How to add loads from different loadsteps?

Rahul_P1

Hi,
I'm running (Radioss NLSTAT)
a simple beam model with
two loads applied on the same node.

calculated in two loadsteps:
Fx in loadstep 1
Fy in loadstep 2

# Both loadsteps are independent,
thus results are independent.

# Now loadstep 2 is defined as CNTNLSUB
BUT the loads Fx and Fy will not be added
(like using OP=MOD in Abaqus, loads are on same node)

Question:
How can I get in loadstep2 the result of
(loadstep1+loadstep2) Fx + Fy?

Is there a way to define loadstep2?(without adding forces in a load- card)

Thanks, Dirk

Rahul_P1

Hi,

I see that CNTNLSUB is intended for complex loading conditions. for instance if the model needs to be loaded and consequently unloaded.

OP=ADD, adds the output request being defined should be added to the output requests defined in previous steps.

your purpose could be served perhaps using derived load cases. Derived Load Steps utility allows you to create a derived load case from other load cases, or from a combination of other load cases and simulation steps.

could you please explain what you are trying to do in detail?

Rahul_P1

Hi,
I want to understand, how to use CNTNLSUB
- if I use plastic material behaviour I can use CNTNLSUB to unload the structure to see the permanent set.
- in this example I want to load the structure in the first loadstep and in the second loadstep I want to load it with a second load without reducing the first load. (the beam should than deflect in 45° direction)

I'm looking for an equivalent formulation to Abaqus OP = MOD,
with the ability to sum up / remain loads.
Abaqus Keyword OP:
Set OP=MOD (default) for existing *CLOADs to remain, with this option modifying existing concentrated loads or defining additional concentrated loads.
...

Best regards, Dirk

Rahul_P1

Hi,
When you use CNTNLSUB, the nonlinear analysis starts from the converged displacement from the preceding subcase to maintain the continuity. Also, the gap status and plastic state variables from the preceding subcase are used as the starting point. However, each subcase has to have a complete set of loading and boundary condition.

Note:CNTNLSUB is mostly relevant in path-dependent problems, such as plasticity or gap/contact analysis with friction/stick. In these problems, subcase continuation can be used to create complex loading paths that will typically produce very different results than simple proportional loading of a single subcase. CNTNLSUB also affects the convergence history and, to some extent, the results in problems that typically are not path-dependent, such as gap/contact analysis without friction.

User can invoke this card from loadstep create>Edit>CNTNLSUB>YES.

Let us know if you face any problem.

Regards
Rahul Rajan

Rahul_P1

Hi,

The CNTNLSUB works as specified above. if I have a combination of a variety of loads that are applied in an order (temp, force, moment), I need to keep all the preceeding loads in each subsequent subcase, otherwise OptiStuct thinks they have been removed, in which case CNTNLSUB will carry analysis from previous subcase. Also this works for NLSTAT and NLGEOM subcases.

I hope this helps.

'Nonlinear subcases may only be continued from other nonlinear subcases of the same analysis type. i.e., geometric linear subcases (ANALYSIS=NLSTAT) may only be continued from other geometric linear subcases, and geometric nonlinear subcases (ANALYSIS=NLGEOM, IMPDYN or EXPDYN) may only be continued from other geometric nonlinear subcases'

Please refer help for more information in CNTNLSUB.

Home topic Reference Guide > Bulk Data Format > Input Data > Subcase Information Section

Rahul_P1

Hi,
your answers give me a good summary!! Thank you!
Now I know, how to use it:
# CNTNLSUB is important for contact, plastification.
# CNTNLSUB can be used for analyses of the same type.
# CNTNLSUB will NOT remain loads, thus every loadcase needs to be loaded complete (new).
Best regards, Dirk

Arno Heidkamp

Though it's already quite old, I'd like to get back to the initial request by Dirk:

# CNTNLSUB is important for contact, plastification.
# CNTNLSUB can be used for analyses of the same type.
# CNTNLSUB will NOT remain loads, thus every loadcase needs to be loaded complete (new).

BUT:

If CNTNLSUB carries over the stresses and strains from the previous subcase, but the loads are *NOT* continued, then I will get a big discontinuity at the beginning of the new subcase, won't I?