# Understanding Multi Step Analysis in PrePoMax **URL:** \ **Category:** General Questions\ **Created:** [February 5, 2024, 9:37pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483 "2024-02-05T21:37:59Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![imgprojts](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@imgprojts](https://prepomax.discourse.group/u/imgprojts)\ **Post date:** [February 5, 2024, 9:37pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/1 "2024-02-05T21:37:59Z")
I was running a multistep today and I have to step back for a moment. [Rod.pmx](https://prepomax.discourse.group/uploads/short-url/cLX0UTZzbSawFtSnSyuVqu75ZzO.pmx) (165.5 KB) So here is a simple rod: ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/1/15ddc2b35f7430f3bf297dc4a85cecebbd6c02c4.jpeg) I want to apply a displacement at each of these three point in a given sequence. For example hold points 2 and 3 fixed, displace down on point 1, then hold that, displace down on point 2 and hold it there and finally displace 3 down and hold it. I’m displacing 0.1mm in this example and what I would have expected is that the final displacement is 0.1 in Y for example. Instead it looks like that is not how “fixed” works. I started looking for answers and found several posts with similar questions. it looks like the locations just reset: > [@Multi-step analysis always maintains previous step deformation?](https://prepomax.discourse.group/t/multi-step-analysis-always-maintains-previous-step-deformation/1482): > > I always thought PrePoMax could not handle multi-step analysis with the previous step being the initial condition for the next one, and even check other threads such as [this one](https://prepomax.discourse.group/t/how-can-i-implement-consecutive-displacement-and-rotation-in-a-multistep-static-analysis/1298) and [that as well.](https://prepomax.discourse.group/t/multi-steps-analysis/516) However, I set a two-step analysis (static with plasticity, 10 increments in each step) in one joint, and the second step’s first increment maintains the final state of the first step! I double-checked the input file, all steps have “OP=NEW” in both boundary, Cloads, and Dloads. How is that even possi… It seems like one has to change a key word \*Boundary, op=New to this: \*Boundary, op=Mod > [@Load Case Creation](https://prepomax.discourse.group/t/load-case-creation/133/9): > > [Analysis.pmx](https://prepomax.discourse.group/uploads/short-url/nCMoHpqxPjXi8YQ6ZPCk7frFV0W.pmx) (373.7 KB) But it is not clear. I’m going to try that now and see if that solves it. the only issue is that one has to run this out of prepomax because the keyword is not modifiable in prepomax as far as I can tell. ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/2/2f61fa864a1ba0c6606359a3bd599dc0291acb84.png) Does anyone know a better way? ---
**Author:** ![imgprojts](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@imgprojts](https://prepomax.discourse.group/u/imgprojts)\ **Post date:** [February 5, 2024, 9:42pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/2 "2024-02-05T21:42:32Z")
Looks like PrePoMax will not run the file with the “New” to “Mod” change. It will simply change it back to New. So trying Calculix only. ---
**Author:** ![imgprojts](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@imgprojts](https://prepomax.discourse.group/u/imgprojts)\ **Post date:** [February 5, 2024, 9:58pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/3 "2024-02-05T21:58:58Z")
Ok, I’ve ran this on Calculix by itself and still there is no change between step 1 and step 2. I’m missing something. ---
**Author:** ![imgprojts](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@imgprojts](https://prepomax.discourse.group/u/imgprojts)\ **Post date:** [February 5, 2024, 10:10pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/4 "2024-02-05T22:10:43Z")
I figured it out! Its actually kind of an ignorant move of me to set 3 rigid body points to the same element set. I Separated the rigid constraints into 3 separate ones and that worked. The rod bends one way first, then another way next. Its great. ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/9/9f71083a20200cfac0bdce05d10f50e8324b5610.jpeg) ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 5, 2024, 10:19pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/5 "2024-02-05T22:19:57Z")
Yeah, it ignores all the rigid body constraints applied to the same nodes apart from the first one. There are warnings about that: ```auto *WARNING reading *RIGID BODY: dof 1 of node 1 belonging to a rigid body is detected on the dependent side of another equation; no rigid body constrained applied ``` Abaqus would throw error messages and refuse to run the analysis. ---
