4 Life-Cycle Properties Of Engineering Systems: The Ilities
4Life-Cycle Properties of Engineering Systems: The IlitiesIn the epoch of great inventions and artifacts, the implicit mandate of theengineer and inventor was to “design for first use.” The aim was to designand build an artifact that would “work” and fulfill its primary functionwhen first turned on or started up. If it did not, it was back to the drawingboard. Immediate functionality was the main focus. Little or no attentionwas paid to side effects or other more subtle behaviors, especially thosethat might be far in the future.In the epoch of engineering systems, the focus has changed. As wediscussed in chapter 3, their evolution over long lifetimes is a significantaspect of large-scale complex systems. Understanding and working withengineering systems requires attention to properties that have long timeexposure. Attention to side effects and the context that establishesground rules and constraints within which systems operate is crucial, asthese factors are part of the systems’ very essence.The Importance of Not Simply “Working”The first automobiles were largely motorized versions of the horsedrawn carriages that preceded them. But as the artifact improved andbegan to work in more demanding operating environments—at higherspeeds, at night, in adverse weather—new subfunctions, beyond theprimary function of the car, became important. Over time, inventorsresponded by adding windshields to cars to protect the eyes and mouthsof drivers from bugs, windshield wipers to ensure visibility in the rain,and headlights so drivers could see in the dark. Lots of other improvements were made over the years, perhaps more than most contemporarydrivers know.It wasn’t long before it was became to address some side effects ofdriving automobiles. For example, the first cars were equipped withDe Weck—Engineering Systems8799 004.indd 656/16/2011 7:30:21 PMQ
66Chapter 4brakes, but only on the rear wheels. Drivers of the time would swerveand skid when they applied the brakes, and stopping required a lot ofdistance.In 1923, the relatively high-priced Buick appeared with brakes on allfour wheels; these four-wheel brakes were invented by Charles F.Kettering (who was responsible for a lot of inventions that reallychanged the way people lived, including safety glass, the automatic transmission, incubators for premature infants—in fact, a list too long toinclude here).By the time Henry Ford’s Model A came out in 1927, four-wheelbrakes were standard, and have remained standard ever since. Furtherimprovements came in the 1930s, when hydraulic four-wheel brakescame into use, allowing for higher brake pressures and shorter stoppingdistances. Later, Europeans pioneered dual hydraulic brakes to addressthe problem of the original single hydraulics—namely, that a loss ofhydraulics meant a loss of all braking ability. Power brakes that increasethe amount of hydraulic pressure debuted in the 1950s. By 1961, ratherrapidly, dual hydraulics became standard in U.S.-made cars, thanks to acompetitive thrust by American Motors Corporation.The early development of automotive braking and many early developments in airplanes are tales of safety becoming a consideration as theartifacts move beyond their first use—that is, the emergence of ilities. Theilities are central to any discussion of engineering systems, and requirea very precise definition:The ilities are desired properties of systems, such as flexibility ormaintainability (usually but not always ending in “ility”), that oftenmanifest themselves after a system has been put to its initial use. Theseproperties are not the primary functional requirements of a system’sperformance, but typically concern wider system impacts with respectto time and stakeholders than are embodied in those primaryfunctional requirements. The ilities do not include factors that arealways present, including size and weight (even if these are describedusing a word that ends in “ility”).1QOver time, greater awareness of safety became characteristic of theepoch of great inventions and artifacts, although engineers concentratedprimarily on making safety-related alterations and adjustments to artifacts (often products), they also participated in changing the underlyingsystems and operating environments within which they function. Qualitywas the other ility to emerge in this early epoch.De Weck—Engineering Systems8799 004.indd 666/16/2011 7:30:21 PM
Life-Cycle Properties of Engineering Systems67As background research for this chapter, we compiled a list of 20 ilitiesthat we have frequently encountered in our work on engineering systems.For each of them, we collected data that would allow us to rank theselife-cycle properties based on how frequently they are mentioned in thescientific literature and on the Internet.2 Figure 4.1 shows the result ofour analysis. The black vertical bars indicate the number of scientificpapers (in thousands) that mention a particular ility in their title orabstract. The gray vertical bars show the number of Google hits (in millions) obtained for each ility.3The results from the scientific database and the number of Internethits are strikingly similar, with the notable exception of sustainability,which we discuss later in this chapter. The top four ilities are, in order,quality, reliability, safety, and flexibility.Quality and safety are so important in part because they havereceived much attention since the beginning of the epoch of great inventions and artifacts. Note that figure 4.1 shows some ilities that are stronglyrelated to quality as being of high importance (e.g., reliability, robustness,Figure 4.1Ranking of the ilities in terms of frequency of occurrence: the black bars indicate scientificjournal articles published from 1884–2010, in thousands (source: Compendex and Inspecdatabases); the gray bars indicate number of hits on the Internet, in millions (source:Google).De Weck—Engineering Systems8799 004.indd 676/16/2011 7:30:22 PMQ
