An introductory review of swarm technology for spacecraft on-orbit servicing

This review paper presents a comprehensive evaluation and forward-looking perspective on the underexplored topic of servicing target objects using spacecraft swarms.Such targets can be known or unknown,cooperative or uncooperative,and pose significant challenges in modern space operations due to their inherent complexity and unpredictability.Successfully servicing space objects is vital for active debris removal and broader on-orbit servicing tasks such as satellite maintenance,repair,refueling,orbital assembly,and construction.Significant effort has been invested in the literature to explore the servicing of targets using a single spacecraft.Given its advantages and benefits,this paper expands the discussion to encompass a swarm approach to the problem.This review covers various single-spacecraft approaches and presents a critical examination of the existing,although limited,body of work dedicated to servicing orbital objects using multiple spacecraft.The focus is also broadened to include some influential studies concerning the characterization,capture,and manipulation of physical objects by general multiagent systems,a subject with significant parallels to the core interest of this manuscript.Furthermore,this article also delves into the realm of simultaneous localization and mapping,highlighting its application within close-proximity operations in space,especially when dealing with unknown uncooperative targets.Special attention is paid to the benefits that this field can receive from distributed multiagent architectures.Finally,an exploration of the promising field of swarm robotics is presented,with an emphasis on its potential to revolutionize the servicing of orbital target objects.Concurrently,a survey of general research directly engaging swarms in the orbital context is conducted.This review aims to bridge the knowledge gap and stimulate further research in the underexplored domain of servicing space targets with spacecraft swarms.

A novel minority sample fault diagnosis method based on multisource data enhancement

Effective fault diagnosis has a crucial impact on the safety and cost of complex manufacturing systems.However,the complex structure of the collected multisource data and scarcity of fault samples make it difficult to accurately identify multiple fault conditions.To address this challenge,this paper proposes a novel deep-learning model for multisource data augmentation and small sample fault diagnosis.The raw multisource data are first converted into two-dimensional images using the Gramian Angular Field,and a generator is built to transform random noise into images through transposed convolution operations.Then,two discriminators are constructed to evaluate the authenticity of input images and the fault diagnosis ability.The Vision Transformer network is built to diagnose faults and obtain the classification error for the discriminator.Furthermore,a global optimization strategy is designed to upgrade parameters in the model.The discriminators and generator compete with each other until Nash equilibrium is achieved.A real-world multistep forging machine is adopted to compare and validate the performance of different methods.The experimental results indicate that the proposed method has multisource data augmentation and minority sample fault diagnosis capabilities.Compared with other state-of-the-art models,the proposed approach has better fault diagnosis accuracy in various scenarios.

A multiscale differential-algebraic neural network-based method for learning dynamical systems

The objective of dynamical system learning tasks is to forecast the future behavior of a system by leveraging observed data.However,such systems can sometimes exhibit rigidity due to significant variations in component parameters or the presence of slow and fast variables,leading to challenges in learning.To overcome this limitation,we propose a multiscale differential-algebraic neural network(MDANN)method that utilizes Lagrangian mechanics and incorporates multiscale information for dynamical system learning.The MDANN method consists of two main components:the Lagrangian mechanics module and the multiscale module.The Lagrangian mechanics module embeds the system in Cartesian coordinates,adopts a differential-algebraic equation format,and uses Lagrange multipliers to impose constraints explicitly,simplifying the learning problem.The multiscale module converts high-frequency components into low-frequency components using radial scaling to learn subprocesses with large differences in velocity.Experimental results demonstrate that the proposed MDANN method effectively improves the learning of dynamical systems under rigid conditions.

Enabling the transfer matrix method to model serial-parallel compliant mechanisms including curved flexure beams

Compliant mechanisms with curved flexure hinges/beams have potential advantages of small spaces,low stress levels,and flexible design parameters,which have attracted considerable attention in precision engineering,metamaterials,robotics,and so forth.However,serial-parallel configurations with curved flexure hinges/beams often lead to a complicated parametric design.Here,the transfer matrix method is enabled for analysis of both the kinetostatics and dynamics of general serial-parallel compliant mechanisms without deriving laborious formulas or combining other modeling methods.Consequently,serial-parallel compliant mechanisms with curved flexure hinges/beams can be modeled in a straightforward manner based on a single transfer matrix of Timoshenko straight beams using a step-by-step procedure.Theoretical and numerical validations on two customized XY nanopositioners comprised of straight and corrugated flexure units confirm the concise modeling process and high prediction accuracy of the presented approach.In conclusion,the present study provides an enhanced transfer matrix modeling approach to streamline the kinetostatic and dynamic analyses of general serial-parallel compliant mechanisms and beam structures,including curved flexure hinges and irregular-shaped rigid bodies.

