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Parametric Design using Digital Project

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Title: Parametric Design using Digital Project


1
Parametric Design using Digital Project
  • 07 Parametric / Feature based model

2
Outline
  • What is Parametric Model?
  • What is Feature based model?
  • What is Parametric CAD?

3
Geometry Modeling
  • Parametric modeling
  • Feature based Modeling

4
What is Parametric Model?
  • Use parameters to define model
  • Parameter
  • handles that allow shape modification
    according to certain constraints and that
    automate the propagation of the changes
  • Characteristics of Parametric Model
  • Topology
  • Constraints
  • Evaluation
  • Variation

5
Topology
  • Geometric relationship (connectivity) between
    geometric elements

6
Constraints
  • Mathematical relationships
  • Dimension
  • Distance
  • Parallel
  • Angle

7
Constraints
8
Evaluation
  • Validity of constraints

Distance / Dimension
Angle
Horizontal
9
Variation
  • Changing values, changing constraints,

10
Parametric Model vs. Parametric Geometry
  • Parametric Model is not always Parametric Geometry

11
Needs for Feature based modeling
  • Deficiency of Geometric model for design
  • Microscopic data
  • Edge, faces, curves, solid primitives, set
    operators
  • Holes, sheet thickness,
  • Lack of design intent
  • Change hole diameter?
  • Single level structure
  • Precisely dimensioned geometric entities for
    sketches in design development?
  • Tedious Construction
  • Reconstructing similar object from the scratch

12
What is Feature?
  • Shape property
  • a means of specification of portions of a model
    that are particular interest. It denotes a subset
    of shape primitives (faces, edges, and vertices)
  • Semantic meaning
  • the engineering meaning or significance of the
    geometry of a part or assembly. Feature can be
    thought of as building blocks for product
    definition or for geometric reasoning.

13
Feature Modeling
  • is an approach where high-level modeling
    entities termed features are utilized to
    provide all the above improvements (macroscopic
    (high level) entities, association with high
    level characteristics and constraints, design
    rationale, design intention, reuse) to ordinary
    geometric modeling techniques.
  • Shah Mantyla, Parametric and Feature Based
    CAD/CAM

14
Types of Features
  • Form features
  • Portions of nominal geometry recurring,
    stereotypical shapes
  • Tolerance features
  • Deviations from nominal form/size/location
  • Assembly features
  • Grouping of various feature types to define
    assembly relations, such as mating conditions,
    part relative position and orientation, various
    kinds of fits, and kinematic relations
  • Functional features
  • Sets of features related to specific functions
    may include design intent, non-geometric
    parameters related to function, performance, etc.
  • Material features
  • Material composition, treatment, condition, etc.

15
Assembly features
WALL
OPENING
WINDOW
16
Assembly features
  • When the window is deleted

WALL
OPENING
WINDOW
17
Assembly features
  • When the wall is deleted

WALL
OPENING
WINDOW
18
Functional features
  • When the wall become a curved wall
  • Window should be curved or not?
  • When the wall is moved
  • Window should follow the wall?

19
Features in CIS/2
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Parametric CAD
  • Reuse, variable
  • Constraints
  • Geometric constraints
  • Design structure constraints (part, assembly)
  • Parameter in numerical equation
  • High level description
  • Evaluation
  • Design intent/Knowledge representation/Expertise

24
Reuse/Variable
  • Reuse - Block
  • Using same object
  • Variable - Template
  • Using template object with different parameters

25
Constraints
  • Geometry constraints
  • Points
  • Edge
  • Surface
  • Non geometry constraints
  • Material
  • Hierarchy
  • Under constrainedOver constrained

26
Parameter in numerical equation
  • Relation with others
  • Mathematical formula

27
High level description
  • Object definition in domain specific terms

28
Design intent
  • Dependency
  • Room to wall
  • Wall to Door
  • Grid line
  • Function and Behavior

29
Parametric Object
  • Wall
  • Door
  • Windows
  • Stairs
  • Ceiling
  • Roof
  • Furniture

30
Parametric Objects in BIM tools
ArchiCad Bentley Architecture
Revit Digital project
31
Custom Parametric Object
  • Needs to define your own object
  • New shape, new parametric relationship and
    constraints
  • Constraints between objects
  • Distance,
  • Object based on other objects parameters
  • Wall and window,
  • Automatic evaluation on changes

32
Limitation in parametric modeling
  • Ambiguity
  • Complexity

33
Ambiguity
  • Model can be created in various ways depending on
    design intent
  • Similar to CSG

34
Complexity
  • Number of parameters and relations are easy to
    grow
  • Changes can cause invalid model
  • Beam Column in precast Concrete connection
  • Over 160 parameters and relations
  • Gearbox
  • 665 features
  • 1363 parameters
  • 1291 constraints

35
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