3D Model Automation Not Just Blowing in the Wind18 Dec, 2007 By: Cadalyst Staff
Custom SolidWorks add-on improves efficiency for engineering consulting firm that specializes in wind analyses on high-rise buildings.
If you are building a project that literally scrapes the sky, you will likely need the rarified services of a company like Rowan Williams Davies & Irwin (RWDI). This Toronto-based consulting firm has provided wind engineering, environmental air quality, and noise management services for many of the largest architectural projects in the world, from Taipei 101 in Taiwan (currently the world's tallest building) to Burj Dubai in the Middle East (which will soon take over the title) to Daniel Libeskind's Freedom Tower at New York's World Trade Center site.
For these substantial projects, RWDI uses a SolidWorks 3D electronic model to output a series of recommended design wind pressures. The company simulates and analyzes many of the environmental effects on superstructures using a variety of tools, including wind tunnel testing, and computational fluid dynamics (CFD) using Fluent and a custom-designed program called VirtualWind. Certain studies, like the wind-tunnel pressure test, require a physical scale model of the proposed building to be constructed, along with the surrounding terrain and cityscape.
"A pressure study looks at the effects of the wind on the exterior envelope of a building in the context of its geographic area. These wind effects will be different in a crowded downtown area than if the structure was built out in the middle of a field. Often times you're dealing with very complex wind flows," explained Matthew Browne, RWDI wind engineering specialist. "The wind tunnel testing gives very accurate, project-specific design information."
A detailed model of a building ready for the wind tunnel test. The building's surroundings are handcrafted using rigid foam.
RWDI constructs its study models using rapid prototyping technology (RP) or stereolithography (SLA) from 3D Systems, which produces a model via the layer-by-layer curing of photosensitive resin. The painstaking part of the work used to be performed manually. Modelmakers had to drill holes on every surface of the model to install all the pressure sensors, or taps, needed for the wind tunnel test.
RWDI sought a way to automate the installation of pressure taps with its eTAPS, or "electronic taps" program, so the model parts could come out of the SLA machine with holes perfectly spaced for testing.
"Typically, we have to install several hundred pressure taps in a model. The eTAPS project is a way of using our RP technology to also incorporate these pressure tubes in the physical model, rather than doing it by hand with a drill and glue," Browne explained.
A SolidWorks model with the holes marked for pressure taps.
Through its in-house R&D department, RWDI developed software to locate the placement of pressure taps over a given building model at optimal spacing. To reach into SolidWorks and automatically change the geometry of the actual model, RWDI enlisted the help of Sungrace Software.
"SolidWorks provides a great deal of functionality in its API that permits geometric analysis and construction of these kinds of complicated features," said Mark Yerry, the senior developer at Sungracei who led the eTAPS project. Automatic conversion of positional coordinates into the solid model features is a conceptually simple task. "In many cases, it's straightforward," Yerry continued. "A tap will fit and have enough space behind the wall to accommodate the pressure tap. For the ones at the edge of the structure, or where there is a cluster of many in one section, we had to develop a more sophisticated set of tools. The most challenging aspects of this project involved the development of a few key algorithms."
For example, some taps needed to slant upward or downward to prevent conflicting with other sensors. "We programmed the Multi-Point Tap design tool to create the custom paths for the more difficult tap placements. So rather than simple holes, these taps follow a path that the user specifies," Yerry said.
A slanted pressure tap in a 3D SolidWorks model.
The eTAPS add-on appears as an extra menu inside SolidWorks, which gives RWDI modelmakers the means to automate the creation of simple pressure taps in the virtual model, the Multi-Point Tap tool for more congested areas, and additional tools for mold fixturing. The tools that make more complex paths still require some human decision making inside SolidWorks, but the prep time to fully instrument a skyscraper is cut to a tiny fraction of the old drill-and-glue technique.
Automating these modeling tasks has increased efficiency at RWDI by about 15%, which in turn increases the company's capacity to perform pressure studies on a monthly basis. Browne commented, "With the new eTAPS we are able to cut a significant amount of time out of a typical project."
The eTAPS SolidWorks add-on is proprietary and not for sale, and given the highly specialized work of RWDI, few others would need it. However, as firms involved in 3D manufacturing and architecture look for new ways to improve efficiencies, many may soon seek a customized modeler of their own.