Comparative analysis on the performance of different types of input-and command-shaping controllers in minimizing payload residual vibration of an overhead crane with an inclined supporting track

Reducing the effects of external disturbance on overhead crane systems is crucial,as they can impair the controller performance and cause excessive vibrations or oscillations of the payloads.One such external disturbance is the inclination of the supporting track of the crane trolley,which causes the system dynamics model to change.An open-loop control strategy is widely utilized to control the payload sway motion and generally does not require any alterations in the physical structure of a system or the installation of sensors and/or actuators.Input and command shaping are two common open-loop control techniques applied to control overhead cranes.In this paper,the effect of moving an overhead crane system along an inclined supporting track is investigated.In addition,the ability of different types of input-and command-shaping control schemes to suppress the residual vibrations due to trolley track inclination is demonstrated.Two types of input-shaping controllers,which are double-step,zero vibration,and one command waveform(WF)shaper based on a trigonometric function,are used and tested.A linear equation of motion of the overhead crane resting on an inclined surface is developed to simulate the overhead crane and payload motion.The effectiveness of the different types of open-loop controllers to suppress residual vibrations is verified by both simulation and experimental results.In addition,a new WF command shaper is proposed and designed to overcome track inclination while eliminating payload residual vibration.A comprehensive comparative analysis,both numerically and experimentally,is performed on the new proposed shaper to measure its effectiveness in handling inclination when compared to other types of open-loop controllers.The new shaper outperforms other controllers in eliminating payload residual vibration for a wider range of inclination angles.

Bidirectional energy-controlled piezoelectric shunt damping technology and its vibration attenuation performance

Piezoelectric material-based semi-active vibration control systems may effectively suppress vibration amplitude without any external power supply,or even harvest electrical energy.This bidirectional electrical energy control phenomenon is theoretically introduced and validated in this paper.A flyback transformer-based switching piezoelectric shunt circuit that can extract energy from or inject energy into piezoelectric elements is proposed.The analytical expressions of the controlled energy and the corresponding vibration attenuation are therefore derived for a classical electromechanical cantilever beam.Theoretical predictions validated by the experimental results show that the structure vibration attenuation can be tuned from−5 to−25 dB under the given electrical quality factor of the circuit and figure of merit of the electromechanical structure,and the consumed power is in the range of−13 to 25 mW,which is a good theoretical basis for the development of self-sensing,self-adapting,and self-powered piezoelectric vibration control systems.

Tool-tip vibration prediction based on a novel convolutional enhanced transformer

Superior surface finish remains a fundamental criterion in precision machining operations,and tool-tip vibration is an important factor that significantly influences the quality of the machined surface.Physics-based models heavily rely on assumptions for model simplification when applied to complex high-end systems.However,these assumptions may come at the cost of compromising the model's accuracy.In contrast,data-driven techniques have emerged as an attractive alternative for tasks such as prediction and complex system analysis.To exploit the advantages of data-driven models,this study introduces a novel convolutional enhanced transformer model for tool-tip vibration prediction,referred to as CeT-TV.The effectiveness of this model is demonstrated through its successful application in ultra-precision fly-cutting(UPFC)operations.Two distinct variants of the model,namely,guided and nonguided CeT-TV,were developed and rigorously tested on a data set custom-tailored for UPFC applications.The results reveal that the guided CeT-TV model exhibits outstanding performance,characterized by the lowest mean absolute error and root mean square error values.Additionally,the model demonstrates excellent agreement between the predicted values and the actual measurements,thus underlining its efficiency and potential for predicting the tool-tip vibration in the context of UPFC.

