# Testing problem, arc length method

**URL:** <https://calculix.discourse.group/t/testing-problem-arc-length-method/2244>\
**Category:** Uncategorized\
**Created:** [April 30, 2024, 6:55am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244 "2024-04-30T06:55:52Z")\
**Posts on this page:** 13\
**Page:** 1

<div class="post-metadata">

**Author:** ![calc4fem](https://avatars.discourse-cdn.com/v4/letter/c/3da27b/32.png) [@calc4fem](https://calculix.discourse.group/u/calc4fem)\
**Post date:** [April 30, 2024, 6:55am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/1 "2024-04-30T06:55:52Z")

</div>

Hello.  
How properly set arc length method (\*control) to solve this testing problem:

> **[nlgeotest-ccx-group.zip](https://drive.google.com/file/d/1HtsuTrvYA7eCIpCCcpwK2_GNRYoI7PLD/view?usp=sharing)**
>
> Google Drive file.

---

<div class="post-metadata">

**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [April 30, 2024, 10:43am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/2 "2024-04-30T10:43:18Z")

</div>

CalculiX doesn’t have the arc length (Riks) solver. The \*CONTROLS keyword is just for the parameters of the Newton-Raphson solver and should be used only when absolutely necessary.

---

<div class="post-metadata">

**Author:** ![calc4fem](https://avatars.discourse-cdn.com/v4/letter/c/3da27b/32.png) [@calc4fem](https://calculix.discourse.group/u/calc4fem)\
**Post date:** [April 30, 2024, 11:04am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/3 "2024-04-30T11:04:14Z")

</div>

Ansys ARCLEN is Newton-Raphson too. Anyway - the question is how to get better convergence (TIME=1)

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<div class="post-metadata">

**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\
**Post date:** [April 30, 2024, 4:22pm UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/4 "2024-04-30T16:22:07Z")

</div>

I think Calc\_em is right but you may try any of these ideas: [Unstable collapse and postbuckling analysis](https://abaqus-docs.mit.edu/2017/English/SIMACAEANLRefMap/simaanl-c-postbuckling.htm)

---

<div class="post-metadata">

**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\
**Post date:** [May 1, 2024, 3:36pm UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/5 "2024-05-01T15:36:08Z")

