Mapping the Potential for Infectious Disease Transmission in a Wide-Body Aircraft Cabin

With more than two billion passengers annually, in-flight transmission of infectious diseases is a major global health concern. It is widely believed that principal transmission risk associated with air travel for most respiratory infectious diseases is limited to within two rows of an infectious passenger. However, several passengers became infected despite sitting several rows away from the contagious passenger. This work thoroughly investigated the potential for disease spread inside airplane cabins using tracer gas to quantify airborne dispersion. Measurements were conducted in a full-scale, 11-row mock-up of a wide-body aircraft cabin. Heated mannequins to simulate passengers’ thermal load were placed on the cabin seats. Tracer gas was injected at the breathing level at four different hypothetical contagious passenger locations. The tracer gas concentration was measured radially up to 3.35 m away from the injection location representing four rows of a standard aircraft. A four-port sampling tree was used to collect samples at the breathing level at four different radial locations simultaneously. Each port was sampled for 30 minutes. A total of 42 tests were conducted in matching pairs to alleviate potential statistical or measurements bias. The results showed that the airflow pattern inside the mock-up airplane cabin plays a major role in determining tracer gas concentration meaning that the concentration at the same radial distance in different directions are not necessarily the same. Also, due to the air distribution pattern and cabin walls, concentrations at some seats may be higher than the source seat.

Optimization of Machining Parameters During Turning of Tungsten Heavy Alloys Using Taguchi Analysis

Tungsten heavy alloys (WHAs) are ideally suited to a wide range of density applications such as counterweights, inertial masses, radiation shielding, sporting goods and ordnance products. Manufacturing of these components essentially require machining to achieve desired finish, dimensions and tolerances However, machining of WHAs are extremely challenging because of higher values of elastic stiffness and hardness. Hence, there is a need to find the right combination of cutting parameters to carry out the machining operations efficiently. In the present work, turning tests are conducted on three different grades of WHAs, namely, 90WHA, 95WHA and 97WHA. Taguchi analysis is carried out to find out the most contributing factor as well as optimum cutting parameters that can give higher metal removal rate (MRR), lower surface roughness and lower cutting forces. It is observed that feed rate is the most prominent factor with percentage contribution varying in the range of 46–61%; whereas cutting speed has least effect on cutting forces, especially for 95WHA and 97WHA. Optimum values of forces, surface roughness and MRR and the corresponding machining parameters to be taken are presented. It is observed that 95W WHA has slightly better machinability as compared to other two grades since it gives highest MRR with lowest cutting forces and surface roughness values. The optimum machining parameter settings, so predicted, can be utilized to machine WHAs efficiently for manufacture of counter weights and inertial masses used in aerospace applications.

Plasma Actuators Optimization Using Stair Shaped Dielectric Layers

Plasma actuators are very simple devices which have been shown to be effective in a wide variety of applications, such as separation control, wake control, aircraft noise reduction, modification of velocity fluctuations and boundary layer control. More recently, it has been also proved their ability for applications within the heat transfer field, such as film cooling of turbine blades or ice accumulation prevention. These simple devices are inexpensive, present robustness, low weight and are fully electronic. Considering the importance of these devices, the improvement of their efficiency is a subject of great interest for worldwide scientific community. It is known that, by reducing the plasma actuator dielectric thickness, the induced flow velocity increases. However, it is also known that, thin plasma actuators present short lifetime and quick dielectric layer degradation. Till now, only actuators with constant dielectric thickness have been studied. In the present work, a new concept of plasma actuator is studied: The stair shaped dielectric barrier discharge plasma actuator. This new device present a dielectric layer which provides a decrease of the dielectric thickness along the covered electrode width. This lead to an extended plasma discharge and an increase of the induced flow velocity and efficiency. In addition, the plasma discharge is weakened on the onset of plasma formation which prevents the quick degradation of the dielectric layer and leads to an increased actuator lifetime.

