Preprints

Filtering by Subject: Fluid Dynamics

Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry

C. Gabriel David, Nina Kohl, Elisa Casella, Alessio Rovere, Pablo Ballesteros, Torsten Schlurmann

Published: 2020-10-21
Subjects: Civil Engineering, Engineering, Environmental Engineering, Environmental Monitoring, Environmental Studies, Fluid Dynamics, Fresh Water Studies, Geographic Information Sciences, Hydraulic Engineering, Other Civil and Environmental Engineering, Other Environmental Sciences, Remote Sensing

Reconstructing the topography of shallow underwater environments using Structure-from-Motion – Multi View Stereo (SfM-MVS) techniques applied to aerial imagery from Unmanned Aerial Vehicles (UAVs) is a challenging problem, as it involves non-linear distortions caused by water refraction. This study presents an experiment with aerial photographs collected with a consumer-grade UAV on the [...]

An analytical solution to the Navier–Stokes equation for incompressible flow around a solid sphere

Ahmad Talaei, Timothy J. Garrett

Published: 2020-08-25
Subjects: Applied Mathematics, Earth Sciences, Engineering, Fluid Dynamics, Mechanical Engineering, Other Mechanical Engineering, Partial Differential Equations, Physical Sciences and Mathematics, Physics, Special Functions

This paper is concerned with obtaining a formulation for the flow past a sphere in a viscous and incompressible fluid, building upon previously obtained well-known solutions that were limited to small Reynolds numbers. Using a method based on a summation of separation of variables, we develop a general analytical solution to the Navier--Stokes equation for the special case of axially symmetric [...]

Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra

Samuel Pegler, David Ferguson

Published: 2020-07-16
Subjects: Earth Sciences, Fluid Dynamics, Geology, Oceanography, Oceanography and Atmospheric Sciences and Meteorology, Other Physical Sciences and Mathematics, Physical Sciences and Mathematics, Physics, Volcanology

Deep-marine volcanism drives Earth’s most energetic transfers of heat and mass between the crust and the oceans. Seafloor magmatic activity has been correlated in time with the appearance of massive enigmatic plumes of hydrothermal fluid, known as megaplumes, yet little is known of the primary source and intensity of the hydrothermal energy release that occurs during [...]

Deep spatial transformers for autoregressive data-driven forecasting of geophysical turbulence

Ashesh Kumar Chattopadhyay, Mustafa Mustafa, Pedram Hassanzadeh, Karthik Kashinath

Published: 2020-07-05
Subjects: Artificial Intelligence and Robotics, Atmospheric Sciences, Climate, Computer Sciences, Dynamical Systems, Earth Sciences, Environmental Sciences, Fluid Dynamics, Geophysics and Seismology, Mathematics, Oceanography and Atmospheric Sciences and Meteorology, Physical Sciences and Mathematics, Physics

A deep spatial transformer based encoder-decoder model has been developed to autoregressively predict the time evolution of the upper layers stream function of a two-layered quasi-geostrophic (QG) system without any information about the lower layers stream function. The spatio-temporal complexity of QG flow is comparable to the complexity of 500hPa Geopotential Height (Z500) of fully coupled [...]

Nonlinear stochastic dissipation in turbulent geophysical flows

Jean-Michel Brankart

Published: 2020-06-19
Subjects: Earth Sciences, Fluid Dynamics, Physical Sciences and Mathematics, Physics

The purpose of this study is to further investigate the assumption that geophysical flows can be described and simulated by direct sampling from a dynamically constrained probability distribution, with a reversible formulation of dissipation. This is done by making the probability of the flow decrease with the deviation of the Lagrangian with respect to local equilibrium, and by assuming that [...]

Sampling geophysical flows from a dynamically constrained probability distribution

Jean-Michel Brankart

Published: 2020-06-19
Subjects: Earth Sciences, Fluid Dynamics, Physical Sciences and Mathematics, Physics

The purpose of this study is to further investigate the problem of explicitly simulating uncertainties in geophysical models. Rather than introducing stochastic processes in forward-in-time partial differential equations, this is done here by reformulating the dynamical equations governing the time evolution of the flow as a probability distribution. Flows can then be drawn directly from the [...]

Event-based contact angle measurements inside porous media using time-resolved micro-computed tomography

Arjen Mascini, Veerle Cnudde, Tom Bultreys

Published: 2020-01-28
Subjects: Earth Sciences, Fluid Dynamics, Hydrology, Physical Sciences and Mathematics, Physics

Hypothesis Capillary-dominated multiphase flow in porous materials is strongly affected by the pore walls’ wettability. Recent micro-computed tomography (mCT) studies found unexpectedly wide contact angle distributions measured on static fluid distributions inside the pores. We hypothesize that analysis on time-resolved mCT data of fluid invasion events may be more directly relevant to the fluid [...]

Dynamics of displacement in mixed-wet porous media

Alessio Scanziani, Qingyang Lin, Abdulla Alhosani, Martin J. Blunt, Branko Bijeljic

Published: 2020-01-22
Subjects: Earth Sciences, Engineering, Fluid Dynamics, Physical Sciences and Mathematics, Physics

We identify a distinct two-phase flow invasion pattern in a mixed-wet porous medium. Time-resolved high-resolution synchrotron X--ray imaging is used to study the invasion of water through a small rock sample filled with oil, characterized by a wide non-uniform distribution of local contact angles both above and below $90^{\circ}$. The water advances in a connected front, but throats are not [...]

