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This document is an introduction to a special issue of the journal Eng, which focuses on experimental and theoretical research in engineering science and technology. The topics covered in the journal include various fields of engineering, such as electrical, chemical, mechanical, civil, and biomedical engineering, with an emphasis on contributing to the circular economy and sustainable development. The special issue contains 34 papers from authors in 25 countries, covering a range of cutting-edge developments in engineering. The author expresses gratitude to the contributors and hopes that the articles will be interesting and inspiring for readers, particularly young scholars. [Extracted from the article]

The document is an editorial introducing selected papers from the 4th International Symposium on Thermal-Fluid Dynamics (ISTFD 2023). Thermal-fluid dynamics is a crucial field that impacts various subjects and technologies, including energy generation, aerospace, automotive engineering, and more. The ISTFD series was established in 2019 to promote research and progress in thermal-fluid dynamics. The 4th symposium was successfully held in Nanjing, China, in 2023, with over 200 participants from 15 countries. This special issue contains 15 peer-reviewed articles showcasing recent research progress in thermal-fluid dynamics and interdisciplinary research. [Extracted from the article]

Aluminum alloys are primary structural materials in aircraft fuel systems, where jet fuel can influence the fatigue crack growth (FCG) behavior of materials. This paper presents a model for calculating the FCG rate of aluminum alloys in jet fuel environment. The model is based on elastoplastic fracture mechanics and revises the interaction terms in the linear superposition model by accounting for the corrosive environment and the crack closure effect. The derivation process of the model is discussed in detail. To validate the efficacy of the model, FCG tests were conducted on three types of aviation aluminum alloys, namely, 2524‐T3, 7050‐T7451, and 7075‐T62 in the jet fuel. The experimental results were compared with FCG rates in the laboratory air environment. Findings indicate that the proposed model effectively captures the primary trends observed in the experimental data. In addition, the failure surfaces of the specimens were observed using a super‐depth‐of‐field optical microscopy system. [ABSTRACT FROM AUTHOR]

The active magnetic compensation coil is of great significance for extensive applications, such as fundamental physics, aerospace engineering, national defense industry, and biological science. The magnetic shielding demand is increasing over past few decades, and better performances of the coil are required. To maintain normal operating conditions for some sensors, active magnetic compensation coils are often used to implement near-zero field environments. Many coil design methods have been developed to design the active compensation coil for different fields. It is opportune to review the development and challenges associated with active magnetic compensation coils. Active magnetic compensation coils are reviewed in this paper in terms of design methods, technology, and applications. Furthermore, the operational principle and typical structures of the coil are elucidated. The developments of the forward design method, inverse design method, and optimization algorithm are presented. Principles of various design methods and their respective advantages and disadvantages are described in detail. Finally, critical challenges in the active magnetic compensation coil techniques and potential research directions have been highlighted. [ABSTRACT FROM AUTHOR]

The design of an aircraft's internal structure, and therefore the appropriate choice of material type, is a direct function of the performed tasks and the magnitude and type of the acting loads. The design of a durable aircraft structure with appropriate stiffness and lightness requires knowledge of the loads that will be applied to the structure. Therefore, this paper presents the results of an aerodynamic experimental test and numerical analysis of a newly designed jet-propelled aerial target. The experimental tests were carried out in a low-speed wind tunnel for a wide range of angles of attack and sideslips. Moreover, they were performed for various configurations of the airplane model. In addition, the results of the experimental test were supplemented with the results of the numerical analysis performed using computational fluid dynamics methods. During numerical analysis, specialized software based on solving partial differential equations using the Finite Volumes Method was used. This article presents the methodology of the conducted research. The results of the aerodynamic analysis are presented in the form of diagrams showing the aerodynamic force and moment components as a function of the angle of attack and sideslip. In addition, qualitative results of the flow around the plane have been presented. The results obtained prove that the adopted methods are sufficient to solve these types of problem. The aerial system was positively verified during the qualification tests of the system at the Polish Air Force training range and finally received the type certificate. [ABSTRACT FROM AUTHOR]

Most space shuttle fuel tanks use a center column to hold the Propellant Management Device (PMD). This paper analyzes the gas–liquid interface state in the tanks with a central column during microgravity experiments conducted in the Chinese Space Station. It launches an extended study to investigate the gas–liquid interface state under different gravity conditions. Using the perturbation method and boundary layer theory, we numerically calculated the morphology of the gas–liquid interface under varying gravity conditions based on the Young–Laplace equation. The results were then compared to those obtained from existing commercial software and were found to be consistent. Based on this, the study develops two types of calculation procedures. The first procedure generates the corresponding shape of the liquid surface by inputting the height of the liquid surface endpoints and the gravity level. The second procedure is based on the targeting method and generates the corresponding liquid surface by inputting the volume of the liquid in the storage tank and the gravity level. The procedures were used to analyze the variation of gas–liquid interface properties under different gravity conditions. This study offers theoretical support for liquid management in aerospace engineering fuel tanks. [ABSTRACT FROM AUTHOR]

The future use of eddy resolving simulations (ERS) such as Large Eddy Simulation (LES), Direct Numerical Simulation (DNS) and related approaches in aerospace is explored. The turbulence modeling requirements with respect to aeroengines and aircraft is contrasted. For the latter, higher Reynolds numbers are more prevalent and this especially gives rise to the need for the hybridization of ERS methods with Reynolds Averaged Navier–Stokes (RANS) approaches. Zones where future use of pure ERS methods is now possible and those where hybridizations with RANS will be needed is outlined. The major focus is the aeroengine for which the component scales are much smaller. This gives rise to generally more benign Reynolds numbers. The use of eddy resolving methods in a wide range of zones in an aeroengine is discussed and the potential benefits and also cost drawbacks with such approaches noted. The tension when using such computationally intensive calculations in an area where the coupling of components and even the airframe and engine is becoming increasingly important is explored. Also, the numerical methods and meshing requirements are considered and the implications of ERS methods for future numerical algorithms. It is postulated that such simulations are ready now for niche uses in industry. However, to perform the scale of simulations that industry requires, to meet pressing environmental needs, challenges remain. For example, there is the need to develop optimal numerical methods that both map to the accuracy requirements for ERS and also future computer architectures. [ABSTRACT FROM AUTHOR]

