Low-velocity impact tests are carried out to explore the energy absorption characteristics of bio-inspired lattices,mimicking the architecture of the marine sponge organism Euplectella aspergillum.These sea sponge-ins...Low-velocity impact tests are carried out to explore the energy absorption characteristics of bio-inspired lattices,mimicking the architecture of the marine sponge organism Euplectella aspergillum.These sea sponge-inspired lattice structures feature a square-grid 2D lattice with double diagonal bracings and are additively manufactured via digital light processing(DLP).The collapse strength and energy absorption capacity of sea sponge lattice structures are evaluated under various impact conditions and are compared to those of their constituent square-grid and double diagonal lattices.This study demonstrates that sea sponge lattices can achieve an 11-fold increase in energy absorption compared to the square-grid lattice,due to the stabilizing effect of the double diagonal bracings prompting the structure to collapse layer-bylayer under impact.By adjusting the thickness ratio in the sea sponge lattice,up to 76.7%increment in energy absorption is attained.It is also shown that sea-sponge lattices outperform well-established energy-absorbing materials of equal weight,such as hexagonal honeycombs,confirming their significant potential for impact mitigation.Additionally,this research highlights the enhancements in energy absorption achieved by adding a small amount(0.015 phr)of Multi-Walled Carbon Nanotubes(MWCNTs)to the photocurable resin,thus unlocking new possibilities for the design of innovative lightweight structures with multifunctional attributes.展开更多
The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional(3 D)st...The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional(3 D)structural solid elements assembled model of a carbon fiber-reinforced polymer(CFRP)-aluminum single-lap joint with a titanium(Ti-6 Al-4 V)fastener and a washer generated with the commercial finite element(FE)software package,ABAQUS/Standard.A progressive failure algorithm written in Fortran code with a set of appropriate degradation rules was incorporated as a user subroutine in ABAQUS to simulate the non-linear damage behavior of the composite component in the composite-aluminum bolted aerospace structure.The assembled 3 DFE model simulated,as well as the specimen for the experimental testing consisted of a carbon-epoxy IMS-977-2 substrate,aluminum alloy 7075-T651 substrate,liquid shim(Hysol EA 9394),solid peelable fiberglass shim,a titanium fastener,and a washer.In distinction to previous investigations,the influence of shim layers(liquid shim and solid peelable fiberglass shim)inserted in-between the faying surfaces(CFRP and aluminum alloy substrates)were investigated by both numerical simulations and experimental work.The simulated model and test specimens conformed to the standard test configurations for both civil and military standards.The numerical simulations correlated well with the experimental results and it has been found that:(1)The shimming procedure as agreed upon by the aerospace industry for the resolution of assembly gaps in bolted joints for composite materials is the same for a composite-aluminum structure;liquid shim series(0.3,0.5 and 0.7 mm thicknesses)prolonged the service life of the composite component whereas a solid peelable fiberglass shim most definitely had a better influence on the 0.9 assembly gap compared with the liquid shim;(2)The shim layers considerably influenced the structural strength of the composite component by delaying its ultimate failure thereby increasing its service life;and(3)Increasing the shim layer′s thickness led to a significant corresponding effect on the stiffness but with minimal effect on the ultimate load.展开更多
This paper investigates the challenges associated with Unmanned Aerial Vehicle (UAV) collaborative search and target tracking in dynamic and unknown environments characterized by limited field of view. The primary obj...This paper investigates the challenges associated with Unmanned Aerial Vehicle (UAV) collaborative search and target tracking in dynamic and unknown environments characterized by limited field of view. The primary objective is to explore the unknown environments to locate and track targets effectively. To address this problem, we propose a novel Multi-Agent Reinforcement Learning (MARL) method based on Graph Neural Network (GNN). Firstly, a method is introduced for encoding continuous-space multi-UAV problem data into spatial graphs which establish essential relationships among agents, obstacles, and targets. Secondly, a Graph AttenTion network (GAT) model is presented, which focuses exclusively on adjacent nodes, learns attention weights adaptively and allows agents to better process information in dynamic environments. Reward functions are specifically designed to tackle exploration challenges in environments with sparse rewards. By introducing a framework that integrates centralized training and distributed execution, the advancement of models is facilitated. Simulation results show that the proposed method outperforms the existing MARL method in search rate and tracking performance with less collisions. The experiments show that the proposed method can be extended to applications with a larger number of agents, which provides a potential solution to the challenging problem of multi-UAV autonomous tracking in dynamic unknown environments.展开更多
The current space launch missions are intense, and the utilization of equipment is frequent, demanding increasingly higher responsiveness and capability in maintenance and support. The aerospace equipment maintenance ...The current space launch missions are intense, and the utilization of equipment is frequent, demanding increasingly higher responsiveness and capability in maintenance and support. The aerospace equipment maintenance and support chain relies on aerospace equipment maintenance and support facilities, deploying various maintenance and support resources rationally according to specific requirements and principles, ultimately forming a unidirectional functional chain or network from the supply side to the demand side. This system helps address the “bottleneck” issue in the generation of aerospace equipment support capability and significantly improves the level of aerospace equipment maintenance and support. The model construction is a prerequisite for analyzing the formation and operation mechanism of the chain, and identifying factors affecting the efficiency and effectiveness of maintenance and support. With consideration of the particularity of aerospace equipment maintenance and support, the paper extensively investigates the construction of the aerospace equipment maintenance and support chain model by drawing on research achievements in modern supply chain and logistics theories, as well as model construction methods. It develops a structural diagram-based chain model, with symbols as key elements, and establishes an evaluation indicator system, providing insights into understanding and grasping the composition of the aerospace equipment maintenance and support chain effectively. Furthermore, it offers a reference for solving other equipment support chains’ construction and optimization problems.展开更多
Background and Objective Electromagnetic navigation technology has demonstrated significant potential in enhancing the accuracy and safety of neurosurgical procedures.However,traditional electromagnetic navigation sys...Background and Objective Electromagnetic navigation technology has demonstrated significant potential in enhancing the accuracy and safety of neurosurgical procedures.However,traditional electromagnetic navigation systems face challenges such as high equipment costs,complex operation,bulky size,and insufficient anti-interference performance.To address these limitations,our study developed and validated a novel portable electromagnetic neuronavigation system designed to improve the precision,accessibility,and clinical applicability of electromagnetic navigation technology in cranial surgery.Methods The software and hardware architecture of a portable neural magnetic navigation system was designed.The key technologies of the system were analysed,including electromagnetic positioning algorithms,miniaturized sensor design,optimization of electromagnetic positioning and navigation algorithms,anti-interference signal processing methods,and fast three-dimensional reconstruction algorithms.A prototype was developed,and its accuracy was tested.Finally,a preliminary clinical application evaluation was conducted.Results This study successfully developed a comprehensive portable electromagnetic neuronavigation system capable of achieving preoperative planning,intraoperative real-time positioning and navigation,and postoperative evaluation of navigation outcomes.Through rigorous collaborative testing of the system’s software and hardware,the accuracy of electromagnetic neuronavigation has been validated to meet clinical requirements.Conclusions This study developed a portable neuroelectromagnetic navigation system and validated its effectiveness and safety through rigorous model testing and preliminary clinical applications.The system is characterized by its compact size,high precision,excellent portability,and user-friendly operation,making it highly valuable for promoting navigation technology and advancing the precision and minimally invasive nature of neurosurgical procedures.展开更多
