Understanding out-of-bound options for time-dependent tables

You can control the out-of-bond values for time-dependent tables. The thermal and parallel flow solvers support the following out-of-bound options:

Constant

Uses the lower bound value for times smaller than the first table entry, and the upper bound value for times larger than the last table entry.

Periodic

Considers the table values to be periodic for the times larger than the last table entry. For times smaller than the first table entry, this option uses the lower bound value.

Period for this behavior is defined as follows: the defined table end time – minus the minimum of the (time-table start time, and solution transient start time).

For example, you define the time-dependent variable A, such as temperature constraint, using the following table.

Time	A
3	2
4	2.5
5	3

Your solution runs from 0s to 10s in intervals of 1s. The values for A depend on the out-of-bound option you select. The following table shows the values for A for all time steps during the transient solution. The period for the periodic function is: 5 – min(0,3) = 5s.

Time	Periodic extension for A	Constant extension for A
0	2	2
1	2	2
2	2	2
3 (defined)	2	2
4 (defined)	2.5	2.5
5 (defined)	3	3
6 (equivalent to 6-5=1)	2	3
7 (equivalent to 7-5=2)	2	3
8 (equivalent to 8-5=3)	2	3
9 (equivalent to 9-5=4)	2.5	3
10 (equivalent to 10-5=5)	3	3

In the following example, the transient run starts at 4s. The rest is the same time. In this case, the period is: 5 – min(3,4) = 2s.

Time	Periodic extension for A	Constant extension for A
4 (defined)	2.5	2.5
5 (defined)	3	3
6 (equivalent to 6-2=4)	2.5	3
7 (equivalent to 7-2=5)	3	3
8 (equivalent to 8-2-2=4)	2.5	3
9 (equivalent to 9-2-2=5)	3	3
10 (equivalent to 10-2-2-2=4)	2.5	3

The same concept is used when you define time-varying time stepping for your solution. In the following example, the parameter A (solution time step) varies with time as defined in the following table.

Time	A
2	1
4	2
7	5

Your solution runs from 0s to 20s using the intervals defined by A. The following table shows the values for A for all time steps during the transient solution. The period for periodic function is: 7 – min(0,2) = 7s.

Time (periodic case)	Integration time (periodic case)	Time (constant case)	Integration time (constant case)
0	1	0	1
1	1	1	1
2 (defined)	1	2	1
3 (interpolated)	1.5	3	1.5
4.5 (interpolated)	2.5	4.5	2.5
7 (defined)	5	7	5
12 (equivalent to 12-7=5)	3	12	5
15 (equivalent to 15-7-7=1)	1	17	5
16 (equivalent to 16-7-7=2)	1	20 (the end time. No more time-stepping is used.)	-
17 (equivalent to 17-7-7=3)	1.5
18.5 (equivalent to 18.5-7-7=4.5)	2.5
20 (the end time. No more time-stepping is used.)	-

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