Proposed Simulation Methodology Research Articles

Variability Study of MWCNT Local Interconnects Considering Defects and Contact Resistances--Part II: Impact of Charge Transfer Doping

In this paper, the impact of charge transfer doping on the variability of multiwalled carbon nanotube (MWCNT) local interconnects is studied by experiments and simulations. We calculate the number of conducting channels of both metallic and semiconducting carbon nanotubes as a function of Fermi level shift due to doping based on the calculation of transmission coefficients. By using the MWCNT compact model proposed in Part I of this paper, we study the charge transfer doping of MWCNTs employing Fermi level shift to reduce the performance variability due to changes in diameter, chirality, defects, and contact resistance. Simulation results show that charge transfer doping can significantly improve MWCNT interconnect performance and variability by increasing the number of conducting channels of shells and degenerating semiconducting shells to metallic shells. As a case study on an MWCNT of 11 nm outer diameter, when the Fermi level shifts to 0.1 eV, up to ~80% of performance and standard deviation improvements are observed. Furthermore, a good match between experimental data and simulation results is observed, demonstrating the effectiveness of doping, the validity of the MWCNT compact model and proposed simulation methodology.

A Modified Version of the RNG k–ε Turbulence Model for the Scale-Resolving Simulation of Internal Combustion Engines

The unsteady and random character of turbulent flow motion is a key aspect of the multidimensional modeling of internal combustion engines (ICEs). A typical example can be found in the prediction of the cycle-to-cycle variability (CCV) in modern, highly downsized gasoline direct injection (GDI) engines, which strongly depends on the accurate simulation of turbulent in-cylinder flow structures. The current standard for turbulence modeling in ICEs is still represented by the unsteady form of Reynold-averaged Navier Stokes equations (URANS), which allows the simulation of full engine cycles at relatively low computational costs. URANS-based methods, however, are only able to return a statistical description of turbulence, as the effects of all scales of motion are entirely modeled. Therefore, during the last decade, scale-resolving methods such as large eddy simulation (LES) or hybrid URANS/LES approaches are gaining increasing attention among the engine-modeling community. In the present paper, we propose a scale-resolving capable modification of the popular RNG k– ε URANS model. The modification is based on a detached-eddy simulation (DES) framework and allows one to explicitly set the behavior (URANS, DES or LES) of the model in different zones of the computational domain. The resulting zonal formulation has been tested on two reference test cases, comparing the numerical predictions with the available experimental data sets and with previous computational studies. Overall, the scale-resolved part of the computed flow has been found to be consistent with the expected flow physics, thus confirming the validity of the proposed simulation methodology.

Analysis of multifinger power HEMTs supported by effective 3-D device electrothermal simulation

The influence of the metallization layer geometry on the electrothermal behavior of the multifinger power high-electron mobility transistors (HEMTs) is studied. The analysis of thermal and electrical behavior is supported by effective 3-D electrothermal device simulation method developed for Synopsys TCAD Sentaurus environment using mixed-mode setup. The proposed methodology allows fast simulation of complex systems from individual semiconductor layers at a frontend up to package and cooling assemblies at a backend. More accurate electrothermal model of power HEMT is proposed and validated by finite element method (FEM) simulations. The analysis points on significant influence of metallization geometry design on electrothermal properties and reliability of the multifinger power HEMTs. The unique identification and visualization of the critical regions allows effective device optimization. Very good comparison between simulation results and experimental data demonstrate validity of the proposed simulation methodology and HEMT structures analysis.

Two-stage method for the simulation of the comminution process in a high-speed beater mill

The paper presents a two-stage simplified method for the simulation of comminution process which takes place in a beater mill. The first stage of the proposed method is a simulation of the flow of gas and ore particles through a mill based on a two-phase continuous-discrete model. It allows to capture the interaction between the fluid flow and embedded particles, to determine trajectories of their motion and average velocities and frequencies of their collisions against the flywheel and the mill's walls. The second stage of the proposed method is a discrete element method simulation of the process of comminution of a single ore particle. It allows to determine the size distribution of created smaller particles in terms of normal velocity and angle of impact and to estimate the global efficiency of the comminution process. The proposed simulation methodology is applied for the verification of the innovative concept of the application of high–speed beater mill for the comminution of the copper ore.

