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No-Slip Boundary Conditions in Smoothed Particle Hydrodynamics by Frank Bierbrauer

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Updating Fluid Variables In SPH fluid variables f are updated through interpolation about a given point (x a,y a ) using information from surrounding points (x b,y b ). Each surrounding point is given a weight W ab with respect to the distance between point a and b.

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Particle Deficiency Near a no-slip boundary there is a particle deficiency Any interpolation carried out in this region will produce an incorrect sum

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Three Ways to Resolve the Particle Deficiency Problem 1.Insert fixed image particles outside the boundary a distance d I away from the boundary c.f. nearest fluid particle at distance d F 2.Insert fixed virtual particles within the fluid and in a direct line to the fixed image particles –Avoids creation of errors when fluid and image particles are not aligned 3. Co-moving image particles with d I = d F

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123123

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Velocity Update Using Image Particles 1.Fixed image approach: u I = u F +(1+d I /d F )(u W - u F ) 2.Virtual image approach: u I = u V +(1+d I /d V )(u W - u V ) –Virtual velocities u V are created through interpolation

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Velocity Update Using the Navier- Stokes Equations Update the velocity using the Navier-Stokes equations and a second order finite difference approximation to the velocity derivatives

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At the no-Slip Wall (W) Navier-Stokes Equations Finite-Difference Approximation at the wall

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Velocity Update Much of this reduces down as, in general, a no-slip wall has condition u W =(U 0,0). Therefore, at the wall, u t = u x = u xx = v= v x = v xx = 0

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The Viscoelastic Case The equations are ( = 1,2) where

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Further Reduction Using giving

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At the Wall As well as

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Non-Newtonian (elastic) Stress Only have the velocity condition u W = (U 0,0) as well as y =0

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Must Solve Need u b and v b and W Need as well as S t and e.g.

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Density Update Equation

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Polymeric Stress Update Equations

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Velocity Update Equations

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Solution for u b and v b

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If x = 0, 21 = 1, = S

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Equivalent Newtonian Update Equations

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Giving

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