometry. Simulating different germanium gradients leads to altered scattered intensity distribution and consequently information on this quantity is obtained for both dome- and barn-shaped islands as well as on the strain fields.

EVOLUTION OF STRAIN STATES AND TEXTURES IN AA 5052 SHEET DURING CROSS-ROLL ROLLING

Cross-roll rolling of AA 5052 sheets was carried out using a rolling mill in which the roll axes are tilted by ±7.5° away from the transverse direction of the rolled sample. Besides cross-roll rolling, normal-rolling using a conventional rolling mill was also carried out with the same rolling schedule for clarifying the effect of cross-roll rolling. The evolution of strain states during cross-roll rolling was investigated by texture measurements and by three-dimensional finite element method (FEM) simulation. Cross-roll rolling gives rise to the operation of all three shear components ε12, ε13and ε23in the roll gap. This complex shear states during cross-roll rolling strongly reduce the intensities of the deformation texture components.

Interpretation of the strain state during cross-roll rolling of aluminum by means of texture analysis

Cross-roll rolling of aluminum alloy sheets was carried out in which the roll axes are tilted by ±7.5° away from the transverse direction of the rolled sample. The evolution of strain states during cross-roll rolling was studied by three-dimensional finite element method (FEM) simulations. The strain states calculated by FEM were verified by texture analysis. Cross-roll rolling was found to impose a large uniform shear strain ε ˙ 23 in the whole sheet thickness; nevertheless, cross-roll rolling gives rise to the formation of plane strain texture plus an asymmetrical rotated cube orientation {0 1 2} 〈1 0 0〉. After recrystallization, the large shear strain ε ˙ 23 led to a refinement of the microstructure, which may be beneficial to the formability of cross-roll rolled aluminum alloy sheet.

Efficient excitation of dielectric-loaded surface plasmon-polariton waveguide modes at telecommunication wavelengths

The excitation of surface plasmon-polariton (SPP) waveguide modes in subwavelength dielectric ridges deposited on a thin gold film has been characterized and optimized at telecommunication wavelengths. The experimental data on the electromagnetic mode structure obtained using scanning near-field optical microscopy have been directly compared to full vectorial three-dimensional finite element method simulations. Two excitation geometries have been investigated where SPPs are excited outside or inside the dielectric tapered region adjoint to the waveguide. The dependence of the efficiency of the SPP guided mode excitation on the taper opening angle has been measured and modeled. Single-mode guiding and strong lateral mode confinement of dielectric-loaded SPP waveguide modes have been characterized with the near-field measurements and compared to the effective-index method model.

Nanoscale polarization profile across a 180° ferroelectric domain wall extracted by quantitative piezoelectric force microscopy

The structure of a single antiparallel ferroelectric domain wall in LiNbO3 is quantitatively mapped by piezoelectric force microscopy (PFM) with calibrated probe geometry. The PFM measurements are performed for 49 probes with the radius varying from 10 to 300 nm. The magnitude and variation of the experimental piezoelectric coefficient across a domain wall match the profiles calculated from a comprehensive analytical theory, as well as three-dimensional finite element method simulations. Quantitative agreement between experimental and theoretical profile widths is obtained only when a finite disk-type tip radius that is in true contact with the sample surface is considered, which is in agreement with scanning electron microscopy images of the actual tips after imaging. The magnitude of the piezoelectric coefficient is shown to be independent of the tip radius, and the PFM profile width is linearly proportional to the tip radius. Finally we demonstrate a method to extract any intrinsic material broadening of the ferroelectric wall width. Surprisingly wide wall widths of up to 100 nm are observed in the limit of zero tip radius.

FEM and metallurgical analysis of modified 6082 aluminium alloys processed by multipass ECAP: Influence of material properties and different process settings on induced plastic strain

Equal channel angular pressing (ECAP) is a very interesting method for modifying microstructure in producing ultra fine grained (UFG) materials. It consists of pressing test samples through a die containing two channels, equal in cross section and intersecting at an angle Φ. As a result of pressing, the sample theoretically deforms by simple shear and retains the same cross sectional area to repeat the pressing for several cycles. Two-dimensional and three-dimensional finite element method (FEM) simulations of both one and four ECAP passes of two modified aluminium alloys were performed in order to investigate the deformation state of processed workpiece and, moreover, the effect of different strain hardening rate, die geometry (in terms of variation of channel outer angle) and friction on deformation distribution and magnitude. FEM results showed a lower equivalent plastic strain on the outer side of both cross and longitudinal sections of the billets after one and four passes. Microhardness tests performed on the same sections of ECAP processed billets supported these findings. Moreover, FEM analysis indicated that a higher strain hardening rate means a greater strain inhomogeneity on cross section of the processed billet when the channel outer angle is small. As the channel outer angle increases and when friction is computed, the effect of strain hardening on strain inhomogeneity tends to decrease, while the die geometry and friction affect plastic strain distribution more than the hardening behaviour of the studied alloys.

