Dear Reader,

I hope you are doing well this week. Here is another newsletter where I reflect on some favourite topics from computational modelling. The content of this newsletter are these:

1. Approaches to implementing PBCs in ABAQUS
2. Behind the Scenes at CM Videos: Community Tab polls
3. Quote of the Week: Are you in the Picture and Brendon Burchard

Approaches for implementing PBCs in ABAQUS

The nature of Periodic Boundary Conditions is such that the user has to define canonical equations based on internal nodes and reference (corner nodes) as shown below. The objective is to transform these canonical equations into feedbacks (kinematic constraints) within a numerical scheme. That basically demands that instructs the FEM solver what to do to the nodes say NA, NB, NC and ND when for example a pure shear loading (shown below) is required with Periodic Boundary Conditions Implemented.

So, the challenge of implementing Periodic Boundary conditions is not trivial and herein lie the difficulty of using PBCs in numerical studies. You find that anyone who has been able to effectively do so often have to resort to developing their interpretation and implementation of such PBCs. In ABAQUS, it is quite common place to use an input multipoint constraint function described as *EQUATION to accomplish this. Here is the typical format of the *EQUATION for say Node NC:

Here are three approaches that I have found common within the community, and will rate then their difficulty index - a measure of how easy or difficult they are to use.

1. The Manual Approach: This is the first approach that is widely understood by users in the community. All you need to do is to manually create the *EQUATIONS above and add that into your ABAQUS input file. You may have to use the ABAQUS CAE constraint GUI to do so but it is quite alright to use a note pad and create the equations following the syntax shown above. Difficulty level = 3 (very hard)
2. The Automatic Approach: This depends on using say an ABAQUS plugin or extra software which will accomplish the same manual approach but without you having to interfer with the identification of nodes, creating of nodal sets and automatic creation of the *EQUATIONS and eventual running of the model. This approach can even extend to imposing the appropriate loading conditions and thene eventual post-processing of the result. Here at CMVideos we have two software that can do so which are: PBCGenLite and PBCGen2D. There is also a widely known code developed by Dr. Sadik Omairey called EasyPBC which has been in the community for a while. Please check the links to these to see more about them. I have also videos on my channel that explore the use of my versions of the automatic codes. Difficulty level = 1 (not hard at all)
3. The Semi-automatic Approach: This is a mid-level approach which is neither automatic nor manual. It is a recent implementation of mine where I offer some of the flavours of automatic writing of the *EQUATIONS but the user will have to guide the software by identifying though manually what the nodal sets and corner nodes are. This has been recently presented in my YouTube Channel and if you want to explore it further, then watch the video below. Difficulty level = 2 (just moderately hard)

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What is apparent from the foregoing is that apply PBCs in numerical schemes especially in ABAQUS is not a trivial exercise but can be incredibly rewarding when you begin to visualize results and generate true micromechanical response without the artefacts of boundary condition type errors.

Behind the Scenes at CM Videos: Community Tab polls

You might have noticed that I have been running a lot of polls on the Community Tab of my YouTube Channel. The plan is to better engage with the community and allow you to steer more directly decisions made on the channel. One of the recent ones was inspired by last week's newsletter where I reflected on what to do when ones journal paper is rejected. I had the idea to maybe make videos on such topics as I know this is the sort of questions/issues you deal with as well as the computational modelling stuff. Below is a snapshot of the poll:

The key feedback from that post that the audience prefer me to talk about wirting literature reviews quickly over how to get it right with journal publishing. Interestingly, I have 2 unlsted videos on the exact topic of literature review which I published for my internal university audience and it gets lots of views from the students.

With the above feedback, I will have to structure and shoot such a video and hopefully you will find it as useful and my current students find such videos. Thanks for the participation on the polls and your lovely comments.

Quote of the Week: Are you in the Picture and Brendon Burchard

This is an intereting quote, taken again from the book I am reading called The Charge by Brendon Bourchard. The quote refers to the necessity of feedback in all you do. With people giving you feedback, you are able to see more clearly and understand how well you are doing. We are not too clever to see every aspect of what we do so some sort of feedback is essential.

Consider the imagery of the quote by Brendon, if you are inside the picture, you will not be able to see the frame that holds the picture. That means, if you are the centre of all eyes, you cannot see the extraneous implications of what you do. You need to voice of another to direct you in how to perceive what you are doing.

The message here is that we should draw from the benefit of having voices of friends, colleagues, supervisors, journal reviewers and even people who disagree with you to speak into your life especially over the research you are doing. This cna only help you better see the boundaries of your ideas (the frame of your picturisque ideas) and then take decisions on how to extend them.

That brings us to the end of yet another newsletter. Thank you for your audience and I will see you next week. Aloha (Bye bye in Hawaiian).