The dynamic measurement of position and attitude information of a long‐distance moving object is a common demand in ground testing of aerospace engineering. Due to the movement from far to near and the limitations of camera resolution, it is necessary to use multi‐binocular cameras for segmented observation at different distances. However, achieving accurate and continuous position and attitude estimation is a challenging task. Therefore, this paper proposes a dynamic monitoring technique for long‐distance movement based on a multi‐binocular videogrammetric system. Aiming to solve the problem that the scale in images changes constantly during the moving process, a scale‐adaptive tracking method of circular targets is presented. Bundle adjustment (BA) with joint segments using an adaptive‐weighting least‐squares strategy is developed to enhance the measurement accuracy. The feasibility and reliability of the proposed technique are validated by a ground testing of relative measurement for spacecraft rendezvous and docking. The experimental results indicate that the proposed technique can obtain the actual motion state of the moving object, with a positioning accuracy of 3.2 mm (root mean square error), which can provide a reliable third‐party verification for on‐orbit measurement systems in ground testing. Compared with the results of BA with individual segments and vision measurement software PhotoModeler, the accuracy is improved by 45% and 30%, respectively. [ABSTRACT FROM AUTHOR]

The Aeroacoustics Laboratory in the Department of Aerospace Engineering at Penn State currently serves several areas of experimental research. Most notable in the laboratory is the Anechoic Chamber of which the Aeroacoustics Wind Tunnel is an integral part. In recent years the dominant areas of research have included model aircraft exhaust jets and model rotors for helicopter applications involving detailed noise experiments. In the jet noise area, the applications have included aircraft in both flyover and take-off configurations. In the flyover application the air flow surrounding the exhaust jet has a significant effect on the radiated noise and must be simulated to produce experimental results that will be most useful in preliminary design of noise suppression applications. The Aeroacoustics Wind Tunnel at Penn State serves the purpose for this simulation. During aircraft take-off, the aircraft airspeed is in a range exceeding 250 ft per second, or Mach number of over M = 0.22. In the years preceding 2022, the velocity of the free jet flow of the Penn State facility was limited to less than 200 ft/sec. This paper reports on a project to design upgrades to the existing wind tunnel to improve the test section flow velocity to values closer to the 250 ft/sec target. The approach began with a preliminary design of the return flow ducting to convert the open jet, open return wind tunnel to a closed return tunnel. The concept is to make use of the flow energy in the exhaust of the tunnel to boost the input energy to the inlet fan that drives the flow to the test section. An integral part of the preliminary design involved making use of an upgraded flow analysis computer code to predict the gain in test section velocity of the new facility. For the available horsepower of two fans in the facility, the configurations of the existing and upgraded wind tunnel were entered into this analysis code based on a quasi-one-dimensional formulation. The code included empirical data formulated to include the various shapes of the components of the tunnels. The relative flow velocities in each section used simple incompressible continuity to calculate all velocities in the component sections. The average dynamic pressure in each section is calculated from the flow (constant) density and the velocity squared. Each section had a non-dimensional pressure loss parameter calculated from empirical data (from the relevant literature). The basic code (using the Excel algorithms) was based on a predictor-corrector concept in which the calculation was initialized with the estimated velocity and pressure of the flow at the entrance to the test section. The loss in each following section is estimated to determine the loss in the total pressure and the cumulated loss compared to the gains made at the two fans in the circuit. The initial guess is adjusted based on the total pressure value at the end of the circuit. During the related experiments, measurements of the total and dynamic pressure were performed at several joints between sections and compared to the values predicted in the analysis code. Various settings of the horsepower of the drive fans were used and the results were compared to flow measurements for the tunnel configurations (predominantly for the open return and closed return tunnel setups available before and after the upgrade project.) Results of the analysis and experiments are presented and analyzed together with the remaining activities planned for the coming months. [ABSTRACT FROM AUTHOR]

The reentry trajectory planning problem of hypersonic vehicles is generally a continuous and nonconvex optimization problem, and it constitutes a critical challenge within the field of aerospace engineering. In this paper, an improved sequential convexification algorithm is proposed to solve it and achieve online trajectory planning. In the proposed algorithm, the Chebyshev pseudo-spectral method with high-accuracy approximation performance is first employed to discretize the continuous dynamic equations. Subsequently, based on the multipliers and linearization methods, the original nonconvex trajectory planning problem is transformed into a series of relaxed convex subproblems in the form of an augmented Lagrange function. Then, the interior point method is utilized to iteratively solve the relaxed convex subproblem until the expected convergence precision is achieved. The convex-optimization-based and multipliers methods guarantee the promotion of fast convergence precision, making it suitable for online trajectory planning applications. Finally, numerical simulations are conducted to verify the performance of the proposed algorithm. The simulation results show that the algorithm possesses better convergence performance, and the solution time can reach the level of seconds, which is more than 97% less than nonlinear programming algorithms, such as the sequential quadratic programming algorithm. [ABSTRACT FROM AUTHOR]

