Simulation, Safety and CAE Insights from FAA Chief Scientist
Joseph Pellettiere, Chief Scientific and Technical Advisor for Crash Dynamics, shares insights on how CAE simulation is used to regulate aircraft safety.
The entire aircraft industry is looking more than ever to CAE simulation, not only to reduce costs but also to provide more insight to engineers in meeting critical targets, from fuel economy to safety. Regulatory agencies, such as the US Federal Aviation Administration (FAA) are certainly looking at how to better use CAE modeling and simulation in certification of aircraft and systems. Critical to proper use of simulations means defining requirements carefully, ensuring the software can predict failures adequately, and handling uncertainty and stochastic phenomenon that are difficult even for physical tests to capture.
Joseph Pellettiere, Chief Scientific and Technical Advisor for Crash Dynamics for the FAA, an expert in seat certifications, provided some specific insights into the way forward for using CAE in this interview.
AeroDef: Can you describe the aircraft safety and crash your responsibilities cover?
I am the Chief Scientific and Technical Advisor for Crash Dynamics. My main focus is on technologies and regulations that protect the occupants in aviation systems. This includes seat dynamic performance and restraint system performance as outlined in regulations for transport aircraft such as 14 CFR 25.561, 25.562, and 25.785 with similarity for other types of aircraft. I am also responsible for monitoring activities related to full-scale aviation simulation of emergency landing conditions for various types of aircraft. This includes development of baseline metallic fuselage models and composite aircraft for determination of equivalent levels of safety via special conditions. I also serve as the link between policy makers and certification engineers and researchers to develop research plans to meet emerging trends in crashworthiness.
AeroDef: How does CAE simulation help you better understand these areas and/or perform your job?
CAE simulation tools provide insight to the complex mechanics during impact. Testing can only collect so much data, but the simulations allow a more detailed analysis. Simulations are also an important part of a test program. Often a model of a new design can be used to set up the test conditions and determine the most critical configuration of interest. For full-scale analysis, it would not be practical to conduct crash tests of every new and novel design such as is done in the automotive world.
AeroDef: How do you employ CAE simulation, or use it, in conjunction with physical test?
We have guidance in the form of an advisory circular, AC 20-146: Methodology for Dynamic Seat Certification by Analysis for Use in Part 23, 25, 27, and 29 Airplanes and Rotorcraft. This guidance details how modeling and simulation can be used to develop and certify seating systems. This guidance does rely on a dynamic test to validate the model. A supporting document is SAE ARP 5765, Analytical Methods for Aircraft Seat Design and Evaluation. This ARP currently describes the process for calibrating a v-ATD (virtual Anthropometric Test Dummy). This is the analytical equivalent of the test dummy used in physical testing. It provides software developers with goals for their v-ATDs to meet in order to simulate the dynamic performance of seats. Simulation is also used on large sections and full aircraft to help compare the performance of new and novel designs to those with acceptable performance. The models themselves will also help to determine what testing is needed in order to validated the model for its acceptable use.
AeroDef: Are there particular CAE tools you use, or direct others to use (such as consultants)?
In general, we do not restrict the use of simulation tools. The paradigm has been to use a building block approach to validate a model from coupons at the material level up to the sub-system or system. Using this approach allows the model and the simulation tool to be checked at each step to determine that it is yielding acceptable performance.
AeroDef: What technology in particular would you like the CAE tool providers to improve, if they could, in the next 3 years or so?
One of the areas missing from simulation tools is code verification. While many of the tools are widely used, there is little information provided on the conformity of the underlying code, including statements of such code verification supplied. If simulation is to be used in the certification process, the FAA needs to know the tool used has been verified for this application and will remain so throughout the process.
There is always a long list that the modeling community would like to see, including tools that are easier to position the v-ATD and set up the model. The ability to quickly and easily switch between an implicit and explicit analysis for various parts of the simulation is also needed. For instance, the positioning of the ATD and the application of the initial conditions such as floor warpage may require an implicit analysis, then the actual simulation of the dynamic event may require an explicit analysis, but then again in the end to determine outcomes such as post-event permanent deformation may again require an implicit analysis.
Published Date : 11/4/2013