Special Issue "Adaptive/Smart Structures and Multifunctional Materials 2016"

A special issue of Aerospace (ISSN 2226-4310).

Deadline for manuscript submissions: closed (30 September 2016).

Special Issue Editor

Dr. Rafic Ajaj
Website
Guest Editor
Department of Aerospace Engineering, Khalifa University, Abu Dhabi, UAE
Interests: morphing aircraft; aircraft design; adaptive/smart structures; aircraft structures; UAVs; acoustic fatigue
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Special Issue Information

Dear Colleagues,

Recent advances in smart structures and multifunctional materials have facilitated many novel aerospace technologies such as morphing aircraft. A morphing aircraft, bio-inspired by natural fliers, has gained a lot of interest as a potential technology to meet the ambitious goals of the Advisory Council for Aeronautics Research in Europe (ACARE) Vision 2020 and the FlightPath 2050 documents. A morphing aircraft continuously adjusts its wing geometry to enhance flight performance, control authority, and multi-mission capability.

In the last 30 years, there have been a number of international research programmes and projects on morphing wings. Many of these programmes are still active, especially in Europe. These programmes/projects have developed many adaptive/smart structures to allow large and small shape changes and they have investigated multifunctional materials to act as actuators and/or sensors. Furthermore, adaptive structures and multifunctional materials have been used to design compliant skins which are one of the main challenges of morphing wings. These skins have to be flexible in the morphing direction but rigid in other directions to maintain the aerodynamic shape of the wing and withstand the aerodynamic loads. The other main challenge facing morphing aircraft is the ability to design light weight, stiff, and robust adaptive structures that require minimal actuation power.

The use of adaptive/smart structures and multifunctional materials is not limited to morphing aircraft but has been used extensively in other fields, such as structural health monitoring, energy harvesting, suspension systems, wind-turbine blades, race cars, and many others. Therefore, we invite papers either addressing the research opportunities outlined here, or in the general topic area of adaptive/smart structures and multifunctional materials that will make a substantive contribution to the state of the art.

Dr. Rafic Ajaj
Guest Editor

Manuscript Submission Information

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Keywords

  • adaptive structures
  • multifunctional materials
  • morphing aircraft
  • actuators
  • sensors
  • energy harvesting
  • structural health monitoring
  • suspension systems
  • wind-turbine blades
  • compliant skins

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Published Papers (7 papers)