Space debris poses a potentially catastrophic risk to large-scale LEO constellations due to its substantial cascading effects, thereby rendering efficient and timely debris removal a critical research area in contemporary aerospace engineering. This paper delves into the application of the three-dimensional traveling salesman problem with orbital transfer constraints for space debris removal task planning. To overcome the challenges of sparse optimal solutions and vulnerability to local optima in addressing large-scale space debris removal task planning problems, we introduce a new Hierarchical Exploration Artificial Bee Colony (HEABC) optimization algorithm. Initially, we present an innovative two-step search strategy that employs a short-and-long term hybrid approach to optimize search time utilization and enhance solution quality, thereby addressing the sparsity of optimal solutions in the HEABC algorithm. Subsequently, to mitigate the issue of converging to local optima in high-dimensional encoding-based search problems, we devise a dual population update strategy aimed at preserving the innate evolutionary driving force of the search population. This strategy ensures the continuous updating of the population, even in the absence of intrinsic driving forces. Ultimately, experimental results substantiate that our proposed HEABC algorithm attains superior task planning sequences in a reduced time span and exhibits heightened adaptability in comparison to various traditional search algorithms. This is corroborated by numerical experiments conducted on one publicly available and one STK-generated space debris datasets. [ABSTRACT FROM AUTHOR]

This paper deals with the uncoupling of linear damped multi-degree-of-freedom gyroscopic potential systems in which the damping is taken to have a specifically chosen form. Necessary and sufficient conditions are obtained that guarantee the uncoupling of such damped systems into independent subsystems with at most two degrees-of-freedom. Along with several other results, it is shown that when the potential (stiffness) matrix of the damped system has distinct eigenvalues--a situation commonly found in civil, mechanical, and aerospace engineering, as well as in nature--the damping matrix must have this specifically chosen form for any such multi-degree-of-freedom system to be capable of being uncoupled. [ABSTRACT FROM AUTHOR]

Complex systems are difficult to manage, operate and maintain. This is why we see teams of highly specialised engineers in industries such as aerospace, nuclear and subsurface. Condition based monitoring is also employed to maximise the efficiency of extensive maintenance programmes instead of using periodic maintenance. A level of automation is often required in such complex engineering platforms in order to effectively and safely manage them. Advances in Artificial Intelligence related technologies have offered greater levels of automation but this potentially pivots the weight of decision making away from the operator to the machine. Implementing AI or complex algorithms into a platform can mean that the Operators' control over the system is diminished or removed altogether. For example, in the Boeing 737 Air Max Disaster, AI had been added to a platform and removed the operators' control of the system. This meant that the operator could not then move outside the extremely reserved, algorithm defined, "envelope" of operation. This paper analyses the challenges of AI driven condition based monitoring where there is a potential to see similar consequences to those seen in control engineering. As the future of society becomes more about algorithm driven technology, it is prudent to ask, not only whether we should implement AI into complex systems, but how this can be achieved ethically and safely in order to reduce risk to life. [ABSTRACT FROM AUTHOR]

Objective: This research aimed to measure the dependence and independence of documents in an Ego-centered citation network to evaluate the quality of scientific outputs in two subject areas "aerospace engineering" and "nuclear technology". Methodology: The present study is applied research and belongs to the category of scientometrics research. In the first step, the required data for creating ego-centric citation networks were extracted and stored from the Web of Science Core Collection (WOSCC) through web scraping (automated data extraction from websites) using the Mimfa Scraper (a software for automated data extraction) and the JavaScript programming language. Afterward, algorithm coding was performed in the MiMFa RAVAR DataLab, and the programming language C# was utilized to answer the research question. Findings: The research findings showed that the study conducted by Allison (2016) with 1535 citations is the most cited document in the field of nuclear technology and ranks first in terms of absolute dependence index. In comparison to the number of references in Allison's paper, 80 percent of the alters in Li's research (2018), the second most cited paper in terms of the absolute dependence index (512 citations), cited ego-related references (58 references); however, this percentage is 46 percent in Allison's paper. A study conducted by Shin has obtained the highest absolute independence index (2015 citations) compared to other highly cited articles in the field of nuclear technology. Leppanen's study (2015) ranks first in terms of the relative independence index with a score of 98 percent compared to other highly cited documents in the field of nuclear technology. Ricker (2015), along with 57 co-authors, has the highest number of citations (1542 citations) in aerospace engineering. Among these citations, 647 alters have cited the documents cited by the ego and obtained the highest absolute dependence index score. Wang's research (2020), with 52 citations, is the first paper to rank the relative independence index in the field of aerospace engineering . Conclusion: The results indicate that the level of relative dependence was higher than independence in both subject areas. Moreover, as the number of citations increases, both absolute dependence and independence increase; however, relative dependence decreases. Additionally, in recent years, the absolute dependence and independence indices have lower values than older years. However, the relative dependence index positively correlates with the year of publication. Moreover, the relative independence index positively correlates with the number of citations; its value has increased in recent years and the number of ego sources does not directly correlate with the increase in the dependence index. [ABSTRACT FROM AUTHOR]

Aerodynamic model identification remains essential for simulator operations and control system design and operations. In this paper, state-of-the-art methodologies for aerodynamic model identification and validation are presented, together with a number of novel applications of the identified models that were recently investigated and developed at the Faculty of Aerospace Engineering of Delft University of Technology. In particular, this paper focuses on methodologies for identifying models of aerodynamic stall from flight data, as well as multivariate spline-based aerodynamic model identification methods, together with their applications in flight simulation and advanced flight control. [ABSTRACT FROM AUTHOR]

Dynamics is a core discipline in Mechanical and Aerospace Engineering programs and with the ubiquitous nature of control in modern-day applications, the field of mechatronics has gained popularity. Mechatronics refers to the field of engineering which integrates the engineering disciplines of mechanical, control, electronics, and computing. To create a testbed to illustrate a tabletop mechatronics system, the paper details the design, and fabrication of an active pendulum whose length can be changed in real-time using solenoids. This permits illustrating two concepts: (1) damping of pendulum oscillations which emulates the sway of a crane and (2) amplification of the oscillations which emulates the pumping of a playground swing. The paper describes the steps prior to experimental validation which includes: modeling, system identification, signal processing, and controller implementation. Numerical simulations are used to prototype the controller and eventually to compare the simulation results to the experimental ones. The results of all the experiments illustrate a close match between the simulated and experimental results. To permit reproduction of the experiment, the design details and code to implement the controllers are posted in a public repository. [ABSTRACT FROM AUTHOR]

