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Learn how to simulate a Static Angle of Repose (SAOR) test using Ansys Rocky.

Understanding Static Repose Angle

The Static Angle of Repose (SAOR, a in the image) is a fundamental property of bulk materials that quantifies their natural tendency to form stable piles. It represents the maximum slope angle a granular material can maintain without flowing, reflecting the balance between gravity and internal friction.

By understanding and utilizing the static angle of repose, industries can optimize their bulk material operations, ensuring efficient material flow, safe storage, and effective processing across various applications. The static angle of repose is crucial in bulk material handling and processing for several reasons:

  • Material Characterization
    Provides insights into internal friction and cohesion and helps predict flow behavior of granular materials.

  • Industrial Design and Operations
    Storage facilities (silos, bunkers, stockpiles), material handling equipment (conveyor belts, chutes, hoppers), and process optimization in mining, construction, and pharmaceutical industries.

  • Safety and Stability
    Assesses stability of material piles, and prevents unexpected collapses or slides.

  • Quality Control and Environmental Management
    Indicator of material property changes (e.g., moisture content, particle size distribution), aids in designing wind barriers and dust control measures for outdoor storage.

  • Theoretical Understanding
    Contributes to the physics of granular materials, bridges microscopic particle properties and macroscopic bulk behavior.

  • Simulation and Modeling
    Key calibration parameter in Discrete Element Method (DEM) simulations, and enables accurate modeling of granular material behavior. It will depend on the material condition as shown below.




The material properties of granular materials play a significant role in determining the static repose angle. These properties include:

  • Particle size distribution
    It refers to the range of particle sizes present in the material. Materials with a wide range of particle sizes tend to have a higher static repose angle, as the smaller particles can fill the voids between the larger particles, increasing the overall stability.
    > Ansys Rocky allows different particle sizes at the same time.

  • Particle shape
    The shape of the particles also affects the static repose angle. Angular particles tend to interlock with each other, resulting in a higher static repose angle compared to rounded particles. Additionally, particles with irregular shapes may have different angles of repose depending on their orientation.
    > Ansys Rocky supports different particle shapes (including customized options).

  • Particle density
    It influences the packing arrangement and the interparticle forces. Materials with higher particle densities generally have a higher static repose angle, as the particles are more tightly packed and have stronger interparticle interactions.
    > The material properties can be modified easily in Ansys Rocky.


In the video shown below, you will learn how to set up a Static Angle of Repose test in Ansys Rocky. The model begins with the definition of the physics involved, including gravity effects, the adhesion model, the rolling resistance model, and the numerical softening factor.

The geometries (in STL file format) are imported into the model. A vertical translation is set up for the container cylinder, where the particles are injected using the volumetric inlet option. This approach ensures that the particle bed will already be formed in the cylinder at the start of the simulation.

The particle size and shape are defined, along with the material properties (boundaries and particles) and the material-material interactions. The postprocessing activities demonstrate how to obtain the Static Angle of Repose using both manual and automatic methods (e.g., Python script).

  • Key finding. The average value obtained using the manual method is 39.6 degrees, but it considers only one plane for the calculation and may be susceptible to operator errors. On the other hand, the result provided by the script is 39.9 degrees and includes 36 planes to cover the entire material. The script is quicker and more accurate.


Post by German Ibarra
July 5, 2024