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vex July 1, 2015 11:04
solidDisplacementFoam displacement
 
1 Attachment(s)
Hi Everyone!

I'm running, what I would consider a rather simple analysis where in I am simulating the change in temperature of a large pipe (300k to 270.75k). I would have expected the displacement of the pipe to show a contraction, but the view seems to indicate an expansion of the material. What gives? Did I do something wrong in my setup? Here's my various inputs:

T:
Code:
dimensions      [0 0 0 1 0 0 0];

internalField  uniform 300;

boundaryField
{
    left
    {
        type            symmetryPlane;
    }
    right
    {
        type            fixedValue;
        value                uniform 270.75;
    }
    down
    {
        type            symmetryPlane;
    }
    up
    {
        type            fixedValue;
        value                uniform 270.75;
    }
    hole
    {
        type            fixedValue;
        value                uniform 270.75;
    }
    frontAndBack
    {
        type            empty;
    }
}
D:
Code:
dimensions      [0 1 0 0 0 0 0];

internalField  uniform (0 0 0);

boundaryField
{
    left
    {
        type            symmetryPlane;
    }
    right
    {
        type            tractionDisplacement;
        traction        uniform ( 0 0 0 );
        pressure        uniform 0;
        value          uniform (0 0 0);
    }
    down
    {
        type            symmetryPlane;
    }
    up
    {
        type            tractionDisplacement;
        traction        uniform ( 0 0 0 );
        pressure        uniform 0;
        value          uniform (0 0 0);
    }
    hole
    {
        type            tractionDisplacement;
        traction        uniform ( 0 0 0 );
        pressure        uniform 0;
        value          uniform (0 0 0);
    }
    frontAndBack
    {
        type            empty;
    }
}
mechanicalProperties:
Code:
rho
{
    type        uniform;
    value      7860;
}

nu
{
    type        uniform;
    value      0.3;
}

E
{
    type        uniform;
    value      201e+9;
}

planeStress    yes;
thermalProperties:
Code:
C
{
    type        uniform;
    value      0.000472;
}

k
{
    type        uniform;
    value      51.4;
}

alpha
{
    type        uniform;
    value      12.9e-06;
}

thermalStress  yes;
fvSchemes:
Code:
d2dt2Schemes
{
    default        steadyState;
}

ddtSchemes
{
    default        Euler;
}

gradSchemes
{
    default        leastSquares;
    grad(D)        leastSquares;
    grad(T)        leastSquares;
}

divSchemes
{
    default        none;
    div(sigmaD)    Gauss linear;
}

laplacianSchemes
{
    default        none;
    laplacian(DD,D) Gauss linear corrected;
    laplacian(DT,T) Gauss linear corrected;
}

interpolationSchemes
{
    default        linear;
}

snGradSchemes
{
    default        none;
}

fluxRequired
{
    default        no;
    D              yes;
    T              yes;
}
fvSolution:
Code:
solvers
{
    "(D|T)"
    {
        solver          GAMG;
        tolerance      1e-06;
        relTol          0.1;
        smoother        GaussSeidel;
        cacheAgglomeration true;
        nCellsInCoarsestLevel 20;
        agglomerator    faceAreaPair;
        mergeLevels    1;
    }
}

stressAnalysis
{
    compactNormalStress no;
    thermalStress  yes;
    nCorrectors    100000;
    D              1e-06;
    T                    1e-06;
}
Attached are my results of the analysis. If I look at the components of the displacement I get the same positive values...

vex July 2, 2015 11:07
I guess my question got lost in the litany of code that I posted: Has anyone noticed that displacement values are always positive when dealing with temperature change?

I have verified that if I go from 300 uniform temperature to 370, the displacement is positive--which is to be expected. The negative temperature change; from 300 to 270 still results in a positive displacement transversely (looking at the pipe face).

Anecdotally; there appears to be a numerical instability or slight calculation of almost 0 applied to a portion longitudinally of the pipe face that results in a contraction of the pipe longitudinally. Obviously there is some aspect of the code that is determining that the thermal contraction is interpreted as a thermal expansion on the transverse portion of the analysis.

