ME 481 Engineering Modeling Prof. Clark Radcliffe Mechanical Engineering

Why do Modeling? Design is a Problem Solving Process Key to the Process is Problem Definition Design Problem Definition states Specifications of Desired Performance Models Predict Performance The Goal: To predict design performance for comparison against definition specifications

Why do Modeling? Engineering Designs are Typically Systems of Many Components Each Component Needs a Separate Subdesign Each Subdesign has Separate “Roll down” of Performance Specifications to Meet Predicting Performance of Components Predicts Performance of the System Then Check: Does System meet Specifications?

Model Types Cost: Money and Time Safety: Pinch Points, Impact, Crush, Ingestion, Temperature, etc … Geometry: Size, Connections, Aesthetics, … Speed: Response Time, Production, … Energy and Power: Operating, Supply, … Reliability: MTBF, Service Life, Strength, … And Many others …

How to Start Sketches are a great start One of the earliest creative artifacts Break up system into components Identify Component Connections “Roll Down” System Specifications to Component Specifications Identify Inputs and Outputs at Connections Block Diagrams can be useful here Select a Model that Predicts The Performance Required for each Specification

Some Example Models Scale Models: Graphical Models: Useful to evaluate geometry Graphical Models: Now replacing some scale models Mathematical Models: A basis for quantitative performance prediction Physical Models use power and energy Prototype Models: To test performance of near final design THE most expensive model

System Modeling Break up System into subsystems Vehicle System Body and Structure Interior and Controls Drivetrain

Break up Subsystems into Components System Modeling Break up Subsystems into Components Drivetrain Subsystem Wheels and Tires Engine Transmission

Drivetrain Example Build Subsystem from Components Drivetrain components linked to show connectivity Drivetrain Transmission Engine Wheels and Tires Drivetrain

System Modeling System is connected subsystems (connections define model type) Vehicle Interior and Controls Body and Structure Drivetrain

System Conceptual Model Shows Components, connections and Systems Organizes Information, Expertise … SAE Formula Car project does it … you can too Provides Information Interfaces where critical connections are defined Helps Identify Critical Parts and Paths

Model Individual Components What design performance specification do you need to evaluate? Develop a model to predict that performance, Put together a subsystem model, and Build a system performance model. Finally predict system performance and Compare with specification.

Modeling Question: What’s the maximum vehicle acceleration? Start with Components… Parameter: Tire Diameter D Wheels and Tires

Modeling Question: What’s the maximum vehicle acceleration? Assemble Subsystem Models… Parameters: Tire Diameter D, Gear Ratio N Drivetrain Transmission Engine Wheels and Tires Engine Torque Map

Modeling Question: What’s the maximum vehicle acceleration? Assemble System Model… Parameters: Body mass mbody, Interior mass mint , Drag fdrag(vveh) Interior and Controls Body and Structure Drivetrain Vehicle

System Modeling Form System from subsystems Result is a system model to be solved either analytically or numerically Iterate on vehicle velocity to find max accel Vehicle

Engineering Modeling involves: Identifying a complex physical process Breaking it up into simple physical component processes Representing the simple physical processes by equations Assembling components into system model Predicting performance for the system

ME 481 Examples Motor Cycle Oil Change Adapter Refrigerator Thermal Storage System 18

Motor Cycle Oil Change Adapter Frame plus motorcycle components Need forces at components connections Write force balances for components assume weights Assemble system force balance equations Solve for connection forces Pipe beam calculation to determine wall thickness of structural components Calculate weights Iterate to solution convergence Calculate weight & cost 19

Thermal Storage System Assume amount of phase change material (PCM) Use thermal circuit to determine heat gain Use latent heat with heat gain to find required mass of PCM Iterate to solution convergence 20

Iteration is common Tools: Excel’s Solver Loaded from Distribution or Internet Matlab Optimization Functions Built in and ready in DECS labs

Sources of Help Books Notes The Web (but be careful) Experts Faculty, other students, Professional Advisor, Staff