Chapter 01 Vincent - WIT Press...balloons to tires, from airships to spacesuits, pneumatic technology has helped realise some of the greatest visions of mankind. Harnessing the dynamic

CHAPTER 9

Compliant habitats

J. Kimpian & C. H. M. JenkinsCompliant Structures Laboratory Mechanical Engineering Department South Dakota School of Mines and Technology Rapid City, SD 57701

Abstract

This chapter provides a brief outline of the use of compliance in habitats, both natural and man-made.

1 Compliant habitats in nature

Early humans likely took ideas for design of their constructed habitats from nature. Several interesting examples are given below of the use of compliant habitats in nature (while other examples, such as spider webs, are given elsewhere in this volume). Examples such as these may have given early humans ideas for rapidly deployable and portable habitats.

1.1 Paper wasps [1]

Paper Wasp is the common name for medium to large size wasps that build nests from a paper-like substance. There are about two dozen species of Paper Wasps in North America and hundreds of species worldwide. A common North American species is the Golden Paper Wasp. The wasps are typically about 2 cm (0.75 inch) long with yellow markings on a brown, black, or reddish body. Nectar is the primary energy source for adults, while the larve feed on caterpillars.

The nests of most species look like an upside down umbrella suspended from a single stem or stalk (Figure 1). The nest consists of a few to several dozen brood cells (larval habitats). The Paper Wasp collects plant and wood fibers, which are then mixed with saliva and chewed into a papier-mâché like material and formed into the thin cells of the nest. Some nests are

www.witpress.com, ISSN 1755-8336 (on-line) WIT Transactions on State of the Art in Science and Engineering, Vol 20, © 2005 WIT Press

doi:10.2495/978-1-85312-941-4/09

194 Compliant Structures in Nature and Engineering

completely enclosed in a paper dome. Nests are constructed in protected areas such as under the eaves of buildings and in dense vegetation.

Figure 1. Paper Wasps attend to their nest.

1.2 Aquatic insects [2]

Many aquatic insects (e.g., Coleoptera and Hemiptera) carry air with them in the form of a bubble. Water bugs are members of the class Insecta and are good examples of insects that use compliant pneumatic habitats . The giant water bug belongs to the family Belostomatidae, one of 50 families in the order Hemiptera. There are approximately 100 species in the family Belostomatidae that live primarily in North America, South Africa and India. Giant water bugs are approximately 4 cm (1.5 inch) in length, with some species growing as long as 10 cm (4 inch) long. The body is brown, flat and oval, giving them an appearance similar to that of a cockroach.

The posterior end of a giant water bug has two retractable, semi-cylindrical appendages which, when held together, form a breathing tube. This tube is used for underwater breathing. Like terrestrial insects, air is exchanged through small openings of the respiratory system called spiracles.

When submerged for long periods of time, giant water bugs carry a temporary external air supply in the form of an air bubble. The bubble is in contact with the bug’s spiracles located between their wings and their abdomen’s upper surface. Patches of hairs or cavities under the wings hold the bubble against the insect’s spiracles. As the insect consumes oxygen, the amount in the bubble decreases and more oxygen diffuses in from the water.


Compliant habitats 195

1.3 Labyrinth fish [3]

Labyrinth fish are very popular for home aquariums because of their beautiful colors and interesting behavior. In the wild, Labyrinth fish extend from China and Korea, all through southern Asia including the Philippines, to Africa. The single most distinguishing trait of the Labyrinth fish, which is unique among species, is the organ they possess that gives them their name. The labyrinth is located above the gills and consists of skin folds, called lamelli, which are filled with blood vessels and through which oxygen can be absorbed from the air. This feature allows the Labyrinth fish to survive in water with very low oxygen levels.

Many Labyrinth species build nest of small air bubbles. These nests are always built by the male, and their size, shape and position depends upon the species. The nest is made at the water surface among floating plants. Some fish incorporate plants into the nest and some are all bubbles. The male courts the female under the nest, where he curls around her and turns belly up. The eggs are extruded and fertilized from this position. They usually float up into the bubble nest and become almost invisible.

2 Compliant architecture

2.1 Indigenous compliant habitats

Indigenous peoples worldwide have made use of compliant habitats for centuries, whenever rapidly deployable shelter was needed. The tipis of the Native American (Indians) are typical examples. Constructed of animal skins supported by wood poles, the tipi provided a portable domicile (Figure 2).

