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pp2008
Posts: 472
Registered: ‎06-23-2008

Re: tutorial or example for machine foundation

07-24-2012 04:59 AM in reply to: alb2

What to you mean by transient response? When changing the frequency of excitation?

In such case time history analysis should be used.

 

FRF analysis is analogous to harmonic analysis with only such difference that instead of one frequency it is performed for series of different frequencies and it gives additional possibilities of output (like diagrams of results in function of frequency) - but both are related to steady-state harmonic vibrations

 

Best regards,



Pawel Pulak
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alb2
Posts: 47
Registered: ‎05-14-2012

Re: tutorial or example for machine foundation

07-24-2012 05:21 AM in reply to: pp2008

Yes, by transient response, i meant the block response when the machine changes its frequency from start to operational frequency considering damping.

I want to plot the chart - response amplitude of a point of the machine/ frequency from 0-50 HZ lets say. as in the picture

Which analisys is suitable? And since in theory, applying the dynamic forces in the centre of concrete base or applying them with rigid link on top of foundation, doesnt make big difference.Does it concern the calculations in RSA??

 

Thanks

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pp2008
Posts: 472
Registered: ‎06-23-2008

Re: tutorial or example for machine foundation

07-24-2012 06:03 AM in reply to: alb2

In such case time history analysis will be necessary - as in this forum topic:

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

 

Moreover instead of constant frequency of forcing function the variable frequency will be necessary - more sophisticated forcing function.

 

Time history analysis will not give you directly the diagram in the function of frequency - only diagrams in the function of time are available in it. So it will be necessary to export some data to for instance MS Excel and generate diagrams there.

 

As concerns the influence of the point of application of dynamic loads (centre of concrete base or centre of mass of rotating part of the machine) it depends whether the distance between these points is significant or not.

 

Best regards,

 

 



Pawel Pulak
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alb2
Posts: 47
Registered: ‎05-14-2012

Re: tutorial or example for machine foundation

07-24-2012 06:06 AM in reply to: pp2008

Thank you.

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alb2
Posts: 47
Registered: ‎05-14-2012

Re: tutorial or example for machine foundation

07-27-2012 05:23 AM in reply to: alb2

Hello,

i have a rigid link with one master node and 4 slave nodes, i want to design another rigid link with a different master node and 4 slave nodes, where 2 of these slave nodes are also slave nodes from the 1st rigid link.as in the picture.

is there a problem regarding this or is just a graphical issue? 

Can this be done selecting 2 nodes as master and the others as slaves? It seems like NOT to me.

 

Thanks

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pp2008
Posts: 472
Registered: ‎06-23-2008

Re: tutorial or example for machine foundation

07-27-2012 06:05 AM in reply to: alb2

Hello,

as it is written in Help: "A node can be defined as a slave node only in one rigid link."

If these 2 rigid links you mentioned are in reality one rigid body then I recommend defining it as one rigid link. I such case  the master node of one or rigid links will change into slave node.

 

If these are in reality 2 separate different bodies then I recommend:

1/ or using finer mesh to use separete slave nodes for them

2/ or replacing rigid links with very rigid bars (in such case necessary to define material or loads and load to mass conversion in such way that mass of these bars will not be taken into account)

 

Regards,



Pawel Pulak
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alb2
Posts: 47
Registered: ‎05-14-2012

Re: tutorial or example for machine foundation

07-27-2012 06:32 AM in reply to: pp2008

I like the second option better,

so in this case Im defining a new material with high modulus of elasticity. Applying the new material to the bars that will connect the mass ( which will be substituted by force) to the bearing points. Is this correct?

 

Thanks

 

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pp2008
Posts: 472
Registered: ‎06-23-2008

Re: tutorial or example for machine foundation

07-27-2012 06:49 AM in reply to: alb2

It cab be even standard Young's modulus of steel (providing section properties are big). What is important is zero unit weight (density) of the new material - to avoid considering it in selfweight and vibrations.

 

Regards,



Pawel Pulak
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