# Is nonlinear stiffness allowed for SPRING1 elements?

I’m trying to set up a model using SPRING1 elements with a nonlinear spring constant.

As a test, to make sure I’m formatting things correctly, the following input file works using a linear constant and gives the expected result.

*NODE,NSET=NALL
1,0.,0.,0.
*ELEMENT,TYPE=SPRING1,ELSET=EALL
1,1
*SPRING,ELSET=EALL
1
1.E6
*BOUNDARY
1,2,3
*STEP
*STATIC
1,1,10.
*NODE PRINT,NSET=NALL
U,RF
*END STEP

However when I change the spring to be nonlinear, such as the following, and using any arbitrary set of spring constants:

*NODE,NSET=NALL
1,0.,0.,0.
*ELEMENT,TYPE=SPRING1,ELSET=EALL
1,1
*SPRING,NONLINEAR,ELSET=EALL
1
-1.E6,-1.
0.,0.
1.E6,1.
*BOUNDARY
1,2,3
*STEP
*STATIC
1,1,10.
*NODE PRINT,NSET=NALL
U,RF
*END STEP

ccx exits with the error:

of freedom was specified
(no decimal point in entry),
however, there are neither
SPRING1 nor SPRING2 elements
in the input deck
1
*ERROR in calinput: no material was assigned
to element 1

Am I doing something wrong? Are nonlinear SPRING1 elements supported? If it matters I’m using version 2.17.

Hello ,
have you looked in the manual ? or tested / looked into the attached examples ?
maybe you find there a solution:

This was bothering me again. I believe there’s a bug, maybe in the input deck parsing. I found that if I create a simple model when there’s a SPRING2 element in addition to a nonlinear SPRING1, ccx computes successfully and gives the expected result with forces shared correctly between the two springs.

``````*NODE,NSET=NALL
1,0.,0.,0.
2,-5.,0.,0.

*ELEMENT,TYPE=SPRING1,ELSET=E1
1,1
*SPRING,ELSET=E1,NONLINEAR
1
-1.,-1.
0.,0.
1.,.01
30.,1.

*ELEMENT,TYPE=SPRING2,ELSET=E2
2,1,2
*SPRING,ELSET=E2
1,1
10.

*BOUNDARY
1,2,3
2,1,3
*STEP,NLGEOM
*STATIC
1,1,10.
*NODE PRINT,NSET=NALL,FREQUENCY=99999
U,RF
*END STEP
``````

Yet if I remove the SPRING2 element leaving the SPRING1 definition unchanged, which seems like it still should solve, ccx still exits with the error in the original post.

``````*NODE,NSET=NALL
1,0.,0.,0.
2,-5.,0.,0.

*ELEMENT,TYPE=SPRING1,ELSET=E1
1,1
*SPRING,ELSET=E1,NONLINEAR
1
-1.,-1.
0.,0.
1.,.01
30.,1.

*BOUNDARY
1,2,3
2,1,3
*STEP,NLGEOM
*STATIC
1,1,10.
*NODE PRINT,NSET=NALL,FREQUENCY=99999
U,RF
*END STEP
``````

Still have this problem. Try to modify the spring6.inp to make a test.
Not working. Does anyone know why?

``````**
**   Structure: spring.
**   Test objective: SPRING1-element.
**
*NODE,NSET=NALL
1,0.,0.,0.
2,1.,0.,0.
*ELEMENT,TYPE=SPRING1,ELSET=EALL
1,2
*BOUNDARY
1,1,3
2,2,3
*SPRING,ELSET=EALL,NONLINEAR
1
0.,0.
10,1.
15,2.
*STEP,NLGEOM
*STATIC
2,1,1.
*NODE PRINT,NSET=NALL
U
*END STEP
``````

I have managed to set up a nonlinear SPRING1 element.
I’m imposing a sinusoidal vertical displacement to test the whole positive and negative response range.

Reactions follow the Force-Elongation shape but values for the reaction forces are wrong. Should be Rz=504=200N
I get
Rz=125
4=500N

For prescribed displacements it gives this warning but ccx can finish the analysis: “*INFO in cascade: linear MPCs and nonlinear MPCs depend on each other common node: 34 in direction 1”
The model doesn’t have a node 34.

When I switch the analysis to Force driven with (-190N,190N) force Range, it gives the following error and this time the analysis fails: “*ERROR in umpc_mean_rot no mean rotation MPC can be generated for the MPC containing node 34”

Find attached the displacement driven inp.
Displacements in the orthogonal direction for the SPRING1 needs to be constrained if not the model fails.
I think direction 1 doesn’t mean the same for the Spring1 than for the Beam at the common node. Maybe that’s the problem.
Note the line corresponding to the degree of freedom that one must input to define the Spring1 DOF is empty. It is the only way it works.

