Aspectos desfavorables - Validación de los resultados obtenidos

CAPÍTULO 3: Validación de los resultados obtenidos

3.4 Aspectos desfavorables

The design of cars is a good example of the impact of constraints on engineering design.

Manufacturers operate within a highly competitive marketplace, with consumers able to choose from many makes and models — many of them produced in countries with much lower labour costs than Australia and New Zealand and possibly with much lower safety and environmental standards for manufacturing (all the vehicles must meet Australian and New Zealand standards for road safety, even if manufactured elsewhere). According to the Australian Automobile Association (2008), there are about 1500 road fatalities across Australia each year and manufacturers are constantly striving for safer designs, while not wanting to increase the cost of their vehicles. How is this achieved?

90 The 2008 Ford Falcon was the first Australian large car to achieve an ANCAP 5 star safety rating. ANCAP is the Australasian New Car Assessment Program, modelled on Euro NCAP. NCAP is a global initiative, with local variations which tests cars in every major marketplace. Ford engineers faced the challenge of achieving this 5 star rating while not significantly increasing the cost of the vehicle. They used around 5000

numerically simulated crash tests and 90 actual full crashes, 310 partial vehicle tests and 600 subsystem tests as verification of the numerical models. They used photography sequences of 1000 frames per second and studied 38 crash scenarios. ANCAP considers three crash modes (Safe Car Guide 2009).

One particular innovation in the Falcon was a new pressure sensor in the doors that serves as an early warning system of side impact. Tiny variations of pressure within a door are detected and the occupant safety measures such as airbags and seat belt tensioning can be initiated within 30 milliseconds — one third of the time it takes to blink your eye. It is that first 30 milliseconds when much of the damage is done to occupants, so controlled crumple zones are designed into the vehicle to absorb energy and provide time for the deployment of the safety technology. All of these features have been developed through the cooperation of a range of engineers — mechanical,

electrical, electronic, software and structural. By better use of technology, a safer car has been delivered with minimal impact on the purchase price — smart design within tight budget constraints.

More recent models to achieve a 5 star rating include small cars such as the Suzuki Swift. The addition of multiple airbags (frontal, side, head and knee) have contributed to the improved safety rating.

Critical thinking

How much are you willing to pay to drive a safe car? What is the trade-off between risk and cost?

91 Engineers must be creative within a constrained environment of resource availability, data, information, knowledge and regulation. How do engineers deal with problems under these conditions? As well as the engineering method, which structures their problem-solving process, they must be able to make judgements about the alternative solutions. The rules applied in this process are a collection of heuristics. The opening quote for this chapter related to heuristics — a problem-solving technique in which the most appropriate solution is selected using rules.

heuristics A problem-solving technique in which the most appropriate solution is selected using rules.

Heuristics are rules of thumb. Before the twentieth century, engineering relied heavily on rules of thumb based on past engineering practices. For example, a rule of thumb when choosing a beam for a particular span is that the depth of the beam will equal the span divided by 20. So, a span of 20 metres requires a beam 1 metre deep.

We now have more complex models and heuristics based on science. The twentieth century saw a revolution in engineering through the application of the scientific principles of

mathematics, physics, chemistry and, more recently, biology, as well as management tools such as economics and psychology. Engineering is sometimes described as ‘applied science’, though this book shows that engineering is much more complex than that and relies on an interdisciplinary combination of science, economics, management and social science.

Even science is a set of sophisticated heuristics (Koen 2003). Think about how science has changed over the last century, particularly since Albert Einstein’s first paper on special relativity in 1905. Every new scientific advance means discarding or modifying old ideas that were considered ‘true’. Before Einstein’s work, Newtonian mechanics was considered an exact description of the laws of motion. We now know that it is a good approximation at small velocities — certainly adequate for day to day living — but not very useful when designing particle accelerators that operate at 99.9999 per cent of the speed of light. Every scientific theory is a new heuristic that is trying to explain reality better than the last theory. Note also that science can’t ‘prove’ theories. It can only stack up supporting evidence. It can, however, disprove theories, by finding contradicting evidence (Popper 1983).

It is important that engineers understand heuristics, because their work is governed by codes of practice that specify minimum or maximum performance standards, such as temperature, pressure, stress, deflection, current, voltage, water quality and so on. These standards may be Australia–New Zealand standards or international standards, and will be discussed in more detail in subsequent chapters.

Engineering is also about trading off cost and risk. Engineers work within available

resources. They are responsible for making the most of resources that might be better spent on another product or service, and constantly work with limited information. Engineers cannot predict future weather events or human events; therefore, engineers are often left to make predictions of future behaviour based on historical trends.

Engineering involves the choice of a best solution or a best change. What is best?

Sometimes it is what is cheapest to build, or it might be what is cheapest over an engineering asset’s total lifespan. It could be what produces the greatest economic return, or it may be the option with the least environmental impact as assessed by a life cycle assessment. Ultimately, engineers must work with communities to help define what is best for them.

