DM:4.4 PRACTICE QUESTIONS
1. List at least five basic methods of geometric modelling, and provide a simple example of each.
2. With reference to the Ideas package used in the laboratory, discuss some computer graphics rendering and display methods, and when they should be used.
3. Describe how you would model the part below using solid modelling techniques Hint: forget dimensions, sketches may help.
4. Short answer problems
a) List at least 10 Input, and output devices used for CAD systems
b) Suggest two approaches to find the mass properties of the irregular shape below and list some mass properties that could be calculated.
c) Give two examples of problems which may result from numerical accuracy in a CAD system. A drawing may help your explanation
d) Give an example of dithering which you have seen, and describe why it was used.
e) What are some of the important features of UNIX and the SGIs
f) Define CAD, CAM, and CIM, then describe what they mean to each other.
g) List the advantages of a CAD system
h) Show in a diagram how computers may be used to enhance the traditional design methods.
i) Describe the roles elemental, surface, and CSG design techniques play in a CAD system like Ideas
j) Give an example of a surface using a spline (a.k.a. skins), and describe how to fit a method of fitting a spline to the surface.
5. You are working for a company that designs CAD/CAM software for specialized tasks. A customer has approached the company about developing a new CAD system for shoe design. Your manager has asked you to develop a short document which outlines the proposed CAD package. With great enthusiasm you accept the job, and decide to produce a document with the following layout.
Section Title Page
1 Executive summary 1
2 Computer Hardware requirements 1
3 Summary of internal geometric model 2
4 Summary of design input 2
5 Summary of display methods 4
6 Suggested analysis techniques 4
8 New corporate communications 5
9 Implementation schedules 6
You should keep in mind that your boss dislikes verbose reports which don’t get to the point quickly. Therefore point form lists, and figures will make your boss happier. Your boss also dislikes reports that are longer than 7 pages. In fact your boss refuses to read past the 7th page.
6. Draw an IDEF0 diagram which outlines the processes used by a team designing a product, such as a bicycle. The basic level 0 diagram is given below.
7. If we are designing an aircraft landing gear we would have to perform some Computer Aided Engineering tasks. Briefly describe the tasks you would have to perform to model, and evaluate the model. For each phase describe why the tests would be done, and how the test results would be used to improve/correct the design.
The Design below represents a hypothetical mechanism for a retractable landing gear on an airplane. We can assume that the wheel retraction slider is fixed in position. Some device to be chosen later (probably a hydraulic cylinder) will be used to push the Wheel Locking Member along the Wheel Retraction Slider. Obviously this will raise and lower the wheel. The wheel support member is pinned on either end, as is the Wheel Locking Member.
8. These short answer questions are testing general knowledge of CAD/CAM.
a) Describe how a shape can be analyzed for Mass Properties using a 2D case for discussion. Describe an alternate method.
b) Assuming you are designing a new hull for a nuclear sub (not the construction of it), describe at least five factors you would want to examine with CAE.
c) What is the fundamental concept behind Concurrent Engineering? List at least three reasons why Concurrent Engineering is gaining popularity. Describe at least two advantages computers provide for Concurrent Engineering.
d) Describe what trimming is and how it differs from at least one other similar method.
e) Although dithering is sometimes necessary, it is not always desired. Why?
f) When would it be useful to use IDEF0 models? What steps would normally be followed when using the IDEF0 methodology? What are some problems that IDEF0 diagrams can reveal?
g) Why are the uses of MRP and Capacity Planning different? What class of scheduling problems do MRP and Capacity Planning not consider?
9. Describe what the output from the following C program will be.
10. What does the IGES file below show? Note: the columns are not exactly placed.
11. These short answer questions involve application of concepts to practical problems.
a) List some benefits the network (in the computer lab) provides that are not available on stand alone computers.
b) Describe the components and operation of an Automated Manufacturing Workcell you have seen.
c) We often discuss when CAD systems should be used. When should they not be used? Give an example.
d) Identify one stage of product development that CAD is not commonly used for, and describe why it is not.
e) Describe one application for which a CAD package like CADKEY would be a better choice than a package like IDEAS. Justify your choice.
f) I was about to produce the part below with stereolithography, but when my boss double checked it he said there was a serious problem that would result in failure. What is the problem? Suggest ways to solve it.
12. You are just about to design a new part, but first you want to look for a similar part on your companies GT system (It uses an OPITZ code). a) Develop the form code for the part below. b) If we find a close match, what other types of useful information could the GT system provide?
13. The workcell below has been designed to put parts on a pallet, and then a robot will assemble them. Suggest how a PLC would be connected, and programmed. If you need other sensors, or other devices state what they are, and how they would be used. (Assume that all the feeders just need a single electrical input to issue one part correctly). The pallets are issued automatically, and the feed rate is set manually.
14. You are the designer at a tent making company that has 100 employees. The basic components of the tents are the frame, and the canvas covering. Some of the larger tents can be hundreds of feet long. As a result there are a number of design problems. When the canvas is hung on the frame, it does not maintain the initial shape of the material, for example drooping under the effects of gravity is one problem. You have just completed an interesting course on CAD and CAE, and you have decided to contact a software company to ask them to write a software package for you. Before meeting the software analyst from the company you must sit down and decide what you want the software to do. For example, rendering and some various forms of FEM would be required. Be more specific than this, and consider other options. Discussion should refer to tents when appropriate. a) List possible computer graphics outputs of the stored design. b) List possible input methods. c) List and justify some CAE options.
15. Describe how the part pictured below would be represented in five different geometric model types (eg. CSG, Surface).
16. Describe which modelling methods are suited to the parts below (how and why).
17. Suggest a method for constructing the parts below using any or all of the Solid Modelling techniques (eg. create cylinder, cut part with cylinder)
18. Data structures form the backbone of every computer program. A data structure is basically a set of well thought out variables and arrays. These structures are designed to hold information, and allow easy use. An example would be a data structure for holding information about the location of office furniture. The figure below shows a list of offices, these each point to a ‘linked-list’ of furniture. The Furniture List stores a list all the furniture, and the use of the ‘next’ field allows many different sub-lists to exist in the larger list.
Your problem involves suggesting a data structure which can store information about a few parts each made with spheres stuck together, like a Mickey Mouse head. The structure should allow for the obvious, as well as color. (Hint: The structure you use may be similar to the one above, but the data fields will definitely have to be customized for your structures)
#4 a) Given the following problem, and the stiffness matrices for the elements, set up the global stiffness matrix. (15%)
#4 b) Assuming that the beams have a cross sectional area of 2cm2, and a Modulus of Elasticity of 50MPa, find the new position for joint 4. (15%)