The latest result as described of the pipe face indicates that the displacement is indeed being calculated as positive in the x and y direction. See the following output:
Code:
dimensions      [0 1 0 0 0 0 0];

internalField  nonuniform List<vector>
400
(
(0.000925418 3.74858e-05 0)
(0.000933421 3.77848e-05 0)
(0.000941427 3.80841e-05 0)
(0.000949431 3.83797e-05 0)
(0.000957436 3.86759e-05 0)
(0.00096544 3.89691e-05 0)
(0.000973446 3.92629e-05 0)
(0.00098145 3.95542e-05 0)
(0.000989456 3.98461e-05 0)
(0.00099746 4.01358e-05 0)
(0.000914368 0.000104882 0)
(0.000922318 0.000105901 0)
(0.000930266 0.000106913 0)
(0.000938217 0.000107929 0)
(0.000946165 0.00010894 0)
(0.000954116 0.000109954 0)
(0.000962065 0.000110964 0)
(0.000970017 0.000111976 0)
(0.000977965 0.000112985 0)
(0.000985917 0.000113996 0)
(0.000907048 0.00018134 0)
(0.000914907 0.000182865 0)
(0.000922771 0.000184396 0)
(0.00093063 0.000185924 0)
(0.000938493 0.000187457 0)
(0.000946353 0.000188987 0)
(0.000954216 0.000190521 0)
(0.000962075 0.000192053 0)
(0.000969938 0.000193589 0)
(0.000977798 0.000195122 0)
(0.000886698 0.000247221 0)
(0.000894393 0.000249463 0)
(0.000902086 0.000251699 0)
(0.000909782 0.000253939 0)
(0.000917476 0.000256174 0)
(0.000925173 0.000258412 0)
(0.000932867 0.000260645 0)
(0.000940564 0.000262881 0)
(0.000948259 0.000265113 0)
(0.000955957 0.000267348 0)
(0.000866551 0.000320527 0)
(0.000874077 0.000323262 0)
(0.000881605 0.000326003 0)
(0.00088913 0.00032874 0)
(0.000896657 0.000331482 0)
(0.000904182 0.000334221 0)
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(0.000934285 0.000345193 0)
(0.000837119 0.000383496 0)
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(0.000851625 0.000390309 0)
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(0.000866132 0.000397118 0)
(0.000873386 0.000400524 0)
(0.00088064 0.000403925 0)
(0.000887896 0.000407329 0)
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(0.000902406 0.000414131 0)
(0.000804943 0.000451732 0)
(0.00081195 0.000455611 0)
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(0.00076684 0.000510335 0)
(0.000773475 0.000514828 0)
(0.000780111 0.000519317 0)
(0.000786746 0.00052381 0)
(0.000793383 0.000528298 0)
(0.000800019 0.000532788 0)
(0.000806656 0.000537276 0)
(0.000813293 0.000541765 0)
(0.000819931 0.000546251 0)
(0.000826569 0.00055074 0)
(0.000723698 0.00057178 0)
(0.000730014 0.000576707 0)
(0.000736327 0.000581638 0)
(0.000742642 0.000586566 0)
(0.000748955 0.000591498 0)
(0.000755269 0.000596428 0)
(0.000761582 0.000601361 0)
(0.000767895 0.000606292 0)
(0.000774207 0.000611226 0)
(0.000780519 0.000616158 0)
(0.000677617 0.000624621 0)
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(0.000689327 0.000635559 0)
(0.000695181 0.000641028 0)
(0.000701038 0.000646494 0)
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(0.000712752 0.000657428 0)
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(0.000724467 0.00066836 0)
(0.000730325 0.000673827 0)
(0.00100547 4.04261e-05 0)
(0.00101347 4.07142e-05 0)
(0.00102147 4.10027e-05 0)
(0.00102948 4.12891e-05 0)
(0.00103748 4.15757e-05 0)
(0.00104549 4.18601e-05 0)
(0.0010535 4.21446e-05 0)
(0.0010615 4.24265e-05 0)
(0.00106951 4.27082e-05 0)
(0.00107751 4.29871e-05 0)
(0.000993866 0.000115003 0)
(0.00100182 0.000116013 0)
(0.00100977 0.00011702 0)
(0.00101772 0.000118028 0)
(0.00102567 0.000119034 0)
(0.00103362 0.000120042 0)
(0.00104157 0.000121046 0)
(0.00104952 0.000122052 0)
(0.00105747 0.000123055 0)
(0.00106542 0.00012406 0)
(0.00098566 0.000196659 0)
(0.00099352 0.000198194 0)
(0.00100138 0.000199732 0)
(0.00100924 0.000201268 0)
(0.0010171 0.000202807 0)
(0.00102496 0.000204344 0)
(0.00103283 0.000205884 0)
(0.00104069 0.000207423 0)
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(0.000963652 0.000269578 0)
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(0.00100214 0.000280729 0)
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(0.00101753 0.000285184 0)
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(0.000941811 0.00034794 0)
(0.000949336 0.000350684 0)
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(0.000971911 0.000358926 0)
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(0.0009532 0.000437919 0)
(0.000960458 0.000441315 0)
(0.000967715 0.00044471 0)
(0.000974974 0.000448106 0)
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(0.000903012 0.000506132 0)
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(0.000931024 0.000521697 0)
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(0.000555363 0.000833321 0)
(0.000490496 0.000874906 0)
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(0.00024733 0.000886804 0)
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(0.000251813 0.000902191 0)
(0.000254056 0.000909886 0)
(0.000256293 0.00091758 0)
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(0.000263008 0.000940665 0)
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(0.000187412 0.000938486 0)
(0.000188941 0.000946346 0)
(0.000190475 0.000954209 0)
(0.000192006 0.000962069 0)
(0.00019354 0.000969932 0)
(0.000195073 0.000977792 0)
(0.000104984 0.000914452 0)
(0.000106005 0.000922402 0)
(0.000107021 0.000930349 0)
(0.00010804 0.0009383 0)
(0.000109054 0.000946247 0)
(0.00011007 0.000954199 0)
(0.000111083 0.000962147 0)
(0.000112098 0.000970098 0)
(0.00011311 0.000978047 0)
(0.000114123 0.000985998 0)
(3.74533e-05 0.000925467 0)
(3.77511e-05 0.000933471 0)
(3.80492e-05 0.000941477 0)
(3.83437e-05 0.00094948 0)
(3.86388e-05 0.000957486 0)
(3.89309e-05 0.00096549 0)
(3.92237e-05 0.000973496 0)
(3.95139e-05 0.0009815 0)
(3.98049e-05 0.000989505 0)
(4.00935e-05 0.00099751 0)
)
;