Motivated by the early works on bidirectional interaction and the breakthrough to estimate seismic response to bidirectional shaking via unidirectional analysis,it is essential to answer the question:When is the inter...Motivated by the early works on bidirectional interaction and the breakthrough to estimate seismic response to bidirectional shaking via unidirectional analysis,it is essential to answer the question:When is the interaction effect significant?Early works concluded that the effect of interaction is pronounced for stiff systems;consequently,the straightforward method for estimating seismic response to bidirectional excitation by using unidirectional analyses is verified primarily for short period systems.Hence,it is essential to identify the domain of significance for bidirectional interaction before adopting this simple methodology in design.Several parametrically defined systems with elastoplastic and degrading hysteresis models are studied under near-fault motions,assuming strength-independent and strength-dependent stiffness.The force-based and displacement-based analyses,conducted in parallel,reveal that the interaction effect is considerable for stiff systems,especially with degrading characteristics in a relatively low inelasticity range.However,the bidirectional effect may be significant even for highly flexible systems,especially for residual deformation,which in earlier works was shrouded.The range of significance depends on the hysteresis model,system parameters,and response indices.Regression analysis is carried out with the results of the case studies,and the derived regression models may be used for a preliminary assessment of the impact of interaction in advance.展开更多
A Shape Memory Polymer Composite(SMPC)is developed by reinforcing an epoxy-based polymer with randomly oriented short glass fibers.Diverging from previous research,which primarily focused on the hot programming of sho...A Shape Memory Polymer Composite(SMPC)is developed by reinforcing an epoxy-based polymer with randomly oriented short glass fibers.Diverging from previous research,which primarily focused on the hot programming of short glass fiber-based SMPCs,this work explores the potential for programming below the glass transition temperature(Tg)for epoxy-based SMPCs.To mitigate the inherent brittleness of the SMPC during deformation,a linear polymer is incorporated,and a temperature between room temperature and Tg is chosen as the deformation temperature to study the shape memory properties.The findings demonstrate an enhancement in shape fixity and recovery stress,alongside a reduction in shape recovery,with the incorporation of short glass fibers.In addition to tensile properties,thermal properties such as thermal conductivity,specific heat capacity,and glass transition temperature are investigated for their dependence on fiber content.Microscopic properties,such as fiber-matrix adhesion and the dispersion of glass fibers,are examined through Scanning Electron Microscope imaging.The fiber length distribution and mean fiber lengths are also measured for different fiber fractions.展开更多
Blending the agility of aerial drones with the covert capabilities of underwater submersibles,the aerial-aquatic rotorcraft has garnered substantial interest due to their unparalleled capacity to traverse both air and...Blending the agility of aerial drones with the covert capabilities of underwater submersibles,the aerial-aquatic rotorcraft has garnered substantial interest due to their unparalleled capacity to traverse both air and water.Nevertheless,a critical hurdle for these vehicles lies in mitigating the adverse effects of repeatedly transitioning between these environments,particularly during water-surface takeoffs.Currently,research on the interference caused by rotors approaching water surfaces remains limited.This paper introduces a novel adaptive rotor aerodynamic model based on continuous finite vortex theory to predict rotor thrust within gas–liquid flow field.Initially,the model's sensitivity to system parameters was analyzed to optimize its predictive capabilities.Subsequently,a comprehensive ground/water experimental setup was designed to investigate the intricate aerodynamic interactions between the rotor flow field and water.By varying rotor sizes,the characteristics of the rotor flow field and water surface were examined at different rotor-water surface distances.The performance of different modeling methods was analyzed based on the rotor experimental data of a diameter of 0.38 m,and the prediction results were quantified using the percentage of the mean-square error.The results show that the average error of the finite vortex rotor model is the smallest.Finally,a novel transition boundary is proposed to divide the rotor flow field of the gas–liquid mixture into two stages.The thrust loss zone is defined to delineate the safe operating range of the aircraft,providing a basis for the design of aerial-aquatic rotorcraft.展开更多
In this comprehensive review,the evolution and progress of bioplastics are examined,with an emphasis on their types,production methods,environmental impact,and biodegradability.In light of the increasing global effort...In this comprehensive review,the evolution and progress of bioplastics are examined,with an emphasis on their types,production methods,environmental impact,and biodegradability.In light of the increasing global efforts to address environmental degradation,bioplastics have emerged as a highly potential substitute for conventional petroleum-based plastics.This review classifies various categories of bioplastics,encompassing both biodegradable and bio-based variations,and assesses their environmental consequences using life cycle evaluations and biodegradability calculations.This paper analyzes the technological advancements that have enhanced the mechanical and thermal characteristics of bioplastics,hence increasing their feasibility for extensive commercial applications in diverse sectors.This review critically examines the possible uses of bioplastics in important industries including packaging,aerospace,and healthcare,emphasizing both achievements and current obstacles.In addition,the assessment addresses the economic and technical obstacles to expanding bioplastic manufacturing,namely concerns about cost,material efficiency,and waste disposal.Moreover,the article forecasts the future potential of bioplastics in furthering a sustainable circular economy and suggests methods to address existing constraints,such as improvements in recycling technology and the establishment of more economically efficient manufacturing methods.The findings are intended to educate policymakers,industry stakeholders,and researchers on the crucial contribution of bioplastics in attaining sustainability objectives and promoting innovation in the field of material science.展开更多
