Finite Element Analysis of Continuum Structures in Python

Section 1: Welcome and Preliminaries

In this short introduction section I’ll set out a roadmap for the course and give you a sense of what to expect. This will give you a good idea of what we’re going to cover during this course. I’ll also briefly comment on assumed prerequisite knowledge – in other words what you should have covered before taking this course, and also what you don’t necessarily need to know. Both of the short lectures in this section can be watched below before enrolling – take a look.

Section 2: The Isoparametric Finite Element Method

In this section we’re going to cover the fundamental theory that the course is built on. We’ll start by introducing some fundamental concepts like shape functions and see how we can apply them when deriving the stiffness matrix for a simple bar element. Then we’ll build on this and introduce the 4 node quadrilateral (quad) element. The middle of this section focuses on the strain-displacement matrix which is a key part of determining the element stiffness matrix. We’ll finish up by explaining how to determine the equivalent nodal forces for self-weight and surface forces. We’ll nail down the basic approach and implement a simple example in this section.

Section 3: Gauss-Legendre Numerical Integration

In this section we’re going to introduce the Gauss-Legendre numerical integration scheme. This is a hugely valuable tool for complex integration and reduced the process down to a simple summation of terms. Like any numerical method, we’ll need to be mindful of how the accuracy of the technique is affected. So as well as demonstrating how to implement the scheme, we’re going spend some time understanding convergence and how to ensure accurate results. Once this section is complete – we’ve covered the bulk of the theory necessary to build our solver.

Section 4: Generating Structure and Mesh Data

To really leverage the power of the finite element analysis technique, we need an efficient way of building a structural mesh to analyse. For this task we’re going to use Blender which can be downloaded for free from Blender.org. There are a number of ways we could go about this, but very few options provide us with the convenience and flexibility of Blender. After modelling a simply supported beam we’ll generate a mesh across that structure and then write some code to capture the mesh definition and export it to a csv file. The final step in this section is to bring this data into our Jupyter Notebook – so we’ll write code that imports this data into our Jupyter Notebook ready for processing in the next section.

Section 5: Implementing the Isoparametric Finite Element Method

This is the section where it all comes together – all of the earlier theory and the mesh data we generated in the previous section. In this section we’re going to build the core of our solver. This means we’ll build the structure stiffness matrix and solve the system of equations that is the mathematical representation of our structure. We’ll round out the section with a validation exercise and compare the deflections from our finite element analysis with those from a simple Euler-Bernoulli deflection calculation. Completing this section is a key milestone in our development as we’ll have implemented the core solver.

Section 6: Visualising the Strain and Stress Fields

This section is about mining for the additional information embedded within our model. We’re going to focus on building stress contour maps that show us how the different stresses vary throughout the structure. Before working through this section, you might find it helpful to review the stress analysis lectures in the appendix. Particularly if you’re not familiar with the concept of normal and shear strains and stresses at a point and the purpose of stress transformation equations. We’ll finish this section with another validation exercise and compare the stress distributions from our finite element analysis with normal and shear stress distributions derived from fundamental beam theory.

Section 7: Implementing Area and Volume Forces

In this section we’re going to implement the ability for our code to simulate the influence of area and body forces. We’ve already implemented both of these calculations for a single element in section 2 – here we’ll just scale this up for our entire structure. We’ll start with body forces or self-weight. After this we’ll move on to surface forces. For surface forces we’ll start off in Blender by identifying the location and magnitude of our surface forces. Once these are defined in Blender, we’ll export this information into our notebook and set about building the functionality. Once this section is complete we’re about 75-80% complete and have a capable solver on our hands.

Section 8: Principal Stresses and von Mises stress:

This section is really about adding bells and whistles or polish to our solver in the form of Principal Stress and von Mises stress distribution plots. We’ll start off with a brief review of principal stresses. If you want to dig a little deeper on the topic before taking this section – jump down to the appendix where I cover principal stresses in more detail. After reviewing principal stress theory – we’ll calculate and then visualise the principal stresses and orientation of the principal planes. After this we’ll take a break from coding and discuss the von Mises failure theory. Once we have the concepts and key equations in hand, we’ll use our principal stress fields to calculate the von Mises stress field.

Section 9: Generating and Analysing Complex Meshes:

The power of the finite element method is its ability to accommodate non-standard or irregular structural shapes. But this requires us to mesh complex 2D geometries, so we need a more robust way of generating the finite element mesh for our structures. We’ll introduce two tools to achieve this in this section and make some amendments to our export code to work with our new more complex meshes. We’re going to base this section around an arched-viaduct structure. This will give us enough complexity to stress test our code and highlight areas that require attention before we can apply our code to more complex geometries.

Appendix: Fundamentals of 2D Stress Analysis and Mohr’s Circle:

To get the most from this course you need to have an understanding of 2D stress analysis – this way our stress contour plots will make a lot more sense. If you’re not familiar with this topic or you only have a vague recollection of the theory from dim and distant past – no problem! I’ve included an appendix, which is basically a whole second course on the topic of 2D stress analysis. In this appendix course, I’ll cover the fundamentals of normal stress, shear stress, principal stresses, principal planes and I’ll even discuss Mohr’s circle which is not strictly necessary – but still good to know!

• Students and professional engineers who’ve studied matrix analysis methods and now want to learn how to analyse continuum structures (2D rather than linear structural elements).
• Students and professional engineers who want to better understand what’s happening behind the scenes of their ‘black box’ commercial finite element software. 
• Students and professional engineers who’ve taken some or all of our previous direct stiffness method courses (see bundle discount at the bottom of this page) and want to continue learning and expanding their abilities.
• Anyone who wants to leverage programming as a tool for structural analysis or within their day-to-day study or work.

The codes developed in this course are for educational purposes only and are not tested or certified for use beyond the educational scope of this course. Always employ your own engineering judgement first and foremost, regardless of what the computer says!