Computational Engineering / From physical structure to analytical model
The model-purpose statement
Five lines that make a model reviewable — and the order they matter in.
Lesson review: expert verification remains open
This lesson has received a full-context editorial review and a check of its technical explanations. Selected arithmetic has been checked separately. This is not independent engineering sign-off.
Checks needed for project use
- A computational engineering reviewer must check algorithms, convergence claims, statistical assumptions and numerical examples beyond the cases explicitly recorded.
- A computational structural specialist should validate abstraction explorer equations, section assumptions and local-model limits before design use.
- Exact shell-node counts and runtime estimates require the actual mesh/solver; the course numbers remain illustrative.
These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.
Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.
Read the lesson register and outstanding review notesWhy this matters
Record the question the model will answer, its assumptions and exclusions, the intended checks and the decision it supports. This gives another engineer a basis for reviewing both the implementation and the choice of model.
By the end of this lesson you should be able to
- Write the five fields of a model-purpose statement
- Say why the question and the invalidation clause come first
- Recognise a statement that is not yet reviewable
- Connect the statement to the model record of Module 13
A model-purpose statement
Record five aspects of the proposed analysis:
- 1.The engineering question.
- 2.Assumptions or changes that could invalidate its use.
- 3.How the result will be checked.
- 4.Behaviours deliberately excluded.
- 5.The decision the result will support.
Set out the checks before seeing the results where practical. Explain why excluded behaviour is acceptable for the intended decision, and revisit that judgement when inputs or margins change.
Example: a secondary floor beam
The question might be the beam's deflection under a specified serviceability combination. State the span, restraint and section assumptions and identify the applicable deflection criterion. A non-composite model excludes slab participation; whether composite action develops depends on the connection and construction, and its stiffness effect needs calculation.
A simply supported uniform-load bending formula, 5wL⁴/(384EI), can check a model with matching assumptions. It is not an independent check of assumptions that both calculations share. Record exclusions such as connection flexibility or construction-stage effects and assess whether they matter to the proposed beam-depth decision.
Review the statement
An incomplete statement can still be examined, but the reviewer may need to obtain missing context or establish assumptions independently. Listing invalidating conditions helps focus that review; it is not the only way to judge model suitability.
A model may answer several questions if its settings and assumptions support them. State each use clearly rather than relying on the length of a sentence to decide whether one or several models are needed.
Try it
Model purpose statement
Five fields. Fill them in and see what a reviewer could and could not do with what you have written.
One sentence. Without it the model has no subject.
The assumption that, if it turned out otherwise, would overturn the result.
Named before the result exists, so it is not chosen to agree.
Comma-separated. Writing an omission down converts it into a decision.
Keeps the model proportionate to the consequence.
- Fields present
- 0 of 5
- Reviewable?
- no
- Next gap to close
- question
Not reviewable, and not yet a model of anything: no question has been stated, so any result it produces answers something nobody wrote down.
Still missing, in the order they matter
- The question this model exists to answer
- What would make this model wrong
- How the result will be checked
- What is deliberately excluded
- What it will be used to decide
What this shows: The gaps are reported in the order they matter: without a question there is no subject, and without an invalidation clause there is nothing to review.
Worked example
Reviewing an incomplete statement
Given
- A model-purpose statement gives the question, the decision, the exclusions and the check
- It does not say what would make the model wrong
Find
What a reviewer can and cannot do
Practice
A model-purpose statement has the question, the check and the exclusions filled in. How many of the five fields are missing?
Practice
A line model at L/d = 3 omits 7.4 % of the deflection. If the deflection limit is span/250 and the model reports span/260, by what percentage of the reported deflection can it increase before reaching the limit, and does the omitted shear term change the conclusion?
Check yourself
Which field of a model-purpose statement does a reviewer need most, and why?
Summary
- Five fields: question, what would make it wrong, check, exclusions, decision
- The question comes first — without it the model has no subject
- The invalidation clause comes second, and it is the one usually missing
- A model that nothing could disprove is not being used to find anything out
- State every intended use and check that the model assumptions support it
- An exclusion is safe only while the margin exceeds the thing excluded