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MOTIVATION
It is a notable difficult to provide
accurate prediction of particle motion and interaction
among particles when they move close to the bed of rivers/channels.
Some of the difficulties are associated to :
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Particles present different motion patterns near bed: sliding, rolling
and saltation.
- Small particles can be ejected from the wall and be
transported by suspension.
- Particles collide with the bed
and among them.
How
can we incorporate all these elements in a model to predict
bedload transport, avoiding empirical correlations?
PROJECT OBJECTIVES
The main objective of this work is to develop a two-phase flow model to
integrate fluid and particle motion using an Eulerian-Lagrangian
approach close to the channel bed. This work focuses on the water flow
close to the wall and the transport of sediment in bed load motion, and
it includes processes that have been disregarded in most existing
models, most notably inter-particle collision.
The specific objectives of this study are:
- To develop and validate an Eulerian-Lagrangian model to
simulate the saltation of particles close to the bed. The Lagrangian
model is intended to be coupled with highly-resolved velocity fields,
using Large Eddy Simulations (LES) or Direct Numerical Simulations
(DNS). Validation of this model is accomplished via-comparison with
experimental data.
- To optimize the computational effort of the Lagrangian
model to calculate particle trajectories and velocities, by revisiting
the formulations for all forces; with special emphasis is put on the
Basset force.
- To examine existing bed-representation sub-models, to
propose a simple yet realistic new approach and to validate it via
comparison with experimental data.
- To gain more understanding about the response of saltating
particles to the velocity fluctuations in the flow (i.e., to
turbulence). To that end, a highly-resolved flow simulation,
considering one-way coupling between phases, is developed.
RESULTS OBTAINED
2-D Particle Tracking Code
A two-dimensional (2-D) particle tracking computational code was
developed in FORTRAN, including a rebound sub-model and a bed roughness
representation. The model was validated through comparison of numerical
predictions with experimental data.
To optimize the computational cost of the particle tracking model, a
new methodology to calculate the Basset force was developed and it was
tested for particles of both small and large size (See Bombardelli,
Gonzalez and Niño, In press).
3-D Particle Tracking Code
A three-dimensional (3-D) particle tracking model was developed in
FORTRAN, which includes the description of both the particle
translational and rotational velocity at every moment. An assessment of
existing sub-models for bed roughness representation is introduced in
this chapter together with a new sub-model. The validation of the best
sub-model is accomplished by comparing its performance with
experimental data. The computational code also considers the motion of
multiple particles and an algorithm to treat the inter-particle
collisions.
Multiple particle simulations under a non
turbulent velocity were performed, using the inter-particle collision
algorithm presented in Yamamoto et al. (2001). A video featuring
an example of two particles colliding using this methodology is
presented here.
Video 1: 2D View of a bed collision and an interparticle
collision event
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