Engineering Modeling and Design

William L. Chapman, A. Terry Bahill, A. Wayne Wymore

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351450942
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Engineering General
• Index: Technology & Engineering

Engineering Modeling and Design is a comprehensive systems engineering text that focuses on systematic principles for designing systems. Concurrent engineering, which requires that from the very start of a project all players (e.g., engineering, maintenance, marketing, customers) are involved as all facets of the system life cycle are considered, is skillfully illustrated through the use of two major case studies. The text describes how a product design proceeds parallel to the process design, explains key duties of systems engineers throughout the product life cycle, and examines the process of system design in terms of life cycle requirements. Projects and problems are presented throughout the text. A homework solutions/instructor's manual is available from the publisher upon request.
Engineering Modeling and Design is an excellent text for engineering design courses in industry and upper division courses on concurrent engineering or total quality management.

chapter one

Systems engineering

The design of big or complex systems requires the cooperation of many people and usually many companies. In most big companies, such design projects are coordinated by the Systems Engineering Department. This department, which has overall responsibility for ensuring that systems designed by the company do what they were intended to do, typically includes electrical engineers, mechanical engineers, business majors, and communications specialists. The Systems Engineering Department must ensure that at the very start of the project and throughout the entire life of the system all players (e.g., customers, marketing, finance, purchasing, suppliers, engineering, manufacturing, testing, and field support) are involved and that all facets of the system life cycle (e.g., requirements specification, concept exploration, and replacement) are considered. This description is often called concurrent engineering. Systems engineering, as presented in this book, is a superset of concurrent engineering. In this chapter we discuss systems engineering, and in Chapter 7 we will examine specific attributes associated with concurrent engineering. Total quality management is an important new term in American industry. Systems engineering, as presented in this book, is a subset of total quality management. Some other components of total quality management are mentioned in Chapter 7.

Systems engineering usually is one of the first courses taken by engineering students. After learning how to design systems, they become specialists in electrical, mechanical, or biomedical engineering. The same sequence is followed in industry and senior design courses, with systems engineering first and electrical, mechanical, and other engineering disciplines covered later.

To understand what a Systems Engineering Departments does, we must first define systems engineering. This is not as easy as it sounds, because systems engineering means different things to different people. In the following paragraphs are some definitions that can be read rapidly. The differences in detail between them are not important; their similarities should be noted.

(1) Systems Engineering is concerned with the design, modeling, and analysis of technological systems that use people and machines, software and hardware, material, and energy for such purposes as communication, health care, transportation, and manufacturing. Research emphasizes tools for modeling and analysis—especially appropriate for large, complex systems—such as concurrent engineering, system theory, decision analysis, and simulation (from a University of Arizona, Systems and Industrial Engineering brochure).

(2) Wayne Wymore, who founded the first academic department of systems engineering at the University of Arizona in 1961, says, “The principal top level function of systems engineering is to ensure that the system satisfies its requirements throughout its life cycle. Everything else follows from this function.”

(3) John G. Truxal, former Dean of Engineering at Brooklyn Polytechnic Institute, says, “Systems engineering includes two parts: modeling, in which each element of the system and the criterion for measuring performance are described; and optimization, in which adjustable elements are set at values that give the best possible performance.”

(4) Jaroslav Jirasec, a world-renowned Czechoslovakian systems scientist and co-founder of the International Institute for Applied Systems Analysis (IIASA), uses the Battle of Borodino from Tolstoy’s War and Peace as his first lecture for his Systems Science class. He thinks the principles used and not used by the rival commanders Napoleon and Kutuzov and their generals define systems engineering.

(5) MIL-STD-499A defines systems engineering in the Department of Defense context. “Systems Engineering is the application of scientific and engineering efforts to (a) transform an operational need into a description of system performance parameters and a system configuration using an iterative process of definition, synthesis, analysis, design, test, and evaluation; (b) integrate related technical parameters and ensure compatibility of all physical, functional, and program interfaces in a manner that optimizes the total system definition and design; and (c) integrate reliability, maintainability, safety, survivability, human, and other such factors into the total engineering effort to meet cost, schedule, and technical performance objectives.”

(6) A major Department of Defense aerospace contractor, Hughes Aircraft Company, starts its definition with the above three points, but adds “(d) verify that the hardware/software units meet their design requirements and the operational needs of the customer through the implementation of an integrated test program; and (e) assure the system meets its design requirements throughout the manufacture and operational life cycle of the system.”

(7) A division manager at Hughes Aircraft Company defined systems engineering as performing: (a) requirements definition, (b) conceptual design, (c) partitioning of a system into subsystems (guidance, propulsion, etc.) for other engineering teams to create, and (d) system validation, i.e., ensuring the system works when the subsystems are put together to form the system. Particular attention must be paid to the interface between the subsystems.

