Range Of Dynamic Pressures Research Articles

Aeroelastic Analysis of Highly Flexible Wings with Linearized Frequency-Domain Aerodynamics

Aeroelastic flutter analysis of configurations with geometric structural nonlinearities typically is done with time-domain analysis. The results from this process are computationally expensive and can yield cumbersome results that may be difficult to manage and interpret. Compared to time-domain methods, frequency-domain flutter analysis can provide additional insight into the characteristics of a flutter instability. By linearizing the aeroelastic problem about the nonlinear equilibrium state, this work applies frequency-domain aeroelastic analysis to the Pazy wing, the subject of the Large Deformation Working Group in the Aeroelastic Prediction Workshop. Generalized aerodynamic forces (GAFs) are computed with both a doublet-lattice method and a computational fluid dynamics solver at a range of reduced frequencies as well as a range of dynamic pressures to account for the dependence of the mode shapes on the nonlinear equilibrium state. These GAFs are used in a flutter solver, which is modified to handle the nonlinear dependence of the stiffness matrix and GAFs on the dynamic pressure. The hump mode flutter mechanism predicted by the linear doublet-lattice method is found to underpredict the severity of the instability, relative to the computational fluid dynamics-based tool, though the overall static and dynamic aeroelastic mechanisms predicted by the two fidelities are similar.

Numerical study of the effect of micro vortices on chaotic flutter

The loading generated by shock wave boundary layer interaction (SBLI) plays a crucial role in the structural design of a high-speed vehicle. They can cause flow separation near the shock impingement, resulting in the onset of chaotic, self-sustained flutter leading to structural failure. This work investigates how a micro-ramp installed upstream of a flexible panel affects its flutter behavior. For this purpose, two-way coupled laminar fluid–structure interaction simulations are performed for two different oblique shock strengths impinging over a flexible panel. A comprehensive study with a micro-ramp, as high as half the boundary layer thickness, is conducted for a wide range of non-dimensional dynamic pressures expected for a supersonic flight. The study provides analysis methodology to characterize the nature of panel oscillations, and the influence of micro-ramp on fluid and structural unsteadiness is evaluated. The results indicate that the chaotic flutter is initiated because of the non-linear interaction between the high-frequency fluid and low-frequency structural unsteadiness. Micro vortices delay the onset of the chaotic flutter by lowering the fluid frequency, thereby synchronizing fluid and structure unsteadiness. The micro vortices also decreased flutter frequency for lower shock strength; however, MVG was somewhat ineffective for some higher shock strength. For the latter taller micro-ramps that can introduce stronger, low-frequency vortices are recommended.

Emulating clinical pressure waveforms in cell culture using an Arduino-controlled millifluidic 3D-printed platform for 96-well plates.

High blood pressure is the primary risk factor for heart disease, the leading cause of death globally. Despite this, current methods to replicate physiological pressures in vitro remain limited in sophistication and throughput. Single-chamber exposure systems allow for only one pressure condition to be studied at a time and the application of dynamic pressure waveforms is currently limited to simple sine, triangular, or square waves. Here, we introduce a high-throughput hydrostatic pressure exposure system for 96-well plates. The platform can deliver a fully-customizable pressure waveform to each column of the plate, for a total of 12 simultaneous conditions. Using clinical waveform data, we are able to replicate real patients' blood pressures as well as other medically-relevant pressures within the body and have assembled a small patient-derived waveform library of some key physiological locations. As a proof of concept, human umbilical vein endothelial cells (HUVECs) survived and proliferated for 3 days under a wide range of static and dynamic physiologic pressures ranging from 10 mm Hg to 400 mm Hg. Interestingly, pathologic and supraphysiologic pressure exposures did not inhibit cell proliferation. By integrating with, rather than replacing, ubiquitous lab cultureware it is our hope that this device will facilitate the incorporation of hydrostatic pressure into standard cell culture practice.

Ultra‐Flexible Biodegradable Pressure Sensitive Field Effect Transistors for Hands‐Free Control of Robot Movements

Sensitive flexible pressure sensors are needed in applications such as health monitoring, robotics, and wearable systems. Herein, crumpled graphene flakes network (c‐GFN) channel based highly sensitive pressure sensing field effect transistors (PRESSFETs) are presented. The solution‐processed PRESSFET devices are developed on ultrathin (≈3 μm thick) biodegradable graphene oxide–chitosan (GO–CS) substrate. The distinctive crumpled morphology of GFN leads to a bandgap of 800 meV, which allows the device to have clear ON and OFF electronic states and low subthreshold swing. The presented device can work over a dynamic pressure range (0.5–2 kPa), while exhibiting good electrical stability and repeatability during rapid switching. The application of the presented device is demonstrated by attaching them to the temple regions of the face and pressing them with flexure and relaxation of respective temporalis muscles for hands‐free control of the movements of a robotic device. The pressure sensing device turns ON when the facial temporalis muscle is flexed and returns to the OFF state when it is relaxed. Finally, the degradability of the devices is presented to demonstrate their easy disposability and potential for zero electronic waste.