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Research

Open AccessArticle
Flight Dynamics and Control Using Folding Wingtips: An Experimental Study
Aerospace 2017, 4(2), 19; https://doi.org/10.3390/aerospace4020019 - 26 Mar 2017
Cited by 6
Abstract
This paper presents an experimental investigation on using FOLDing wingtips sERving as cONtrol effectorS (FOLDERONS) for a mini Unmanned Aerial Vehicle (UAV). A representative off-the-shelf mini-UAV with a conventional configuration was selected. The main theme of this paper is to utilise FOLDERONS as [...] Read more.
This paper presents an experimental investigation on using FOLDing wingtips sERving as cONtrol effectorS (FOLDERONS) for a mini Unmanned Aerial Vehicle (UAV). A representative off-the-shelf mini-UAV with a conventional configuration was selected. The main theme of this paper is to utilise FOLDERONS as a control effector (mainly in roll) to augment the control authority of conventional control surfaces. Furthermore, the impact of actuation rate on the effectiveness of FOLDERONS is assessed. The paper describes the preliminary and detailed design and sizing of the morphing wing. In addition, the manufacturing of the wing system and its integration with the UAV are addressed. Wind-tunnel testing in the RJ Mitchell wind-tunnel at the University of Southampton was performed. Both static (straight and sideslip) and dynamic (straight flight) tests are conducted at a range of airspeeds and Angles Of Attack (AOAs). The impact of folding wingtips on the lateral and directional stability is analysed. The main finding of this paper is that FOLDERONS are effective (especially at large dynamic pressure and AOAs) in controlling the lateral and directional stability. Finally, this study shows that FOLDERONS cannot fully replace conventional ailerons especially at low dynamic pressures, and their strong dependence on the AOA makes them prone to a roll reversal phenomena when the wing (and FOLDERONS) is operating at negative AOAs. Full article
(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)
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Open AccessArticle
Effects of Varied Shear Correction on the Thermal Vibration of Functionally-Graded Material Shells in an Unsteady Supersonic Flow
Aerospace 2017, 4(1), 12; https://doi.org/10.3390/aerospace4010012 - 01 Mar 2017
Cited by 1
Abstract
A model is presented for functionally-graded material (FGM), thick, circular cylindrical shells under an unsteady supersonic flow, following first-order shear deformation theory (FSDT) with varied shear correction coefficients. Some interesting vibration results of the dynamics are calculated by using the generalized differential quadrature [...] Read more.
A model is presented for functionally-graded material (FGM), thick, circular cylindrical shells under an unsteady supersonic flow, following first-order shear deformation theory (FSDT) with varied shear correction coefficients. Some interesting vibration results of the dynamics are calculated by using the generalized differential quadrature (GDQ) method. The varied shear correction coefficients are usually functions of FGM total thickness, power law index, and environment temperature. Two parametric effects of the environmental temperature and FGM power law index on the thermal stress and center deflection are also presented. The novelty of the paper is that the maximum flutter value of the center deflection amplitude can be predicted and occurs at a high frequency of applied heat flux for a supersonic air flow. Full article
(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)
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Open AccessArticle
SMA-Based System for Environmental Sensors Released from an Unmanned Aerial Vehicle
Aerospace 2017, 4(1), 4; https://doi.org/10.3390/aerospace4010004 - 24 Jan 2017
Abstract
In the work at hand, a shape memory alloy (SMA)-based system is presented. The system, conceived for releasing environmental sensors from ground or small unmanned aerial vehicles, UAV (often named UAS, unmanned aerial system), is made of a door, integrated into the bottom [...] Read more.
In the work at hand, a shape memory alloy (SMA)-based system is presented. The system, conceived for releasing environmental sensors from ground or small unmanned aerial vehicles, UAV (often named UAS, unmanned aerial system), is made of a door, integrated into the bottom of the fuselage, a device distributor, operated by a couple of antagonistic SMA springs, and a kinematic chain, to synchronize the deployment operation with the system movement. On the basis of the specifications (weight, available space, energy supply, sensors size, etc.), the system design was addressed. After having identified the main system characteristics, a representative mock-up was manufactured, featuring the bottom part of the reference fuselage. Functionality tests were performed to prove the system capability to release the sensors; a detailed characterization was finally carried out, mainly finalized at correlating the kinematic chain displacement with the SMA spring temperature and the supplied electrical power. A comparison between theoretical predictions and experimental outcomes showed good agreement. Full article
(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)
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Open AccessArticle
Manganese and Zinc Spinel Ferrites Blended with Multi-Walled Carbon Nanotubes as Microwave Absorbing Materials
Aerospace 2017, 4(1), 2; https://doi.org/10.3390/aerospace4010002 - 14 Jan 2017
Cited by 18
Abstract
Magnetic and dielectric materials can be blended to enhance absorption properties at microwave frequencies, although the materials may have relatively weak attenuation capabilities by themselves. The specific goal of this work is to enhance microwave absorption properties of materials with interesting dielectric behavior [...] Read more.
Magnetic and dielectric materials can be blended to enhance absorption properties at microwave frequencies, although the materials may have relatively weak attenuation capabilities by themselves. The specific goal of this work is to enhance microwave absorption properties of materials with interesting dielectric behavior by blending them with magnetic materials based on transition metals. The synthesized Mn1−xZnxFe2O4 (x = 0.0 and 1.0) spinel ferrite nanoparticles (MZF NPs) were blended with commercial multi-walled carbon nanotubes (MWCNTs) in various proportions with a binder matrix of paraffin. This simple and efficient process did not cause a significant variation in the energy states of MWCNTs. MZF NPs were synthesized with a citric acid assisted sol–gel method. Their electromagnetic characteristics and microwave absorption properties were investigated. These properties were derived from the microwave scattering parameters measured via the transmission line technique by using a vector network analyzer (VNA) in conjunction with an X band waveguide system. The return loss (RL) values of the samples were obtained from the electromagnetic constitutive parameters (permittivity and permeability). The results indicate that the minimum RL value and the bandwidth change significantly with the amount of ferrite material in the blend. These results encourage further development of MWCNTs blended with ferrite nanoparticles for broadband microwave applications. Full article