This article discusses the development and application of an event-triggered distributed observer for a leader-following consensus problem in multiple rigid body systems. The authors present a design framework called the distributed observer based approach, which involves designing control laws and a distributed observer to estimate the state of the leader. The main result of the article is the existence of upper bounds for certain variables in the system. The article also discusses the convergence of the system and presents a lemma and theorem to prove the convergence. Additionally, the article applies the event-triggered distributed observer to the leader-following adaptive consensus problem of multiple uncertain rigid body systems and provides a numerical example to illustrate the result. The paper concludes by acknowledging support received and suggesting future directions for improvement. [Extracted from the article]

Sandwich composites are widely used in aviation, aerospace and marine engineering fields because of their excellent comprehensive properties. However, it is difficult to accurately predict the ultimate performance of sandwich composite structures because of their complex failure modes and uncoordinated damage processes. In this paper, the ultimate load, progressive failure process and failure mode of sandwich composite T-joints under three-point bending and lateral bending loads are predicted and verified by using an improved progressive damage analysis program. Moreover, the bio-inspired optimization of the composite T-joint is carried out, and the corner shape and material combination of the T-joint are designed and optimized based on the contour of the flange bone of the bird. The main factors affecting the bearing capacity of T-joint are further discussed, and a reasonable and feasible bio-inspired optimization scheme is obtained, which provides some reference for the design of marine composite T-joint. [ABSTRACT FROM AUTHOR]

Carbon fibres used as a honeycomb core material (subject to a proper in-depth analysis of their reinforcement patterns) allows solving the thermo-dimensional stability problem of the units for space systems. Based on the results of numerical simulations with the support of finite element analysis, the paper provides an evaluation of the accuracy of analytical dependencies for the determination of the moduli of elasticity of a carbon fibre honeycomb core in tension/compression and shear. It is shown that a carbon fibre honeycomb reinforcement pattern has a significant impact on the mechanical performance of the carbon fibre honeycomb core. For example, for honeycombs measuring 10 mm in height, the maximum shear modulus values corresponding to the reinforcement pattern of ±45° exceed the minimum values for a reinforcement pattern of 0° and 90° by more than 5 times in the XOZ plane and 4 times for the shear modulus in the YOZ plane. The maximum modulus of the elasticity of the honeycomb core in the transverse tension, corresponding to a reinforcement pattern of ±75°, exceeds the minimum modulus for the reinforcement pattern of ±15° more than 3 times. We observe a decrease in the values of the mechanical performance of the carbon fibre honeycomb core depending on its height. With a honeycomb reinforcement pattern of ±45°, the decrease in the shear modulus is 10% in the XOZ plane and 15% in the YOZ plane. The reduction in the modulus of elasticity in the transverse tension for the reinforcement pattern does not exceed 5%. It is shown that in order to ensure high-level moduli of elasticity with respect to tension/compression and shear at the same time, it is necessary to focus on a reinforcement pattern of ±64°. The paper covers the development of the experimental prototype technology that produces carbon fibre honeycomb cores and structures for aerospace applications. It is shown by experiments that the use of a larger number of thin layers of unidirectional carbon fibres provides more than a 2-time reduction in honeycomb density while maintaining high values of strength and stiffness. Our findings can permit a significant expansion of the area of application relative to this class of honeycomb cores in aerospace engineering. [ABSTRACT FROM AUTHOR]

Abstract: In a recent paper by Jin Erdong and Sun Zhaowei [Robust controllers design with finite time convergence for rigid spacecraft attitude tracking control, Aerospace Science and Technology 12 (2008) 324–330], a terminal sliding mode control technique has been applied to the attitude control problem of rigid spacecraft. Unfortunately, the controller has singularity problem which will cause the instability of the closed-loop system of attitude tracking errors. In this article, a nonsingular terminal sliding mode controller is presented to overcome this problem. [Copyright &y& Elsevier]

An important step towards improving performance while reducing weight and maintenance needs is the integration of composite materials into mechanical and aerospace engineering. This subject explores the many aspects of composite application, from basic material characterization to state-of-the-art advances in manufacturing and design processes. The major goal is to present the most recent developments in composite science and technology while highlighting their critical significance in the industrial sector—most notably in the wind energy, automotive, aerospace, and marine domains. The foundation of this investigation is material characterization, which offers insights into the mechanical, chemical, and physical characteristics that determine composite performance. The papers in this collection discuss the difficulties of gaining an in-depth understanding of composites, which is necessary to maximize their overall performance and design. The collection of articles within this topic addresses the challenges of achieving a profound understanding of composites, which is essential for optimizing design and overall functionality. This includes the application of complicated material modeling together with cutting-edge simulation tools that integrate multiscale methods and multiphysics, the creation of novel characterization techniques, and the integration of nanotechnology and additive manufacturing. This topic offers a detailed overview of the current state and future directions of composite research, covering experimental studies, theoretical evaluations, and numerical simulations. This subject provides a platform for interdisciplinary cooperation and creativity in everything from the processing and testing of innovative composite structures to the inspection and repair procedures. In order to support the development of more effective, durable, and sustainable materials for the mechanical and aerospace engineering industries, we seek to promote a greater understanding of composites. [ABSTRACT FROM AUTHOR]

Continuous fiber-reinforced composite truss structures have broad application prospects in aerospace engineering owing to their high structural bearing efficiency and multifunctional applications. This paper presents the design and fabrication of multilayer truss structures with controlled mechanical properties based on continuous fiber-reinforced thermoplastic composite 3D printing. Continuous fiber composite pyramid trusses fabricated by 3D printing have high specific stiffness and strength, with maximum equivalent compression modulus and strength of 401.91 MPa and 30.26 MPa, respectively. Moreover, the relative density of a truss structure can be as low as 1.45%. Additionally, structural units can be extended in any direction to form a multilayer truss structure. Structural performance can be controlled by designing the parameters of each layer. This study offers a novel approach for designing a multifunctional multilayer truss structure, a structure with low-density needs and unique load-bearing effects. [ABSTRACT FROM AUTHOR]

