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An injury risk function defines the probability of an injury as a function of certain measurable or known predictors. In this paper, wavelet analysis is employed for the non-parametric estimation of injury risk functions. After a brief introduction of the wavelet theory, the representation of density function by wavelet series is given. A procedure for the estimation of density function is described. The risk function estimation for right-censored data is investigated by introducing hazard rate function and its wavelet estimator. The use of the developed method is illustrated in a case study, where two sets of data are used: simulation data with known distribution and censoring information, and thoracic impact testing data, which are assumed to be right- censored. Comparisons are made between the wavelet-based approach and the empirical Kaplan-Meier non-parametric method.

The use of digital human modeling in optimal injury prevention and reduction was studied and is described in this paper. The optimal injury prevention and reduction was treated as an optimization problem of a biomechanical system consisting of the safety unit and occupant. The issues of incorporating the Articulated Total Body (ATB) model, a digital human modeling tool, into an optimization process for the modeling and simulation of the biomechanics of the occupant were addressed. Modifications were made on the ATB source code, turning it into a subroutine that can be used in optimization. General considerations were also given to the creation of an interface that uses ATB as an analysis tool in the approximate optimizations. As a practical engineering application, the optimization of the ejection seat cushion impact properties for the minimization of the risk of spinal injuries was investigated.

Investigations were made on computational analyses of ejection seat cushions, which include the characterization of the impact properties of ejection seat cushions, computational modeling of an ejection seat cushion system using a rigid multi-body dynamics program, parametric optimization of the cushion impact properties, and global sensitivity analysis of the safety performance of a cushion to its impact properties. The results indicate that computational analyses can be used to effectively evaluate and improve the cushion performance in the prevention and reduction of spinal injuries.

Ejection seat cushions in current U.S. Air Force aircraft are not suitable for comfort during extended missions. Specific physiological problems such as buttock, leg and back pain, numbness and tingling in the extremities, and overall fatigue have been documented in past laboratory research and operational use [1,2,3,5,6]. Designing a single cushion to address the physiological problems of the entire aircrew population is a significant challenge. Cushion material selection, cockpit space restrictions, and limited ability to reposition during flight contribute to discomfort during extended missions. Ejection seat dimensions and contours are fixed in most cases, causing accommodation problems for large and small occupants. A pilot study was performed at the Air Force Research Laboratory at Wright-Patterson Air Force Base to investigate objective test methods for determining cushion comfort. Five volunteer subjects were tested with a variety of operational and prototype cushions.

Modeling and simulation of complex biomechanical systems can be developed to provide insight into the loading of otherwise immeasurable conditions. Ejection from an aircraft is a highly dynamic event with a risk of injury during the entire sequence. During one of the phases of ejection, spinal compression injury is a definite possibility and test manikins are used to asses this risk. However, care must be taken before accepting the relationship between the measured load in a manikin an the assumed load in a human. Human impact tests are often conducted to asses the biodynamics at a sub-injury level. Correlating these human biodynamics with manikin dynamics, can provide this relationship. To complete this correlation, modeling and simulation can be used to augment the available human test data so that the parameters of interest can be calculated. To this end, a rigid body dynamics model was constructed to represent a vertical impact for both humans and manikins.

The detrimental effects of prolonged sitting during long-duration flights include deep vein thrombosis, pressure sores, and decreased awareness and performance. However, the cushion is often the only component of the ejection seat system that can be modified to mitigate these effects. This study investigated the long-duration effects of sitting in four ejection seat cushions over eight hours. Subjective comfort survey data and cognitive performance data were gathered along with comparative objective data, including seated pressures, muscular fatigue levels, and lower extremity oxygen saturation. Peak seated pressures ranged from 1.22–3.22 psi. Oxygen saturation in the lower extremities decreased over the eight hours. Cognitive performance increased over time regardless of cushion with the exception of the dynamic cushion, which induced a decrease in performance for females.

Two series of tests were conducted to investigate the performance of ejection seat cushions for safety and comfort, respectively. In the safety study, seven operational and prototype cushions were tested on the vertical deceleration tower, where the cushions were placed between the seat pan and the occupant (a 50th percentile Hybrid III manikin) and subjected to +Gz impact at 8, 10, and 12 g, respectively. In the comfort investigation, twenty volunteer subjects (12 females and 8 males) with a range of anthropometry were tested on four operational and prototype cushions over eight-hour durations. The safety performance of a cushion is evaluated by the impact transmissibility from the carriage acceleration to the peak lumbar load, whereas the sitting comfort performance is assessed in terms of the peak contact pressure and subjective survey data.

Ejection seat cushions in current U.S. Air Force aircraft are not suitable for comfort during extended missions. Specific physiological problems such as buttock, leg and back pain, numbness and tingling in the extremities, and overall fatigue have been documented in past laboratory research and operational use [1,2,3,4,5]. Designing a single cushion to address the physiological problems of the entire aircrew population is a significant challenge. Cushion material selection, cockpit space restrictions, and limited ability to reposition during flight contribute to discomfort during extended missions. Ejection seat dimensions and contours are fixed in most cases, causing accommodation problems for large and small occupants and often times the cushion itself is the only item that can be replaced to improve comfort. A study was performed at the Air Force Research Laboratory at Wright-Patterson Air Force Base to investigate objective test methods for determining cushion comfort.