Module 06
From physical structure to analytical model
Abstraction as an engineering decision — what each level keeps, what it throws away, and what it may then be asked.
What this module covers
- Describe abstraction as a choice about which behaviours to discard
- Compute what a line model discards, rather than asserting it is small
- Use Saint-Venant's principle as the licence to simplify locally
- Match a question to the cheapest level of model that answers it honestly
- Estimate the cost of each level before building it
- Write a model-purpose statement that makes the model reviewable
Lessons
A line model has no shear deformation. Here is exactly how much that costs.
Start lesson →Matching the question to the cheapest model that can answer it — and pricing the alternatives first.
Start lesson →Five lines that make a model reviewable — and the order they matter in.
Start lesson →
Module checkpoint
Check what you have taken in
3 questions
Question 1
A frame model of a building is asked for the stress at a beam cope. What happens?
Question 2
A member has a bending deflection of 4.20 mm and a shear deflection of 0.55 mm. What percentage of the true deflection does an Euler–Bernoulli line model omit?
Question 3
A shell model has 111 432 degrees of freedom at a 0.5 m mesh. Approximately how many would it have at a 0.25 m mesh, assuming the frame nodes are negligible?