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Special Issue "Smart Structures and Systems: Actual Scientific and Industrial Research"

A special issue of Applied Mechanics (ISSN 2673-3161).

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 14415

Special Issue Editors

Prof. Dr. Martin Wiedemann
E-Mail Website
Guest Editor
Institute of Composite Structures and Adaptive Systems, German Aerospace Center, 38108 Brunswick, Germany
Interests: lightweight structures; function integration into composites; life cycle management of lightweight structures; 3D fiber printing; multifunctional aircraft structures; production technologies for composite structures; structure mechanics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Hans Peter Monner
E-Mail Website
Guest Editor
Institute of Composite Structures and Adaptive Systems, German Aerospace Center, 38108 Brunswick, Germany
Interests: morphing structures; active vibration reduction; active noise reduction; 3D fiber printing
Special Issues, Collections and Topics in MDPI journals
Dr. Malte Misol
E-Mail Website
Guest Editor
Institute of Composite Structures and Adaptive Systems, German Aerospace Center, 38108 Brunswick, Germany
Interests: active control of sound and vibration; structural dynamics and acoustics; active feedforward control; algorithms for active control
Special Issues, Collections and Topics in MDPI journals
Dr. Thomas Haase
E-Mail Website
Guest Editor
Institute of Composite Structures and Adaptive Systems, German Aerospace Center, 38108 Brunswick, Germany
Interests: active control of sound and vibration; optimization of smart structures; hybrid laminar flow control; functional materials
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Prof. Dr. Tobias Melz
E-Mail Website
Guest Editor
Fraunhofer Institute for Structural Durability and System Reliability LBF, 64289 Darmstadt, Germany
Interests: reliable functionalized and smart structures; facilitate even ultra-lightweight structures by new design rules and efficient usage of new (polymer) materials; overall product life cycle in the design phase
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Dr. Sven Herold
E-Mail Website
Guest Editor
Fraunhofer Institute for Structural Durability and System Reliability LBF, 64289 Darmstadt, Germany
Interests: optimized properties (mainly dynamics) of complex systems and smart structures; efficient frontloading methods for structural dynamics and vibration control (and monitoring); multidisciplinary development of smart structures and new transducers
Special Issues, Collections and Topics in MDPI journals
Dr. Ursula Eul
E-Mail Website
Guest Editor
Fraunhofer Group MATERIALS, 64289 Darmstadt, Germany
Interests: materials; smart materials and systems; lightweight construction; structural durability and system reliability; materials for additive manufacturing; digitalization of materials; research strategy
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Based on our 4SMARTS conference this Special Issue aims to summarize the recent advances in the field of smart structures and systems. It is intended to cover both university research and industrial applications.

The focus will be on the interdisciplinary topic area of active, intelligent and adaptive—in short: smart structures and systems.

Starting with materials, over the virtualization and optimization of components as well as the integration of functions, up to ensuring the reliability of smart structures and systems, this Special Issue covers all relevant fields of technology. In addition to the classic applications of active vibration, sound and shape control, numerous other applications are addressed, including condition and structural health monitoring or autonomous systems.

We would like to invite the whole smart structures and system community to contribute to this Special Issue.

With kind regards,

Prof. Dr. Martin Wiedemann
Prof. Dr. Hans Peter Monner
Dr. Malte Misol
Dr. Thomas Haase
Prof. Dr. Tobias Melz
Dr. Sven Herold
Dr. Ursula Eul
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. Applied Mechanics is an international peer-reviewed open access quarterly 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 1000 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

  • smart systems
  • active control of sound and vibration
  • structural health monitoring/condition monitoring
  • functional materials
  • actuators and sensors
  • signal processing for smart systems
  • morphing structures
  • energy harvesting
  • reliability of smart systems

Published Papers (7 papers)