boundaryField
{
    left
    {
        type            symmetryPlane;
    }
    right
    {
        type            tractionDisplacement;
        traction        uniform (0 0 0);
        pressure        uniform 0;
        value          nonuniform List<vector> 10((0.00108151 4.31261e-05 9.34967e-25) (0.00106939 0.00012456 4.7054e-25) (0.00106033 0.000211276 8.64706e-23) (0.00103677 0.000290748 -1.74095e-22) (0.00101329 0.000374048 -1.75053e-22) (0.000978598 0.0004498 1.86909e-24) (0.000941523 0.000527534 -2.10808e-24) (0.000896286 0.000597817 -7.02752e-25) (0.000846769 0.000667986 3.52888e-22) (0.000791857 0.00073118 -1.54931e-29));
    }
    down
    {
        type            symmetryPlane;
    }
    up
    {
        type            tractionDisplacement;
        traction        uniform (0 0 0);
        pressure        uniform 0;
        value          nonuniform List<vector> 10((0.000731318 0.000791957 -7.02718e-25) (0.000667895 0.00084665 -3.51022e-22) (0.000597965 0.00089639 7.02527e-25) (0.000527455 0.000941432 -2.31904e-25) (0.000449954 0.0009787 1.40562e-24) (0.000373981 0.00101324 1.7646e-22) (0.000290903 0.00103686 1.77369e-22) (0.000211219 0.00106033 -1.63739e-24) (0.000124715 0.00106947 9.34347e-25) (4.30747e-05 0.00108156 2.32146e-25));
    }
    hole
    {
        type            tractionDisplacement;
        traction        uniform (0 0 0);
        pressure        uniform 0;
        value          nonuniform List<vector>
20
(
(0.000921409 3.73341e-05 5.95293e-25)
(0.000910389 0.000104374 5.17184e-23)
(0.00090311 0.000180575 -1.0344e-22)
(0.000882846 0.0002461 -7.96172e-25)
(0.000862782 0.000319156 1.39108e-24)
(0.000833488 0.000381791 1.39144e-24)
(0.000801435 0.000449788 9.96412e-25)
(0.000763518 0.000508087 1.9398e-25)
(0.000720537 0.000569312 -2.30926e-29)
(0.000674686 0.000621883 1.19742e-24)
(0.000622009 0.000674801 2.00451e-25)
(0.000569212 0.000720421 -2.00438e-25)
(0.000508211 0.000763642 2.0046e-25)
(0.00044971 0.000801341 1.39123e-24)
(0.000381908 0.000833608 1.98676e-24)
(0.000319099 0.000862725 4.00942e-25)
(0.000246207 0.000882953 1.58882e-28)
(0.000180535 0.000903102 1.03834e-22)
(0.000104474 0.000910474 -3.83547e-28)
(3.73023e-05 0.000921458 1.39153e-24)
)
;
    }
    frontAndBack
    {
        type            empty;
    }
}


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