Aerospace

348 KiB

Open AccessArticle

On a Non-Symmetric Eigenvalue Problem Governing Interior Structural–Acoustic Vibrations

by Heinrich Voss

Aerospace 2016, 3(2), 17; https://doi.org/10.3390/aerospace3020017 - 17 Jun 2016

Cited by 1 | Viewed by 6295

Small amplitude vibrations of a structure completely filled with a fluid are considered. Describing the structure by displacements and the fluid by its pressure field, the free vibrations are governed by a non-self-adjoint eigenvalue problem. This survey reports on a framework for taking [...] Read more.

Small amplitude vibrations of a structure completely filled with a fluid are considered. Describing the structure by displacements and the fluid by its pressure field, the free vibrations are governed by a non-self-adjoint eigenvalue problem. This survey reports on a framework for taking advantage of the structure of the non-symmetric eigenvalue problem allowing for a variational characterization of its eigenvalues. Structure-preserving iterative projection methods of the the Arnoldi and of the Jacobi–Davidson type and an automated multi-level sub-structuring method are reviewed. The reliability and efficiency of the methods are demonstrated by a numerical example. Full article

(This article belongs to the Special Issue Fluid-Structure Interactions)

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7159 KiB

Open AccessArticle

A Shape Memory Alloy Application for Compact Unmanned Aerial Vehicles

by Salvatore Ameduri, Antonio Concilio, Nunzia Favaloro and Lorenzo Pellone

Aerospace 2016, 3(2), 16; https://doi.org/10.3390/aerospace3020016 - 31 May 2016

Cited by 17 | Viewed by 11265

Abstract

Shape memory alloys materials, SMA, offer several advantages that designers can rely on such as the possibility of transmitting large forces and deformations, compactness, and the intrinsic capability to absorb loads. Their use as monolithic actuators, moreover, can lead to potential simplifications of [...] Read more.

Shape memory alloys materials, SMA, offer several advantages that designers can rely on such as the possibility of transmitting large forces and deformations, compactness, and the intrinsic capability to absorb loads. Their use as monolithic actuators, moreover, can lead to potential simplifications of the system, through a reduction of number of parts and the removal of many free play gaps among mechanics. For these reasons, technological aerospace research is focusing on this kind of technology more and more, even though fatigue life, performance degradation, and other issues are still open. In the work at hand, landing gear for unmanned aerial vehicles, UAV, is presented, integrated with shape memory alloys springs as actuation devices. A conceptual prototype has been realized to verify the system ability in satisfying specs, in terms of deployment and retraction capability. Starting from the proposed device working principle and the main design parameters identification, the design phase is faced, setting those parameters to meet weight, deployment angle, energy consumption, and available room requirements. Then, system modeling and performance prediction is performed and finally a correlation between numerical and experimental results is presented. Full article

(This article belongs to the Collection Unmanned Aerial Systems)

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2470 KiB

Open AccessArticle

Theoretical and Numerical Modeling of Acoustic Metamaterials for Aeroacoustic Applications

by Umberto Iemma

Aerospace 2016, 3(2), 15; https://doi.org/10.3390/aerospace3020015 - 26 May 2016

Cited by 23 | Viewed by 7168 | Correction

Abstract

The advent, during the first decade of the 21st century, of the concept of acoustic metamaterial has disclosed an incredible potential of development for breakthrough technologies. Unfortunately, the extension of the same concepts to aeroacoustics has turned out to be not a trivial [...] Read more.

The advent, during the first decade of the 21st century, of the concept of acoustic metamaterial has disclosed an incredible potential of development for breakthrough technologies. Unfortunately, the extension of the same concepts to aeroacoustics has turned out to be not a trivial task, because of the different structure of the governing equations, characterized by the presence of the background aerodynamic convection. Some of the approaches recently introduced to circumvent the problem are biased by a fundamental assumption that makes the actual realization of devices extremely unlikely: the metamaterial should guarantee an adapted background aerodynamic convection in order to modify suitably the acoustic field and obtain the desired effect, thus implying the porosity of the cloaking device. In the present paper, we propose an interpretation of the metamaterial design that removes this unlikely assumption, focusing on the identification of an aerodynamically-impermeable metamaterial capable of reproducing the surface impedance profile required to achieve the desired scattering abatement. The attention is focused on a moving obstacle impinged by an acoustic perturbation induced by a co-moving source. The problem is written in a frame of reference rigidly connected to the moving object to couple the convective wave equation in the hosting medium with the inertially-anisotropic wave operator within the cloak. The problem is recast in an integral form and numerically solved through a boundary-field element method. The matching of the local wave vector is used to derive a convective design of the metamaterial applicable to the specific problem analyzed. Preliminary numerical results obtained under the simplifying assumption of a uniform aerodynamic flow reveal a considerable enhancement of the masking capability of the convected design. The numerical method developed shows a remarkable computational efficiency, completing a simulation of the entire field in a few minutes on mid-end workstations. The results are re-interpreted in term of boundary impedance, assuming a locally-reacting behavior of the outer boundary of the cloaking layer. The formulation is currently being extended to the analysis of arbitrarily complex external flows in order to remove the limitation of the background uniform stream in the host. Full article