It is important for engineers to be conscious of the models and the assumptions made (heuristics), what the client wants (what is best), what resources are available (usually money) and what is and is not understood about the problem of interest (limited information).

92 summary

This chapter has provided an overview of what it means to work as an engineer, using the engineering method, which begins with a problem statement, generates alternatives, evaluates those alternatives and recommends a solution. This basic problem-solving process is wrapped in project management processes to ensure that time, resources and other constraints are properly acknowledged. Within the engineering method, systems thinking is an essential skill to make sure that the correct problem is being solved. Any engineering project will progress through a life cycle from strategic planning to decommissioning. Each engineer needs to develop reflective practice skills to improve their performance as they move from one project to the next. We will now briefly revisit each of the chapter learning objectives.

Describe the activities that constitute the engineering method and apply the method to an identified problem

The engineering method starts with the client’s need, which is identified in a client brief. The engineering method requires the collection of data and other research, which yields

alternative solutions to the problem. These solutions are evaluated against the criteria defined by the client. After this, checks are made of all of the important processes and conclusions and a recommendation is communicated to the client about the most appropriate solution to the problem. A car-buying scenario was used in this chapter to illustrate these problem-solving steps.

Identify a range of system definitions for a problem and use these definitions to present different solutions to a problem

Systems thinking is required to make sure that the right problem is being solved. It defines a problem by seeking to identify its boundary, its components and the interactions between the components, as well as those between the systems and its environment (across the boundary).

Key questions to ask are:

Are you setting out to solve the right problem?

Are there other ways of looking at the problem?

Do you have all the facts?

A congested freeway example was used to illustrate how, by redefining the problem, a range of other solutions become possible.

Apply basic project management principles to plan a project and maintain organised project documentation

Project management is the process of managing projects. A project is a temporary endeavour designed to produce a specific product or service. A key skill required in project management is scheduling. A Gantt chart is a simple way of mapping the tasks between the commencement of the project and its required completion date. Resources need to be mapped against the schedule. When and where are they required? Also, consider accuracy. How accurate an answer is required? How much effort is required to get that level of accuracy? Is this justified within the time and resources available? Risk is also an important consideration. What risks may impact your project? What is the likelihood of these risks occurring, and what are the possible consequences? What can you do about them?

Describe the role of an engineer throughout the life cycle of an engineering asset, including the differences between conceptual design and detailed design All engineering projects pass through quite distinct stages of development. These include big picture thinking such as strategic planning, and research and development. From here,

93 design proceeds in two stages: firstly, conceptual design — considering what solutions are available; and, secondly, detailed design — considering how the preferred solution will be implemented. Implementation in the field then requires some form of manufacturing or construction, followed by commissioning, testing and operation. At some point, the project will have outlived its usefulness and will be decommissioned. Conceptual design is the process of identifying a suitable solution to a problem by considering many alternatives.

Detailed design is the process of taking a conceptual design and detailing its components so they are ready for implementation.

1. In the car-buying scenario in this chapter, an attempt was made to identify suitable cars for a client to purchase. Outline other solutions available if you expand the system boundary for this problem (e.g. other transport solutions). Analyse what options are more cost

effective and document the trade-offs to be made with personal convenience and time taken for each trip with the alternative solutions.

2. How much time do you have to devote to your studies each week? You are likely to have a timetable that shows all your scheduled classes. Work out how many hours you spend attending classes each week and the amount of study you need to do for all of your subjects. You may be able to schedule some of these hours between your contact hours, utilising your library or other study spaces available to you. If you are a distance education student, you may find you spend hours online, keeping up-to-date with study requirements and communicating with course coordinators. With careful organisation, you can avoid having to spend every evening and much of the weekend studying. University study is a full-time job, which, with careful organisation, you should be able to do between 9 am and 5 pm, five days per week.

94 3. Use a reflective journal to think about all of your studies this semester. Which subjects are

going well? Which ones are not going so well? Which ones do you enjoy more or find easy? Why might this be? Identify some ways in which you could improve your

performance. Are there skills that you need to learn (e.g. computing skills, oral presentation skills or library skills)? How will you learn these skills?

4. Choose an engineering project in a discipline area to which you are attracted. Write a brief description of the type of work that would be done at each of the seven common stages of the engineering life cycle — strategic planning; research and development; conceptual design; detailed design; implementation; commissioning, testing and operations; and decommissioning.

project activity

Consider a problem of need in your area. It could be an energy problem to reduce greenhouse gases, or a water, traffic or communication problem. Write a short, hypothetical client brief based on this problem. Now shift your focus to the engineer’s perspective. Using the

engineering method, find potential solutions to this problem. Prepare a conceptual design for it, generating a short list of solutions that are superior to other alternatives. Now conduct a detailed design analysis of a component of one of your preferred solutions in order that you can specify it ready for implementation. Prepare a report that is based on your

recommendation. Your design file and communication skills should help with this.

Additional resources

Optional additional resources and activities for this chapter are available online.

References

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