Third Concept: Sector-Shaped Gear
2.5 C ASE S TUDY IN U RBAN P OWER I NFRASTRUCTURES
In Section 2.1, we introduced the 14 Grand Challenges from the National Academy of Engineering and stated it will require sound design thinking to address the enormous theoretical and practical issues that each challenge poses. Although mechanical engineers will play signifi cant roles in each challenge, a few of the challenges will demand lead roles from them. One such challenge is to restore and improve urban infrastructure. In this challenge, urban infrastructure consists of the fundamental systems that support a community, region, or country, including transportation, communication, water, sewer, power, and gas. In this case study, we trace the development of a design concept to meet a set of needs that leverages both the transportation and power infrastructure.
Requirements Development
A number of countries around the world have aging power infrastructures, and many are near a breaking point due to the increasingly heavy demands as urban centers grow. As more nations continue to modernize and establish these critical infrastructures, urban centers will continue to require more and more power. Rolling blackouts (intentional power outages) are part of daily life in many countries, including Nepal, Pakistan, Cameroon, Nigeria, South Africa, and Egypt. Such blackouts have also been experienced at times in portions of the United States, including Texas, California, New York, and New Jersey. Therefore, there is a dire need to design strategies, products, and systems to reduce the strain on the power grid in a large modern city.
A design team is tasked with designing a system to meet this need. After defi ning the basic design problem and need, a set of requirements must be developed, accounting for all the possible stakeholders.
The design team develops the following set of system requirements. These requirements state what the system must do, not how. Determining how starts in the conceptual design stage.
• Affordable: Despite the global problems of renewing infrastructures and supplying energy being on the verge of a crisis, any realistic solution must be affordable for the customer buying the system and for the manufacturer producing it. The end customers could be individuals or county/state/national governments.
• Reliable: Any product or system that is integrated into a national power infrastructure must be absolutely reliable; otherwise, the system is considered a failure.
System requirements
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• Effi cient: This system must be as effi cient as possible at collecting or creating energy and at converting it to a usable form of energy.
Unnecessarily wasting energy in the collection, creation, or conversion process only further complicates the problem.
• Aesthetically attractive/unobtrusive: Whatever system is designed, it must be visually appealing to those impacted by its placement. Preferably, it should be integrated into the existing natural landscape or installed out of sight.
• Minimize noise levels: The system must minimize the amount of noise produced during its operation.
• Simple to install: The system needs to be easy to install regardless of whether it is installed in a small private application or in a large public application.
• Adaptable: To have a wide global impact, the system needs to work across a wide range of geographies, climates, cultures, cities, and landscapes.
• Easy to maintain: All engineered systems will degrade over time. This system needs to provide all customers with a simple maintenance and repair plan.
• Safe to use: Because the system will be handling power of various types, there is potential for serious or fatal injury if the system is not designed well from a safety perspective. The system must meet all governmental codes for safety and minimize all risk of harm.
• Easy to manufacture: This requirement aims to minimize the manufacturing cost associated with producing the system. Minimizing overall product costs helps in keeping prices down.
• Small installation footprint: Because the solution is focused on urban centers, space will almost always be a concern. The system must not require large installation footprints in areas where available space is at a minimum.
Conceptual Design
Once the requirements have been established, the design team moves to the ideation phase, where many concepts are generated. Although a number of effective ideation techniques exist, the design team chooses to use a group brainstorming technique in which each member generates fi ve ideas, passing them on to the next member, who then either generates new ideas or improves on the ideas handed to them. This process continues until the ideas are returned to the originator. The result of this divergent thinking phase is captured in Table 2.1 on page 64.