Elastic/acoustic metamaterials hold many exceptional mechanical properties, and provide a new way for the vibration and noise reduction of equipment in aerospace engineering and ship engineering. This paper presents an experimental study on vibration attenuations via a multi-cell and locally-resonant metamaterial. First, the paper discusses the wave propagations of metamaterials inside and outside the bandgap by means of the dispersion analysis, the wave transmissibility analysis, as well as the numerical computations on the vibrations of a periodic metamaterial. Second, the paper introduces a lightweight configuration of periodic locally-resonant metamaterial with bandgaps at the low frequency range. The experimental results show that the vibration transmissibility decreases by 30 dB in the frequency range of 15— 45 Hz, exhibiting a good performance of vibration attenuation connecting space truss structure. [ABSTRACT FROM AUTHOR]

Assumptions are commonly introduced to fill gaps in knowledge during the engineering design process. However, the uncertainty inherent in these assumptions constitutes a risk that ought to be mitigated. That is, assumptions can negatively impact the system if they turn out to be invalid. Adverse effects may include system failure, violation of requirements, or budget and schedule overruns. In this paper, the relationships between assumptions and margins are made explicit, with the purpose of aiding risk mitigation, as well as accommodating future opportunities such as product evolvability. To this end, a novel assumption management framework is proposed, which consists of a taxonomy of margins, an algorithm for change absorber localisation, and an interactive approach for margin trade-off. The proposed framework is demonstrated with a conceptual aircraft design use case, which shows that the most relevant margins can be identified, given a revision of a set of assumptions. It is also demonstrated that the application of the method allowed the margins to be adjusted according to the confidence in the assumptions, while maintaining satisfaction of all design constraints, without unacceptable compromise of system performance. [ABSTRACT FROM AUTHOR]

Operational modal analysis (OMA) methods are nowadays common in civil, mechanical and aerospace engineering to identify and monitor structural systems without any knowledge on the structural excitation provided that the latter is due to ambient vibrations. For this reason, OMA methods are embedded with stochastic concepts and then it is difficult for users that have no-knowledge in signal analysis and stochastic dynamics. In this paper an innovative method useful for structural health monitoring (SHM) is proposed. It is based on the signal filtering and on the Hilbert transform of the correlation function matrix. Specifically, the modal shapes are estimated from the correlation functions matrix of the filtered output process and then the frequencies and the damping ratios are estimated from the analytical signals of the mono-component correlation functions: a complex signals in which the real part represents the correlation function and the imaginary part is its Hilbert transform. This method is very simple to use since requires only few interactions with the users and thus it can be used also from users that are not experts in the aforementioned areas. In order to prove the reliability of the proposed method, numerical simulations and experimental tests are reported also considering comparisons with the most popular OMA methods. [ABSTRACT FROM AUTHOR]

Piezoelectric rotary actuators are widely used for their high precision and large torque in various fields, such as optical engineering and aerospace. However, traditional piezoelectric rotary motors have a complex structure, requiring separate stator and rotor fixing devices, and they have a low space utilization rate, making them unsuitable for driving joint rotation of robotic arms. To address these issues, a novel stator-rotor integrated piezoelectric actuator is proposed in this paper, which uses the piezoelectric vibrator as both the driving vibration source and the rotor, simplifying the overall structure of the rotary actuator. By using in-plane longitudinal and out-of-plane bending vibration, the actuator achieves high-precision rotation along the diameter of a circular ring, while also providing a hollow structure for optical fibers and wires. Through parametric scanning finite element analysis, the size parameters of the annular rotor are determined. The contact conditions of stator and rotor is analyzed, and an intermittent contact model between stator and rotor is established. The experimental results show that the prototype motor weighs 52 g, has a rotation speed of 1470 deg/s, can bear a load of 63 mN m, and has a minimum resolution of 72 μrad. This research demonstrates the great potential of this rotating actuator for use in space optical instruments and aerospace applications. • The actuator has the characteristics of integrated rotor and stator. • The two groups of piezoelectric ceramics simultaneously excite longitudinal vibration and bending vibration to drive. • The actuator has the characteristics of high torque and high precision. • The proposed actuator has application potential in the field of precision drive. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are gaining popularity in the fields of automotive and aerospace engineering due to their unique thermomechanical properties. This paper proposes a numerical implementation of a comprehensive constitutive model for simulating the thermomechanical behavior of shape memory alloys, with temperature and strain as control variables to adjust the shape memory effect and super elasticity effect of the material. By implementing this model as a user subroutine in the FE code Abaqus/Standard, it becomes possible to account for variations in material properties in complex components made of shape memory alloys. To demonstrate the potential of the proposed model, a skid plate system design is presented. The system uses bistable actuators with shape memory alloy springs to trigger plate movement. The kinematics and dynamics of the system are simulated, and effective loads are generated by the shape memory alloy state change due to the real temperature distribution in the material, which depends on the springs' geometrical parameters. Finally, the performance of the actuator in switching between different configurations and maintaining stability in a specific configuration is assessed. The study highlights the promising potential of shape memory alloys in engineering applications and demonstrates the ability to use them in complex systems with accurate simulations. [ABSTRACT FROM AUTHOR]

