yade-dev team mailing list archive

[noreply@xxxxxxxxxxxxx]

------------------------------------------------------------
revno: 3471
committer: jduriez <jerome.duriez@xxxxxxxxxxx>
timestamp: Tue 2014-10-14 11:28:52 -0600
message:
  getStress() considers now an adequate volume value for non-periodic case (values passed as parameters may still also be taken into account)
modified:
  pkg/dem/Shop_02.cpp
  py/_utils.cpp


--
lp:yade
https://code.launchpad.net/~yade-pkg/yade/git-trunk

Your team Yade developers is subscribed to branch lp:yade.
To unsubscribe from this branch go to https://code.launchpad.net/~yade-pkg/yade/git-trunk/+edit-subscription

=== modified file 'pkg/dem/Shop_02.cpp'
--- pkg/dem/Shop_02.cpp	2014-10-14 15:52:06 +0000
+++ pkg/dem/Shop_02.cpp	2014-10-14 17:28:52 +0000
@@ -351,7 +351,12 @@
 
 Matrix3r Shop::getStress(Real volume){
 	Scene* scene=Omega::instance().getScene().get();
-	if (volume==0) volume = scene->isPeriodic?scene->cell->hSize.determinant():1;
+	Real volumeNonPeri = 0;
+	if (!scene->isPeriodic) {
+	  py::tuple extrema = Shop::aabbExtrema();
+	  volumeNonPeri = py::extract<Real>( (extrema[1][0] - extrema[0][0])*(extrema[1][1] - extrema[0][1])*(extrema[1][2] - extrema[0][2]) );
+	}
+	if (volume==0) volume = scene->isPeriodic?scene->cell->hSize.determinant():volumeNonPeri;
 	Matrix3r stressTensor = Matrix3r::Zero();
 	const bool isPeriodic = scene->isPeriodic;
 	FOREACH(const shared_ptr<Interaction>&I, *scene->interactions){