Two-stage method for the simulation of the comminution process in a high-speed beater mill

The paper presents a two-stage simplified method for the simulation of comminution process which takes place in a beater mill. The first stage of the proposed method is a simulation of the flow of gas and ore particles through a mill based on a two-phase continuous-discrete model. It allows to capture the interaction between the fluid flow and embedded particles, to determine trajectories of their motion and average velocities and frequencies of their collisions against the flywheel and the mill's walls. The second stage of the proposed method is a discrete element method simulation of the process of comminution of a single ore particle. It allows to determine the size distribution of created smaller particles in terms of normal velocity and angle of impact and to estimate the global efficiency of the comminution process. The proposed simulation methodology is applied for the verification of the innovative concept of the application of high–speed beater mill for the comminution of the copper ore.

Mitigation of erroneous oscillations in electromagnetic transient simulations using analogue filter theory

An efficient and simplified procedure is proposed for the reduction of high-frequency oscillations and erroneous magnitude peaks in electromagnetic transient simulations in power transmission systems modelled by the lumped electric parameters approach. This procedure consists of the inclusion of analogue filters in the equivalent representation of multiconductor transmission lines without modifying its electromagnetic propagation characteristics. The analogue filter modelling is conducted as a function of the line length and line parameters. The proposed simulation methodology is applied directly in the line modelling, which means that the filtering/correction process represents a real-time process during simulations, without post-processing filtering techniques using digital filters or variations in the solution methods. The results obtained directly in the time domain by the proposed modelling/simulation methodology are compared with simulations obtained from well-established line models using the numerical Laplace transform and the Bergeron method.

Fast Fourier-based simulation of off-resonance artifacts in steady-state gradient echo MRI applied to metal object localization.

PurposeTo accelerate simulation of off‐resonance artifacts in steady‐state gradient echo MRI by using fast Fourier transforms and demonstrate its applicability to metal object localization.Theory and MethodsBy exploiting the repetitive nature of steady‐state pulse sequences it is possible to use fast Fourier transforms to calculate the MR signal. Based on this principle, a method for fast simulation of off‐resonance artifacts was designed. The method was validated against Bloch simulations and MRI scans. Its clinical relevance was demonstrated by employing it for template matching‐based metal object localization, as applied to a titanium cylinder, an oxidized zirconium knee implant, and gold fiducials.ResultsThe fast simulations were accurate compared with actual MRI scans of the objects. The differences between the fast simulations and Bloch simulations were minor, while the acceleration scaled linearly with the number of phase‐encoding lines. The object localization method accurately localized the various metal objects.ConclusionThe proposed simulation methodology provided accurate 3D simulations of off‐resonance artifacts with a lower computational complexity than Bloch simulations. The speed of the simulations opens up possibilities in image reconstructions involving off‐resonance phenomena that were previously infeasible due to computational limitations, as demonstrated for metal object localization. Magn Reson Med 78:2035–2041, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Adhesion investigation of stacked coatings in organic light-emitting diode display architecture

Abstract Organic light-emitting diode (OLED) display is considered one of the promising portable electronic devices given that the application requirements for the Internet of Things are necessary. Composed of multi-stacked thin films, OLED display needs to bear external gas moisture and various mechanical loadings, such as bend, torsion, and fold. Under these mechanical loadings, OLED devices undergo numerous critical failure modes, one of which is the delamination of stacked films bonded by a glued layer of OLED encapsulation that has become an important reliability concern. Accordingly, this study uses a nonlinear finite element analysis based on fracture mechanics using J-integral and modified virtual crack closure technique. The proposed method is adopted to estimate the adhesions of several concerned interfaces of dissimilar materials bonded with glue through the index of energy release rates. To validate the reliability of the proposed simulation methodology, the adhesion measurement of glue/SiN passivation is performed through a four-point bending test. The analytic results show that a cracking energy up to 20.4 J/m2 is achieved when the initial delaminated length is ~ 10 μm and when a glue with an elastic modulus of 22 MPa is considered. In addition, a long interfacial crack length appears to promote the fracture growth of ITO/SiN stacked layers under an ultra-small bending radius of 1 mm.