Once the concepts are generated, the design team can move to convergent thinking where the ideas are narrowed down until one is selected. An initial screening of the concepts is performed using a series of economic and technical feasibility assessments. If a concept is not economically and/or technically Divergent thinking
Convergent thinking
2.5 Case Study in Urban Power Infrastructures
feasible, it is eliminated. Of the 30 original ideas, 19 are eliminated and 11 are kept for further analysis. Each of the remaining 11 concepts are then evaluated using the list of system requirements. Each concept is rated on a scale of 1–10 on how well it would meet each requirement. Without full working prototypes of each concept, these ratings can be subjective, but should utilize research on similar systems, engineering estimations (see Chapter 3), prototype testing if appropriate, and previous experience. After rating each of the remaining 11 concepts, the top fi ve concepts, in order, are found to be:
• Energy-producing sidewalks • Treadles
• Gym production systems
Table 2.1
Power Infrastructure Alleviation Concepts
Mini wind turbines placed on roofs of buildings Sidewalks that produce energy when walked on
Mini turbines in toilets that generate energy when fl ushed Batteries using new high-kappa materials
Hybrid cars that charge the grid when not in use A large array of roof-mounted solar panels across the city Wind turbines located near a city
A power plant using a Rankine cycle with rocket-derived combustion A plasma-arc gasifi cation plant to burn garbage to produce power Increasing the number and effi ciency of traditional steam power plants Developing a series of hydroelectric dams
Geothermal plants that exploit in-ground temperature differences Generating power from humans using a Matrix style farm Developing a fusion reactor
Extracting methane clathrates trapped in natural deposits Using algae as a biofuel
Developing a revolving door generator for use in large commercial buildings Photovoltaic steel to generate energy
Photovoltaic paint to generate power on all buildings
Generating power in gyms (treadmills, bicycles, elliptical machines) Using running animals to generate power
Food recycle science system to capture methane Genetically engineering microbes to output octane
Space-based solar power array to send power to Earth from space Organic Rankine cycle to recover heat from lower-temperature sources Tidal generator that uses the tides to move turbines
System to collect the massive power in a hurricane A network of under-desk treadles to generate power Capturing energy from sound using microphone membranes Smart meters to monitor and conserve energy
Darrieus rotors placed around city as sculpture exhibit
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• Smart meters • Toilet turbines
Having a set of highly ranked concepts allows a company to be fl exible with its development process and to generate multiple solutions for different markets.
Detailed Design
In the next phase, the design team develops the design details for the chosen concept(s). For instance, if the team decided to develop innovative energy-producing sidewalks, they would have to design or choose each component of the system, determine the fi nal layout, and develop a production plan. This would require the team to consider the following issues:
• The calculation of the compressive force created by a person walking • How to design the sidewalk surface so that a small defl ection creates
energy but does not alter the normal experience of walking on a sidewalk (Will it require a mechanical, chemical, or electrical mechanism?) • The calculation of voltages, currents, and a plan to transform the power
into a suitable, storable form
• A plan to both retrofi t existing sidewalks in an effi cient manner and integrate the system into the design of new sidewalks
• Analysis of the impact of different geographies, including temperature, humidity, altitude, and corrosion
• Ensuring that all governmental codes on safety and environment are strictly met
• Patenting of any new technology and not infringing on any current patent
• The calculation of fatigue limits of all components because they will undergo many cycles
• Contacting material and component suppliers and determining production and assembly process
• Manufacturing cost estimates and price projections • Component sizing and layout
The product layout is most commonly and effi ciently developed using CAD technology, which facilitates integration with manufacturing, suppliers, inventory, and customers. For example, Figure 2.22 (see on page 66) shows a general layout for a piezoelectric system to be installed inside sidewalks. The system is sized to match the average human foot. The power recovery system also includes a transformer to convert the low-current and high-voltage output from the piezoelectric crystals to a higher current and to a suitable lower voltage. From the recovery system, the AC current is converted to a DC current that is capable of charging a lithium-ion polymer battery.
2.5 Case Study in Urban Power Infrastructures
Many times a CAD model is used not only to represent geometrical layouts but also to simulate the product’s performance.