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Biomimetics
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Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?
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Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?

A special issue of Biomimetics (ISSN 2313-7673).

Deadline for manuscript submissions: closed (20 August 2024) | Viewed by 12043

Special Issue Editors

Dr. Antonio Concilio

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Guest Editor
Department of Adaptive Structures, Centro Italiano Ricerche Aerospaziali, 81043 Capua, CE, Italy
Interests: adaptive structures; smart structures; morphing; structural health monitoring; integrated vehicle health monitoring; vibroacoustic control
Special Issues, Collections and Topics in MDPI journals
Dr. Cristian Vendittozzi

E-Mail Website
Guest Editor
Course of Aerospace Engineering, FGA-Campus, UnB, Brasilia 72444-240, DF, Brazil
Interests: smart materials; space systems; photonic sensors; adaptive solutions; biomimetics
Special Issues, Collections and Topics in MDPI journals
Dr. Rosario Pecora

E-Mail Website
Guest Editor
Department of Industrial Engineering—Aerospace Division, University of Naples “Federico II”, Via Claudio, 21, 80125 Napoli, NA, Italy
Interests: smart structures; smart aircraft technologies; morphing structures; structural dynamics; vibration control; dynamic aeroelasticity; non-linear dynamics; mechanics and experimental dynamics
Special Issues, Collections and Topics in MDPI journals
Dr. Salvatore Ameduri

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Guest Editor
Italian Aerospace Research Centre, Capua, Italy
Interests: morphing wings; smart materials; noise and vibration control
Special Issues, Collections and Topics in MDPI journals
Dr. Yu Yang

E-Mail Website
Guest Editor
Aviation Industry Corporation of China, China
Interests: morphing; smart materials

Special Issue Information

Dear Colleagues,

Morphing systems have been extensively researched, with several achieving advanced technology levels and, in some cases, undergoing flight testing. In 2015, flight tests were conducted on the Gulfstream III jet within the Adaptive Compliant Trailing Edge project, a project led by NASA in partnership with Flexsys and the (US) AFRL, among others. These achievements follow a tradition whereby types of morphing architectures are widely studied and then undergo operational testing, as in the 1980s and 1990s when a mission-adaptive wing was mounted onto the F111. Following each successful trial, such an adaptive technology experiences a pause in experimental activities and is returned to development. At present, it can be stated that, although the feasibility of designing and deploying adaptive wings has been proven, certain aspects must be further investigated before these challenging systems can be really deployed in a context of regular aircraft and broadly exploited on the commercial market.

The need to fully develop this technology has become more urgent in recent years. With the scenario evolution, it has become not just a matter of further improving the already excellent state-of-the-art aircraft efficiency, but also of addressing new challenges proposed by the modified needs and demands of the air transport. The increased use of UAV, as well the expected rise of the urban air mobility, offer considerable benefits through systems capable of adapting the wing shape (which can extend to other aerodynamic surfaces, such us tail-planes) without reverting to standard, massive and bulky, hyperlift devices.

As the proposed architectures are investigated, it may be concluded that two kinds of logics are generally implemented: kinematic and compliant. Upon closer examination, it becomes clear that these arrangements are heavily contaminated by each other. The explanation is straightforward: while kinematic devices namely ensure the full controllability of the target shape, compliant systems aim to achieve a smooth geometry in any configuration. This allows them to fully utilize their adaptability to the greatest possible extent. At this stage, it is believed that engineering should ponder over a driving question for its future developments: can kinematic and compliant visions be merged into a single approach, or should their incompatibility be retained, each with their respective strengths and weaknesses? Perhaps the limitations hindering the full development of morphing systems can be summarized by the antagonistic perspectives these architectures have been historically drawn from; however, combining their positives through a stereoscopic fusion may reveal unforeseen opportunities that would otherwise remain out of reach.

This Special Issue wants to provide a further stimulus to researchers involved in this fascinating discipline, encouraging them to expose the value of kinematic or compliant morphing systems,  highlighting their peculiar advantages and limitations. Their contribution may inspire the development of novel strategies and finally amalgamate these systems, overcoming their inherent drawbacks while preserving their undiscussed potentialities. Where and if applicable, the use of smart materials should be considered as a possible key factor in ensuring adequate structural resistance and continuous shape variability.

