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Articles 1 - 19 of 19
Full-Text Articles in Engineering
Thermal Conduction In Molecular Materials Using Coarse Grain Dynamics: Role Of Mass Diffusion And Quantum Corrections For Molecular Dynamics Simulations, Ya Zhou, Alejandro Strachan
Thermal Conduction In Molecular Materials Using Coarse Grain Dynamics: Role Of Mass Diffusion And Quantum Corrections For Molecular Dynamics Simulations, Ya Zhou, Alejandro Strachan
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
We use a mesodynamical method, denoted dynamics with implicit degrees of freedom DID, to characterize thermal transport in a model molecular crystal below and above its melting temperature. DID represents groups of atoms molecules in this case using mesoparticles and the thermal role of the intramolecular degrees of freedom DoFs are described implicitly using their specific heat. We focus on the role of these intramolecular DoFs on thermal transport. We find that thermal conductivity is independent of intramolecular specific heat for solid samples and a linear relationship between the two quantities in liquid samples with the coefficient of proportionality being …
Stochastic Analysis Of Electrostatic Mems Subjected To Parameter Variations, Nitin Agarwal, Narayana R. Aluru
Stochastic Analysis Of Electrostatic Mems Subjected To Parameter Variations, Nitin Agarwal, Narayana R. Aluru
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
This paper presents an efficient stochastic framework for quantifying the effect of stochastic variations in various design parameters such as material properties, geometrical features, and/or operating conditions on the performance of electrostatic microelectromechanical systems (MEMS) devices. The stochastic framework treats uncertainty as a separate dimension, in addition to space and time, and seeks to approximate the stochastic dependent variables using sparse grid interpolation in the multidimensional random space. This approach can be effectively used to compute important information, such as moments (mean and variance), failure probabilities, and sensitivities with respect to design variables, regarding relevant quantities of interest. The approach …
Entropy Considerations In Numerical Simulations Of Non-Equilibrium Rarefied Flows, Sruti Chigullapalli, A. Venkattraman, M. S. Ivanov, Alina A. Alexeenko
Entropy Considerations In Numerical Simulations Of Non-Equilibrium Rarefied Flows, Sruti Chigullapalli, A. Venkattraman, M. S. Ivanov, Alina A. Alexeenko
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
Non-equilibrium rarefied flows are encountered frequently in supersonic flight at high altitudes, vacuum technology and in microscale devices. Prediction of the onset of non-equilibrium is important for accurate numerical simulation of such flows. We formulate and apply the discrete version of Boltzmann’s H-theorem for analysis of non-equilibrium onset and accuracy of numerical modeling of rarefied gas flows. The numerical modeling approach is based on the deterministic solution of kinetic model equations. The numerical solution approach comprises the discrete velocity method in the velocity space and the finite volume method in the physical space with different numerical flux schemes: the first-order, …
An Unstructured Finite Volume Method For Incompressible Flows With Complex Immersed Boundaries, Lin Sun, Sanjay Mathur, Jayathi Y. Murthy
An Unstructured Finite Volume Method For Incompressible Flows With Complex Immersed Boundaries, Lin Sun, Sanjay Mathur, Jayathi Y. Murthy
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
A numerical method is developed for solving the 3D, unsteady, incompressible flows with immersed moving soldis of arbitrary geometrical complexity. A co-located (non-staggered) finite volume method is employed to solve the Navier-Stokes governing equeations for flow region using arbitrary convex polyhedral meshes. The solid region is represented by a set of material points with known position and velocity. Faces in the flow region located in the immediate vicinity of the solid body are marked as immersed boundary (IB) faces. At every instant in time, the influence of the body on the flowis accounted for by reconstructing implicitly the velocity the …
Phase Stability And Transformations In Niti From Density, Karthik Guda Vishnu, Alejandro Strachan
Phase Stability And Transformations In Niti From Density, Karthik Guda Vishnu, Alejandro Strachan
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
