scholarly journals Theoretical Chemistry and the Calculation of the Atmospheric State

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 727
Author(s):  
Adrian F. Tuck
Keyword(s):  
Fluid Dynamics ◽  
Molecular Dynamics ◽  
Numerical Models ◽  
Hard Spheres ◽  
Physical Method ◽  
Atmospheric Temperature ◽  
Theoretical Chemistry ◽  
Navier Stokes Equation ◽  
Hydrodynamic Behaviour ◽  
Atmospheric State

Theoretical chemists have been actively engaged for some time in processes such as ozone photodissociation, overtone photodissociation in nitric acid, pernitric acid, sulphuric acid, clusters and in small organic acids. The last of these have shown very different behaviours in the gas phase, liquid phase and importantly at the air–water interface in aqueous aerosols. The founder of molecular dynamics, B J Alder, pointed out long ago that hydrodynamic behaviour emerged when the symmetry of a random, thermalised population of hard spheres—billiard balls—was broken by a flux of energetic molecules. Despite this, efforts over two centuries to solve turbulence by finding top-down solutions to the Navier–Stokes equation have failed. It is time for theoretical chemistry to try a bottom-up solution. Gibbs free energy that drives the circulation arises from the entropy difference between the incoming low-entropy beam of visible and ultraviolet photons and the outgoing higher-entropy flux of infrared photons over the whole 4π solid angle. The role of the most energetic molecules with the highest velocities will affect the rovibrational line shapes of water, carbon dioxide and ozone in the far wings, where there is the largest effect on radiative transfer and hence on calculations of atmospheric temperature. The atmospheric state is determined by the interaction of radiation, chemistry and fluid dynamics on the microscopic scale, with propagation through the mesoscale to the macroscale. It will take theoretical chemistry to simulate that accurately. A challenging programme of research for theoretical chemistry is proposed, involving ab initio simulation by molecular dynamics of an air volume, starting in the upper stratosphere. The aim is to obtain scaling exponents for turbulence, providing a physical method for upscaling in numerical models. Turbulence affects chemistry, radiation and fluid dynamics at a fundamental, molecular level and is thus of basic concern to theoretical chemistry as it applies to the atmosphere, which consists of molecules in motion.

scholarly journals CFD Investigation of Trout-Like Configuration Holding Station near an Obstruction

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 204
Author(s):  
Kamran Fouladi ◽  
David J. Coughlin
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Laboratory Experiment ◽  
Numerical Models ◽  
Interaction Model ◽  
Underwater Vehicle ◽  
Water Stream ◽  
Hydrodynamic Analysis ◽  
Structure Interaction ◽  
Vehicle Systems

This report presents the development of a fluid-structure interaction model using commercial Computational fluid dynamics software and in-house developed User Defined Function to simulate the motion of a trout Department of Mechanical Engineering, Widener University holding station in a moving water stream. The oscillation model used in this study is based on the observations of trout swimming in a respirometry tank in a laboratory experiment. The numerical simulations showed results that are consistent with laboratory observations of a trout holding station in the tank without obstruction and trout entrained to the side of the cylindrical obstruction. This paper will be helpful in the development of numerical models for the hydrodynamic analysis of bioinspired unmanned underwater vehicle systems.

scholarly journals Event-Driven Molecular Dynamics Simulation of Hard-Sphere Gas Flows in Microchannels

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Volkan Ramazan Akkaya ◽  
Ilyas Kandemir
Keyword(s):  
Molecular Dynamics ◽  
Hard Sphere ◽  
Stokes Equations ◽  
Hard Spheres ◽  
Flow Characteristics ◽  
Dynamics Simulation ◽  
Navier Stokes ◽  
Gas Flows ◽  
Linearized Boltzmann Equation ◽  
Event Driven

Classical solution of Navier-Stokes equations with nonslip boundary condition leads to inaccurate predictions of flow characteristics of rarefied gases confined in micro/nanochannels. Therefore, molecular interaction based simulations are often used to properly express velocity and temperature slips at high Knudsen numbers (Kn) seen at dilute gases or narrow channels. In this study, an event-driven molecular dynamics (EDMD) simulation is proposed to estimate properties of hard-sphere gas flows. Considering molecules as hard-spheres, trajectories of the molecules, collision partners, corresponding interaction times, and postcollision velocities are computed deterministically using discrete interaction potentials. On the other hand, boundary interactions are handled stochastically. Added to that, in order to create a pressure gradient along the channel, an implicit treatment for flow boundaries is adapted for EDMD simulations. Shear-Driven (Couette) and Pressure-Driven flows for various channel configurations are simulated to demonstrate the validity of suggested treatment. Results agree well with DSMC method and solution of linearized Boltzmann equation. At low Kn, EDMD produces similar velocity profiles with Navier-Stokes (N-S) equations and slip boundary conditions, but as Kn increases, N-S slip models overestimate slip velocities.

