Convection–diffusion equation
The convection-diffusion equation is a more general version of the scalar transport equation. It is a combination of the diffusion and convection (advection) equations. It describes physical phenomena where particles, energy, or other physical quantities are transferred inside a physical system due to two processes: diffusion and convection.
\[\dfrac{\partial c}{\partial t} = \mathbf{\nabla} \cdot (D \mathbf{\nabla} c - \mathbf{v} c) + R\]

\[\dfrac{\partial c}{\partial t} = \underbrace{\mathbf{\nabla} \cdot (D \mathbf{\nabla} c)}_{\text{diffusion}}-\overbrace{\underbrace{\mathbf{\nabla}\cdot (\mathbf{v} c)}_{\text{advection}}}^\text{convection} + \overbrace{\underbrace{R}_\text{destruction}}^\text{creation}\]

\(\mathbf{\nabla} \cdot (D \mathbf{\nabla} c)\) is the contribution of diffusion.
\(- \mathbf{\nabla}\cdot (\mathbf{v} c)\) is the contribution of convection or advection.
\(R\) describes the creation or destruction of the quantity.

where
\(c\) is the variable of interest.
\(D\) is the diffusivity.
\(\mathbf{v}\) is the velocity field, and
\(R\) is the sources or sinks of the quantity \(c\).

#Convection #Diffusion #Transport #Advection #Equation #ConvectionDiffusionEquation #DifferentialEquations #AdvectionEquation #DiffusionEquation #TransportEquation #ConvectionEquation

An example of an error indicator is driven non-conforming mesh adaptivity for #advection problem using upwind high order #DG. Wind velocity is discretised by vector potential function in H1 one space. #MOFEM can do very cool things. That technology is implemented for 2d/3d problems. #FEM #FEA #HPC

Example #code is here:
http://mofem.eng.gla.ac.uk/mofem/html/tutorial_level_set.html

MoFEM: ADV-3: DG Upwind for advection problem or level set

Our new paper on modelling the #spatiotemporal dynamics of a beneficial genetic variant is out @eLife.
Muktupavela et al: https://elifesciences.org/articles/73767
Plus a digest highlight here: https://elifesciences.org/digests/73767/evolving-through-time-and-space

We extend a #diffusion method for inferring the spread of a strongly selected allele, originally developed by Novembre et al. (https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0030339). We now incorporate #ancientDNA and allow for #advection dynamics.

#EvolutionaryGenetics #Evolution #Genetics #EcoEvo #archaeology #HumanEvolution

Modeling the spatiotemporal spread of beneficial alleles using ancient genomes

A new method for inferring the spatiotemporal dynamics governing the spread of an advantageous mutation using ancient DNA.

eLife

@MPI_Meteo

The most computationally expensive part of such models is the transport (by #advection and #diffusion) of #biogeochemical #tracers (zoo and #phytoplankton #nutrients, organic and inorganic #carbon, etc) with the #ocean #flow.

The more tracers we include to represent the complexity of #ocean biogeochemistry, the slower are the model runs. Same problem arises when the #spatial #resolution of an #ESM increases.

Biogeochemistry models can become a bottleneck in #ESM computations. 2/