Regarding some users testing fails I would say that SPRING1 and SPRING2 elements doesn’t have too much sense if they don’t restrain something. That would explain why some isolated tests have fail.

Hope it helps to debug the element.

``````** Generated by Mecway 19.0
*NODE
1,-0.25,0,0.1
2,0.25,0,0.1
3,0,0,0.1
4,-0.5,0,0.1
5,0.5,0,0
6,0.5,0,0.1
*ELEMENT,TYPE=B31
1,4,1
2,1,3
3,3,2
4,2,6
*ELEMENT,TYPE=SPRING1
5,6,5
*ELSET,ELSET=ES1
5
*ELSET,ELSET=Default
1
2
3
4
*SURFACE,NAME=Reaction_Force
4,S4
*MATERIAL,NAME=Material(2)
*ELASTIC,TYPE=ISOTROPIC
100000000000,0
*BEAM SECTION,ELSET=Default,MATERIAL=Material(2),SECTION=RECT
0.1,0.1
0,1,0
*BOUNDARY
1,4,,0
2,4,,0
3,4,,0
4,4,,0
6,1,,0
6,2,,0
6,4,,0
*BOUNDARY
5,1,,0
5,2,,0
5,3,,0
*BOUNDARY
4,1,,0
4,2,,0
4,3,,0
*AMPLITUDE,NAME=A_1
0,0
0.0154,0.0009661013358811
0.0266,0.001663557190434
0.0368,0.002291664134369
0.0462,0.002862235511151
0.0553,0.003405108358846
0.0639,0.003907953908989
0.0722,0.004382456471931
0.0802,0.004828544928858
0.0883,0.005267777828312
0.0961,0.005677862779101
0.1038,0.006069320601934
0.1113,0.006436963166205
0.1187,0.006785700178192
0.126,0.007115356772093
0.1331,0.007421630304731
0.1402,0.007713136448015
0.1438,0.00785511386224
0.1474,0.007993072455067
0.151,0.008126941644331
0.1546,0.008256652940081
0.1582,0.008382139979621
0.1617,0.008500030397096
0.1652,0.008613810275299
0.1687,0.008723424591291
0.1722,0.008828820336563
0.1756,0.008927116924094
0.1791,0.00902404873105
0.1825,0.009114032766354
0.186,0.009202318473659
0.1894,0.009283820852162
0.1928,0.00936108652976
0.1962,0.009434080246018
0.1996,0.009502768690024
0.203,0.009567120515588
0.2064,0.009627106355554
0.2097,0.009681126712973
0.2131,0.009732430768367
0.2165,0.009779293398307
0.2199,0.009821693216884
0.2232,0.009858559792233
0.2266,0.009892110550602
0.2299,0.009920357562909
0.2333,0.00994499981166
0.2366,0.009964577209353
0.24,0.009980267284283
0.2433,0.009991140377693
0.2467,0.009997850477173
0.25,0.01
0.2535,0.00999758204437
0.2571,0.009990051114953
0.2607,0.00997740909079
0.2643,0.009959662439775
0.2678,0.009937523454746
0.2714,0.009909738432995
0.275,0.009876883405951
0.2786,0.009838975182853
0.2822,0.009796033158248
0.2858,0.009748079302069
0.2894,0.009695138148396
0.293,0.0096372367829
0.2966,0.009574404828991
0.3003,0.009504723437497
0.3039,0.009431994664274
0.3076,0.009352217514007
0.3112,0.009269744901797
0.3149,0.009180039798892
0.3186,0.009085373479378
0.3223,0.008985797104267
0.326,0.008881364488135
0.3297,0.008772132070046
0.3334,0.008658158883041
0.3372,0.00853623535623
0.341,0.008409445822982
0.3448,0.008277862558563
0.3486,0.008141560570865
0.3524,0.008000617557646
0.3562,0.00785511386224
0.3601,0.007701125854042
0.364,0.007542513807361
0.368,0.007375131173582
0.3753,0.007057726608992
0.3827,0.006720825345193
0.3902,0.006364552312166
0.3979,0.005984085043929
0.4057,0.005584402626408
0.4137,0.00516055018574
0.422,0.004707039321653
0.4305,0.004229345970853
0.4382,0.003786163096634
0.4462,0.003316342851951
0.4546,0.002814037036393
0.4636,0.002267193032343
0.4719,0.001756416444025
0.4811,0.001184732900878
0.514,-0.0008785119655074
0.5274,-0.001713101039383
0.5346,-0.002156898086792
