EDEM CFD Coupling Interface: Programming Guide

Transcription

1 EDEM CFD Coupling Interface: Programming Guide EDEM 2.4, Revision 1

2 Copyrights and Trademarks Copyright 2012 DEM Solutions. All rights reserved. Information in this document is subject to change without notice. The software described in this document is furnished under a license agreement or nondisclosure agreement. The software may be used or copied only in accordance with the terms of those agreements. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or any means electronic or mechanical, including photocopying and recording for any purpose other than the purchaser s personal use without the written permission. DEM Solutions 49 Queen Street Edinburgh EH2 3NH UK EDEM incorporates CADfix translation technology. CADfix is owned, supplied by and Copyright TranscenData Europe Limited, All Rights Reserved. This software is based in part on the work of the Independent JPEG Group. EDEM uses the Mersenne Twister random number generator, Copyright , Makoto Matsumoto and Takuji Nishimura, All rights reserved. EDEM includes CGNS (CFD General Notation System) software. See the Online Help for full copyright notice. EDEM and Particle Factory are registered trademarks of DEM Solutions. EDEM CFD Coupling Interface is a Trademark of DEM Solutions. All other brands or product names are the property of the respective owners. 1

3 Contents INTRODUCTION... 3 COUPLED SIMULATION OVERVIEW... 4 EDEM CFD COUPLING PACKAGING... 5 THE SIMULATION SEQUENCE... 6 RETRIEVING PARTICLE DATA FROM EDEM... 7 USING SAMPLE POINTS TO REPRESENT PARTICLES... 8 SETTING EXTERNAL FORCE AND TORQUE ON PARTICLES... 9 REGISTERING AND USING CUSTOM PARTICLE PROPERTIES Registering a New Custom Particle Property Using Custom Particle Properties APPENDIX A CUSTOM PARTICLE PROPERTY UNIT TYPES

4 Introduction EDEM is the leading DE (Discrete Element) simulation software platform designed for the simulation and analysis of bulk particle handling and processing equipment in a wide variety of industries. This programming guide provides an overview of how to use the EDEM CFD Coupling Interface to couple with a generic CFD code. Additional information for the data manipulation methods is also provided and can be found in the EDEM CFD Coupling Interface class, ICfdCoupling. The CFD Coupling Interface enables users to construct a coupled fluid - particle simulation between a CFD package and EDEM (Figure 1). It enables two independent programs to operate synchronously, sharing data to create a single coupled simulation. The CFD Coupling Interface adopts TCP/IP client server architecture which uses messages for communication between the two separate programs. Users may implement a new coupling with a CFD solver using C++, to program a solution utilizing the CFD Coupling Interface. The CFD Coupling Interface is an addition to EDEM and can only be used when its license is available. Figure 1: Communication between EDEM and a CFD package using the CFD Coupling Interface 3

5 Coupled EDEM-CFD Simulation Overview EDEM integrates fluid drag forces and torques into the particle simulation on an individual particle level. When EDEM performs a step of the simulation the external forces act upon the particles in addition to any gravitational or collision forces. Figure 2 depicts the stages of the EDEM simulation loop and the point at which it interacts with the CFD solver. For completeness, components of the EDEM Application Programming Interface (API), such as the Particle Factory, Contact Model, and Particle Body Forces, have also been shown at their interaction stages with the EDEM solver loop. Figure 2: The EDEM simulation cycle with CFD simulation included During a coupled EDEM CFD simulation, the CFD solver and EDEM simulate, in an alternating manner, with the CFD solver first creating a fluid field into which particles are introduced. The CFD solver will simulate ahead in time and then pass any equired data across to EDEM for it to be allowed to simulate to the same point in time. This alternating pattern continues until the simulation time has reached the specified end time, shown in Figure 3. Due to the explicit time integration methods implemented in EDEM, it is common that multiple time-steps are required to simulate the same time period as a single time-step of a CFD simulation. Therefore time-steps between the two solvers are potentially different, however the simulation-steps are the same. 4