Purpose: Flight simulators are one of the noticeable breakthroughs in aerospace engineering. One of the main compartments of flight simulators is its control loading system (CLS). The CLS functions as a generator of virtual aerodynamic control-loads over control columns of a simulator. This paper aims to present the design of a high-fidelity six six degrees of freedom (6DOF) nonlinear CLS for the Boeing-747 aircraft simulator. Design/methodology/approach: An introduction to CLS for flight motion simulators are first recapitulated. Afterward, the commanding devices are explained through schematics available in an engineering sense. This paper then presents in detail, the active control loading strategy and hardware design for the CLS, while also introducing the aerodynamic model structure. The satisfactory computer numerical simulations are presented before the paper ends up in concluding remarks. Findings: The multiple input multiple output (MIMO) 6DOF nonlinear CLS for Boeing-747 flight simulator has been successfully developed. The outcome of computer simulations in real-time verifies practicality of the design strategy. The research presented in this paper could be a simple roadmap for prototyping high-fidelity 6DOF nonlinear CLS for flight motion simulators. Originality/value: The available control architecture and hardware technologies cannot enable a high-fidelity load realization in a CLS. The existing research has not yet presented a 6DOF nonlinear MIMO CLS architecture along with the underlying controller setup for a high-fidelity load realization. In this paper, the design of a high-fidelity 6DOF nonlinear MIMO CLS for flight simulator of a large transport aircraft has been accomplished. [ABSTRACT FROM AUTHOR]

Abstract Origami, the art of folding paper, has inspired the development of rigid foldable structures for various applications in aerospace, biomedical, and packaging applications. In order to drive and control origami structure with thick panels, a novel rigid Miura-Ori structure with bistable anti-symmetric carbon fibre reinforced polymer (CFRP) shells was proposed in this paper. Based on the membrane hinge technique, a theoretical model of the Miura-Ori structure with thick panels combined with bistable CFRP shells was established based on the principle of minimum potential energy. Bistable CFRP shells were used as the connection and driving parts of the whole structure instead of thin-walled materials or hinged structures. Finite element simulations were conducted to explore the deformations and trigger forces. The coincident boundary conditions were provided, which were the same as those used in the compression tests using the universal tensile testing machine. Experiments were conducted to validate the simulation results. The results showed that there is good agreement between the simulation and experimental results, indicating that the bistability of the origami structure is achieved under the control of the CFRP cylindrical shells. [ABSTRACT FROM AUTHOR]

Studies have shown that the proper selection of core materials in sandwich structures improves the overall structural performance in terms of bending stiffness and strength. The core materials used in such systems, such as foam, corrugated, and honeycomb, are frequently applied in aerospace engineering. However, they are a costly option for civil engineering applications. This paper investigates the bending performance of the proposed GFRP softwood sandwich beams assembled using pultruded GFRP with adhesive connection methods for potential applications in prefabricated building construction. The ultimate load capacity, load–deflection responses, failure modes, bending stiffness, load–axial-strain behaviour, and degree of composite action were experimentally evaluated. The effects of varying shear-span-to-depth ratios a/d between 2 and 6.5, as well as different timber fibre directions of the softwood core, on the overall structural performance were clarified. The results showed that changing the timber fibres' orientation from vertical to longitudinal shifted the failure mode from a brittle to progressive process. Moreover, the adhesive bonding was able to provide full composite action until the failure occurred. Finally, numerical modelling was developed to understand failure loads, deformation, failure modes, and strain responses, and to evaluate bending stiffness and composite action. The results showed satisfactory agreement with the experiments. [ABSTRACT FROM AUTHOR]

• Object: This paper further studied the unique characteristics of turbo-generator system, which is an important development direction of future aviation power. Aiming at the real runaway failure in the ground test, this paper expounded the root cause and direct cause of runaway failure, put forward the protection method of runaway failure and carried out the experimental verification, which provided the useful references for the configuration design and ground test of series hybrid aero propulsion system. • Method: As a whole, the paper adopted the iterative research method of "test-simulation-test". Firstly, it analyzed the real phenomenon of overspeed runaway failure in the engineering system, then established a simulation model to deeply study the causes of the failure, and finally carried out the feasibility analysis of the protective actions by combining simulation with test. The special highlight is that not only the corresponding solutions to the cause of failure were put forward in this paper，but also the experimental verification was included. • Conclusion: In this paper, the main conclusions of the research on runaway failure include:1) The fundamental cause of runaway failure lies in the small rotational inertia of high-speed turbo-generator set, and the direct cause is the unbalanced relationship between power supply and demand of the microgrid; 2) If the maximum power of battery meets the requirements, the failure risk can be eliminated by control methods; 3) Once the failure inevitably occurs, the resistors can be used to consume power to prevent the situation from getting worse. • Novelty: In this paper, the failure risk of turbine disk burst in a special application scenario was discovered through ground tests. Different from the traditional aviation power plant, the root cause and direct cause of the failure in the turbo-generator set were analyzed in detail, and a simulation model was established to support the viewpoint. Secondly, compared to the traditional mechanical designs, this paper skillfully solved mechanical problems by using control methods and electric methods. Finally, the test showed that the two protective actions can effectively avoid the overspeed runaway failure. • Significance: In order to meet the development goal of higher power density of turbo-generator system, in addition to the application of special motors, Permanent Magnet Synchronous Motors show a development trend of higher speed. The failure protective actions proposed in this paper can effectively avoid or delay the occurrence of runaway failure, improve the safety performance of the high-speed turbo-generator system, and lay the foundation for the development of series hybrid aero propulsion system with higher power and speed. Based on a series hybrid aero propulsion system with power class of 200 kW, voltage of 540 V and speed of 21000r/min, proceeding from the occurrence of the runaway failure during experiment, this study reveals the characteristics and causes of a traditional turbine engine failure in a new application context, focuses on optimizing mechanical issues from the perspective of control strategies and electrical equipment, combined with mechanism analysis and experimental validation. The main conclusions are as follows: the fundamental reason for the high-speed turbo-generator set facing the risk of overspeed runaway is the small rotational inertia of the rotor system, with the direct cause being the power imbalance between the supply side and the demand side of the propulsion system. Experimental verification demonstrated that the active protection scheme based on voltage regulation by battery can keep the speed and voltage of turbine-generator set fluctuations below 0.3 % and adjustment time within 0.5 s for load changes within the battery power range, effectively preventing runaway failures caused by minor power fluctuations. Additionally, the passive protection scheme based on power dissipation through resistors reduced the speed of the power turbine from 7000r/min to 2000r/min no more than 2 s, indicating the effectiveness of this measure in restricting the speed within a safe range. [ABSTRACT FROM AUTHOR]