An immersed interface methodology for simulating supersonic spacecraft parachutes with fluid–structure interaction

The capability of a computational fluid–structure interaction method for simulating thin shell structures with an immersed boundary method and a nonlinear structural dynamics solver is extended in order to simulate supersonic spacecraft parachutes. Methodologies for the representation and motion tracking of thin, sub-grid resolution, thickness Lagrangian geometries in a static Eulerian background mesh are presented in detail. Logical functions for constructing reliable near-wall finite difference operators in the presence of thin geometries and trapped/concave volumes of space are presented. The Darcy–Forchheimer momentum equation is solved as a jump condition at the immersed interface in order to model the porosity of parachute broadcloth. A parallel contact identification and enforcement strategy based on first principles is introduced and validated. The coupled method is then used to simulate wind tunnel experiments conducted to support the Mars Science Laboratory (MSL) mission. In these experiments, a sub-scale MSL disk-gap-band parachute is inflated in a range of Mach numbers and dynamic pressures. The computational method shows good agreement with the experimental data, and where available, other simulation and empirical data, in terms of the opening load magnitude at various Mach numbers and the sustained aerodynamic performance measured by the coefficient of drag. Following quantitative comparison, a qualitative analysis is performed to investigate the effect of freestream Mach number, material porosity, and the bluff upstream payload on the main flow features.

Wide-Bandwidth Nanocomposite-Sensor Integrated Smart Mask for Tracking Multiphase Respiratory Activities.

Wearing masks has been a recommended protective measure due to the risks of coronavirus disease 2019 (COVID-19) even in its coming endemic phase. Therefore, deploying a "smart mask" to monitor human physiological signals is highly beneficial for personal and public health. This work presents a smart mask integrating an ultrathin nanocomposite sponge structure-based soundwave sensor (≈400µm), which allows the high sensitivity in a wide-bandwidth dynamic pressure range, i.e., capable of detecting various respiratory sounds of breathing, speaking, and coughing. Thirty-one subjects test the smart mask in recording their respiratory activities. Machine/deep learning methods, i.e., support vector machine and convolutional neural networks, are used to recognize these activities, which show average macro-recalls of ≈95% in both individual and generalized models. With rich high-frequency (≈4000Hz) information recorded, the two-/tri-phase coughs can be mapped while speaking words can be identified, demonstrating that the smart mask can be applicable as a daily wearable Internet of Things (IoT) device for respiratory disease identification, voice interaction tool, etc. in the future. This work bridges the technological gap between ultra-lightweight but high-frequency response sensor material fabrication, signal transduction and processing, and machining/deep learning to demonstrate a wearable device for potential applications in continual health monitoring in daily life.

Frequency-selective acoustic and haptic smart skin for dual-mode dynamic/static human-machine interface.

Accurate transmission of biosignals without interference of surrounding noises is a key factor for the realization of human-machine interfaces (HMIs). We propose frequency-selective acoustic and haptic sensors for dual-mode HMIs based on triboelectric sensors with hierarchical macrodome/micropore/nanoparticle structure of ferroelectric composites. Our sensor shows a high sensitivity and linearity under a wide range of dynamic pressures and resonance frequency, which enables high acoustic frequency selectivity in a wide frequency range (145 to 9000 Hz), thus rendering noise-independent voice recognition possible. Our frequency-selective multichannel acoustic sensor array combined with an artificial neural network demonstrates over 95% accurate voice recognition for different frequency noises ranging from 100 to 8000 Hz. We demonstrate that our dual-mode sensor with linear response and frequency selectivity over a wide range of dynamic pressures facilitates the differentiation of surface texture and control of an avatar robot using both acoustic and mechanical inputs without interference from surrounding noise.

