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Investigation of nanoscale heat transport in sub-10 nm carbon nanotube field-effect transistors based on the finite element method

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THERMAL SCIENCE AND ENGINEERING PROGRESS 2021年 25卷

作者： Rezgui, Houssem Nasri, Faouzi Ben Aissa, Mohamed Fadhel Guizani, Amen Allah Res & Technol Ctr Energy Lab Thermal Proc PB 95 Hammam Lif 2050 Tunisia Univ Tunis El Manar Univ Campus Tunis Manar II Tunis 2092 Tunisia EBInnov Sch Ind Biol EBI Cergy France

During the past few years, computational approaches and engineering thermal optimizations have been investigated due to its essential role in heat conduction problems related to the next-generation transistors. This paper probes the significance of thermal management applications in carbon nanotube field-effect transistors (CNTFETs). In this work, we refer to the phonon hydrodynamic model for thermal modeling of sub-10nm CNTFETs. Here, we report the nanoscale heat transport within CNTFETs based on the finite-element method (FEM). The excellent agreement between the phonon Boltzmann transport equation (BTE) and our model prediction provides the validity of the present methodology. Our computation techniques suggest that limiting the heat propagation can be ensured by increasing specular phonon reflection inside the channel region. In addition, enhancing the thermal conductivity of CNTs with a small thermal boundary resistance is a feasible way to improve the heat dissipation ability.

关键词： Nanoscale thermal transport CNTs field-effect transistors Phonon hydrodynamic model Thermal mapping finite-element method

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A quasi-implicit characteristic-based penalty finite-element method for incompressible laminar viscous flows

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INTERNATIONAL JOURNAL FOR NUMERICAL methodS IN ENGINEERING 2018年第2期114卷 147-171页

作者： Jiang, Chen Zhang, Zhi-Qian Han, Xu Liu, Guirong Gao, Guang-Jun Lin, Tao Hunan Univ State Key Lab Adv Technol Design & Mfg Vehicle Bo Changsha 410082 Hunan Peoples R China Univ Cincinnati Dept Aerosp Engn & Engn Mech Cincinnati OH USA ASTAR Inst High Performance Comp Singapore Singapore Cent S Univ Sch Traff & Transportat Engn Key Lab Traff Safety Track Minist Educ Changsha Hunan Peoples R China

In this paper, a novel characteristic-based penalty (CBP) scheme for the finite-element method (FEM) is proposed to solve 2-dimensional incompressible laminar flow. This new CBP scheme employs the characteristic-Galerkin method to stabilize the convective oscillation. To mitigate the incompressible constraint, the selective reduced integration (SRI) and the recently proposed selective node-based smoothed FEM (SNS-FEM) are used for the 4-node quadrilateral element (CBP-Q4SRI) and the 3-node triangular element (CBP-T3SNS), respectively. Meanwhile, the reduced integration (RI) for Q4 element (CBP-Q4RI) and NS-FEM for T3 element (CBP-T3NS) with CBP scheme are also investigated. The quasi-implicit CBP scheme is applied to allow a large time step for sufficient large penalty parameters. Due to the absences of pressure degree of freedoms, the quasi-implicit CBP-FEM has higher efficiency than quasi-implicit CBS-FEM. In this paper, the CBP-Q4SRI has been verified and validated with high accuracy, stability, and fast convergence. Unexpectedly, CBP-Q4RI is of no instability, high accuracy, and even slightly faster convergence than CBP-Q4SRI. For unstructured T3 elements, CBP-T3SNS also shows high accuracy and good convergence but with pressure oscillation using a large penalty parameter;CBP-T3NS produces oscillated wrong velocity and pressure results. In addition, the applicable ranges of penalty parameter for different proposed methods have been investigated.