This paper describes the development and coding of a design tool for waverider parameterization based on the Taylor-Maccoll equation and streamline tracing method. This tool, intended for undergraduates studying in the field of aerodynamics, illustrates the relationship among various parameters in terms of their effect on the aerodynamic performance of waverider models with the same freestream Mach number. The design procedure is evaluated and validated for multiple shock wave profiles and freestream Mach numbers, and is found to be in good agreement with the CFD results. For undergraduates studying aeronautical engineering, the suggested design tool offers an intuitive image of waverider creation and a clear picture of the guiding principles of waveriders. By imposing a set of design criteria, the tool also gives students enough freedom to arrive at their own waverider shape. [ABSTRACT FROM AUTHOR]

Large-scale short carbon fibre-reinforced silicon carbide (Csf/SiC) ceramic matrix composites (CMCs) have important applications in the field of aerospace engineering. This study proposed the use of material extrusion based additive manufacturing to fabricate large-scale Csf/SiC CMC preforms. In this paper, we determined how the key material extrusion parameters, including solid loading, nozzle diameter and layer height impact the stability of the additively manufactured Csf/SiC CMCs. The solid loading significantly influenced the stability of the Csf/SiC CMCs, and the slurry with 50 vol.% solid loading was better for additive manufacturing. The layer height played a significant role in the void formation in CMCs. It was appropriate for structure retention to set the layer height as 60-75% of the nozzle diameter. The effect of angle from vertical on the stability of out-of-plane structure was also investigated. When the angle was over 40o, the out-of-plane structure additively manufactured without supports tended to collapse. Large-scale Csf/SiC CMC preforms with out-of-plane structures were finally successfully fabricated. This study is believed to provide some fundamental understanding for the fabrication of large-scale fibre-reinforced ceramic matrix composites. [ABSTRACT FROM AUTHOR]

In order to reduce the vibration fatigue test time of aeronautical engineering components made of aluminum alloy, a random vibration fatigue acceleration model under narrow‐band excitation is proposed in this paper. A three‐parameter S–N curve is adopted to consider the effect of small stress response, while a scale factor α is introduced to consider the effect of stress distribution. The random vibration fatigue tests of 2024‐T3 and 7075‐T6 aluminum alloy specimens with elliptical holes are performed, where the vibration fatigue lives of load spectra with the same bandwidth and different excitation acceleration levels are obtained. The test results show that the proposed model is in sound agreement with the test results. Highlights: A vibration fatigue acceleration model under narrow‐band excitation is proposed.A scale factor α is introduced to consider the effect of stress distribution.A three‐parameter S–N curve is adopted to consider small stress response effect.The random vibration fatigue tests are performed for verification. [ABSTRACT FROM AUTHOR]

In civil, mechanical, and aerospace structures, full-field measurement has become necessary to estimate the precise location of precise damage and controlling purposes. Conventional full-field sensing requires dense installation of contact-based sensors, which is uneconomical and mostly impractical in a real-life scenario. Recent developments in computer vision-based measurement instruments have the ability to measure full-field responses, but implementation for long-term sensing could be impractical and sometimes uneconomical. To circumvent this issue, in this paper, we propose a technique to accurately estimate the full-field responses of the structural system from a few contact/non-contact sensors randomly placed on the system. We adopt the Compressive Sensing technique in the spatial domain to estimate the full-field spatial vibration profile from the few actual sensors placed on the structure for a particular time instant, and executing this procedure repeatedly for all the temporal instances will result in real-time estimation of full-field response. The basis function in the Compressive Sensing framework is obtained from the closed-form solution of the generalized partial differential equation of the system; hence, partial knowledge of the system/model dynamics is needed, which makes this framework physics-guided. The accuracy of reconstruction in the proposed full-field sensing method demonstrates significant potential in the domain of health monitoring and control of civil, mechanical, and aerospace engineering systems. [ABSTRACT FROM AUTHOR]

• A rigid multibody dynamic model of the stacked satellite system is established. • A contact detection algorithm is proposed based on convex optimization. • Three contact-free releasing approaches for the system are proposed and compared. Stacked satellites have a promising application in aerospace engineering for the merits of high launch efficiency and networking capability. As one of the key technical points, releasing tens or even hundreds of satellites from the stacked state in a simple and contact-free manner is of importance. In this paper, the contact-free release dynamics of tens of stacked satellites is studied with only the initial multiaxial rotations of the system. First of all, a rigid multibody dynamic model of the stacked satellite system is established via the natural coordinate formulation (NCF). The NCF modeling scheme is able to describe the large overall motions of the satellites without any singularity and makes it possible to simplify the varying constraints between the satellites. Then, the orbital dynamics of the stacked satellite system is derived via coordinate transformation by taking the Coriolis forces, centrifugal forces, and gravity gradient into consideration. In order to rapidly and accurately detect the possible contact between satellites, a convex optimization model for minimum distance computation is proposed by using a hyperelliptic approximation for a cubic satellite. Finally, a benchmark example is given to validate the contact detection algorithm and three release dynamic cases for the stacked satellites are presented to demonstrate the effectiveness of the contact-free releasing approach with multiaxial rotations. [ABSTRACT FROM AUTHOR]

This is a reply to a recently published comment [1] on our paper [4] . [ABSTRACT FROM AUTHOR]

