//- write force displacement to file
if(historyPatchID != -1)
{
    Info << "Writing disp-force to file for patch " << historyPatchName
        << endl;

    //- for small strain or moving mesh
    //scalar force = gSum(
    //    direction &
    //    (mesh.boundary()[historyPatchID].Sf() & sigma.boundaryField()[historyPatchID])
    //);

    //- for large strain total lagrangian
    //tensorField F = I + gradU.boundaryField()[historyPatchID];
    //vector force = gSum(mesh.Sf().boundaryField()[historyPatchID] & (sigma.boundaryField()[historyPatchID] & F));

    //- for large strain updated lagrangian
    vector force = gSum(mesh.Sf().boundaryField()[historyPatchID] & sigma.boundaryField()[historyPatchID]);

    vector disp = gAverage(U.boundaryField()[historyPatchID]);


    Info << "Writing strain-stress to file for patch " << historyPatchName
        << endl;

    // avaerage stress strain
    symmTensor stress = gAverage(sigma.boundaryField()[historyPatchID]);
    symmTensor strain = gAverage(epsilon.boundaryField()[historyPatchID]);


    // write to file
    if(Pstream::master())
    {
         OFstream& forceDispFile = *forceFilePtr;
         label width = 20;
         forceDispFile << disp.x() << " " << disp.y() << " " << disp.z();
         forceDispFile.width(width);
         forceDispFile << force.x() << " " << force.y() << " " << force.z()
             << endl;

         OFstream& stressStrainFile = *stressFilePtr;
         stressStrainFile << strain.xx() << " " << strain.xy() << " " << strain.xz() << " "
             << strain.yy() << " " << strain.yz() << " " << strain.zz();
         stressStrainFile.width(width);
         stressStrainFile << stress.xx() << " " << stress.xy() << " " << stress.xz() << " "
             << stress.yy() << " " << stress.yz() << " " << stress.zz()
             << endl;
    }
}