Reliable Bridge Scour Simulation Using Eulerian Two-Phase Flow Theory

AbstractA CFD-based simulation methodology for bridge scour using an Eulerian two-phase flow model is proposed in the present study. The basic conservation equations and four unique simulation issues are firstly addressed during the model establishment process. The solutions are given to each of the four simulation challenges, and the discrepancies between the two-phase and single-phase modeling methods are clarified. Secondly, based on the Eulerian two-phase flow theory, a three dimensional (3D) bridge scour model is numerically established by redeveloping a commercial computational fluid dynamics (CFD) program. A comparison between the numerical results and measurements in a classic experiment from the literature validate the proposed simulation methodology that can comprehensively predict the flow field and scour (riverbed) profile. The accuracy advantages over the single-phase flow model are demonstrated from three aspects including the scour-hole profile, flow field, and scour depth. Finally, a param...

Tri-axial Seismic Simulation of Solar Inverter – Productivity Improvement

Often, earthquake is a tri-axial event, as in, it excites the system in all three directions. Evaluation of big systems like high capacity solar inverters for such events through testing is quite expensive. Trend these days is to qualify the system using CAE simulation, in contrast to testing. Simulation of big systems is always a challenge, as it becomes computationally expensive due to high node count and large number of modes in the frequency range of interest. In this work, seismic analysis is performed using commercial FEA software ANSYS. Conventional way of seismic simulation in ANSYS is to first excite the system separately in the orthogonal directions and then compute the tri-axial response by superposition of responses in individual directions. In this paper, based on the response spectrum analysis, a tri-axial seismic analysis methodology is proposed and implemented on complicated high capacity solar inverters. Proposed methodology calculates a resultant mode participation factor from mode participation factors due to excitation in individual directions and then performs the mode combination. It was observed that computational time was reduced to 1/3rd without any compromise in the accuracy of response. Also, proposed simulation methodology doesn’t require separate static analysis to account for the effect of missing mass. This further increases the productivity of a seismic engineer performing a finite element analysis.

Validated finite element techniques for quasi-static cyclic response analyses of braced frames at sub-member scales

In this study, a numerically robust finite element procedure is described, which is based on explicit time-stepping, for high-fidelity simulations of inelastic and post-buckling cyclic responses of braced frame systems. The use of an explicit time-stepping method with properly chosen increments permits accurate results while avoiding (implicit) equilibrium iterations throughout the entire loading history, during which multiple yielding and buckling events occur. A number of essential techniques for properly calibrating the discrete models and to constrain their responses in order to obtain quasi-static outcomes are provided. The procedure is globally and locally validated (verified) using experimental data (implicit numerical simulations) from three types of specimens—namely, individual braces, and single and multi-story braced frame systems with diagonal and X-brace arrangements—under both monotonic and cyclic loading protocols. Results from these validation and verification studies indicate that the proposed simulation methodology can accurately capture sub-member (i.e., plastic hinges), member, and system behavior very accurately; and thus, it can be confidently used—e.g., as a virtual laboratory—to predict the responses of braced frames with configurations and dimensions other than those tested, and to seek optimum designs beyond those offered by basic guidelines.

Thermo-Magnetic Effects in Nano-Scaled MOSFET: An Experimental, Modeling, and Simulation Approach

A numerical simulation methodology for incorporating thermo-magnetic effects on the MOSFET gate tunneling current is introduced. The methodology is based on the solution of the Schrödinger-Poisson coupled system, which allows simulating the influence of a static magnetic field and temperature on the wave functions and gate tunneling current of MOSFET devices. In addition to the preliminary results on the simulation methodology, experimental results on the effect of the magnetic field on the subthreshold slope, the off-current, and transconductance, are also introduced. The proposed simulation methodology, in conjunction with experimental data, is useful for device degradation and reliability studies in nano-scaled MOSFET devices. This experimental characterization technique sets also the basis for the development of a magnetic force nanoscopy technique, where the conductive properties, thanks to the Lorentz force, can be two-dimensionally mapped over the nano-scaled MOSFET channel plane.

