Computational fluid dynamics (CFD) has been used in several programs to analyze the airworthiness of airplanes. The aerodynamic characteristics of a massive aircraft can be accurately analyzed only if its detailed geometry
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Subtle dimensional differences between the new (top) and used (bottom) Schick shavers.
and shape can be precisely modeled. The digital 3D scanning technology is the most effective method to ensure this accuracy. 3DScanCo/GKS Global Services once scanned an entire Airbus A319 with the Trimble GS200, a scan- ner for capturing large-scale objects. The scan data were used to generate a CAD model of the aircraft by reverse engineering. Figure 2.15a shows the scanning of the aircraft. Figure 2.15b illustrates the raw scan data, show- ing holes and other imperfections on the model surface. Figure 2.15c and d depicts the polygonal wireframe model and the CAD rendering, respec- tively. Computational Methods, an aerodynamic analysis company, later applied this CAD data and CFD analysis to evaluate the performance of an Airbus A319 aircraft installed with custom-built parts (3DScanCo/GKS Global Services, 2009b).
The 1954 Chevy 3100 is an American classic and vintage truck. Southern Motor Company partnered with Panoz Automotive to bring this legacy car back into production. Panoz contracted 3DScanCo/GKS Global Services to scan and reverse engineer the body of this automobile and to capture the bolt hole locations on the chassis. 3DScanCo/GKS Global Services scanned and generated the point cloud data for the auto body. In order to actually capture the location and size of the bolt hole locations on the chassis, 3DScanCo/GKS Global Services used the Konica Minolta vivid 9i scanner along with pho- togrammetry to establish a data file within 0.002 in. in precision. Applying reverse engineering with these scan data, 3DScanCo/GKS Global Services modeled the entire truck body in smooth CAD surfaces, which could then be incorporated into Southern Motor Company’s manufacturing process.
Figure 2.16a and b shows the STL polymesh used as a basis for reverse engi- neering and the CAD rendered in this project, respectively (3DScanCo/GKS Global Services, 2009c).
In another case, Capture 3D, Inc. utilized two complementary noncontact data acquisition devices to capture the full exterior surfaces of a Falcon-20 aircraft that has a span of 16.3 m (53 ft 6 in.), length of 17.15 m (56 ft 3 in.), and height of 5.32 m (17 ft 5 in.). Despite the large size of the airplane and its complex geometric surface features, the measurement of the full aircraft was done in one coordinate system. This project was commissioned by the Aerodynamics Laboratory of the National Research Council (NRC) Institute for Aerospace Research in Ottawa, Canada, for simulated CFD analysis with computer-generated models. To obtain the actual surface data of the aircraft as built, reverse engineering played a key role in linking the physical and dig- ital model environments. The reverse engineering devices used and the fun- damental principles applied in this study will be briefly discussed below.
In the early 1990s, a digitizing system, Advanced Topometric Sensor (ATOS), was developed primarily for automotive industry applications. The system was utilized to capture the geometric information from automobiles and their components to generate CAD models. Today, ATOS is used for many indus- trial measuring applications. The first device used in the Capture 3D/NRC Falcon-20 project is an ATOS II digitizer that is equipped with structured white-
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(a) Scanning of the aircraft. (b) Surface model from raw scan data. (c) Wireframe model of A319.
(d) CAD rendering. (All reprinted from 3DScanCo/GKS Global Services. With permission.)
light projection for optical scanning. This optical measurement technology is based on the principle of triangulation, and the software can calculate the 3D coordinates up to 4 million object points per measurement. The complete 3D data set can be exported into standard formats for further processing.
The TRITOP is an optical coordinate measuring device. It is used to coor- dinate scanning and measurement. It applies the principle of photogram- metry, and uses reference markers to generate a global reference system on large or complex objects. These markers will be used for both the TRITOP and ATOS II scan processes. They are the reference grid for the individual ATOS scans needed to cover the full surface. TRITOP scanning is conducted manually with a high-resolution digital camera, which is used to take mul- tiple pictures from varying positions around the aircraft. These images are then automatically triangulated and bundled together, producing a global reference system to be utilized later by the ATOS II scanner for scan patch placement. Figure 2.17a and b illustrates the ATOS/TRITOP scanning pro- cess of a Falcon-20 aircraft. Figure 2.17a shows the aircraft with reference marks under scanning. Figure 2.17b shows the fringe patterns that are pro- jected onto the object’s surface with a white light and are recorded by two cameras during the scanning process.
For the components where detailed features are required, multiple scans (i.e., measurements) are performed. The scanning software will align all the measurements to the same coordinate position and then generate a
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(a) STL polymesh. (b) CAD render. (Both reprinted from 3DScanCo/GKS Global Services. With permission.)
normalized final data set. The ATOS system uses the TRITOP generated ref- erence file for automatic scan patch orientation. As each scan is taken, the ATOS software responds with information on the quality of the scan and the fit of the scan patch in the global reference system. The system will then auto- matically merge that scan into the reference system and existing point cloud.
The engineer can actually watch a real-time buildup of the point cloud on the screen as the Falcon-20 is scanned. This helps to ensure complete and effec- tive scanning. After the aircraft has been scanned, the ATOS polygonizing module will fine-tune the alignment and generate the point cloud STL file to meet the requested density and resolution. These data can then be processed in various ways and exported out in ASCII, STL, IGES, or VDA format.
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(b) FIgurE 2.17 (See color insert following p. 142.)
(a) A Falcon-20 aircraft with reference marks under scanning. (b) Fringe patterns. (Both reprinted from Capture 3D. With permission.)