6 EDEM simulation t 0 t 1 1 Time-step 1 Simulation-step t 1 t 2 t 2 t 3 t 0 t 1 CFD simulation Real time t 1 t 2 t 2 t 3 t 3 1 Simulation-step Simulation time Figure 3: The alternating sequence of a coupled simulation Each time the CFD Coupling Interface sends a message to EDEM it blocks any further messages from being sent until EDEM returns a response. This synchronous behavior effectively pauses the CFD solver until EDEM has calculated the required simulation step. EDEM CFD Coupling Interface Packaging The EDEM CFD Coupling Interface comprises client and server components. The server component resides within EDEM and the client component is to be used by the thirdparty code to interact with EDEM. The EDEM Coupling Client (Figure 4) interface class provides users with a number of methods for setup, simulation and data control. With the methods provided in ICfdCoupling.h particle data can be retrieved from EDEM so that external forces and torques are applied to the particles. In addition to the quantities of force and torque, users can register, retrieve and update custom particle properties. The ability to manipulate custom properties from the CFD Coupling Interface allows users to interact with custom EDEM API models and any custom particle properties that they might incorporate. Figure 4: Overview of the packaging of the EDEM CFD Coupling Interface 5

7 The Simulation Sequence The sequence of a coupled simulation is shown in Figure 5, with the CFD Coupling Interface relaying information on CFD forces and particle data between the two solvers. Once a coupling is successfully initialized between EDEM and the CFD solver, EDEM is ready to start simulating (Steps 1-3). Simulation in EDEM will commence when the CFD solver sends fluid forces to apply to the particles in the simulation (Steps 5, 7, 9). If this is the first step of a simulation, and there are no particles to apply forces to, then this can be omitted before starting the EDEM simulation-step. Figure 5: The coupled simulation sequence After EDEM completes the simulation-step, it is possible to retrieve the new or updated particle data from the simulation. This data is then returned to the CFD solver (Steps 6, 8, 10), in order to update the CFD solver s variables and simulation. Any custom properties included in the simulation can be updated and retrieved following a similar sequence at the beginning and end of each EDEM simulation-step. 6

8 Retrieving Particle Data from EDEM EDEM CFD Coupling Programming Guide Particle data can be retrieved from EDEM using the getparticledata method. This method will return the data for all the particles currently in the simulation. The operation is usually performed at the end of the EDEM simulation step, after the position of the particles has been updated. An important factor to remember when using this method is that it returns a pointer to the start of the particle data array. It is the user s responsibility to delete the array of particle data when it is no longer required. The particle data does not represent particles as mono- or multi-spherical. Instead, their position is calculated at their centroid and volume is returned as a scalar value. More detailed information about particle shapes can be calculated from the particle sample points. An explanation of their operation can be found in the Using Sample Points to Represent Particles section (see page 8). Particle data in the array is organized in order of particle type. Particle type data is structured in order of particle index. However, particle indices may change between simulation time-steps and therefore the index cannot be relied upon as a method for persistent particle tracking. Instead, persistent tracking can be accomplished through the unique integer identifier (ID) found in each particle data set, which persists throughout the entirety of the simulation. If the user wishes to perform operations on all of the particles of one type, independently of the particle ID, then it is more efficient to do so by accessing the array of particle data by index. For ID-dependant operations, the particle ID must be checked to ensure the correct particle is being manipulated. Particle IDs can be managed between simulation-steps through implementation of a map structure n-1 n... n+m-1... n+m+ p-1 Type 0 Type 1 Type 2 Figure 6: Diagram of the particle data array 1 An example of such an implementation exists in the source code of the Ansys Fluent coupling example. 7

9 The above diagram shows the particle data array from a simulation with three types (0, 1 and 2). The data of each type is organized such that particle data is accessible using the index. In this case, particles of Type 0 occupy array indices 0 to (n-1), while Type 1 particles occupy the indices n to (n+m-1) and finally particles of Type 2 occupy indices (n+m) to (n+m+p-1). The number of particle types and particles belonging to each type can be queried at any time using the getnumparticletypes and getnumparticles methods from the EDEM CFD Coupling Interface. Using Sample Points to Represent Particles The drag models used to calculate particle drag forces must also take into account the volume of particles found in each cell of the mesh. To achieve this the user may implement their own solution using custom properties or any other method. However, EDEM provides another easy to use representation of particle volume. The representation of volume provided by the EDEM Coupling Interface is based on multiple sample points, generated using the Monte Carlo method. EDEM takes regular sample points within the bounding box of a particle and keeps the points that lie within the particles bounding surfaces as in Figure 7. Figure 7: Sample points within a particle Each point is checked to determine which CFD mesh cell it lies within. The solid volume fraction within a particular mesh cell is, therefore, the percentage of the number of sample points that lie within that mesh cell as, given by: ε = 1 ε = s particles nc V N p Where n c is the number of sample points contained within the mesh cell of particle p and N the total number of sample points of the particle. V p is the volume of the particle. Sample points are generated for each of the particle types defined in the simulation. Using the position, orientation and scaling of the individual particles, the precise coordinates for the points representing each particle can be calculated. Provided no additional particle types are later added to the simulation, sample points need only be collected once, at the start of a simulation. The method used to request sample points from EDEM is collectsamplepoints. The sample points for a particle type are returned as an array of 3D values (C3dValue objects) of size n. The user is responsible for allocating and deleting memory to store the sample points for the simulation. 8

