📘 Contents

1 Introduction
2. Select Model
2.1 Description and theory 2.2 Setting up
3 Material properties
3.1 Description and theory 3.2 Setting up
4. Particle Force Models
4.1 Description and theory
4.1.1 Gravity force 4.1.2 Collision force

Gran-DEM Documentation

Version : 1.0 Updated : 31 May 2026

Gran-DEM Documentation is a centralized knowledge base designed to help users understand, manage, and utilize all features of the Gran-DEM platform. It provides comprehensive guides, setup instructions, best practices, troubleshooting resources, and technical references to ensure a smooth and efficient user experience.

1 Introduction

The Gran-DEM particle flow simulator is a commercial particle flow DISCRETE ELEMENT METHOD (DEM) application that can be used to simulate particle flow in any type of pre-designed 3-D domain. This 3-D domain can be a mesh file (.msh) imported into the Gran-DEM application. The Gran-DEM application set-up (version 1.0) can be licensed and downloaded from (gran-dem.com) and installed. The procedure to do this is provided hereby;

 

The application can next be started from the start menu. The Gran-DEM particle flow simulator is operated using a tailor developed User interface for easy formulation and set-up. The Gran-DEM UI opens immediately after starting it from the start menu. The UI design consists of 3 vertical panes LEFT (red), MIDDLE (green) and RIGHT (blue) and a horizontal TOP (orange) pane that can be seen in Fig 1.1. The UI set-up consists of 7 main functionalities organized sequentially in the left most pane of the UI. These main functionalities are MATERIAL PROPERTIES, FORCE MODELS, SYSTEM MOTION, INJECTION INITIALIZATION, MODEL COUPLING, EXECUTE AND PARAVIEW VISUALIZATION.

 

Fig. 1.1: UI layout design and its main subdivided functionalities.

When any of the above main functionalities is selected the sub-selections for these appear in the middle pane. The right large pane is used for visualization. The top pane (orange) consists of File, Edit, Source, Filters, Tools and Help that are described later in Section 8.1. In the following sections various aspects of the UI operations are discussed sequentially.

2. Select Model

2.1 Description and theory

The LnE multiphase CFD simulator is a multipurpose tool for carrying out both Lagrangian (granular) and Eulerian (Fluid) flow simulations in various flexible combinations. The Lagrangian particle flow modelling uses the Discrete Element Method (DEM) for treating collision mechanism. The Eulerian (fluid) flow modelling is done by using the coupled pressure-velocity model that involves fundamentally the continuity Equation and Navier Stokes Equation solved on a 3D grid domain. 

Within the CFD framework this is also called the SIMPLE algorithm that stands for Semi-Implicit Method for Pressure Linked Equation proposed by Spalding and Patankar (1978). Typically, most commercial CFD solvers for unstructured grid domains use the finite volume method. This means both the pressure and velocity fields are defined for cell centre positions. However, the formulation used here is a staggered grid approach where the scalars, like pressure is defined at cell centre and vectors like velocity is defined at face centre (or staggered) position.

The Eulerian fluid flowsolver can be coupled 2-ways for momentum transfer or exchange with discrete particle phase or DEM. The switch for this is provided here. 

The Single phase Eulerian can be solved with or without heat transfer (energy balance) and multi-component mass transfer. Both these models can also be coupled with the DEM for heat and mass exchange.

2.2 Setting up

  simulation can be Fixed field, Single phase Eulerian and Single phase Eulerian (Ansys Fluent). 

 

 The select model icon is the first selection from sub-pane which on selection shows the model choices available in the left pane. 

3 Material properties

3.1 Description and theory

The flow behaviour of materials is fundamentally characterised by their physical properties. Therefore, material properties of Eulerian fluids (liquid or gas) and Lagrangian particles (liquid or solid) during CFD flow simulations are extremely important while simulating system flow behavior. The Eulerian Fluid phase can be single component or multiple component. Depending on the choices made in select model for species transport components can be added to Eulerian fluids and their physical properties entered the check boxes.