Computational Steering of Interactive Material Flow Simulations

2008 ◽  
Author(s):  
Stefan Lietsch ◽  
Christoph Laroque ◽  
Henning Zabel
Keyword(s):  
Fluid Dynamics ◽  
Molecular Dynamics ◽  
Material Flow ◽  
High Performance ◽  
Flow Simulation ◽  
Computational Steering ◽  
Flow Simulations ◽  
Distributed Simulations ◽  
Computational Fluid Dynamics Cfd ◽  
Performance Computing

In this paper we present the integration of computational steering techniques into the interactive material flow simulation d3FACT insight. This kind of simulation differs from traditional, long running High Performance Computing (HPC) simulations such as Computational Fluid Dynamics (CFD) or Molecular Dynamics in many aspects. One very important aspect is that these simulations run in (soft) real-time, thus the corresponding visualization needs to be updated after every step of the simulation. In turn, this allows to let changes, made through the visualization, impact the actual simulation and again, to see the effects in visualization. To allow this kind of control over the simulation and to further provide a flexible basis to integrate several instances of simulation, visualization and steering components, we used and enhanced a self-developed computational steering platform, which fits best for the needs of highly interactive and distributed simulations. Thereby we are able to realize multi-user and comparative scenarios which were not possible in this field of simulations before.

Circular Cylinder Exposed to Cross Flow Fluid Forces – Parameters of Influence – Limits of Numerical Models

2003 ◽  
Author(s):  
Christoph Reichel ◽  
Klaus Strohmeier
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Models ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Rigid Cylinder ◽  
Fluid Forces ◽  
Wide Range ◽  
Dynamics Simulations

In many technical fields, e.g. heat exchangers, circular cylinders are involved in Fluid Structure Interaction (FSI) problems. Therefore correct frequency and magnitude of fluid forces, respectively Strouhal number, drag and lift coefficient are needed. If fluid forces are evaluated with Computational Fluid Dynamics (CFD), mostly flow around a rigid cylinder is used to verify model and numerical methods. Unfortunately experimental as well as numerical results show great variation, making verification and testing of models difficult. Reynolds number is regarded as main influencing parameter for a rigid cylinder in cross flow. Most of experimental deviations can be related to other parameters, which differ from experiment to experiment. In this paper such parameters are specified and it is shown, that a closer look is needed, if one really wants to verify a model. Besides experimental results, which can be found in literature, some parameters are investigated by numerical simulation. Like experiments CFD (Computational Fluid Dynamics) simulations show a huge bandwidth of results, even when the same turbulence model is used. Flow around cylinders separates over a wide range of Reynolds numbers. It will be demonstrated that, using CFD, large deviations in fluid forces can often be related to miscalculation of the point of separation.

scholarly journals Modelling river history and evolution

2012 ◽  
Vol 370 (1966) ◽  
pp. 2123-2142 ◽  
Author(s):  
T. J. Coulthard ◽  
M. J. Van De Wiel
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Landscape Evolution ◽  
Numerical Models ◽  
Flow Characteristics ◽  
Sedimentary Facies ◽  
Cellular Models ◽  
Depositional Processes ◽  
Alluvial Architecture ◽  
Dynamics Models

Over the last few decades, a suite of numerical models has been developed for studying river history and evolution that is almost as diverse as the subject of river history itself. A distinction can be made between landscape evolution models (LEMs), alluvial architecture models, meander models, cellular models and computational fluid dynamics models. Although these models share some similarities, there also are notable differences between them, which make them more or less suitable for simulating particular aspects of river history and evolution. LEMs embrace entire drainage basins at the price of detail; alluvial architecture models simulate sedimentary facies but oversimplify flow characteristics; and computational fluid dynamics models have to assume a fixed channel form. While all these models have helped us to predict erosion and depositional processes as well as fluvial landscape evolution, some areas of prediction are likely to remain limited and short-term owing to the often nonlinear response of fluvial systems. Nevertheless, progress in model algorithms, computing and field data capture will lead to greater integration between these approaches and thus the ability to interpret river history more comprehensively.

scholarly journals New Aura Microwave Limb Sounder observations of BrO and implications for Br<sub>y</sub>

2012 ◽  
Vol 5 (7) ◽  
pp. 1741-1751 ◽  
Author(s):  
L. Millán ◽  
N. Livesey ◽  
W. Read ◽  
L. Froidevaux ◽  
D. Kinnison ◽  
...  
Keyword(s):  
Error Analysis ◽  
Systematic Error ◽  
State Of The Art ◽  
Numerical Models ◽  
Inversion Algorithm ◽  
Broad Agreement ◽  
Atmospheric State

Abstract. This paper introduces a new inversion algorithm for retrievals of stratospheric BrO from the Aura Microwave Limb Sounder. This version is based on the algorithm described by Livesey et al. (2006a) but uses a more realistic atmospheric state to constrain the retrieval. A description of the methodology and an error analysis are presented. Single daily profile precision uncertainty, when taking the ascending-descending (day-night) difference, was found to be up to 40 pptv while systematic error biases were estimated to be less than about 3 pptv. Monthly mean comparisons show broad agreement with other measurements as well as with state-of-the-art numerical models. We infer a 2005 yearly total inorganic Bry using the measured MLS BrO to be 20.3 ± 4.5 pptv, which implies a contribution from very short lived substances to the stratospheric bromine budget of 5 ± 4.5 pptv.

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