The data-driven machine learning paradigm typically requires high-quality,large-scale datasets for training neural networks,which are often unavailable in many scientific and engineering applications.Integrating physi...The data-driven machine learning paradigm typically requires high-quality,large-scale datasets for training neural networks,which are often unavailable in many scientific and engineering applications.Integrating physics equations into machine learning models,either fully or partially,can mitigate these data requirements and improve generalizability;however,such approaches frequently rely on differentiable programming frameworks.This ability poses significant challenges when legacy or commercial numerical solvers,which are often nondifferentiable and difficult to modify without introducing code changes,are integrated.This work addresses these challenges by leveraging the mini-batching iterative ensemble Kalman inversion(EKI)algorithm as a gradientfree training framework for hybrid neural models.The use of stochastic mini-batching significantly enhances the computational efficiency and convergence of EKI,making it well-suited for high-dimensional learning problems.The proposed method is demonstrated for modeling a fiber-reinforced composite plate,where heterogeneous local constitutive laws are parameterized by a trainable neural network embedded within the FEniCS finite element solver.Using the displacement field as indirect data,the hybrid neural FEM solver successfully predicts deformations by learning the local constitutive laws,even for unseen fiber volume fraction distributions and varying test loading conditions.These results demonstrate the effectiveness of iterative EKI in training hybrid neural models with non-differentiable components,paving the way for broader adoption of hybrid neural models in scientific and engineering applications.展开更多
Aluminum alloys are widely used in industry due to their light weight.These alloys are generally exposed to abrasive wear,which diminishes their effective lifespan.The wear resistance of these alloys is enhanced by ad...Aluminum alloys are widely used in industry due to their light weight.These alloys are generally exposed to abrasive wear,which diminishes their effective lifespan.The wear resistance of these alloys is enhanced by adding various reinforcements,however,this enhancement comes at the cost of reduced fracture toughness.This paradox of increased wear resistance versus decreased fracture toughness in aluminum alloys can be resolved by using functionally graded materials (FGMs).This study focuses on the abrasive wear behavior of functional graded aluminum matrix composites reinforced with Al_(3)Ti particles.The wear properties of the composites were investigated by considering the characteristics of the composite such as matrix type and various composite zones,as well as the wear parameters such as abrasive particle diameter,load,sliding speed and distance.Taguchi method was used in the abrasive wear tests in order to get more reliable results in a timeefficient manner.Experiment recipes were created based on the L_(27)(3^(6)) orthogonal series.As a result of the study,it is observed that the wear resistance of the composites increases with an increase in Al_(3)Ti reinforcement content and hardness of the matrix.In addition,the size of abrasive particles and the applied load are significant factors affecting abrasive wear.展开更多
Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems ca...Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems can be identified.This approach has been pioneered by Brunton et al.(2016,PNAS)with sparse identification of nonlinear dynamics.Complex systems,however,cannot be expected to benefit from such simple analytical descriptions.Yet,smoothness may be exploited by analytical local descriptions.In this paper,we identify a clusterwise polynomial dynamics from time-resolved snapshot data.The full state space is partitioned into clusters with a reduced-order polynomial description for each cluster and a global patching strategy.The resulting clusterwise modeling is entirely data-driven and requires no prior knowledge of the system dynamics.We illustrate the approach on the well-known chaotic Lorenz and Rössler systems,on the more challenging chaotic fluid flow dynamics of higher state-space dimensions,on a noisy electrocardiogram signal,and finally on the time evolution of the monthly sunspot number.Clusterwise modeling offers a powerful and interpretable paradigm for dynamical modeling.Nonlinear dynamics can be approximated by assembling many simple local models of different resolutions,opening new paths to understand and control intricate nonlinearities.展开更多
The growing demand for flexible,lightweight,and highly processable electronic devices makes high-functionality conducting polymers such as poly(3,4-ethylene dioxythiophene):polystyrene sulfonate(PEDOT:PSS)an attractiv...The growing demand for flexible,lightweight,and highly processable electronic devices makes high-functionality conducting polymers such as poly(3,4-ethylene dioxythiophene):polystyrene sulfonate(PEDOT:PSS)an attractive alternative to conventional inorganic materials for various applications including thermoelectrics.However,considerable improvements are necessary to make conducting polymers a commercially viable choice for thermoelectric applications.This study explores nanopatterning as an effective and unique strategy for enhancing polymer functionality to optimize thermoelectric parameters,such as electrical conductivity,Seebeck coefficient,and thermal conductivity.Introducing nanopatterning into thermoelectric polymers is challenging due to intricate technical hurdles and the necessity for individually manipulating the interdependent thermoelectric parameters.Here,array nanopatterns with different pattern spacings are imposed on free-standing PEDOT:PSS films using direct electron beam irradiation,thereby achieving selective control of electrical and thermal transport in PEDOT:PSS.Electron beam irradiation transformed PEDOT:PSS from a highly ordered quinoid to an amorphous benzoid structure.Optimized pattern spacing resulted in a remarkable 70%reduction in thermal conductivity and a 60%increase in thermoelectric figure of merit compared to non-patterned PEDOT:PSS.The proposed nanopatterning methodology demonstrates a skillful approach to precisely manipulate the thermoelectric parameters,thereby improving the thermoelectric performance of conducting polymers,and promising utilization in cutting-edge electronic applications.展开更多
The efficacy of spacecraft propulsion systems significantly depends on the choice of propellant.This study utilized laser-induced breakdown spectroscopy(LIBS)to investigate the impact of different fuel types,fuel rati...The efficacy of spacecraft propulsion systems significantly depends on the choice of propellant.This study utilized laser-induced breakdown spectroscopy(LIBS)to investigate the impact of different fuel types,fuel ratios,and laser energies on the plasma parameters of ammonium dinitramide(ADN)-based liquid propellants.Our findings suggest that 1-allyl-3-methylimidazolium dicyanamide(AMIMDCA)as a fuel choice led to higher plasma temperatures compared to methanol(CH_3OH)and hydroxyethyl hydrazine nitrate(HEHN)under the same experimental conditions.Optimization of the fuel ratio proved critical,and when the AMIMDCA ratio was 21wt.%the propellants could achieve the best propulsion performance.Increasing the incident laser energy not only enhanced the emission spectral intensity but also elevated the plasma temperature and electron density,thereby improving ablation efficiency.Notably,a combination of 100 mJ laser energy and 21wt.%AMIMDCA fuel produced a strong and stable plasma signal.This study contributes to our knowledge of pulsed laser micro-ablation in ADN-based liquid propellants,providing a useful optical diagnostic approach that can help refine the design and enhance the performance of spacecraft propulsion systems.展开更多
This study investigates the combustion characteristics of reactive aluminium alloys in combination with fluoropolymer oxidizers. Aluminium-magnesium(Al-Mg) and aluminium-titanium(Al-Ti) alloys were selected as metalli...This study investigates the combustion characteristics of reactive aluminium alloys in combination with fluoropolymer oxidizers. Aluminium-magnesium(Al-Mg) and aluminium-titanium(Al-Ti) alloys were selected as metallic fuels, while polyvinylidene fluoride(PVDF) was employed as the oxidizer. Composite samples were prepared using two methods: electrostatic spraying(ES) and physical mixing(PM). The ES method yielded samples with a PVDF-coated structure, whereas the PM method produced simple mixtures. The samples and their combustion products were characterized using scanning electron microscopy(SEM), X-ray diffraction(XRD), combustion experiments, and thermal analysis. The results indicate that compared to the PM samples, the ES-coated samples exhibited more effective dispersion of metallic particles, reduced particle agglomeration, increased combustion heat release temperature, decreased maximum flame area and height, and mitigated or eliminated explosive or micro-explosive phenomena during combustion, thereby achieving stable combustion. Additionally, the ES samples demonstrated a significant reduction in the particle size of condensed-phase products after combustion, alleviated sintering and agglomeration, decreased the formation of metal oxides, and minimized residual metallic fuel, allowing for the full release of combustion heat. Thermal analysis revealed that the coating structure of the ES samples lowered the activation energy for the reaction between the metallic fuel and PVDF, thereby enhancing the chemical reactivity.展开更多
