Risk Assessment for Model and Simulation Credibility Characteristics

The Department of Defense (DoD) uses the principles of risk assessment extensively throughout the acquisition process to identify, manage, and mitigate risk in many areas including software (both simulation software and software embedded in materiel systems). The approach to assessing the risks associated with using results from Models and Simulations (M&S) to influence decision-making that is described here is used by the Naval Air Systems Command (NAVAIR) 5.4H Verification, Validation, and Accreditation office. The focus of the risk assessment is on ten specific characteristics of M&S Capability, Accuracy, and Usability that have the most potential impact on the intended uses. In this method, the characteristics of the M&S are evaluated against standard criteria, and then assigned a color-rating of Green, Yellow, or Red based on the actual data obtained from the M&S itself. A simple computation is then used to weigh the ratings of the characteristics into the likelihood of error aspect of the risk of using the M&S. A thorough understanding of the M&S and its application is a prerequisite to using this approach since the analyst is required to provide a technical justification for the rating assigned to a characteristic. Should the assigned rating for a characteristic of the M&S not be green, the analyst is required to recommend actions and/or mitigations for the M&S developer to take that would improve the rating to green.

Transforming systems engineering through digital engineering

This article describes Department of Defense (DoD) Systems Engineering Research Center (SERC) efforts leading to and supporting the DoD Digital Engineering (DE) initiative. Topics include the SERC’s initial collaboration with Naval Air Systems Command (NAVAIR) in 2013 as well as ongoing SERC DE research. The article also identifies future research needed to continue to develop the DE ecosystem for system of systems acquisition, which will require rapidly changing mission strategies to address ever-evolving threats.

Selected Cr(VI) replacement options for aluminum alloys: a literature survey

There is a significant move away from the use of hexavalent chromium, Cr(VI), which is a mature, trusted, and relatively inexpensive treatment that has been used for many years by industry to reduce corrosion. Although Cr(VI) is effective at reducing corrosion, it poses a substantial health hazard. While there is a need to define a process that will be able to replace Cr(VI), the process must be able to provide the same level of corrosion protection currently provided by hexavalent treatments. In addition, it needs to do this without the associated environmental problems. This paper focuses mainly, but not exclusively, on the trivalent chromium pretreatment (TCP) and its commercially available variants. The TCP was developed by the Naval Air Systems Command (NAVAIR) and is used by the US military. The rationale for the focus of this paper is that in the near term, the aeronautics industry needs to move away from Cr(VI) towards a more benign commercially available chemical treatment that can help protect the aluminum alloys used by that industry. TCPs are currently available commercially and have undergone numerous tests by multiple organizations to establish their effectiveness in reducing corrosion of both bare and painted aluminum alloys.

Helicopter Airframe Fatigue Spectra Truncation and Verification

Helicopter airframe fatigue cracking is a cause of significant and growing cost of ownership and operational readiness concerns for the operators of (primarily) metallic airframe helicopters. Airframe fatigue has often had relatively low priority for helicopters, with research and design concentrated on the fatigue of flight critical rotating structural components such as rotor blades and pitch links. The Australian Defence Science and Technology Organisation (DSTO) and Naval Air Systems Command (NAVAIR) of the US Navy are collaborating to develop improved methods and technologies that can be used to assess the fatigue damage accrued by ageing helicopter airframes. The flight load sequences, or fatigue spectra, experienced by a helicopter airframe in its lifetime contain many billions of load cycles due to rotor revolutions. The application of spectra containing such vast numbers of load cycles is often impractical for reasons of test duration and cost, therefore spectra simplification techniques must be employed. To this end, truncation is a technique that is used to eliminate non-or lesser-damaging load cycles, producing spectra equivalent in terms of theoretical fatigue damage but with substantially fewer load cycles. This paper describes several truncation techniques that have recently been developed at DSTO specifically to deal with the very large numbers of load cycles that are characteristic of helicopter airframe fatigue spectra. These techniques, which include both sequence and frequency based approaches, feature tunable levels of truncation and allow for large reductions in numbers of turning points while maintaining high-fidelity and realistic fatigue spectra. Also detailed are preliminary results from a comprehensive coupon test program, which DSTO is using to experimentally verify that truncated and un-truncated spectra are approximately equivalent in terms of the fatigue damage that they produce.