Random-Walk Drift-Diffusion Charge-Collection Model For Reverse-Biased Junctions Embedded in Circuits

A new computational model for charge transport based on parallelized random-walk drift-diffusion is proposed. This approach models the radiation-induced charge carriers as charge packets in a 3-D structure and the transport modeling are based on simple physical equations without any fitting parameter. This model has been dynamically coupled with a SPICE circuit simulator to take into account temporal variations of the electric fields in the charge collection process. Thus, the circuit electrical response modulates the charge collection efficiency. Three simulation cases have been explored and compared with TCAD simulations or radiation experiments in 65 nm technology to validate the accuracy of the proposed approach. These simulations demonstrate the capability of the proposed model to accurately estimate the soft error rate of complex structures, such as flip-flops over a large range of ionizing particle linear energy transfer. The proposed simulation methodology is also able to take into account charge-sharing phenomenon, and this point is highlighted by a specific investigation on the considered flip-flop.

Atomistic Pseudo-Transient BTI Simulation With Inherent Workload Memory

Bias Temperature Instability (BTI) is a major concern for the reliability of decameter to nanometer devices. Older modeling approaches fail to capture time-dependent device variability or maintain a crude view of the device's stress. Previously, a two-state atomistic model has been introduced, which is based on gate stack defect kinetics. Its complexity has been preventing seamless integration in simulations of large device inventories over typical system lifetimes. In this paper, we present an approach that alleviates this complexity. We introduce a novel signal representation for the gate stress. Using this format, atomistic BTI simulations require less model iterations while exhibiting minimum accuracy degradation. We also enable full temperature and voltage supply dependency since these attributes are far from constant in modern integrated systems. The proposed simulation methodology retains both the atomistic property and the workload memory that remain major differentiators of defect-based BTI simulation, in comparison to state-of-the-art approaches.

Simulation of non‐planar three‐dimensional hydraulic fracture propagation

SUMMARYHydraulic fracturing is the method of choice to enhance reservoir permeability and well efficiency for extraction of shale gas. Multi‐stranded non‐planar hydraulic fractures are often observed in stimulation sites. Non‐planar fractures propagating from wellbores inclined from the direction of maximum horizontal stress have also been reported. The pressure required to propagate non‐planar fractures is in general higher than in the case of planar fractures. Current computational methods for the simulation of hydraulic fractures generally assume single, symmetric, and planar crack geometries. In order to better understand hydraulic fracturing in complex‐layered naturally fractured reservoirs, fully 3D models need to be developed. In this paper, we present simulations of 3D non‐planar fracture propagation using an adaptive generalized FEM. This method greatly facilitates the discretization of complex 3D fractures, as finite element faces are not required to fit the crack surfaces. A solution strategy for fully automatic propagation of arbitrary 3D cracks is presented. The fracture surface on which pressure is applied is also automatically updated at each step. An efficient technique to numerically integrate boundary conditions on crack surfaces is also proposed and implemented. Strongly graded localized refinement and analytical asymptotic expansions are used as enrichment functions in the neighborhood of fracture fronts to increase the computational accuracy and efficiency of the method. Stress intensity factors with pressure on crack faces are extracted using the contour integral method. Various non‐planar crack geometries are investigated to demonstrate the robustness and flexibility of the proposed simulation methodology. Copyright © 2014 John Wiley & Sons, Ltd.

Influence of the Diesel Injector Hole Geometry on the Flow Conditions Emerging from the Nozzle

Engine performances are correlated to the overall fluid dynamic characteristics of the injection system that, in turns, are strictly correlated to the fluid dynamic performance of the injector geometry. It is particularly true for actual GDI and Diesel engines where micro-orifice configurations are associated to very high injection pressure.In relation to the Common Rail Diesel engines, over the last decade different injector hole shapes have been tested. Actually, the most used configurations are: cylindrical, k, and ks. In this paper, the performance of all these three injector hole shapes are evaluated in order to find out the influence of orifice conicity and hydro-grinding level on the main fluid dynamic characteristics like cavitation evolution inside the injector as well as the flow properties at nozzle exit. The fluid dynamic behavior of each considered hole is evaluated over the injection time by performing a fully transient CFD multiphase simulation (i.e. the needle motion is reproduced during the simulation). By the proposed simulation methodology, the evaluation of the cavitating flow evolution inside the injector is performed not only from the point of view of the overall spray characteristics emerging from the injector holes but also from the cavitation erosion risk over needle, nozzle, and hole internal surfaces.