</div>

try this, looks correct. Probably an be improved. I still need to understand why I am not able to continue a static case with dynamic one (should be faster). In this small problem a dynamic case from the beginning works well, further check on density and damping used is needed.

```auto
*NODE, NSET=Nall
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     207,3.014750016153e+01,3.953761812826e+01,0.000000000000e+00
     208,2.918793676131e+01,3.926162454669e+01,0.000000000000e+00
     209,2.823537862657e+01,3.896234645389e+01,0.000000000000e+00
     210,2.729039068366e+01,3.863996134047e+01,0.000000000000e+00
     211,2.635353336435e+01,3.829466039921e+01,0.000000000000e+00
     212,2.542536228378e+01,3.792664841518e+01,0.000000000000e+00
     213,2.450642790267e+01,3.753614364143e+01,0.000000000000e+00
     214,2.359727520459e+01,3.712337767088e+01,0.000000000000e+00
     215,2.269844337131e+01,3.668859529836e+01,0.000000000000e+00
     216,2.181046546580e+01,3.623205437676e+01,0.000000000000e+00
     217,2.093386811258e+01,3.575402566253e+01,0.000000000000e+00
     218,2.006917118435e+01,3.525479265419e+01,0.000000000000e+00
     219,1.921688750043e+01,3.473465142809e+01,0.000000000000e+00
     220,1.837752251390e+01,3.419391045772e+01,0.000000000000e+00
     221,1.755157402003e+01,3.363289043573e+01,0.000000000000e+00
     222,1.673953185848e+01,3.305192408248e+01,0.000000000000e+00
     223,1.594187761817e+01,3.245135594543e+01,0.000000000000e+00
     224,1.515908435743e+01,3.183154219879e+01,0.000000000000e+00
     225,1.439161631587e+01,3.119285042631e+01,0.000000000000e+00
     226,1.363992864983e+01,3.053565941180e+01,0.000000000000e+00
     227,1.290446715784e+01,2.986035891136e+01,0.000000000000e+00
     228,1.218566801139e+01,2.916734941763e+01,0.000000000000e+00
     229,1.148395750164e+01,2.845704192700e+01,0.000000000000e+00
     230,1.079975178469e+01,2.772985769408e+01,0.000000000000e+00
     231,1.013345663495e+01,2.698622798195e+01,0.000000000000e+00
     232,9.485467207209e+00,2.622659380957e+01,0.000000000000e+00
     233,8.856167798098e+00,2.545140568566e+01,0.000000000000e+00
     234,8.245931619487e+00,2.466112334272e+01,0.000000000000e+00
     235,7.655120578802e+00,2.385621546654e+01,0.000000000000e+00
     236,7.084085062675e+00,2.303715941613e+01,0.000000000000e+00
     237,6.533163728485e+00,2.220444093943e+01,0.000000000000e+00
     238,6.002683308503e+00,2.135855389288e+01,0.000000000000e+00
     239,5.492958408107e+00,2.049999993638e+01,0.000000000000e+00
     240,5.004291323535e+00,1.962928824178e+01,0.000000000000e+00
     241,4.536971865408e+00,1.874693519634e+01,0.000000000000e+00
     242,4.091277181454e+00,1.785346408694e+01,0.000000000000e+00
     243,3.667471595707e+00,1.694940479612e+01,0.000000000000e+00
     244,3.265806451447e+00,1.603529348782e+01,0.000000000000e+00
     245,2.886519959338e+00,1.511167228304e+01,0.000000000000e+00
     246,2.529837059841e+00,1.417908894667e+01,0.000000000000e+00
     247,2.195969286070e+00,1.323809655322e+01,0.000000000000e+00
     248,1.885114642429e+00,1.228925316950e+01,0.000000000000e+00
     249,1.597457485296e+00,1.133312151955e+01,0.000000000000e+00
     250,1.333168411891e+00,1.037026864457e+01,0.000000000000e+00
     251,1.092404161519e+00,9.401265573979e+00,0.000000000000e+00
     252,8.753075223468e-01,8.426686986815e+00,0.000000000000e+00
     253,6.820072452553e-01,7.447110864514e+00,0.000000000000e+00
     254,5.126179695117e-01,6.463118157460e+00,0.000000000000e+00
     255,3.672401531035e-01,5.475292432778e+00,0.000000000000e+00
     256,2.459600134794e-01,4.484219528199e+00,0.000000000000e+00
     257,1.488494773847e-01,3.490487212214e+00,0.000000000000e+00
     258,7.596613688733e-02,2.494684823942e+00,0.000000000000e+00
     259,2.735321658119e-02,1.497402938824e+00,0.000000000000e+00
     260,3.039546729674e-03,4.992330047075e-01,0.000000000000e+00
*ELEMENT, TYPE=B32, ELSET=Eall
     4, 3, 132, 4
     5, 4, 133, 5
     6, 5, 134, 6
