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January 8, 2020, 03:08 |
The Bounded Second Order Implicit scheme
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#1 |
Senior Member
Ruiyan Chen
Join Date: Jul 2016
Location: Hangzhou, China
Posts: 162
Rep Power: 9 |
Hi Guys,
For transient simulations we have the option of using Bounded Second Order Implicit or Second Order Implicit. What does the Bounded keyword actually do? I understand that it "would provide better stability, since time discretization would always ensure the bounds for variables, if available." (From FLUENT Users' Guide). I myself have such experience, that the simulation runs stable with the Bounded option, and crashes without it. But what does it actually do? Does it add additional terms during the calculation process or do something else? Thanks, Ruiyan |
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January 9, 2020, 01:36 |
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#2 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65 |
See Temporal Discretization. Implicit time-integration is given by 18.3-19 for some F. If one takes F to be the form of 18.3-16 then that is first-order. If one takes 18.3-17 then that's second order. Second order is un-bounded.
The bounded second-order is obtained by weighting 18.3-16 and 18.3-17. Effectively, you are changing the weight coeffients in 18.3-17 (from 3, -4, and 1) using smart values such that the value at the new time-step is always positive. |
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