EDEM Simulation Run Time

Stephen Cole

Often the time it takes to get results is the number one most significant factor in determining the feasibility of running any simulation.

Reducing time taken doesn’t necessarily mean faster solver speed or faster processors (although of course these things do help). If we plan our projects and make the appropriate assumptions we can get answers within the required time-frame.

Can we model every grain of dust in a mine? No. Can we cut the model down to a few square meters of material, calibrate appropriately to remove the necessity to model the fines/dust and check our designs with a range of operating conditions? Yes.

Images courtesy VR Steel – The reality is we can’t model all the dust and fines but with an appropriate material model different designs can be analysed. As per the image on the right, the material model is suitable to answer the design questions without needing to be overly complicated.

 

Too often we see simulations set-up that will take an unfeasible  amount of time to complete, some initial time planning can ensure that the run times are within reasonable expectations and project deadlines can be hit.

How do we know if our simulation is going to take 1 hour or 1 day or 1 week? The factors that impact the run time are:

1. Time-Step size (usually the Rayleigh Time-Step). Primarily influenced by:

• Particle Size
• Particle Density
• Particle Shear Modulus

The time-step, or calculation cycle, is a fixed value per simulation/material model. The forces acting on each particle are calculated for every cycle. The size of the time-step is critical in that it has to be small enough to ensure stability but large enough to be able to obtain results in a reasonable time.

2. Time it takes your CPU to calculate 1 time-step. Influenced by:

• Number of Particles
• Hardware
• Licenses

The number of particles influence the time in an (almost) linear way, double the number of particles = double the calculation time.  The quicker your computer can calculate the faster you get your results. 

The ability to plan our work and estimate simulation run time is therefore a very important step in any DEM simulation project, the Altair Script and Knowledge library has an estimating simulation runtime spreadsheet and post to aid in EDEM simulation project planning.

Related :

• EDEM Benchmarks
• Particle Shear Modulus
• EDEM Particle Simulation: CUDA GPU and Precision Modes
• How to select a GPU (Graphics Processing Unit) for EDEM
• 10 Common Questions about EDEM GPU Answered
• Estimating EDEM simulation run time

To get started with EDEM:

• 4 steps to accelerate your EDEM learning curve!

 

Dmondal

Hi Stephen,

I have a question regarding the 'Fixed Time Step'.

I am using a breakage model and I need to keep the 'Fixed Time Step' at 20% of the 'Rayleigh Time Step'.

But it is fluctuating. It is going up most of the times. The increase in time step is not at all desirable for my calculation.

Could you please help me how do I fix the 'Fixed Time Step' at the constant value.

 

Thanks

 

Debanga Mondal

Stephen Cole

Dmondal said:

Hi Stephen,

I have a question regarding the 'Fixed Time Step'.

I am using a breakage model and I need to keep the 'Fixed Time Step' at 20% of the 'Rayleigh Time Step'.

But it is fluctuating. It is going up most of the times. The increase in time step is not at all desirable for my calculation.

Could you please help me how do I fix the 'Fixed Time Step' at the constant value.

 

Thanks

 

Debanga Mondal

Hi Dmondal,

 

"Fixed time-step" gives a set time-step value in seconds and this is based on the particle size in the simulation (and factors like the particle stiffness). 

With the breakage model the time-step % will change if the particle size changes, so one option is to set a time step value in seconds which is based on the smallest particle to be created.  It's a linear relationship so if you know the smallest particle is going to be 10x smaller than the particles at t=0 s then you can set a value 10x lower than 20% at t=0 and this should be suitable for the full simulation.

This does mean that you end up running the simulation initially slower than you need to until the particles break, you can choose the "Auto time Step" option which sets the time-step to be fixed at 20% always and takes into account changing particle size.

 

Regards

Stephen 

Dmondal

Stephen Cole_21117 said:

Dmondal said:

Hi Stephen,

I have a question regarding the 'Fixed Time Step'.

I am using a breakage model and I need to keep the 'Fixed Time Step' at 20% of the 'Rayleigh Time Step'.

But it is fluctuating. It is going up most of the times. The increase in time step is not at all desirable for my calculation.

Could you please help me how do I fix the 'Fixed Time Step' at the constant value.

 

Thanks

 

Debanga Mondal

Hi Dmondal,

 

"Fixed time-step" gives a set time-step value in seconds and this is based on the particle size in the simulation (and factors like the particle stiffness). 