Three-dimensional finite element method simulation of sheet metal single-point incremental forming and the deformation pattern analysis

Further research of the sheet metal single-point incremental forming (SPIF), which is a flexible sheet metal numerical forming method without dedicated dies, has used finite element method (FEM) simulation to analyse the forming principle and the effect of process parameters on the forming. In SPIF, the located region of the blank in contact with the forming tool is formed incrementally along the trajectory. There is no symmetric load and geometry condition, so the FEM model could not be simplified to a symmetrical model and the efficiency of simulation is bad. In this paper, brick elements are used to establish the whole three-dimensional FEM model and a simplified three-dimensional FEM model of a truncated cone and truncated pyramid. Comparison of the simulation results from the two models indicates that both models fit the simulation of SPIF but the simplified model is more efficient. Therefore, based on the simplified FEM model of a truncated pyramid, the SPIF process with different parameters was simulated to study the incremental forming principle. It was found that the deformed blank could be divided into three regions with different deformation patterns and the main character of the deformation could be conceded as a combination of bending and stretching.

Optimization of LCD Pixel Structure for Continuous Pinwheel Alignment (CPA) Mode

In this article, we report our theoretical study on the electro-optical properties of continuous pinwheel alignment (CPA) mode. We performed three-dimensional finite element method (3D-FEM) simulations on various CPA electrode patterns and compared our simulation results with the conventional vertical alignment (VA) mode. Each CPA pixel pattern was carefully examined with respect to the transmission, dynamic response, and contrast ratio as well as viewing characteristics in an effort to optimize the electrode pattern. Our numerical study revealed that the optimum dimension for the thickness of the liquid crystal (▵d) should be chosen as 2.9 μm where CPA mode can exhibit superior performance on VA mode in terms of transmission as well as viewing characteristics. Further, our numerical simulation demonstrated that the transmittance of CPA mode can be improved over VA mode by 81% while the viewing angle characteristics can be improved by 22%.

Three-Dimensional Boundary Element Method and Finite Element Method Simulations Applied to Stray Current Interference Problems. A Unique Coupling Mechanism That Takes the Best of Both Methods

Abstract In this paper it will be demonstrated how a boundary element method (BEM) model based on so-called pipe elements and a finite element method (FEM) model that is limited in space can be cou...

Correction of Dielectric Losses in Practical Leaky-wave Antenna Designs

In this paper, the leaky-mode theory is applied to take into account for the dielectric losses in millimetre waveband inhomogeneous leaky-wave antennas. A practical dielectric-filled cosine-tapered periodic leaky-wave antenna working in the 45 GHz band is studied, showing how the desired sidelobes level and directivity are spoilt due to the effect of the losses. An iterative procedure is used to correct the negative effects of the losses in the radiation patterns of the leaky-wave structure. It is also shown the practical limits of the proposed correction approach. The leaky-mode theory is applied for the first time to compensate the losses in a practical leaky-wave antenna in hybrid waveguide printed circuit technology. This leaky-mode theory is validated with full-wave three-dimensional finite element method simulations of the designed antenna.

A magnetic field source system for magnetic refrigeration and its interaction with magnetocaloric material

The magnetic field source system constitutes an important component of magnetic refrigeration. A specific methodology for its' dimensioning is proposed in this paper. It is based on analytical calculation models and takes into account the geometry of the system, the magnetic properties of the magnetocaloric material and the magnetothermal cycle (direct or active magnetic regenerative refrigeration). The analytical calculation of the field is first developed and applied to usual permanent magnet-based field sources with and without soft magnetic materials. Then the forces generated by the interaction between the field and the magnetocaloric effect material are analytically evaluated considering the real field distribution. All calculations are validated thanks to two- or three-dimensional finite element method simulations.

Influence of Electrode Position on the Characterization of Artery Stenotic Plaques by Using Impedance Catheter

Use of balloon impedance catheters (BIC) for the characterization of plaques in vessels can support an optimal medical treatment of plaques. The sensitivity of impedance diagnoses with BIC is related with the distribution of electric fields determined by the electrode configuration. Using the three-dimensional finite element method (FEM) simulation, it was estimated how the relative positions of electrode array to the lipid in the vessel affect on the total impedance magnitude. Further, the short-circuiting effect was investigated with respect to the separation distance on the angular axis between the electrode arrays of angular set. By aid of FEM simulations, it is possible to design the sets of multielectrode arrays which have an optimized resolution for individual vessels.

Finite element simulation of chip formation coupled with process dynamics

The vibrations occurring in the machining process affect the component surface and the production quality. For improved process examination, the three-dimensional finite element method (FEM) simulation of the chip formation is illustrated using the example of longitudinal surface turning while taking the process dynamics into account. Owing to the tool holder and the component with the clamping device, a system limit is defined with a flexibility which will be determined through experiments. The dynamics of the machine tool are illustrated with the FEM using simplified substitute models and coupled to the finite element model of the chip formation. As a result, in addition to the dynamics of the machine tool, the complex mechanisms of the chip formation resulting from the major deformations and heating are also approximately taken into account through the simulation of the chip formation. The results include not only the machining forces and the temperatures in the component and chips, but also determination of the movements of the component and tool holder, and with them the illustration of the vibrations.