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
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
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
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
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
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
Car body design in view of structural performance and lightweighting is a challenging task due to all the performance targets that must be satisfied such as vehicle safety and ride quality.In this paper,material repla...Car body design in view of structural performance and lightweighting is a challenging task due to all the performance targets that must be satisfied such as vehicle safety and ride quality.In this paper,material replacement along with multidisciplinary design optimization strategy is proposed to develop a lightweight car body structure that satisfies the crash and vibration criteria while minimizing weight.Through finite element simulations,full frontal,offset frontal,and side crashes of a full car model are evaluated for peak acceleration,intrusion distance,and the internal energy absorbed by the structural parts.In addition,the first three fundamental natural frequencies are combined with the crash metrics to form the design constraints.The wall thicknesses of twenty-two parts are considered as the design variables.Latin Hypercube Sampling is used to sample the design space,while Radial Basis Function methodology is used to develop surrogate models for the selected crash responses at multiple sites as well as the first three fundamental natural frequencies.A nonlinear surrogate-based optimization problem is formulated for mass minimization under crash and vibration constraints.Using Sequential Quadratic Programming,the design optimization problem is solved with the results verified by finite element simulations.The performance of the optimum design with magnesium parts shows significant weight reduction and better performance compared to the baseline design.展开更多
This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transfo...This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transformation （CST） is employed to generate airfoil coordinates. With this approach, airfoil shape is considered in terms of design variables. The optimization process is constructed by integrating several programs developed by author. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight. The trim condition must be attainable. This paper considers rotor blade configuration for the hover flight condition only, so that the required power in hover is chosen as the objective function of the optimization problem. Sensitivity analysis of each design variable shows that airfoil shape has an important role in rotor performance. The optimum rotor blade reduces the required hover power by 7.4% and increases the figure of merit by 6.5%, which is a good improvement for rotor blade design.展开更多
In present,there are increasing interests in the research on mechanical and control system of underwater vehicles.These ongoing research efforts are motivated by more pervasive applications of such vehicles including ...In present,there are increasing interests in the research on mechanical and control system of underwater vehicles.These ongoing research efforts are motivated by more pervasive applications of such vehicles including seabed oil and gas explorations, scientific deep ocean surveys,military purposes,ecological and water environmental studies,and also entertainments. However,the performance of underwater vehicles with screw type propellers is not prospective in terms of its efficiency and maneuverability.The main weaknesses of this kind of propellers are the production of vortices and sudden generation of thrust forces which make the control of the position and motion difficult. On the other hand,fishes and other aquatic animals are efficient swimmers,posses high maneuverability,are able to follow trajectories,can efficiently stabilize themselves in currents and surges,create less wakes than currently used underwater vehicle, and also have a noiseless propulsion.The fish's locomotion mechanism is mainly controlled by its caudal fin and paired pectoral fins.They are classified into Body and/or Caudal Fin(BCF)and Median and/or paired Pectoral Fins(MPF).The study of highly efficient swimming mechanisms of fish can inspire a better underwater vehicles thruster design and its mechanism. There are few studies on underwater vehicles or fish robots using paired pectoral fins as thruster.The work presented in this paper represents a contribution in this area covering study,design and implementation of locomotion mechanisms of paired pectoral fins in a fish robot.The performance and viability of the biomimetic method for underwater vehicles are highlighted through in-water experiment of a robotic fish.展开更多
This paper proposes a new three-dimensional optimal guidance law for impact time control with seeker’s Field-of-View(FOV) constraint to intercept a stationary target. The proposed guidance law is devised in conjuncti...This paper proposes a new three-dimensional optimal guidance law for impact time control with seeker’s Field-of-View(FOV) constraint to intercept a stationary target. The proposed guidance law is devised in conjunction with the concept of biased Proportional Navigation Guidance(PNG). The guidance law developed leverages a nonlinear function to ensure the boundedness of velocity lead angle to cater to the seeker’s FOV limit. It is proven that the impact time error is nullified in a finite-time under the proposed method. Additionally, the optimality of the biased command is theoretically analyzed. Numerical simulations confirm the superiority of the proposed method and validate the analytic findings.展开更多
This paper addresses the cooperative control problem of multiple unmanned aerial vehicles(multi-UAV)systems.First,a new distributed consensus algorithm for second-order nonlinear multi-agent systems(MAS)is formulated ...This paper addresses the cooperative control problem of multiple unmanned aerial vehicles(multi-UAV)systems.First,a new distributed consensus algorithm for second-order nonlinear multi-agent systems(MAS)is formulated under the leader-following approach.The algorithm provides smooth input signals to the agents’control channels,which avoids the chattering effect generated by the conventional sliding mode-based control protocols.Second,a new formation control scheme is developed by integrating smooth distributed consensus control protocols into the geometric pattern model to achieve three-dimensional formation tracking.The Lyapunov theory is used to prove the stability and convergence of both distributed consensus and formation controllers.The effectiveness of the proposed algorithms is demonstrated through simulation results.展开更多