关键词： characteristic-Galerkin scheme finite-element method laminar flow node-based smoothed finite-element method penalty formulation selective reduced integration

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Developing New Numerical Modeling for Sloshing Behavior in Two-Dimensional Tanks Based on Nonlinear finite-element method

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JOURNAL OF ENGINEERING MECHANICS 2019年第12期145卷

作者： Farmani, Sajedeh Ghaeini-Hessaroeyeh, Mahnaz Hamzehei-Javaran, Saleh Shahid Bahonar Univ Kerman Fac Engn Dept Civil Engn POB 76169-133 Kerman *** Iran

In this paper, the nonlinear sloshing behavior of a liquid in a partially filled tank is studied using the finite-element method (FEM) based on new spherical Hankel shape functions. The liquid free surface is one of the important parameters in the modeling of the sloshing problems. The main aim of this study is the determination of the free surface location using a new finite-element technique. In this new method, the finite-element method with new shape functions is developed and reformulated. These shape functions are derived using the first and second kind of Bessel functions and have properties such as piecewise continuity. Using these new functions, the number of elements can be reduced, while the accuracy of the results can be increased. The application and accuracy of the proposed method are investigated by several problems related to the sloshing behavior of the liquid. The obtained results indicate that the new method is capable of computing the free surface elevation with a lower number of elements with good accuracy. (C) 2019 American Society of Civil Engineers.

关键词： Nonlinear sloshing Spherical Hankel shape functions finite-element method Liquid free surface Bessel functions Piecewise continuity

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A high-order multiscale finite-element method fortime-domain acoustic-wave modeling

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JOURNAL OF COMPUTATIONAL PHYSICS 2018年 360卷 120-136页

作者： Gao, Kai Fu, Shubin Chung, Eric T. Los Alamos Natl Lab Geophys Grp Los Alamos NM 87545 USA Chinese Univ Hong Kong Dept Math Hong Kong Hong Kong Peoples R China

Accurate and efficient wave equation modeling is vital for many applications in such as acoustics, electromagnetics, and seismology. However, solving the wave equation in large-scale and highly heterogeneous models is usually computationally expensive because the computational cost is directly proportional to the number of grids in the model. We develop a novel high-order multiscale finite-element method to reduce the computational cost of time-domain acoustic-wave equation numerical modeling by solving the wave equation on a coarse mesh based on the multiscale finite-element theory. In contrast to existing multiscale finite-element methods that use only first-order multiscale basis functions, our new method constructs high-order multiscale basis functions from local elliptic problems which are closely related to the Gauss-Lobatto-Legendre quadrature points in a coarse element. Essentially, these basis functions are not only determined by the order of Legendre polynomials, but also by local medium properties, and therefore can effectively convey the fine-scale information to the coarse-scale solution with high-order accuracy. Numerical tests show that our method can significantly reduce the computation time while maintain high accuracy for wave equation modeling in highly heterogeneous media by solving the corresponding discrete system only on the coarse mesh with the new high-order multiscale basis functions. (c) 2018 Elsevier Inc. All rights reserved.

关键词： Acoustic-wave equation Multiscale method finite-element method Spectral-element method Heterogeneous medium

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Acoustic reflection well logging modeling using the frequency-domain finite-element method with a hybrid PML

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Applied Geophysics 2018年第1期15卷 35-45,148页

作者： Wang Bing Kuo Zhang Guo Tao He Liu Zhang Xiao-Liang State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum Beijing 102249 China China Center for Information Industry Development Beijing CCID Publishing ＆ Media Co. Ltd. Beijing 100048 China Department of Petroleum Geoscience Khalifa University Abu Dhabi United Arab Emirates 2533 Well Logging Company Western Drilling Engineering Corporation CNPC Karamay Xinjiang 834000 China

In this paper, we propose a hybrid PML （H-PML） combining the normal absorption factor of convolutional PML （C-PML） with tangential absorption factor of Mutiaxial PML （M-PML）. The H-PML boundary conditions can better suppress the numerical instability in some extreme models, and the computational speed of finite-element method and the dynamic range are greatly increased using this HPML. We use the finite-element method with a hybrid PML to model the acoustic reflection of the interface when wireline and well logging while drilling （LWD）, in a formation with a reflector outside the borehole. The simulation results suggests that the PS- and SP- reflected waves arrive at the same time when the inclination between the well and the outer interface is zero, and the difference in arrival times increases with increasing dip angle. When there are fractures outside the well, the reflection signal is clearer in the subsequent reflection waves and may be used to identify the fractured zone. The difference between the dominant wavelength and the model scale shows that LWD reflection logging data are of higher resolution and quality than wireline acoustic reflection logging.