Figure 2. View of a Native American Sioux tipi camp on the open prairie, Dakota Territory, showing a covered entry and timber piles with two figures in the distance (courtesy Western History/Genealogy Department, Denver Public Library)



2.2 Modern compliant architecture

Throughout the past millennium, inflatable structures have been at the frontier of scientific exploration wherever lightness, deployability, or structural economy was a prerequisite. From balloons to tires, from airships to spacesuits, pneumatic technology has helped realise some of the greatest visions of mankind. Harnessing the dynamic power of air, man escaped the constraints of gravity and friction; in challenging these constraints he furthermore discovered that huge structures could be deployed with a speed unknown to traditional types of construction.

Air-inflated structures came into their own during the Second World War when military imperatives sparked an unprecedented demand for deployable structures, like life rafts, escape slides, shelters and hangars that drove inflatable technology forward (Figure 3). In the 1950s, freed from the confines of military functionalism, these technological advances brought to light the great potential that instantaneous enclosures offered to architecture. Accordingly, air structures gained ground as a revolutionary construction technique, which would eliminate lengthy construction periods, be flexible and affordable, and functionally well integrated.

Figure 3. Examples of several inflatable terrestrial structures.



In the post-war era, freed from the confines of military functionalism, these technological advances brought to light the potential which ‘instantaneous’ inflatable enclosures offered to architecture. For the architects and designers of the time recent childhood memories of vast flying structures were a genuine source of inspiration that fuelled a utopian vision of the future in which multiform, adaptable and curved forms replaced the rigid and rectilinear architecture of the past. Inflatable form, which is organic in appearance and ephemeral by its very nature, offered the 1960s’ generation liberation from architectural orthodoxy. Pneumatic structures also appealed to a whole generation of radical young engineers. Since no part of the pneumatic structures is in flexure or torsion, they are among the lightest forms of construction.

However, the optimistic hopes for flexible and affordable buildings, which culminated in the multitude of inflatable pavilions at the 1970 Osaka Expo, were short-lived. Inflatables fell victim to a series of technical and design problems (Figure 4). The difficulties inherent in designing and simulating curved form, manipulating dynamic structural behaviour, as well as inadequate materials and imprecise manufacturing led to poor designs and a decline of interest in pneumatic construction. Neither could simple membranes provide a universal solution that could satisfy the complex demands on a building skin. By the mid-1970s, the image of a glamorous architectural language, unbounded by material concerns and gravity, gave way to practical concerns over an awkward design process involving a perpetually vanishing building material (air), severe limitations in form and tectonic language, unpredictable structural performance, and a monolithic and uniform aesthetic. It was not until three decades later that science and technology caught up with the visions of the past and these problems could be re-assessed.

Figure 4. Inflatable tennis court enclosure at the University of New Mexico. Skin damage can be easily seen in the figure.

During the 1980s the emphasis shifted to canopy structures, which were used almost exclusively in roofing where they are less affected by membrane vulnerability and fire problems and still relatively inexpensive to “haul into place”. Their success lay in the fact that rigidizing membranes through high tension conveniently eliminated unpredictable dynamics, unreliable pumps, and wrinkly, bulging forms (Figure 5). However tensile membranes also



required a supporting structure, and detailing was more costly due to the higher stresses involved.

Figure 5. Tension fabric roof at the Denver (Colorado) International Airport

Transparency also remained a problematic area but since the mid-1990s. Foil cushions combined with rigid lightweight frames and cable net structures have begun to appear on the market (Figure 6). Their advantage over tensile membranes is that they provide much better thermal insulation and acoustic properties than conventional tensile membrane structures with substantially less supporting structure. These low-pressure transparent cushions have led a move back towards inflatable structures, albeit as forgiving cladding systems for curved buildings rather than genuine air-supported structures. The turn of the Millennium saw many of the 1960s’ designs realised in this way, most famously the Eden Project by Nicholas Grimshaw and Partners, which strikes a strong resemblance to Buckminster Fuller’s famous Pillowdome. Another notable example was Branson Coates’ design for Powerhouse::UK, which highlighted a touring exhibition of British Design. Lighting effects dramatically enhanced the curves of four steel-framed silver cushion-clad drums, which were linked in the center by a tensile roof. The combination of concave (tensile) and convex (inflatable) membranes was reminiscent of Frei Otto’s [4] and Antoine Stinco’s similar proposals from the 1960s. However none of these structures used air for structural support or took advantage of its dynamic properties. Instead they are efficient tensile structures where lightweight air-inflated cushions act as ‘solid’ elements in a rigid structure.



