diff --git a/DEMSystems/sphereDEMSystem/sphereFluidParticles.cpp b/DEMSystems/sphereDEMSystem/sphereFluidParticles.cpp
index 386ac859..9b3a44b0 100644
--- a/DEMSystems/sphereDEMSystem/sphereFluidParticles.cpp
+++ b/DEMSystems/sphereDEMSystem/sphereFluidParticles.cpp
@@ -54,6 +54,13 @@ pFlow::sphereFluidParticles::sphereFluidParticles(
 		)
 {} 
 
+bool pFlow::sphereFluidParticles::beforeIteration()
+{
+	sphereParticles::beforeIteration();
+	zeroFluidForce_H();
+	zeroFluidTorque_H();
+	return true;
+}
 
 
 bool pFlow::sphereFluidParticles::iterate() 
diff --git a/DEMSystems/sphereDEMSystem/sphereFluidParticles.hpp b/DEMSystems/sphereDEMSystem/sphereFluidParticles.hpp
index 48b73f34..9890dac8 100644
--- a/DEMSystems/sphereDEMSystem/sphereFluidParticles.hpp
+++ b/DEMSystems/sphereDEMSystem/sphereFluidParticles.hpp
@@ -48,12 +48,24 @@ protected:
 	realx3PointField_HD& 	fluidTorque_;
 
 
+	void zeroFluidForce_H()
+	{
+		fluidForce_.fillHost(zero3);
+	}
+
+	void zeroFluidTorque_H()
+	{
+		fluidTorque_.fillHost(zero3);
+	}
+
 public:
 
 	/// construct from systemControl and property 
 	sphereFluidParticles(systemControl &control, const property& prop);
 	
-
+	/// before iteration step 
+	bool beforeIteration() override;
+	
 	/// iterate particles 
 	bool iterate() override;