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## Robot Structural Analysis

Mentor
Posts: 213
Registered: ‎10-08-2011

# Bar Force Node Vs Nodal Force

629 Views, 8 Replies
01-18-2013 09:14 AM

ive entered a load on beam by :

1. using bar force method

2. using Nodal force.

the results was completly different ( the first one is very unfavorale ).

I 'am missing something ?

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Product Support
Posts: 5,111
Registered: ‎12-17-2010

# Re: Bar Force Node Vs Nodal Force

01-21-2013 12:28 AM in reply to: faisal.aaouatif

My assumption is that we are discussing applying the nodal force at the end or at the beginning of the bar and the table results. The results displayed in the table for 2 points are the nodal results 'taken' directly from the solver whereas the values in tables when more than two points are displayed and for diagrams are calculated based on results in nodes and load applied along a bar. As this bar force is seen as being 'slightly' off the node (on the bar) it is not seen in the nodal results display.

You can either:
1. Display results in more than 2 points in the table

2. Define this bar point load not at x=0m but e.g. at x = 1 cm from the origin of the bar.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Artur Kosakowski
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Mentor
Posts: 213
Registered: ‎10-08-2011

# Re: Bar Force Node Vs Nodal Force

01-21-2013 02:56 AM in reply to: Artur.Kosakowski

Hi Artur ,

I m sorry for not being accurate when asking my question.

so , The problem im trying to notice is concerning a beam loaded in a point between its ends ( for my case 0.43* Length ).

Doing calculation by the first method i.e : by creating a node ( at ~ 0.43*Length of the bar ) and affecting a load to it gave me results very different of those obtained by using a bar force method in the load defintion form.

i think there is a probleme with the bar force method ( see attachement ).

model available if needed.

Thank you

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Product Support
Posts: 5,111
Registered: ‎12-17-2010

# Re: Bar Force Node Vs Nodal Force

01-21-2013 05:23 AM in reply to: faisal.aaouatif

Attach the model please.

Artur Kosakowski
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Mentor
Posts: 213
Registered: ‎10-08-2011

# Re: Bar Force Node Vs Nodal Force

01-22-2013 01:06 AM in reply to: Artur.Kosakowski

Bar Force method : http://we.tl/hdj7SeHk2N

Nodal Foce method : http://we.tl/K0vwBhvYym

The Problem raised for bar n° 764

thank you

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Product Support
Posts: 5,111
Registered: ‎12-17-2010

# Re: Bar Force Node Vs Nodal Force

01-22-2013 05:05 AM in reply to: faisal.aaouatif

There are two reasons that cause this situation:

1. Definition of point load with generation of calculation node

2. Use of kinematic constrains rather than generation of coherent meshes

This resulted in generation of the constrain that included this calculation node and influenced the results. If you modify the bar forces defined in cases 6 and 7 removing the generation of the calculation node to avoid such situation results will be the same as for the other model.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Artur Kosakowski
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Mentor
Posts: 213
Registered: ‎10-08-2011

# Re: Bar Force Node Vs Nodal Force

01-22-2013 07:25 AM in reply to: Artur.Kosakowski

Thank you for you answer.

As far as i understood , the use the TWO conditions at the same time leads to this error.

I ve re-run the model by :

1.Use only of Generation of calculation Node on Bar ( Iterative Adjustement of mesh instead of Kinematic Constrains )

2.Use only of Kinematic Constrains for meshs without Generation of calculation Node on Bar.

Both of these two method gives good results.

On the other hand , in what situations would you recommend the use or not of the Kinematic constrains method ?

What are differences (advantages and inconveniences) between the use of Kinematic constrains and iterative adjustement ?

Thank You

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Product Support
Posts: 5,111
Registered: ‎12-17-2010

# Re: Bar Force Node Vs Nodal Force

01-22-2013 07:44 AM in reply to: faisal.aaouatif

On the other hand , in what situations would you recommend the use or not of the Kinematic constrains method ?

My choice would be to generate coherent meshes (iterative adjustment) and decide on kinematic constrains only in the locations where I deliberately decided to have larger and smaller elements for neighboring panels (or when such situation happens e.g. in one place along the common edge which I'm aware of and I don't need to spend time to correct meshes).

What are differences (advantages and inconveniences) between the use of Kinematic constrains and iterative adjustement ?

Mainly the number of surface elements in the model but you should examine the results carefully.

Artur Kosakowski
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Mentor
Posts: 213
Registered: ‎10-08-2011

# Re: Bar Force Node Vs Nodal Force

01-22-2013 11:34 AM in reply to: faisal.aaouatif

Ok ,

Thank you Very Much

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