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TABRND1 referenced by RANDPS data returned a negative value for each frequency. This is probably due to extrapolation of the TABRND1 data. No results can be calculated.

Hello All,

I am performing random vibration analysis. I am getting following error,

*** ERROR # 2813 ***
TABRND1 referenced by RANDPS data returned a negative value for each
frequency. This is probably due to extrapolation of the TABRND1 data.
No results can be calculated.

Does anyone have solution for this error?

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English

OptiStruct

v2022.2

Accepted answers

All comments

Adriano_Koga

could you share your TABRND1 values?

As mentioned by the error message, if your table ends with a decreasing slope, the solver might extrapolate linearly to the out-of-range values, and this might result into negative values, which don't make sense for PSD input.

N_Pat

Hello Adriano,

Thak you for prompt response. As you point out correctly my input table is with decreasing slope, here is some input details

10	0.02
12	0.06
75	0.005
100	0.0018
350	0.0018
800	0.0001

Is there any way to solve this error?

Xiaolei

Hello Adriano,

Thak you for prompt response. As you point out correctly my input table is with decreasing slope, here is some input details

10 0.02
12 0.06
75 0.005
100 0.0018
350 0.0018
800 0.0001
Is there any way to solve this error?

Hi, when you define tabrnd1, there is a FLAT option to specify the handling method for y-values outside the specified range of x-values in the table.

When FLAT=FLAT or 1, If an x-value input is outside the range of x-values specified on the table, the corresponding y-value is equal to the start or end points, respectively.

https://help.altair.com/hwsolvers/os/topics/solvers/os/tabrnd1_bulk_r.htm?zoom_highlight=tabrnd1

Alternatively, you can define the PSD values for 0-10 Hz and above 800Hz in order to have a better control over the PSD input(avoid extrapolation).