     7, 6, 135, 7
     8, 7, 136, 8
     9, 8, 137, 9
    10, 9, 138, 10
    11, 10, 139, 11
    12, 11, 140, 12
    13, 12, 141, 13
    14, 13, 142, 14
    15, 14, 143, 15
    16, 15, 144, 16
    17, 16, 145, 17
    18, 17, 146, 18
    19, 18, 147, 19
    20, 19, 148, 20
    21, 20, 149, 21
    22, 21, 150, 22
    23, 22, 151, 23
    24, 23, 152, 24
    25, 24, 153, 25
    26, 25, 154, 26
    27, 26, 155, 27
    28, 27, 156, 28
    29, 28, 157, 29
    30, 29, 158, 30
    31, 30, 159, 31
    32, 31, 160, 32
    33, 32, 161, 33
    34, 33, 162, 34
    35, 34, 163, 35
    36, 35, 164, 36
    37, 36, 165, 37
    38, 37, 166, 38
    39, 38, 167, 39
    40, 39, 168, 40
    41, 40, 169, 41
    42, 41, 170, 42
    43, 42, 171, 43
    44, 43, 172, 44
    45, 44, 173, 45
    46, 45, 174, 46
    47, 46, 175, 47
    48, 47, 176, 48
    49, 48, 177, 49
    50, 49, 178, 50
    51, 50, 179, 51
    52, 51, 180, 52
    53, 52, 181, 53
    54, 53, 182, 54
    55, 54, 183, 55
    56, 55, 184, 56
    57, 56, 185, 57
    58, 57, 186, 58
    59, 58, 187, 59
    60, 59, 188, 60
    61, 60, 189, 61
    62, 61, 190, 62
    63, 62, 191, 63
    64, 63, 192, 64
    65, 64, 193, 65
    66, 65, 194, 66
    67, 66, 195, 67
    68, 67, 196, 68
    69, 68, 197, 69
    70, 69, 198, 70
    71, 70, 199, 71
    72, 71, 200, 72
    73, 72, 201, 73
    74, 73, 202, 74
    75, 74, 203, 75
    76, 75, 204, 76
    77, 76, 205, 77
    78, 77, 206, 78
    79, 78, 207, 79
    80, 79, 208, 80
    81, 80, 209, 81
    82, 81, 210, 82
    83, 82, 211, 83
    84, 83, 212, 84
    85, 84, 213, 85
    86, 85, 214, 86
    87, 86, 215, 87
    88, 87, 216, 88
    89, 88, 217, 89
    90, 89, 218, 90
    91, 90, 219, 91
    92, 91, 220, 92
    93, 92, 221, 93
    94, 93, 222, 94
    95, 94, 223, 95
    96, 95, 224, 96
    97, 96, 225, 97
    98, 97, 226, 98
    99, 98, 227, 99
   100, 99, 228, 100
   101, 100, 229, 101
   102, 101, 230, 102
   103, 102, 231, 103
   104, 103, 232, 104
   105, 104, 233, 105
   106, 105, 234, 106
   107, 106, 235, 107
   108, 107, 236, 108
   109, 108, 237, 109
   110, 109, 238, 110
   111, 110, 239, 111
   112, 111, 240, 112
   113, 112, 241, 113
   114, 113, 242, 114
   115, 114, 243, 115
   116, 115, 244, 116
   117, 116, 245, 117
   118, 117, 246, 118
   119, 118, 247, 119
   120, 119, 248, 120
   121, 120, 249, 121
   122, 121, 250, 122
   123, 122, 251, 123
   124, 123, 252, 124
   125, 124, 253, 125
   126, 125, 254, 126
   127, 126, 255, 127
   128, 127, 256, 128
   129, 128, 257, 129
   130, 129, 258, 130
   131, 130, 259, 131
   132, 131, 260, 1
** Names based on fix
*NSET,NSET=fix 
1, 
3, 
** Names based on Line1
*ELSET,ELSET=Line1 
4, 
5, 
6, 
7, 
8, 
9, 
10, 
11, 
12, 
13, 
14, 
15, 
16, 
17, 
18, 
19, 
20, 
21, 
22, 
23, 
24, 
25, 
26, 
27, 
28, 
29, 
30, 
31, 
32, 
33, 
34, 
35, 
36, 
37, 
38, 
39, 
40, 
41, 
42, 
43, 
44, 
45, 
46, 
47, 
48, 
49, 
50, 
51, 
52, 
53, 
54, 
55, 
56, 
57, 
58, 
59, 
60, 
61, 
62, 
63, 
64, 
65, 
66, 
67, 
68, 
69, 
70, 
71, 
72, 
73, 
74, 
75, 
76, 
77, 
78, 
79, 
80, 
81, 
82, 
83, 
84, 
85, 
86, 
87, 
88, 
89, 
90, 
91, 
92, 
93, 
94, 
95, 
96, 
97, 
98, 
99, 
100, 
101, 
102, 
103, 
104, 
105, 
106, 
107, 
108, 
109, 
110, 
111, 
112, 
113, 
114, 
115, 
116, 
117, 
118, 
119, 
120, 
121, 
122, 
123, 
124, 
125, 
126, 
127, 
128, 
129, 
130, 
131, 
132, 
** Names based on load
*NSET,NSET=load 
66, 
*MATERIAL,NAME=mat
*ELASTIC
3.0000E+07,0.3
*DENSITY
1.0000E+00
*damping,structural=0.01
*EXPANSION
0.0000E+00
*BEAM SECTION,MATERIAL=mat,ELSET=Eall,OFFSET1=0.0000E+00,OFFSET2=0.0000E+00,SECTION=rect
5.0000E-01,5.0000E-01
0.0000E+00,0.0000E+00,-1.0000E+00
*BOUNDARY
fix,1,1,0
fix,2,2,0
** fix,3,3,0
fix,4,4,0
fix,5,5,0
fix,6,6,0
*BOUNDARY
Nall,3,3,0
*AMPLITUDE,NAME=A1,TIME=TOTAL TIME
0.0,0.0000E+00,
0.4,0.8000E+03,
1.0,2.0000E+03,
*STEP,NLGEOM,INC=1000
*DYNAMIC
0.0001,1.0
*CLOAD,amplitude=A1
load,2,-1.
*NODE FILE 
U,
*EL FILE
S,
*NODE PRINT,NSET=fix
RF
*NODE PRINT,NSET=fix
RF
*NODE PRINT,NSET=Nall
RF
*END STEP

