if(divDSigmaExpMethod == "standard")
  {
    divDSigmaExp = fvc::div
      (
       (mu*gradDU.T())
       + (lambda*(I*tr(gradDU)))
       - ((mu + lambda)*gradDU),
       "div(sigma)"
       );
  }
 else if(divDSigmaExpMethod == "surface")
   { 
     divDSigmaExp =
       fvc::div(
		mesh.magSf()
		*(
		  muf*(n&fvc::interpolate(gradDU.T()))
		  + lambdaf*tr(fvc::interpolate(gradDU))*n
		  - (muf + lambdaf)*(n&fvc::interpolate(gradDU))
		  )
		);
     // divDSigmaExp = fvc::div
     //   (
     // 	muf*(mesh.Sf() & fvc::interpolate(gradDU.T()))
     // 	+ lambdaf*(mesh.Sf() & I*fvc::interpolate(tr(gradDU)))
     // 	- (muf + lambdaf)*(mesh.Sf() & fvc::interpolate(gradDU))
     // 	);
   }
 else if(divDSigmaExpMethod == "decompose")
   {
     surfaceTensorField shearGradDU =
       ((I - n*n)&fvc::interpolate(gradDU));
     
     divDSigmaExp =
       fvc::div(
		mesh.magSf()
		*(
		  - (muf + lambdaf)*(fvc::snGrad(DU)&(I - n*n))
		  + lambdaf*tr(shearGradDU&(I - n*n))*n
		  + muf*(shearGradDU&n)
		  )
		);
     // divDSigmaExp = fvc::div
     //   (
     // 	mesh.magSf()
     // 	*(
     // 	  - (muf + lambdaf)*(fvc::snGrad(DU)&(I - n*n))
     // 	  + lambdaf*tr(shearGradDU&(I - n*n))*n
     // 	  + muf*(shearGradDU&n)
     // 	  )
     // 	);
   }
 else if(divDSigmaExpMethod == "laplacian")
   {
     divDSigmaExp =
       - fvc::laplacian(mu + lambda, DU, "laplacian(DDU,DU)")
       + fvc::div
       (
	mu*gradDU.T()
	+ lambda*(I*tr(gradDU)),
	"div(sigma)"
	);
   }
 else
   {
     FatalError << "divDSigmaExp method " << divDSigmaExpMethod << " not found!" << endl;
   }