COMPUTER AIDED DESIGN 2 MARK WITH ANSWER

1. ME6501- COMPUTER AIDED DESIGN (CAD)
IMPORTANT TWO MARK QUESTIONS WITH ANSWERS
UNIT 1 TO 5
Unit -1(FUNDAMENTALS OF COMPUTER GRAPHICS)
1. What is the design process? Mention the steps involved in Shigley’s
model for the design process.
Design process is an approach for breaking down a large project into
manageable portions.
 Recognition of need
 Definition of Problem
 Synthesis
 Analysis and Optimization
 Evaluation
 Presentation
2. Mention any four applications of computer aided design in Mechanical
Engineering.
 Computer-aided engineering (CAE) and Finite element analysis (FEA)
 Computer-aided manufacturing (CAM) including instructions to
Computer Numerical Control (CNC) machines
 Photorealistic rendering and Motion Simulation.
 Document management and revision control using Product Data
Management
3. List and differentiate the types of 2D geometric transformations.
 Translation- moves an object to a different position on the screen.
 Rotation - rotate the object at particular angle θ (theta) from its
origin.
 Scaling - change the size of an object
 Reflection - mirror image of original object
 Shear - slants the shape of an object
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AL AMEEN ENGINEERING COLLEGE
DEPARTMENT OF MECHANICAL ENGINEERING

2. 4. What is Homogeneous Coordinate
 In homogeneous coordinates, we add a third coordinate to a point.
Instead of being represented by a pair of numbers (x,y), each point
is represented by a triple (x,y,W).
 Two sets of homogeneous coordinates (x,y,W) and (x',y',W')
represent the same point if one is a multiple of the other. Thus,
(4,5,6) and (8,10,12) are the same points represented by different
coordinate triples.
 "That is, each point has many different homogeneous coordinate
representations. Also one of the homogeneous coordinates must be
nonzero: (0,0,0) is not allowed. If the W coordinate is nonzero, we
can divide by it: (x,y,W) represents the same point as (x/W, y/W,
1).
 When W is nonzero, we normally do this division, and the numbers
x/W and y/W are called the cartesian coordinates of the
homogeneous point. The points with W=0 are called points of
infinity.
5. What do you mean by synthesis of design?
 Synthesis is a scheme to generate a possible way the product work.
 It will also be called as concept design.
 In the design process a number of concepts will be identified and
then the best concept is chosen for further development.
6. List the various stages in the life cycle of a product
 Developing the product concept
 Evolving the design
 Engineering the Product
 Manufacturing the product
 Marketing and
 servicing
7. Define Clipping.
Any procedure that identifies those portions of a picture that are
clipping.
Types of Clipping
 Point Clipping
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either inside or outside of a specified region or space is known as

3.  Line clipping
 Area Clipping
 Text Clipping
8. What is viewing transformations?
 The mapping of a part of a world-coordinate scene to device
coordinates is referred to as a viewing transformation.
Sometimes the two-dimensional viewing transformation is simply
referred to as the window-to-viewport transformation or the
windowing transformation.
 A world-coordinate area selected for display is called a window.
 An area on a display device to which a window is mapped is
called a viewport.
 The window defines what is to be viewed; the viewport defines
where it is to be displayed.
Unit - 2 (GEOMETRIC MODELING)
1. What are the limitations of Hermite Curves?
 Hermite curve is limited to 3rd
degree polynomial therefore the
curve is
 quite stiff.
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4.  Hard to guess behavior between 2 defined points for arbitrary end
point slopes.
 Hermite curves are designed using two control points and tangent
segments at each control point.
 It can be seen from the Action script demo that it is difficult to
determine how long to make a tangent handle in order to produce a
desired shape.
2. State advantages of Bezier Curve
 Very Simple
 3 points uniquely determine a parabola.
 It’s easy to calculate points.
 The numerical algorithm is stable. (i.e. given reasonable input,
the algorithm won’t blow up.)