Based on these considerations, articles on one or more of the following topics are mainly searched for:

  • Morphing kinematic architectures;
  • Morphing compliant architectures;
  • Hybrid morphing kinematic-compliant architectures;
  • Integrated morphing skins;
  • Integrated actuator networks;
  • Integrated sensor networks;
  • Integrated control systems;
  • Aeroelastic issues of adaptive aircraft;
  • Performance of adaptive aircraft;
  • Ground testing of morphing systems;
  • Scaling issues of morphing systems;
  • Fight testing of morphing systems;
  • Integration of morphing architectures into aircraft systems;
  • Requirements vs regulations;
  • SWOT assessment of morphing systems;
  • TRL assessment of morphing systems;
  • FHA assessment of morphing systems.

Dr. Antonio Concilio
Dr. Cristian Vendittozzi
Dr. Rosario Pecora
Dr. Salvatore Ameduri
Dr. Yu Yang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Biomimetics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • morphing
  • morphing kinematic systems
  • morphing compliant systems
  • morphing skins
  • adaptive structures
  • smart structures
  • smart materials
  • actuator networks
  • sensor networks
  • control systems
  • morphing aircraft aeroelasticity
  • morphing aircraft performance
  • adaptive structures experimental characterization
  • ground tests of morphing systems
  • flight tests of morphing systems
  • SWOT assessment of morphing systems
  • TRL assessment of morphing systems
  • FHA assessment of morphing systems

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Published Papers (8 papers)