The mechanical properties of minerals in planetary materials are not only interesting from a fundamental point of view but also critical to the development of future space missions.Here we present nanoindentation expe...The mechanical properties of minerals in planetary materials are not only interesting from a fundamental point of view but also critical to the development of future space missions.Here we present nanoindentation experiments to evaluate the hardness and reduced elastic modulus of olivine,(Mg,Fe)_(2)SiO_(4),in meteorite NWA 12008,a lunar basalt.Our experiments suggest that the olivine grains in this lunaite are softer and more elastic than their terrestrial counterparts.Also,we have performed synchrotron-based high-pressure X-ray diffraction(HP-XRD)measurements to probe the compressibility properties of olivine in this meteorite and,for comparison purposes,of three ordinary chondrites.The HP-XRD results suggest that the axial compressibility of the orthorhombic b lattice parameter of olivine relative to terrestrial olivine is higher in NWA 12008 and also in the highly-shocked Chelyabinsk meteorite.The origin of the observed differences is discussed.A simple model combining the results of both our nanoindentation and HP-XRD measurements allows us to describe the contribution of macroscopic and chemical-bond related effects,both of which are necessary to reproduce the observed elastic modulus softening.Such joint analysis of the mechanical and elastic properties of meteorites and returned samples opens up a new avenue for characterizing these highly interesting materials.展开更多
Space exploration is significant for scientific innovation,resource utilization,and planetary security.Space exploration involves several systems including satellites,space suits,communication systems,and robotics,whi...Space exploration is significant for scientific innovation,resource utilization,and planetary security.Space exploration involves several systems including satellites,space suits,communication systems,and robotics,which have to function under harsh space conditions such as extreme temperatures(−270 to 1650℃),microgravity(10^(-6)g),unhealthy humidity(<20%RH or>60%RH),high atmospheric pressure(~1450 psi),and radiation(4000–5000 mSv).Conventional energy-harvesting technologies(solar cells,fuel cells,and nuclear energy),that are normally used to power these space systems have certain limitations(e.g.,sunlight dependence,weight,degradation,big size,high cost,low capacity,radioactivity,complexity,and low efficiency).The constraints in conventional energy resources have made it imperative to look for non-conventional yet efficient alternatives.A great potential for enhancing efficiency,sustainability,and mission duration in space exploration can be offered by integrating triboelectric nanogenerators(TENGs)with existing energy sources.Recently,the potential of TENG including energy harvesting(from vibrations/movements in satellites and spacecraft),self-powered sensing,and microgravity,for multiple applications in different space missions has been discussed.This review comprehensively covers the use of TENGs for various space applications,such as planetary exploration missions(Mars environment monitoring),manned space equipment,In-orbit robotic operations/collision monitoring,spacecraft’s design and structural health monitoring,Aeronautical systems,and conventional energy harvesting(solar and nuclear).This review also discusses the use of self-powered TENG sensors for deep space object perception.At the same time,this review compares TENGs with conventional energy harvesting technologies for space systems.Lastly,this review talks about energy harvesting in satellites,TENG-based satellite communication systems,and future practical implementation challenges(with possible solutions).展开更多
With rapid advancements in Infra-Red (IR) detection techniques, the range from where the IR-guided missiles are able to lock the target aircraft has increased. To avoid the detection and tracking by modern IR-guided m...With rapid advancements in Infra-Red (IR) detection techniques, the range from where the IR-guided missiles are able to lock the target aircraft has increased. To avoid the detection and tracking by modern IR-guided missiles, the aircraft and helicopters also demand progress in its stealth techniques. Hence, study of Infra-Red Signature Suppression (IRSS) systems in aircraft and helicopters has become vital even in design stage. Optical blocking (masking) is one of the effective IRSS techniques used to block the Line- Of-Sight (LOS) of the hot engine parts of the exhaust geometry. This paper reviews the various patents on IR signature suppression systems based on the optical blocking method or a combination of IRSS techniques. The performance penalties generated due to installation of various IRSS methods in aircraft and helicopters are also discussed.展开更多
Experimental study of synthetic jet produced by pulsed direct current （DC） discharge is presented. High velocity jet is acti- vated electro-thermally by high frequency pulsed DC discharge in small cavity. A cavity o...Experimental study of synthetic jet produced by pulsed direct current （DC） discharge is presented. High velocity jet is acti- vated electro-thermally by high frequency pulsed DC discharge in small cavity. A cavity of 2.38 mm diameter cylinder bounded by circular electrode is made in a ceramic plate and a small orifice of 1.78 mm diameter is drilled in the middle of cavity. High frequency pulsed DC discharge instantaneously heats air in the cavity and produces high velocity jet at the exit of the orifice. Schlieren imaging at high framing rate of 100 kHz reveals the presence of supersonic precursor shock followed by the jet emerg- ing from the orifice. The jet velocity reaches as high as about 300 m/s. Jet with smaller cavity volume produces lesser effect and jet velocity reaches maximum at certain cavity volume with given discharge current and orifice size. As duty time of pulse increases from 5 to 20 μs at fixed frequency of 5 kHz, the jet velocity also increases and becomes nearly constant with further increase in duty time. At fixed duty time of 20 μs, higher frequency pulsing of 10 kHz produces degradation of the jet as the discharge pulse continues. The jet developed in this study is demonstrated to be strong enough to penetrate deep into supersonic boundary layer and to produce a bow shock when the jet is issued into Mach 3 supersonic flow.展开更多
In this paper, the effects of icing on an NACA 23012 airfoil have been studied. Exper- iments were applied on the clean airfoil, runback ice, horn ice, and spanwise ridge ice at a Reynolds number of 0.6 x 10^6 over an...In this paper, the effects of icing on an NACA 23012 airfoil have been studied. Exper- iments were applied on the clean airfoil, runback ice, horn ice, and spanwise ridge ice at a Reynolds number of 0.6 x 10^6 over angles of attack from -8° to 20% and then results are compared. Gener- ally, it is found that ice accretion on the airfoil can contribute to formation of a flow separation bubble on the upper surface downstream from the leading edge. In addition, it is made clear that spanwise ridge ice provides the greatest negative effect on the aerodynamic performance of the airfoil. In this case, the stall angle drops about 10^6 and the maximum lift coefficient reduces about 50% which is hazardous for an airplane. While horn ice leads to a stall angle drop of about 4°and a maximum lift coefficient reduction to 21%, runback ice has the least effect on the flow pattern around the airfoil and the aerodynamic coefficients so as the stall angle decreases 2% and the maximum lift reduces about 8%.展开更多
基金supported by the Khalifa University of Science and Technology internal grants(Nos.2021-CIRA-109,2020-CIRA-007,and 2020-CIRA-024).
