Extraction of nodal forces after the analysis
satish Paudel
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Many thanks and have a nice day
Best Regards,
Dr. Satish Paudel
Postdoctoral scholar, Department of Civil and Environment Engineering, University of Nevada, Reno
Email: paudel...@gmail.com, sat...@unr.edu.np, Sat...@nce.edu.np
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l...@schwer.net
If you are looking for internal force, rather than reaction forces, try *DATABASE_CROSS_SECTION --len
From: ls-d...@googlegroups.com <ls-d...@googlegroups.com> On Behalf Of satish Paudel
Sent: Tuesday, March 12, 2024 10:19 AM
To: ls-d...@googlegroups.com
Subject: [LS-DYNA2] Extraction of nodal forces after the analysis
Hi all,
I was wondering if anyone is facing the same issue that I am currently facing.
I am not able to get the nodal forces as an output from the LSDYNA even though I used the associated cards, like creating the nodforce in ASCII, creating the card nodal force group, and creating the history node set (see attachments). I have created a set of node
My problem is a very simple system of beam under flexure bending (4-point loading). I need to extract the nod forces from the program and compare them with the test results.
I have been using the program for several years and have never faced this issue before.
The only change I have made recently is to run the program in an interactive environment, launch a terminal, and use commands to run LS-DYNA. It is something like a virtual environment, using the server/installed license on different PC, Is it because of that?
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Many thanks and have a nice day
Best Regards,
Dr. Satish Paudel
Postdoctoral scholar, Department of Civil and Environment Engineering, University of Nevada, Reno
Email: paudel...@gmail.com, sat...@unr.edu.np, Sat...@nce.edu.np
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James Kennedy
Dear Satish,,
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*DATABASE_CROSS_SECTION_OPTION1_{OPTION2}
OPTION1 includes: PLANE, SET
To define an ID and heading for the database cross section, set OPTION2 to: ID
Purpose: Define a cross section for resultant forces written to ASCII file secforc.
1. For the PLANE option, a set of two cards defines a cutting plane, see Figure
16-2. Based on this cutting plane, a node set and element set(s) which comprise
the cross section are internally generated. Using the variable ICRFILE in
*CONTROL_OUTPUT, those sets may be output for the purpose of displaying
the nodes and elements of the cross section using LS-PrePost.
2. If the SET option is used, just one card is needed which identifies a node set
and at least one element set. In this case the node set(s) defines the cross section,
and the forces from the elements belonging to the element set(s) are
summed up to calculate the section forces. Thus, the element set(s) should
include elements on only one side (not both sides) of the cross section.
The cross-section should cut through deformable elements only, not rigid bodies.
Cutting through master segments for deformable solid element spot welds can lead to
incorrect section forces since the constraint forces are not accounted for in the force and
moment summations. Beam element modeling of welds do not require any special
precautions.
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Perhaps the following can help:
http://www.dynasupport.com/howtos/general/cross-section/
LS-DYNA has a facility to calculate and output section forces if the user provides
*database_cross_section/*database_secforc entries or through LS-PrePost as given in
the following comments.
The SPlane interface allows sections to be defined interactively and LS-PrePost computes
the section quantities if shell resultants are available in d3plot files. Generally this data is
available in d3plot files unless it is turned off by the use of *DATABASE_EXTENT_
BINARY options.
Jacob Krebs recently provided this very nice, concise explanation for SPlane to the Google
LS-PrePost User's Group:
FixS (fixed in space) means that the section plane will not move once defined.
FixM (fixed to model) means that the section plane can move if the nodes used to define
it move.
Lagr (lagrangian) means that a group of elements is cut initially, and then those same
elements are tracked throughout the animation (and are not confined to a flat plane as the
model deforms). This option is most similar to *database_cross_section.
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A note taken from the User's Manual for *database_cross_section:
If the SET option is used, just one card is needed which identifies a node set and at least
one element set. In this latter case the node set defines the cross section and the forces
from the elements belonging to the element set(s) are summed up to form the section
forces. Thus the element set(s) should include elements to only one side (not both sides)
of the cross section. The cross section should cut through deformable elements only, not
rigid bodies.
One final comment:
LS-PrePost uses element stress resultants to calculate section forces. LS-DYNA, on the
other hand, uses nodal forces (which are not available in the d3plot). *database_secforc
is the most accurate section force output you can obtain.
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Some additional/similar comments shared by Jacob Krebs :
1. The stress is multiplied by the area of intersection for each element to calculate a force.
The forces are then summed across all intersected elements. The calculation is less accurate
if the section plane does not cut cleanly through the center of the element, by the way.
2. NODFOR reports a force of zero for internal nodes unless an external load is applied
directly to the node.
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Sincerely,
James M. Kennedy
KBS2 Inc.
March 12, 2024
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satish Paudel
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l...@schwer.net
Have you tried
SPCFORC SPC reaction forces. See *BOUNDARY_SPC_OPTION ?
From: ls-d...@googlegroups.com <ls-d...@googlegroups.com> On Behalf Of satish Paudel
Sent: Tuesday, March 12, 2024 11:16 AM
To: James Kennedy <j...@kbs2.com>
Cc: L...@schwer.net; ls-d...@googlegroups.com
Subject: Re: [LS-DYNA2] Extraction of nodal forces after the analysis
Many thanks for the prompt response.
Actually. I was searching for the external force (support reaction) generated on the support due to the prescribed displacement applied at the top of the beam. My program does not provide any output for those, even though I have provided the input to generate them, as I mentioned in the previous email.
Could you help me with that. Many thanks
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satish Paudel
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SUMAN KUMAR
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SUMAN KUMAR
satish Paudel
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