关键词： Frequency domain finite-element method hybrid PML boundary wireline well logging logging while drilling

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Nonlinear Axisymmetric Magnetostatic Analysis for Electromagnetic Device Using TLM-Based finite-element method

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IEEE TRANSACTIONS ON MAGNETICS 2017年第4期53卷 1-9页

作者： Yang, Wenying Peng, Fei Dinavahi, Venkata Harbin Inst Technol Sch Elect Engn & Automat Harbin 150001 Peoples R China Univ Alberta Dept Elect & Comp Engn Edmonton AB T6G 2V4 Canada

finite-element method (FEM) has been widely used in industrial applications for many years. With the increase of finite-element model complexity and the number of elements, computation burden has become a serious issue and requires more attention. In this paper, the transmission line method (TLM) is adopted to the solution of FEM-based nonlinear axisymmetric magnetostatic problem and an equivalent finite-element network's circuit model is given. Several methods were investigated to speed up the computation, such as Newton preconditioners, simplification of nonlinear equation solution and parallel computation. Compared with traditional Newton FEM iteration, our results show that the proposed method has more obvious advantages on computational efficiency at the same calculation accuracy. The method is applicable and valuable in the characteristic analysis and design of the magnetic device with a cylindrical structure.

关键词： Axisymmetric magnetostatic analysis electromagnetic device finite-element method multi-thread nonlinear magnetostatic parallel processing transmission line method (TLM)

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Evaluation of Through-Thickness Residual Stresses by Neutron Diffraction and finite-element method in Thick Weld Plates

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JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME 2017年第3期139卷 031401-031401页

作者： Jiang, Wenchun Woo, Wanchuck Wan, Yu Luo, Yun Xie, Xuefang Tu, S. T. Korea Atom Energy Res Inst Neutron Sci Div 1045 Daedeok Daero Daejeon 305353 South Korea China Univ Petr East China Coll Chem Engn State Key Lab Heavy Oil Proc Qingdao 266580 Peoples R China East China Univ Sci & Technol Sch Mech & Power Engn Key Lab Pressure Syst & Safety MOE Shanghai 200237 Peoples R China

Through-thickness distributions of the welding residual stresses were studied in the range of 50-100mm thick plates by using finite-element modeling (FEM) and neutron diffraction measurements. In order to simulate the residual stresses through the thickness of the thick weld joints, this paper proposes a two-dimensional generalized plane strain (GPS) finite-element model coupled with the mixed work hardening model. The residual stress distributions show mostly asymmetric parabola profiles through the thickness of the welds and it is in good correlation with the neutron diffraction results. Both the heat input and plate thickness have little influence on the residual stress distributions due to the relatively large constraints of the thick specimen applied for each welding pass. A general formula has been suggested to evaluate the distributions of the through-thickness residual stresses in thick welds based on FEM and neutron diffraction experimental results.

关键词： weld residual stress finite-element method neutron diffraction measurements heat input

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Analysis of transpression within contractional fault steps using finite element method

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JOURNAL OF STRUCTURAL GEOLOGY 2017年第Mar.期96卷 1-20页

作者： Nabavi, Seyed Tohid Alavi, Seyed Ahmad Mohammadi, Soheil Ghassemi, Mohammad Reza Frehner, Marcel Shahid Beheshti Univ Dept Geol Fac Earth Sci Tehran Iran Univ Tehran Sch Civil Engn High Performance Comp Lab Tehran Iran Geol Survey Iran Res Inst Earth Sci Tehran Iran Swiss Fed Inst Technol Inst Geol E3Sonneggstr 5 Zurich Switzerland