文摘Low-velocity impact tests are carried out to explore the energy absorption characteristics of bio-inspired lattices,mimicking the architecture of the marine sponge organism Euplectella aspergillum.These sea sponge-inspired lattice structures feature a square-grid 2D lattice with double diagonal bracings and are additively manufactured via digital light processing(DLP).The collapse strength and energy absorption capacity of sea sponge lattice structures are evaluated under various impact conditions and are compared to those of their constituent square-grid and double diagonal lattices.This study demonstrates that sea sponge lattices can achieve an 11-fold increase in energy absorption compared to the square-grid lattice,due to the stabilizing effect of the double diagonal bracings prompting the structure to collapse layer-bylayer under impact.By adjusting the thickness ratio in the sea sponge lattice,up to 76.7%increment in energy absorption is attained.It is also shown that sea-sponge lattices outperform well-established energy-absorbing materials of equal weight,such as hexagonal honeycombs,confirming their significant potential for impact mitigation.Additionally,this research highlights the enhancements in energy absorption achieved by adding a small amount(0.015 phr)of Multi-Walled Carbon Nanotubes(MWCNTs)to the photocurable resin,thus unlocking new possibilities for the design of innovative lightweight structures with multifunctional attributes.
基金the Innovation Foundation of National Research Center for Commercial Aircraft Manufacturing Engineering Technology in China (No. SAMC13-JS-13-021)Jiangsu Key Laboratory of Precision and Micro-Manufacturing Technology for the provision of financial support
文摘The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional(3 D)structural solid elements assembled model of a carbon fiber-reinforced polymer(CFRP)-aluminum single-lap joint with a titanium(Ti-6 Al-4 V)fastener and a washer generated with the commercial finite element(FE)software package,ABAQUS/Standard.A progressive failure algorithm written in Fortran code with a set of appropriate degradation rules was incorporated as a user subroutine in ABAQUS to simulate the non-linear damage behavior of the composite component in the composite-aluminum bolted aerospace structure.The assembled 3 DFE model simulated,as well as the specimen for the experimental testing consisted of a carbon-epoxy IMS-977-2 substrate,aluminum alloy 7075-T651 substrate,liquid shim(Hysol EA 9394),solid peelable fiberglass shim,a titanium fastener,and a washer.In distinction to previous investigations,the influence of shim layers(liquid shim and solid peelable fiberglass shim)inserted in-between the faying surfaces(CFRP and aluminum alloy substrates)were investigated by both numerical simulations and experimental work.The simulated model and test specimens conformed to the standard test configurations for both civil and military standards.The numerical simulations correlated well with the experimental results and it has been found that:(1)The shimming procedure as agreed upon by the aerospace industry for the resolution of assembly gaps in bolted joints for composite materials is the same for a composite-aluminum structure;liquid shim series(0.3,0.5 and 0.7 mm thicknesses)prolonged the service life of the composite component whereas a solid peelable fiberglass shim most definitely had a better influence on the 0.9 assembly gap compared with the liquid shim;(2)The shim layers considerably influenced the structural strength of the composite component by delaying its ultimate failure thereby increasing its service life;and(3)Increasing the shim layer′s thickness led to a significant corresponding effect on the stiffness but with minimal effect on the ultimate load.
基金supported by the National Natural Science Foundation of China(Nos.12272104,U22B2013).
文摘This paper investigates the challenges associated with Unmanned Aerial Vehicle (UAV) collaborative search and target tracking in dynamic and unknown environments characterized by limited field of view. The primary objective is to explore the unknown environments to locate and track targets effectively. To address this problem, we propose a novel Multi-Agent Reinforcement Learning (MARL) method based on Graph Neural Network (GNN). Firstly, a method is introduced for encoding continuous-space multi-UAV problem data into spatial graphs which establish essential relationships among agents, obstacles, and targets. Secondly, a Graph AttenTion network (GAT) model is presented, which focuses exclusively on adjacent nodes, learns attention weights adaptively and allows agents to better process information in dynamic environments. Reward functions are specifically designed to tackle exploration challenges in environments with sparse rewards. By introducing a framework that integrates centralized training and distributed execution, the advancement of models is facilitated. Simulation results show that the proposed method outperforms the existing MARL method in search rate and tracking performance with less collisions. The experiments show that the proposed method can be extended to applications with a larger number of agents, which provides a potential solution to the challenging problem of multi-UAV autonomous tracking in dynamic unknown environments.
文摘The current space launch missions are intense, and the utilization of equipment is frequent, demanding increasingly higher responsiveness and capability in maintenance and support. The aerospace equipment maintenance and support chain relies on aerospace equipment maintenance and support facilities, deploying various maintenance and support resources rationally according to specific requirements and principles, ultimately forming a unidirectional functional chain or network from the supply side to the demand side. This system helps address the “bottleneck” issue in the generation of aerospace equipment support capability and significantly improves the level of aerospace equipment maintenance and support. The model construction is a prerequisite for analyzing the formation and operation mechanism of the chain, and identifying factors affecting the efficiency and effectiveness of maintenance and support. With consideration of the particularity of aerospace equipment maintenance and support, the paper extensively investigates the construction of the aerospace equipment maintenance and support chain model by drawing on research achievements in modern supply chain and logistics theories, as well as model construction methods. It develops a structural diagram-based chain model, with symbols as key elements, and establishes an evaluation indicator system, providing insights into understanding and grasping the composition of the aerospace equipment maintenance and support chain effectively. Furthermore, it offers a reference for solving other equipment support chains’ construction and optimization problems.
基金funded by National Natural Science Foundation of China(No.82272134)Innovative Research Group Project of the National Natural Science Foundation of China(No.82272134,Xiao-lei Chen).
文摘Background and Objective Electromagnetic navigation technology has demonstrated significant potential in enhancing the accuracy and safety of neurosurgical procedures.However,traditional electromagnetic navigation systems face challenges such as high equipment costs,complex operation,bulky size,and insufficient anti-interference performance.To address these limitations,our study developed and validated a novel portable electromagnetic neuronavigation system designed to improve the precision,accessibility,and clinical applicability of electromagnetic navigation technology in cranial surgery.Methods The software and hardware architecture of a portable neural magnetic navigation system was designed.The key technologies of the system were analysed,including electromagnetic positioning algorithms,miniaturized sensor design,optimization of electromagnetic positioning and navigation algorithms,anti-interference signal processing methods,and fast three-dimensional reconstruction algorithms.A prototype was developed,and its accuracy was tested.Finally,a preliminary clinical application evaluation was conducted.Results This study successfully developed a comprehensive portable electromagnetic neuronavigation system capable of achieving preoperative planning,intraoperative real-time positioning and navigation,and postoperative evaluation of navigation outcomes.Through rigorous collaborative testing of the system’s software and hardware,the accuracy of electromagnetic neuronavigation has been validated to meet clinical requirements.Conclusions This study developed a portable neuroelectromagnetic navigation system and validated its effectiveness and safety through rigorous model testing and preliminary clinical applications.The system is characterized by its compact size,high precision,excellent portability,and user-friendly operation,making it highly valuable for promoting navigation technology and advancing the precision and minimally invasive nature of neurosurgical procedures.
