Mastering the Iterative Design Process in Engineering
The Iterative Design Process
The iterative design process is one of the most traditional processes for the design of any engineering component or system. It is used widely throughout many industries. The process is not very efficient! With the advent of more streamlined digital workflows, we aim to cut out excess iterations from our process. The majority of your projects will likely follow this process.
Stages of the Iterative Design Process
Initial Ideation → Planning → Implementation →
Requirements Definition → Design & Analysis →
Deployment → Testing → Evaluation → (loop back to start)
Where Do I Start?
How many of you have been given a job to do and wondered, “Where do I start?” What’s the answer?
Project Fundamentals: Scope, Time, and Budget
Scope / Requirements • Time • Budget
Scope and Requirements
This should always be obvious—often it is not. It is often your job as an engineer to fully define the scope of your task. This is why specifications are very important, as they allow us to know if we have achieved what we set out to do. All three aspects of the triangle can affect the overall quality.
Real-World Project Examples
Project 1 – Queen Elizabeth Class Carrier
Time: July 2015; Time actual – Feb 2018
Cost: £3.5 billion; Cost actual – £6.1 billion
Scope: 70,600 tonnes; 26 knots (30 mph); 250–9,000 troops; capable of carrying more than 70 aircraft.
Project 2 – Tyne Tunnel 2
Time: Mar 2004 – Jan 2012; Time actual – Mar 2004 – Nov 2011
Cost: £139 million; Cost actual – £260 million
Scope: Build a second Tyne tunnel between Jarrow and Howden; refurbish existing tunnel.
Project 3 – Aidan’s Dissertation
Time: 9 months; Time actual – 8 months 3 weeks
Cost: £0; Cost actual – £0
Scope: Demonstrate the capability of ANSYS Fluent in predicting turbulent flow behavior and wind noise induced by air traveling around a car wing mirror.
Time Planning
How do you plan time for a project? Use Project Timelines, Gantt Charts, and Progress Reviews. (Time planning is revisited in a later lecture.)
Budget Estimation
How do I know how much a project will cost? Most engineering projects follow the same budgetary trend from beginning to end. Typical cost categories include Man-hours, Materials, Logistics, and Overheads. All must be estimated early to set a budget. Once estimated, record all costs against the project budget.
Bill of Materials (BoM)
An engineering BoM tracks all materials required for a project. It should include:
- Description of component
- Quantity ordered
- Supplier
- Item or order numbers/details
- Price per unit
- Total cost
- Lead time
Design Specification
A detailed document that defines the requirements, constraints, and criteria a design solution must meet. It acts as a blueprint for designers, engineers, and manufacturers, ensuring everyone works toward the same objectives.
Key Characteristics
- Clear Requirements: Functionality, performance, features.
- Constraints: Budget, time, safety, regulations, materials.
- Quantifiable Details: Dimensions, tolerances, weight, power, etc.
- User-Centered: Usability, accessibility, safety.
- Testable Criteria: How success is measured.
Why Design Specifications Matter
They prevent miscommunication, provide an evaluation basis, manage trade-offs, and support quality assurance and compliance. It is the first thing created in the design process, informed by user research and standards, and continuously refined as prototypes are tested; it is a living document that evolves with the project.
Examples of Requirements
- Chair: Must support 120 kg, weigh < 8 kg, stackable, fire-safe.
- Mobile App: Load < 3 s, work offline, support iOS & Android.
- Bridge: Span 200 m, withstand 120 km/h wind, use local materials.
Case Study: Bridge Launch Mechanism
Specification: What happens when you don’t stick to the requirements? “A camel is a horse designed by a committee.”
The Design Stage
Focus: Translate insights (user needs, requirements, constraints) into solutions.
Output: Initial concepts, models, and plans for prototypes.
Core Goals
- Generate creative solutions.
- Ensure alignment with user needs, technical feasibility, and business goals.
- Balance innovation with practical constraints.
Core Activities
Brainstorming & Ideation → Sketching & Wireframing → Digital Design → Storyboarding → Information Architecture (CAD models, BoMs).
Collaboration and Communication
Engage stakeholders (users, customers, business leaders). Use visual artifacts like wireframes, mock-ups, and diagrams. Encourage early feedback to avoid costly redesigns.
Analysis, Testing, and Prototyping
Analysis
Initial checks on design (hand calculations, FEA, CFD). Analysis is cheap—software cost is less than prototype cost. It allows many analyses and quick redesigns. This includes manufacturing simulation to assess tooling wear, costs, and bespoke tooling needs.
Testing vs. Analysis
Testing involves physical prototypes; it is more expensive but provides real-world validation for complex scenarios that cannot be simulated. It is useful for user experience and feedback.
Why Build Prototypes?
To test specific variables, observe real behavior, and gauge user feedback. However, prototype production is costly, as each new part requires manufacturing.
Combat Bridge Launcher Example
Considerations: Bridge weight, mud load, wind/water loading, stowage, manufacturability, assembly, systems interaction, health & safety, and user proofing.
How to Save Time and Money
- Make fewer prototypes.
- Address issues at the analysis stage if possible.
- Fail fast, learn early, and improve cheaply.
Prototyping Levels
- Low-Fidelity: Sketches, paper mock-ups, storyboards (quick and cheap).
- Medium-Fidelity: Digital models, simple wood/card mock-ups (balanced).
- High-Fidelity: Polished, functional, and close to final (for usability testing).
Evaluation and Deployment
Evaluation
Evaluate test results. Did everything work? If not, why? Verify usability, accessibility, and effectiveness. Identify strengths, weaknesses, and improvement areas. Compare performance to requirements and success criteria to provide evidence for design decisions.
Evaluation Methods
- Usability Testing: Observe users.
- Surveys & Interviews: Gather feedback.
- Heuristic Evaluation: Expert review.
- Analytics & Metrics: Task success rate, time on task, error rate.
Share findings clearly with designers and stakeholders. Treat evaluation as a learning opportunity, not a pass/fail.
Deployment and Maintenance
Engineer responsibility continues after launch. Maintenance is essential—have a plan. Examples include a toothbrush (cost, service life, maintenance plan) and a Rolls Royce jet engine (cost, service life, maintenance plan). Remember disposal too!
Engineering Reality and Project Success
Bad Project: Too much time building (expensive), not enough design checking → more errors → more evaluation time.
Good Project: More time on design & analysis → fewer manufacturing issues, less testing time, cheaper overall.
Engineers like to make things, but we must design and analyze first! Some engineers distrust analysis software due to a lack of training—be the driving force for change.
Rule: As few iterations as possible. Fail fast and fail cheap.
Diagram References
- Iterative loop diagram: Circular flow of stages.
- Combat Bridge Launcher: Illustration of loads and constraints.
- Prototype fidelity scale: Low → Medium → High.
- Evaluation cycle: Test → Assess → Refine → Repeat.
That’s the full raw content for Section 1. Would you like me to continue with Section 2: Engineering Drawings next?