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Research

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Article
Increase in Elastic Stress Limits by Plastic Conditioning: Influence of Strain Hardening on Interference Fits
Appl. Mech. 2022, 3(2), 375-389; https://doi.org/10.3390/applmech3020023 - 31 Mar 2022
Viewed by 2247
Abstract
This paper presents a novel method for the design of purely elastic interference fits by exploiting the plastic properties of a material. In this process, the elastic potential of the material is expanded by the targeted application of residual stresses and material strengthening, [...] Read more.
This paper presents a novel method for the design of purely elastic interference fits by exploiting the plastic properties of a material. In this process, the elastic potential of the material is expanded by the targeted application of residual stresses and material strengthening, in such a way that additional operational loads due to rotating bending moments, torsion, temperature changes, and centrifugal forces are absorbed by the hub in a purely elastic manner, and plastic deformations are avoided. In the ideal case, the performance shown by the connection can be almost doubled compared to conventional elastically joined interference fits. Compared with conventional elastically–plastically joined interference fits, a specifically defined additional safety against plastic deformation can be guaranteed. In addition to the prerequisites of plasticity theory, the fundamental aspects of the process are presented and investigated on the basis of two-dimensional numerical calculation models. Both ideal plastic and hardening material models were used. The results of this work showed that previous stress limits can be significantly increased up to full plastic loading and that the utilization of plastic material properties is also made possible by plastic conditioning for applications that were previously designed to be purely elastic. Full article
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Article
Operational Modal Analysis of an Axial Compressor Rotor and Casing System for the Online Identification of a Digital Twin
Appl. Mech. 2022, 3(1), 244-258; https://doi.org/10.3390/applmech3010017 - 07 Mar 2022
Viewed by 1700
Abstract
Modal parameter identification can be a valuable tool in mechanical engineering to predict vibrational behaviour and avoid machine damage during operation. Operational modal analysis is an output-only identification tool motivated by the structural identification of civil engineering structures, which are excited by ambient [...] Read more.
Modal parameter identification can be a valuable tool in mechanical engineering to predict vibrational behaviour and avoid machine damage during operation. Operational modal analysis is an output-only identification tool motivated by the structural identification of civil engineering structures, which are excited by ambient conditions. This technique is increasingly applied in mechanical engineering in order to characterise the system behaviour during operation as modal parameters can vary under operating conditions. The following study investigates the application of operational modal analysis on an axial compressor under operating conditions. Since the modal parameters of the system change depending on the life history and during the operation of the system, a corresponding data analysis might allow us to identify the present status of the system. Eigenfrequencies and eigenvectors are studied for the use of structural health monitoring approaches. According to the analysis, eigenfrequencies represent robust parameters for the studied purpose. Eigenvectors are sensitive to damages but need further investigation, especially for rotating machinery. This study will help the user to set up a virtual model, which describes the system behaviour for different boundary conditions. This in turn, will provide an accurate prediction of the vibrational behaviour in order to assure a safe operation. Full article
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Article
A Coupling Method for the Design of Shape-Adaptive Compressor Blades
Appl. Mech. 2022, 3(1), 182-209; https://doi.org/10.3390/applmech3010014 - 11 Feb 2022
Cited by 1 | Viewed by 1426
Abstract
The design of flexible and efficient aircraft engines and propulsion systems plays a crucial role in the development of future low-emission aircraft. Implementing shape-variable blades to compressor front stage rotors presents a high potential for increasing efficiency, since through adaptation, the blades are [...] Read more.