“One for two” strategy of fully integrated textile based supercapacitor powering an ultra-sensitive pressure sensor for wearable applications

Textile-based energy storage devices help realize the full potential of flexible electronics as they combine the functionality of wearable devices with the inherent high-power density and fast charging/discharging capability of supercapacitors. In this work, Nickel di-selenide (NiSe2) is grown on carbon cloth (CC) via a facile one-pot hydrothermal technique and is used for supercapacitor and pressure sensor to demonstrate a textile-based fully integrated system. In a three-electrode configuration, the NiSe2 electrode produces a half-cell specific capacitance of 980 Fg−1 at 1 Ag−1, indicating its high-rate capability. Further, the NiSe2 electrode is combined with activated carbon (AC) electrodes generated from biomass to construct an asymmetric supercapacitor device (ASC) with a 1.6 V of output voltage. The ASC device delivers maximum specific energy of 50 Whkg−1 at a current density of 1 Ag−1 and a maximum specific power of 900 Wkg−1 at 10 Ag−1. An ultra-sensitive pressure sensor is fabricated by sandwiching the NiSe2 grown carbon cloth between thin layers of PDMS, which exhibits a sensitivity of 0.91 kPa−1 in the wide dynamic pressure range of 1– 80 kPa−1. An exceptional mechanical stability is obtained for an unloading/loading of 1 kPa of pressure for 5000 cycles. Further, it is powered using the NiSe2/CC || AC/CC AFSC for steady and reliable detection of radial pulse pressure on the human wrist in real-time. This work paves a new path in exploring the potential of textiles when combined with nanomaterials to develop low-cost, self-powered healthcare systems for real-time monitoring of health parameters.

Performance analysis of a strut-aided hypersonic scramjet by full-scale IDDES modeling

The uninstalled performance of a full-scale scramjet operating over Mach 7 to 10 and altitudes of 28 to 40 km was numerically analyzed by using high-fidelity Improved Delayed Detached Eddy Simulation (IDDES) with 125.10 million cells and Dynamic Zone Flamelet model (DZFM) with 21,294 flamelet zones. The inviscid thrust can be well correlated with dynamic pressure in the form of a gaussian function, whereas the viscous drag increases almost linearly with dynamic pressure. For the examined scramjet, net thrust is achieved for the low dynamic pressure range below 37 kPa and the high range above 55 kPa. The rule of mixed is burnt is observed, and the final combustion efficiencies vary from 66% to 82%. The upstream propagation of combustion occurs for most of the cases in the current strut-based combustor, and unstart occurs for the case of Mach 7 at 30 km.

Nonlinear supersonic flutter of multibay cross-stream shallow shells

This work investigates the interaction between adjacent bays and the effect of the curvature ratio in the nonlinear response of cross-stream curved panels. The study presents a numerical investigation of shallow shells’ linear and nonlinear dynamic behavior exposed to supersonic flutter. The finite element model embedding the aerodynamic piston theory and the Newmark method for direct time-domain integration of the nonlinear aeroelastic equations are used. Results show that the downwind bay of a two-bay cross-stream curved panel oscillates with much higher amplitudes than the equivalent single panel approach for all curvature ratios under consideration. Jump discontinuities in the LCO amplitudes were observed for a range of post-flutter dynamic pressure. The mutual existence of LCO branches in the amplitude envelope was checked through the sensitivity to initial conditions. No sudden jump in the LCO amplitudes was found for the higher curvatures, whereas a more complex behavior is encountered, especially for the downwind bay. Amplitude envelopes show that the nonlinear coupling between adjacent bays severely influences the dynamic behavior of curved panels subjected to cross-stream supersonic flow. Consequently, relying on single panel modeling may be unsafe for structural design and fatigue-life prediction for supersonic panel flutter suppression.

Analytical model for the air permeability of parachute fabric and structure parameters sensitivity analysis

To explore the effect of structure parameters on the air permeability of parachute fabric, the parachute fabric was treated as a porous medium. A nonlinear model of the viscosity and the inertia coefficient of the parachute fabric was established based on the Ergun formula, and an an alytical model of the fabric permeability with the fabric structure parameters was established considering the air permeability of fabric with the standard differential pressure. The results, which were compared with the two-point reverse estimation method showed that the new model is more accurate and has a wider applicable dynamic pressure range. Based on this, a sensitivity analysis of the effect of the fabric structure parameters on the air permeability of parachute fabric was conducted. The results showed that (1) the air permeability of fabric decreases with the increasing fabric planar weight and increases with the increasing fiber density and fabric thickness, and (2) the fabric planar weight has a greater influence on the air permeability of the fabric when the fabric structure parameter is less than the standard structure parameter. The thickness of the fabric has a significant effect on the air permeability of fabrics when the fabric structure parameter is greater than the standard structure parameter.