Figure 6. Examples of canopy and pneumatic cushion roofs.

During the mid-1990s, pneumatics began to experience a renaissance elsewhere. In 1992 Festo, a multinational engineering corporation specialising in the design and manufacture of pneumatic components for automation, decided to embark on a re-branding exercise. Led by the Director of Corporate Design, Professor Axel Thallemer, the company opted for an approach that would capitalize on the sensational image of pneumatic structures by marrying “fun” with high-tech. Festo had the financial muscle, as well as the motive, to adopt engineering feats from parallel industries to demonstrate new possibilities in pneumatic design. With each new endeavour they produced a major breakthrough for pneumatic structures.



Their initial project was a design for two hot-air balloons flying together, one of them inverted. In 1996 they erected an inflatable exhibition hall, ‘Airtecture’, which was the first pneumatic building to have parallel walls and a cubic form. The walls were made of spacer fabrics, with intermittent ET foil sections for transparency. Pneumatic roof beams, linked by depressurised fabric chambers, formed the roof structure. The building is flanked by pneumatic columns of minimal structural purpose but which define the articulation of the building. The structure is beautifully detailed and relies on pressure sensors and pneumatic pumps to maintain its structural integrity. The building’s fabricators were inflatable boat manufacturers DSB, who were pioneers in adapting spacer fabrics for such use.

Festo’s next project was ‘Stingray’, a pneumatic ‘flying object’ that was a cross between an airship and an aircraft. Its magnificent shape, sculpted by a succession of air chambers reminded the viewer of the giant manta ray (Figure 7). Two further inflatable aircrafts followed. Their most remarkable features were the wings, the shape of which could be gradually adjusted through the pressure regulation of the wing chambers. Unlike solid metal pneumatic/hydraulic parts, which have a motion lag, these pneumatic objects were the first to take advantage of progressive shape-change in compliant membranes. Professor Thallemer’s group was the first to implement pneumatically controlled dynamic shape change in a saleable product. In the process they came up with a truly ‘smart’ membrane.

Figure 7. Inflatable aircraft.



A new wave of young designers is keen to explore new compliant design opportunities. Kimpian presented a design for a portable inflatable auditorium that demonstrates solutions for some of the obstacles that pneumatic architecture encountered in the past (Figure 8). Instead of suppressing the dynamic properties of air-inflated structures, the design took full advantage of them. Soft linkages allowed for the swaying of the beams in wind. Reconfiguration of the beams was achieved on the one hand by ‘air film’ technique, harnessing the power of ‘expelled’ air, and on the other, by 2D mechanisms. The sensors, the processing power and the programming mathematics necessary for the operation of such a structure are now readily available from the manufacturers of pneumatic systems. This form of tuneable geometric control of space and volume represents a new approach to construction and is particularly suited to the brief of the inflatable auditorium where the building can adapt to changing user requirements, and where the shape-change itself is part of the theatrical scene. The scheme also incorporated new membrane materials that are strong yet harmless to the environment. The structure’s integrity was tested with software that had initially been developed for simulating parachute deployment.

Figure 8. Portable inflatable auditorium concept.



3 Conclusion

Since the earliest of times, nature has realized the efficacy of compliant habitats. Several examples have been given at the outset of the chapter. Humans are likely to gain inspiration from these natural designs. Over the last several decades, many examples can be shown of human-engineered membrane/inflatable habitats. Currently, experimentation, worldwide exhibitions, and a series of new publications suggest that the enthusiasm for pneumatic structures is far from exhausted. On the contrary, current technological advances suggest that we are getting closer to the source of fascination that inspired the visionary optimism of the post-war generation.

References

[1] www.everythingabout.net/articles/ biology/animals/arthropods/insects/wasps/paper_wasp/ [2] www.zoo.org/educate/fact_sheets/waterbug/waterbug.htm [3] badmanstropicalfish.com/labyrinthfish.html [4] Otto, Frei (editor), Tensile Structures, MIT Press, 1973


Documents

Chapter 01 Vincent - WIT Press...balloons to tires, from airships to spacesuits, pneumatic technology has helped realise some of the greatest visions of mankind. Harnessing the dynamic