NUMERICAL COUPLING BETWEEN DEM (DISCRETE ELEMENT METHOD) AND FEA (FINITE ELEMENTS ANALYSIS). Daniel Schiochet Nasato - ESSS Prof. Dr. José Roberto Nunhez Unicamp Dr. Nicolas Spogis - ESSS Fabiano Nunes Diesel - ESSS
Agenda Objectives DEM Method EDEM ANSYS Coupling Validation and real case Conclusions
Objectives Develop an 1-way coupling between Discrete Element Method (DEM) and Finite Element Method (FEM). Propose a numerical validation to evaluate the method accuracy. Simulate a transfer chute using the developed method to solve a real problem.
DEM Method Governing equations for the translational and rotational motion of particle i with mass m i and moment of inertia I i : v i and ω i are the translational and angular velocities of particle i, F c ij and M ij are the contact force and torque acting on particle i by particle j or walls, F nc ik is the noncontact force acting on particle i by particle k or other sources, F f i is the particle fluid interaction force on particle i, F g i is the gravitational force.
DEM Contact Detection To detect contacts between particles and structure, EDEM splits the geometry in triangular surface mesh (StL file format), a 3-dimensional surface geometry; The surface is tessellated or broken down logically into a series of small triangles (facets); Each facet is described by a perpendicular direction and three points representing the vertices (corners) of the triangle.
EDEM-ANSYS Coupling EDEM was used as Discrete Element Method (DEM) tool and ANSYS was used as Finite Element Method (FEM) tool.
EDEM-ANSYS 1-way coupling Setup ANSYS Model Run EDEM Model Create Named Surface Export EDEM Loads Interpolate Loads Python Script And ANSYS APDL Solve and Evaluate ANSYS Results
EDEM-ANSYS coupling methods Developed 1-Way DEM-FEA Coupling - Steady State Static Structural Analysis 1-Way DEM-FEA Coupling - Transient Transient Structural Analysis Under development 2-Way DEM-FEA Coupling - Transient Force Displacement
Interpolation Method Load is transferred from EDEM to ANSYS using a conservative interpolation; Each element face is divided into n number of IP faces, where n is the number of nodes on the face; IP faces are converted onto a two-dimensional polygon; Polygons on the sending side are intersected with the IP polygons on the receiving side; The polygon intersection creates many overlapped areas used to transfer loads between the two sides.
Interpolation Method During interpolation, the total force balance over the surface is preserved. For loss less data transfer between particle and structural code, both numerical models must be coincident in space
Validation Tests It was built a small box with 1x1x1m in EDEM and it was created 2000 particles with 40mm diameter and 2500kg/m 3 density; It was performed 3s of simulation to ensure that particles have no velocity in Y direction; Total forces (X, Y and Z) and surface mesh nodes position are exported from EDEM in a single time step. Force on Y direction calculated on EDEM was compared with analytical results.
Validation Tests Test 1 - ANSYS coarse mesh, EDEM coarse mesh Test 2 - ANSYS intermediate mesh, EDEM coarse mesh Test 3 - ANSYS refined mesh, EDEM coarse mesh Analytical EDEM force Test 1 - Coarse Test 2 - Intermediate Test 3 - Refined Force Y (N) 1643,8 1645,8 1575,2 1617,6 1663,5 Error % 0,1 4,3 1,7 1,1
Industrial Application Geometry directly imported from CAD on ACIS (.sat) format. Simulation: Conveyor belt Transfer chute Vibrating screens Dynamics: Sinusoidal translation Sinusoidal rotation Moving plane (for belt)
EDEM Results
Screen force distribution High impact velocities zones (up to 7 m/s) on screen. Wear and structural problems. High forces on chute discharge.
EDEM-ANSYS coupling The developed scripts and macros automatically interpolates EDEM forces (normal and tangential) on the structural elements.
Static Structural Analysis Total Deformation Equivalent Strain The Static Analysis performed shows stresses & Strains under the yield limit OK
Conclusions EDEM ANSYS Coupling showed good results; For numerical validation error was smaller than 5%; EDEM ANSYS Coupling showed great potential to be used as a commercial tool. Interpolation takes a few minutes to be done for big simulations cases.