We used density functional theory to characterize various crystalline phases of NiTi alloys: (i) high-temperature austenite phase B2; (ii) orthorhombic B19; (iii) the monoclinic martensite phase B190; and (iv) a body-centered orthorhombic phase (BCO), theoretically predicted to be the ground state. We also investigated possible transition pathways between the various phases and the energetics involved. We found B19 to be metastable with a 1 meV energy barrier separating it from B190. Interestingly, we predicted a new phase of NiTi, denoted B1900, that is involved in the transition between B190 and BCO. B1900 is monoclinic and can exhibit shape memory; furthermore, …
A Numerical Fatigue Damage Model For Life Scatter Of Mems Devices, Behrooz Jalalahmadi, Farshid Sadeghi, Dimitrios Peroulis
A Numerical Fatigue Damage Model For Life Scatter Of Mems Devices, Behrooz Jalalahmadi, Farshid Sadeghi, Dimitrios Peroulis
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
This paper presents a fatigue damage model to estimate fatigue lives of microelectromechanical systems (MEMS) devices and account for the effects of topological randomness of material microstructure. For this purpose, the damage mechanics modeling approach is incorporated into a new Voronoi finite-element model (VFEM). The VFEM developed for this investigation is able to consider both intergranular crack initiation (debonding) and propagation stages. The model relates the fatigue life to a damage parameter "D" which is a measure of the gradual material degradation under cyclic loading. The fatigue damage model is then used to investigate the effects of microstructure randomness on …
Numerical Simulation Of Gas-Phonon Coupling In Thermal Transpiration Flows, Xiaohui Guo, Dhruv Singh, Jayathi Murthy, Alina A. Alexeenko
Numerical Simulation Of Gas-Phonon Coupling In Thermal Transpiration Flows, Xiaohui Guo, Dhruv Singh, Jayathi Murthy, Alina A. Alexeenko
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
Thermal transpiration is a rarefied gas flow driven by a wall temperature gradient and is a promising mechanism for gas pumping without moving parts, known as the Knudsen pump. Obtaining temperature measurements along capillary walls in a Knudsen pump is difficult due to extremely small length scales. Meanwhile, simplified analytical models are not applicable under the practical operating conditions of a thermal transpiration device, where the gas flow is in the transitional rarefied regime. Here, we present a coupled gas-phonon heat transfer and flow model to study a closed thermal transpiration system. Discretized Boltzmann equations are solved for molecular transport …
Squeeze-Film Damping Of Flexible Microcantilevers At Low Ambient Pressures: Theory And Experiment, Jin Woo Lee, Ryan Tung, Arvind Raman, Hartono Sumali, John Sullivan
Squeeze-Film Damping Of Flexible Microcantilevers At Low Ambient Pressures: Theory And Experiment, Jin Woo Lee, Ryan Tung, Arvind Raman, Hartono Sumali, John Sullivan
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
An improved theoretical approach is proposed to predict the dynamic behavior of long, slender and flexible microcantilevers affected by squeeze-film damping at low ambient pressures. Our approach extends recent continuum gas damping models which were originally derived for a rigid oscillating plate near a wall, to flexible microcantilevers for calculating and predicting squeeze-film damping ratios of higher order bending modes at reduced ambient pressures. Theoretical frequency response functions are derived for a flexible microcantilever beam excited both inertially and via external forcing. Experiments performed carefully at controlled gas pressures are used to validate our theoretical approach over five orders of …
Modeling Of Subcontinuum Thermal Transport Across Semiconductor-Gas Interfaces, Dhruv Singh, Xiaohui Guo, Alina Alexeenko, Jayathi Y. Murthy, Timothy S. Fisher
Modeling Of Subcontinuum Thermal Transport Across Semiconductor-Gas Interfaces, Dhruv Singh, Xiaohui Guo, Alina Alexeenko, Jayathi Y. Murthy, Timothy S. Fisher
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
A physically rigorous computational algorithm is developed and applied to calculate subcontinuum thermal transport in structures containing semiconductor-gas interfaces. The solution is based on a finite volume discretization of the Boltzmann equation for gas molecules in the gas phase and phonons in the semiconductor. A partial equilibrium is assumed between gas molecules and phonons at the interface of the two media, and the degree of this equilibrium is determined by the accommodation coefficients of gas molecules and phonons on either side of the interface. Energy balance is imposed to obtain a value of the interface temperature. The classic problem of …
Non-Gray Phonon Transport Using A Hybrid Bte-Fourier Solver, James Loy, Druv Singh, Jayathi Y. Murthy
