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March 17, 2015, 12:33 |
double derivative with respect to time
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#1 |
Member
Muhammad Usman
Join Date: Feb 2014
Posts: 91
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Hye i am new user of openFoam i need to calculate double derivative with respect to time of a scalar.
i have a scalar CoMx i tried to find its double derivative by scalar DDTCoMx = d2dt2(CoMx); but i got error error: ‘d2dt2’ was not declared in this scope scalar DDTCoMx = d2dt2(CoMx); please help me... is there any need to add some header file explaining d2dt2???? if yes then where this header file lies and how to add it in make/options??? |
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March 18, 2015, 08:00 |
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#2 |
Member
ali alkebsi
Join Date: Jan 2012
Location: Strasbourg, France
Posts: 82
Rep Power: 14 |
hi
the d2dt2 is defined within fvm, fvc,.........etc. to call it you should write fvc::d2dt2(CoMx) if you want to calculate ( which i think is your case) fvm:d2dt2(CoMx) in case you want to generate the coefficient matrix to solve an equation try this and tell me if it works or not. |
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March 18, 2015, 10:22 |
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#3 |
Member
Muhammad Usman
Join Date: Feb 2014
Posts: 91
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There is still an error sir
myInterFoamDDT.C: In function ‘int main(int, char**)’: myInterFoamDDT.C:121:34: error: no matching function for call to ‘d2dt2(Foam::scalar&)’ scalar DDTCoMx = fvc::d2dt2 (CoMx); myInterFoamDDT.C:121:34: note: candidates are: In file included from /opt/openfoam231/src/finiteVolume/lnInclude/fvcD2dt2.H:74:0, from /opt/openfoam231/src/finiteVolume/lnInclude/fvc.H:46, from /opt/openfoam231/src/finiteVolume/lnInclude/fvCFD.H:8, from myInterFoamDDT.C:40: /opt/openfoam231/src/finiteVolume/lnInclude/fvcD2dt2.C:44:1: note: template<class Type> Foam::tmp<Foam::GeometricField<Type, Foam::fvPatchField, Foam::volMesh> > Foam::fvc::d2dt2(const Foam::GeometricField<Type, Foam::fvPatchField, Foam::volMesh>&) d2dt2 /opt/openfoam231/src/finiteVolume/lnInclude/fvcD2dt2.C:44:1: note: template argument deduction/substitution failed: myInterFoamDDT.C:121:34: note: mismatched types ‘const Foam::GeometricField<Type, Foam::fvPatchField, Foam::volMesh>’ and ‘Foam::scalar {aka double}’ scalar DDTCoMx = fvc::d2dt2 (CoMx); In file included from /opt/openfoam231/src/finiteVolume/lnInclude/fvcD2dt2.H:74:0, from /opt/openfoam231/src/finiteVolume/lnInclude/fvc.H:46, from /opt/openfoam231/src/finiteVolume/lnInclude/fvCFD.H:8, from myInterFoamDDT.C:40: /opt/openfoam231/src/finiteVolume/lnInclude/fvcD2dt2.C:59:1: note: template<class Type> Foam::tmp<Foam::GeometricField<Type, Foam::fvPatchField, Foam::volMesh> > Foam::fvc::d2dt2(const volScalarField&, const Foam::GeometricField<Type, Foam::fvPatchField, Foam::volMesh>&) d2dt2 /opt/openfoam231/src/finiteVolume/lnInclude/fvcD2dt2.C:59:1: note: template argument deduction/substitution failed: myInterFoamDDT.C:121:34: note: cannot convert ‘CoMx’ (type ‘Foam::scalar {aka double}’) to type ‘const volScalarField& {aka const Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh>&}’ scalar DDTCoMx = fvc::d2dt2 (CoMx); myInterFoamDDT.C:121:8: warning: unused variable ‘DDTCoMx’ [-Wunused-variable] scalar DDTCoMx = fvc::d2dt2 (CoMx); In file included from myInterFoamDDT.C:61:0: /opt/openfoam231/src/finiteVolume/lnInclude/readTimeControls.H:38:8: warning: unused variable ‘maxDeltaT’ [-Wunused-variable] scalar maxDeltaT = |
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March 18, 2015, 10:51 |
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#4 |
Member
ali alkebsi
Join Date: Jan 2012
Location: Strasbourg, France
Posts: 82
Rep Power: 14 |
is CoMx a volScalarField?
could you specify how you define CoMx The code is searching for a version of d2dt2 that matches the type of your CoMx ( I think) but couldn't find one. |
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March 18, 2015, 11:06 |
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#5 |
Member
Muhammad Usman
Join Date: Feb 2014
Posts: 91
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sir here is code i have got center of mass and indivisual components of center of mass i want to get its time derivatives
CoM = sum(rho*mesh.V()*mesh.C().dimensionedInternalField ())/sum(rho*mesh.V()); Info << "Center of Mass " << CoM.dimensions() << " = " << CoM << nl << endl; scalar CoMx = CoM.value().x(); Info << "Center of Mass x component = " << CoMx << nl << endl; scalar CoMy = CoM.value().y(); Info << "Center of Mass y component = " << CoMy << nl << endl; scalar CoMz = CoM.value().z(); Info << "Center of Mass z component = " << CoMz << nl << endl; and for time derivative i used scalar DDTCoMx = fvm::d2dt2 (CoMx); but got error |
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March 18, 2015, 11:08 |
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#6 |
Member
Muhammad Usman
Join Date: Feb 2014
Posts: 91
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i defined CoMx as scalar and got values but when i tried d2dt2 could not succeed
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March 18, 2015, 11:18 |
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#7 |
Member
ali alkebsi
Join Date: Jan 2012
Location: Strasbourg, France
Posts: 82
Rep Power: 14 |
Could you explain your case a little bit more???
what is it you are trying to model here? |
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March 18, 2015, 11:25 |
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#8 |
Member
Muhammad Usman
Join Date: Feb 2014
Posts: 91
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i and just trying to calculate center of mass of fluid when fluid moves in damBreak tutorial and then find acceleration of center of mass. acceleration in x y and z direction.
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March 18, 2015, 11:29 |
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#9 |
Member
ali alkebsi
Join Date: Jan 2012
Location: Strasbourg, France
Posts: 82
Rep Power: 14 |
well the function called d2dt2 is not appropriate in this case my dear friend.
This function is used to discretize and not to calculate derivatives. You should search for a utility that would do your task; i dont know if one exists or not. but what you can do is simply a=(Vnew-Vold)/dt where V is done in the same manner |
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March 18, 2015, 11:53 |
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#10 |
Member
Muhammad Usman
Join Date: Feb 2014
Posts: 91
Rep Power: 0 |
ohhh sir it means i will have to apply some numerical method to calculate derivative????
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