68QChapter 4durability). We will consider such relationships a little later in thechapter.As we entered the epoch of complex systems, usability—which, ofcourse, had always been a significant concern of inventors and engineers—emerged as a specific ility, largely from how users (humans) perceivedquality as well as from unanticipated difficulties in operating complexsystems. Engineers also began to worry—to a greater or lesser degree—about the maintainability of the artifact(s) and, sometimes, the systemswithin which the artifact(s) function. This was driven in part by thegrowing realization that perfect reliability and durability were impossibleto achieve and hence an unrealistic expectation, leading to focus on bothpreventive and corrective types of maintenance.We think of these four aspects of artifacts and systems—safety, quality,usability, and reliability—as the classical ilities of engineering. In ourpresent epoch of engineering systems, the list has grown much longer.This can be attributed partly to the fact that more attention to ilities ledto more complex systems, and vice versa. More ilities emerged becausegrowing complexity and scale of deployment led to more and moreimportant side effects; the rapidly increasing rate of change in systemsand concomitant social changes also spurred this expansion of the ilities(as we discussed in chapter 1). No one wanted to pay for things that didnot contribute directly to the primary functionality of the artifact, butover time it became untenable to run systems without paying attentionto characteristics—even if it sometimes took decades of use to realizethis. Today, there is an increasing realization that much of the value thatengineering systems generate depends on the degree to which theypossess certain life-cycle properties, or ilities.4The cumulative number of scientific articles published in the engineering literature on our set of 20 ilities from 1884 (the earliest date forwhich such data was available) to 2010 illustrates this point. Figure 4.2shows only the top 15, to demonstrate more clearly the timedependence.Indeed, quality and safety were given consideration early on, first inthe building of national infrastructure such as railroads and bridges andlater in the twentieth century when various electromechanical productsbecame available to a wider population. Over time, during the epoch ofcomplex systems and then in our current epoch of engineering systems,new ilities became the subject of intense interest and scientific research.Let’s look at some examples of the ilities in greater detail, more orless in the order in which they emerged.De Weck—Engineering Systems8799 004.indd 686/16/2011 7:30:22 PM
Life-Cycle Properties of Engineering Systems69Figure 4.2Cumulative number of journal articles in which an ility appears in the title or abstract ofthe paper (1884–2010). Source: Inspec and Compendex, accessed via Engineering Village(8 August 2010).QualityThe first “ility” of traditional engineering to be discussed at length isquality. An extensive literature on quality exists, defining this ility frommultiple perspectives. One conceptual framework categorizes quality astranscendent (some abstract philosophical, perceptual, moral, or religious entity), product based (fit for use, performance, safety, and dependability), user based (able to satisfy human needs), manufacturing based(conforming to engineering and design specifications), or value based(difference between conforming to specifications and monetary cost).4The latter category has a lot to do with perception; put simply, somethingthat exhibits a high level of conformance and relatively low cost wouldbe “high value.”5In our engineering systems context, quality means that the artifact orsystem is well made to achieve its function. In this respect, opening andDe Weck—Engineering Systems8799 004.indd 696/16/2011 7:30:23 PMQ
70QChapter 4closing without squeaking is a sign of quality in a door. In strictly engineering terms, such quality is often a direct result of “tolerance”—thepermissible limits of variation in a physical dimension or some measuredvalue or physical property of an artifact or, for that matter, anything ina system. The story of Henry Martyn Leland illustrates how quality inengineering grew to become an important ility.Leland was a machinist who made tools and micrometers usingextremely tight tolerances of fractions of an inch. Settling in Detroit, heachieved tolerances as tight as 1/2,000th of an inch (astonishing for thosedays) and was recruited directly into automobile manufacturing. Later,he became the founding president of Cadillac Motor Company, whichby 1905 was one of the world’s leading automakers.Cadillac automobiles were known, as one writer of the time put it, forbeing “free of temperament” because of their high levels of workmanship (or craftsmanship) and reliability (an ility that “supports” quality, aswe will see later). Perfectionism in the pursuit of quality was the touchstone of Leland’s approach, and given that Cadillac used standardized,machine-produced parts, the achievement was remarkable. Most automakers of the time bought into the notion that hand-made parts weremore refined and precise.Ideally, an artifact or system should work all the time and in the wayintended, but that was usually an unrealistic expectation. Leland’s story