(8) Martin Marietta, another Department of Defense and National Aeronautics and Space Administration (NASA) aerospace contractor, says that systems engineering must ensure delivery of a system, optimized to satisfy mission requirements, that has the greatest probability of success and lowest cost. It must tie the total system together through each of the phases of the system life cycle. Thus, systems engineering can be viewed as the technical arm of program management.

(9) A draft version of MIL-STD-499B, which will replace MIL-STD-499A that was written in 1969, contains the following definition: Systems engineer- ing is the management and technical process that controls all engineering activities throughout the life cycle in order to achieve an optimum balance of all system elements to ensure satisfaction of system requirements while providing the highest degree of mission success. It has two main activities: (a) interpreting the customer’s needs and translating them into a set of requirements that can be met by individual design and speciality disciplines and (b) validating that the system satisfies the customer’s needs through analysis, simulation and testing. Although originally created to help with the development of complex weapons systems, the elements of systems engineering are applicable at all design levels and to all business applications.

(10) Systems Engineering Manual 1-1, prepared by the U.S. Air Force Aeronautical Systems Division, defines it this way: The systems engineering process is the integrated sequence of activities and decisions that transforms a defined need into an operational, life-cycle-optimized system that achieves an integrated and optimal balance of its components. The systems engineering process produces initial, intermediate, and final products (data, equipment, trade study reports, plans, etc.) that document progress. The main tasks of systems engineering are: (a) Requirements analysis. The definition and refinement of all customer needs in terms of performance requirements and primary functions that must be performed. (b) Functional analysis. Functional analysis can be performed top down by decomposing primary functions into lower and lower subfunctions. This functional decomposition continues until each subfunction can be accomplished by a definable element. (c) Allocation. The assignment of performance requirements to the subfunctions defined by the functional analysis. (d) Synthesis. Synthesis identifies the subfunctions that must be resolved by the same element and then assigns their performance requirements to that element. (e) Trade-off studies. Trade-offs among stated customer needs shall be identified and assessed. Trade-off studies formulate and assess alternative courses of action to achieve an integrated and optimally balanced system solution.

(11) The University of Arizona catalogue says that systems engineers design and build systems to meet the needs of people. As computing speed and analytic sophistication have increased, society’s needs have become more varied and complex. Graduates of the Systems Engineering program are prepared to face these needs. The goal of a systems engineer is to make the best use of resources. Stated formally, systems engineering is concerned with the processes and methodology of modeling, analyzing, and designing technologically advanced systems that function safely, effectively, and economically. It requires appreciation and understanding of nature, machines, people, software, hardware, materials, and energy. Systems engineers work on a wide range of activities and applications, including communication systems, computer networks, manufacturing systems, robotics, health care systems, societal problems, and all phases of both industrial and military research and design. To prepare students for careers of such exceptional diversity, the Systems Engineering curriculum includes courses in computing, probability, statistics, numerical methods, operations research, concurrent engineering, knowledge-based systems, robotics, and human-system integration. This is clearly a broader and more abstract program than most traditional engineering disciplines

(12) A Case Western Reserve University brochure says, “Systems Engineering…emphasizes that problems be attacked holistically to ensure a balanced treatment of all components and their interactions…. It focuses on both the theory and methodology for the analysis and design of complex technological systems and their interactions with society, economic, and environmental systems…. The standard tools used in systems engineering are techniques from system modeling, optimization, decision analysis, engineering economics, control engineering, mathematics, and statistics…. The systems engineering approach emphasizes critical thinking and problem solving and unifies these aspects in a mathematically rigorous framework.”

(13) A U.S. Naval Academy brochure states,” Systems Engineering has many definitions limited only by the number of people who attempt to define it…. Systems Engineering is concerned with the design and analysis of the whole system to achieve optimum results…. Since most modern complex systems are feedback in nature, the Systems Engineering program at the U.S. Naval Academy emphasizes and focuses special attention on systems engineering aspects in the light of control theory…. The control engineer is placed in a unique position for solving complex problems due to his knowledge of electrical and mechanical systems and his specialized knowledge of modeling, simulation, computers, and control theory.”

(14) A University of Virginia brochure states, “Systems Engineering is the intellectual, academic, and professional discipline concerned primarily with improving processes of problem-solving and decision-making throughout the life cycle of large-scale, complex man/machine/software systems in both private and public sectors.”

(15) IBM says, “Systems Engineering is the iterative but controlled process in which user needs are understood and evolved—through increasingly detailed levels of requirement specification and system design—to an operational system.”

(16) The following is from a syllabus for a course taught by Dr. A. Terry Bahill, University of Arizona. “When an engineering project becomes too big, too complicated, or too long-lived for one Chief Engineer to keep all the details in his head, then responsibility for the project must be spread out amongst three or more engineers. This creates a new problem of having these engineers work independently while still being sure that their individual components will interact correctly. Ensuring that components made by different people or companies can function together is one purpose of systems engineering. A second purpose of systems engineering is to ensure that the problem is stated correctly and that tests are defined to ensure that the final system satisfies the original requirements.”