=== modified file 'py/_utils.cpp'
--- py/_utils.cpp	2014-10-14 15:52:06 +0000
+++ py/_utils.cpp	2014-10-14 17:28:52 +0000
@@ -453,7 +453,7 @@
 	py::def("normalShearStressTensors",Shop__normalShearStressTensors,(py::args("compressionPositive")=false,py::args("splitNormalTensor")=false,py::args("thresholdForce")=NaN),"Compute overall stress tensor of the periodic cell decomposed in 2 parts, one contributed by normal forces, the other by shear forces. The formulation can be found in [Thornton2000]_, eq. (3):\n\n.. math:: \\tens{\\sigma}_{ij}=\\frac{2}{V}\\sum R N \\vec{n}_i \\vec{n}_j+\\frac{2}{V}\\sum R T \\vec{n}_i\\vec{t}_j\n\nwhere $V$ is the cell volume, $R$ is \"contact radius\" (in our implementation, current distance between particle centroids), $\\vec{n}$ is the normal vector, $\\vec{t}$ is a vector perpendicular to $\\vec{n}$, $N$ and $T$ are norms of normal and shear forces.\n\n:param bool splitNormalTensor: if true the function returns normal stress tensor split into two parts according to the two subnetworks of strong an weak forces.\n\n:param Real thresholdForce: threshold value according to which the normal stress tensor can be split (e.g. a zero value would make distinction between tensile and compressive forces).");
 	py::def("fabricTensor",Shop__fabricTensor,(py::args("splitTensor")=false,py::args("revertSign")=false,py::args("thresholdForce")=NaN),"Compute the fabric tensor of the periodic cell. The original paper can be found in [Satake1982]_.\n\n:param bool splitTensor: split the fabric tensor into two parts related to the strong and weak contact forces respectively.\n\n:param bool revertSign: it must be set to true if the contact law's convention takes compressive forces as positive.\n\n:param Real thresholdForce: if the fabric tensor is split into two parts, a threshold value can be specified otherwise the mean contact force is considered by default. It is worth to note that this value has a sign and the user needs to set it according to the convention adopted for the contact law. To note that this value could be set to zero if one wanted to make distinction between compressive and tensile forces.");
 	py::def("bodyStressTensors",Shop__getStressLWForEachBody,"Compute and return a table with per-particle stress tensors. Each tensor represents the average stress in one particle, obtained from the contour integral of applied load as detailed below. This definition is considering each sphere as a continuum. It can be considered exact in the context of spheres at static equilibrium, interacting at contact points with negligible volume changes of the solid phase (this last assumption is not restricting possible deformations and volume changes at the packing scale).\n\nProof: \n\nFirst, we remark the identity:  $\\sigma_{ij}=\\delta_{ik}\\sigma_{kj}=x_{i,k}\\sigma_{kj}=(x_{i}\\sigma_{kj})_{,k}-x_{i}\\sigma_{kj,k}$.\n\nAt equilibrium, the divergence of stress is null: $\\sigma_{kj,k}=\\vec{0}$. Consequently, after divergence theorem: $\\frac{1}{V}\\int_V \\sigma_{ij}dV = \\frac{1}{V}\\int_V (x_{i}\\sigma_{kj})_{,k}dV = \\frac{1}{V}\\int_{\\partial V}x_i\\sigma_{kj}n_kdS = \\frac{1}{V}\\sum_bx_i^bf_j^b$.\n\nThe last equality is implicitely based on the representation of external loads as Dirac distributions whose zeros are the so-called *contact points*: 0-sized surfaces on which the *contact forces* are applied, located at $x_i$ in the deformed configuration.\n\nA weighted average of per-body stresses will give the average stress inside the solid phase. There is a simple relation between the stress inside the solid phase and the stress in an equivalent continuum in the absence of fluid pressure. For porosity $n$, the relation reads: $\\sigma_{ij}^{equ.}=(1-n)\\sigma_{ij}^{solid}$.\n\nThis last relation may not be very useful if porosity is not homogeneous. If it happens, one can define the equivalent bulk stress a the particles scale by assigning a volume to each particle. This volume can be obtained from :yref:`TesselationWrapper` (see e.g. [Catalano2014a]_)");
-	py::def("getStress",Shop::getStress,(py::args("volume")=0),"Compute and return Love-Weber stress tensor:\n\n $\\sigma_{ij}=\\frac{1}{V}\\sum_b f_i^b l_j^b$, where the sum is over all interactions, with $f$ the contact force and $l$ the branch vector (joining centers of the bodies). Stress is negativ for repulsive contact forces, i.e. compression. $V$ can be passed to the function. If it is not, it will be equal to one in non-periodic cases, or equal to the volume of the cell in periodic cases.");
+	py::def("getStress",Shop::getStress,(py::args("volume")=0),"Compute and return Love-Weber stress tensor:\n\n $\\sigma_{ij}=\\frac{1}{V}\\sum_b f_i^b l_j^b$, where the sum is over all interactions, with $f$ the contact force and $l$ the branch vector (joining centers of the bodies). Stress is negativ for repulsive contact forces, i.e. compression. $V$ can be passed to the function. If it is not, it will be equal to the volume of the cell in periodic cases, or to the one deduced from utils.aabbDim() in non-periodic cases.");
 	py::def("getCapillaryStress",Shop::getCapillaryStress,(py::args("volume")=0,py::args("mindlin")=false),"Compute and return Love-Weber capillary stress tensor:\n\n $\\sigma^{cap}_{ij}=\\frac{1}{V}\\sum_b l_i^b f^{cap,b}_j$, where the sum is over all interactions, with $l$ the branch vector (joining centers of the bodies) and $f^{cap}$ is the capillary force. $V$ can be passed to the function. If it is not, it will be equal to one in non-periodic cases, or equal to the volume of the cell in periodic cases. Only the CapillaryPhys interaction type is supported presently. Using this function with physics MindlinCapillaryPhys needs to pass True as second argument.");
 	py::def("getBodyIdsContacts",Shop__getBodyIdsContacts,(py::args("bodyID")=0),"Get a list of body-ids, which contacts the given body.");
 	py::def("maxOverlapRatio",maxOverlapRatio,"Return maximum overlap ration in interactions (with :yref:`ScGeom`) of two :yref:`spheres<Sphere>`. The ratio is computed as $\\frac{u_N}{2(r_1 r_2)/r_1+r_2}$, where $u_N$ is the current overlap distance and $r_1$, $r_2$ are radii of the two spheres in contact.");