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Research

18 pages, 11937 KiB  
Article
CGull: A Non-Flapping Bioinspired Composite Morphing Drone
by Peter L. Bishay, Alex Rini, Moises Brambila, Peter Niednagel, Jordan Eghdamzamiri, Hariet Yousefi, Joshua Herrera, Youssef Saad, Eric Bertuch, Caleb Black, Donovan Hanna and Ivan Rodriguez
Biomimetics 2024, 9(9), 527; https://doi.org/10.3390/biomimetics9090527 - 31 Aug 2024
Viewed by 1478
Abstract
Despite the tremendous advances in aircraft design that led to successful powered flights of aircraft as heavy as the Antonov An-225 Mriya, which weighs 640 tons, or as fast as the NASA-X-43A, which reached a record of Mach 9.6, many characteristics of bird [...] Read more.
Despite the tremendous advances in aircraft design that led to successful powered flights of aircraft as heavy as the Antonov An-225 Mriya, which weighs 640 tons, or as fast as the NASA-X-43A, which reached a record of Mach 9.6, many characteristics of bird flight have yet to be utilized in aircraft designs. These characteristics enable various species of birds to fly efficiently in gusty environments and rapidly change their momentum in flight without having modern thrust vector control (TVC) systems. Vultures and seagulls, as examples of expert gliding birds, can fly for hours, covering more than 100 miles, without a single flap of their wings. Inspired by the Great Black-Backed Gull (GBBG), this paper presents “CGull”, a non-flapping unmanned aerial vehicle (UAV) with wing and tail morphing capabilities. A coupled two degree-of-freedom (DOF) morphing mechanism is used in CGull’s wings to sweep the middle wing forward and the outer feathered wing backward, replicating the GBBG’s wing deformation. A modular two DOF mechanism enables CGull to pitch and tilt its tail. A computational model was first developed in MachUpX to study the effects of wing and tail morphing on the generated forces and moments. Following the biological construction of birds’ feathers and bones, CGull’s structure is mainly constructed from carbon-fiber composite shells. The successful flight test of the proof-of-concept physical model proved the effectiveness of the proposed morphing mechanisms in controlling the UAV’s path. Full article
(This article belongs to the Special Issue Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?)
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28 pages, 9007 KiB  
Article
Towards Design Optimization of Compliant Mechanisms: A Hybrid Pseudo-Rigid-Body Model–Finite Element Method Approach and an Accurate Empirical Compliance Equation for Circular Flexure Hinges
by Masoud Kabganian and Seyed M. Hashemi
Biomimetics 2024, 9(8), 471; https://doi.org/10.3390/biomimetics9080471 - 3 Aug 2024
Viewed by 1266
Abstract
Innovative designs such as morphing wings and terrain adaptive landing systems are examples of biomimicry and innovations inspired by nature, which are actively being investigated by aerospace designers. Morphing wing designs based on Variable Geometry Truss Manipulators (VGTMs) and articulated helicopter robotic landing [...] Read more.
Innovative designs such as morphing wings and terrain adaptive landing systems are examples of biomimicry and innovations inspired by nature, which are actively being investigated by aerospace designers. Morphing wing designs based on Variable Geometry Truss Manipulators (VGTMs) and articulated helicopter robotic landing gear (RLG) have drawn a great deal of attention from industry. Compliant mechanisms have become increasingly popular due to their advantages over conventional rigid-body systems, and the research team led by the second author at Toronto Metropolitan University (TMU) has set their long-term goal to be exploiting these systems in the above aerospace applications. To gain a deeper insight into the design and optimization of compliant mechanisms and their potential application as alternatives to VGTM and RLG systems, this study conducted a thorough analysis of the design of flexible hinges, and single-, four-, and multi-bar configurations as a part of more complex, flexible mechanisms. The investigation highlighted the flexibility and compliance of mechanisms incorporating circular flexure hinges (CFHs), showcasing their capacity to withstand forces and moments. Despite a discrepancy between the results obtained from previously published Pseudo-Rigid-Body Model (PRBM) equations and FEM-based analyses, the mechanisms exhibited predictable linear behavior and acceptable fatigue testing results, affirming their suitability for diverse applications. While including additional linkages perpendicular to the applied force direction in a compliant mechanism with N vertical linkages led to improved factors of safety, the associated increase in system weight necessitates careful consideration. It is shown herein that, in this case, adding one vertical bar increased the safety factor by 100N percent. The present study also addressed solutions for the precise modeling of CFHs through the derivation of an empirical polynomial torsional stiffness/compliance equation related to geometric dimensions and material properties. The effectiveness of the presented empirical polynomial compliance equation was validated against FEA results, revealing a generally accurate prediction with an average error of 1.74%. It is expected that the present investigation will open new avenues to higher precision in the design of CFHs, ensuring reliability and efficiency in various practical applications, and enhancing the optimization design of compliant mechanisms comprised of such hinges. A specific focus was put on ABS plastic and aluminum alloy 7075, as they are the materials of choice for non-load-bearing and load-bearing structural components, respectively. Full article
(This article belongs to the Special Issue Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?)
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18 pages, 7237 KiB  
Article
Ground Strength Test Technique of Variable-Camber Wing Leading Edge
by Shanshan Li, Xianmin Chen, Zhigang Wang and Yuanbo Liang
Biomimetics 2024, 9(8), 467; https://doi.org/10.3390/biomimetics9080467 - 1 Aug 2024
Viewed by 958
Abstract
Morphing wing technology is crucial for enhancing the flight performance of aircraft. To address the monitoring challenges of full-scale variable-camber leading edges under flight conditions, this study introduces a ground-based strength testing technique aimed at precisely evaluating the deformation patterns and structural strength [...] Read more.