The design of flexible and efficient aircraft engines and propulsion systems plays a crucial role in the development of future low-emission aircraft. Implementing shape-variable blades to compressor front stage rotors presents a high potential for increasing efficiency, since through adaptation, the blades are capable of optimizing their shape for different flight phases and aerodynamic conditions. Modifying the shape of the blades by using structurally integrated actuators allows this adaptation and therefore helps enhance their aerodynamic behavior for different flight regimes. Since up to now no morphing compressor or any other aircraft engine blades exist, here a multidisciplinary method for their design is introduced. This new method brings together existing structural and aerodynamic design methodologies, couples them together already at the earliest stages of the design process, while addressing the challenges that arise with a tightly coupled multidisciplinary design. As a result, first performance gain evaluations applied to the NASA 67 rotor test case are presented, showing the potential of morphing compressor blades and the potential of the introduced design methodology. Full article
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Article
Microscale Thermal Modelling of Multifunctional Composite Materials Made from Polymer Electrolyte Coated Carbon Fibres Including Homogenization and Model Reduction Strategies
Appl. Mech. 2021, 2(4), 739-765; https://doi.org/10.3390/applmech2040043 - 01 Oct 2021
Cited by 2 | Viewed by 2038
Abstract
Polymer electrolyte coated carbon fibres embedded in polymeric matrix materials represent a multifunctional material with several application scenarios. Structural batteries, thermal management materials as well as stiffness adaptive composites, made from this material, are exposed to significant joule heat, when electrical energy is [...] Read more.
Polymer electrolyte coated carbon fibres embedded in polymeric matrix materials represent a multifunctional material with several application scenarios. Structural batteries, thermal management materials as well as stiffness adaptive composites, made from this material, are exposed to significant joule heat, when electrical energy is transferred via the carbon fibres. This leads to a temperature increase of up to 100 K. The thermal behaviour of this composite material is characterized in this numerical study based on a RVE representation for the first time. Compared to classical fibre reinforced plastics, this material comprises a third material phase, the polymer electrolyte coating, covering each individual fibre. This material has not been evaluated for effective thermal conductivity, specific heat and thermal behaviour on the microscale before. Therefore, boundary conditions, motivated from applications, are applied and joule heating by the carbon fibres is included as heat source by an electro-thermal coupling. The resulting temperature field is discussed towards its effect on the mechanical behaviour of the material. Especially the temperature gradient is pronounced in thickness direction, leading to a temperature drop of 1 °Cmm, which needs to be included in thermal stress analysis in future thermo-mechanically coupled models. Another important emphasis is the identification of suitable homogenization and model reduction strategies in order to reduce the numerical effort spent on the thermal problem. Therefore, traditional analytical homogenization methods as well as a newly proposed “Two-Level Lewis-Nielsen” approach are discussed in comparison to virtually measured effective quantities. This extensive comparison of analytical and numerical methods is original compared to earlier works dealing with PeCCF composites. In addition, the accuracy of the new Two-Level Lewis-Nielsen method is found to fit best compared to classical methods. Finally, a first efficient and accurate 2D representation of the thermal behaviour of the PeCCF composite is shown, which reduces computational cost by up to 97%. This benefit comes with a different Temperature drop prediction in thickness direction of 1.5 °Cmm. In the context of future modelling of multifunctional PeCCF composite materials with multiphysical couplings, this deviation is acceptable with respect to the huge benefit for computational cost. Full article
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Article
Fluid–Structure Interaction of Symmetrical and Cambered Spring-Mounted Wings Using Various Spring Preloads and Pivot Point Locations
Appl. Mech. 2021, 2(3), 591-612; https://doi.org/10.3390/applmech2030034 - 27 Aug 2021
Cited by 1 | Viewed by 1761
Abstract
The fluid–structure interaction of a pivoting rigid wing connected to a spring and subjected to freestream airflow in a wind tunnel is presented. Fluid–structure interactions can, on the one hand, lead to undesirable aerodynamic behaviour or, in extreme cases, to structural failure. On [...] Read more.