(This article belongs to the Special Issue Recent Advances in Aeroacoustics)

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4175 KiB

Open AccessArticle

Fixed-Wing UAV Attitude Estimation Using Single Antenna GPS Signal Strength Measurements

by Jason Gross, Yu Gu and Matthew Rhudy

Aerospace 2016, 3(2), 14; https://doi.org/10.3390/aerospace3020014 - 13 May 2016

Cited by 13 | Viewed by 8373

Abstract

This article considers a novel approach to using global positioning system (GPS) signal strength readings and estimated velocity vector for estimating the attitude of a small fixed-wing unmanned aerial vehicle (UAV). This approach has the benefit being able to estimate full position, velocity [...] Read more.

This article considers a novel approach to using global positioning system (GPS) signal strength readings and estimated velocity vector for estimating the attitude of a small fixed-wing unmanned aerial vehicle (UAV). This approach has the benefit being able to estimate full position, velocity and attitude states of a UAV using only the data from a single GPS receiver and antenna. Two different approaches for utilizing GPS signal strength within measurement updates for UAV attitude in a nonlinear Kalman filter are discussed and assessed using recorded UAV flight data. Comparisons of UAV pitch and roll estimates against measurements from a high-grade mechanical gyroscope are used to show that approximately 5° error with respect to both mean and standard-deviation on both axes is achievable. Full article

(This article belongs to the Collection Unmanned Aerial Systems)

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4124 KiB

Open AccessArticle

Suppression of Low-Frequency Shock Oscillations over Boundary Layers by Repetitive Laser Pulse Energy Deposition

by Akira Iwakawa, Tatsuro Shoda, Hoang Son Pham, Takahiro Tamba and Akihiro Sasoh

Aerospace 2016, 3(2), 13; https://doi.org/10.3390/aerospace3020013 - 27 Apr 2016

Cited by 10 | Viewed by 7301

Abstract

The effect of repetitive energy deposition on low Strouhal number oscillations of the shock wave induced by boundary-layer interaction over a cylinder-flare model was studied. The fluctuation of the energy deposition frequency was induced in the flow, because the bubble generated by the [...] Read more.

The effect of repetitive energy deposition on low Strouhal number oscillations of the shock wave induced by boundary-layer interaction over a cylinder-flare model was studied. The fluctuation of the energy deposition frequency was induced in the flow, because the bubble generated by the energy deposition flowed downstream along the surface repeatedly. The region before the bubble size was affected by the energy deposition directly, so the fluctuation frequency was equal to the energy deposition frequency. However, the flare shock behavior at a position farther from the surface than the bubble size was also affected strongly by the energy deposition. For low-frequency unsteadiness and the effect of energy deposition on its unsteadiness, two categories have been observed. In the relatively small flare angle case, the flare shock was oscillated owing to the fluctuation induced by the boundary-layer interaction at the shock foot, and its oscillation occurred at 2.1 kHz with a small amplitude. The amplitude of this oscillation was decreased by highly repetitive energy depositions, and its amplitude could not be detected at a highly repetitive energy deposition. In the longer cylinder section case, the region of the shock-wave interaction was widened, and the amplitude of the flare shock oscillation was increased. In this case, the amplitude drastically decreased because of energy deposition. Full article

(This article belongs to the Special Issue Feature Papers in Aerospace)

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2376 KiB

Open AccessArticle

Experimental Aeroelastic Models Design and Wind Tunnel Testing for Correlation with New Theory

by Deman Tang and Earl H. Dowell

Aerospace 2016, 3(2), 12; https://doi.org/10.3390/aerospace3020012 - 14 Apr 2016

Cited by 30 | Viewed by 10986

Abstract

Several examples of experimental model designs, wind tunnel tests and correlation with new theory are presented in this paper. The goal is not only to evaluate a new theory, new computational method or new aeroelastic phonomenon, but also to provide new insights into [...] Read more.