```

the results:

 ![dyn2](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/3/32fd48520ac17a8859363a7a200226dfd41c019a.png)

---

<div class="post-metadata">

**Author:** ![xyont](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/xyont/32/3553_2.png) [@xyont](https://calculix.discourse.group/u/xyont)\
**Post date:** [May 2, 2024, 4:43am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/6 "2024-05-02T04:43:06Z")

</div>

it seems this type of analysis can be solved with currently algorithm available in CalculiX, needed to assign as displacement i.e 1.5R then record and plot reactions.

 ![2024-05-02 11_35_49-](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/3/3b16f87fef01a59c9a0a43a4da6e6649c5e51f11.png)

 ![2024-05-02 11_32_37-Plot](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/5/5cc0c74f13f0cf0b005df046c3767a11935c85bb.png)

---

<div class="post-metadata">

**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\
**Post date:** [May 2, 2024, 8:26am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/7 "2024-05-02T08:26:18Z")

</div>

right, I noticed later. However your load does not look like fitting the proposed example. Did you change any parameter? cross section, material, etc…

---

<div class="post-metadata">

**Author:** ![JuanP74](https://avatars.discourse-cdn.com/v4/letter/j/b5a626/32.png) [@JuanP74](https://calculix.discourse.group/u/JuanP74)\
**Post date:** [May 2, 2024, 8:50am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/8 "2024-05-02T08:50:52Z")