Morphing wing technology is crucial for enhancing the flight performance of aircraft. To address the monitoring challenges of full-scale variable-camber leading edges under flight conditions, this study introduces a ground-based strength testing technique aimed at precisely evaluating the deformation patterns and structural strength during actual operation. Firstly, the motion characteristics of the variable-camber leading edge were analyzed using numerical simulation based on kinematic theory. Secondly, a tracking loading test rig was designed and constructed to simulate the actuated deformation and aerodynamic loads of the leading edge. Next, mechanical boundary numerical simulation was then utilized to predict the motion trajectories of loading points on the upper and lower wing surfaces, and a multi-point coordinated control system was developed to achieve accurate experimental control. Finally, a multi-sensor iterative method was employed to ensure loading precision throughout the testing process. A case study was conducted using a leading edge test piece from a specific commercial aircraft. The results indicated that in the motion test of the variable-camber leading edge, the average error of the deflection angle was 4.59%; in the strength test, the average errors in the magnitude and direction of the applied load were 0.54% and 0.24%, respectively. These findings validate the effectiveness of the proposed technique in simulating the flight conditions of deforming wings and accurately obtaining the leading edge shape change curve, deformation accuracy curve, and strain curves of the upper and lower wing surfaces under deflection angles. Furthermore, this paper compares the deformation accuracy of different testing methods under test conditions, providing scientific evidence and technical support for the testing and evaluation of variable-camber leading edges. Full article
(This article belongs to the Special Issue Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?)
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13 pages, 5223 KiB  
Article
A UDF-Based Approach for the Dynamic Stall Evaluation of Airfoils for Micro-Air Vehicles
by Diana-Andreea Sterpu, Daniel Măriuța and Lucian-Teodor Grigorie
Biomimetics 2024, 9(6), 339; https://doi.org/10.3390/biomimetics9060339 - 4 Jun 2024
Viewed by 992
Abstract
A numerical method for generating dynamic stall using ANSYS Fluent and a user-defined function (UDF), with the complete script shared for reference, is introduced and tested. The study draws inspiration from bird flight, exploring dynamic stall as a method for achieving enhanced aerodynamic [...] Read more.
A numerical method for generating dynamic stall using ANSYS Fluent and a user-defined function (UDF), with the complete script shared for reference, is introduced and tested. The study draws inspiration from bird flight, exploring dynamic stall as a method for achieving enhanced aerodynamic performance. The numerical method was tested on NACA 0012 airfoils with corresponding chord lengths of c1=40 mm, c2=150 mm, and c3=300 mm at Reynolds numbers ranging from Re1=2.8×104 up to Re5=1.04×106. Airfoil oscillations were settled for all cases at ω=0.55 Hz. Detached eddy simulation (DES) is employed as the turbulence model for the simulations presented, ensuring the accurate representation of the flow characteristics and dynamic stall phenomena. The study provides a detailed methodology, encouraging further exploration by researchers, especially young academics and students. Full article
(This article belongs to the Special Issue Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?)
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20 pages, 21171 KiB  
Article
Design and Validation of the Trailing Edge of a Variable Camber Wing Based on a Two-Dimensional Airfoil
by Jin Zhou, Xiasheng Sun, Qixing Sun, Jingfeng Xue, Kunling Song, Yao Li and Lijun Dong
Biomimetics 2024, 9(6), 312; https://doi.org/10.3390/biomimetics9060312 - 23 May 2024
Viewed by 1490
Abstract
Variable camber wing technology stands out as the most promising morphing technology currently available in green aviation. Despite the ongoing advancements in smart materials and compliant structures, they still fall short in terms of driving force, power, and speed, rendering mechanical structures based [...] Read more.
Variable camber wing technology stands out as the most promising morphing technology currently available in green aviation. Despite the ongoing advancements in smart materials and compliant structures, they still fall short in terms of driving force, power, and speed, rendering mechanical structures based on kinematics the preferred choice for large long-range civilian aircraft. In line with this principle, this paper introduces a linkage-based variable camber trailing edge design approach. Covering coordinated design, internal skeleton design, flexible skin design, and drive structure design, the method leverages a two-dimensional supercritical airfoil to craft a seamless, continuous two-dimensional wing full-size variable camber trailing edge structure, boasting a 2.7 m span and 4.3 m chord. Given the significant changes in aerodynamic load direction, ground tests under cruise load utilize a tracking-loading system based on tape and lever. Results indicate that the designed single-degree-of-freedom Watt I mechanism and Stephenson III drive mechanism adeptly accommodate the slender trailing edge of the supercritical airfoil. Under a maximum cruise vertical aerodynamic load of 17,072 N, the structure meets strength requirements when deflected to 5°. The research in this paper can provide some insights into the engineering design of variable camber wings. Full article
(This article belongs to the Special Issue Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?)
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19 pages, 1571 KiB  
Article
Trajectory Tracking Control of Variable Sweep Aircraft Based on Reinforcement Learning
by Rui Cao and Kelin Lu
Biomimetics 2024, 9(5), 263; https://doi.org/10.3390/biomimetics9050263 - 27 Apr 2024
Viewed by 1440
Abstract