Multiphase flows are ubiquitous in our daily life and engineering applications. It is important to investigate the flow structures to predict their dynamical behaviors ef- fectively. Lagrangian coherent structures （...Multiphase flows are ubiquitous in our daily life and engineering applications. It is important to investigate the flow structures to predict their dynamical behaviors ef- fectively. Lagrangian coherent structures （LCS） defined by the ridges of the finite-time Lyapunov exponent （FTLE） is utilized in this study to elucidate the multiphase interactions in gaseous jets injected into water and time-dependent turbu- lent cavitation under the framework of Navier-Stokes flow computations. For the gaseous jets injected into water, the highlighted phenomena of the jet transportation can be observed by the LCS method, including expansion, bulge, necking/breaking, and back-attack. Besides, the observation of the LCS reveals that the back-attack phenomenon arises from the fact that the injected gas has difficulties to move toward downstream re- gion after the necking/breaking. For the turbulent cavitating flow, the ridge of the FTLE field can form a LCS to capture the front and boundary of the re-entraint jet when the ad- verse pressure gradient is strong enough. It represents a bar- rier between particles trapped inside the circulation region and those moving downstream. The results indicate that the FFLE field has the potential to identify the structures of mul- tiphase flows, and the LCS can capture the interface/barrier or the vortex/circulation region.展开更多
Micro air vehicles （MAV＇s） have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV＇s＇ small size, flight regi...Micro air vehicles （MAV＇s） have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV＇s＇ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV＇s, inclu- ding massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment （larger dimension） is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.展开更多
In this paper, a new approach has been proposed to identify and model the dynamics of a highly maneuverable fighter aircraft through artificial neural networks（ANNs）. In general, aircraft flight dynamics is consider...In this paper, a new approach has been proposed to identify and model the dynamics of a highly maneuverable fighter aircraft through artificial neural networks（ANNs）. In general, aircraft flight dynamics is considered as a nonlinear and coupled system whose modeling through ANNs, unlike classical approaches, does not require any aerodynamic or propulsion information and a few flight test data seem sufficient. In this study, for identification and modeling of the aircraft dynamics, two known structures of internal and external recurrent neural networks（RNNs） and a proposed structure called hybrid combined recurrent neural network have been used and compared.In order to improve the training process, an appropriate evolutionary method has been applied to simultaneously train and optimize the parameters of ANNs. In this research, it has been shown that six ANNs each with three inputs and one output, trained by flight test data, can model the dynamic behavior of the highly maneuverable aircraft with acceptable accuracy and without any priori knowledge about the system.展开更多
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 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 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.
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%.
基金This material is based on the work supported by the U.S.Department of Energy under Award number DE-EE0002323.
文摘Car body design in view of structural performance and lightweighting is a challenging task due to all the performance targets that must be satisfied such as vehicle safety and ride quality.In this paper,material replacement along with multidisciplinary design optimization strategy is proposed to develop a lightweight car body structure that satisfies the crash and vibration criteria while minimizing weight.Through finite element simulations,full frontal,offset frontal,and side crashes of a full car model are evaluated for peak acceleration,intrusion distance,and the internal energy absorbed by the structural parts.In addition,the first three fundamental natural frequencies are combined with the crash metrics to form the design constraints.The wall thicknesses of twenty-two parts are considered as the design variables.Latin Hypercube Sampling is used to sample the design space,while Radial Basis Function methodology is used to develop surrogate models for the selected crash responses at multiple sites as well as the first three fundamental natural frequencies.A nonlinear surrogate-based optimization problem is formulated for mass minimization under crash and vibration constraints.Using Sequential Quadratic Programming,the design optimization problem is solved with the results verified by finite element simulations.The performance of the optimum design with magnesium parts shows significant weight reduction and better performance compared to the baseline design.
基金co-supported by National Foundation for Science and Technology Development(NAFOSTED) of Vietnam (Project No. 107.04-2012.25)the Agency for Defense Development in the Republic of Korea under contract UD100048JDthe project KARI-University Partnership Program 2009-09-2
文摘This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transformation （CST） is employed to generate airfoil coordinates. With this approach, airfoil shape is considered in terms of design variables. The optimization process is constructed by integrating several programs developed by author. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight. The trim condition must be attainable. This paper considers rotor blade configuration for the hover flight condition only, so that the required power in hover is chosen as the objective function of the optimization problem. Sensitivity analysis of each design variable shows that airfoil shape has an important role in rotor performance. The optimum rotor blade reduces the required hover power by 7.4% and increases the figure of merit by 6.5%, which is a good improvement for rotor blade design.
