# Impulse Time step?

• I
Hi

I have a question regarding the dt timestep of an impulse load as discussed in the following video:

He uses dt=10ms. If we set dt=8 or 9 or 11 we get widely different values for Fmax.

Thus, a lot of such impulse loading boils down to the correct selection of dt.

I was wondering if anyone knows of a way or a more advanced method for reverse engineering a system to obtain dt? I have a system that includes a dt from impulse loading and as discussed above get very different results for small changes in dt.

Any help greatly appreciated.

Thanks
Graham

Last edited:

anorlunda
Staff Emeritus
He uses dt=10ms. If we set dt=8 or 9 or 11 we get widely different values for Fmax.

Thus, a lot of such impulse loading boils down to the correct selection of dt.

I was wondering if anyone knows of a way or a more advanced method for reverse engineering a system to obtain dt? I have a system that includes a dt from impulse loading and as discussed above get very different results for small changes in dt.

If you are modeling a real life system, then the shapes and materials and how elastic the objects are all play critical roles. So in the idealized model shown, all of the dt values might be correct for some unknown physical system.

Perhaps the lesson for you to learn is the sensitivity of Fmax to dt.

ZapperZ
Staff Emeritus
Hi

I have a question regarding the dt timestep of an impulse load as discussed in the following video:

He uses dt=10ms. If we set dt=8 or 9 or 11 we get widely different values for Fmax.

Thus, a lot of such impulse loading boils down to the correct selection of dt.

I was wondering if anyone knows of a way or a more advanced method for reverse engineering a system to obtain dt? I have a system that includes a dt from impulse loading and as discussed above get very different results for small changes in dt.

Any help greatly appreciated.

Thanks
Graham

I don't quite understand your question. Why would dt be anything else but 10 ms? The graph of the applied force clearly shows the time period that the force is acting. Why should it be 8 or 9 of 11 ms?

This is not something arbitrary or a matter of preference. dt in this case has a specific meaning, not simply any old "time".

Zz.

sophiecentaur