[EDEM] How can i use particle custom property and contact custom property at the same time?

KJHSNU

Introduction
Hello, I am currently developing a customized contact model using the API.
For reference, I based my code on the Customized Bonding V2 model shared in the EDEM discussion forum.

link : https://community.altair.com/discussion/35365/edem-api-contact-model-example-updated-bond-model-example-of-customisation-of-bond-model#latest

That model only used a contact custom property. However, I would like to introduce and use a particle custom property called SELFFRICTION.

The purpose of this custom property is to check whether a specific calculation has already been performed for each particle.

Detailed Description
I want to define a particle custom property named SelfFriction, which has no units like a bond status indicator to represent certain states.

At each time step, forces "between" particles are calculated.

The forces for each particle can be divided into two types: Self Friction and Coupled Friction.

• Self Friction must be calculated only once per particle per time step (similar to a body force).
• Coupled Friction must be calculated between all connected particles at every time step.

To implement this, I used the fact that the delta value of a custom property (the value for the next time step) is reset to the default value of 0.0 at the beginning of each time step. I then used this mechanism to mark which particles have already had their self friction computed.

Problem
The problem I am facing is as follows:
When I run my code, the simulation stops with an error indicating that it is accessing an invalid pointer. After several tests, I discovered that this issue occurs because the pointer for the particle custom property is not created correctly. To summarize, my main problem is that I do not know how to use and assign both particle custom properties and contact custom properties simultaneously.

Questions

1. How can I properly create both particle custom properties and contact custom properties, manage them with the API manager, and ultimately access their "value" and "delta" correctly in the calculateForce function?
2. At each time step, is the delta value of a custom property indeed initialized to 0.0, as defined in the getDetailsForProperty function with oss << 0.0?
3. Is there a way to declare and use an array that maintains values within a single time step but resets when the time step changes? If this is possible, I would not need to use a particle custom property at all.

Thank for advance!

Here's my codes.

ContactAPI.zip

Renan

Hi @KJHSNU,

The getDetailsForProperty method can be used to set the custom property initial value, not the value of the delta. From the API documentation:

Also, deltas are used to update property values and are reset at every timestep. This means that your check in line 405 (if (m_elem1_SelfFrictionDelta && m_elem1_SelfFrictionDelta[0] == 0.0)) will always be true and the calculation that follows will be performed at every timestep. The right way to check if the calculation was already performed is to check if the custom property value, not the delta, has changed.

I'd recommend you check out the Collision Metrics API. In that API, the collision relative velocity is calculated only once for each collision. You could apply the same logic to your code.

However, if you want to perform a calculation only once per particle per timestep, the best way to accomplish this is using a particle body force. Otherwise, even if you use a custom property, the same calculation may be performed multiple times in a single timestep if you are running your simulation on a GPU/multiple CPU cores.

Best regards,

Renan