Computer aided design and analysis

computer aided design and applications and computer aided design examples
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Dr.TomHunt,United States,Teacher
Published Date:23-07-2017
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16.810 16.810 Engineering Design and Rapid Prototyping Engineering Design and Rapid Prototyping Lecture 4 Computer Aided Design (CAD) Instructor(s) Prof. Olivier de Weck January 6, 2005 Plan for Today „ CAD Lecture (ca. 50 min) „ CAD History, Background „ Some theory of geometrical representation „ SolidWorks Introduction (ca. 40 min) „ Led by TA „ Follow along step-by-step „ Start creating your own CAD model of your part (ca. 30 min) „ Work in teams of two „ Use hand sketch as starting point 16.810 2 Course Concept today 16.810 3 Course Flow Diagram (2005) Learning/Review Deliverables Problem statement Design Intro / Sketch (A) Hand Sketch Hand sketching (B) Initial Airfoil CAD design CAD Introduction FEM/Solid Mechanics FEM/Xfoil analysis (C) Initial Design Xfoil Airfoil Analysis optional Optimization Design Optimization Revise CAD design CAM Manufacturing (D) Final Design Training Parts Fabrication (E) Completed Wing Structural & Wind Assembly Tunnel Testing Assembly (F) Test Data & Test Cost Estimation Final Review (G) CDR Package 16.810 4 What is CAD? „ Computer Aided Design (CAD) „ A set of methods and tools to assist product designers in „ Creating a geometrical representation of the artifacts they are designing „ Dimensioning, Tolerancing „ Configuration Management (Changes) „ Archiving „ Exchanging part and assembly information between teams, organizations „ Feeding subsequent design steps „ Analysis (CAE) „ Manufacturing (CAM) „ …by means of a computer system. 16.810 5 Basic Elements of a CAD System Main System Output Devices Input Devices Computer CAD Software Keyboard Hard Disk Database Mouse Network Ref: menzelus.com Printer CAD keyboard Plotter Templates Space Ball Human Designer 16.810 6 Brief History of CAD „ 1957 PRONTO (Dr. Hanratty) – first commercial numerical- control programming system „ 1960 SKETCHPAD (MIT Lincoln Labs) „ Early 1960’s industrial developments „ General Motors – DAC (Design Automated by Computer) „ McDonnell Douglas – CADD „ Early technological developments „ Vector-display technology „ Light-pens for input „ Patterns of lines rendering (first 2D only) „ 1967 Dr. Jason R Lemon founds SDRC in Cincinnati „ 1979 Boeing, General Electric and NIST develop IGES (Initial Graphic Exchange Standards), e.g. for transfer of NURBS curves „ Since 1981: numerous commercial programs „ Source: http://mbinfo.mbdesign.net/CAD-History.htm 16.810 7 Major Benefits of CAD „ Productivity (=Speed) Increase „ Automation of repeated tasks „ Doesn’t necessarily increase creativity „ Insert standard parts (e.g. fasteners) from database „ Supports Changeability „ Don’t have to redo entire drawing with each change „ EO – “Engineering Orders” „ Keep track of previous design iterations „ Communication „ With other teams/engineers, e.g. manufacturing, suppliers „ With other applications (CAE/FEM, CAM) „ Marketing, realistic product rendering „ Accurate, high quality drawings „ Caution: CAD Systems produce errors with hidden lines etc… „ Some limited Analysis „ Mass Properties (Mass, Inertia) „ Collisions between parts, clearances 16.810 8 Generic CAD Process Start Engineering Sketch Settings Units, Grid (snap), … 3D 2D dim Construct Basic - Create lines, radii, part Solids contours, chamfers = extrude, rotate Boolean Operations Add cutouts & holes (add, subtract, …) Annotations Dimensioning CAD file Drawing (dxf) Verification Output x.x IGES file 16.810 9 Example CAD A/C Assembly Loft Nacelle „ Boeing (sample) parts „ A/C structural assembly „ 2 decks „ 3 frames FWD Decks „ Keel „ Loft included to show interface/stayout zone to Kee A/C l „ All Boeing parts in Catia file format „ Files imported into SolidWorks by converting to IGES format (Loft not shown) Frames Aft Decks 16.810 10 Vector versus Raster Graphics Raster Graphics .bmp -raw data format „ Grid of pixels „ No relationships between pixels „ Resolution, e.g. 72 dpi (dots per inch) „ Each pixel has color, e.g. 8-bit image has 256 