Realization of nonreciprocal acoustic energy transfer using an asymmetric strong nonlinear vibroacoustic system

In this paper,an asymmetric vibroacoustic system that can passively realize nonreciprocal transmission of acoustic energy is reported.This experimental system consists of a waveguide,a strongly nonlinear membrane,and three acoustic cavities with different sizes.The theoretical modeling of the system is verified by experiments,and parametric analysis is also carried out.These intensive studies reveal the nonreciprocal transmission of acoustic energy in this prototype system.Under forward excitation,internal resonance between the two nonlinear normal modes of the vibroacoustic system occurs,and acoustic energy is irreversibly transferred from the waveguide to the nonlinear membrane.However,under backward excitation,there is no internal resonance in the system.Energy spectra and wavelet analysis are used to highlight the mechanism of nonreciprocal transfer of acoustic energy.Consequently,nearly unidirectional(preferential)transmission of acoustic energy transfer is shown by this system.The nonreciprocal acoustic energy transfer method illustrated in this paper provides a new way to design the odd acoustic element.

Development of new electromagnetic suspension-based high-speed Maglev vehicles in China:Historical and recent progress in the field of dynamical simulation

High-speed Maglev is a cutting-edge technology brought back into the focus of research by plans of the Chinese government for the development of a new 600 km/h Maglev train.A Chinese‐German cooperation with industrial and academic partners has been established to pursue this ambitious goal and bring together experts from multiple disciplines.This contribution presents the joint work and achievements of CRRC Qingdao Sifang,thyssenkrupp Transrapid,CDFEB,and the ITM of the University of Stuttgart,regarding research and development in the field of high‐speed Maglev systems.Furthermore,an overview is given of the historical development of the Transrapid in Germany,the associated development of dynamical simulation models,and recent developments regarding high-speed Maglev trains in China.

Wave control of a flexible space tether based on elastic metamaterials

This study proposes a spider‐web elastic metamaterial to suppress vibrations in space slender structures,such as flexible space tethers.The metamaterial consists of unit cells that are periodically distributed on the space tether to obtain band gaps.The finite element model of the unit cell is established by employing the absolute nodal coordinate formulation(ANCF)due to the large deformation of the structure.The eigenfrequencies and corresponding vibration modes of the unit cell are obtained by ANCF.Moreover,the band gap of the unit cell is calculated based on the phonon crystal theory.The relationship between the vibration modes and the band gaps is analyzed.Finally,an experiment is conducted to verify the vibration transmission characteristics of finite period cells.The results show the effectiveness of the spider‐web elastic metamaterial for vibration suppression of a flexible tether.This study provides insights into the use of elastic metamaterials for vibration isolation in space tether systems.

Effect of coronary artery dynamics on the wall shear stress vector field topological skeleton in fluid–structure interaction analyses

In this paper,we investigate the impact of coronary artery dynamics on the wall shear stress(WSS)vector field topology by comparing fluid–structure interaction(FSI)and computational fluid dynamics(CFD)techniques.As one of the most common causes of death globally,coronary artery disease(CAD)is a significant economic burden;however,novel approaches are still needed to improve our ability to predict its progression.FSI can include the unique dynamical factors present in the coronary vasculature.To investigate the impact of these dynamical factors,we study an idealized artery model with sequential stenosis.The transient simulations made use of the hyperelastic artery and lipid constitutive equations,non‐Newtonian blood viscosity,and the characteristic out‐of‐phase pressure and velocity distribution of the left anterior descending coronary artery.We compare changes to established metrics of time‐averaged WSS(TAWSS)and the oscillatory shear index(OSI)to changes in the emerging WSS divergence,calculated here in a modified version to handle the deforming mesh of FSI simulations.Results suggest that the motion of the artery can impact downstream patterns in both divergence and OSI.WSS magnitude is also decreased by up to 57%due to motion in some regions.WSS divergence patterns varied most significantly between simulations over the systolic period,the time of the largest displacements.This investigation highlights that coronary dynamics could impact markers of potential CAD progression and warrants further detailed investigations in more diverse geometries and patient cases.

