Help Springs in MSC Adams

[ValeriaKa]

Hi,
I have more than 300 springs in a model, anyone know an easy form to determine if a spring is supporting compression or tension force.

Thanks for your attention.

 

[GregLocock]

Is the spring longer or shorter than its installed length? I hope I have misunderstood your question.

Cheers

Greg Locock


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[ValeriaKa]

Well, the problem is that I don't know how to determine the length of the spring, before or after the simulation. On the other hand, my model is complex, I have several bones and they are connected by a lot of springs as cartilage and ligaments (over 300), so it's difficult to me to know the installed length of each one, at least by measurement.

What I'm trying to do is to know which springs are under a tension force (longer length than installed), or a compression force (shorter length than installed) at the end of the simulation.

Maybe this question is kind of dumb, but I have few experience in MSC Adams and I really need to work this thing out.

I'd appreciate any help anyone can give me.

 

[ValeriaKa]

by the way, I forgot to say that I'm working in Adams/View...

 

[GregLocock]

OK, what you need to do is add a measure to each spring, indicating either its length or the force in one of the abutments caused by the spring. As you can imagine for 300 springs that is going to be a bit tedious, so you need to learn how to write macros for View, or export your model as an adm file, then add the appropriate text to the adm, and reimport it. I suspect the former will be a better use of your time. Then at the end of the sim export your measurements into a csv file and then use excel to sort them by force.



Cheers

Greg Locock


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[ValeriaKa]

I made some tests with a smaller model, just a couple of springs and boxes. Then I did what you told me, I exported it as .adm and add a function that calculates the final length of a spring by using "DM(point1,point2)", where point1 and 2 are the points where the spring is connected to each box (MARKERS). After that, I imported the file to View and ran the simulation, in the results of the sim I can see the "final" length of the spring.

But, I noticed that if I interchange the action and reaction body of the spring, the final length changes. For example, I have a spring where its action body is "A" and reaction body is "B", and I know that the spring is supporting compression force, it means that the final length must be shorter than the installed (which can be determine in the .adm file). Say that looking at the results of the sim, the final length is shorter, but when I modify the spring and makes body "A" as the reaction body and "B" as the action body, the final length is grater than the installed; it has the same deformation but as it were in tension, which is not right.

Then my question is, why is this happening? Shouldn't be it the same result no matter which is the action or reaction body?. In my model, it's hard to know which spring might be in tension or compression, so how do I know which can be the action body?, how can I trust this results?

Thank you for your help

 

[GregLocock]

I'm not familiar with your action and reaction bodies, for springs.

A spring statement looks like this


MARKER/1190059,PART=190 right FRONT coil spring to LOWER SHOCK
, QP=1577.0,514.06,643.77

MARKER/1149058,PART=149 right FRONT coil spring to SUBFRAME
, QP=1577.0,472.35,892.3
SPRING/112,TRA,I=1190059,J=1149058,K=124,L=332.006

REQ/15158,
, F2=DM(118959,114958)\ Left Displacement
, F3=FM(118959,114958)\ Left Force
, F4=DM(1190059,1149058)\ Right Displacement
, F6=FM(1190059,1149058)\ Right Force
, C=FRONT COIL SPRING STATISTICS, TITLE=Coil_Spring_Statistics_FRONT
, RESULTS_NAME=Coil_Spring_Statistics_FRONT
, CNAMES = ""
, "Left_Displacement"
, "Left_Force"
, "Right_Displacement"
,""
, "Right_Force"
, CLABELS = "","mm","N" ,"mm","","N","",""

How does your experiment alter that?

Cheers

Greg Locock


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[ValeriaKa]

Hi again,
I don't know, maybe it's my version of ADAMS 2012, but in View one can modify this action and reaction body of a spring, which I don't see its utility. On the other hand in the .adm file, the way how it's stated a spring is quite different than how you are telling me, I don't know if I'm exporting the wrong file from View.

I tried to introduce the format of your code into my .adm file in many ways, but I always got an error when I imported it to View.

I attached the .adm file that View gives me (of the smaller model). It would be nice if you confirm if that is the correct one or I'm exporting the wrong one.

Thanks for your help

 

[GregLocock]

No the adm is correct. It is machine generated so is verbose and overcomplex and includes a bunch of graphics stuff.

I suspect the action and reaction bodies are irrelevant for a spring, it is just switching the I and J markers.

The actual force is generated by

SFORCE/3
, TRANSLATIONAL
, I = 11
, J = 12
, FUNCTION = - 10.0*(dm(11,12)-206.1552812809)
, + 0
, + 0.0

The deflection and froce that you get reported is given by


! adams_view_name='SPRING_3.deformation'
VARIABLE/7
, FUNCTION = DM(13,14) - 206.1552812809
!

!
! adams_view_name='SPRING_3.force'
VARIABLE/9
, FUNCTION = (DX(13,14)*FX(13,14) +
, DY(13,14)*FY(13,14) +
, DZ(13,14)*FZ(13,14))/
, DM(13,14)


Since DM(13,14)=DM(14,13) you should get no change in reported deflection when you swap I and J

Cheers

Greg Locock


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[ValeriaKa]

Well, I understand what you are saying and some of the .adm code, I even tried to modify it a bit, but it didn't change my wired results. The thing is that in ADAMS/View, in the "GUI", when I modify a spring this action and reaction body boxes appears, and I noticed that when I interchange them, the results varies as I said before. I even added a variable in the .adm that just gives me the final length of the spring using "DM(13,14)", and then when I checked the results in the post-processor in View, it could show a larger length of the spring no matter if the spring was in compression, depending on which body was action and which reaction (force also varies from negative to positive or viceversa).

This thing is driving me crazy, because I don't know what I'm doing wrong. I'm thinking that the program is not well installed, but that is very unlikely.

Thanks again for your help...

I'd appreciate any other idea you can bring me...

 

[GregLocock]

Pretty sure it isn't the installation.

Have you contacted MSC support?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?