Several examples of experimental model designs, wind tunnel tests and correlation with new theory are presented in this paper. The goal is not only to evaluate a new theory, new computational method or new aeroelastic phonomenon, but also to provide new insights into nonlinear aeroelastic phenomena, flutter, limit cycle oscillation (LCO) and gust response. Full article

(This article belongs to the Special Issue Innovations in Wind Tunnel Testing)

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5987 KiB

Open AccessArticle

A Six Degrees of Freedom Dynamic Wire-Driven Traverse

by Thomas J. Lambert, Bojan Vukasinovic and Ari Glezer

Aerospace 2016, 3(2), 11; https://doi.org/10.3390/aerospace3020011 - 14 Apr 2016

Cited by 27 | Viewed by 8611

Abstract

A novel support mechanism for a wind tunnel model is designed, built, and demonstrated on an aerodynamic platform undergoing dynamic maneuvers, tested with periodic motions up to 20 Hz. The platform is supported by a 6-DOF (six degrees of freedom) traverse that utilizes [...] Read more.

A novel support mechanism for a wind tunnel model is designed, built, and demonstrated on an aerodynamic platform undergoing dynamic maneuvers, tested with periodic motions up to 20 Hz. The platform is supported by a 6-DOF (six degrees of freedom) traverse that utilizes eight thin wires, each mounted to a servo motor with an in-line load cell to accurately monitor or control the platform motion and force responses. The system is designed such that simultaneous control of the servo motors effects motion within ±50 mm translations, ±15° pitch, ±9° yaw, and ±8° roll at lower frequencies. The traverse tracks a desired trajectory and resolves the induced forces on the platform at 1 kHz. The effected motion of the platform is measured at 0.6 kHz with a motion capture system, which utilizes six near-infrared (NIR) cameras for full spatial and temporal resolution of the platform motion, which is used for feedback control. The traverse allows different platform model geometries to be tested, and the present work demonstrates its capabilities on an axisymmetric bluff body. Programmable timed outputs are synchronized relative to the model motion and can be used for triggering external systems and processes. In the present study, particle image velocimetry (PIV) is used to characterize the realized wakes of the platform undergoing canonical motions that are effected by this new wind tunnel traverse. Full article

(This article belongs to the Special Issue Innovations in Wind Tunnel Testing)

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8364 KiB

Open AccessArticle

Vertical Wind Tunnel for Prediction of Rocket Flight Dynamics

by Hoani Bryson, Hans Philipp Sültrop, George Buchanan, Christopher Hann, Malcolm Snowdon, Avinash Rao, Adam Slee, Kieran Fanning, David Wright, Jason McVicar, Brett Clark, Graeme Harris and Xiao Qi Chen

Aerospace 2016, 3(2), 10; https://doi.org/10.3390/aerospace3020010 - 29 Mar 2016

Cited by 4 | Viewed by 10705

Abstract

A customized vertical wind tunnel has been built by the University of Canterbury Rocketry group (UC Rocketry). This wind tunnel has been critical for the success of UC Rocketry as it allows the optimization of avionics and control systems before flight. This paper [...] Read more.

A customized vertical wind tunnel has been built by the University of Canterbury Rocketry group (UC Rocketry). This wind tunnel has been critical for the success of UC Rocketry as it allows the optimization of avionics and control systems before flight. This paper outlines the construction of the wind tunnel and includes an analysis of flow quality including swirl. A minimal modelling methodology for roll dynamics is developed that can extrapolate wind tunnel behavior at low wind speeds to much higher velocities encountered during flight. The models were shown to capture the roll flight dynamics in two rocket launches with mean roll angle errors varying from 0.26° to 1.5° across the flight data. The identified model parameters showed consistent and predictable variations over both wind tunnel tests and flight, including canard–fin interaction behavior. These results demonstrate that the vertical wind tunnel is an important tool for the modelling and control of sounding rockets. Full article

(This article belongs to the Special Issue Innovations in Wind Tunnel Testing)

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721 KiB

Open AccessCommunication

Semi-Empirical Prediction of Airfoil Hysteresis

by Lance W. Traub

Aerospace 2016, 3(2), 9; https://doi.org/10.3390/aerospace3020009 - 24 Mar 2016

Cited by 10 | Viewed by 9990

Abstract

A semi-empirical method is presented to estimate the angular excursion and the lift loss associated with static hysteresis on an airfoil. Wind tunnel data of various airfoils is used to define and validate the methodology. The resulting equation provides a relationship between the [...] Read more.

A semi-empirical method is presented to estimate the angular excursion and the lift loss associated with static hysteresis on an airfoil. Wind tunnel data of various airfoils is used to define and validate the methodology. The resulting equation provides a relationship between the size of the hysteresis loop and characteristics of the airfoil. Comparisons of the equation with experiment show encouraging agreement both in terms of the magnitude of the lift loss and the extent of the loop. Full article

(This article belongs to the Special Issue Feature Papers in Aerospace)

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Aerospace, Volume 3, Issue 2 (June 2016) – 9 articles

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