Free vibration of functionally graded sandwich plates in thermal environments

This paper presents an analytical solution for the free vibration of functionally graded material(FGM)sandwich plates in a thermal environment.An equivalentsingle‐layer(ESL)plate theory with four variables is used to obtain the solution.Two types of sandwich plates are examined in this study:one with FGM face sheets and a homogeneous core and the other with an FGM core and homogeneous face sheets.The governing equations of motion are derived based on Hamilton's principle and then solved using the Navier method.The results of natural frequencies of simply supported FGM sandwich plates are compared with the available solutions in the literature.The effects of volume fraction distribution,geometrical parameters,and temperature increments on the free vibration characteristics are discussed in detail.

A complex solution on the dynamic response of sandwich graphene-reinforced aluminum-based composite beams with copper face sheets under two moving constant loads on an elastic foundation

An analytical solution was used to investigate the elastic response of a sandwich beam with a graphene-reinforced aluminum-based composite(GRAC)on an elastic foundation using copper as the face layer of the functionally graded composite beam and a simply supported boundary condition.Mantari's higher-order shear deformation theory was utilized to derive the equations,which were solved in Laplace space and then converted into space–time using Laplace inversion.The exact response of the GRAC sandwich beam was obtained by considering the displacement at the mid-span of the sandwich beam.Two moving loads with different speed ratios were applied at a single point,and the effect of various parameters,including the spring constant,the speed ratio,the percentage of graphene,the moving load speed,and the distribution pattern,was investigated.This study aimed to eliminate any overlap and improve the accuracy of the results.The exact solving method presented has not been reported in other articles so far.Additionally,due to the difficulty of solving mathematical equations,this method is only applicable to simple boundary conditions.

Orthotropic plate model for the vibration of multilayered molybdenum disulfide

Molecular dynamics(MD)simulation and orthotropic continuum model that considers interlayer shear are used to investigate the transverse deformation and free transverse vibration of multilayered rectangular molybdenum disulfide(MoS2).The interlayer shear effect is considered in the continuum model by considering the multilayered MoS_(2) as a continuous uniform orthotropic material.A method for obtaining mode shapes using a single thermal vibration MD simulation is proposed.The frequencies and mode shapes predicted using the orthotropic continuum model and MD simulation agree well.The mechanical problem of multilayered two‐dimensional material plate resonator can be solved easily and efficiently by using the finite element method for the orthotropic continuum model.

Effect of temperature on tensile and vibration properties of bilayer boron nitride

Hexagonal boron nitride(h‐BN)is a semiconductor material with a wide band gap,holding promising potential for applications in thermal conductivity devices and nanoresonators in the field of microelectronics.Here,molecular dynamics is simulated to investigate the tensile and vibrational behaviors of bilayer h‐BN under five different stacking modes across varying temperatures.The mechanical properties of five different stacking modes of h‐BN at various temperatures are focused on,including Young's modulus,the ultimate stress,and the ultimate strain.Results indicate that bilayer h‐BN nanosheets exhibit anisotropic characteristics,with their tensile properties decreasing as temperature increases.Additionally,we explore the influence of temperature on the natural frequency of bilayer h‐BN under five different stacking modes.These results establish a fundamental understanding of the mechanical and vibrational characteristics of bilayer h‐BN nanosheets under different stacking modes,contributing to their potential applications in advanced nanodevices operating in extremely high‐temperature environments.

Alleviating vibrations along a harmonically driven nonuniform Euler-Bernoulli beam by imposing nodes

A passive approach is developed to quench excess vibration along a harmonically driven,arbitrarily supported,nonuniform Euler-Bernoulli beam with constant thickness(height)and varying width.Vibration suppression is achieved by attaching properly tuned vibration absorbers to enforce nodes,or points of zero vibration,along the beam.An efficient hybrid method is proposed whereby the finite element method is used to model the nonuniform beams,and a formulation based on the assumed modes method is used to determine the required attachment force supplied by each absorber to induce the desired nodes.Knowing the attachment forces needed to induce nodes,design plots are generated for the absorber parameters as a function of the tolerable vibration amplitude for each absorber mass.When the node locations are judiciously chosen,it is possible to dramatically suppress the vibration along a selected region of the beam.As such,sensitive instruments can be placed in this region and will remain nearly stationary.Numerical studies illustrate the application to several systems with various types of nonuniformity,boundary conditions,and attachment and node locations;these examples validate the proposed method to passively control excess vibration by inducing nodes on nonuniform beams subjected to harmonic excitations.

