Computer-aided design Introduction

Introduction Design  problem solving Specification of dimensions, materials, and operations to structures to meet functional requirements Design is usually as cyclic

1.Begin with a specification of functional requirements and an initial design specifications 2.Analysis is used to predict the performance 3.The performance is then compared to the functional requirements 4.Redesign ….

Analysis Redesign 創造、經驗導向、 決策 理論公式、數值 計算、設計規範

地形、地質查勘 可行性規劃 初步設計 分析 細部設計 規範檢核 繪圖 施工營造 維護檢修 N.G. OK

CAD The subject of the computer-aided design (CAD) concerns the productivity tools that facilitate the design process CAD can be useful in both parts of the design cycle, both analysis and synthesis (redesign) Providing efficient ways to help the designer revise the design

TYPES OF DESIGN Innovation,invention  the initial concept of the structure Conceptual design  components, materials, function Configuration design  number and arrangement of components Parametric design  values for all key design parameters are set Detail design (component design)  produce the final, complete description of each components

THE ROLE OF THE COMPUTER IN DESIGN Calculation  the oldest use of CAD Bookkeeping / record keeping  characterized by complex relationships between information and the management of large volumes of numbers Visualization  computer can be used to transfer information visually Networking  sharing and transferring information, concurrent engineering

HISTORICAL BACKGROUND Early –Finite-element method –Simulation of dynamic systems –Optimization Later –Graphics –Geometry Most recently –Algebraic manipulation –Spreadsheets –Combinations (electronic notebooks)

calculation Record keeping visualization optimization Finite element method simulation geometry graphics spreadsheets Algebraic manipulation

CHARACTERISTICS OF DESIGN Iterative vs. direct –Numerical methods –Design problem lead to parameter optimization in an iterative fashion –Iterative method concerning with convergence criteria and way toobtain the initil starting point –Algorithms used in computer graphic are mostly direct

Synthesis (initial design) vs. redesign –Redesign follows iterative paradigm (concerning with convergence) –The generation of the stating point is usually neglected in redesign (the previous design serves as a starting point) –Initial design most starting by hand rather than via CAD

Incremental design –Problems involving redesign can be also be called incremental design –Focusing more on design changes than the underlying design

Remapping –Design process involving changes that is sweeping than incremental –Involving increasing levels of detail and information –Proceeding from relatively simple to relatively complex models with more information content

Hierarchy –Design on problem frequently can be characterized by a hierarchy structure –An organization of problem –Hierarchy is always context-dependent

Decomposition and recursion –Decomposition is a solution procedure where the initial problem is replaced by a set of simultaneous smaller problems (a hierarchy tree) –The key characteristic of decomposition is that the subproblems are independent –Recursion is appropriate for a system that is a collection of subproblems of a subsystem is itself a collection of subsystems –Recursion is fundamentally different from iteration. In an iterative approach a fully defined solution is changed sequentially to a better solution

Self-reference –Advanced design techniques and software development tools must be considered in the design of design system

DESIGN PARADIGMS Design as search –Design consists of a set of variables, each with a set of acceptable values –Design process simply involving choosing between these competitive designs

Design as optimization –Design has been characterized as optimization –Optimization is search, but search within a tightly structured design space –Optimization can take place within continuous space and /or within discrete space

Design as compilation –Algorithm or programs must be coded in high- level language and mapped (compiled) into a lower-level language Design as constraint satisfaction –Design is the process of determining values that satisfy all constraints

COMPONENTS OF CAD Numerical methods Graphics Geometry Interface package Database manager Data structures toolbox

calculation Record keeping visualization numerical methods library Graphics library Data structures toolbox Database manager Geometry package Interface package

A COMPREHENSIVE LIBRARY INCLUDES THESE FUNCTIONS Function manipulation –Interpolation –Extrapolation –Integration –Differentiation –Root finding –Least squares –Spline fitting

A COMPREHENSIVE LIBRARY INCLUDES THESE FUNCTIONS (CONT.) Matrix manipulation –Multiplication –Decomposition (inversion) –Eigenvalue extraction Integration of differential equations Optimization algorithms

Interface package actually consists of these four separate software libraries –Window manager –Menu manager –Interactive-device manager –Help text manager