Physics engine-driven visualization of deactivated elements and its application in bridge collapse simulation

Element deactivation is one of the most suitable methods in a finite element (FE) analysis of discontinuous features of collapse accidents. However, deactivated elements are typically invisible in the general purpose FE analysis, leading to a very incomplete outcome. To visualize the deactivated elements, a 3D simulation method of fragments based on a physics engine is proposed herein. A working system for fragment simulation is designed by integrating a graphics engine, an FE analysis and a physics engine. To reduce the extensive computational workload due to massive fragments, a grid-clustering algorithm for fragment modeling is also proposed. Using the proposed simulation methodology, the collapse processes of two bridges are completely replicated. The results demonstrate a realistic and real-time visual simulation of deactivated elements, which complements the limitations of the general FE analysis results. This study provides an important reference for conducting detailed investigations of bridge collapse accidents.

Time-Progressive Dynamic Assessment of Abrupt Cable-Breakage Events on Cable-Stayed Bridges

Although long-span bridges are usually designed with sufficient structural redundancy, particular concerns arise about the abrupt breakage of bridge cables, which may cause progressive failure such as zipper-like collapse. The time-progressive nonlinear dynamic analysis approach is proposed to investigate the abrupt cable-breakage event of a cable-stayed bridge. Compared with existing studies, the proposed methodology focuses on the simulation of cable loss scenarios in a more realistic manner through incorporating stochastic moving traffic loads, dynamic bridge–vehicle interactions, and associated dynamic initial states of the abrupt cable-breakage event. Several important issues associated with the proposed simulation methodology, such as the finite-element modeling option of cable breakage, different initial states of cable breakage, nonlinearity, and traffic loads, are investigated through a prototype bridge example. Finally, the response envelopes in terms of moments and stresses along the whole bridge are obtained and compared by means of the proposed nonlinear dynamic simulation approach, the static approach, and the pseudodynamic approach with a dynamic amplification factor of 2.0 as recommended by the Post-Tensioning Institute.

The analysis of the effect of flicker noise on orthogonal frequency-division multiplexing systems

In this article, we proposed a new flicker noise simulation methodology within an orthogonal frequency-division multiplexing (OFDM) PHY layer, which offers accurate analyses of the flicker noise effect.To prove this effect, we examine bit error rate performance with flicker noise by generating raw and channel-coded data. Experiment results are demonstrated using Reed Solomon channel coding. The proposed simulation methodology offers precise results for deciding flicker noise requirement on RF building blocks for OFDM systems. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1171–1174, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27502

Design evaluation of a follower cam with variable valve lift mechanism

PurposeThe purpose of this paper is to present a methodology for design, analysis and evaluation of cam‐follower systems used for the control of valve movement in internal combustion engines. The strategy begins with the inverse engineering of existing motor parts, designing them with the CATIA CAD Software and consequentially the created assembly is simulated using real time conditions in SimDesigner software, with the Adams Solver.Design/methodology/approachThe cam profile is generated and the kinematic and dynamic analysis of the variable valve mechanism is presented. The whole mechanism is verified in a dynamics analysis to check the validity of the criteria for the follower‐cam system design. Comparisons with standard profiles of motion were made, while it is also evaluated in an experimental device, where the actual valve displacement was measured.FindingsThe variable valve lift mechanism is designed to have maximum lifts greater than the lift of the conventional mechanism, with the geometrical constraints, profile of forces, velocities and accelerations to be better, in terms of stresses and work required, than the design of conventional mechanisms.Originality/valueThe novelty of the paper is consisted in presenting an integrated simulation methodology in order to precisely model, in component and assembly basis, the follower cam mechanisms with variable valve lift, and using the available software to perform the kinematic and dynamic analysis. The proposed simulation methodology can be easily adapted by a design engineer to model and to analyzed kinematically and dynamically moving components and assemblies found in internal combustion engines and not only.