文摘Motivated by the early works on bidirectional interaction and the breakthrough to estimate seismic response to bidirectional shaking via unidirectional analysis,it is essential to answer the question:When is the interaction effect significant?Early works concluded that the effect of interaction is pronounced for stiff systems;consequently,the straightforward method for estimating seismic response to bidirectional excitation by using unidirectional analyses is verified primarily for short period systems.Hence,it is essential to identify the domain of significance for bidirectional interaction before adopting this simple methodology in design.Several parametrically defined systems with elastoplastic and degrading hysteresis models are studied under near-fault motions,assuming strength-independent and strength-dependent stiffness.The force-based and displacement-based analyses,conducted in parallel,reveal that the interaction effect is considerable for stiff systems,especially with degrading characteristics in a relatively low inelasticity range.However,the bidirectional effect may be significant even for highly flexible systems,especially for residual deformation,which in earlier works was shrouded.The range of significance depends on the hysteresis model,system parameters,and response indices.Regression analysis is carried out with the results of the case studies,and the derived regression models may be used for a preliminary assessment of the impact of interaction in advance.
文摘A Shape Memory Polymer Composite(SMPC)is developed by reinforcing an epoxy-based polymer with randomly oriented short glass fibers.Diverging from previous research,which primarily focused on the hot programming of short glass fiber-based SMPCs,this work explores the potential for programming below the glass transition temperature(Tg)for epoxy-based SMPCs.To mitigate the inherent brittleness of the SMPC during deformation,a linear polymer is incorporated,and a temperature between room temperature and Tg is chosen as the deformation temperature to study the shape memory properties.The findings demonstrate an enhancement in shape fixity and recovery stress,alongside a reduction in shape recovery,with the incorporation of short glass fibers.In addition to tensile properties,thermal properties such as thermal conductivity,specific heat capacity,and glass transition temperature are investigated for their dependence on fiber content.Microscopic properties,such as fiber-matrix adhesion and the dispersion of glass fibers,are examined through Scanning Electron Microscope imaging.The fiber length distribution and mean fiber lengths are also measured for different fiber fractions.
基金the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(No.KYCX24_0532)the Key Laboratory of Cross-Domain Flight Interdisciplinary Technology,China(Nos.2024-KF03001,2024-KF03003)the National Natural Science Foundation of China(No.12272169)for the financial support。
文摘Blending the agility of aerial drones with the covert capabilities of underwater submersibles,the aerial-aquatic rotorcraft has garnered substantial interest due to their unparalleled capacity to traverse both air and water.Nevertheless,a critical hurdle for these vehicles lies in mitigating the adverse effects of repeatedly transitioning between these environments,particularly during water-surface takeoffs.Currently,research on the interference caused by rotors approaching water surfaces remains limited.This paper introduces a novel adaptive rotor aerodynamic model based on continuous finite vortex theory to predict rotor thrust within gas–liquid flow field.Initially,the model's sensitivity to system parameters was analyzed to optimize its predictive capabilities.Subsequently,a comprehensive ground/water experimental setup was designed to investigate the intricate aerodynamic interactions between the rotor flow field and water.By varying rotor sizes,the characteristics of the rotor flow field and water surface were examined at different rotor-water surface distances.The performance of different modeling methods was analyzed based on the rotor experimental data of a diameter of 0.38 m,and the prediction results were quantified using the percentage of the mean-square error.The results show that the average error of the finite vortex rotor model is the smallest.Finally,a novel transition boundary is proposed to divide the rotor flow field of the gas–liquid mixture into two stages.The thrust loss zone is defined to delineate the safe operating range of the aircraft,providing a basis for the design of aerial-aquatic rotorcraft.
基金the financial support given by the Ministry of Higher Education Malaysia(MOHE)under the Higher Institution Centre of Excellence(HICOE2.0/5210004)at the Institute of Tropical Forestry and Forest Products.
文摘In this comprehensive review,the evolution and progress of bioplastics are examined,with an emphasis on their types,production methods,environmental impact,and biodegradability.In light of the increasing global efforts to address environmental degradation,bioplastics have emerged as a highly potential substitute for conventional petroleum-based plastics.This review classifies various categories of bioplastics,encompassing both biodegradable and bio-based variations,and assesses their environmental consequences using life cycle evaluations and biodegradability calculations.This paper analyzes the technological advancements that have enhanced the mechanical and thermal characteristics of bioplastics,hence increasing their feasibility for extensive commercial applications in diverse sectors.This review critically examines the possible uses of bioplastics in important industries including packaging,aerospace,and healthcare,emphasizing both achievements and current obstacles.In addition,the assessment addresses the economic and technical obstacles to expanding bioplastic manufacturing,namely concerns about cost,material efficiency,and waste disposal.Moreover,the article forecasts the future potential of bioplastics in furthering a sustainable circular economy and suggests methods to address existing constraints,such as improvements in recycling technology and the establishment of more economically efficient manufacturing methods.The findings are intended to educate policymakers,industry stakeholders,and researchers on the crucial contribution of bioplastics in attaining sustainability objectives and promoting innovation in the field of material science.
基金supported by the Air Force Office of Scientific Research(AFOSR),United States of America(Grant No.FA9550-22-1-0065).
文摘The data-driven machine learning paradigm typically requires high-quality,large-scale datasets for training neural networks,which are often unavailable in many scientific and engineering applications.Integrating physics equations into machine learning models,either fully or partially,can mitigate these data requirements and improve generalizability;however,such approaches frequently rely on differentiable programming frameworks.This ability poses significant challenges when legacy or commercial numerical solvers,which are often nondifferentiable and difficult to modify without introducing code changes,are integrated.This work addresses these challenges by leveraging the mini-batching iterative ensemble Kalman inversion(EKI)algorithm as a gradientfree training framework for hybrid neural models.The use of stochastic mini-batching significantly enhances the computational efficiency and convergence of EKI,making it well-suited for high-dimensional learning problems.The proposed method is demonstrated for modeling a fiber-reinforced composite plate,where heterogeneous local constitutive laws are parameterized by a trainable neural network embedded within the FEniCS finite element solver.Using the displacement field as indirect data,the hybrid neural FEM solver successfully predicts deformations by learning the local constitutive laws,even for unseen fiber volume fraction distributions and varying test loading conditions.These results demonstrate the effectiveness of iterative EKI in training hybrid neural models with non-differentiable components,paving the way for broader adoption of hybrid neural models in scientific and engineering applications.