Similarly, the particles properties are added into in a separate section on left pane depending on if DEM has been selected in ‘Select Model’. The particle flow dramatically affect phenomena such as segregation, wettability, heat and mass transfer, etc within process systems. The fundamental properties of particle material needed for DEM simulations are density, viscosity, thermal conductivity, species diffusivity and heat capacity. Properties like viscosity are relevant only when discrete particles are actually droplets or particles are wet. Similarly, properties like thermal conductivity are relevant when heat transfer is considered or simulations are non-isothermal.

3.2 Setting up

  1. On the Main UI, select ‘Material Properties’ from the left pane. This causes the component materials adding additional tabs in the middle pane to appear. This consists of the buttons ‘Add component’ and ‘Delete component’. 
  2. Using the ‘Add component’ button new components can be added successively which appear one below the other as ‘Component 1’, ‘Component 2’, etc. (Fig. 2.1). 
  3. Under each component, check boxes are provided for adding the ‘Component name’ and ‘Molecular Weight’ of the component. It also has a switch called ‘volatile’ indicating if the component is volatile or not and a button called ‘physical properties.
  4. The ‘volatile’ switch is switch on for components that can vaporise from the Lagrangian or discrete particles into the surroundings. It is typically switched on for components like water that can vaporize and leave the discrete phase. But for components like fertilizers, aluminum, iron oxide, etc. that do not typically vaporize during DEM simulations it need not be switched on.
  5. When the ‘physical properties’ button is clicked (see Fig. 2.2) it opens a tab to enter in the properties ‘density, viscosity, thermal conductivity, species diffusivity and heat capacity’. Note that as discrete particles are in either solid or liquid phase these properties that are to be entered are in one of these phases.
  6. If the volatile switch is on, all the above mentioned (point 5) properties are duplicated to add properties in gaseous state as well. This is essential to evaluate process parameters such as vaporization rate, vapor pressure, etc.
  7. It also provides for a thermodynamic stability factor (Rm[GU1] ) that gives the stability coefficient between the volatile component and non-volatile component.

Fig. 2.1: The component setting in the middle pane.

 

 

 

Fig. 2.2: Insertion of physical properties of individual component without (left) and with volatility (right)

 

 

4. Particle Force Models

4.1 Description and theory

The Discrete element method-based particle tracking is governed by Newton’s law of motion. The dynamic motion of any particle ‘a’, defined vectorially in a 3-D space by position vector ‘ra’ and mass ‘ma’, is determined by the sum of the forces acting on the particle. This balance is provided hereby in Eq. 3.1;

                                                                                                                 (3.1)

Where: \(F_G\) is the gravity force, \(F_C\) is the contact collision force and \(F_D\) is the drag force acting on the particle.

 

4.1.1 Gravity force

Gravity defines the natural influence of gravitation acting on the particle mass. It is given by Eq. (3.2):

                                                                                                          (3.2)

Where;   \( \vec{g} \) is the gravitational force vector defined at the center of mass of particle. 

4.1.2 Collision force

Collision force is the summation of all direct contact collision forces experienced by the particle. The collision forces are treated by the soft sphere approach where a spring-dashpot method is applied. Therefore, any given particle ‘a’ can be simultaneously in collision with multiple particles ‘b’. Thus. the total collision force acting on any particle ‘a’ is sum of collision force with all contact particles ‘b’ in its contact space given by;

                                                                                                 (3.3)

Where,  \(F_{ab} \) is the contact force due to collision between any particle ‘a’ and ‘b’. This individual force defined by the spring-dashpot method is given by;  

                                                                            (3.4)

Where;  \(k_n\) is the normal spring stiffness and  \( \eta_n \) is the normal restitution coefficient.  \( \overrightarrow{n_{ab}} \)  and  \( \overrightarrow{v_{ab}} \) are the positional unit normal vector and relative velocity between given particles ‘a’ and ‘b’, respectively.  \( \delta_n \) is the prevailing contact overlap between the two particles. The normal overlap is given by;

                                                                          (3.5)

Where,  \(\vec{r}_a\) and  \(\vec{r}_b\) represent the position vector for the colliding particles and  \(\vec{r}_a\) and \(\vec{r}_b\) are the radii of respective particles.  

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