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Geometry of escape and transition dynamics in the presence of dissipative and gyroscopic forces in two degree of freedom systems

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arXiv 2019年

作者： Zhong, Jun Ross, Shane D. Engineering Mechanics Program Virginia Tech BlacksburgVA24061 United States Department of Aerospace and Ocean Engineering Virginia Tech BlacksburgVA24061 United States

Escape from a potential well can occur in different physical systems, such as capsize of ships, resonance transitions in celestial mechanics, and dynamic snap-through of arches and shells, as well as molecular reconfigurations in chemical reactions. The criteria and routes of escape in one-degree of freedom systems has been well studied theoretically with reasonable agreement with experiment. The trajectory can only transit from the hilltop of the one-dimensional potential energy surface. The situation becomes more complicated when the system has higher degrees of freedom since it has multiple routes to escape through an equilibrium of saddle-type, specifically, an index-1 saddle. This paper summarizes the geometry of escape across a saddle in some widely known physical systems with two degrees of freedom and establishes the criteria of escape providing both a methodology and results under the conceptual framework known as tube dynamics. These problems are classified into two categories based on whether the saddle projection and focus projection in the symplectic eigenspace are coupled or not when damping and/or gyroscopic effects are considered. For simplicity, only the linearized system around the saddle points is analyzed, but the results generalize to the nonlinear system. We define a transition region, Th, as the region of initial conditions of a given initial energy h which transit from one side of a saddle to the other. We find that in conservative systems, the boundary of the transition region, ∂Th, is a cylinder, while in dissipative systems, ∂Th is an ellipsoid. Copyright © 2019, The Authors. All rights reserved.

关键词： Energy dissipation

Highly Elastic Interconnected Porous Hydrogels through Self-Assembled Templating for Solar Water Purification

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Angewandte Chemie 2021年第3期134卷

作者： Youhong Guo Dr. Luize Scalco de Vasconcelos Dr. Neha Manohar Dr. Jiafeng Geng Prof. Keith P. Johnston Prof. Guihua Yu Materials Science and Engineering Program and Walker Department of Mechanical Engineering The University of Texas at Austin Austin TX 78712 USA Department of Aerospace Engineering and Engineering Mechanics The University of Texas at Austin Austin TX 78712 USA McKetta Department of Chemical Engineering The University of Texas at Austin Austin TX 78712 USA Department of Chemical Engineering Chang'an University Xi'an Shannxi 710061 China

Interfacial evaporation using porous hydrogels has demonstrated highly effective solar evaporation performance under natural sunlight to ensure an affordable clean water supply. However, it remains challenging to realize scalable and ready-to-use hydrogel materials with durable mechanical properties. Here, self-assembled templating (SAT) is developed as a simple yet effective method to fabricate large-scale elastic hydrogel evaporators with excellent desalination performance. The highly interconnected porous structure of the hydrogels with low tortuosity and tunable pore size enables high level of tunability on the water transport rate. With superior elasticity, the porous hydrogels are easy to process with a rapid shape recovery after being rolled, folded, and twisted over hundred times, and exhibit highly effective and stable evaporation with an evaporation rate of ≈2.8 kg m −2 h −1 and ≈90 % solar-to-vapor efficiency. It is anticipated that this SAT strategy, without the typical need for freeze-drying, will accelerate the industrialization of hydrogel solar evaporators for practical applications.

关键词： elasticity interconnectivity porous hydrogels solar water purification template synthesis

Simulation of hybridized nanofluids flowing and heat transfer enhancement via 3-D vertical heated plate using finite element technique

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Scientific reports 2022年第1期12卷 11658页

作者： Muhammad Bilal Hafeez Marek Krawczuk Hasan Shahzad Amjad Ali Pasha Mohammad Adil Faculty of Mechanical Engineering and Ship Technology Institute of Mechanics and Machine Design Gdansk University of Technology Narutowicza 11/12 80-233 Gdańsk Poland. Muhammad.bilal.hafeez@pg.edu.pl. Faculty of Mechanical Engineering and Ship Technology Institute of Mechanics and Machine Design Gdansk University of Technology Narutowicza 11/12 80-233 Gdańsk Poland. Faculty of Materials and Manufacturing College of Mechanical Engineering and Applied Electronics Technology Beijing University of Technology Beijing China. Aerospace Engineering Department King Abdulaziz University Jeddah 21589 Saudi Arabia. Mechanical Engineering Program Physical Science and Engineering Division King Abdullah University of Science and Technology Thuwal 23955-6900 Saudi Arabia. KAUST Clean Combustion Research Center King Abdullah University of Science and Technology Thuwal 23955-6900 Saudi Arabia.