Helicopter Airframe Fatigue Spectra Generation

Helicopter airframe fatigue cracking is a cause of significant and growing cost of ownership and operational readiness concerns for the operators of (primarily) metallic airframe helicopters. Airframe fatigue has often had relatively low priority for helicopters, with research and design concentrated on the fatigue of flight critical rotating structural components such as rotor blades and pitch links. The Australian Defence Science and Technology Organisation (DSTO) and the US Naval Air Systems Command are collaborating to develop improved methods and technologies that can be used to assess the fatigue damage endured by ageing helicopter airframes. The flight load sequencesor fatigue spectraexperienced by a helicopter airframe in its lifetime contain many billions of load cycles due to rotor revolutions. Fatigue spectra developed for helicopter airframe certification tests are heavily simplified for reasons such as computational efficiency, test practicality and cost. Real airframe fatigue spectra are likely to be influenced by the modes of vibration that might be present on the airframe, the attenuation of the vibratory loading that is introduced at the main and tail rotors and the relative magnitudes and influences of both quasi-static (manoeuvre induced) and vibratory loading. To better capture such complexity, more realistic, higher fidelity fatigue spectra are required. Fatigue spectra generation involves creating realistic flight-by-flight sequences of flight conditions and assigning high-fidelity flight loads data to those sequences. This paper details DSTOs development of a novel computer-automated process which pseudo-randomly generates realistic sequences of flight conditions to match a known or assumed usage spectrum.

Hearing Protection With Integrated In-Ear Dosimetry: A Noise Dose Study

Military personnel working in high noise environments can be exposed to continuous noise levels up to 150 dB. United States (US) Department of Defense (DoD) Hearing Conservation Programs (HCPs) [1–3] set safe noise exposure limits to reduce the risk for noise induced hearing loss. These daily noise exposure limits were based on ambient noise levels and the duration of time spent in that noise environment. Current dosimeters, worn on the lapel of personnel and at least one system worn under a hearing protector, were designed to measure noise levels and calculate noise dose, but do not provide a validated measure of noise dose external to or under a hearing protector. Noise dose under hearing protectors can be estimated by subtracting the real ear attenuation (REAT) data, collected in accordance with the American National Standards Institute (ANSI) S12.6 [4], at each octave band from the ambient octave band noise. This procedure gives accurate results for group data, but does not account for individual variations in effective attenuation. To address this issue, the US Naval Air Systems Command (NAVAIR) led the development of ship suitable in-ear dosimetry integrated into a hearing protector, and co-sponsored an effort executed by the Air Force Research Laboratory (AFRL) to calibrate in-ear noise dose readings. This was accomplished by conducting human noise exposure experiments, with and without hearing protection, which calculated noise dose from temporary threshold shifts (TTS) in hearing. Ten subjects participated in the study. Noise levels were 91, 94, and 97 dB for up to 2 hrs, 1 hr, and 30 minutes respectively. These exposure levels were well within US DoD safe noise exposure guidelines (DoD HCP) [1–3]. Data will be presented describing the open and occluded (protected) ear TTS response to noise dose achieved by subjects in the experiment. Preliminary findings indicate that human subject data is extremely important in developing and validating calibration factors for any type of noise dosimeter but is especially important for in-ear dosimetry. Results from this study demonstrated that the REAT noise dose estimations and the in-ear dosimetry earplugs consistently overestimated the effective noise dose received by subjects. However, more than 10 subjects are required to improve the confidence level of the estimated calibration factor.