ME 6501 COlVIPUTER AIDED DESIGNFi I1h Semester

Mechanical Engineering(Reguiations2013 )

Unit - 2PART-A

l. Generate the conical surface obtained by rotation of the line segment Al3 around the z-axis with A (LOJ) and B (7.0,7) (N/D - 15)

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3. What are the limitations of Hermite curve? (M/.I- 16)

4. What are the advantages and disadvantages of wire frame modeling? (M/J·- 16)

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5. State advantages of Bczicr curves. (NID - 16)

6. Why B-rep modeling approach arc widely followed than CSG approach? (N/D - 16)

Unit- 2PART -B

1. (a) Briefly explain the different schemes used to generate a solid model.(NiD - 15) (16)

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6. (b) (i) Explain in detail Bsrep solid modeling approach. (N/D -- 16) (8)

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Geometry Topology It is the actual dimensions that defines the entities of the object

It is the visible geometry and graphical

information at user point of view

It is also called as metric information

It is the connectivity and associativity of the object entities

It is the non-graphical relational information

stored in the solid model database in user point

of view

It is also called as combinatorial structure

ME6501 – Computer Aided Design

Unit – II

Part – A

1. What is Bezier surface?

A tensor product Bezier surface is an extension of the Bezier curve in two parametric directions u and v.

Bezier surface allows only global control of the surface. Bezier surface is formed as the Cartesian product

of the blending functions of two orthogonal Bezier curves and is defined by a set of control points. A two-

dimensional Bezier surface can be defined as a parametric surface where the position of a point has a

function of the parametric coordinates u, v.

2. What are the characteristics of B-spline surface? A rectangular set of data or control points creates the surface. It is the general surface as Bezier surface but with the advantage of permitting local control of the surface. This set forms the vertices of the

characteristic polyhedron that approximates and controls the shape of the resulting surface. The degree of

the surface is independent of the number of control points and continuity is automatically maintained

throughout the surface by virtue of the form of blending functions.

3. What are the limitations of Hermite Curve? The curve follows the cubic polynomial and hence the number of control points is only three. With three

control points, complicated shapes cannot be produced. Hence it has its limitations in constructing.

4. What do mean by intersection in surface? The intersection problem involving surfaces is complex and non-linear in nature. It depends on whether it

is a surface/curve or surface/surface interaction as well as on the representation, parametric or implicit of

the surface or curves.

5. Differentiate Geometry and topology.

6. What are the advantages and disadvantages of wire frame modeling Advantages: 1. Hidden line can be visible with dotted line in wire frame modeling. 2. Interior parts can

be visible.

Disadvantages: 1. Subsequent process of assembly or features cannot be done in wire frame modeling.

7. Define domain in representation schemes. The domain of a representation scheme is the class of objects that the scheme can represent or it is the

geometric coverage of the scheme. The parts or entities under the domain representation are governed by

domain characteristics both geometric and visual representation.

8. How Validity checks are achieved in representation schemes? The validity checks are achieved in three ways: a) Test the resulting database via given algorithm b) Build

checks into the scheme generator or design scheme elements c) Manipulate via given syntax. Syntax

language called as backend codes are written specifically to perform validity check. Error postulates are

employed to eliminate degree of deviation and autocorrected.

Analytic Curves Synthetic Curves The Analytic curves are defines by analytic equations.

Analytic curves are easy in computation but

not flexible for designers Lines, conics are analytic curves

The Synthetic curves are defines by the set of data points or control points

Synthetic curves are hard in computation but

very flexible to designers in making new models

Splines, Bezier curves are synthetic curves

9. What are rational curves importances? A rational curve is defined by algebraic ratio of two polynomials. A parametric curve in homogeneous

form is referred to as a rational curve. They draw their theories from projective geometry. Importance is

under projective transformation that is the perspective image of a rational curve is a rational curve.

Space curve: F(u) = ( x(u), y(u), z(u), w(u) )

Plane curve : F(u) = ( x(u), y(u), w(u) )

Where u is a parameter in some closed interval [a, b]

10. Distinguish Analytic and Synthetic curve

11. What do you mean by Sculptured surface? Sculptured surfaces are used in geometric modeling to describe all sorts of bendy things like aero plane wings, car bodies, gas-turbine blades, ship's hulls and so on that can't be described by simple curved

surfaces such as cylinders and cones.. These complex surfaces are known as sculptured or free-form

surfaces.

12. What is surface segmentation? Surface segmentation is a reparametrization or parameter transformation of the surface while keeping the degree of its polynomial in u and v unchanged. Efficient segmentation of globally optimal surfaces

representing object boundaries in volumetric data sets is important and challenging in many medical

image analysis applications. Surface segmentation is employed in BIW (Body in White) automotive

modeling

13. Differentiate between analytical curves, interpolated curves, and approximated curves.

Analytical curve: This type of curve can be represented by a simple mathematical equation such as circle or ellipse. They have fixed form and cannot be modified to achieve a shape that violates the mathematical

equation.

Interpolated curve: An interpolated curve is drawn by interpolating the given data points, dictated by the

given data points. These curves have some limited flexibility in shape creation, dictated by the data

points.

Approximated curves: These curves provide the most flexibility in drawing curves of very complex

shapes. The model of a curved automobile fender can be easily created with the help of approximated

curves and surfaces.

14. Differentiate CSG and B-Rep Models. CSG refers to Constructive Solid Geometry. It uses standard primitives like Block, Cylinder, Cone, Cube

etc. shapes and solid model can be generated by using Boolean operations of Addition, Subtraction,

Union, Intersection etc.

In B-Rep or Boundary Representation Models, Vertex, edges, faces, surfaces will be defined using

Euler’s equation and building the blocks with representation of these entities.