A bedform phase diagram for dense granular currents

Gregory Smith, Pete Rowley, Rebecca Williams, Guido Giordano, Matteo Trolese, Aurora Silleni, Daniel R. Parsons, Samuel Capon

Published: 2019-07-04
Subjects: Earth Sciences, Fluid Dynamics, Geology, Physical Sciences and Mathematics, Physics, Sedimentology, Volcanology

Pyroclastic density currents are a life-threatening volcanic hazard. Our understanding and hazard assessments of these flows primarily rely on interpretations of their deposits. The occurrence of stratified layers, cross-stratification, and dune bedforms in these deposits has been assumed as indicative of dilute, turbulent, flows causing traction-dominated deposition. Here we show, through [...]

Data-driven prediction of a multi-scale Lorenz 96 chaotic system using deep learning methods: Reservoir computing, ANN, and RNN-LSTM

Ashesh Kumar Chattopadhyay, Pedram Hassanzadeh, Devika Subramanian

Published: 2019-06-20
Subjects: Applied Mathematics, Artificial Intelligence and Robotics, Atmospheric Sciences, Climate, Computer Sciences, Dynamic Systems, Earth Sciences, Fluid Dynamics, Non-linear Dynamics, Oceanography and Atmospheric Sciences and Meteorology, Physical Sciences and Mathematics, Physics

In this paper, the performance of three deep learning methods for predicting short-term evolution and for reproducing the long-term statistics of a multi-scale spatio-temporal Lorenz 96 system is examined. The methods are: echo state network (a type of reservoir computing, RC-ESN), deep feed-forward artificial neural network (ANN), and recurrent neural network with long short-term memory [...]

Minimal surfaces in porous media: pore-scale imaging of multiphase flow in an altered-wettability Bentheimer sandstone

Qingyang Lin, Branko Bijeljic, Steffen Berg, Ronny Pini, Martin J. Blunt, Sam Krevor

Published: 2019-03-28
Subjects: Earth Sciences, Fluid Dynamics, Physical Sciences and Mathematics, Physics

We observed features of pore scale fluid distributions during oil-brine displacement in a mixed-wet sandstone rock sample. High-resolution X-ray imaging was used in combination with differential pressure measurements to measure relative permeability and capillary pressure simultaneously during a steady-state waterflood experiment on a sample of Bentheimer sandstone 51.6 mm long and 6.1 mm in [...]

Hydrodynamic control of gas-exchange velocity in small streams

Andreas Lorke, Pascal Bodmer, Kaan Koca, Christian Noss

Published: 2019-03-02
Subjects: Civil and Environmental Engineering, Earth Sciences, Engineering, Environmental Sciences, Fluid Dynamics, Hydraulic Engineering, Physical Sciences and Mathematics, Physics, Planetary Sciences

Gas exchange is a critical component of any biogeochemical mass balance model of dissolved gases in aquatic systems, yet the magnitude and drivers of spatial and temporal variations of air-water exchange rates in shallow streams are poorly understood. We investigated the relationships between gas exchange velocity of carbon dioxide and methane and flow hydraulics at different sections along a [...]

Calibration of astigmatic particle tracking velocimetry based on generalized Gaussian feature extraction

Simon Franchini, Alexandros Charogiannis, Christos N. Markides, Martin J. Blunt, Sam Krevor

Published: 2018-11-20
Subjects: Artificial Intelligence and Robotics, Computer Sciences, Earth Sciences, Engineering, Fluid Dynamics, Hydrology, Life Sciences, Physical Sciences and Mathematics, Physics

Flow and transport in porous media are driven by pore scale processes. Particle tracking in transparent porous media allows for the observation of these processes at the time scale of ms. We demonstrate an application of defocusing particle tracking using brightfield illumination and a CMOS camera sensor. The resulting images have relatively high noise levels. To address this challenge, we [...]

Tracking CO2 plumes in clay-rich rock by distributed fiber optic strain sensing (DFOSS): a laboratory demonstration

Yi Zhang, Ziqiu Xue, Hyuck Park, Jiquan Shi, Tamotsu Kiyama, Xinglin Lei, Yankun Sun, Yunfeng Liang

Published: 2018-04-25
Subjects: Earth Sciences, Environmental Monitoring, Environmental Sciences, Fluid Dynamics, Geology, Geophysics and Seismology, Hydrology, Mineral Physics, Oil, Gas, and Energy, Optics, Physical Sciences and Mathematics, Physics

Monitoring the migration of pore pressure, deformation, and saturation plumes with effective tools is important for the storage and utilization of fluids in underground reservoirs, such as geological stores of carbon dioxide (CO2) and natural gas. Such tools would also verify the security of the fluid contained reservoir–caprock system. Utilizing the swelling strain attributed to pressure [...]

Numerical solution of a non-linear conservation law applicable to the interior dynamics of partially molten planets

Dan J. Bower, Patrick Sanan, Aaron S. Wolf

Published: 2017-11-21
Subjects: Applied Mathematics, Computer Sciences, Earth Sciences, Fluid Dynamics, Geophysics and Seismology, Numerical Analysis and Computation, Numerical Analysis and Scientific Computing, Physical Sciences and Mathematics, Physics

The energy balance of a partially molten rocky planet can be expressed as a non-linear diffusion equation using mixing length theory to quantify heat transport by both convection and mixing of the melt and solid phases. Crucially, in this formulation the effective or eddy diffusivity depends on the entropy gradient, dS/dr, as well as entropy itself. First we present a simplified model with [...]

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