Impulse Load Timestep: Reverse Engineering to Obtain dt?

[gmseed]

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

 

[anorlunda]

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.

You don't say your criteria for deciding which answer is correct.

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]

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]

Surely the use of the concept of Impulse removes the need for a delta t. The value of the impulse is an integral over the total time that a variable force is applied. If you need an idea about the ‘effective delta t’ then an ‘effective’or average for the applied Force would be needed.