The advent of plentiful computing has produced a major change in the way engineering design is practiced. While engineers were among the first professional groups to adapt the computer to their needs, the early applications chiefly were computationally intensive ones, using a high-level language like FORTRAN. The first computer applications were conducted in batch mode, with the code prepared on punch cards. Overnight turnaround was the norm. Later, remote access to computer mainframes through terminals became common, and the engineer could engage in interactive (if still slow) computation. The development of the microprocessor and the proliferation of personal computers and engineering workstations with computational power equivalent to that of a mainframe 10 years ago has created a revolution in the way an engineer approaches and carries out problem solving and design.
The greatest impact of computer-aided engineering has been in engineering drawing. The automation of drafting in two dimensions has become commonplace. The ready ability to make changes and to use parts of old designs in new drawings offers a great saving in time. Three-dimensional modeling has become prevalent as it has become available on desktop computers. Three-dimensional solid modeling provides a complete geometric and mathematical description of the part geometry. Solid models can be sectioned to reveal interior details, or they can be readily converted into conventional two-dimensional engineering drawings. Such a model is very rich in intrinsic information so that it can be used not only for physical design but also for analysis, design optimization, simulation, rapid prototyping, and manufacturing. For example, geometric three-dimensional modeling ties in nicely with the extensive use of finite-element modeling (FEM) and makes possible interactive simulations in such problems as stress analysis, fluid flow, the kinematics of mechanical linkages, and numerically controlled tool-path generation for machining operations. The ultimate computer simulation is virtual reality, where the viewer feels like a part of the graphical simulation on the computer screen. Chapter 10 considers modeling in engineering design and discusses a broad spectrum of computer-aided engineering (CAE) design tools.
The computer extends the designer’s capabilities in several ways. First, by organizing and handling time consuming and repetitive operations, it frees the designer to concentrate on more complex design tasks. Second, it allows the designer to analyze complex problems faster and more completely. Both of these factors make it possible to carry out more iterations of design. Finally, through a computer-based information system the designer can share more information sooner with people in the company, like manufacturing engineers, process planners, tool and die designers, and purchasing agents. The link between computer-aided design (CAD) and computer-aided manufacturing (CAM) is particularly important. Moreover, by using the Internet and satellite telecommunication, these persons can be on different continents ten time zones away.
Boeing 777
The boldest example of the use of CAD is with the Boeing 777 long-range transport. Started in fall 1990 and completed in April 1994, this was the world’s first completely paperless transport design. Employing the CATIA 3-D CAD system, it linked all of Boeing’s design and manufacturing groups in Washington, as well as suppliers of systems and components worldwide. At its peak, the CAD system served some 7000 workstations spread over 17 time zones.
As many as 238 design teams worked on the project at a single time. Had they been using conventional paper design, they might have experienced many interferences among hardware systems, requiring costly design changes and revised drawings. This is a major cost factor in designing a complex system. The advantage of being able to see what everyone else was doing, through an integrated solid model and digital data system, saved in excess of 50 percent of the change orders and rework expected for a design of this magnitude.
The Boeing 777 has more than 130,000 unique engineered parts, and when rivets and other fasteners are counted, there are more than 3 million individual parts. The ability of the CAD system to identify interferences eliminated the need to build a physical model (mockup) of the airplane. Nevertheless, those experienced with transport design and construction reported that the parts of the 777 fit better the first time than those of any earlier commercial airliner.
Concurrent engineering is greatly facilitated by the use of computer-aided engineering. Concurrent engineering is a team-based approach in which all aspects of the product development process are represented on a closely communicating team. Team members perform their jobs in an overlapping and concurrent manner so as to minimize the time for product development (see Sec 2.4.4). A computer database in the form of a solid model that can be accessed by all members of the design team, as in the Boeing 777 example, is a vital tool for this communication. More and more the Internet, with appropriate security, is being used to transmit 3-D CAD models to tool designers, part vendors, and numerical-control programmers for manufacturing development in a highly networked global design and manufacturing system.
Computer-aided engineering became a reality when the power of the PC workstation, and later the laptop PC, became great enough at an acceptable cost to free the design engineer from the limitations of the mainframe computer. Bringing the computing power of the mainframe computer to the desktop of the design engineer has created great opportunities for more creative, reliable, and cost-effective designs.
CAE developed in two major domains: computer graphics and modeling, and mathematical analysis and simulation of design problems. The ability to do 3-D modeling is within the capability of every engineering student. The most common computer modeling software packages at the undergraduate level are AutoCAD, ProE, and SolidWorks. CAE analysis tools run the gamut from spreadsheet calculations to complex finite-element models involving stress, heat transfer, and fluid flow.
Spreadsheet applications may seem quaint to engineering students, but spreadsheet programs are useful because of their ability to quickly make multiple calculations without requiring the user to reenter all of the data. Each combination of row and column in the spreadsheet matrix is called a cell. The quantity in each cell can represent either a number entered as input or a number that the spreadsheet program calculates according to a prescribed equation.13 The power of the spreadsheet is based on its ability to automatically recalculate results when new inputs have been entered in some cells. This can serve as a simple optimization tool as the values of one or two variables are changed and the impact on the output is readily observed. The usefulness of a spreadsheet in cost evaluations is self-evident. Most spreadsheets contain built-in mathematical functions that permit engineering and statistical calculations. It is also possible to use them to solve problems in numerical analysis.
The solution of an equation with a spreadsheet requires that the equation be set up so that the unknown term is on one side of the equal sign. In working with equations it often is useful to be able to solve for any variable. Therefore, a class of equationsolving programs has been developed for small computations on the personal computer. The best-known examples are TK Solver, MathCAD, and Eureka. Another important set of computational tools are the symbolic languages that manipulate the symbols representing the equation. Most common are Mathematica, Maple, and MatLab. MatLab 14 has found a special niche in many engineering departments because of its user-friendly computer interface, its ability to be programmable (and thus replace Fortran, Basic, and Pascal as programming languages), its excellent graphics features, excellent ability to solve differential equations, and the availability of more than 20 “toolboxes” in various applications areas.
Specialized application programs to support engineering design are appearing at a rapid rate. These include software for finite element modeling, QFD, creativity enhancement, decision making, and statistical modeling. Useful software packages of this type will be mentioned as these topics are introduced throughout the text.
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