**Author:** ![lucas\_bueno](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/lucas_bueno/32/1168_2.png) [@lucas\_bueno](https://prepomax.discourse.group/u/lucas_bueno)\ **Post date:** [February 5, 2024, 10:52pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/6 "2024-02-05T22:52:57Z")
Did it work in PrePoMax alone? ---
**Author:** ![imgprojts](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@imgprojts](https://prepomax.discourse.group/u/imgprojts)\ **Post date:** [February 6, 2024, 12:06am UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/7 "2024-02-06T00:06:55Z")
Yes it did. Probably not exactly what you were looking for since this is only displacements. I didn’t have to use the “Fix” BC. I used displacement BCs set to either 0.1mm or “Fixed” in the vertical direction. ---
**Author:** ![imgprojts](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@imgprojts](https://prepomax.discourse.group/u/imgprojts)\ **Post date:** [February 6, 2024, 12:09am UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/8 "2024-02-06T00:09:31Z")
> [@FEAnalyst](#): > > aqus would throw error messages and refuse to run the analysis. I wouldn’t have guessed, but I am growing my intuition with this tool. I almost impressed my self from guessing that this was the problem lol. ---
**Author:** ![DanielC](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DanielC](https://prepomax.discourse.group/u/DanielC)\ **Post date:** [February 12, 2024, 9:16am UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/9 "2024-02-12T09:16:00Z")
@ imgprojts As far as I know, Calculix does not recognize “op=New,” even though it is listed as a valid option in the Calculix documentation itself. Consequently, I chose to omit the optional parameter by simply deleting it, leaving only “Boundary.” “op=mod” represents the default behavior in Calculix, so it reverts to this mode. I hope this clarifies the situation. Daniel ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 12, 2024, 9:27am UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/10 "2024-02-12T09:27:22Z")
> [@DanielC](#): > > As far as I know, Calculix does not recognize “op=New,” even though it is listed as a valid option in the Calculix documentation itself. Doesn’t it apply to some old releases of CalculiX ? I’ve seen several cases where there was an expected difference when OP=MOD was used vs OP=NEW (e.g. fixed BC wasn’t redefined leading to non-convergence). ---
**Author:** ![DanielC](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DanielC](https://prepomax.discourse.group/u/DanielC)\ **Post date:** [February 12, 2024, 9:46am UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/11 "2024-02-12T09:46:59Z")
The version I used was 2.20. Others I don’t know. ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/e/eec6f4acc204563566a62c2819532bf11dd5dfb5.png) But it works just fine, when omiting the parameter. ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 12, 2024, 10:28am UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/12 "2024-02-12T10:28:21Z")
This warning is weird, I will ask Guido if it’s necessary when I contact him about other issues. But apparently it just means that MOD is used by default and doesn’t have to be specified. If NEW is specified then there are no such warnings and a proper change in behavior can be observed. Thus, it seems that it’s all working as it should and maybe just the warning is obsolete or the parameter should be NEW or not added at all (then it behaves like with MOD). ---
**Author:** ![lucas\_bueno](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/lucas_bueno/32/1168_2.png) [@lucas\_bueno](https://prepomax.discourse.group/u/lucas_bueno)\ **Post date:** [February 12, 2024, 1:42pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/13 "2024-02-12T13:42:51Z")
> [@DanielC](#): > > As far as I know, Calculix does not recognize “op=New,” It throws some warnings if you define it more than once in the same step in the input deck. I never tested op=mod to see if the same applies. ---
**Author:** ![DanielC](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DanielC](https://prepomax.discourse.group/u/DanielC)\ **Post date:** [February 12, 2024, 4:16pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/14 "2024-02-12T16:16:46Z")
I just defined it once. ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 17, 2024, 1:27pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/15 "2024-02-17T13:27:49Z")
I asked Guido about this warning. His reply: > I had a quick glance at the code and I do not treat OP=MOD because it is, as you say, default. I will remove this warning. ---
**Author:** ![DanielC](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DanielC](https://prepomax.discourse.group/u/DanielC)\ **Post date:** [February 17, 2024, 1:49pm UTC](https://prepomax.discourse.group/t/understanding-multi-step-analysis-in-prepomax/1483/16 "2024-02-17T13:49:15Z")
Thank you for providing clarification. It confirms my initial assumption and is now officially confirmed. 👍