Time History Analysis

[Anonymous]

If it will be possible  a video or a tutorial how to design the following example. I don't understand how to apply the loads in the time history analysis. It is force and acceleration / time

It will be very good to add some expels of the spectra, time history analysis etc, in the next RSA example tutorials (including results), the 2010 version doesn't help much.

Thanks for the time and effort

[Rafal.Gaweda]

Some threads with time history examples:

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/TIME-HISTORY-ANALYSIS-Moving-dynamic-loads/m...

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Time-History-Analysis-for-a-rotating-motor/m...

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Problems-with-time-history-analysis/m-p/3488...

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Mass-Velocity-Loads-amp-Dynamic-Response/m-p...

[Anonymous]

Can you please verify this model with the results of the pdf file. it seems im getting the right ones only for the static load case. Still dont understand what am I doing wrong?

Thanks

[Rafal.Gaweda · Accepted solution]

Keep in mind that Staad in not any reference for us.

Keep in mind that we do not know exactly how it works, esspecially whether the description of syntax is correct and complete or not.

Our understanding of the staad data and results:

1. Material data is not explicit in staad file so the differences in modal results may come from different material density

2. It seems that staad uses also masses from load case 1 in modal analysis despite it is not clearly said in this example.

So the correct (giving similar results to staad) modal definition in robot:

As far as we understood tha description: only unit Fx forces applied in nodes 8 and 12 are considered for THA analysis so in fact new case is required with such loads defined. This load case will be used in THA case.

Your time history function is not correct.

It should be like that:

Comparing THA results we can see:

Robot file :https://www.filemail.com/dl.aspx?id=DSKEQEHXASTUKNK 

[Anonymous]

Thank you guys for everything

[Anonymous]

Can you guys please explain the following uncertainties??

Thanks

[Pawel.Pulak]

As concerns situations when factor for forcing function should be 9.81 m/s2 see this post: http://forums.autodesk.com/t5/Autodesk-Robot-Structural/great-work/td-p/3729078

In general case when you have accelerogramm expressed in relative accelerations (parts of g) and you use "DirectionX", "DirectionY" or  "DirectionZ cases then it is necessary to define 9.81 factor for forcing function to convert relative accelerations into m/s2:

In case of harmonic excitement with frequency of 60 Hz and angle expressed in Radians the expression should be "30*sin(2*3.14*60*t)". What "coeff." do you mean? - the coefficient before sine function in independent from the angle unit, it is some scaling of the amplitude of harmonic oscillations.

Regards,

[Anonymous]

So for a machine rotating with F=25Hz and a dynamic force 0.962kN the following pictures are correct for radians and degrees?

I applied in the THA vertical dynamic load to the sin function, and horizontal dynamic load to the cos function.

The THA will give results for both vertical and horizontal dynamic forces actiing on the block for the time and functioned specified??

In case I want to analyze only the vertical displacement, a new THA must be added, only with horizontal dynamic force with the sin function.  Are this statements correct?

Thanks

[Pawel.Pulak · Accepted solution]

So for a machine rotating with F=25Hz and a dynamic force 0.962kN the following pictures are correct for radians and degrees?

The expression in "radians.jpg" is correct for radians.

The expression in "2.jpg" is correct for degrees.

I applied in the THA vertical dynamic load to the sin function, and horizontal dynamic load to the cos function.

The THA will give results for both vertical and horizontal dynamic forces actiing on the block for the time and functioned specified??

Yes, simultaneous action of vertical force according to sine and horizontal force according to cosine with the same frequency and amplitude will result in rotating resultant force with above frequency. Rotating means acting both vertically and horizontally.

In case I want to analyze only the vertical displacement, a new THA must be added, only with horizontal dynamic force with the sin function.  Are this statements correct?

I suppose you have made some mistake linking "vertical displacement" with "horizontal dynamic force".

If you want to analyse only the vertical excitation you can remove horizontal excitation from the existing time history load case or to define a new one time history load case, containing only vertical excitation.

Regards,

[rigid_joint]

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The https://www.filemail.com/dl.aspx?id=DSKEQEHXASTUKNK file no longer exists.

Could it be possible to re-upload it, 'cause it's quite intersting?

 

[Rafal.Gaweda]

Here you are http://we.tl/xrZHQBXxSg

[Anonymous]

I want to calculate beam (bridge span) for moving load.  Where can I get "Time Function" for "Time history analysis" ??? How this function can be founded?

[Rafal.Gaweda]

http://forums.autodesk.com/t5/Robot-Structural-Analysis/TIME-HISTORY-ANALYSIS-Moving-dynamic-loads/m...

http://forums.autodesk.com/t5/Robot-Structural-Analysis/Time-History-Analysis-for-a-rotating-motor/m...

http://forums.autodesk.com/t5/forums/searchpage/tab/message?location=forum-board%3A351&q=time+histor...

[mgaafar]

Rafal,

         I know this was long time age, do you still have the file you posted because the link has expired?

Thanks

[Rafal.Gaweda]

Maybe this one: http://we.tl/Vf8gb1Pd0N

[mgaafar]

Thanks Rafal for the file, I have few questions that relates to dynamic analysis in ROBOT:

1: when using harmonic analysis, how RSA knows the loads/masses that contribute in the dynamic analysis? does it use all the load cases in the excitation?

2: I was not able to display any diagrams for harmonic analysis (displacement, velocity and acceleration), it only shows for time history analysis. can it be shown or the feature is not available for this type of analysis? 

3: it seems that in the modal analysis, the weight of the structure is taken by default, is it possible to force RSA to ignore selfweight and only use assigned masses?

4: for time history analysis, the capture screen feature does not work for the displayed diagrams( velocity, acceleration, displacement), so I can't copy to clip board and paste to my design calculation word file. please fix the bug.

Thanks

[Rafal.Gaweda]

3: it seems that in the modal analysis, the weight of the structure is taken by default, is it possible to force RSA to ignore selfweight and only use assigned masses?

[Rafal.Gaweda]

2: I was not able to display any diagrams for harmonic analysis (displacement, velocity and acceleration), it only shows for time history analysis. can it be shown or the feature is not available for this type of analysis? 

"Displacement, internal force and reaction amplitudes are the results of the harmonic analysis."

http://help.autodesk.com/view/RSAPRO/2015/ENU/?guid=GUID-4FA73A58-0FD1-461D-B09F-09E6A3739487

[Rafal.Gaweda]

1: when using harmonic analysis, how RSA knows the loads/masses that contribute in the dynamic analysis? does it use all the load cases in the excitation?

2: I was not able to display any diagrams for harmonic analysis (displacement, velocity and acceleration), it only shows for time history analysis. can it be shown 

See movie:

[Rafal.Gaweda]

4: for time history analysis, the capture screen feature does not work for the displayed diagrams( velocity, acceleration, displacement), so I can't copy to clip board and paste to my design calculation word file. please fix the bug.

Thanks for reporting.

Workaround: