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Coupling at the Interfaces (9)<br />

Time integration flowchart is as follows:<br />

• Let complete solution be known at time t n : U , U<br />

, U<br />

n n n<br />

i i i<br />

p n ∆t<br />

n<br />

• Compute mid-step velocities (i.e. predictors): U i<br />

U i<br />

+ U<br />

i<br />

2<br />

n p<br />

• Compute new configurations: U = U +∆t U <br />

i i i<br />

• Solve free problem for accelerations:<br />

U<br />

= M F<br />

−1<br />

i,free<br />

i i<br />

p t<br />

• Compute new free velocities: U ∆<br />

i,free U i<br />

+ U<br />

i,free<br />

2<br />

∆t<br />

−<br />

• Compute: 1 T<br />

− 1 T<br />

H ( CM<br />

1 1<br />

C1 + CM<br />

2 2<br />

C2<br />

) and<br />

2<br />

d CU<br />

1 1,free<br />

+ CU<br />

2 2,free<br />

<br />

<br />

117<br />

Coupling at the Interfaces (10)<br />

• Solve linear system for the Lagrange multipliers:<br />

−1<br />

H Λ= d → Λ= H d<br />

H is diagonal for<br />

conforming interface!<br />

• Compute interaction forces:<br />

R<br />

i<br />

= C Λ<br />

T<br />

i<br />

−1<br />

• Compute link accelerations: <br />

U M R<br />

i,link<br />

i i<br />

M is diagonal!<br />

• Compute total accelerations: U i<br />

= U i,free + U<br />

i,link<br />

t<br />

• Compute new velocities: U ∆<br />

i<br />

= U i,free + U<br />

i,link<br />

2<br />

118<br />

59

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