isabout quality being associated with tolerances and translating into reliability and an assurance that the artifact is well made. Quality becameimportant because its absence creates more side effects and exacerbatesproblems related to other ilities such as maintainability and reliability. Thefocus on maintainability and reliability gave rise to the need for serviceorganizations. Car dealerships were never only in the business of sellingcars, but offered an important service of making needed repairs to thosecars. This may be a significant antecedent of the modern service economy.No discussion of quality would be complete without a mention of W.Edwards Deming, an American statistician who is often referred to asthe father of quality management. In the period after World War II,Deming worked as a census consultant to the Japanese governmentunder General Douglas MacArthur. It was in Japan that he began toteach business leaders statistical process control methods. The rest ishistory, and Deming is thought to have had more impact on Japanesemanufacturing and business than any other non-Japanese person.Asked by the Japanese Union of Scientists and Engineers to teachstatistical process control and concepts of quality, Deming gave a seriesDe Weck—Engineering Systems8799 004.indd 706/16/2011 7:30:23 PM
Life-Cycle Properties of Engineering Systems71of eight lectures in the summer of 1950 in which he convinced top Japanese managers that improving quality would reduce their expenses whileincreasing their productivity and market share.7 This flew in the face ofthe long-held conventional wisdom, which was that there was an inverserelationship between quality and productivity, and that improvements inthe former would always lead to a decrease in the latter. Japanese manufacturers embraced Deming’s ideas, much more so than those in theUnited States (that was to begin only two decades later), and thewide application of his techniques led to unprecedented quality andproductivity levels, which lowered costs and boosted global demand forJapanese products.Over time, the understanding of quality evolved to the point wherequality became something engineers sought to achieve from the verybeginning of the design process rather than at the end of the manufacturing process, by filtering out parts that did not meet some required tolerance threshold. In the epoch of complex systems, the objective of achieving“perfect first-time quality” was one of the prime motivators behind theToyota Production System we mentioned in chapter 1 and cover moredeeply in chapter 6. With a high level of quality from the outset, theartifact or system is far more likely to last a long time, thus giving itdurability and requiring comparatively less preventive maintenance andrepair, and hence generating fewer of the side effects (operating costs,etc.) associated with these problems. The longstanding reputation ofToyota cars as highly being reliable—the company’s significant problemsof early 2010 notwithstanding—speak to this very point.Toyota was an early adopter of the ideas of Genichi Taguchi, a Japanese engineer and statistician who, beginning in the 1950s, developed amethod for improving the quality of manufactured goods through theapplication of statistics. His work expanded Deming’s ideas while alsointroducing some new concepts.In Taguchi’s philosophy of quality, design is used to obtain the minimumdeviation from what customers desire from the outset. The goal of designand manufacture is then to minimize the “Taguchi loss function,” whichcaptures how far an artifact is from the ideal or desired target state. Inaddition, the design is optimized so that any unachievable or overlyexpensive tolerance does not affect the customer or overall quality goalby making the system’s behavior relatively insensitive to such difficultto-control parameters. Thus, the artifact is designed to be immune touncontrollable environmental factors and internal variables that are difficult to control. This is the key concept of robustness, an ility whoseDe Weck—Engineering Systems8799 004.indd 716/16/2011 7:30:23 PMQ
72QChapter 4importance and emergence are captured in figures 4.1 and 4.2. Taguchialso emphasized that the cost of quality should be measured as a functionof this deviation, and that it should be measured systemwide.8One thing about quality that should be mentioned is that it tends tobe relative. The Toyota story makes this point very clearly. Prior to thewidespread availability of Toyotas in the United States and Europe, U.S.and European automakers performed at essentially the same level withrespect to quality within their peer groups. That meant that for Americanand European consumers, the relative quality they perceived in cars wasdefined by their available suppliers. This changed rather suddenly withthe introduction of competition from Japan.Most of the preceding examples have been about manufacturingbased quality, but what about user-based quality? The early history ofthe telephone also tells us a lot about how quality was viewed from theuser perspective and how it has evolved as an ility.In 1910, some 10 million telephones were in use around the world; 7million were in the United States, and 5 million of those were part ofwhat came to be known as the Bell System or AT&T.9 The earliest telephone systems had a limit of about 20 miles, but in 1910, voice could betransmitted from Boston to Denver, and the expectation of coast-tocoast transmission soon was high. It took an operator about a minute tofind another user.For the earliest telephone users, the amount of time it took to place acall was likely secondary to the primary quality issue: the