Parametric Design using Digital Project

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Parametric Design using Digital Project

• 07 Parametric / Feature based model

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Outline

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

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Geometry Modeling

• Parametric modeling
• Feature based Modeling

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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

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Topology

• Geometric relationship (connectivity) between
  geometric elements

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Constraints

• Mathematical relationships
• Dimension
• Distance
• Parallel
• Angle

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Constraints
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Evaluation

• Validity of constraints

Distance / Dimension
Angle
Horizontal
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Variation

• Changing values, changing constraints,

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Parametric Model vs. Parametric Geometry

• Parametric Model is not always Parametric Geometry

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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

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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.

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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

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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.

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Assembly features
WALL
OPENING
WINDOW
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Assembly features

• When the window is deleted

WALL
OPENING
WINDOW
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Assembly features

• When the wall is deleted

WALL
OPENING
WINDOW
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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?

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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

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Reuse/Variable

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

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Constraints

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

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Parameter in numerical equation

• Relation with others
• Mathematical formula

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High level description

• Object definition in domain specific terms

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Design intent

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

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Parametric Object

• Wall
• Door
• Windows
• Stairs
• Ceiling
• Roof
• Furniture

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Parametric Objects in BIM tools
ArchiCad Bentley Architecture
Revit Digital project
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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

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Limitation in parametric modeling

• Ambiguity
• Complexity

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Ambiguity

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

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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

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Questions?