A Solid Job in AutoCAD (Tech Trends Feature)30 Apr, 2008 By: Kenneth Wong
An engineer uses AutoCAD to generate 3D models of the U.S. Navy's Hyperbaric Diving Simulation Facility.
When Rob Burchett began his AutoCAD training, he never thought his drafting skills would land him at the bottom of a pit. But underneath a hyperbaric chamber in a dive simulator was precisely where he found himself when Técnico, a Chesapeake, Virginia–headquartered firm specializing in marine and industrial equipment repair and fabrication, hired him to create engineering drawings of the U.S. Navy's Hyperbaric Diving Simulation Facility (DSF) in Panama City, Florida, in 2007.
Armed with a caliper and tape measure and assistance from his colleagues, Burchett measured components then created a digital model of the entire DSF, from the outer geometry to the electrical parts and pipes within and even the knobs and dials on the control panels (figure 1). And he completed the project not in a parametric modeling system, as most people might have recommended. Instead, he produced it using AutoCAD 2008.
From the Ground Up
When Burchett, an associate at Técnico, told people he built the entire DSF setup "from a blank sheet," he wasn't exaggerating. He started without the usual source materials — no blueprints, no schematics, nothing. The DSF at the Naval Diving and Salvage Training Center (NDSTC) in Panama City consists of very few standard parts, so Burchett couldn't even rely on the manufacturers' catalogs to obtain the dimensions. Most were custom assemblies, like the compression chamber (known among the Navy staff as the Igloo) and the dive tank (nicknamed the Wet Pot by users), so he had to get up close and personal.
Figure 1. Rob Burchett from Técnico spearheaded the effort to document the U.S. Navy s Hyperbaric Diving Simulation Facility. The project involved recording not just the outer geometry but also the internal components.
"I went inside the chamber with my caliper and a notepad. I took measurements. Sometimes, I would get spare inventory parts, bring them back to my workstation, measure every nut and bolt on it, and build a solids model of it," he recalled.
In the beginning, Burchett routinely drove to the Naval Support Activity (NSA) center where the dive simulator is located, sketched the equipment layout, recorded the measurements, and then drove back to Técnico's Panama City office. The destinations were close by — the two-mile trip across Highway 98 and Thomas Drive took only five minutes.
"But they might as well be five hours away," said Burchett. He felt the back-and-forth commute was such an impediment that he petitioned for an on-site workstation at the NSA office. After he was set up with a dual-core Pentium PC with 3 GB of RAM, the project began to make dramatic progress.
If the dive simulator had been made up of complex surfaces, he might have used laser-equipped scanning devices to capture their shapes as point clouds. But that was not the case. "Most of the objects were just round chambers," Burchett observed. So he simply used his drafting skills to reproduce them in AutoCAD.
Edmond Delanoy, the officer in charge of the hyperbaric maintenance division and a retired diving warrant officer for the U.S. Navy, called Burchett a "Godsend." He remarked, "The drawings Burchett completed played a crucial role in maximizing modern-day methods of recording vital [system] information in those same drawings, which is crucial to the lifecycle of the system."
Despite the challenges and the seven-month-long toil, Burchett believes the solids model was well worth the effort. "It was tremendously beneficial to all of us at Técnico for forming and fitting piping, tubing, and general design arrangement of hyperbaric components," he noted.
The Job and the Tool
The Navy's requirement — and consequently part of the reason Técnico was contracted for the job — was to have a complete set of engineering drawings: construction, weld-joint identifications, schematics, and as-built assemblies (figure 2). Burchett was certain that only an accurate solid model would enable Técnico to provide the Navy with the best set of engineering drawings.
Figure 2. Técnico s solid model, built in AutoCAD 2008, represents the as-built condition of the Hyperbaric Diving Simulation Facility.
With a degree in mechanical engineering, Burchett was skilled in parametric 3D CAD modeling with packages such as Pro/ENGINEER and SolidWorks. He realized AutoCAD might not be the first choice for a large-scale, solid-modeling project for most users. But the NDSTC's workflow was standardized on AutoCAD, and the management wanted Técnico to deliver the documents in the same format.
Because AutoCAD is not parametric, Burchett couldn't expect the software to automatically adjust the sizes and shapes of the associated valves and pipes whenever he modified the geometry of a chamber or a panel. To be efficient, he had to meticulously plan out his layering systems.
"The layering system is absolutely the key," he said. "From the engineering standpoint, it's crucial that you can layer up or layer down to anything you want, to be able to nest files and cross-reference them in a sequence."
To document the complex network of pipes, Burchett took advantage of AutoCAD's Sweep command. "With this command, I can simply turn a three-dimensional polyline into a pipe," he pointed out. "I connected the line segments then entered the diameter of the pipe — say, a quarter of an inch — and had the software execute a Sweep along the path."
Another feature upon which Burchett relied was the Flatshot command. "This gave me the opportunity to use the 3D assembly model to create stunning 2D views that would otherwise be impossible to produce in a traditional 2D CAD program.
"Flatshot was a tremendous leap, a great progress in producing 2D drawings from a 3D solid model, but it still requires cleanup," he added. "In the automatically produced drawings, lots of unwanted entities still show up." Burchett said he hopes the upcoming AutoCAD 2009 might address this problem.
Swimming in Solids
Burchett's model of the dive simulator was the foundation for Técnico's refurbishing of one of the three DSFs operated by the Navy. At the end of the project, the chosen facility became fully automated.
"In the past, to operate the system, an operator would have to crank up the valves manually," said Burchett. "No more of that. Now it's computerized. Dive profiles are loaded into the computer, and the system is controlled from a console [also part of the 3D model]."
U.S. Navy's Delanoy pointed out, "In the past, it could sometimes take one or two days for one of my technicians [to get repair and routine maintenance information], going through reams of technical documentation to find the answer we need. Our quality-assurance program requires development of very detailed Re-Entry Control work packages for everything we do. So we always have to prove how we did the job, the parts we used, all the assembly specifications, and so on. With this info now embedded in the interactive drawings, we can now just point and click [see figure 3]."
Figure 3. A simple click or a zoom reveals the make and model of an assembly component, eliminating the need for technicians to search through archival drawings for this information.
For maintenance work, the solid model offered additional intelligence that could not have been derived from 2D drawings. "For example, you can unfold the pipes and easily get the total length," Burchett said. "You can perform volumetric studies or finite-element analyses. You can better understand the pipe intersections and the weld joints."
The dive training center is responsible for training all divers in the U.S. Armed Forces, the Department of Defense, and state and local law enforcement. Every year, roughly 1,500 to 1,800 students receive their dive qualifications from the facility, now maintained and automated using Burchett's AutoCAD 2008 model.