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Boundary conditions for modeling deposition in a stochastic Lagrangian particle model
Umeå University, Faculty of Science and Technology, Department of Physics. FOI.
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The Swedish defence agency (FOI) has developed a particle model (called Pello) that simulates the dispersion of aerosols and gases. At the boundaries, such as the ground, the particles can either reflect back into the domain (the atmosphere) or be absorbed. Which of the events that occurs is decided by a certain probability, which in the present model depends on mere physical properties. In this thesis we have investigated a newly proposed boundary behaviour which also depends on the time step used in the numerical simulations. We verified the accuracy of the new model by using a dispersion model with an explicit solution. To gain a better understanding of how important parameters at the boundary influence each other, we performed a sensitivity analysis.

Simulations showed an overall improving concentration profile as the time step became smaller and the new model working well. The convergence order of the simulations was found to be close to 0.5. In this thesis we have shown that there exist an upper limit for the time step, which depends on the specific model. The present used time step at FOI does not have this versatile property. But having this upper limit for the time step close to the boundary, and a uniform time step can be time demanding. This lead us to the conclusion that an adaptive time step should be implemented.

Place, publisher, year, edition, pages
2015. , 63 p.
Keyword [en]
Lagrangian dispersion model, Boundary behavior, time step
National Category
Mathematical Analysis Meteorology and Atmospheric Sciences
URN: urn:nbn:se:umu:diva-106706OAI: diva2:844114
Subject / course
Examensarbete i teknisk fysik
Educational program
Master of Science Programme in Engineering Physics
Available from: 2015-08-17 Created: 2015-08-03 Last updated: 2015-08-17Bibliographically approved

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