DOI: 10.2514/1.J050617 The goal of the United States Air Force to field durable platforms capable of sustained hypersonic flight and responsive access to space depends on the ability to predict the response and the life of structures under combined aerothermal andaeropressure loading. However,current predictive capabilities are limitedfor these conditions due in part to the inability to seamlessly address fluid-thermal-structural interactions. This study aims to quantify the significance of a frequently neglected interaction, namely: the mutual coupling of structural deformation and aerodynamic heating, on response prediction. The quasi-static response of a carbon–carbon skin panel is investigated. It is found that the significance of this coupling depends largely on the in-plane boundary conditions, since increasing resistance to thermal expansion results in buckling and increasing deflections into the flow. Including these deformations in aerodynamic heating results in O10% increase in peak temperature and O100% increase in surface ply failure index for deflections O1% of panel length. In these cases, the locations of peaktemperaturesandstressesaresignificantlyaltered.Finally,neglectingdeformationsintheaeroheatinganalysis results in the prediction of snap-through for a gradual heating trajectory, whereas, inclusion leads to a higher mode dominated, dynamically stable response.

Impact of Fluid-Thermal-Structural Coupling on Response Prediction of Hypersonic Skin Panels

Recently, several factors have contributed to an increase in interest in the evaluation of comfort experienced by passengers in vehicles. Due to rising mobility, the time that people spend in vehicles has grown substantially. The criteria applied by consumers have changed on account of generally heightened expectations, resulting in a growing demand for enhanced ride comfort. Also, there are marketing factors, from the car manufacturers' point of view, because differentiation between models in the same market segment is becoming more difficult to establish on grounds of performance or aesthetics. The comfort experienced by humans in a given environment can be classified as a subjective assessment, because it is possible to find a considerable variation in responses of different people to the same situation. Nevertheless, the factors on which the opinions of people on comfort level are based are physical variables that characterize the surroundings, e.g. temperature, air velocity, acceleration, and light intensity. So, the first step in any assessment is to list the different kinds of stimulus that can be detected by human senses and judged a cause of annoyance, leading thus to a sensation of discomfort. In the case of passengers riding in vehicles, the following are the main aspects that should be considered: temperature, air quality, noise, vibration, light, and ergonomics. Many different measuring and evaluation methods have been developed to study the comfort of occupied spaces, involving one or more of the aforementioned stressors. Besides discrete measured values of relevant physical parameters, comfort indices related to human sensitivity and weighting the influences of different variables have also been built in for each kind of stimulus. Subjective assessments from evaluation panels are also extensively used. Because researchers are conscious of the importance of the interaction between the passengers and the environment, various measuring mannequins with the capability of simulating some human functions, e.g. thermal regulation or breathing, have been developed.

http://iopscience.iop.org/article/10.1088/0957-0233/13/6/201/pdf

Measurements of comfort in vehicles

Judgements of overall seating comfort in dynamic conditions sometimes correlate better with the static characteristics of a seat than with measures of the dynamic environment. This study developed qualitative models of overall seat discomfort to include both static and dynamic seat characteristics. A dynamic factor that reflected how vibration discomfort increased as vibration magnitude increased was combined with a static seat factor which reflected seating comfort without vibration. The ability of the model to predict the relative and overall importance of dynamic and static seat characteristics on comfort was tested in two experiments. A paired comparison experiment, using four polyurethane foam cushions (50, 70, 100, 120 mm thick), provided different static and dynamic comfort when 12 subjects were exposed to one-third octave band random vertical vibration with centre frequencies of 2.5 and 5.5 Hz, at magnitudes of 0.00, 0.25 and 0.50 m.s-2 rms measured beneath the foam samples. Subject judgements of ...

Qualitative models of seat discomfort including static and dynamic factors.

https://krishi.icar.gov.in/jspui/bitstream/123456789/3293/1/Seating%20discomfort%20for%20tractor%20operators%20%7d%20a%20critical%20review.pdf

Seating discomfort for tractor operators – a critical review

Hypersonic vehicle control system design and simulation require models that contain a low number of states. Modeling of hypersonic vehicles is complicated due to complex interactions between aerodynamic heating, heat transfer, structural dynamics, and aerodynamics. Although there exist techniques for analyzing the effects of each of the various disciplines, thesemethods often require solution of large systems of equations, which is infeasible within a control design and evaluation environment. This work presents an aerothermoelastic framework with reducedorder aerothermal, heat transfer, and structural dynamicmodels for time-domain simulation of hypersonic vehicles. Details of the reduced-order models are given, and a representative hypersonic vehicle control surface used for the study is described. Themethodology is applied to a representative structure to provide insight into the importance of aerothermoelastic effects on vehicle performance. The effect of aerothermoelasticity on total lift and drag is found to result in up to an 8% change in lift and a 21% change in drag with respect to a rigid control surface for the four trajectories considered. An iterative routine is used to determine the angle of attack needed to match the lift of the deformed control surface to that of a rigid one at successive time instants.Application of the routine todifferent cruise trajectories shows a maximum departure from the initial angle of attack of 8%.