Two-dimensional finite-element modelling of elastic Newtonian rheology is used to compute stress distribution and strain localization patterns in a transpression zone between two pre-existing right stepping, left-lateral strike-slip fault segments. Three representative fault segment interactions are modelled: underlapping, neutral, and overlapping. The numerical results indicate that at the onset of deformation, displacement vectors are oblique to the regional compression direction (20-90 degrees). The orientations of the local sigma(1) (the maximum compressive stress) and sigma(3) (the minimum compressive stress) directions strongly depend on the structural position within the transpression zone. For neutral and overlapping fault steps, there is a contractional linking damage zone between the fault segments. For overlapping faults, the cri trajectories within the transpression zone deflects significantly forming a sigmoidal pattern, which is created by two rotational flow patterns close to the fault tips. These flow patterns are related to friction effects and different shear deformation, from pure shear outside of the fault steps toward simple shear along the fault segments. Interaction between the two fault segments perturbs the stress field and reflects the heterogeneous nature of deformation. A lozenge- (for under lapping steps), rhomboidal- (for neutral steps), and sigmoidal-shaped (for overlapping steps) transpression zone developed between the two segments. The modelled mean stress pattern shows a similar pattern to that of the contractional steps, and decrease and increase in underlapping and overlapping fault steps, respectively. Comparison of the Kuh-e-Hori transpression zone, between the Esmail-abad and West Neh left-stepping right-lateral strike-slip fault segments in SE Iran, with the modelling results shows strong similarities with the neutral step configuration. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Transpression Strike-slip fault Fault segment Contractional step finite-element method

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Comparison of Inductance Gradient and Electromagnetic Force in Two Types of Railguns With Two Projectiles by finite-element method

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IEEE TRANSACTIONS ON PLASMA SCIENCE 2017年第8期45卷 2387-2392页

作者： Keshtkar, Asghar Khorrami, Zahra Jafari Gharib, Leila Imam Khomeini Int Univ Qazvin *** Iran

Nowadays lunching masses to faraway distances is an important issue. One of important electromagnetic launcher for this purpose is duble-projectil railgun because it can launch synchronously two separated projectiles. It has been obtained before that two-turn railgun have better inductance gradient and performance than simple railgun. Also, self-inductance gradient and mutual-inductance gradient in two-turn railgun depend on the initial position of armatures. In this paper, we want to calculate the inductance gradient of a new structure that we named it plus railgun. The plus railgun has one barrel between two-pair rails by two separated armatures and two pairs of rails are powered by one pulse power at the same time. A 3-D finite-element method is applied to the transient analysis of the magnetic field, current distribution, and the inductance gradient of railguns. Finally, we will compare the parameters of two-turn and plus railguns.

关键词： Electromagnetic force electromagnetic launcher finite-element method inductance gradient railgun

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Predicting the Earthquake-Induced Permanent Deformation of Concrete Face Rockfill Dams Using the Strain-Potential Concept in the finite-element method

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2017年第11期17卷 04017100-04017100页

作者： Fu, Zhongzhi Chen, Shengshui Wang, Tingbo Nanjing Hydraul Res Inst Geotech Engn Dept 34 Hujuguan Rd Nanjing 210024 Jiangsu Peoples R China Minist Water Resource Key Lab Failure Mech & Safety Control Tech Earth 225 Guangzhou Rd Nanjing 210029 Jiangsu Peoples R China

Presented in this paper is a modified strain-potential method for the prediction of earthquake-induced permanent deformation of concrete face rockfill dams (CFRDs). The concept of decomposing the total strain of rockfill materials into a viscoelastic part and a plastic part during dynamic loading was explained based on experimental observations. Use of the strain-decomposition concept in the finite-element method resulted in two residual strain-related terms on the right-hand side of the dynamic equilibrium equation. An approach to predict the equivalent number of loading cycles, which is an independent variable in a residual strain model, was proposed. It was assumed that the energy dissipated in an element during an irregular strain history equals that dissipated in an equivalent regular one. The energy-based approach was proved effective in numerically evaluating the equivalent number of loading cycles by simple column tests considering both compression and shearing. The modified strain-potential method can be easily implemented in an equivalent linear analysis program, and the history of permanent deformation accumulation can be directly obtained without recourse to sophisticated constitutive models. Effectiveness of the method was demonstrated by a successful application in a high CFRD. (C) 2017 American Society of Civil Engineers.

关键词： Concrete face rockfill dam (CFRD) Permanent deformation Earthquake finite-element method Equivalent linear analysis

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