With the breakage model the time-step % will change if the particle size changes, so one option is to set a time step value in seconds which is based on the smallest particle to be created.  It's a linear relationship so if you know the smallest particle is going to be 10x smaller than the particles at t=0 s then you can set a value 10x lower than 20% at t=0 and this should be suitable for the full simulation.

This does mean that you end up running the simulation initially slower than you need to until the particles break, you can choose the "Auto time Step" option which sets the time-step to be fixed at 20% always and takes into account changing particle size.

 

Regards

Stephen 

Hi Stephen,

 

Thanks.

"you can choose the "Auto time Step" option which sets the time-step to be fixed at 20% always and takes into account changing particle size."-----You mean that "Auto time Step" chooses 20% of the 'Rayleigh time step' irrespective of any model and any particle size?

 

Regards

 

Dmondal

Stephen Cole

Dmondal said:

Stephen Cole_21117 said:

Dmondal said:

Hi Stephen,

I have a question regarding the 'Fixed Time Step'.

I am using a breakage model and I need to keep the 'Fixed Time Step' at 20% of the 'Rayleigh Time Step'.

But it is fluctuating. It is going up most of the times. The increase in time step is not at all desirable for my calculation.

Could you please help me how do I fix the 'Fixed Time Step' at the constant value.

 

Thanks

 

Debanga Mondal

Hi Dmondal,

 

"Fixed time-step" gives a set time-step value in seconds and this is based on the particle size in the simulation (and factors like the particle stiffness). 

With the breakage model the time-step % will change if the particle size changes, so one option is to set a time step value in seconds which is based on the smallest particle to be created.  It's a linear relationship so if you know the smallest particle is going to be 10x smaller than the particles at t=0 s then you can set a value 10x lower than 20% at t=0 and this should be suitable for the full simulation.

This does mean that you end up running the simulation initially slower than you need to until the particles break, you can choose the "Auto time Step" option which sets the time-step to be fixed at 20% always and takes into account changing particle size.

 

Regards

Stephen 

Hi Stephen,

 

Thanks.

"you can choose the "Auto time Step" option which sets the time-step to be fixed at 20% always and takes into account changing particle size."-----You mean that "Auto time Step" chooses 20% of the 'Rayleigh time step' irrespective of any model and any particle size?

 

Regards

 

Dmondal

Hi, that's correct, Auto time-step always goes to 20% Raleigh time-step for the particles in the simulation any the given point in time.

 

So the "Auto" option will keep the fixed % but change the value (s).

Salma Hassan

Hi Stephen,

Am using EDMEpy to measure the angle of repose and I have to edit the analysis setting in the  Dynamic_angle_of_repose_settings.txt file according to the case.

How I can calculate the time-step ratio?

the total simulation time 1.5second

20% fixed time step of the 'Rayleigh Time Step'

Would you help to define the time-step ratio value?

 

Thank you 

Regards

Salma Nouh

 

 

Stephen Cole

Salma Hassan said:

Hi Stephen,

Am using EDMEpy to measure the angle of repose and I have to edit the analysis setting in the  Dynamic_angle_of_repose_settings.txt file according to the case.

How I can calculate the time-step ratio?

the total simulation time 1.5second

20% fixed time step of the 'Rayleigh Time Step'

Would you help to define the time-step ratio value?

 

Thank you 

Regards

Salma Nouh

 

 

hi Salma, the time step ratio is for the temporal averaging of the simulation results over the start and and time point.  I would generally recommend ratio of 1 unless you have a lot of save data points and the analysis is taking a lot of time.

 

Stephen Cole

Dmondal said:

Hi Stephen,

I have a question regarding the 'Fixed Time Step'.

I am using a breakage model and I need to keep the 'Fixed Time Step' at 20% of the 'Rayleigh Time Step'.

But it is fluctuating. It is going up most of the times. The increase in time step is not at all desirable for my calculation.

Could you please help me how do I fix the 'Fixed Time Step' at the constant value.

 

Thanks

 

Debanga Mondal

Hi Debanga,

 

The fixed time-step refers to the time-step value in s not the % value.  In the breakage model the particle size decreases meaning the Raleigh time-step also decreases.  If you have set a fixed time-step this will remain unchanged but the % value compared to Rayleigh will have changed.

 

20% Rayleigh for a 10 mm particle is a different fixed time-step value to 20% Rayleigh for a 1 mm particle so you can expect the % to change if the particle size is changing.  if you want to keep 20% you can choose "auto time-step" which will mean the time-step value will change but this will always be kept to 20% of the Rayleigh value.

Salma Hassan

Hi Stephen,

Yes, I got it,

I have a few saved data points so I will try the recommended value.

 

Thank You so much

Salma,