Robust active suppression for body-freedom flutter of a flying-wing unmanned aerial vehicle

Flying-wing unmanned aerial vehicles have received extensive attention over the past decade because of their excellent aerodynamic and stealth performance. However, the aeroelastic interaction problems among unsteady aerodynamics, flight dynamics, and structural dynamics, such as the body-freedom flutter, are still open. This paper presents the study of a robust control scheme for active body-freedom flutter suppression of a flexible flying-wing unmanned aerial vehicle. The control objective is to expand the boundary of body-freedom flutter and to enhance the control robustness to external unknown disturbance simultaneously. The paper begins with the modeling procedure of a parameter-varying aeroservoelastic plant for the design of control law. Then, it presents how to synthesize a robust controller so as to suppress the flutter instability for a wide flight range of dynamic pressures. Afterwards, the paper shows how to analyze the flutter stability of the closed-loop system and the robustness of the controller, respectively. The numerical results demonstrate that the proposed robust controller can not only expand the flutter boundary of the unmanned aerial vehicle by 30%, but also exhibit the strong robustness to external disturbance.

The effect of curvature in nonlinear supersonic flutter of panels with adjacent bays

Structural skins of aerospace vehicles are typically made of large, internally reinforced curved panels. The presence of stiffening components subdivides the panel into several bays that interact structurally. In this context, the present study investigates the effects of adjacent bays interaction in curved panels under supersonic flutter. The analyses reveal severe jumps in the post-flutter LCO amplitudes and sub-critical bifurcation with the coexistence of different LCO branches for a specific range of dynamic pressure. These discontinuities consist of abrupt changes in the LCO amplitudes, directly related to the nonlinear coupling between adjacent bays under supersonic flutter with strong sensitivity to initial conditions.

Static Aeroelasticity Using High Fidelity Aerodynamics in a Staggered Coupled and ROM Scheme

Current technology in evaluating the aeroelastic behavior of aerospace structures is based on the staggered coupling between structural and low fidelity linearized aerodynamic solvers, which has inherent limitations, although tried and trusted outside the transonic region. These limitations arise from the assumptions in the formulation of linearized aerodynamics and the lower fidelity in the description of the flowfield surrounding the structure. The validity of low fidelity aerodynamics also degrades fast with the deviation from a typical aerodynamic shape due to the inclusion of various control devices, gaps, or discontinuities. As innovative wings tend to become more flexible and also include a variety of morphing devices, it is expected that using low fidelity linearized aerodynamics in aeroelastic analysis will tend to induce higher levels of uncertainty in the results. An obvious solution to these issues is to use high fidelity aerodynamics. However, using high fidelity aerodynamics incurs a very high computational cost. Various formulations of reduced order models have shown promising results in reducing the computational cost. In the present work, the static aeroelastic behavior of three characteristic aeroelastic problems is obtained using both a full three-dimensional staggered coupled scheme and a time domain Volterra series based reduced order model (ROM). The reduced order model’s ability to remain valid for a wide range of dynamic pressures around a specific Mach number (and Reynolds number regime if viscous flow is considered) and the capability to modify structural parameters such as damping ratios and natural frequencies are highlighted.

Passive Suppression of Panel Flutter Using a Nonlinear Energy Sink

A nonlinear energy sink (NES) is used to suppress panel flutter. A nonlinear aeroelastic model for a two-dimensional flat panel with an NES in supersonic flow is established using the Galerkin method. First-order piston aerodynamic theory is adopted to build the aerodynamic load. The effects of NES parameters on flutter boundaries of the panel are investigated using Lyapunov’s indirect method. The mechanism of the NES suppression of panel flutter is studied through energy analysis. Effects of NES parameters on aeroelastic responses of the panel are obtained, and a design technique is adopted to find a suitable combination of parameter values of the NES that suppresses the panel flutter effectively. Results show that the NES can increase or reduce the onset dynamic pressure of the panel flutter and it can reduce the aeroelastic response amplitude effectively within a certain range of dynamic pressure behind the onset dynamic pressure. The installation position of the NES depends on the direction of the airflow. The robust characteristics should be considered to find the suitable combination of parameter values of the NES.