Best Structural Theories for Free Vibrations of Sandwich Composites via Machine Learning

This work presents a novel methodology for the development of refined structural theories for the modal analysis of sandwich composites. Such a methodology combines three well-established techniques, namely, the Carrera Unified Formulation (CUF), the Axiomatic/Asymptotic Method (AAM), and Artificial Neural Networks (NN). CUF generates structural theories and finite element arrays hierarchically. CUF provides the training set for the NN in which the structural theories are inputs and the natural frequencies targets. AAM evaluates the influence of each generalized displacement variable, and NN provides Best Theory Diagrams (BTD), i.e., curves providing the minimum number of nodal degrees of freedom required to satisfy a given accuracy requirement. The aim is to build BTD with far less computational cost than in previous works. The numerical results consider sandwich spherical shells with soft cores and different features, such as thickness and curvature to investigate their influence on the choice of generalized displacement variables. The numerical results show the importance of third-order generalized displacement variables and prove that the present framework can be of interest to evaluate the performance of any structural theory as typical design parameters change and provide guidelines to the analysts on the most convenient computational model to save computational cost without accuracy penalties.

Effect of Property of Interphase Layer on Damping Properties of Polymer Composites Using Sensitivity Analysis

This work studies the damping property of Nanocomposites through simulating wave propagation using the Finite Element Method (FEM). For this purpose Representative Volume Element (RVE) of the composite material is created using Random Sequential Absorption (RSA) algorithm. Damping property is represented using the wave attenuation coefficient. The matrix material is assumed to be isotropic visco-elastic in nature with randomly dispersed stiff elastic spherical fillers. In order to model mechanical imperfections at the boundary of fillers and matrix, the interphase layer is modeled surrounding the spherical fillers. Determining the thickness and stiffness of this interphase region is a challenging task. Therefore this study aims at investigating the effect of variation in thickness and stiffness values of the interphase region on damping property of whole composite using sensitivity analysis. Two specific cases with a volume fraction of 5 % and 8.6 % are selected for sensitivity analysis. It has been found that both the thickness and stiffness of the interphase region plays an important role in deciding the damping properties of the polymer composite. Value of attenuation coefficient is more sensitive to the thickness of interphase than stiffness and hence it is important to choose the value of thickness correctly for accurate predictions.

Structural Dynamic Testing Results for Air-Independent Proton Exchange Membrane (PEM) Fuel Cell Technologies for Space Applications

In 2016, the National Aeronautics and Space Administration (NASA) Advanced Exploration Systems (AES) project office funded testing at the NASA Glenn Research Center to evaluate the maturity of the Proton Exchange Membrane (PEM) fuel cell technology and its viability for supporting launch vehicle and space applications. This technology evaluation included vibration, reactant purity, and vacuum exposure sensitivity testing. The evaluation process did not include microgravity testing. This paper discusses the vibration sensitivity testing of two air-independent fuel cell stacks provided by different vendors to assess the ability of currently available fuel cell stack hardware to survive the projected random vibrational environment that would be encountered in an upper stage launch vehicle. Baseline performance testing was utilized to quantify stack performance and overboard leak rate at standard atmospheric conditions in order to provide a reference for posttest comparison. Both fuel cell stacks were tested at a random vibration qualification level of 10.4 grms for five minutes in each axis. Low-level sinusoidal sweeps were conducted before and after each random vibration level run to see if any significant change in resonances were detected. Following vibration facility testing, the baseline performance testing was repeated. Test results demonstrated no measurable change in fuel cell electrochemical or mechanical performance, indicating that the two evaluated PEM fuel cell stacks may be suitable for space applications pending microgravity testing.

