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+"CFDEMproject Website"_lws - "Main Page"_main :c
+
+:link(lws,http://www.cfdem.com)
+:link(main,CFDEMcoupling_Manual.html)
+
+:line
+
+otherForceModel gravityEff command :h3
+
+[Syntax:]
+
+Defined in "couplingProperties"_CFDEMcoupling_dicts.html#couplingProperties
+dictionary.
+
+otherForceModels
+(
+  gravityEff
+);
+gravityEffProps
+{
+    voidfractionFieldName "voidfraction";
+    rhoPart number1;
+} :pre
+
+{voidfraction} = name of the finite volume void fraction field :l
+{number1} = particle density :l
+
+:ule
+
+[Examples:]
+
+otherForceModels
+(
+  gravityEff
+);
+gravityEffProps
+{
+  voidfractionFieldName "voidfraction";
+  rhoPart 1500;
+} :pre
+
+[Description:]
+
+An effective gravitational source term, {gravityEff}, that is necessery to drive the flow only in
+case of periodic box simulations. This source term is added to the momentum equation. In case of
+simulating periodic boxes with assuming "Homogenous no flow condition" we will have:
+
+:c,image(Eqs/otherForceModels_gravityEff_pic1.jpg)
+
+This equation depicts that in "no flow consition" static pressure gradient balances the mixture weight.
+Therefore, to derive the flow in the periodic box simulations, a dynamic pressure gradien is defined as,
+
+:c,image(Eqs/otherForceModels_gravityEff_pic2.jpg)
+
+If one replaces the static pressure gradient of the fluid momentum equation with,
+
+:c,image(Eqs/otherForceModels_gravityEff_pic3.jpg)
+
+The fluid momentum equation solved in case of periodic box simulations will be,
+
+:c,image(Eqs/otherForceModels_gravityEff_pic4.jpg)
+
+The {gravityEff} source term is the third term in the RHS of the momentum equation. Note that 
+the gravitational body force of the fluid momentum equation is considered with this source term.
+
+In the basic implementation of {gravityEff}, first we calculate the density of the mixture and then
+the source term is calculated based on the third term in the RHS of the momentum equation.
+[Restrictions:]
+
+none
+
+[Related commands:]
+
+"otherForceModels"_otherForceModels.html
+