文摘In present,there are increasing interests in the research on mechanical and control system of underwater vehicles.These ongoing research efforts are motivated by more pervasive applications of such vehicles including seabed oil and gas explorations, scientific deep ocean surveys,military purposes,ecological and water environmental studies,and also entertainments. However,the performance of underwater vehicles with screw type propellers is not prospective in terms of its efficiency and maneuverability.The main weaknesses of this kind of propellers are the production of vortices and sudden generation of thrust forces which make the control of the position and motion difficult. On the other hand,fishes and other aquatic animals are efficient swimmers,posses high maneuverability,are able to follow trajectories,can efficiently stabilize themselves in currents and surges,create less wakes than currently used underwater vehicle, and also have a noiseless propulsion.The fish's locomotion mechanism is mainly controlled by its caudal fin and paired pectoral fins.They are classified into Body and/or Caudal Fin(BCF)and Median and/or paired Pectoral Fins(MPF).The study of highly efficient swimming mechanisms of fish can inspire a better underwater vehicles thruster design and its mechanism. There are few studies on underwater vehicles or fish robots using paired pectoral fins as thruster.The work presented in this paper represents a contribution in this area covering study,design and implementation of locomotion mechanisms of paired pectoral fins in a fish robot.The performance and viability of the biomimetic method for underwater vehicles are highlighted through in-water experiment of a robotic fish.
文摘This paper proposes a new three-dimensional optimal guidance law for impact time control with seeker’s Field-of-View(FOV) constraint to intercept a stationary target. The proposed guidance law is devised in conjunction with the concept of biased Proportional Navigation Guidance(PNG). The guidance law developed leverages a nonlinear function to ensure the boundedness of velocity lead angle to cater to the seeker’s FOV limit. It is proven that the impact time error is nullified in a finite-time under the proposed method. Additionally, the optimality of the biased command is theoretically analyzed. Numerical simulations confirm the superiority of the proposed method and validate the analytic findings.
基金This work was supported by the Deanship of Scientific Research(DSR)at King Abdulaziz University,Jeddah(G-363-135-1438).
文摘This paper addresses the cooperative control problem of multiple unmanned aerial vehicles(multi-UAV)systems.First,a new distributed consensus algorithm for second-order nonlinear multi-agent systems(MAS)is formulated under the leader-following approach.The algorithm provides smooth input signals to the agents’control channels,which avoids the chattering effect generated by the conventional sliding mode-based control protocols.Second,a new formation control scheme is developed by integrating smooth distributed consensus control protocols into the geometric pattern model to achieve three-dimensional formation tracking.The Lyapunov theory is used to prove the stability and convergence of both distributed consensus and formation controllers.The effectiveness of the proposed algorithms is demonstrated through simulation results.
文摘Multiphase flows are ubiquitous in our daily life and engineering applications. It is important to investigate the flow structures to predict their dynamical behaviors ef- fectively. Lagrangian coherent structures （LCS） defined by the ridges of the finite-time Lyapunov exponent （FTLE） is utilized in this study to elucidate the multiphase interactions in gaseous jets injected into water and time-dependent turbu- lent cavitation under the framework of Navier-Stokes flow computations. For the gaseous jets injected into water, the highlighted phenomena of the jet transportation can be observed by the LCS method, including expansion, bulge, necking/breaking, and back-attack. Besides, the observation of the LCS reveals that the back-attack phenomenon arises from the fact that the injected gas has difficulties to move toward downstream re- gion after the necking/breaking. For the turbulent cavitating flow, the ridge of the FTLE field can form a LCS to capture the front and boundary of the re-entraint jet when the ad- verse pressure gradient is strong enough. It represents a bar- rier between particles trapped inside the circulation region and those moving downstream. The results indicate that the FFLE field has the potential to identify the structures of mul- tiphase flows, and the LCS can capture the interface/barrier or the vortex/circulation region.
基金a Multidisciplinary University Research Initiative (MURI) project sponsored by AFOSR
文摘Micro air vehicles （MAV＇s） have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV＇s＇ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV＇s, inclu- ding massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment （larger dimension） is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.
文摘In this paper, a new approach has been proposed to identify and model the dynamics of a highly maneuverable fighter aircraft through artificial neural networks（ANNs）. In general, aircraft flight dynamics is considered as a nonlinear and coupled system whose modeling through ANNs, unlike classical approaches, does not require any aerodynamic or propulsion information and a few flight test data seem sufficient. In this study, for identification and modeling of the aircraft dynamics, two known structures of internal and external recurrent neural networks（RNNs） and a proposed structure called hybrid combined recurrent neural network have been used and compared.In order to improve the training process, an appropriate evolutionary method has been applied to simultaneously train and optimize the parameters of ANNs. In this research, it has been shown that six ANNs each with three inputs and one output, trained by flight test data, can model the dynamic behavior of the highly maneuverable aircraft with acceptable accuracy and without any priori knowledge about the system.