colors 16.810 12 Vector Graphics .emf format CAD Systems use vector graphics Most common interface file: IGES „ Object Oriented „ relationship between pixels captured „ describes both (anchor/control) points and lines between them „ Easier scaling & editing 16.810 13 Major CAD Software Products „ AutoCAD (Autodesk) Æ mainly for PC „ Pro Engineer (PTC) „ SolidWorks (Dassault Systems) „ CATIA (IBM/Dassault Systems) „ Unigraphics (UGS) „ I-DEAS (SDRC) 16.810 14 Some CAD-Theory Geometrical representation (1) Parametric Curve Equation vs. Nonparametric Curve Equation (2) Various curves (some mathematics ) -Hermite Curve -BezierCurve -B-Spline Curve - NURBS (Nonuniform Rational B-Spline) Curves Applications: CAD, FEM, Design Optimization 16.810 15 Curve Equations Two types of equations for curve representation (1) Parametric equation (u or θ ) x, y, z coordinates are related by a parametric variable (2) Nonparametric equation x, y, z coordinates are related by a function Example: Circle (2-D) Parametric equation xR= cos θ, y= R sin θ (0 ≤θ≤ 2π ) Nonparametric equation 2 2 2 x + y − R = 0 (Implicit nonparametric form) 2 2 (Explicit nonparametric form) y =± R − x 16.810 16 Curve Equations Two types of curve equations (1) Parametric equation Point on 2-D curve: p= () xu y() u Point on 3-D surface: p= () xu y() uz() u u : parametric variable and independent variable yf= () x : 2-D , z= f (x, y) : 3-D (2) Nonparametric equation : Parametric equation Which is better for CAD/CAE? It also is good for xR= cos θ , y= R sin θ (0 ≤θ≤ 2π ) calculating the points at a certain ∆θ interval along a curve 2 2 2 x +y− R = 0 2 2 y=± R− x 16.810 17 Parametric Equations – Advantages over nonparametric forms 1. Parametric equations usually offer more degrees of freedom for controlling the shape of curves and surfaces than do nonparametric forms. e.g. Cubic curve 3 2 Parametric curve: xa= u + bu + c+u d 3 2 ye= u + fu + g+x h 3 2 Nonparametric curve: ya= x + bx + c+x d 2. Parametric forms readily handle infinite slopes dy dy / du =⇒ dx / du=0 indicates dy/ dx =∞ dx dx / du 3. Transformation can be performed directly on parametric equations e.g. Translation in x-dir. 3 2 Parametric curve: xa= u + bu + c+u+d x 0 3 2 ye= u + fu + g+x h 3 2 Nonparametric curve: y=a(xx− )+b(xx − ) +c(xx− ) +d 0 0 0 16.810 18 Hermite Curves Most of the equations for curves used in CAD software are of degree 3, because two curves of degree 3 guarantees 2nd derivative continuity at the connection point Æ The two curves appear to one. Use of a higher degree causes small oscillations in curve and requires heavy computation. u Simplest parametric equation of degree 3 P() u= () xuy(u)z(u) 2 3 END START = a+ a u+ a u+ a u (0≤ u≤ 1) 0 1 2 3 (u= 1) (u= 0) aa , , a , a : Algebraic vector coefficients 0 1 2 3 The curve’s shape change cannot be intuitively anticipated from changes in these values 16.810 19 Hermite Curves 2 3 P() u = a + au + au + au (0 ≤ u≤ 1) 0 1 2 3 Instead of algebraic coefficients, let’s use the position vectors and the tangent vectors at the two end points Position vector at starting point: P= P(0) = a 0 0 u Position vector at end point: P= P(1) = a+ a+ a+ a 1 0 1 2 3 ′ P ′ 0 P P 1 0 P ′ 1 ′ Tangent vector at starting point: P= P (0) = a 0 1 START END ′ (u= 0) ′ Tangent vector at end point: P= P (1) = a + 2a+ 3a 1 1 2 3 (u= 1) P ⎡ ⎤ 0 Blending functions ⎢⎥ P 1 ⎢⎥ 2 3 2 3 2 3 2 3 : Hermit curve P() u =− 1 3u + 2u 3 u − 2 u− u 2+uu − uu + ⎢⎥ ′ P 0 ⎢ ⎥ ⎢ ⎥ ′ P ⎣ 1 ⎦ No algebraic coefficients ′′ PP , , P , P : Geometric coefficients 0 0 1 1 The curve’s shape change can be intuitively anticipated from changes in these values 16.810 20 Effect of tangent vectors on the curve’s shape P ⎡ ⎤ P(0) ⎡⎤ 0 ⎢ ⎥ ⎢ ⎥ P P (1) 1 ⎢ ⎥ ⎢ ⎥ = : Geometric coefficient matrix 1 1 ⎡ ⎤ ⎢ ⎥ ⎢ ⎥ Is this what you really wanted? ′ ′ P P (0) 0 ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ 5 1 ⎢ ⎥ ⎢ ⎥ ′ ′ P (1) ⎢ ⎥ P ⎣ ⎦ ⎣ 1 ⎦ 11 ⎡ ⎤ ⎢ ⎥ 13 13 ⎢ ⎥ 51 ⎢ ⎥ Geometric coefficient matrix ⎢ ⎥ 13 -13 ⎣ ⎦ controls the shape of the curve ⎢ ⎥ 55 11 ⎡ ⎤ ⎢ ⎥ ⎢ ⎥ 5-5 ⎣ ⎦ 51 ⎢ ⎥ 11 ⎡ ⎤ ⎢ ⎥ 22 ⎢ ⎥ ⎢ ⎥ 51 2-2 ⎢ ⎥ ⎣ ⎦ ⎢ ⎥ 11 11 ⎡⎤ ⎢ ⎥ ⎢⎥ 1-1 51 ⎣ ⎦ ⎢ ⎥ ⎢⎥ 40 ⎢⎥ 40 START (1, 1) END (5, 1) ⎣⎦ u ( u = 0) ( u = 1) dy dy / du 0 = == 0 dx dx / du 4 16.810 21