</div>

I’ve redone it, however load curve does not match.

```auto
*NODE, NSET=Nall
       1,0.000000000000e+00,0.000000000000e+00,0.000000000000e+00
       2,4.100000000000e+01,0.000000000000e+00,0.000000000000e+00
       3,8.200000000000e+01,0.000000000000e+00,0.000000000000e+00
       4,8.198784226358e+01,9.983919949007e-01,0.000000000000e+00
       5,8.195137626461e+01,1.996191883056e+00,0.000000000000e+00
       6,8.189062362964e+01,2.992807908889e+00,0.000000000000e+00
       7,8.180562038861e+01,3.987649019237e+00,0.000000000000e+00
       8,8.169641695356e+01,4.980125213469e+00,0.000000000000e+00
       9,8.156307808881e+01,5.969647892553e+00,0.000000000000e+00
      10,8.140568287235e+01,6.955630210076e+00,0.000000000000e+00
      11,8.122432464888e+01,7.937487419928e+00,0.000000000000e+00
      12,8.101911097469e+01,8.914637221755e+00,0.000000000000e+00
      13,8.079016355412e+01,9.886500105522e+00,0.000000000000e+00
      14,8.053761816661e+01,1.085249969877e+01,0.000000000000e+00
      15,8.026162458693e+01,1.181206310493e+01,0.000000000000e+00
      16,7.996234649581e+01,1.276462124546e+01,0.000000000000e+00
      17,7.963996138286e+01,1.370960919687e+01,0.000000000000e+00
      18,7.929466044238e+01,1.464646652279e+01,0.000000000000e+00
      19,7.892664845901e+01,1.557463760948e+01,0.000000000000e+00
      20,7.853614368511e+01,1.649357199793e+01,0.000000000000e+00
      21,7.812337771446e+01,1.740272470247e+01,0.000000000000e+00
      22,7.768859534178e+01,1.830155654164e+01,0.000000000000e+00
      23,7.723205441960e+01,1.918953445332e+01,0.000000000000e+00
      24,7.675402570332e+01,2.006613181474e+01,0.000000000000e+00
      25,7.625479269330e+01,2.093082874977e+01,0.000000000000e+00
      26,7.573465146408e+01,2.178311244219e+01,0.000000000000e+00
      27,7.519391049122e+01,2.262247743547e+01,0.000000000000e+00
      28,7.463289046783e+01,2.344842593393e+01,0.000000000000e+00
      29,7.405192411275e+01,2.426046810028e+01,0.000000000000e+00
      30,7.345135597273e+01,2.505812234648e+01,0.000000000000e+00
      31,7.283154222118e+01,2.584091561500e+01,0.000000000000e+00
      32,7.219285044627e+01,2.660838366073e+01,0.000000000000e+00
      33,7.153565942817e+01,2.736007133190e+01,0.000000000000e+00
      34,7.086035892258e+01,2.809553283023e+01,0.000000000000e+00
      35,7.016734942389e+01,2.881433198227e+01,0.000000000000e+00
      36,6.945704192817e+01,2.951604249723e+01,0.000000000000e+00
      37,6.872985769117e+01,3.020024821798e+01,0.000000000000e+00
      38,6.798622797457e+01,3.086654337150e+01,0.000000000000e+00
      39,6.722659379961e+01,3.151453280108e+01,0.000000000000e+00
      40,6.645140567124e+01,3.214383221332e+01,0.000000000000e+00
      41,6.566112332304e+01,3.275406839533e+01,0.000000000000e+00
      42,6.485621544210e+01,3.334487943868e+01,0.000000000000e+00
      43,6.403715938531e+01,3.391591495826e+01,0.000000000000e+00
      44,6.320444090337e+01,3.446683629475e+01,0.000000000000e+00
      45,6.235855384839e+01,3.499731671865e+01,0.000000000000e+00
      46,6.149999988293e+01,3.550704162275e+01,0.000000000000e+00
      47,6.062928817933e+01,3.599570871053e+01,0.000000000000e+00
      48,5.974693512498e+01,3.646302817128e+01,0.000000000000e+00
      49,5.885346400961e+01,3.690872285595e+01,0.000000000000e+00
      50,5.794940471431e+01,3.733252844143e+01,0.000000000000e+00
      51,5.703529339940e+01,3.773419358613e+01,0.000000000000e+00