3. Classification of wireframe entities.
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5. 4. Differentiate between analytical curves, approximated curves and
interpolated curves.
 Analytic Curves are points, lines, arcs and circles,
fillets and chamfers, and conics (ellipses, parabolas,
and hyperbolas)
5. Comparison of CSG and B-rep.
6. Why B-rep modelling approach is widely followed than CSG approach?
 Boundary representation is more flexible and has a much richer
operation set.
 In addition to the Boolean operations, B-rep has extrusion (or
sweeping), chamfer, blending, drafting, shelling, tweaking and
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6. other operations which make use of these.
7. What are the advantages and disadvantages of wire frame modelling?
Advantages of Wireframe model:
1. Simple to construct
2. Designer needs little training
3. System needs little memory
4. Take less manipulation time
5. Retreiving and editing can be done easy
6. Consumes less time
7. Best suitable for manipualations as orthographic isometric and
perspective views.
Disadvantages of Wireframe model:
1. Image causes confusion
2. Cannot get required indormation from this model
3. Hidden line removal features not available
4. Not possible for volume and mass calculation, NC programming
cross sectioning etc
5. Not suitable to represent complex solids
Unit - 3 (VISUAL REALISM)
1. List out various visualization approaches.
 Hidden Line Removal – Priority Algorithm , Area Oriented
Algorithm
o Visibility Techniques- Minimax test, Containment test,
Surface test, Computing silhouettes, Edge intersections,
Segment comparisons, Homogeneity test
 Hidden Surface removal – Z-buffer algorithm, Warnock’s
algorithm
 Hidden Solid removal – ray tracing algorithm
2. List the shading models.
 Diffuse reflection
 Specular reflection
 Ambient light
3. What are silhouettes?
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7. A set of edges that separates visible faces from invisible faces of an object
with respect to a given viewing direction is called silhouette edges.
4. What is meant by visible surface determination in 3D computer graphics.
 In 3D computer graphics surface determination (also known as
hidden surface removal (HSR), occlusion culling (OC) or visible
surface determination (VSD))
 It is the process used to determine which surfaces and parts of
surfaces are not visible from a certain viewpoint.
 A hidden surface determination algorithm is a solution to the
visibility problem, which was one of the first major problems in the
field of 3D computer graphics.
5. Name the different types of light sources.
 Ambient light - Intensity is the same at all points (no direction)
 Point source - given only by point
 Distant light - given only by direction
 Spotlight - from source in direction
 Light source described by a luminance -Each color is described
separately
 Directional lighting
6. Define key framing.
 Keyframing is the process of assigning a specific parameter value
to an object at a specific point in time.
 For example, if you want a title to change from green to blue over
time, you would set two keyframes at two different points in time.
The first one would define the text’s color as green, and the second
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8. keyframe would set the color to blue.
 The computer then automatically fills in the missing frames by
smoothly interpolating between those positions and change
smoothly from green to blue.
7. Define interpolative shading. List the two methods used for interpolative
shading.
Interpolative shading is to avoid computing the full lighting equation
at each pixel by interpolating quantites at the vertices of the faces.
There are two methods used for interpolative shading:
Gouraud Shading - The radiance values are computed at the
vertices and then linearly interpolated within each triangle.
Phong shading - The normal values at each vertex are linearly
interpolated within each triangle, and the radiance is computed at
each pixel.
Gouraud shading is more efficient, but Phong shading is more a
ccurate.
8. Define Gouraud Shading.
 It is an intensity interpolation scheme.
 It renders a polygon surface by linearly interpolating intensity values across
the surface.
 Intensity values for each polygon are matched with the values of adjacent
polygons along the common edges, thus eliminating the intensity
discontinuities that can occur in flat shading.
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9. For Gouraud shading, the intensity at point
4 is linearly interpolated from the
intensities at vertices 1 and 2.
The intensity at point 5 is linearly
interpolated from intensities at vertices 2
and 3.
An interior point p is then assigned an
intensity value that is linearly interpolated
from intensities at positions 4 and 5.
9. Define Phong Shading.
 A more accurate method for rendering a polygon surface is to
interpolate normal vectors, and then apply the illumination
model to each surface point.
 This method, developed by Phong Bui Tuong, is called Phong
shading, or normal- vector interpolation shading.
 It displays more realistic highlights on a surface and greatly
reduces the Mach-band effect.
Figure: Interpolation of surface normals along a polygon edge
10. Define RGB color model.
The Red, Green, Blue (RGB) cube uses a Cartesian coordinate method to
create any color from the three RGB basics. In the RGB cube, black is at
the starting point and represented by (0,0,0) and white is represented end
point by (1,1,1).
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10. 11. What are the improvements brought by Gouraud Shading compared with
other shading techniques?
 It removes the intensity discontinuities existing in constant shading
model.
 It can be combined with a hidden surface algorithm to fill in the
visible polygons along each scan line.
12. Define CMY color model.
 CMY color model defines for Cyan Magenta Yellow and is utilized
for devices for hardcopy.
 In contrast to color on the display unit, the color in printing acts
subtractive and not additive.
 A printed color that appears red attracts the other two
components Green and Blue and reflects Red.
 Thus its color is Green + Blue = CYAN. Likewise Red + Blue =
MAGENTA and Red + Green = YELLOW. The CMY is
considered a subtractive model since the model main colors deduct
some color from white light.
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AP/MECH-AEC