Statistical Engineering for Wind Tunnel Testing of Mars Parachute Designs

Formal experiment design and analysis techniques featuring design of experiments were applied to a Mars parachute wind tunnel test. The experiments were part of an extensive study conducted in 2014 by the NASA Engineering and Safety Center to evaluate the performance of two candidate parachute systems. Reduced scale models of the legacy Disk-Gap-Band (DGB) parachute and new Supersonic Ringsail (SSRS) were compared for both model fidelity and performance measures. Two tests, conducted in the NASA Langley Transonic Dynamics Tunnel, are described with emphasis on statistical engineering principles. The first test compared drag coefficients between models of the same canopy at Earth atmospheric pressure but at mission dynamic pressures. The experiment proved that any manufacturing differences between models were not detectable in drag coefficient measurements. The second test focused on parachute drag coefficient modeling for both canopy designs and two fabric permeabilities over a representative range of mission dynamic pressures and Mach numbers. The SSRS was found to have higher drag coefficients in comparison to the DGB for both canopy material permeabilities over the operational range of Mach numbers and dynamic pressures.

Identification of nonlinear aerodynamic systems with application to transonic aeroelasticity of aircraft structures

In this study, identification of nonlinear aerodynamic systems based on an improved nonlinear state-space modeling approach is presented to predict transonic aeroelastic behaviors of aircraft structures. It starts with identifying a linear state-space aerodynamic model by using the eigensystem realization algorithm and observer/Kalman filter identification methods. Subsequently, the remaining parameters of the nonlinear state-space aerodynamic model are determined through an output error-minimization procedure, based on a new training data generation methodology. To illustrate the approach, two- and three-dimensional transonic aeroelastic configurations are studied. The transonic aeroelastic behaviors predicted via the proposed approach agree well with those obtained via computational fluid dynamics technique in the interested range of dynamic pressure.

Multi-objective optimization of parachute triggering algorithm for Mars exploration

A multi-objective optimization procedure to design parachute triggering algorithm, based on Monte Carlo analysis of flight uncertainties, has been developed in this paper. Most of Mars explorations missions utilize parachute for a safe descent through the lowest of the atmosphere. The parachute triggering algorithm is designed to accommodate the range of off-nominal entry trajectories, and is aimed to parachute opening in certain range of Mach numbers, dynamic pressure and altitude. Our novel algorithm takes the fight uncertainty into the account through Monte Carlo analysis, selects maximization of altitude statistical mean and minimization of Mach number statistical mean as two objectives, then employs multi-objective evolutionary algorithm based on decomposition (MOEA/D), to search the Pareto-front framework. Such a methodology can be implemented on the future design of entry, descent, and landing (EDL) mission.

All-in-one cellulose based hybrid tribo/piezoelectric nanogenerator

Aybrid tribo/piezoelectric nanogenerators (HTPENG) have been proven to be highly efficient and versatile as far as the collection and conversion of ambient energy are concerned, and the introduction of flexible and green materials is a key step for their potential applications. Here, we developed a HTPENG by using nitrocellulose nanofibril paper as the triboelectric layer and BaTiO3/MWCNT@bacterial cellulose paper as the piezoelectric layer. The output of the triboelelctric paper has considerable performance as fluorinated ethylene propylene, and the output of piezoelectric paper is more than ten times higher than the BTO/polydimethylsiloxane structure. The integrated outputs of the sandwich structured HTPENG are 18 V and 1.6 µA·cm−2, which are capable of lighting up three LED bulbs and charging a 1 µF capacitor to 2.5 V in 80 s. In addition, the voltage signal generated by the HTPENG in contact-separation mode can be used for dynamic pressure detection. The linear range of dynamic pressure is from 0.5 to 3 N·cm−2 with a high sensitivity of 8.276 V·cm2 N−1 and a detection limit of 0.2 N·cm−2. This work provides new insights into the design and application of cellulose-based hybrid nanogenerators with high flexibility and simple structure.

Highly Sensitive Diode-Based Micro-Pirani Vacuum Sensor with Low Power Consumption.

Micro-Pirani vacuum sensors usually operate at hundreds of microwatts, which limits their application in battery-powered sensor systems. This paper reports a diode-based, low power consumption micro-Pirani vacuum sensor that has high sensitivity. Optimizations to the micro-Pirani vacuum sensor were made regarding two aspects. On the one hand, a greater temperature coefficient was obtained without increasing power consumption by taking advantage of series diodes; on the other hand, the sensor structure and geometries were redesigned to enlarge temperature variation. After that, the sensor was fabricated and tested. Test results indicated that the dynamic vacuum pressure range of the sensor was from 10−1 to 104 Pa when the forward bias current was as low as 10 μA with a power consumption of 50 μW. Average sensitivity was up to 90 μV/Pa and the sensitivity of unit power consumption increased to 1.8 V/W/Pa. In addition, the sensor could also work at a greater forward bias current for better sensor performance.