      52,5.611167218810e+01,3.811348007831e+01,0.000000000000e+00
      53,5.517908884449e+01,3.847016297782e+01,0.000000000000e+00
      54,5.423809644483e+01,3.880403075091e+01,0.000000000000e+00
      55,5.328925305496e+01,3.911488539356e+01,0.000000000000e+00
      56,5.233312139640e+01,3.940254255012e+01,0.000000000000e+00
      57,5.137026851479e+01,3.966683162204e+01,0.000000000000e+00
      58,5.040126543756e+01,3.990759587062e+01,0.000000000000e+00
      59,4.942668684269e+01,4.012469250792e+01,0.000000000000e+00
      60,4.844711071454e+01,4.031799278245e+01,0.000000000000e+00
      61,4.746311800260e+01,4.048738205521e+01,0.000000000000e+00
      62,4.647529227023e+01,4.063275986880e+01,0.000000000000e+00
      63,4.548421935895e+01,4.075404000514e+01,0.000000000000e+00
      64,4.449048703338e+01,4.085115053790e+01,0.000000000000e+00
      65,4.349468464026e+01,4.092403387431e+01,0.000000000000e+00
      66,4.249740274799e+01,4.097264679039e+01,0.000000000000e+00
      67,4.149923280678e+01,4.099696045568e+01,0.000000000000e+00
      68,4.050076679315e+01,4.099696045081e+01,0.000000000000e+00
      69,3.950259685696e+01,4.097264677595e+01,0.000000000000e+00
      70,3.850531497178e+01,4.092403385066e+01,0.000000000000e+00
      71,3.750951258447e+01,4.085115050524e+01,0.000000000000e+00
      72,3.651578026589e+01,4.075403996386e+01,0.000000000000e+00
      73,3.552470736321e+01,4.063275981941e+01,0.000000000000e+00
      74,3.453688163719e+01,4.048738199771e+01,0.000000000000e+00
      75,3.355288892804e+01,4.031799271643e+01,0.000000000000e+00
      76,3.257331280913e+01,4.012469243480e+01,0.000000000000e+00
      77,3.159873422138e+01,3.990759579027e+01,0.000000000000e+00
      78,3.062973115172e+01,3.966683153485e+01,0.000000000000e+00
      79,2.966687827799e+01,3.940254245647e+01,0.000000000000e+00
      80,2.871074662601e+01,3.911488529333e+01,0.000000000000e+00
      81,2.776190324517e+01,3.880403064515e+01,0.000000000000e+00
      82,2.682091085401e+01,3.847016286670e+01,0.000000000000e+00
      83,2.588832751577e+01,3.811347996089e+01,0.000000000000e+00
      84,2.496470631259e+01,3.773419346373e+01,0.000000000000e+00
      85,2.405059500418e+01,3.733252831362e+01,0.000000000000e+00
      86,2.314653571646e+01,3.690872272345e+01,0.000000000000e+00
      87,2.225306460816e+01,3.646302803408e+01,0.000000000000e+00
      88,2.137071156553e+01,3.599570857139e+01,0.000000000000e+00
      89,2.049999987483e+01,3.550704148290e+01,0.000000000000e+00
      90,1.964144591963e+01,3.499731657707e+01,0.000000000000e+00
      91,1.879555887517e+01,3.446683615207e+01,0.000000000000e+00
      92,1.796284040023e+01,3.391591481259e+01,0.000000000000e+00
      93,1.714378435169e+01,3.334487929115e+01,0.000000000000e+00
      94,1.633887647912e+01,3.275406824637e+01,0.000000000000e+00
      95,1.554859414037e+01,3.214383206415e+01,0.000000000000e+00
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     260,3.039546729674e-03,4.992330047075e-01,0.000000000000e+00
*ELEMENT, TYPE=B32, ELSET=Eall
     4, 3, 132, 4
     5, 4, 133, 5
     6, 5, 134, 6
     7, 6, 135, 7
     8, 7, 136, 8
     9, 8, 137, 9
    10, 9, 138, 10
    11, 10, 139, 11
    12, 11, 140, 12
    13, 12, 141, 13
    14, 13, 142, 14
    15, 14, 143, 15
    16, 15, 144, 16
    17, 16, 145, 17
    18, 17, 146, 18
    19, 18, 147, 19
    20, 19, 148, 20
    21, 20, 149, 21
    22, 21, 150, 22
    23, 22, 151, 23
    24, 23, 152, 24
    25, 24, 153, 25