The present study probed the creation of heat energy and concentrating into Newtonian liquids across vertical 3D-heated plates. The role of the Soret and Dufour theories in concentrating and energy formulas is discussed. The role of hybrid nanoparticles is introduced to illustrate particle efficiency in terms of solute and thermal energy. It is removed a viscous dissipation process and a changing magnetic field. The proposed approach is motivated by the need to maximize solute and thermal energy uses in biological and industrial domains. The constructed system of (partial differential equations) PDEs includes concentration, momentum, and thermal energy equations within various thermal characteristics. Transformations are used to formulate the system of (ordinary differential equations) ODEs for solution. To assess various features vs various variables, a Galerkin finite element approach is used. Motion into nanoscale components is shown to be smaller than motion into hybrid nanoparticles. Furthermore, fluctuations in heat energy and solute particle counts are seen in relation to changes in Soret, Eckert, magnetic, and Dufour numbers. The basic finding is that the generation of thermal energy for hybridized nanomaterials is much higher.

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Core collapse supernova gravitational wave emission for progenitors of 9.6, 15, and 25M⊙

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Physical Review D 2023年第4期107卷 043008-043008页

作者： Anthony Mezzacappa Pedro Marronetti Ryan E. Landfield Eric J. Lentz R. Daniel Murphy W. Raphael Hix J. Austin Harris Stephen W. Bruenn John M. Blondin O. E. Bronson Messer Jordi Casanova Luke L. Kronzer Department of Physics and Astronomy University of Tennessee 1408 Circle Drive Knoxville Tennessee 37996-1200 USA Physics Division National Science Foundation Alexandria Virginia 22314 USA National Center for Computational Sciences Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge Tennessee 37831-6164 USA Physics Division Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge Tennessee 37831-6354 USA Joint Institute for Nuclear Physics and its Applications Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge Tennessee 37831-6374 USA Department of Physics Florida Atlantic University 777 Glades Road Boca Raton Florida 33431-0991 USA Department of Physics North Carolina State University Raleigh North Carolina 27695-8202 USA Physics Program Community College of Denver P.O. Box 173363 Denver Colorado 80217-3363 USA Department of Aerospace Engineering and Mechanics University of Alabama Box 870280 Tuscaloosa Alabama 35487-0280 USA

We present gravitational wave emission predictions based on three core collapse supernova simulations corresponding to three different progenitor masses. The masses span a large range, between 9.6 and 25M⊙, are all initially nonrotating, and are of two metallicities: zero and solar. We compute both the temporal evolution of the gravitational wave strains for both the plus and the cross polarizations, as well as their spectral decomposition and characteristic strains. The temporal evolution of our zero metallicity 9.6M⊙ progenitor model is distinct from the temporal evolution of our solar metallicity 15M⊙ progenitor model and our zero metallicity 25M⊙ progenitor model. In the former case, the high-frequency gravitational wave emission is largely confined to a brief time period ∼75 ms after bounce, whereas in the latter two cases high-frequency emission does not commence until ∼125 ms after bounce or later. The excitation mechanisms of the high-frequency emission in all three cases correspond to proto-neutron star convection and accretion onto the proto-neutron star from the convective gain layer above it, with the former playing the dominant role for most of the evolution. The low-frequency emission in all three models exhibits very similar behavior. At frequencies below ∼250 Hz, gravitational waves are emitted by neutrino-driven convection and the standing accretion shock instability (SASI). This emission extends throughout the simulations when a gain region is present. In all three models, explosion is observed at ∼125, ∼500, and ∼250 ms after bounce in the 9.6, 15, and 25M⊙ progenitor models, respectively. At these times, the low-frequency gravitational wave emission is joined by very low-frequency emission, below ∼10 Hz. These very low-frequency episodes are the result of explosion and begin at the above designated explosion times in each of our models. Our characteristic strains tell us that, in principle, all three gravitational wave signals would be detec

关键词： Gravitation Gravitational waves Novae & supernovae Transient & explosive astronomical phenomena

Modeling subgrid-scale force and divergence of heat flux of compressible isotropic turbulence by artificial neural network

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Physical Review Fluids 2019年第10期4卷 104605-104605页

作者： Chenyue Xie Ke Li Chao Ma Jianchun Wang Shenzhen Key Laboratory of Complex Aerospace Flows Center for Complex Flows and Soft Matter Research Department of Mechanics and Aerospace Engineering Southern University of Science and Technology Shenzhen 518055 People's Republic of China Institute of Computational Mathematics and Scientific Engineering Computing Chinese Academy of Sciences Beijing 100190 People's Republic of China The Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

