Parametric Modeling. Presentation Overview Types of computer design parameters Review of geometric...
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Transcript of Parametric Modeling. Presentation Overview Types of computer design parameters Review of geometric...
![Page 1: Parametric Modeling. Presentation Overview Types of computer design parameters Review of geometric constraints Parametric constraints Creation of parametric.](https://reader036.fdocuments.us/reader036/viewer/2022062516/56649dd45503460f94acba35/html5/thumbnails/1.jpg)
Parametric Modeling
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Presentation Overview
• Types of computer design parameters
• Review of geometric constraints
• Parametric constraints
• Creation of parametric equations that maintain geometric proportions
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Parameters
• 3D CAD programs use parameters to define a model of a design solution
• A parameter is a property of a system whose value determines how the system will behave
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Types of Parameters
• 3D CAD programs typically have three types of user-defined parameters:– Geometric Constraints (review)– Parametric Constraints– Assembly Constraints (discussed later)
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Review of Geometric Constraints
• Non-numerical geometric relationships that the user assigns to sketched elements.
• Examples– Making two lines parallel– Making two arcs concentric– Making a line horizontal
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Review of Geometric Constraints
Perpendicular, Parallel, Tangent, Coincident, Concentric, Collinear
Horizontal, Vertical, Equal, Fix, Symmetric
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Parametric Constraints
• Are used to control the size and location of geometry
• May take the form of simple numeric values such as 2 inches or 25 degrees
• May take the form of abstract algebraic formulas such as (d2*d0)/d5
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Parametric Constraints
• Can be tied to spreadsheets that allow for more complex mathematical formulas
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Parametric Equations
• Algebraic equations that use variables can be substituted for individual numeric values
• The resulting dimensional value may change, but the formula will remain constant
d7 = ((d2*d0)/d5)+2 in.
Symbols: + - * /add subtract multiply divide
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Parametric Equations
• Scenario: A child’s proportions are similar to those of an adult
• A chair could be dimensioned so that changing the seat height uniformly scales all other chair features
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Each dimension is given a designation, starting with d0.
Parametric Equations
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d1d0
All location and size dimensions are given designations. Geometric constraints, such as the perpendicular and parallel edges, do not have designations.
Parametric Equations
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• Extrusion and taper angle values are also given designations
Parametric Equations
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Parametric Equations
• Problem– The Overall Plate Depth (d0) and the Overall
Plate Width (d1) must maintain a constant ratio
– If the plate were scaled up or down, the overall dimensions would remain proportional to each other.
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Parametric Equations
• If the Overall Plate Depth and Overall Plate Width must maintain a constant ratio, then the current dimensional values can be used to establish the ratio
5 in.
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Parametric Equations
• If the Overall Plate Depth and Overall Plate Width must maintain a constant ratio, then the current dimensional values can be used to establish the ratio
5 : 3 or 5/3 or 1.666673 : 5 or 3/5 or .6
Note: unit-less values
5 in.
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Parametric Equations
• If dimension d0 is the only linear dimension that will have a numeric value, then it must be used to develop an equation that will maintain proportionality
5 in.
d1 = d0 in.*(5/3) d1 = d0 in./(3/5)or
5 in. = 3 in. x 1.66667 5 in. = 3 in. .6
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Parametric Equations
• Both equations work, so either may be used in the CAD program as a parametric equation for dimension d1 to maintain proportionality
5 in.
d1 = d0 in.*(5/3) d1 = d0 in./(3/5)or
5 in. = 3 in. x 1.66667 5 in. = 3 in. .6
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Parametric Equations
• Each parametric equation must tie back directly (e.g., d0/2) or indirectly (e.g., d1*.8 = (d0*(5/3))*.8) to a dimension that has a true value. In this case dimension d0 has a true value of 3 in.