    26, 25, 154, 26
    27, 26, 155, 27
    28, 27, 156, 28
    29, 28, 157, 29
    30, 29, 158, 30
    31, 30, 159, 31
    32, 31, 160, 32
    33, 32, 161, 33
    34, 33, 162, 34
    35, 34, 163, 35
    36, 35, 164, 36
    37, 36, 165, 37
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    39, 38, 167, 39
    40, 39, 168, 40
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    47, 46, 175, 47
    48, 47, 176, 48
    49, 48, 177, 49
    50, 49, 178, 50
    51, 50, 179, 51
    52, 51, 180, 52
    53, 52, 181, 53
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    55, 54, 183, 55
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    57, 56, 185, 57
    58, 57, 186, 58
    59, 58, 187, 59
    60, 59, 188, 60
    61, 60, 189, 61
    62, 61, 190, 62
    63, 62, 191, 63
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    70, 69, 198, 70
    71, 70, 199, 71
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    76, 75, 204, 76
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    80, 79, 208, 80
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    83, 82, 211, 83
    84, 83, 212, 84
    85, 84, 213, 85
    86, 85, 214, 86
    87, 86, 215, 87
    88, 87, 216, 88
    89, 88, 217, 89
    90, 89, 218, 90
    91, 90, 219, 91
    92, 91, 220, 92
    93, 92, 221, 93
    94, 93, 222, 94
    95, 94, 223, 95
    96, 95, 224, 96
    97, 96, 225, 97
    98, 97, 226, 98
    99, 98, 227, 99
   100, 99, 228, 100
   101, 100, 229, 101
   102, 101, 230, 102
   103, 102, 231, 103
   104, 103, 232, 104
   105, 104, 233, 105
   106, 105, 234, 106
   107, 106, 235, 107
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   109, 108, 237, 109
   110, 109, 238, 110
   111, 110, 239, 111
   112, 111, 240, 112
   113, 112, 241, 113
   114, 113, 242, 114
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   118, 117, 246, 118
   119, 118, 247, 119
   120, 119, 248, 120
   121, 120, 249, 121
   122, 121, 250, 122
   123, 122, 251, 123
   124, 123, 252, 124
   125, 124, 253, 125
   126, 125, 254, 126
   127, 126, 255, 127
   128, 127, 256, 128
   129, 128, 257, 129
   130, 129, 258, 130
   131, 130, 259, 131
   132, 131, 260, 1
** Names based on fix
*NSET,NSET=fix 
1, 
3, 
** Names based on Line1
*ELSET,ELSET=Line1 
4, 
5, 
6, 
7, 
8, 
9, 
10, 
11, 
12, 
13, 
14, 
15, 
16, 
17, 
18, 
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25, 
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28, 
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100, 
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102, 
103, 
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113, 
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115, 
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118, 
119, 
120, 
121, 
122, 
123, 
124, 
125, 
126, 
127, 
128, 
129, 
130, 
131, 
132, 
** Names based on load
*NSET,NSET=load 
66, 
*MATERIAL,NAME=mat
*ELASTIC
3.0000E+07,0.3
*DENSITY
0.0000E+00
*EXPANSION
0.0000E+00
*BEAM SECTION,MATERIAL=mat,ELSET=Eall,OFFSET1=0.0000E+00,OFFSET2=0.0000E+00,SECTION=rect
5.0000E-01,5.0000E-01
0.0000E+00,0.0000E+00,-1.0000E+00
*BOUNDARY
fix,1,1,0
fix,2,2,0
** fix,3,3,0
fix,4,4,0
fix,5,5,0
fix,6,6,0
*BOUNDARY
Nall,3,3,0
*surface,name=S66
66,S6

*STEP,NLGEOM,INC=1000
*STATIC
0.1,1
*boundary
load,2,2,-66.1
*NODE FILE
U,RF
*EL FILE
S,
*section print,surface=S66,name=SP66
SOF
** *NODE PRINT,NSET=fix
** RF
** *NODE PRINT,NSET=load
** RF
** *NODE PRINT,NSET=Nall
** RF
*END STEP