基金financially supported by the Scientific Research Project Coordinatorship (BAP) of Yildiz Technical University (YTU) (Project No: FYL-2021-3825)。
文摘Aluminum alloys are widely used in industry due to their light weight.These alloys are generally exposed to abrasive wear,which diminishes their effective lifespan.The wear resistance of these alloys is enhanced by adding various reinforcements,however,this enhancement comes at the cost of reduced fracture toughness.This paradox of increased wear resistance versus decreased fracture toughness in aluminum alloys can be resolved by using functionally graded materials (FGMs).This study focuses on the abrasive wear behavior of functional graded aluminum matrix composites reinforced with Al_(3)Ti particles.The wear properties of the composites were investigated by considering the characteristics of the composite such as matrix type and various composite zones,as well as the wear parameters such as abrasive particle diameter,load,sliding speed and distance.Taguchi method was used in the abrasive wear tests in order to get more reliable results in a timeefficient manner.Experiment recipes were created based on the L_(27)(3^(6)) orthogonal series.As a result of the study,it is observed that the wear resistance of the composites increases with an increase in Al_(3)Ti reinforcement content and hardness of the matrix.In addition,the size of abrasive particles and the applied load are significant factors affecting abrasive wear.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172109,12202121,and 12302293)the China Postdoctoral Science Foundation(Grant Nos.2023M730866 and 2023T160166)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant No.2022A1515011492)the Shenzhen Science and Technology Program(Grant Nos.JCYJ20220531095605012,KJZD20230923115210021,and 29853MKCJ202300205).
文摘Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems can be identified.This approach has been pioneered by Brunton et al.(2016,PNAS)with sparse identification of nonlinear dynamics.Complex systems,however,cannot be expected to benefit from such simple analytical descriptions.Yet,smoothness may be exploited by analytical local descriptions.In this paper,we identify a clusterwise polynomial dynamics from time-resolved snapshot data.The full state space is partitioned into clusters with a reduced-order polynomial description for each cluster and a global patching strategy.The resulting clusterwise modeling is entirely data-driven and requires no prior knowledge of the system dynamics.We illustrate the approach on the well-known chaotic Lorenz and Rössler systems,on the more challenging chaotic fluid flow dynamics of higher state-space dimensions,on a noisy electrocardiogram signal,and finally on the time evolution of the monthly sunspot number.Clusterwise modeling offers a powerful and interpretable paradigm for dynamical modeling.Nonlinear dynamics can be approximated by assembling many simple local models of different resolutions,opening new paths to understand and control intricate nonlinearities.
基金supported by Characterization of Mechanical/Thermal/Chemical Properties of EUV Absorption/Transmission Materials through the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT(Grant 2020-M3H4A3081882)by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Ministry of Trade,Industry and Energy(MOTIE)(No.2021202080023D)the Characterization Platform for Advanced Materials(KRISS-2022-GP2022-0013)funded by the Korea Research Institute of Standards and Science。
文摘The growing demand for flexible,lightweight,and highly processable electronic devices makes high-functionality conducting polymers such as poly(3,4-ethylene dioxythiophene):polystyrene sulfonate(PEDOT:PSS)an attractive alternative to conventional inorganic materials for various applications including thermoelectrics.However,considerable improvements are necessary to make conducting polymers a commercially viable choice for thermoelectric applications.This study explores nanopatterning as an effective and unique strategy for enhancing polymer functionality to optimize thermoelectric parameters,such as electrical conductivity,Seebeck coefficient,and thermal conductivity.Introducing nanopatterning into thermoelectric polymers is challenging due to intricate technical hurdles and the necessity for individually manipulating the interdependent thermoelectric parameters.Here,array nanopatterns with different pattern spacings are imposed on free-standing PEDOT:PSS films using direct electron beam irradiation,thereby achieving selective control of electrical and thermal transport in PEDOT:PSS.Electron beam irradiation transformed PEDOT:PSS from a highly ordered quinoid to an amorphous benzoid structure.Optimized pattern spacing resulted in a remarkable 70%reduction in thermal conductivity and a 60%increase in thermoelectric figure of merit compared to non-patterned PEDOT:PSS.The proposed nanopatterning methodology demonstrates a skillful approach to precisely manipulate the thermoelectric parameters,thereby improving the thermoelectric performance of conducting polymers,and promising utilization in cutting-edge electronic applications.
文摘The efficacy of spacecraft propulsion systems significantly depends on the choice of propellant.This study utilized laser-induced breakdown spectroscopy(LIBS)to investigate the impact of different fuel types,fuel ratios,and laser energies on the plasma parameters of ammonium dinitramide(ADN)-based liquid propellants.Our findings suggest that 1-allyl-3-methylimidazolium dicyanamide(AMIMDCA)as a fuel choice led to higher plasma temperatures compared to methanol(CH_3OH)and hydroxyethyl hydrazine nitrate(HEHN)under the same experimental conditions.Optimization of the fuel ratio proved critical,and when the AMIMDCA ratio was 21wt.%the propellants could achieve the best propulsion performance.Increasing the incident laser energy not only enhanced the emission spectral intensity but also elevated the plasma temperature and electron density,thereby improving ablation efficiency.Notably,a combination of 100 mJ laser energy and 21wt.%AMIMDCA fuel produced a strong and stable plasma signal.This study contributes to our knowledge of pulsed laser micro-ablation in ADN-based liquid propellants,providing a useful optical diagnostic approach that can help refine the design and enhance the performance of spacecraft propulsion systems.
基金National Natural Science Foundation of China (NSFC,Grant Nos.52176114 and 52306145)Natural Science Foundation of Jiangsu Province (Grant No.BK20230929)+2 种基金China Postdoctoral Science Foundation (Grant No.2024M764222)Fundamental Research Funds for the Central Universities (Grant No.30924010505)Jiangsu Funding Program for Excellent Postdoctoral Talent。
文摘This study investigates the combustion characteristics of reactive aluminium alloys in combination with fluoropolymer oxidizers. Aluminium-magnesium(Al-Mg) and aluminium-titanium(Al-Ti) alloys were selected as metallic fuels, while polyvinylidene fluoride(PVDF) was employed as the oxidizer. Composite samples were prepared using two methods: electrostatic spraying(ES) and physical mixing(PM). The ES method yielded samples with a PVDF-coated structure, whereas the PM method produced simple mixtures. The samples and their combustion products were characterized using scanning electron microscopy(SEM), X-ray diffraction(XRD), combustion experiments, and thermal analysis. The results indicate that compared to the PM samples, the ES-coated samples exhibited more effective dispersion of metallic particles, reduced particle agglomeration, increased combustion heat release temperature, decreased maximum flame area and height, and mitigated or eliminated explosive or micro-explosive phenomena during combustion, thereby achieving stable combustion. Additionally, the ES samples demonstrated a significant reduction in the particle size of condensed-phase products after combustion, alleviated sintering and agglomeration, decreased the formation of metal oxides, and minimized residual metallic fuel, allowing for the full release of combustion heat. Thermal analysis revealed that the coating structure of the ES samples lowered the activation energy for the reaction between the metallic fuel and PVDF, thereby enhancing the chemical reactivity.