In this paper, the subgrid-scale (SGS) force and the divergence of SGS heat flux of compressible isotropic turbulence are modeled directly by an artificial neural network (ANN), which serves as a data-driven SGS modeling tool for large-eddy simulations (LESs). The unclosed SGS force and divergence of SGS heat flux are modeled based on the local stencil geometry with Galilean invariance. The input features include the first-order and second-order derivatives of filtered velocity and temperature, filtered density, and its first-order derivative. It is shown that the proposed ANN-F7 model shows an advantage over the gradient model in the a priori test. Specifically, the ANN-F7 model gives larger correlation coefficients and smaller relative errors than the gradient model. In an a posteriori analysis, the ANN-F7 model performs better than the dynamic Smagorinsky model (DSM) and dynamic mixed model (DMM) in the prediction of the statistical properties of flow fields at the Taylor microscale Reynolds number Reλ ranging from 180 to 250. The DSM and DMM models lead to the typical tilted spectral distribution of velocity, where low wave numbers are too energy rich, while those near the cutoff are damped too strongly. In contrast, it is shown that the velocity spectrum predicted by the ANN-F7 model almost overlaps with the filtered direct numerical simulation data. Besides, the ANN-F7 model reconstructs the probability density functions of SGS force and divergence of SGS heat flux much better than the DSM and DMM models. An artificial neural network with reasonable physical input features can deepen our understanding of turbulence modeling.

关键词： Compressible flows Turbulence Artificial neural networks

Correction to: Near Real Time Satellite Event Detection, Characterization, and Operational Assessment Via the Exploitation of Remote Photoacoustic Signatures

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The Journal of the Astronautical Sciences 2021年第2期68卷 550-550页

作者： Spurbeck, Justin Jah, Moriba K. Kucharski, Daniel Bennett, James C. S. Webb, James G. Aerospace Engineering and Engineering Mechanics Department Cockrell School of Engineering The University of Texas at Austin Austin USA Research Fellow Space Environment Research Centre SERC Canberra Australia. Visiting Researcher Institute for Computational Engineering and Sciences The University of Texas at Austin Austin USA Astrodynamics Group Leader EOS Space Systems Pty Ltd Queanbeyan Australia. Research Program Leader Space Environment Research Center Canberra Australia Instrument Scientist EOS Space Systems Pty Ltd Queanbeyan Australia

A Correction to this paper has been published: https://***/10.1007/s40295-021-00265-0

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Densification of single-walled carbon nanotube films: Mesoscopic distinct element method simulations and experimental validation

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arXiv 2020年

作者： Drozdov, Grigorii Ostanin, Igor Xu, Hao Wang, Yuezhou Dumitrică, Traian Grebenko, Artem Tsapenko, Alexey P. Gladush, Yuriy Ermolaev, Georgy Volkov, Valentyn S. Eibl, Sebastian Rüde, Ulrich Nasibulin, Albert G. Scientific Computation Program University of Minnesota Twin CitiesMN55455 United States Multi-Scale Mechanics Faculty of Engineering Technology MESA+ University of Twente Enschede7500 AE Netherlands Skolkovo Institute of Science and Technology Nobel St. 3 Moscow Russia Department of Aerospace Engineering and Mechanics University of Minnesota Twin CitiesMN55455 United States Integrated Engineering Minnesota State University MankatoMN56001 United States Department of Mechanical Engineering University of Minnesota Twin CitiesMN55455 United States Moscow Institute of Physics and Technology Institute Lane 9 Dolgoprudniy Russia Department of Applied Physics Aalto University School of Science AaltoFI-00076 Finland Center for Photonics and 2D Materials Moscow Institute of Physics and Technology Dolgoprudny141700 Russia Friedrich-Alexander University Erlangen-Nuremberg Cauerstr.11 Erlangen91052 Germany Aalto University Department of Materials Science and Engineering Aalto00076 Finland

Nanometer thin single-walled carbon nanotube (CNT) films collected from the aerosol chemical deposition reactors have gathered attention for their promising applications. Densification of these pristine films provides an important way to manipulate the mechanical, electronic, and optical properties. To elucidate the underlying microstructural level restructuring, which is ultimately responsible for the change in properties, we perform large scale vector-based mesoscopic distinct element method simulations in conjunction with electron microscopy and spectroscopic ellipsometry characterization of pristine and densified films by drop-cast volatile liquid processing. Matching the microscopy observations, pristine CNT films with finite thickness are modeled as self-assembled CNT networks comprising entangled dendritic bundles with branches extending down to individual CNTs. Simulations of the film under uniaxial compression uncover an ultra-soft densification regime extending to a ~75% strain, which is likely accessible with the surface tensional forces arising from liquid surface tension during the evaporation. When removing the loads, the pre-compressed samples evolve into homogeneously densified films with thickness values depending on both the pre-compression level and the sample microstructure. The significant reduction in thickness, confirmed by our spectroscopic ellipsometry, is attributed to the underlying structural changes occurring at the 100 nm scale, including the zipping of the thinnest dendritic branches. Copyright © 2020, The Authors. All rights reserved.