Non-Gray Phonon Transport Using A Hybrid Bte-Fourier Solver, James Loy, Druv Singh, Jayathi Y. Murthy
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
Non-gray phonon transport solvers based on the Boltzmann transport equation (BTE) are frequently employed to simulate sub-micron thermal transport. Typical solution procedures using sequential solution schemes encounter numerical difficulties because of the large spread in scattering rates. For frequency bands with very low Knudsen numbers, strong coupling between the directional BTEs results in slow convergence for sequential solution procedures. In this paper, we present a hybrid BTE-Fourier model which addresses this issue. By establishing a phonon group cutoff (say Kn=0.1), phonon bands with low Knudsen numbers are solved using a modified Fourier equation which includes a scattering term as well …
Squeeze-Film Damping Of Flexible Microcantilevers At Low Ambient Pressures: Theory And Experiment, Jin Lee, Ryan C. Tung, Arvind Raman, Hartono Sumali, John Sullivan
Squeeze-Film Damping Of Flexible Microcantilevers At Low Ambient Pressures: Theory And Experiment, Jin Lee, Ryan C. Tung, Arvind Raman, Hartono Sumali, John Sullivan
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
An improved theoretical approach is proposed to predict the dynamic behavior of long, slender and flexible microcantilevers affected by squeeze-film damping at low ambient pressures. Our approach extends recent continuum gas damping models (Veijola 2004 J. Micromech. Microeng. 14 1109–18, Gallis and Torczynski 2004 J. Microelectromech. Syst. 13 653–9), which were originally derived for a rigid oscillating plate near a wall, to flexible microcantilevers for calculating and predicting squeeze-film damping ratios of higher order bending modes at reduced ambient pressures. Theoretical frequency response functions are derived for a flexible microcantilever beam excited both inertially and via external forcing. Experiments performed …
Vertical Carbon Nanotube Devices With Nanoscale Lengths Controlled Without Lithography, Aaron D. Franklin, Robert A. Sayer, Timothy D. Sands, David B. Janes, Timothy S. Fisher
Vertical Carbon Nanotube Devices With Nanoscale Lengths Controlled Without Lithography, Aaron D. Franklin, Robert A. Sayer, Timothy D. Sands, David B. Janes, Timothy S. Fisher
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
Vertical single-walled carbon nanotubes (vSWCNTs) are synthesized within highly ordered porous anodic alumina (PAA) templates supported on Si substrates. A process for obtaining thin-film PAA with long-range ordered nanopores is presented in this paper. Each nanopore contains at most one v-SWCNT that is supported by a dielectric and addressed by electrochemically formed Pd nanowire source contacts and evaporated Pd drain contacts. Characteristics of these completely vertical, two-terminal nanotube devices are presented. Control of the v-SWCNT length is demonstrated using a straightforward etching process with lengths of less than 100 nm achieved without the need for complex/expensive lithography. This effective nanoscale …
Unified Theory Of Gas Damping Of Flexible Microcantilevers At Low Ambient Pressures, Rahul Bidkar, Ryan Tung, Alina Alexeenko, Sumali Hartono, Arvind Raman
Unified Theory Of Gas Damping Of Flexible Microcantilevers At Low Ambient Pressures, Rahul Bidkar, Ryan Tung, Alina Alexeenko, Sumali Hartono, Arvind Raman
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
Predicting the gas damping of microcantilevers oscillating in different vibration modes in unbounded gas at low pressures is relevant for increasing the sensitivity of microcantilever-based sensors. While existing free-molecular theories are valid only at very high Knudsen numbers, continuum models are valid only at very low Knudsen numbers. We solve the quasisteady Boltzmann equation and compute a closed-form fit for gas damping of rectangular microcantilevers that is valid over four orders of magnitude of Knudsen numbers spanning the free-molecular, the transition, and the low pressure slip flow regimes. Experiments are performed using silicon microcantilevers under controlled pressures to validate the …
Compact Model Of Squeeze-Film Damping Based On Rarefied Flow Simulations, Xiaohui Guo, Alina Alexeenko
Compact Model Of Squeeze-Film Damping Based On Rarefied Flow Simulations, Xiaohui Guo, Alina Alexeenko
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
