diff --git a/ProcessLib/StokesFlow/StokesFlowProcessData.h b/ProcessLib/StokesFlow/StokesFlowProcessData.h
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+/**
+ * \file
+ * \copyright
+ * Copyright (c) 2012-2021, OpenGeoSys Community (http://www.opengeosys.org)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/project/license
+ *
+ */
+
+#pragma once
+
+#include <Eigen/Eigen>
+#include <memory>
+
+#include "MeshLib/PropertyVector.h"
+
+namespace MaterialPropertyLib
+{
+class MaterialSpatialDistributionMap;
+}
+
+namespace ProcessLib
+{
+namespace StokesFlow
+{
+struct StokesFlowProcessData
+{
+    std::unique_ptr<MaterialPropertyLib::MaterialSpatialDistributionMap>
+        media_map;
+    /// an external force that applies in the bulk of the fluid, like gravity.
+    Eigen::VectorXd const specific_body_force;
+
+    MeshLib::PropertyVector<double>* pressure_interpolated = nullptr;
+};
+
+}  // namespace StokesFlow
+}  // namespace ProcessLib