sound, andhence the understandability, of the voice. The first transmitters had problems, and horrible noise accompanied speakers’ voices with the earlygrounded wire system. The invention and use of “doubled wire” did a lotto eliminate ground and induction effects. Over time, more improvements in cables—mostly changes in insulation—were also critical toimproving voice quality (and also to reducing costs).Among many important innovations, the Pupin Coil stands out in thehistory of the telephone. In electronics, loading coils are used to increasea circuit’s inductance. Oliver Heaviside, a self-taught English physicist,mathematician, and electrical engineer, had theorized in 1881 abouttransmission lines in studying the slow speed of the trans-Atlantic telegraph cable.10 Representing the line as a network of infinitesimally smallcircuit elements, Heaviside concluded that distortion of the signal transmitted on the line could be mitigated by adding inductance to preventamplitude decay and time delay. The mathematical condition for distortionless transmission came to be known as the Heaviside condition.De Weck—Engineering Systems8799 004.indd 726/16/2011 7:30:23 PM
Life-Cycle Properties of Engineering Systems73In 1894, Mihajlo (Michael) Pupin, a Serbian immigrant to the UnitedStates, patented a type of coil that “loads” the line with capacitors ratherthan inductors—an approach that was largely dismissed by others. AT&Tfought a patent battle with Pupin. The short version of the story is thatPupin’s approach ultimately prevailed. It greatly reduced the amount ofcopper required (at that time, expensive copper could account for halfof the capital investment required to set up long-distance telephonelines) and made longer distances feasible.Improved versions of the Pupin Coil developed by AT&T were calledrepeaters. Basically, a repeater is a device that amplifies the signal so itcan be “regenerated” and passed along without diminishing its quality.This is, of course, the realm of analog signal processing, well beforeinformation theory and digital communications were invented.11Research began in 1912, and by 1915 success had been achieved to thepoint where long-distance phones were working between New York andSan Francisco.Telephone quality in the early days revolved around very importantconcepts that would emerge much more strongly in the epoch of complexsystems and even more so in the epoch of engineering systems: humanfactors and ergonomics.12 These are discussed later in this chapter.SafetyThe story of the automated traffic signal illustrates both safety, discussedhere, and maintainability (detailed later). Police officers had long beenstationed at busy intersections to direct traffic in cities, even before theintroduction of the automobile. In 1868 in London, a revolving gasilluminated lantern with red and green lights—indicating “stop” and“caution,” respectively—was installed at one busy intersection;
Q De Weck—Engineering Systems 4 Life-Cycle Properties of Engineering Systems: The Ilities In the epoch of great inventions and artifacts, the implicit mandate of the engineer and inventor was to “design for first use.” The aim was to design and build an artifact that would “work” and fulfill its primary function
2.1 Life cycle techniques in life cycle sustainability assessment 5 2.2 (Environmental) life cycle assessment 6 2.3 Life cycle costing 14 2.4 Social life cycle assessment 22 3 Life Cycle Sustainability Assessment in Practice 34 3.1 Conducting a step-by-step life cycle sustainability assessment 34 3.2 Additional LCSA issues 41 4 A Way Forward 46
life cycles. Table of Contents Apple Chain Apple Story Chicken Life Cycle Cotton Life Cycle Life Cycle of a Pea Pumpkin Life Cycle Tomato Life Cycle Totally Tomatoes Watermelon Life Cycle . The Apple Chain . Standards of Learning . Science: K.7, K.9, 2.4, 3.4, 3.8, 4.4 .
Insect Life Cycle Level L 5 6 These animals have a different kind of life cycle. A life cycle is the series of changes an animal goes through during its life. Insects have fascinating life cycles. Some insects have a four-stage life cycle. The insect lives as an egg, larva (LAR-vuh), pupa (PYOO-puh), and an adult. Others have a three-stage life
Life Cycle Impact Assessment—phase of life cycle assessment aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product. Life Cycle Interpretation—phase of life cycle assessment in which the findings of either the
4.UNEP/SETAC (2011). Global Guidance Principles for Life Cycle Assessment Databases. UNEP/SETAC Life-Cycle Initiative. ISBN: 978-92-807-3021-. 5.UNEP (2003). Evaluation of environmental impacts in Life Cycle Assessment, Division of Technology, Industry and Economics (DTIE), Production and Consumption Unit, Paris. 6.ISO 14040 (2006).
3.1 life cycle 3.2 life cycle assessment 3.3 life cycle inventory analysis 3.4 life cycle impact assessment 3.5 life cycle interpretation 3.6 comparative assertion 3.7 transparency 3.8 environmental aspect 3.9 product 3.10 co-product 3.11 process 3.12 elementary flow 3.13 energy flow 3.14 feedstock energy 3.15 raw material LCA MODULE A1 18
Life Cycle Impact Assessment (LCIA) "Phase of life cycle assessment aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product" (ISO 14040:2006, section 3.4) Life Cycle Interpretation "Phase of life cycle assessment in which the .
2.0 Life Cycle Assessment (LCA) 5 2.1 Life Cycle Inventory (LCI) 7 2.2 Life Cycle Impact Assessment (LCIA) 11 2.3 Framework 13 2.4 System Boundaries 16 2.5 Limitation and Problems 19 3.0 Life Cycle Cost Assessment (LCCA) 20 3.1 Life Cycle Cost (LCC) 20 3.2 Levelized Cost of Energy (LCOE) 22 3.3 Financial Supplementary Measures 23