基金Financial support from the project PID2021-128062NB-I00 funded by the Spanish Ministerio de Ciencia,Innovación y Universidades MCIU(doi:10.13039/501100011033)is acknowledged,as well as the Spanish program Unidad de Excelencia María de Maeztu CEX2020-001058-M.The ALBA-CELLS synchrotron is acknowledged for granting beamtime at the MSPD beamline under projects 2021095390 and 2022025734.PG-T acknowledges the financial support from the Spanish MCIU through the FPI predoctoral fellowship PRE2022-104624.JS acknowledges the financial support from projects 2021-SGR-00651 and PID2020-116844RB-C21.EP-A acknowledges financial support from the LUMIO project funded by the Agenzia Spaziale Italiana(2024-6-HH.0).DE thanks the financial support from Spanish MCIU under projects PID2022-138076NB-C41 and RED2022-134388-T from Generalitat Valenciana(GVA)through grants CIPROM/2021/075 and MFA/2022/007,which are part of the Advanced Materials program and is supported with funding from the European Union Next Generation EU(PRTR-C17.I1).RT and DE(PB and DE)thank GVA for the Postdoctoral Fellowship CIAPOS/2021/20(CIAPOS/2023/406).JS-M thanks the Spanish MCIU for the PRE2020-092198 fellowship.NWA 12008 has been studied within the framework of an international European consortium led by IFP.Special acknowledge to I.Weber for providing the NWA 12008 meteorite thin section.This work is part of the doctoral thesis of PG-T(Doctoral Program in Physics at Universitat Autònoma de Barcelona).
文摘The mechanical properties of minerals in planetary materials are not only interesting from a fundamental point of view but also critical to the development of future space missions.Here we present nanoindentation experiments to evaluate the hardness and reduced elastic modulus of olivine,(Mg,Fe)_(2)SiO_(4),in meteorite NWA 12008,a lunar basalt.Our experiments suggest that the olivine grains in this lunaite are softer and more elastic than their terrestrial counterparts.Also,we have performed synchrotron-based high-pressure X-ray diffraction(HP-XRD)measurements to probe the compressibility properties of olivine in this meteorite and,for comparison purposes,of three ordinary chondrites.The HP-XRD results suggest that the axial compressibility of the orthorhombic b lattice parameter of olivine relative to terrestrial olivine is higher in NWA 12008 and also in the highly-shocked Chelyabinsk meteorite.The origin of the observed differences is discussed.A simple model combining the results of both our nanoindentation and HP-XRD measurements allows us to describe the contribution of macroscopic and chemical-bond related effects,both of which are necessary to reproduce the observed elastic modulus softening.Such joint analysis of the mechanical and elastic properties of meteorites and returned samples opens up a new avenue for characterizing these highly interesting materials.
基金supported by Swedish Research Council(Vetenskapsradet,2023-04962).
文摘Space exploration is significant for scientific innovation,resource utilization,and planetary security.Space exploration involves several systems including satellites,space suits,communication systems,and robotics,which have to function under harsh space conditions such as extreme temperatures(−270 to 1650℃),microgravity(10^(-6)g),unhealthy humidity(<20%RH or>60%RH),high atmospheric pressure(~1450 psi),and radiation(4000–5000 mSv).Conventional energy-harvesting technologies(solar cells,fuel cells,and nuclear energy),that are normally used to power these space systems have certain limitations(e.g.,sunlight dependence,weight,degradation,big size,high cost,low capacity,radioactivity,complexity,and low efficiency).The constraints in conventional energy resources have made it imperative to look for non-conventional yet efficient alternatives.A great potential for enhancing efficiency,sustainability,and mission duration in space exploration can be offered by integrating triboelectric nanogenerators(TENGs)with existing energy sources.Recently,the potential of TENG including energy harvesting(from vibrations/movements in satellites and spacecraft),self-powered sensing,and microgravity,for multiple applications in different space missions has been discussed.This review comprehensively covers the use of TENGs for various space applications,such as planetary exploration missions(Mars environment monitoring),manned space equipment,In-orbit robotic operations/collision monitoring,spacecraft’s design and structural health monitoring,Aeronautical systems,and conventional energy harvesting(solar and nuclear).This review also discusses the use of self-powered TENG sensors for deep space object perception.At the same time,this review compares TENGs with conventional energy harvesting technologies for space systems.Lastly,this review talks about energy harvesting in satellites,TENG-based satellite communication systems,and future practical implementation challenges(with possible solutions).
基金the Indian Institute of Technology Bombay’s Post-Doctoral Research Program, vide appointment no. AO/Admn1/33/2018 dated 10.Aug’2018 for providing funding
文摘With rapid advancements in Infra-Red (IR) detection techniques, the range from where the IR-guided missiles are able to lock the target aircraft has increased. To avoid the detection and tracking by modern IR-guided missiles, the aircraft and helicopters also demand progress in its stealth techniques. Hence, study of Infra-Red Signature Suppression (IRSS) systems in aircraft and helicopters has become vital even in design stage. Optical blocking (masking) is one of the effective IRSS techniques used to block the Line- Of-Sight (LOS) of the hot engine parts of the exhaust geometry. This paper reviews the various patents on IR signature suppression systems based on the optical blocking method or a combination of IRSS techniques. The performance penalties generated due to installation of various IRSS methods in aircraft and helicopters are also discussed.
文摘Experimental study of synthetic jet produced by pulsed direct current （DC） discharge is presented. High velocity jet is acti- vated electro-thermally by high frequency pulsed DC discharge in small cavity. A cavity of 2.38 mm diameter cylinder bounded by circular electrode is made in a ceramic plate and a small orifice of 1.78 mm diameter is drilled in the middle of cavity. High frequency pulsed DC discharge instantaneously heats air in the cavity and produces high velocity jet at the exit of the orifice. Schlieren imaging at high framing rate of 100 kHz reveals the presence of supersonic precursor shock followed by the jet emerg- ing from the orifice. The jet velocity reaches as high as about 300 m/s. Jet with smaller cavity volume produces lesser effect and jet velocity reaches maximum at certain cavity volume with given discharge current and orifice size. As duty time of pulse increases from 5 to 20 μs at fixed frequency of 5 kHz, the jet velocity also increases and becomes nearly constant with further increase in duty time. At fixed duty time of 20 μs, higher frequency pulsing of 10 kHz produces degradation of the jet as the discharge pulse continues. The jet developed in this study is demonstrated to be strong enough to penetrate deep into supersonic boundary layer and to produce a bow shock when the jet is issued into Mach 3 supersonic flow.
文摘In this paper, the effects of icing on an NACA 23012 airfoil have been studied. Exper- iments were applied on the clean airfoil, runback ice, horn ice, and spanwise ridge ice at a Reynolds number of 0.6 x 10^6 over angles of attack from -8° to 20% and then results are compared. Gener- ally, it is found that ice accretion on the airfoil can contribute to formation of a flow separation bubble on the upper surface downstream from the leading edge. In addition, it is made clear that spanwise ridge ice provides the greatest negative effect on the aerodynamic performance of the airfoil. In this case, the stall angle drops about 10^6 and the maximum lift coefficient reduces about 50% which is hazardous for an airplane. While horn ice leads to a stall angle drop of about 4°and a maximum lift coefficient reduction to 21%, runback ice has the least effect on the flow pattern around the airfoil and the aerodynamic coefficients so as the stall angle decreases 2% and the maximum lift reduces about 8%.