10 Setting External Force and Torque on Particles Particles can have external forces and torques, calculated by the external CFD solver, applied to them before EDEM executes a simulation-step. This is achieved using the setforceandtorque method provided by the interface class, ICfdCoupling. Separate arrays exist for both force and torque. The arrays are both created as serialized 3D vectors that match the order of the particle data. Because of this, it is important that up-to-date particle data is obtained and any force or torque is applied to the particles during one simulation-step, before EDEM is allowed to simulate again Type 0 Type 1 Type nn+ m... 3n+2 Type 0 Figure 8: Particle data array for force or torque For a particle type 0 of a multi-particle type simulation, the array for either force or torque should be constructed in the manner shown above. The index for the force applied to particle n starts at position(3n) and finishes at position (3n+2) of the array. Therefore, the correct index for the force applied to particle 0 starts at 0 and finishes at 2. Additional particle types in the simulation are ordered after the first particle type, in the same manner as the example for particle data. 9

11 Registering and Using Custom Particle Properties Registering a New Custom Particle Property Custom properties can be created by the user to store new variables that represent particle properties that EDEM does not support natively. Creation of new custom properties allows manipulation both with the CFD Coupling Interface and the custom EDEM API models. In order to register a custom property for use in a new EDEM deck, the following information is required: 1. A string containing the name This allows the custom property to be identified in the property manager within EDEM. 2. The number of property elements The number of elements that make up a property for a particle. For example, a scalar property would have one property element and a 3D vector value would have three. 3. Unit type An integer identifying the unit type of the new property. (See Appendix A for a full list of unit types). 4. Initial value The initial value used to initialize the custom property. 5. The data type This determines the variable data type used to store the data. Currently the only supported type is double and it is selected using the default value supplied (zero). When a custom property has been registered, a unique integer custom property index will be returned. When using the get and set methods, this index may be used to identify the property throughout the simulation process. If the property has already been registered it will not be duplicated and the index of the existing property is returned. Using Custom Particle Properties Custom particle properties are stored in arrays that match the particle data array. During the simulation, there are two methods available for interaction with the custom properties, the getvalueforproperty and the setvalueforproperty methods. These methods can be used between simulation-steps to retrieve and update the custom properties. The specific custom properties are accessed using their unique property index. As previously noted, data returned in an array using the getvalueforproperty must be deleted by the user when no longer required. When custom property data is returned from EDEM it is returned in an order that matches the particle data, described in section Retrieving Particle Data from EDEM. It is again important that the particle data and custom property data are retrieved after any new simulation-step and any updates are performed. 10

12 Custom properties with more than one element have the elements stored sequentially, in the same manner as the force and torque arrays. Therefore, a two element property for a single particle type simulation would be structured as follows:... Type 0 Figure 9: Particle data array for a custom property A value for a custom property is set by creating an array following the structure described. It is then possible to update the custom property values in EDEM using the setvalueforcustomprop. The user must then delete the array that they have created to perform the custom property update. 11

13 Appendix A Custom Particle Property Unit Types Unit Type Identifier SI Units Other 0 Unknown unit None 1 Unitless Acceleration 2 m/s 2 Angle 3 Rad Angular Acceleration 4 rad/s 2 Angular Velocity 5 rad/s Density 6 kg/m Energy 7 J Work Function 8 J Force 9 N Charge 10 C Length 11 M Mass 12 Kg Moment of Inertia 13 kg/m 2 Shear Modulus 14 Pa Time 15 S Torque 16 Nm Velocity 17 m/s Volume 18 m 3 Frequency 19 Hz Temperature 20 K 12

14 Heat Flux 21 W Stiffness 22 N/m Stress 23 Pa Mass Flow 24 kg/s Stiffness per Unit Area 25 N/m 3 13