David Moorcroft

Computational model of the pregnant occupant: predicting the risk of injury in automobile crashes

OBJECTIVE The goal of this study was to create a computational model of the pregnant occupant of a motor vehicle to predict fetal outcome in crashes. STUDY DESIGN A finite element uterine model of a 7-month pregnant woman was created and integrated into a multibody human model. Unrestrained, three-point belt, and three-point belt plus airbag tests were simulated at speeds that ranged from 13 to 55 km per hour. RESULTS Peak uterine strain, as determined by the model, correlated well with the risk of fetal death, as determined by investigations of car crashes. The strain in the uterine wall exceeded the limits of the tissue in simulations of no restraint at 35 km per hour and three-point belt tests at 45 and 55 km per hour. The safest restraint for the pregnant driver is the combination three-point belt and airbag. CONCLUSION The model is a good first step toward the prediction of the risk of fetal death and verified experimental findings that note the importance of proper restraint use for the pregnant occupant.

Preliminary FAA-Hybrid III Spinal Injury Criteria for Oblique-Facing Aircraft Seats

Occupant injury potential to oblique loading at aircraft crash severities is unknown. The objective of the present study was to derive preliminary injury criteria for the Federal Aviation Administration (FAA) Hybrid III anthropomorphic test device (ATD) under oblique loading conditions. Twelve sled tests were conducted at four pulse severities and three configurations. An acceleration pulse representative of the one specified in Title 14 Code of Federal Regulations Part 25.562, emergency landing dynamic condition for horizontal impact was used as an input. Pulses were scaled in magnitude at 50, 61, 75 and 100% of the peak acceleration 13.7, 10.2, 8.6 and 6.8 m/s, respectively. The three conditions were: 45-degrees, no arm rest, pelvis restrained with two belts, legs restrained; 45-degrees, with arm rest, single lap belt, legs restrained; 30-degrees, no arm rest, two lap belts, legs unrestrained. The ATD was placed on a generic seat representative of aircraft seat geometry and the seat was oriented obliquely. ATD accelerations, thoracic and lumbar spine forces, and restraint forces were recorded. Peak tension forces in the thoracic and lumbar spine ranged from 10–12.7 kN at the highest pulse to 3.6–4.2 kN at the lowest pulse. Previously reported in-house post mortem human surrogate (PMHS) tests provided a matched-paired dataset for combining injuries with ATD metrics. From this limited sample set, 5.2 kN tension force in the spine is suggested for the FAA-Hybrid III ATD as a preliminary injury criteria in oblique loading in the aviation environment.Copyright

Impact of Numerical Model Verification and Validation Within FAA Certification

The mission of the Federal Aviation Administration (FAA) is to provide the safest, most efficient aerospace system in the world. The FAA Aircraft Certification Service is responsible for the design and production approval and airworthiness certification of all U.S. civil aviation products. Historically, design approval has required physical tests, however the FAA allows for the use of modeling and simulation (M&S) to demonstrate compliance with federal regulations. This allows an applicant to reduce the number of tests required to certify a design by relying on the results of M&S. As with all M&S use, verification and validation are fundamental in establishing the credibility of the computational models of aircraft components. Through several government-industry workshops, there is an apparent need for better guidance and training for both parties to understand how to communicate M&S and Verification and Validation (V&V) activities to support certification decisions. Current efforts focus on the level of detail required to document the M&S and V&V activities by an applicant such that the FAA can make an informed certification decision resulting in safe aircraft.

Certification by analysis and simulation validation

Modelling and simulation is increasingly being used to represent occupant behaviour of human subjects and anthropomorphic test devices. Future trends are towards the application of certification by analysis whereby a product, such as an aircraft seat, can be partially certified through analytical means. A robust and objective method to discriminate different features of the model comparison is needed to determine model validity so that the certification authority can objectively determine the model acceptability. Expert opinion could introduce bias and lead to inconsistent results. In any testing, there is some inherent uncertainty and variation in the measured responses that affects the baseline comparison data. Each individual response should be treated as a separate case. A method derived from Sprague and Geers was developed and applied to occupant models of seat simulations. Using test data, acceptable error levels were calculated that represent the uncertainty and provide consistent and objective results.

Use of a head component tester to evaluate the injury potential of an aircraft head-up display

Title 14 of the Code of Federal Regulations Part 25, §25.785 requires that seats and adjacent parts of the airplane be designed so that occupants will not suffer serious injury during an emergency landing as a result of expected inertial forces. The Federal Aviation Administration (FAA) guidance material cites several component impact test methods for use in determining whether an item or surface is potentially injurious. A head component tester (HCT) developed at the National Institute for Aviation Research of the Wichita State University was selected to assess the injury potential of a new cockpit-installed head-up display (HUD)s combiner glass. A test procedure complying with the intent of the FAA guidance material was developed and validated by the Civil Aerospace Medical Institute (CAMI), Oklahoma City, OK. Subsequently, a computer model of the HCT impact into the HUD was developed by The Engineering Institute, Farmington, AR, and was correlated with CAMI test data. This model is useful for evaluating the effect of design parameters on HUD injury potential.