Discrete Element Modeling

DEM (discrete element method) is a numerical technique that models the interaction between individual particles and boundaries to predict bulk solids behavior.  This tool can easily model moving boundaries and is used to gain better understanding of particle flow dynamics.  The knowledge is then applied to design more efficient equipment, thus improving process efficiency and product quality.

DEM is used to predict:
RockChute_15sec

  • Bulk material flow patterns
  • Bulk material flow rates
  • Force, torque, and power consumption of equipment
  • Impact forces on particles and boundary surface
  • Wear patterns on boundary surface
  • Velocity profiles and dead zones
  • Particle distribution in segregation and blending

Technology

Your process is modeled by our engineers with our in-house developed proprietary code that has been extensively used to solve many handling problems around the world in industries including mining, chemical, agriculture, food processing, pharmaceutical, and power.  These project examples below are proof that our DEM capabilities are a dependable tool to quickly develop the right solutions for your material handling process.

Jenike & Johanson has a passion for particles.  We know that though spheres are computationally attractive, they in many cases will not provide accurate or representative DEM modeling respects.  Look at the simulation below, illustrating the behavior of a sphere vs. clustered spheres vs. polyhedral particles.  Clearly the spheres and clusters do not mimic the true flow behavior of the shaped particles.

As shown below, we can accurately model particle shape using our 3D particle scanner and our polyhedral algorithm in our code.  Computational speed does matter for efficient engineering, thus, using polyhedral algorithms with particles having extraneous facets is not beneficial to the DEM analysis because every facet must undergo tracking and calculations for acceleration, velocity, position, and impact, torque, sliding, etc.  We’ve optimized our DEM code to use polyhedral geometries that reflect you material processing so you get prediction results that can help engineer improvement to your bottom line.
Simplified_Scan_Sequence

DEM examples – blending in a mass flow in-bin tumbler and paddle mixer

This DEM Analysis shows the action of gentle tumble blending of a binary mixture in a mass flow in-bin blender.  DEM analysis allows a design of experiments (DOE) to computationally evaluate factors of fill level, blender rotational speed, layering, and blend time.  Jenike & Johanson also has the ability to run full-scale blending physical models via use of V-blenders and mass flow in-bin tumble blenders to validate our computational modeling.

We have experienced engineers who are knowledgeable and specialize in DEM practices to perform accurate analytical modeling.  We understand the importance of making sure the models are scaled geometrically and calibrated to measured bulk material flow properties.  Our laboratories can measure the relevant flow properties for DEM analyses, such as bulk density, cohesive strength, wall friction (coefficient of sliding friction; both dynamic and static), particle density and shape, and abrasive wear.

In this DEM analysis, Jenike & Johanson engineers modeled mixing of materials in a paddle blender.  Through this analysis we were able to determine fill level, paddle sizes/numbers/angles, as well as paddle shaft speeds.  This model was vital in determining direction of blender selection and operating conditions.


DEM example – hopper filling and discharge of candies

Jenike & Johanson has the modeling technology to model particle shapes during flow through equipment, such as hoppers.  In some DEM codes, only spherical particles are possible, which may not accurately simulate flow of interlocking particle behaviors.  In this demonstration the rounded cylindrical shapes of the candies is vital to the study conclusions.  The accurate shape of the particles greatly affects the bed porosity (packing density) and flow of material.  Note also the particle alignment during discharge whereby the flow path orients the candies in an efficient manner for hopper discharge.


DEM example – handling of chips on a let-down chute

A customer of Jenike & Johanson asked us if we could model chips moving through a process and if attrition could be expected.  We tested the chips to estimate force needed to break them, and then we developed the design of a let-down slide to gently aid in filling of a surge bin.  Note that particle shape is critical to this to this analysis, along with particle-to-surface friction and particle-to particle-friction.  The chips tumble and slide along the surface, whereas spheres would not accurately model the necessary flow behavior.


DEM example – truck dump simulation with iron ore

We have developed an accurate model to replicate stress-dependent cohesion of bulk solids for use in our DEM simulations.  This is critical for representative modeling of materials moving in and out of trucks, flow through hoppers, and in transfer chutes.  Using outdated calibration methods, such as those based on angle of repose or angle of drawdown do not allow scale effects to enter into the simulation, thus, since cohesion is directly affected by pressure (vis-à-vis scale), it is critical that proper material calibration techniques are used.

Note in this truck dump simulation, the iron ore on the left side remains in the truck due to traditional adhesion/cohesion modeling using angle of repose/drawdown angle calibration methods.  Whereas on the right side, the adhesion/cohesive stress dependent model accurately reflects field experience at the client’s mine site.  As we know throughout the field of bulk solids, stress does matter!


As reflected in the data below, flow functions for bauxite and limestone confirm the stress-dependent behavior for the strong majority of bulk solids.  The graph illustrates the “flow functions” for these materials, whereby their unconfined yield strength is plotted as a function of major consolidating stress.  The results show that the simulations with JKR modeling of cohesion do not match experimentally determined flow functions, whereas the J&J cohesion model/algorithm does in a highly accurate manner.

Consolidation Pressure

DEM example – abrasive wear analysis

Handling abrasive bulk materials, such as iron ore, sand, roofing granules, or alumina can rapidly induce erosive wear in transfer chutes, as well as in hoppers.  Jenike & Johanson has the capability to predict abrasive wear profiles in equipment, such as the transfer chute shown below.  Our proprietary DEM code allows determination of forces on a surface, and with input on a material’s wear ratio (a measure of abrasiveness against a surface as a function of force), we can predict how long a surface will last due to sliding wear effects.

Hood_Chute  DEM_Wear_Hood Prediction_Observed_3

DEM example – particle motion on multiple complexity levels

Our DEM code has the ability to model motion on multiple levels of complexity and degrees of freedom.  As shown in the DEM simulation below, the motion is occurring at three separate, but interactive, levels:

  1. The screw (auger) is rotating the flights about its central shaft
  2. The screw is following a sweeping motion around the cone interior surface
  3. The screw shaft is pivoted from the cone’s center to the periphery

This simulation is extremely complex, yet, vital for understanding how a planetary mixer operates.

Experience

When you partner with us, you are working with experts who know how bulk materials flow and how to apply the best DEM technology to your material handling process.  We are able to model your unique system in a matter of days.

At Jenike & Johanson, we use a highly effective and efficient DEM engineering tool, for modeling flow of your iron ore in a chute at 14000 tph, filling a dump truck with 100 t of limestone, or loading odd-shaped candy into a small volume unit package.  We have the tools and engineering knowledge to reduce risk and ensure your project’s success.

Full Service

While working with us, you have the full support of the world’s leading materials handling firm with over a half-century of bulk material experience.  When we model your process using DEM, we provide you with both the data generated from the model and the experience to apply that information in a meaningful way.  Our engineers work with you to find solutions that best meet your operational and business needs.  Learn More.

What’s Next?

Contact us to discuss how we can model your unique process, validate your designs, or develop specialized analytical models that accurately reflect your bulk material application.