Effect of Cryogenic Temperature Rolling on High Speed Impact Behavior of AA 6082 Thin Targets

Aluminium alloy AA 6082-T6 was rolled at cryogenic and room temperatures to final thickness of 0.5 mm after 75% thickness reduction and subjected to high speed impact. The deformed alloy was investigated for its ballistic properties due to potential applications in aerospace and automotive sectors. The cryogenic and room temperature rolled samples were subjected to normal high-speed impact using a gas gun arrangement to shoot nosed projectiles at velocities higher than the ballistic limits. Phantom ‘V611’ high-speed camera was used to measure the initial and residual velocities of the projectile. Nano-indentation was performed to relate hardness of the initial sample with the observed impact behaviour. Detailed fractographic studies were conducted using Scanning Electron Microscopy (SEM) to substantiate the possible failure mechanisms upon impact. Electron Backscatter Diffraction (EBSD) and Energy Dispersive X-ray Spectroscopy (EDS) were used to characterize the microstructure of the deformed samples. The high speed impact data is correlated with the metallographic observations in this study.

Analytical and Numerical Modelling of Sheet Plate Cold Expanded Hole Subjected to Reverse Yielding

Predicting and mitigating the effect of expansion induced by cold working on damage fatigue accumulation and life assessment of aluminum alloy is a common process in the aeronautics industry, especially to extend the fatigue lifetime of their structures. This process aims at generating residual stresses and increases thereby the strength of hollow parts including aluminum alloy plate holes that are employed in manufacturing the airplane fuselage. An analytical model to predict the residual stresses induced during the expansion process due to the cold strain hardening is developed. The proposed model is based on an elasto-plastic behavior, with a power law material behaviour and relies on the theory of autofrettaged thick wall cylinders in plane strain state to which reverse yielding is incorporated. The application of Hencky theory of plastic deformation is used in the analytical calculations of the stresses and strains. Finite-element numerical simulation is used to validate the developed analytical model by comparison of the radial, Hoop, longitudinal and equivalent stresses for both the loading and unloading phases. The obtained results show clearly that the level of residual stresses depends mainly on the interference and strain hardening while reverse yielding reduce the stresses near the hole.

Large-Deformation Analysis of Elastomeric Structures by Carrera Unified Formulation

Based on the well-known nonlinear hyperelasticity theory and by using the Carrera Unified Formulation (CUF) as well as a total Lagrangian approach, the unified theory of slightly compressible elastomeric structures including geometrical and physical nonlinearities is developed in this work. By exploiting CUF, the principle of virtual work and a finite element approximation, nonlinear governing equations corresponding to the slightly compressible elastomeric structures are straightforwardly formulated in terms of the fundamental nuclei, which are independent of the theory approximation order. Accordingly, the explicit forms of the secant and tangent stiffness matrices of the unified 1D beam and 2D plate elements are derived by using the three-dimensional Cauchy-Green deformation tensor and the nonlinear constitutive equation for slightly incompressible hyperelastic materials. Several numerical assessments are conducted, including uniaxial tension nonlinear response of rectangular elastomeric beams. Our numerical findings demonstrate the capabilities of the CUF model to calculate the large-deformation equilibrium curves as well as the stress distributions with high accuracy.

A Case Study of the Unsteady Response of a Hingeless Helicopter Rotor Blade

The helicopter is an essential means of transport for numerous tasks including carrying passengers and equipment, providing air medical services, firefighting, and other military and civil tasks. While in operation, the nature of the unsteady aerodynamic environment surrounding the rotor blades gives rise to a significant amount of vibration to the helicopter. In this study, the unsteady forced response of the Bo 105 hingeless helicopter rotor blade is investigated at the forward flight in terms of the coupled flapping, lead-lag, and torsional deformations. The mathematical model for the steady-state response of the rotor blade is modified to include the unsteady airfoil behavior by using the Theodorsen’s lift deficiency function for three degrees of freedom of motion. The nonlinear mathematical model is solved by the generalized method of lines in terms of the time-varying deflections of the rotor blade. The unsteady airloads are found to create larger deformations compared to that of the steady-state condition for a given advance ratio. The azimuth locations of the peak loadings also vary with different degrees of freedom. The first three natural frequencies and mode shapes of the rotor blade are presented. The model for the forced response analysis is validated by finite element results.