(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)
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Open AccessFeature PaperArticle
On the Importance of Morphing Deformation Scheduling for Actuation Force and Energy
Aerospace 2016, 3(4), 41; https://doi.org/10.3390/aerospace3040041 - 25 Nov 2016
Cited by 1
Abstract
Morphing aircraft offer superior properties as compared to non-morphing aircraft. They can achieve this by adapting their shape depending on the requirements of various conflicting flight conditions. These shape changes are often associated with large deformations and strains, and hence dedicated morphing concepts [...] Read more.
Morphing aircraft offer superior properties as compared to non-morphing aircraft. They can achieve this by adapting their shape depending on the requirements of various conflicting flight conditions. These shape changes are often associated with large deformations and strains, and hence dedicated morphing concepts are developed to carry out the required changes in shape. Such intricate mechanisms are often heavy, which reduces, or even completely cancels, the performance increase of the morphing aircraft. Part of this weight penalty is determined by the required actuators and associated batteries, which are mainly driven by the required actuation force and energy. Two underexposed influences on the actuation force and energy are the flight condition at which morphing should take place and the order of the morphing manoeuvres, also called morphing scheduling. This paper aims at highlighting the importance of both influences by using a small Unmanned Aerial Vehicle (UAV) with different morphing mechanisms as an example. The results in this paper are generated using a morphing aircraft analysis and design code that was developed at the Delft University of Technology. The importance of the flight condition and a proper morphing schedule is demonstrated by investigating the required actuation forces for various flight conditions and morphing sequences. More importantly, the results show that there is not necessarily one optimal flight condition or morphing schedule and a tradeoff needs to be made. Full article
(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)
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Open AccessArticle
Effect of the Backward-Facing Step Location on the Aerodynamics of a Morphing Wing
Aerospace 2016, 3(3), 25; https://doi.org/10.3390/aerospace3030025 - 11 Aug 2016
Cited by 4
Abstract
Over the last decade, aircraft morphing technology has drawn a lot of attention in the aerospace community, because it is likely to improve the aerodynamic performance and the versatility of aircraft at different flight regimes. With the fast paced advancements in this field, [...] Read more.
Over the last decade, aircraft morphing technology has drawn a lot of attention in the aerospace community, because it is likely to improve the aerodynamic performance and the versatility of aircraft at different flight regimes. With the fast paced advancements in this field, a parallel stream of research is studying different materials and designs to develop reliable morphing skins. A promising candidate for a viable morphing skin is the sliding skin, where two or more rigid surfaces remain in contact and slide against each other during morphing. The overlapping between each two panels create a backward-facing step on the airfoil surface which has a critical effect on the aerodynamics of the wing. This paper presents a numerical study of the effect of employing a backward-facing step on the suction side of a National Advisory Committee for Aeronautics (NACA) 2412 airfoil at a high Reynolds number of 5.9 × 106. The effects of the step location on the lift coefficient, drag coefficient and critical angle of attack are studied to find a favorable location for the step along the chord-wise direction. Results showed that employing a step on the suction side of the NACA 2412 airfoil can adversely affect the aforementioned aerodynamic properties. A drop of 21.1% in value of the lift coefficient and an increase of 120.8% in the drag coefficient were observed in case of a step located at 25% of the chord length. However, these effects are mitigated by shifting the step location towards the trailing edge. Introducing a step on the airfoil caused the airfoil’s thickness to change, which in turn has affected the transition point of the viscous boundary layer from laminar to turbulent. The location of the step, prior or post the transition point, has a noteworthy effect on the pressure and shear stress distribution, and consequently on the values of the lift and drag coefficients. Full article
(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)
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Open AccessArticle
Large Scale Applications Using FBG Sensors: Determination of In-Flight Loads and Shape of a Composite Aircraft Wing
Aerospace 2016, 3(3), 18; https://doi.org/10.3390/aerospace3030018 - 23 Jun 2016
Cited by 36
Abstract
Technological advances have enabled the development of a number of optical fiber sensing methods over the last few years. The most prevalent optical technique involves the use of fiber Bragg grating (FBG) sensors. These small, lightweight sensors have many attributes that enable their [...] Read more.
Technological advances have enabled the development of a number of optical fiber sensing methods over the last few years. The most prevalent optical technique involves the use of fiber Bragg grating (FBG) sensors. These small, lightweight sensors have many attributes that enable their use for a number of measurement applications. Although much literature is available regarding the use of FBGs for laboratory level testing, few publications in the public domain exist of their use at the operational level. Therefore, this paper gives an overview of the implementation of FBG sensors for large scale structures and applications. For demonstration, a case study is presented in which FBGs were used to determine the deflected wing shape and the out-of-plane loads of a 5.5-m carbon-composite wing of an ultralight aerial vehicle. The in-plane strains from the 780 FBG sensors were used to obtain the out-of-plane loads as well as the wing shape at various load levels. The calculated out-of-plane displacements and loads were within 4.2% of the measured data. This study demonstrates a practical method in which direct measurements are used to obtain critical parameters from the high distribution of FBG sensors. This procedure can be used to obtain information for structural health monitoring applications to quantify healthy vs. unhealthy structures. Full article
(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)
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