Problem with acceleration value in hyperview

Altair Forum User

Hello,

I try to read the angular acceleration using TH/Node because I can't do it with accelerometer  TH/ACCEL (there is only the linear acceleration). So i try first to see the linear acceleration on the same node using both (Th/node and TH/accel) to see if i have the same result but i don't. I read that there is some filter to use but i didn't find it (i have v13 version).

Thank you for your help! (Sorry if it's not clear i don't speak english very well /emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' />

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Simon Križnik

Hi Momo,

 

to access filters in Hyperview/Hypergraph:

File>Load>Preference File>Vehicle Safety Tools

Filter category will then become available in the menu bar.

Altair Forum User

Hey Ivan; thank you for your answer. 

I tried the filters available in the menu (Ideal, SAE, SAE J211/1) but i can't have the same value i have in the accelerometer. (when i choose the filter Ideal/low pass/1.65 cut off, i get closer to the accelerometer result but still not the same).

I don't really know witch filter to use. If someone could explain
Thank you!

Simon Križnik

 

Use the filter in the menu bar and choose from many types. Then shift+click the curve and define filtering parameters.

NHTSA Butterworth was used in the below example, where the only parameter is the cut-off frequency to tune the response.

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These are similar queries:

https://community.altair.com/community?id=community_question&sys_id=dd86c83a1b2bd0908017dc61ec4bcbef

https://community.altair.com/community?id=community_question&sys_id=6e868c3a1b2bd0908017dc61ec4bcb13

 

Altair Forum User

Thank you for your answer!

But i jsut don't know which filter to use; because for linear acceleration for example, the difference between the result with the accelerometer and TH/node is huge for my case. And i can't find the appropiate filter to use. Thanks

Simon Križnik

You're welcome.

 

From Radioss help on /ACCEL:

 

 

1

The accelerometer option computes a filtered acceleration in a skew system.

2

These filtered accelerations provided by an accelerometer are used in either the Sensor option or in post-processing acceleration Time History without aliasing problems.

3

A 4-pole Butterworth filter is used.

4

The recommended value for F_cut is 1650 Hz (1.65 ms^-1) to obtain a class 1000 SAE filtering.

5

In addition to these filtered accelerations, the accelerometer also allows output to Time History, the integrals of X, Y and Z raw accelerations projected onto the skew. These quantities are not used by Sensor.

6

If the skew is moving, the integrals of X, Y and Z raw accelerations projected onto the skew are not the same as the velocities projected onto the skew, as described in Time Histories. But these integrals in derivating Time History post-processor allows to retrieve the accelerations projected to skew without aliasing problems (Integration / Derivation acting like another filter than the 4-pole Butterworth).

 

 

 

Share the model if the issue persists.