0.5413,-0.002565930268586
0.5477,-0.002952411776767
0.5538,-0.003316342851951
0.5611,-0.003745418628589
0.5681,-0.004149473356075
0.5749,-0.004534305742521
0.5815,-0.004899911516442
0.5879,-0.005246398307287
0.5942,-0.005579189341122
0.6004,-0.005898166752433
0.6065,-0.006203267579766
0.614,-0.00656585755753
0.6213,-0.006904785223184
0.6285,-0.007224846428533
0.6356,-0.007525988203531
0.6426,-0.007808231048089
0.6495,-0.008071664232464
0.6564,-0.008319928555514
0.6632,-0.00854929978755
0.6699,-0.008760038123271
0.6766,-0.008955254333159
0.68,-0.00904827052466
0.6833,-0.009134602508836
0.6899,-0.009295450028949
0.6932,-0.009369896415803
0.6965,-0.009440314641411
0.703,-0.009567120515588
0.7063,-0.009625404644893
0.7095,-0.009677971003289
0.7128,-0.009728082268385
0.716,-0.009772681235682
0.7199,-0.009821693216884
0.7238,-0.009864807893164
0.7277,-0.009901999376888
0.7316,-0.009933245336924
0.7355,-0.009958527012052
0.7394,-0.009977829222227
0.7433,-0.009991140377693
0.7472,-0.009998452485945
0.751,-0.009999802608561
0.7549,-0.009995260990317
0.7588,-0.009984717850692
0.7627,-0.009968179520173
0.7666,-0.009945655928981
0.7705,-0.009917160601106
0.7744,-0.009882710646188
0.7783,-0.009842326749244
0.7822,-0.009796033158248
0.7861,-0.00974385766957
0.79,-0.009685831611286
0.794,-0.009620276715861
0.7979,-0.009550509929818
0.8019,-0.009472997728491
0.8058,-0.009391662074157
0.8098,-0.009302383506006
0.8138,-0.009207229353052
0.8178,-0.009106259716696
0.8218,-0.008999538371525
0.8259,-0.008884250360262
0.8299,-0.008766092018086
0.834,-0.008639234171928
0.8381,-0.00850664336885
0.8422,-0.00836840759551
0.8462,-0.008228190963956
0.8502,-0.00808277723063
0.8542,-0.007932258241964
0.8583,-0.007772777489658
0.8624,-0.007608138757186
0.8665,-0.00743845129807
0.8706,-0.007263827716146
0.8748,-0.007079947992313
0.879,-0.006891138083873
0.8833,-0.006692862355703
0.8876,-0.006489701430067
0.8919,-0.006281803596468
0.8963,-0.006064325819335
0.9008,-0.005837112809325
0.9053,-0.005605233700647
0.9099,-0.005363571960577
0.9144,-0.005122827117559
0.9189,-0.004877987164925
0.9236,-0.004618105371479
0.9283,-0.004354196521478
0.938,-0.003797790955218
0.9482,-0.003197531978827
0.9587,-0.002565930268586
0.9701,-0.001867640883566
0.9827,-0.001084851766028
1,-2.449212707645E-18
*SPRING,ELSET=ES1, NONLINEAR

-200.0 ,-0.01000
-199.8 ,-0.00950
-198.3 ,-0.00900
-194.7 ,-0.00850
-188.4 ,-0.00800
-179.3 ,-0.00750
-167.4 ,-0.00700
-153.0 ,-0.00650
-136.5 ,-0.00600
-118.6 ,-0.00550
-100.0 ,-0.00500
-81.4 ,-0.00450
-63.5 ,-0.00400
-47.0 ,-0.00350
-32.6 ,-0.00300
-20.7 ,-0.00250
-11.6 ,-0.00200
-5.3 ,-0.00150
-1.7 ,-0.00100
-0.2 ,-0.00050
0.0 ,0.00000
0.2 ,0.00050
1.7 ,0.00100
5.3 ,0.00150
11.6 ,0.00200
20.7 ,0.00250
32.6 ,0.00300
47.0 ,0.00350
63.5 ,0.00400
81.4 ,0.00450
100.0 ,0.00500
118.6 ,0.00550
136.5 ,0.00600
153.0 ,0.00650
167.4 ,0.00700
179.3 ,0.00750
188.4 ,0.00800
194.7 ,0.00850
198.3 ,0.00900
199.8 ,0.00950
200.0 ,0.01000
*STEP,NLGEOM=YES,INC=110,AMPLITUDE=STEP
*STATIC
0.01,1,0,0.01
*BOUNDARY,AMPLITUDE=A_1
6,3,,1
*NODE FILE,GLOBAL=YES
U,RF
*EL FILE
S,NOE,E,ENER
*END STEP

``````
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