11. 13. Mention the importance of Colouring of three dimensional objects in Computer
graphics.
 Colouring is a significant component of computer aided
visualization of information, concepts and ideas.
 The Value of colour determines how light or dark the colour is in
its shade.
 This aspect of color is used extensively to depict the spatial form of
an object.
Unit - 4 (ASSEMBLY OF PARTS)
1. What is meant by assembly modelling?
 Assembly modelling is the collection of individual parts.
 The assembly is mating of the individual parts by axis, surface
mates etc.
2. Define top-down assembly approach.
• In this approach, the assembly file is created first with an assembly
layout sketch.
• The parts are made in the assembly file or the concept drawing of
the parts are inserted and finalized in the assembly file.
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12. 3. List down the mating conditions in assembly modelling.
 Coincidence
 Concentric
 Tangent
 Coplanar
 Parallel
 Perpendicular
4. List out the advantages of Tolerance Analysis.
1. Accurate part assembly.
2. Elimination of assembly rework
3. Improvement in assembly quality.
4. Reduction of assembly cost.
5. High customer satisfaction.
6. Effectiveness of out-sourcing.
5. Mention the importance of Geometric tolerance.
 Geometric tolerances are used to control more precisely the shape
and form of a component.
 Geometric tolerance permits explicit definition of datum with clear
specification of the datum precedence in relation to each tolerance
specification.
6. What are the uses of tolerance stack ups?
 Tolerance Stack-Ups are vital to address mechanical fit and
mechanical performance requirements.
 Tolerance stack-up calculations represent the cumulative effect of
part tolerance with respect to an assembly requirement.
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13.  The idea of tolerances “stacking up” would refer to adding
tolerances to find total part tolerance, then comparing that to the
available gap or performance limits in order to see if the design will
work properly.
7. What is coincident mating condition?
 The coincident mating condition is applied between to planar faces.
 Each face is specified by its unit normal vector, n, and a point on
the surface, P. The coincident condition is satisfied by forcing n1
and n2 to be opposite of each other, and the two faces touch each
other such that P1 and P2 are coincident
8. What is Concentric mating condition?
 The concentric mating condition is applied between to cylindrical
faces
 The concentric mating condition is achieved by forcing the axes to
become collinear. Each axis is defined by two points
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14. 9. . List out parameters calculated by mass property calculations.
 Mass
 Centroid
 First moment of inertia
Second moment of inertia
10. Difference between geometric and mass properties.
 Geometric properties are
those that can be derived
from the geometry of a solid
body or particle.
 Mass Properties are
physical attributes of a
mechanical part that relate
to how the component will
behave in an environment.
 Length, area, surface area
and volume
 Mass, centroid, first
moment of inertia, second
moment of inertia
11. What are the types of Mechanism Simulation?
 Kinematics simulation
 Dynamics simulation
 Computer simulation
 Virtual simulation
12. What are the types of fits?
 Clearance fit
 Transition fit
 Interference fit
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15. 13. What is Interference Checking?
 Interference Checking is the process of checking if any parts of an
assembly overlap each other or not.
 When working with multiple parts or the components of an
assembly, you should frequently check for interference among
them.
 If interference is detected between two parts, the CAD system
displays the interference volume to allow users to examine and
eliminate it.
Unit - 5 (CAD STANDARDS)
1. State the needs for data exchange standards.
 Design Projects require data to be shared between suppliers
 Different companies often used different CAD systems
 All CAD systems have their own database formats
 They are mostly proprietary and often confidential
 Data conversion between systems become necessary
2. What is meant by CAD date exchange? Mention its importance.
 CAD data exchange is a modality of data exchange used to translate data
between different Computer-aided design (CAD) authoring systems or
between CAD and other downstream systems.
 Neutral file exchange uses an intermediary neutral format to translate data
between CAD systems.
 NC programming typically requires that the geometry received from a CAD
system, whether in wireframe, surface, solid or combined formats, be free from
any irregularities and inconsistencies that may have occurred in the CAD phase
of geometry creation. Data exchange from CAD to CAM must therefore
include tools for identifying and repairing those inconsistencies. These tools
are typically included in the data exchange software of each CAM solution-set.
3. What is the importance of standards in CAD?
 CAD Standards are necessary and very important to the industry to
allow for designs and drawings to be interchanged between teams
on projects.
 Sometimes large projects use multiple CAD platforms, so CAD
Standards are essential for the project to function.
 It helped us to link the different hardware and software from
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16. various vendors in such a way to integrate according to the need of
industries.
4. Write any three CAD standards for exchange of modelling data.
 IGES – Initial Graphics Exchange Specification
 STEP – Standard for Exchange of Product model data
 DXF- Drawing Exchange Format
5. Compare the shape based and the product data based exchange standards.
 IGES - the shape based - both geometric and topological
information
 STEP - product data based
6. Define GKS cell array.
 The GKS cell array function displays raster like images in a device-
independent manner.
 The cell array function takes the two corner points of a rectangle
that you specify a number of divisions (M) in the X direction and a
number of divisions (N) in the Y direction.
 It then partitions the rectangle into M x N sub rectangles called
cells.
 Assign each cell a colour and create the final cell array by
colouring each individual cell with its assigned colour.
7. What are the neutral formats?
 IGES
 STEP
 DXF
8. What are the three types of data types in IGES?
 Geometric
 Annotation
 Structure
9. What are the three layers of architecture in STEP?
 Application layer
 Logical layer
 Physical layer
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17. 10. Mention the different file section in IGES.
 Flag section
 Start Section
 Global section
 Directory entry section
 Parameter data section
 Terminal section
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