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Abstract
Discrete Element Method (DEM) simulations are a promising approach to accurately predict agglomeration and deposition of micronsized adhesive particles. However, the mechanistic models in DEM combined with high particle stiffness for most common materials require time step sizes in the order of nanoseconds, which makes DEM simulations impractical for more complex applications.
In this study, analytically derived guidelines on how to reduce computational time by using a reduced particle stiffness are given. The guidelines are validated by comparing simulations of particles with and without reduced particle stiffness to experimental data. Then two welldefined test cases are investigated to show the applicability of the guidelines.
When introducing a reduced particle stiffness in DEM simulations by reducing the effective Young's modulus from E to E_{mod}, the surface energy density γ in the adhesive JohnsonKendallRoberts (JKR) model by Johnson et al. [1] should be modified as γ_{mod} = γ (E_{mod}/E)^{2/5}. Using this relation, the stick/rebound threshold remains the same but the collision process takes place over a longer time period, which allows for a higher time step size. When rolling motion is important, the commonly used adhesive rolling resistance torque model proposed by Dominik and Tielens [2,3], Krijt et al. [4] can be used by modifying the contact radius ratio (a/a_{0})^{3/2} to (a_{mod}/a_{0,mod})^{3/2}, while keeping the other terms unaltered in the description of the rolling resistance torque M_{r,mod} = −4F_{C} (a/a_{0})^{3/2}ξ. Furthermore, as the particle stiffness is reduced from E to E_{mod}, the time period for collisions (or oscillations when particles stick upon impact) Δtcol is found to vary as Δt_{col},mod = Δt_{col}(E/E_{mod})^{2/5}. As the collision duration and the collision time step size are directly related, this criterion can be used to estimate how much the time step size can be changed when a reduced particle stiffness is introduced.
Introducing particles with a reduced particle stiffness has some limitations when strong external forces are acting to breakup formed agglomerates or reentrain particles deposited on a surface out into the free stream. Therefore, care should be taken in flows with high local shear to make sure that an external force, such as a fluid drag force, acting to separate agglomerated particles, is several orders of magnitude lower than the critical force required to separate particles.
In this study, analytically derived guidelines on how to reduce computational time by using a reduced particle stiffness are given. The guidelines are validated by comparing simulations of particles with and without reduced particle stiffness to experimental data. Then two welldefined test cases are investigated to show the applicability of the guidelines.
When introducing a reduced particle stiffness in DEM simulations by reducing the effective Young's modulus from E to E_{mod}, the surface energy density γ in the adhesive JohnsonKendallRoberts (JKR) model by Johnson et al. [1] should be modified as γ_{mod} = γ (E_{mod}/E)^{2/5}. Using this relation, the stick/rebound threshold remains the same but the collision process takes place over a longer time period, which allows for a higher time step size. When rolling motion is important, the commonly used adhesive rolling resistance torque model proposed by Dominik and Tielens [2,3], Krijt et al. [4] can be used by modifying the contact radius ratio (a/a_{0})^{3/2} to (a_{mod}/a_{0,mod})^{3/2}, while keeping the other terms unaltered in the description of the rolling resistance torque M_{r,mod} = −4F_{C} (a/a_{0})^{3/2}ξ. Furthermore, as the particle stiffness is reduced from E to E_{mod}, the time period for collisions (or oscillations when particles stick upon impact) Δtcol is found to vary as Δt_{col},mod = Δt_{col}(E/E_{mod})^{2/5}. As the collision duration and the collision time step size are directly related, this criterion can be used to estimate how much the time step size can be changed when a reduced particle stiffness is introduced.
Introducing particles with a reduced particle stiffness has some limitations when strong external forces are acting to breakup formed agglomerates or reentrain particles deposited on a surface out into the free stream. Therefore, care should be taken in flows with high local shear to make sure that an external force, such as a fluid drag force, acting to separate agglomerated particles, is several orders of magnitude lower than the critical force required to separate particles.
Original language  English 

Journal  Powder Technology 
Volume  319 
Pages (fromto)  472482 
Number of pages  11 
ISSN  00325910 
DOIs  
Publication status  Published  Sept 2017 
Keywords
 Discrete Element Method
 Reduced particle stiffness
 Adhesive particles
 JKR adhesive model
 Rolling resistance torque
 Computational efficiency
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Dive into the research topics of 'On the Adhesive JKR Contact and Rolling Models for Reduced Particle Stiffness Discrete Element Simulations'. Together they form a unique fingerprint.Projects
 1 Finished

THERMCYC  Advanced thermodynamic cycles utilising lowtemperature heat sources
Hærvig, J. (Project Participant), Sørensen, K. (Project Manager), Condra, T. (Project Manager) & Singh, S. (Project Participant)
15/09/2014 → 14/09/2017
Project: Research
Research output
 87 Citations
 1 PhD thesis

On the Adhesive Behaviour of Micronsized Particles in Turbulent Flow: A Numerical Study Coupling the Discrete Element Method and Large Eddy Simulations
Hærvig, J., 2017, Aalborg Universitetsforlag. 227 p.Research output: PhD thesis
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