A new compact model of squeeze-film damping is developed based on the numerical solution of the Boltzmann kinetic equation. It provides a simple expression for the damping coefficient and the quality factor valid through the slip, transitional and free-molecular regimes. In this work, we have applied statistical analysis to the current model using the chi-squared test. The damping predictions are compared with both Reynolds equation-based models and experimental data. At high Knudsen numbers, the structural damping dominates the gas squeeze-film damping. When the structural damping is subtracted from the measured total damping force, good agreement is found between the model …
Toward Surround Gates On Vertical Single-Walled Carbon Nanotube Devices, Aaron D. Franklin, Robert A. Sayer, Timothy D. Sands, Timothy S. Fisher, David B. Janes
Toward Surround Gates On Vertical Single-Walled Carbon Nanotube Devices, Aaron D. Franklin, Robert A. Sayer, Timothy D. Sands, Timothy S. Fisher, David B. Janes
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
The one-dimensional, cylindrical nature of single-walled carbon nanotubes (SWCNTs) suggests that the ideal gating geometry for nanotube field-effect transistors (FETs) is a surround gate (SG). Using vertical SWCNTs templated in porous anodic alumina, SGs are formed using top-down processes for the dielectric/metal depositions and definition of the channel length. Surround gates allow aggressive scaling of the channel to 25% of the length attainable with a bottom-gate geometry without incurring short-channel effects. The process demonstrated here for forming SGs on vertical SWCNTs is amenable for large-scale fabrication of multinanotube FETs.
Parallel Reactive Molecular Dynamics: Numerical Methods And Algorithmic Techniques, Hasan Metin Aktulga, Joseph C. Fogarty, Sagar A. Pandit, Ananth Y. Grama
Parallel Reactive Molecular Dynamics: Numerical Methods And Algorithmic Techniques, Hasan Metin Aktulga, Joseph C. Fogarty, Sagar A. Pandit, Ananth Y. Grama
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
No abstract provided.
A Stochastic Collocation Approach To Bayesian Inference In Inverse Problems, Youssef Marzouk, Dongbin Xiu
A Stochastic Collocation Approach To Bayesian Inference In Inverse Problems, Youssef Marzouk, Dongbin Xiu
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
We present an efficient numerical strategy for the Bayesian solution of inverse problems. Stochastic collocation methods, based on generalized polynomial chaos (gPC), are used to construct a polynomial approximation of the forward solution over the support of the prior distribution. This approximation then defines a surrogate posterior probability density that can be evaluated repeatedly at minimal computational cost. The ability to simulate a large number of samples from the posterior distribution results in very accurate estimates of the inverse solution and its associated uncertainty. Combined with high accuracy of the gPC-based forward solver, the new algorithm can provide great efficiency …
Coarse Grain Modeling Of Spall Failure In Molecular Crystals: Role Of Intra-Molecular Degrees Of Freedom, Karen Lynch, Alexander Thompson, Alejandro Strachan
Coarse Grain Modeling Of Spall Failure In Molecular Crystals: Role Of Intra-Molecular Degrees Of Freedom, Karen Lynch, Alexander Thompson, Alejandro Strachan
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
We use a recently developed thermodynamically accurate mesodynamical method (Strachan and Holian 2005 Phys. Rev. Lett. 94 014301) where groups of atoms are represented by mesoparticles to characterize the shock compression and dynamical failure (spall) of a model molecular crystal. We characterize how the temperature rise caused by the shockwave depends on the specific heat of the degrees of freedom (DoFs) internal to the mesoparticles (Cint) and the strength of the coupling between the internal DoFs and the mesoparticles. We find that the temperature of the shocked material decreases with increasing Cint and decreasing coupling and quantify these effects. Our …
A Generalized Polynomial Chaos Based Ensemble Kalman Filter, Jia Li, Dongbin Xiu
A Generalized Polynomial Chaos Based Ensemble Kalman Filter, Jia Li, Dongbin Xiu
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
As one of the most adopted sequential data assimilation methods in many areas, especially those involving complex nonlinear dynamics, the ensemble Kalman filter (EnKF) has been under extensive investigation regarding its properties and efficiency. Compared to other variants of the Kalman filter (KF), EnKF is straightforward to implement, as it employs random ensembles to represent solution states. This, however, introduces sampling errors that affect the accuracy of EnKF in a negative manner. Though sampling errors can be easily reduced by using a large number of samples, in practice this is undesirable as each ensemble member is a solution of the …