Calibrate a FEA model of a frontal impact of a commercial aircraft. This work is needed because detailed engineering data of commercial aircraft is proprietary. Our model, meant to have some of the structural properties of a Boeing 767-200ER, was constructed using publicly available data and was calibrated using the Riera approach.
In 1968, Riera published a paper that analyzed the impact of an aircraft on a rigid surface; J. D. RIERA, "On the stress analysis of structures subjected to aircraft impact forces," Nuclear Engineering and Design, 8:415-426, 1968. The paper abstracted an aircraft into a longitudinal array of crush zones of different characteristics and a mass distribution. The approach allowed Riera to compute an approximate variation of the total reaction in the impacted structure over time. The resulting load curves were then used to study the dynamic response of the impacted structure numerically.
In 1988, Sandia Labs conducted an experiment crashing an F-4 jet into a large concrete barrier. This provided researchers an opportunity to check Riera's approach. Some of the results are shown in pictures culled from the literature [A, B, C, D]. They indicate good agreement between the Riera approach and actual measurements.
Since then, the Riera approach has become an accepted practice to simplify impact models; e.g., SUGANO, T., TSUBOTA, H., KASAI, Y., KOSHIKA, N., OHNUMA, H., VON RIESEMANN, W. A., BICKEL, D. C., and PARKS, M. B.: "Full-scale aircraft impact test for evaluation of impact force." Nuclear Engineering and Design, 140:373-385, 1993.
For our airplane model, we computed the mass distribution and used the Riera approach to approximate the impact force time variation in the case of the airplane hitting a rigid wall. We simulated the frontal impact of our plane model with a large concrete barrier, like the one used in the 1988 Sandia Labs F-4 crash test and computed the reaction force variation during the simulated crash duration.
The problem is set up using LS-Dyna with no fuel in the tanks. The problem size is approximately 20,000 nodes, and the total computing time was 99 hours on a dual-opteron workstation for a simulation time of 0.2 sec.
Click Images to Enlarge after 0.01 sec(eroded elements not shown) Animation, Low Resolution
Our studies confirmed that the Riera approach is an efficient way to approximate the loads imparted during a high-velocity impact of an airplane on a near-rigid surface. However, we found that certain scaling factors necessary to correlate time-variation of impact loads from the Riera approach to those from full complexity analyses cannot be generalized. Nonetheless, we found the Riera approach to be useful because it allows exploring different impact scenarios with a reduced demand for computing time. In our computations, it corroborated that the FEA model of the aircraft used in the WTC impact studies is realistic.
This work has been supported in part by NSF grant DSC-0325227. Simulations were carried out on dual-core Opteron machines in the Bowen Civil Engineering Laboratory for Large Scale Research.