```

 ![imagen](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/0/06475d1c37a62a4256fb021a2f7da439d47139e4.png)

---

<div class="post-metadata">

**Author:** ![xyont](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/xyont/32/3553_2.png) [@xyont](https://calculix.discourse.group/u/xyont)\
**Post date:** [May 2, 2024, 9:11am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/9 "2024-05-02T09:11:53Z")

</div>

sorry i did not mention before in building similar model from scratch without refer to original geometry, section and loads. Previously i doubt using beam element for such cases, then rebuild another model using linear solid element with reduced integration.

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<div class="post-metadata">

**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [May 2, 2024, 9:39am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/10 "2024-05-02T09:39:19Z")

</div>

There is a nice snap-through example in CalculiX here: [https://www.youtube.com/watch?v=qkjnP1HwPLw](https://www.youtube.com/watch?v=qkjnP1HwPLw)

Arc-length would be the desired method to solve such problems but displacement-controlled NR may often handle them too. Unfortunately, there’s no stabilization for statoc steps so one could try with \*DYNAMIC.

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<div class="post-metadata">

**Author:** ![xyont](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/xyont/32/3553_2.png) [@xyont](https://calculix.discourse.group/u/xyont)\
**Post date:** [May 2, 2024, 11:31am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/11 "2024-05-02T11:31:25Z")

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the capabilities of snap through buckling analysis has been mention since early version as shown by last [examples](http://www.dhondt.de/examples.htm) in official webs. However, as notified it may have limitation in complex buckling and force controlled (load type) so Riks algorithm still needed also interesting to implement but not yet has been done.

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<div class="post-metadata">

**Author:** ![calc4fem](https://avatars.discourse-cdn.com/v4/letter/c/3da27b/32.png) [@calc4fem](https://calculix.discourse.group/u/calc4fem)\
**Post date:** [May 6, 2024, 1:24pm UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/12 "2024-05-06T13:24:12Z")

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I’ve found mistake at my inp. file.  
The section is 1x0.5, not 0.5x0.5  
now seems ok

> **[NLGEOTEST\_2.zip](https://drive.google.com/file/d/1_rCEEmcWJLQD7ztj6S94DAppAvwcKa9J/view?usp=drive_link)**
>
> Google Drive file.

![Screenshot_](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/3/3507ed7c6ca214d5a6f13828ad3a1a6dbf349bb3.png)

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<div class="post-metadata">

**Author:** ![xyont](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/xyont/32/3553_2.png) [@xyont](https://calculix.discourse.group/u/xyont)\
**Post date:** [May 16, 2024, 7:17am UTC](https://calculix.discourse.group/t/testing-problem-arc-length-method/2244/13 "2024-05-16T07:17:57Z")

</div>

another example for non-symmetric condition similar to this [link](https://www.youtube.com/watch?v=Vq9QF8QUEe4), result seems identical and CalculiX is fast in convergences.

![anim1](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/c/c2ab86336852b7cc905c292309b33abfa4020a90.gif)

 ![2024-05-16 13_46_55-Plot](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/2/236f4e430dd98d7b56c9f931637e4ef52dfb9fb2.png)

 ![2024-05-16 14_16_24-Plot](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/5/5e6314659b6f1448e94fc4f7ea9b73b65dee6a83.png)