An incremental deep deterministic policy gradient (IDDPG) algorithm is devised for the trajectory tracking control of a four-wing variable sweep (FWVS) aircraft with uncertainty. The IDDPG algorithm employs the line-of-sight (LOS) method for path tracking, formulates a reward function based on position and [...] Read more.
An incremental deep deterministic policy gradient (IDDPG) algorithm is devised for the trajectory tracking control of a four-wing variable sweep (FWVS) aircraft with uncertainty. The IDDPG algorithm employs the line-of-sight (LOS) method for path tracking, formulates a reward function based on position and attitude errors, and integrates long short-term memory (LSTM) units into IDDPG algorithm to enhance its adaptability to environmental changes during flight. Finally, environmental disturbance factors are introduced in simulation to validate the designed controller’s ability to track climbing trajectories of morphing aircraft in the presence of uncertainty. Full article
(This article belongs to the Special Issue Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?)
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18 pages, 6194 KiB  
Article
Morphological Reconstruction for Variable Wing Leading Edge Based on the Node Curvature Vectors
by Jie Zeng, Qingfeng Zhu, Yueqi Zhao, Zhigang Wang, Yu Yang, Qi Wu and Jinpeng Cui
Biomimetics 2024, 9(4), 250; https://doi.org/10.3390/biomimetics9040250 - 20 Apr 2024
Viewed by 1324
Abstract
Precise morphology acquisition for the variable wing leading edge is essential for its bio-inspired adaptive control. Therefore, this study proposes a morphological reconstruction method for the variable wing leading edge, utilizing the node curvature vectors-based curvature propagation method (NCV-CPM). By establishing a strain–arc [...] Read more.
Precise morphology acquisition for the variable wing leading edge is essential for its bio-inspired adaptive control. Therefore, this study proposes a morphological reconstruction method for the variable wing leading edge, utilizing the node curvature vectors-based curvature propagation method (NCV-CPM). By establishing a strain–arc curvature function, the method fundamentally mitigates the impact of surface curvature angle on curvature computation accuracy at sensing points. We introduce a technique that uses high-order curvature fitting functions to determine the curvature vectors of arc segment nodes. This method reduces cumulative errors in curvature computation linked to the linear interpolation-based curvature propagation method (LI-CPM) at unattached sensor positions. Integrating curvature–strain functions aids in wing leading-edge strain field reconstruction, supporting structural health monitoring. Additionally, a particle swarm algorithm optimizes the sensing point distribution, reducing network complexity. This study demonstrates significantly enhanced morphological reconstruction accuracy compared to those obtained with conventional LI-CPM. Full article
(This article belongs to the Special Issue Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?)
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28 pages, 22730 KiB  
Article
Numerical Simulation of the Transient Flow around the Combined Morphing Leading-Edge and Trailing-Edge Airfoil
by Musavir Bashir, Mir Hossein Negahban, Ruxandra Mihaela Botez and Tony Wong
Biomimetics 2024, 9(2), 109; https://doi.org/10.3390/biomimetics9020109 - 12 Feb 2024
Cited by 3 | Viewed by 1984
Abstract
An integrated approach to active flow control is proposed by finding both the drooping leading edge and the morphing trailing edge for flow management. This strategy aims to manage flow separation control by utilizing the synergistic effects of both control mechanisms, which we [...] Read more.
An integrated approach to active flow control is proposed by finding both the drooping leading edge and the morphing trailing edge for flow management. This strategy aims to manage flow separation control by utilizing the synergistic effects of both control mechanisms, which we call the combined morphing leading edge and trailing edge (CoMpLETE) technique. This design is inspired by a bionic porpoise nose and the flap movements of the cetacean species. The motion of this mechanism achieves a continuous, wave-like, variable airfoil camber. The dynamic motion of the airfoil’s upper and lower surface coordinates in response to unsteady conditions is achieved by combining the thickness-to-chord (t/c) distribution with the time-dependent camber line equation. A parameterization model was constructed to mimic the motion around the morphing airfoil at various deflection amplitudes at the stall angle of attack and morphing actuation start times. The mean properties and qualitative trends of the flow phenomena are captured by the transition SST (shear stress transport) model. The effectiveness of the dynamically morphing airfoil as a flow control approach is evaluated by obtaining flow field data, such as velocity streamlines, vorticity contours, and aerodynamic forces. Different cases are investigated for the CoMpLETE morphing airfoil, which evaluates the airfoil’s parameters, such as its morphing location, deflection amplitude, and morphing starting time. The morphing airfoil’s performance is analyzed to provide further insights into the dynamic lift and drag force variations at pre-defined deflection frequencies of 0.5 Hz, 1 Hz, and 2 Hz. The findings demonstrate that adjusting the airfoil camber reduces streamwise adverse pressure gradients, thus preventing significant flow separation. Although the trailing-edge deflection and its location along the chord influence the generation and separation of the leading-edge vortex (LEV), these results show that the combined effect of the morphing leading edge and trailing edge has the potential to mitigate flow separation. The morphing airfoil successfully contributes to the flow reattachment and significantly increases the maximum lift coefficient (cl,max)). This work also broadens its focus to investigate the aerodynamic effects of a dynamically morphing leading and trailing edge, which seamlessly transitions along the side edges. The aerodynamic performance analysis is investigated across varying morphing frequencies, amplitudes, and actuation times. Full article
(This article belongs to the Special Issue Compliant vs Kinematic Morphing Architectures: Complementary or Alternatives?)
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