关键词： Carbon films

Self-assembled periodic nanostructures using martensitic phase transformations

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arXiv 2020年

作者： Prakash, Abhinav Wang, Tianqi Bucsek, Ashley Truttmann, Tristan K. Fali, Alireza Cotrufo, Michele Yun, Hwanhui Kim, Jong-Woo Ryan, Philip J. Mkhoyan, K. Andre Alù, Andrea Abate, Yohannes James, Richard D. Jalan, Bharat Department of Chemical Engineering and Materials Science University of Minnesota – Twin Cities MinneapolisMN55455 United States Department of Aerospace Engineering and Mechanics University of Minnesota – Twin Cities MinneapolisMN55455 United States Department of Mechanical Engineering University of Michigan Ann ArborMI48109 United States Department of Physics and Astronomy University of Georgia AthensGA30602 United States Photonics Initiative Advanced Science Research Center City University of New York NY10031 United States Advanced Photon Source Argonne National Laboratory ArgonneIL60439 United States Physics Program Graduate Center City University of New York New YorkNY10016 United States

We describe a novel approach for the rational design and synthesis of self-assembled periodic nanostructures using martensitic phase transformations. We demonstrate this approach in a thin film of perovskite SrSnO3 with reconfigurable periodic nanostructures consisting of regularly spaced regions of sharply contrasted dielectric properties. The films can be designed to have different periodicities and relative phase fractions via chemical doping or strain engineering. The dielectric contrast within a single film can be tuned using temperature and laser wavelength, effectively creating a variable photonic crystal. Our results show the realistic possibility of designing large-area self-assembled periodic structures using martensitic phase transformations with the potential of implementing "built-to-order" nanostructures for tailored optoelectronic functionalities. Copyright © 2020, The Authors. All rights reserved.

关键词： Thin films

Mechanical and vibrational characteristics of functionally graded Cu-Ni Nanowire: A molecular dynamics study

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arXiv 2019年

作者： Islam, Mahmudul Hoque Thakur, Md Shajedul Mojumder, Satyajit Amin, Abdullah Al Islam, Md Mahbubul Dhaka1000 Bangladesh Theoretical and Applied Mechanics Program Northwestern University EvanstonIL60208 United States Department of Mechanical and Aerospace Engineering Case Western Reserve University 10900 Euclid Avenue ClevelandOH44106-7222 United States Department of Mechanical Engineering Wayne State University 5050 Anthony Wayne Drive DetroitMI48202 United States

- Functionally graded material (FGM) is a class of advanced materials, consisting of two (or more) different constituents, that possesses a continuously varying composition profile. With the advancement of nanotechnology, applications of FGMs have shifted from their conventional usage towards sophisticated micro and nanoscale electronics and energy conversion devices. Therefore, the study of mechanical and vibrational properties of different FGM nanostructures is crucial in exploring their feasibility for different applications. In this study, for the first time, we employed molecular dynamics (MD) simulations to investigate the mechanical and vibrational properties of radially graded Cu-Ni FGM nanowires (NW). Distribution of Cu and Ni along the radial direction follows power-law, exponential and sigmoid functions for FGM NWs under consideration. Our results demonstrate that, distribution function parameters play an important role in modulating the mechanical (elastic modulus and ultimate tensile strength) and vibrational (natural frequency and quality factor) properties of FGM NWs. The study also suggests that, elastic moduli of FGM NWs can be predicted with relatively good accuracy using Tamura and Reuss micromechanical models. We found that, Euler-Bernoulli beam theory under-predicts the natural frequencies of FGM NWs, whereas He-Lilley model closely approximates the MD results. Interestingly, FGM NWs are always found to exhibit beat vibration because of their asymmetrical cross sections, which have significant applications in nano electromechanical systems. Finally, this is the first atomistic scale study of FGMs that directly compares MD simulations with continuum theories and micromechanical models to investigate and understand the underlying mechanisms that govern the mechanical and vibrational properties of FGM NWs in nanoscale. Copyright © 2019, The Authors. All rights reserved.

关键词： Nanowires