Isola in a linear one-degree-of-freedom feedback system with actuator rate saturation

This short communication uses numerical continuation to highlight the existence of an isola in a simple one-degree-of-freedom harmonically forced feedback system with actuator rate limiting as its only nonlinear element.It was found that the isola(1)contains only rate-limited responses,(2)merges with the main branch when the forcing amplitude is sufficiently large,and(3)includes stable solutions that create a second attractor in regions where rate limiting is not expected.Furthermore,the isola is composed of two solutions for a given forcing frequency.These solutions have the same amplitudes in the state(pitch rate)projection;however,they have distinct phases,and their amplitudes are also distinct when projected onto the integrator state in the controller.The rich dynamics observed in such a simple example underlines the impact of rate limiting on feedback systems.Specifically,the combination of feedback and rate limiting can create detrimental dynamics that is hard to predict and requires careful analysis.

Probing electron and lattice dynamics by ultrafast electron microscopy: Principles and applications

Microscale charge and energy transfer is an ultrafast process that can determine the photoelectrochemical performance of devices.However,nonlinear and nonequilibrium properties hinder our understanding of ultrafast processes;thus,the direct imaging strategy has become an effective means to uncover ultrafast charge and energy transfer processes.Due to diffraction limits of optical imaging,the obtained optical image has insufficient spatial resolution.Therefore,electron beam imaging combined with a pulse laser showing high spatial–temporal resolution has become a popular area of research,and numerous breakthroughs have been achieved in recent years.In this review,we cover three typical ultrafast electron beam imaging techniques,namely,time-resolved photoemission electron microscopy,scanning ultrafast electron microscopy,and ultrafast transmission electron microscopy,in addition to the principles and characteristics of these three techniques.Some outstanding results related to photon–electron interactions,charge carrier transport and relaxation,electron–lattice coupling,and lattice oscillation are also reviewed.In summary,ultrafast electron beam imaging with high spatial–temporal resolution and multidimensional imaging abilities can promote the fundamental under-standing of physics,chemistry,and optics,as well as guide the development of advanced semiconductors and electronics.

Analysis of friction‐related acoustic emission in bolted joint structures

A bolted joint may be in a state of continuous fretting friction and wear under random oscillatory loading,which makes the bolted joint prone to loosening.Therefore,it is essential to find a way to monitor the contact state of a bolted joint on time and handle it adeptly.Acoustic emission(AE)signals will be generated during the reciprocating friction of the bolted joint interface.Exploring the relationship between the frictional slip features and the acoustic emission characteristics under different bolt preloads can lay the foundation for using the acoustic emission techniques to monitor the pretightening state of bolted joints.This paper experimentally investigates the acoustic emission signals of a bolted joint structure during friction under different preloads,three repeated tests are implemented.The relationship between friction behavior and acoustic emission characteristics under different preloads is studied.The evolution of classical acoustic emission parameters and kinematic parameters with bolt preload levels is also analyzed.The 3‐D topography of the specimens after parametric tests is analyzed.The results show that the characteristics of both burst‐type and continuous‐type acoustic emission can reflect different friction behavior under different bolt preloads.The evolution curves of acoustic emission parameters changed under the interaction of both frictional kinematic parameters and bolt preload levels.For the 3‐D surface topography,the reciprocating friction shears the peaks and fills the surface valleys,and the topography of the scratched surface areas is redistributed.

Design,fabrication,and dynamic mechanical responses of fiber-reinforced composite lattice materials

Fiber-reinforced composites are a popular lightweight materials used in a variety of engineering applications,such as aerospace,architecture,automotive,and marine construction,due to their attractive mechanical properties.Constructing lattice materials from fiber-reinforced composites is an efficient approach for developing ultra-lightweight structural systems with superior mechanical proper-ties and multifunctional benefits.In contrast to corrugated,foam,and honeycomb core materials,composite lattice materials can be manufactured with various architectural designs,such as woven,grid,and truss cores.Moreover,lattice materials with open-cell topology provide multifunctional advantages over conventional closed-cell honeycomb and foam structures and are thus highly desirable for developing aerospace systems,hypersonic vehicles,long-range rockets and missiles,ship and naval structures,and protective systems.The objective of this study is to review and analyze dynamic mechanical behavior performed by different researchers in the area of composite lattice materials and to highlight topics for future research.