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II II II II II I - Waste Isolation Pilot Plant - U.S. Department of Energy

II II II II II I - Waste Isolation Pilot Plant - U.S. Department of Energy

II II II II II I - Waste Isolation Pilot Plant - U.S. Department of Energy

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3.2 Explicit Time Integration<br />

SANTOS uses a modified central difference scheme to integrate the equations <strong>of</strong> motion through time. By this<br />

we mean that the velocities are integrated with a forward difference, while the displacements are integrated with a<br />

backward difference. The integration scheme for a node is expressed as<br />

tit=<br />

t<br />

( )<br />

f ‘XT – ftNT / M<br />

(3.2.1)<br />

‘t+At<br />

=ut+Atut<br />

(3.2.2)<br />

and<br />

‘t+At = Ut =tAt tit+& (3.2.3)<br />

where f t~andft ~ are the external and internal nodal forces, respectively, M is the nodal point lumpedmass,<br />

and At is the time increment.<br />

The central difference operator is conditionally stable. It can be shown that the Courant stability limit for the<br />

operator is given in terms <strong>of</strong> the highest eigenvalue in the system (Max):<br />

At

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