/pdf/reduced-order-aerothermoelastic-framework-for-hypersonic-4cagfxahld.pdf

Reduced-Order Aerothermoelastic Framework for Hypersonic Vehicle Control Simulation

NASA Langley Research Center has conducted three groups of studies on human response to sonic booms: laboratory, "inhome," and field. The laboratory studies were designed to: (1) quantify loudness and annoyance response to a wide range of shaped sonic boom signatures and (2) assess several noise descriptors as estimators of sonic boom subjective effects. The studies were conducted using a sonic boom simulator capable of generating and playing, with high fidelity, both user-prescribed and recorded boom waveforms to test subjects. Results showed that sonic boom waveform shaping provided substantial reductions in loudness and annoyance and that perceived level was the best estimator of subjective effects. Booms having asymmetrical waveforms were found to be less loud than symmetrical waveforms of equivalent perceived level. Subjective responses to simulated ground-reflected waveforms were fully accounted for by perceived level. The inhome study presented participants with simulated sonic booms played within their normal home environment. The results showed that the equal energy theory of annoyance applied to a variety of multiple sonic boom exposures. The field studies concluded that sonic boom annoyance is greater than that in a conventional aircraft noise environment with the same continuous equivalent noise exposure.

Summary of recent NASA studies of human response to sonic booms.

A series of experimental studies utilizing approximately 2200 test subjects has led to the development of a general empirical model for the prediction of passenger ride discomfort in the presence of complex noise and vibration inputs The ranges of vibration and noise stimuli used to derive the model included the amplitudes and frequencies that are known to most influence passenger comfort The ride quality model accounts for the effects of combined axis vibrations (up to three axes simultaneously) and includes corrections for the effect of vibration duration and interior noise Output of the model consists of an estimate of the passenger discomfort produced by a given noise and/or vibration environment The discomfort estimate is measured along a continuous scale that spans the range from below discomfort threshold to values of discomfort that are far above discomfort threshold

A Design Tool for Estimating Passenger Ride Discomfort Within Complex Ride Environments

A laboratory investigation was directed at the development of criteria for the prediction of ride quality in a noise‐vibration environment. The stimuli for the study consisted of octave bands of noise centered at 500 and 2000 Hz and vertical floor vibrations composed of either 5 Hz sinusoidal vibration, or random vibrations centered at 5 Hz and with a 5 Hz bandwidth. The noise stimuli were presented at A‐weighted sound pressure levels ranging from ambient to 95 dB and the vibration at acceleration levels ranging from 0.02–0.13 grms. Results indicated that the total subjective discomfort response could be divided into two subjective components. One component consisted of subjective discomfort to vibration and was found to be a linear function of vibration acceleration level. The other component consisted of discomfort due to noise which varied logarithmically with noise level (power relationship). However, the magnitude of the noise discomfort component was dependent upon the level of vibration present in the combined environment. Based on the experimental results, a model of subjective discomfort that accounted for the interdependence of noise and vibration was developed. The model was then used to develop a set of criteria (constant discomfort) curves that illustrate the basic design tradeoffs available between noise and vibration.

Development of noise and vibration ride comfort criteria

An experimental investigation was conducted (1) to determine the effects of combined environmental noise and vertical vibration upon human subjective discomfort response, (2) to develop a model for the prediction of passenger discomfort response to the combined environment, and (3) to develop a set of noise-vibration curves for use as criteria in ride quality design. Subjects were exposed to parametric combinations of noise and vibrations through the use of a realistic laboratory simulator. Results indicated that accurate prediction of passenger ride comfort requires knowledge of both the level and frequency content of the noise and vibration components of a ride environment as well as knowledge of the interactive effects of combined noise and vibration. A design tool in the form of an empirical model of passenger discomfort response to combined noise and vertical vibration was developed and illustrated by several computational examples. Finally, a set of noise-vibration criteria curves were generated to illustrate the fundamental design trade-off possible between passenger discomfort and the noise-vibration levels that produce the discomfort.

/pdf/human-discomfort-response-to-noise-combined-with-vertical-wy0dmnvlnt.pdf

Human discomfort response to noise combined with vertical vibration

Results are presented of a series of thermal-acoustic tests conducted on the NASA Langley Research Center Thermal-Acoustic Test Apparatus to (1) investigate techniques for obtaining strain measurements on metallic and carbon-carbon materials at elevated temperature; (2) document the dynamic strain response characteristics of several superalloy honeycomb thermal protection system panels at elevated temperatures of up to 1200 F; and (3) determine the strain response and sonic fatigue behavior of four carbon-carbon panels at both ambient and elevated temperatures. A second study tested four carbon-carbon panels to document panel dynamic response characteristics at ambient and elevated temperature, determine time to failure and faliure modes, and collect continuous strain data up to panel failure. Strain data are presented from both types of panels, and problems encountered in obtaining reliable strain data on the carbon-carbon panels are described. The failure modes of the carbon-carbon panels are examined.

Jack D. Leatherwood

Papers

Summary of recent NASA studies of human response to sonic booms.

A Design Tool for Estimating Passenger Ride Discomfort Within Complex Ride Environments

Development of noise and vibration ride comfort criteria

Human discomfort response to noise combined with vertical vibration

Acoustic Testing of High-Temperature Panels