The fluid–structure interaction of a pivoting rigid wing connected to a spring and subjected to freestream airflow in a wind tunnel is presented. Fluid–structure interactions can, on the one hand, lead to undesirable aerodynamic behaviour or, in extreme cases, to structural failure. On the other hand, improved aerodynamic performance can be achieved if a controlled application within certain limitations is provided. One application is the reduction of drag of road vehicles at higher speeds on a straight, while maintaining downforce at lower speeds during cornering. Conversely, another application concerns increased downforce at higher windspeeds, enhancing vehicle stability. In our wind tunnel experiments, the angle of incidence of the spring-mounted wing is either increased or decreased depending on the pivot point location and spring torque. Starting from a specified initial angle, the aerodynamic forces overcome a pre-set spring preload at incrementally increased freestream velocity. Reynolds numbers at a range of Re = 3 × 104 up to Re = 1.37 × 105 are considered. The application of a symmetrical NACA 0012 and a cambered NACA 6412 airfoil are tested in the wind tunnel and compared. For both airfoils mounted ahead of the aerodynamic centre, stable results were achieved for angles above 15 and below 12 degrees for the symmetrical airfoil, and above 25 and between 10 and −2 degrees for the cambered airfoil. Unsteady motions were observed around the stall region for both airfoils with all spring torque settings and also below −2 degrees for the cambered airfoil. Stable results were also found outside of the stall region when both airfoils were mounted behind the aerodynamic centre, although the velocity ranges were much smaller and highly dependent on the pivot point location. An analysis is reported concerning how changing the spring torque settings at each pivot point location effects performance. The differences in performance between the symmetrical and cambered profiles are then presented. Finally, an evaluation of the systems’ effects was conducted with conclusions, future improvements, and potential applications. Full article
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Article
Person Identification by Footstep Sound Using Convolutional Neural Networks
Appl. Mech. 2021, 2(2), 257-273; https://doi.org/10.3390/applmech2020016 - 11 May 2021
Cited by 3 | Viewed by 1871
Abstract
Human gait is very individual and it may serve as biometric to identify people in camera recordings. Comparable results can be achieved while using the acoustic signature of human footstep sounds. This acoustic solution offers the opportunity of less installation space and the [...] Read more.
Human gait is very individual and it may serve as biometric to identify people in camera recordings. Comparable results can be achieved while using the acoustic signature of human footstep sounds. This acoustic solution offers the opportunity of less installation space and the use of cost-efficient microphones when compared to visual system. In this paper, a method for person identification based on footstep sounds is proposed. First, step sounds are isolated from microphone recordings and separated into 500 ms samples. The samples are transformed with a sliding window into mel-frequency cepstral coefficients (MFCC). The result is represented as an image that serves as input to a convolutional neural network (CNN). The dataset for training and validating the CNN is recorded with five subjects in the acoustic lab of DLR. These experiments identify a total number of 1125 steps. The validation of the CNN reveals a minimum F1-score of 0.94 for all five classes and an accuracy of 0.98. The Grad-CAM method is applied to visualize the background of its decision in order to verify the functionality of the proposed CNN. Subsequently, two challenges for practical implementations, noise and different footwear, are discussed using experimental data. Full article
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Review

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Review
Sensory Utilizable Design Elements: Classifications, Applications and Challenges
Appl. Mech. 2022, 3(1), 160-173; https://doi.org/10.3390/applmech3010012 - 04 Feb 2022
Viewed by 1333
Abstract
The sensory acquisition of in situ data in technical systems is one of the key requirements set by ongoing digitalization. The sensory utilization of mechanical design elements is a step towards the accomplishment of this requirement. To set a common ground for further [...] Read more.
The sensory acquisition of in situ data in technical systems is one of the key requirements set by ongoing digitalization. The sensory utilization of mechanical design elements is a step towards the accomplishment of this requirement. To set a common ground for further research in the context of sensory utilizable design elements, this paper reviews the current state of research in this topic. First, the aim, potentials and classification of sensory utilizable design elements are introduced. Next, examples of sensory utilizable design elements are presented. These examples are used to demonstrate the technical and methodical challenges that have to be addressed in order to establish sensory utilizable design elements as a solution for the requirements of digitalization. Full article
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