We sent questionnaires to 650 alumni who received degrees in Systems Engineering at the University of Arizona over the past 30 years. We asked them what they thought systems engineers did, and this is a consensus of their responses: Systems engineers are involved in all phases of the system life cycle. They translate the customer’s business needs into system requirements, evaluate alternative designs, design and evaluate prototypes, specify system testing, decompose functions into subfunctions, allocate subfunctions to physical components, analyze performance, and are involved in maintenance and operation. Systems engineers do modeling, simulation, analyses, and a lot of information gathering, writing, and planning. The following words appeared in many of their statements: multidisciplined, interdisciplinary, divergent, wide variety, interviewing the customer, communications skills, coordinate, top-down design, integrate, interface, model, trade studies, optimize, and test. Finally, several alumni expressed this sentiment: What do systems engineers do? Just about anything they want to do.

One part of this alumni questionnaire asked, “In which courses did you learn the tools, concepts, and skills that you now consider the most important?” No one course or group of courses was consistently rated the most useful. However, the courses that received the most votes were those that used computers, systems modeling courses, and project courses with written and oral reports. There was no consensus for the question, “In which courses did you learn the material that you now consider the least important?” Almost every course in and out of the department got votes. In response to the question, “What should we have taught you that we did not, or what should we have taught more of?”, our alumni said that they would have liked to have had more communications skills, laboratories, computer usage, design projects, and systems modeling. The question that generated the most interesting responses was, “Who were the best teachers you had?” Almost everyone in our department got votes! In particular, two professors who normally got very low student evaluations got high marks from the alumni. This questionnaire showed that systems engineers work in diverse fields and perform a wide variety of tasks.

An important concept that can be gleaned from the definitions in this chapter is that systems engineering is responsible for the “big picture.” Systems engineers must coordinate full-scale engineering, manufacturing, and component acquisition. They must design tests and evaluate proposed engineering changes during the operation phase. Finally, they are responsible for writing proposals and specifications during the design and replacement phase of the system life cycle.

Many professional groups and societies are writing standards and trying to derive a consensus on what systems engineering is and what systems engineers do. Some of these are: IEEE Systems Engineering Industry Standards Committee; IEEE Systems, Man, and Cybernetics Society; Electronic Industry Association (EIA) G-47 Committee; National Council on Systems Engineering (NCOSE); Worldwide International Systems Institutions Network (WISINET); Defense Systems Management College; U.S. Air Force Systems Command; U.S. Air Force Aeronautical Systems Division Directorate of Systems Engineering; and Department of Defense (DoD) Production and Logistics Branch.

Each of these definitions highlights different aspects of systems engineering. Taken as a whole, they might encompass systems engineering, but as the definitions themselves imply, there is no unique way to do systems engineering. In this book we present one generic approach. No company does it exactly this way, but we believe that it will be easier for the reader to understand each company’s approach having first encountered this general approach.

Problems

1. Systems engineering principles illustrated in War and Peace. Jaroslav Jirasec—a world renowned Czechoslovakian systems scientist and co-founder of IIASA, a multinational systems science think tank in Austria—told us that his first lecture to his Systems Science class is based on the Battle of Borodino from Tolstoy’s War and Peace.

For the first homework assignment, read the sections of War and Peace that cover August 25 and 26,1812 (in some books they are labeled Sections 19 to 39 of Part 2 of Book III), and point out the good and bad systems engineering principles used by the rival commanders Napoleon and Kutuzov and their generals.

2. Defining systems engineering. Provide a consensus of the various definitions of systems engineering that were given in this chapter.

3. The expedient engineer. Once upon a time a mathematics student, a physics student, and an engineering student were bragging about the quality of their education. They decided to have a contest to determine who had been educated the best. The mathematics student proposed a challenge. He said, “I have been told that all odd numbers are prime. I will now use everything my professors have taught me to evaluate the truth of this hypothesis.” He started thinking aloud like this: “1…3…5…7…9…11…13…15…17…19…21…. Whoops! No, the hypothesis is not true, because 21 is an odd number and it is not prime.”

Next the physics student took up the gauntlet. He said, “I will now use everything my professors have taught me to evaluate the truth of the hypothesis that all odd numbers are prime.” He started thinking aloud like this: “1… 3…5…7…9…11…13…15….15? Well that might just be experimental error…17 …19…21. No, the hypothesis is not true.”

Finally, the engineering student attacked the problem. He said, “I will now use everything my professors have taught me to evaluate the truth of the hypothesis that all odd numbers are prime.” He thought aloud like this: “1… 3…5…7” and said, “Yep, it’s true.”

chapter two

The system design process

2.1 Introduction

The design process in the United States is a ...