Discussion Groups

Robot Structural Analysis

Reply
Active Contributor
alb2
Posts: 47
Registered: ‎05-14-2012
Accepted Solution

tutorial or exaple for machine foundation

1355 Views, 17 Replies
07-11-2012 06:54 AM

Does anyone have a tutorial or example for RSA, how to design concrete blocks or pedestals for steam or  gas turbines or smth similar. Modal,time history analysis or harmonis (FRF), how to apply the dynamic forces that act in the neutral axisof the turbine which is above the foundations, what load combinations to use, what type of mashing is the best chooise in this case.

Anything that can be helpfull.

 

Thanks

Please use plain text.
Valued Mentor
tony.ridley
Posts: 653
Registered: ‎09-07-2011

Re: tutorial or exaple for machine foundation

07-12-2012 04:55 AM in reply to: alb2
Please use plain text.
Product Support
pp2008
Posts: 529
Registered: ‎06-23-2008

Re: tutorial or exaple for machine foundation

07-12-2012 05:56 AM in reply to: tony.ridley

Additional explanations to link provided by Tony:

1/ depending on soil data and necessity to consider deformation of foundation or treating it as rigid body it is possible to model it as

- node with added mass and elastic support

- panel on elastic supports

- solid on elastic supports

2/ eccentricity between foundation and turbine can be modeled using rigid links

 

---------------------------------------------
If this post answers your question please click "Accept as Solution". It will help everyone to find answer more quickly!

 

Regards,

 



Pawel Pulak
Please use plain text.
Active Contributor
alb2
Posts: 47
Registered: ‎05-14-2012

Re: tutorial or example for machine foundation

07-12-2012 06:14 AM in reply to: pp2008

Thank you for the answer,

can you please show in a picture or I a small model how to model the eccentricities with rigid links?

 

Thanks

Please use plain text.
Product Support
pp2008
Posts: 529
Registered: ‎06-23-2008

Re: tutorial or example for machine foundation

07-12-2012 08:59 AM in reply to: alb2

The screen capture below shows some example when modeling by solid. Top (master) node corresponds to the center of mass of the turbine. Bottom nodes correspond to the connection of the turbine with the block. Of course the distribution of these nodes corresponds to real geometry of turbine and details of connection.

turbine.png

 

In case of rigid links connected to solid it will be necessary to activate RLINK algorithm for rigid links in Job Preferences>Structure Analysis

 

---------------------------------------------
If this post answers your question please click "Accept as Solution". It will help everyone to find answer more quickly!

 

Regards,



Pawel Pulak
Please use plain text.
Active Contributor
alb2
Posts: 47
Registered: ‎05-14-2012

Re: tutorial or example for machine foundation

07-18-2012 06:28 AM in reply to: pp2008

Mr. Pulak,

I am trying to model the following as in picture 1, as you explained in the previous email, and I am getting the following error,picture 2. What am I doing wrong?

 

Thanks

Please use plain text.
Product Support
pp2008
Posts: 529
Registered: ‎06-23-2008

Re: tutorial or example for machine foundation

07-18-2012 07:11 AM in reply to: alb2

Solid elements have no degrees of freedom (stiffness) in rotation. So if you have defined rigid links with only pairs of nodes (one master and one slave) these rigid links can rotate about nodes belonging to solids - at the bottom ends of rigid links shown on your screen capture.

 

One of the methods to avoid it is to define rigid links with at least 3 non-collinear slave nodes to connect to solid in 3 points - like below:turbine1.png

 

---------------------------------------------
If this post answers your question please click "Accept as Solution". It will help everyone to find answer more quickly!

 

Regards,



Pawel Pulak
Please use plain text.
Active Contributor
alb2
Posts: 47
Registered: ‎05-14-2012

Re: tutorial or example for machine foundation

07-23-2012 02:31 AM in reply to: pp2008

Hi,

how can isolated nodes with attributes be included in the mesh? I am trying with Emitters, but no luck, is there a meshing option that includes all nodes where node forces are applied before meshing?

And also getting the following warning:It is neccesary to divide tapered bar to calculation elements for nonlinear analysis.

What does it mean? since i have no bars in the model ( its a concrete block) and how can it it be done?

 

Thanks

Please use plain text.
Product Support
pp2008
Posts: 529
Registered: ‎06-23-2008

Re: tutorial or example for machine foundation

07-23-2012 06:53 AM in reply to: alb2

If FE mesh is not frozen it is enough to run analysis and during model generation FE mesh will be adapted to new surface nodes.

In case of local mesh generation (as in the video available there: http://screencast.com/t/tNiJTBWiZk ) FE mesh is adapted to new surface nodes for unfrozen and  frozen FE meshes.

 

Above remarks are valid for solids meshed using standard tetrahedral FE mesh generation.

 

In case of mapped meshing of solids generated using extrude or revolve commands adapting mesh is not possible for side faces - but your screen capture suggests that you do not use this feature.

 

As concerns the warning related to tapered members it is not justified and can be ignored.

 

Best regards,



Pawel Pulak
Please use plain text.
Active Contributor
alb2
Posts: 47
Registered: ‎05-14-2012

Re: tutorial or example for machine foundation

07-24-2012 03:55 AM in reply to: pp2008

Mr Pulak,

In order to obtain a) steady state response of a concrete block on which a machine is operating with a xx frequency:

 

1) calculated the right modal frequencies with all dead loads converted into mass

 

2) calculated the dynamic forces and moments ( in phase and out of phase in all directions) acting to the centre of concrete base area, and applied these forces to this point as a new load case (in phase Y).

 

3) the load case (in phase Y) chanced to a harmonic analysis with excitation frequency of the machine ( 50 hz in this case)

 

4) results - displacement - for case 5 ( in phase Y)

 

b) transient amplitude

same as a) till point 2) but instead of harmonic analysis will be Harmonic (FRF) from 0.5-50 Hz ( this time for out of phase Y)

 

3) results- advanced- FRF tables or diagrams

 

Please confirm if the above steps are correct

 

Thanks

Please use plain text.