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Tension revisited: Rhino

News | July 1, 2008 | By:

The first of Fabric Architecture’s series of reviews of tension structure software ran in these pages 10 years ago. Time for an update.

The idea that “as innovative visionary designers, we are limited only by our creativity” seems to be a cliché. Yes, we can dream. It embodies our aspirations and reflects our time, its values, tools and the prevalent technology. However, the notion that anything is possible seems Utopian. Transcending dreams to reality is a collaborative process, requiring communication of ideas with fellow designers, craftsmen, engineers, draftsmen, fabricators and installers. Historically, master builders have relied on an array of tools: stone tablets, papyrus, models, drafting boards and so on. Today, a designer’s tool kit consists of an array of software run on silicone-based computers, but the basic question remains: which is the best tool for the task at hand? Each tool brings a set of benefits and limitations, enabling designers to explore boundaries previously unchartered. It is appropriate to say that today’s designers are dependent on application software and the forms it can generate.

FTL’s approach to skin design and engineering stands apart from conventional wisdom.* Form generation is more than an image; it’s a process of finding surfaces that respond to design criteria yet are optimized to transfer forces. The process always begins with sketches, followed by a digital model or physical form finding (usually the latter). The form derived is optimized by analyzing it for varied loading requirements and tweaked as required. At all times the process is in a state of flux until an optimal surface is achieved.

Much can be said about Rhino, but we’ll limit our thoughts to a basic review. Rhino’s obvious strength is in its ability to rapidly create complex double curved (anticlastic) surfaces. This allows visualization and evaluation of the spatial characteristic of a surface topology before time is invested in a physical model. On the most basic level, one key feature is the ease with which Rhino can export/import with other more traditional CAD applications. This is of increasing importance because the use of any single application in a modern design studio is becoming obsolete, if it is not already. The Rhino interface is highly user friendly and intuitive, with a command line prompt and commands similar enough to AutoCAD’s to make users of that industry staple feel quickly comfortable. Additionally, right click panning and orbit is a feature that streamlines modeling. Unfortunately, this leaves the user frustrated when using other modeling applications that don’t have this feature.

We find Rhino most useful during schematic design and, to a lesser extent, at design development. It models static surfaces quickly and cleanly, something that would require great effort in other applications. By modeling as little as two lines one can begin to generate double curved surfaces that are accurate enough to get a feel for the form. When visualizing tensile structures, such as a conical form, all that is needed is a base profile, top profile and a curve that defines the curvature of the surface between the two profiles. Of course, as the surfaces become more complex more information is needed to define the topology. However, as with any tool, there are limitations and drawbacks that require some creative manipulation to achieve the desired effect. For example, the majority of our work involves undevelopable surfaces which, by definition, are created by the tensile forces in the surface material to achieve the desired shape. Rhino does not see surfaces as being under tensile stress. This results in the generated surfaces being approximations defined within the limitations of the Rhino algorithm. At best, the designer can manipulate points on the surface to fine tune the form, but this all becomes guess work and “eyeballing.” In short, to achieve proper results a designer must understand the desired shape before beginning to model because the application cannot do it for you.

When it comes to the design of tensile structures, Rhino is a useful visualization tool. Its current form, however, lacks a level of refinement to replace physical modeling in the design process.

Ashish Soni is a senior architect in the New York consulting firm FTL Design Engineering Studio; Matthew Hilyard is a designer at FTL.
*FTL is the abbreviation for FTL Design Engineering Studio, a New York City consulting firm.

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