This paper presents the embedded systems along with the first in-orbit results of FloripaSat-I, a complete CubeSat mission developed at the Federal University of Santa Catarina, Brazil. The satellite's service module has three main subsystems, each with an embedded processor and its peripherals. This paper presents an overview of the nanosatellite architecture designed for the mission, including the embedded systems, functionalities, and components. Launched in December 2019 atop a Chinese Long March 4B rocket, FloripaSat-I has been since then transmitting mission data, which is a metric used to validate its open-source service platform through flight heritage. The results collected in orbit are presented and discussed, as well as the student's perception about the challenges in the project. With the analysis of the results, it is possible to identify technical points to be improved by external groups with interest to reuse the open-source service platform for the next missions, and the impact that this teaching–learning methodology has in the students. • We present the FloripaSat-I embedded systems. • Flight results regarding the first three months are presented. • We validate the FloripaSat-I service platform with flight inheritance. [ABSTRACT FROM AUTHOR]

The original innovation is the fundamental source of China’s aerospace industry development. This paper summarizes the experience and approach of science and technology innovation by analyzing the practices in aerospace engineering. Furthermore, some concepts applicable to the breakthrough in aeronautical and aerospace engineering are put forward, including independent exploration of scientific problems, dialectical analysis of technical connotation, and system engineering approach to performance improvement. [ABSTRACT FROM AUTHOR]

The introduction of game-based learning techniques has significantly swayed learning, motivation, and information processing in both traditional and digital learning environments. This paper studies the footprint that the implementation of ten short-duration digital escape rooms has had on the creation of an environment of positive emotions in the educational field. The digital escape rooms were created by employing the Genial.ly platform and RPG Maker MZ software. A feelings/satisfaction questionnaire has been conducted to study what emotions students have experienced, as well as the students' opinions about essential elements of digital escape rooms, to study whether positive feelings predominate in the performance of these activities. Results show a high incidence of positive emotions, and a very favorable opinion on the tools employed and the positive feelings on the acquisition of knowledge and skills. [ABSTRACT FROM AUTHOR]

In aerospace engineering, it is attractive to combine additive manufacturing (AM) with lightweight design to reduce the weight of primary load-bearing structures. In this paper, a double-layer pyramidal lattice truss sandwich cylinder was designed and printed by selective laser melting (SLM) method, which has advantages in integrally manufacturing end frames and bolt holes. With diameter of 0.493 m, this cylinder is one of the lattice truss sandwich structures with the largest diameter at present. Free vibration testing was carried out to reveal the free vibration responses of the cylinder. The first-order vibration turns from a circle to an oval in the plane of the cross section. The fundamental frequency is 133.9 Hz. An equivalent shell free vibration theory was proposed and finite element models (FEMs) based on discrete model and equivalent shell model were applied to predict the natural frequencies and mode shapes of the cylinder. Advantages of the AM method in making light and stiff large-sized aerospace structures are confirmed through this research. [ABSTRACT FROM AUTHOR]

—In aerospace engineering, implementing interpretable fault diagnosis technology is critical for improving the credibility of diagnostic results and ensuring the reliability of complex electromechanical systems. As a typical interpretable modeling method, the belief rule base (BRB) approach still faces two challenges that need to be addressed for its application in interpretable fault diagnosis: 1) The lengthy rule structures raise the cost of model interpretability, and 2) over-optimization of parameters diminishes the interpretability. To solve these problems, this paper proposes a modified micro-belief rule structure and develops a new micro-belief rule base (MBRB) model based on this structure. In addition, considering the independence of rules and the correlations between multiple BRBs, a cautious conjunctive rule-based reasoning process is established as the inference engine of MBRB. Moreover, an interpretable optimization method based on projection covariance matrix adaptive evolutionary strategy (PCMAES-I) is proposed for the MBRB model to balance model interpretability and diagnostic accuracy. Finally, the availability and effectiveness of the proposed MBRB is verified through an electromagnetic relay experiment. [ABSTRACT FROM AUTHOR]

Investigating the mechanical behavior and damage patterns of ultra-thin-ply composite joints is essential for ensuring their widespread application in the aerospace field. It is currently an advanced method of exploring the damage patterns of composite joint structures via a combination of acoustic emission and machine learning algorithms. However, the existing research lacks the evaluation indexes for the determination of the number of damage categories, and on the other hand, the overlapping area and noise of the monitored damage data cannot be accurately identified. In this paper, load-bearing performance of ultra-thin-ply composite hybrid bonded/bolted interference-fit joints is studied, then the SDI(Structural Damage Index) evaluation index is proposed to quantitatively analyze the number of damage categories of the complex joints, and finally the adaptive optimization algorithm based on the credal partition for the complex joints of composite is studied. The experimental results demonstrate the accuracy and generalization of the SDI formulae, and the introduction of the credal partition that submits data where overlapping regions cannot be accurately identified to ensembles of special single classes (meta-clusters) obtains deeper insights into the damage data and improves identification and isolation of noise. • The mechanical properties of ultra-thin-ply HBBI joints were investigated. • An SDI evaluation index based on damage data is proposed. • SDI provides an analysis of the number of damage categories in joint structures. • Credit partition is introduced to design an adaptive optimization algorithm. • Credit partition provides more deeper insights into damage data. [ABSTRACT FROM AUTHOR]

The goal of robust motion planning consists of designing open-loop controls which optimally steer a system to a specific target region while mitigating uncertainties and disturbances which affect the dynamics. Recently, stochastic optimal control has enabled particularly accurate formulations of the problem. Nevertheless, despite interesting progresses, these problem formulations still require expensive numerical computations. In this paper, we start bridging this gap by leveraging statistical linearization. Specifically, through statistical linearization we reformulate the robust motion planning problem as a simpler deterministic optimal control problem subject to additional constraints. We rigorously justify our method by providing estimates of the approximation error, as well as some controllability results for the new constrained deterministic formulation. Finally, we apply our method to the powered descent of a space vehicle, showcasing the consistency and efficiency of our approach through numerical experiments. [ABSTRACT FROM AUTHOR]