scholarly journals Real-time dynamics and structures of supported subnanometer catalysts via multiscale simulations

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yifan Wang ◽  
Jake Kalscheur ◽  
Ya-Qiong Su ◽  
Emiel J. M. Hensen ◽  
Dionisios G. Vlachos
Keyword(s):  
Co Adsorption ◽  
Metastable Equilibrium ◽  
Modeling Framework ◽  
Time Dynamics ◽  
Structure Changes ◽  
Rapid Sintering ◽  
Equilibrium Structures ◽  
Far From Equilibrium ◽  
Multiscale Modeling Framework ◽  
Spectroscopic Probe

AbstractUnderstanding the performance of subnanometer catalysts and how catalyst treatment and exposure to spectroscopic probe molecules change the structure requires accurate structure determination under working conditions. Experiments lack simultaneous temporal and spatial resolution and could alter the structure, and similar challenges hinder first-principles calculations from answering these questions. Here, we introduce a multiscale modeling framework to follow the evolution of subnanometer clusters at experimentally relevant time scales. We demonstrate its feasibility on Pd adsorbed on CeO2(111) at various catalyst loadings, temperatures, and exposures to CO. We show that sintering occurs in seconds even at room temperature and is mainly driven by free energy reduction. It leads to a kinetically (far from equilibrium) frozen ensemble of quasi-two-dimensional structures that CO chemisorption and infrared experiments probe. CO adsorption makes structures flatter and smaller. High temperatures drive very rapid sintering toward larger, stable/metastable equilibrium structures, where CO induces secondary structure changes only.

Material Characterization of Additively Manufactured Part via Multi-Level Stochastic Upscaling Method

2015 ◽  
Author(s):  
Recep M. Gorguluarslan ◽  
Sang-In Park ◽  
David W. Rosen ◽  
Seung-Kyum Choi
Keyword(s):  
Material Characterization ◽  
Modeling Framework ◽  
Upscaling Technique ◽  
Simulation Based ◽  
Scale Models ◽  
Multiple Levels ◽  
Multiscale Modeling Framework ◽  
Input Uncertainties

An integrated multiscale modeling framework that incorporates a simulation-based upscaling technique is developed and implemented for the material characterization of additively manufactured cellular structures in this paper. The proposed upscaling procedure enables the determination of homogenized parameters at multiple levels by matching the probabilistic performances between fine and coarse scale models. Polynomial chaos expansion is employed in upscaling procedure to handle the computational burden caused by the input uncertainties. Efficient uncertainty quantification is achieved at the mesocale level by utilizing the developed upscaling technique. The homogenized parameters of mesostructures are utilized again at the macroscale level in the upscaling procedure to accurately obtain the overall material properties of the target cellular structure. Actual experimental results of additively manufactured parts are integrated into the developed procedure to demonstrate the efficacy of the method.

A Multilevel Upscaling Method for Material Characterization of Additively Manufactured Part Under Uncertainties

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Recep M. Gorguluarslan ◽  
Sang-In Park ◽  
David W. Rosen ◽  
Seung-Kyum Choi
Keyword(s):  
Material Characterization ◽  
Modeling Framework ◽  
Upscaling Technique ◽  
Simulation Based ◽  
Scale Models ◽  
Multiple Levels ◽  
Multiscale Modeling Framework ◽  
Input Uncertainties

An integrated multiscale modeling framework that incorporates a simulation-based upscaling technique is developed and implemented for the material characterization of additively manufactured cellular structures in this paper. The proposed upscaling procedure enables the determination of homogenized parameters at multiple levels by matching the probabilistic performance between fine and coarse scale models. Polynomial chaos expansion (PCE) is employed in the upscaling procedure to handle the computational burden caused by the input uncertainties. Efficient uncertainty quantification is achieved at the mesoscale level by utilizing the developed upscaling technique. The homogenized parameters of mesostructures are utilized again at the macroscale level in the upscaling procedure to accurately obtain the overall material properties of the target cellular structure. Actual experimental results of additively manufactured parts are integrated into the developed procedure to demonstrate the efficacy of the method.

scholarly journals On the Land–Ocean Contrast of Tropical Convection and Microphysics Statistics Derived from TRMM Satellite Signals and Global Storm-Resolving Models

2016 ◽  
Vol 17 (5) ◽  
pp. 1425-1445 ◽  
Author(s):  
Toshi Matsui ◽  
Jiun-Dar Chern ◽  
Wei-Kuo Tao ◽  
Stephen Lang ◽  
Masaki Satoh ◽  
...  
Keyword(s):  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Atmospheric Model ◽  
Evaluation Framework ◽  
Convective Precipitation ◽  
Modeling Framework ◽  
Near Surface ◽  
Microwave Scattering ◽  
Microwave Imager ◽  
Multiscale Modeling Framework

Abstract A 14-yr climatology of Tropical Rainfall Measuring Mission (TRMM) collocated multisensor signal statistics reveals a distinct land–ocean contrast as well as geographical variability of precipitation type, intensity, and microphysics. Microphysics information inferred from the TRMM Precipitation Radar and Microwave Imager show a large land–ocean contrast for the deep category, suggesting continental convective vigor. Over land, TRMM shows higher echo-top heights and larger maximum echoes, suggesting taller storms and more intense precipitation, as well as larger microwave scattering, suggesting the presence of more/larger frozen convective hydrometeors. This strong land–ocean contrast in deep convection is invariant over seasonal and multiyear time scales. Consequently, relatively short-term simulations from two global storm-resolving models can be evaluated in terms of their land–ocean statistics using the TRMM Triple-Sensor Three-Step Evaluation Framework via a satellite simulator. The models evaluated are the NASA Multiscale Modeling Framework (MMF) and the Nonhydrostatic Icosahedral Cloud Atmospheric Model (NICAM). While both simulations can represent convective land–ocean contrasts in warm precipitation to some extent, near-surface conditions over land are relatively moister in NICAM than MMF, which appears to be the key driver in the divergent warm precipitation results between the two models. Both the MMF and NICAM produced similar frequencies of large CAPE between land and ocean. The dry MMF boundary layer enhanced microwave scattering signals over land, but only NICAM had an enhanced deep convection frequency over land. Neither model could reproduce a realistic land–ocean contrast in deep convective precipitation microphysics. A realistic contrast between land and ocean remains an issue in global storm-resolving modeling.

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