The dynamics of the moving-with-constant-velocity internal pressure acting on the inner surface of the hollow circular cylinder surrounded by an infinite elastic medium is studied within the scope of the piecewise hom...The dynamics of the moving-with-constant-velocity internal pressure acting on the inner surface of the hollow circular cylinder surrounded by an infinite elastic medium is studied within the scope of the piecewise homogeneous body model by employing the exact field equations of the linear theory of elastodynamics.It is assumed that the internal pressure is point-located with respect to the cylinder axis and is axisymmetric in the circumferential direction.Moreover,it is assumed that shear-spring type imperfect contact conditions on the interface between the cylinder and surrounding elastic medium are satisfied.The focus is on the influence of the mentioned imperfectness on the critical velocity of the moving load and this is the main contribution and difference of the present paper the related other ones.The other difference of the present work from the related other ones is the study of the response of the interface stresses to the load moving velocity,distribution of these stresses with respect to the axial coordinates and to the time.At the same time,the present work contains detail analyses of the influence of problem parameters such as the ratio of modulus of elasticity,the ratio of the cylinder thickness to the cylinder radius,and the shear-spring type parameter which characterizes the degree of the contact imperfection on the values of the critical velocity and stress distribution.Corresponding numerical results are presented and discussed.In particular,it is established that the values of the critical velocity of the moving pressure decrease with the external radius of the cylinder under constant thickness of that.展开更多
The estimation of the Number of Sources(NoS)is a significant challenge in signal processing,particularly due to the impact of colored noise on the performance of NoS estimation.This paper proposes a Multidimensional F...The estimation of the Number of Sources(NoS)is a significant challenge in signal processing,particularly due to the impact of colored noise on the performance of NoS estimation.This paper proposes a Multidimensional Feature Network(MFNet)which is designed for NoS estimation by extracting features of the sampled received signals and Sampled Covariance Matrix(SCM).The MFNet treats the raw signal and the SCM as two different types of data,and is able to achieve NoS estimation under colored noise and imperfect array.MFNet employs the Gated Recurrent Unit(GRU)to capture sequential information from the original signal data and to construct the Pseudo Covariance Matrix(PCM).Subsequently,various dimensional features,including eigenvalues and the Gerschgorin disk radius,are extracted from both the PCM and SCM,which are then jointly input into the subsequent network.An overall accuracy of 82%can be achieved after network training.The ablation experimental results demonstrate the effectiveness of multiple inputs.And simulation results demonstrate that the proposed MFNet achieves higher estimation accuracy compared to existing algorithms and exhibits greater robustness against colored noise.展开更多
Addressing the limitations of inadequate stochastic disturbance characterization during wind turbine degradation processes that result in constrained modeling accuracy,replacement-based maintenance practices that devi...Addressing the limitations of inadequate stochastic disturbance characterization during wind turbine degradation processes that result in constrained modeling accuracy,replacement-based maintenance practices that deviate from actual operational conditions,and static maintenance strategies that fail to adapt to accelerated deterioration trends leading to suboptimal remaining useful life utilization,this study proposes a Time-Based Incomplete Maintenance(TBIM)strategy incorporating reliability constraints through stochastic differential equations(SDE).By quantifying stochastic interference via Brownian motion terms and characterizing nonlinear degradation features through state influence rate functions,a high-precision SDE degradation model is constructed,achieving 16%residual reduction compared to conventional ordinary differential equation(ODE)methods.The introduction of age reduction factors and failure rate growth factors establishes an incomplete maintenance mechanism that transcends traditional“as-good-as-new”assumptions,with the TBIM model demonstrating an additional 8.5%residual reduction relative to baseline SDE approaches.A dynamic maintenance interval optimization model driven by dual parameters—preventive maintenance threshold R_(p) and replacement threshold R_(r)—is designed to achieve synergistic optimization of equipment reliability and maintenance economics.Experimental validation demonstrates that the optimized TBIM extends equipment lifespan by 4.4%and reducesmaintenance costs by 4.16%at R_(p)=0.80,while achieving 17.2%lifespan enhancement and 14.6%cost reduction at R_(p)=0.90.This methodology provides a solution for wind turbine preventive maintenance that integrates condition sensitivity with strategic foresight.展开更多
Over-the-air computation(AirComp)enables federated learning(FL)to rapidly aggregate local models at the central server using waveform superposition property of wireless channel.In this paper,a robust transmission sche...Over-the-air computation(AirComp)enables federated learning(FL)to rapidly aggregate local models at the central server using waveform superposition property of wireless channel.In this paper,a robust transmission scheme for an AirCompbased FL system with imperfect channel state information(CSI)is proposed.To model CSI uncertainty,an expectation-based error model is utilized.The main objective is to maximize the number of selected devices that meet mean-squared error(MSE)requirements for model broadcast and model aggregation.The problem is formulated as a combinatorial optimization problem and is solved in two steps.First,the priority order of devices is determined by a sparsity-inducing procedure.Then,a feasibility detection scheme is used to select the maximum number of devices to guarantee that the MSE requirements are met.An alternating optimization(AO)scheme is used to transform the resulting nonconvex problem into two convex subproblems.Numerical results illustrate the effectiveness and robustness of the proposed scheme.展开更多
This study aims to investigate the propagation of harmonic waves in nonlocal magneto-electro-elastic(MEE)laminated composites with interface stress imperfections using an analytical approach.The pseudo-Stroh formulati...This study aims to investigate the propagation of harmonic waves in nonlocal magneto-electro-elastic(MEE)laminated composites with interface stress imperfections using an analytical approach.The pseudo-Stroh formulation and nonlocal theory proposed by Eringen were adopted to derive the propagator matrix for each layer.Both the propagator and interface matrices were formulated to determine the recursive fields.Subsequently,the dispersion equation was obtained by imposing traction-free and magneto-electric circuit open boundary conditions on the top and bottom surfaces of the plate.Dispersion curves,mode shapes,and natural frequencies were calculated for sandwich plates composed of BaTiO3 and CoFe2O4.Numerical simulations revealed that both interface stress and the nonlocal effect influenced the tuning of the dispersion curve and mode shape for the given layup.The nonlocal effect caused a significant decrease in the dispersion curves,particularly in the high-frequency regions.Additionally,compared to the nonlocal effect,the interface stress exerted a greater influence on the mode shapes.The generalized analytical framework developed in this study provides an effective tool for both the theoretical analysis and practical design of MEE composite laminates.展开更多
This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary ...This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary conditions,the system is subject to the combined external lateral loads and internal pulsating fluid excitations.The nonlinear dynamic model is established with the Euler-Lagrange equations and then systematically discretized via the Galerkin method.The multi-scale analysis reveals how material properties and geometric imperfections influence the internal resonance.Particular emphasis is placed on elucidating,through the modal energy analysis,the energy exchange mechanisms between the first two vibration modes.展开更多
Based on the objective reality of channel estimation error,this paper introduces a novel artificial noise(AN)aided spatial modulation(SM)secrecyenhancing scheme under imperfect channel state information(CSI).In the pr...Based on the objective reality of channel estimation error,this paper introduces a novel artificial noise(AN)aided spatial modulation(SM)secrecyenhancing scheme under imperfect channel state information(CSI).In the proposed scheme,SM is used to activate one antenna from the transmit antennas,and the information symbols will be transmitted with the designed AN at each timeslot.By utilizing the legitimate channel’s imperfect CSI,AN is generated across two adjacent timeslots.Because the CSI is known at the legitimate receiver,then it can perfectly cancel the AN.However,the eavesdropper knows nothing of the legitimate channel’s CSI,so it can not recover any useful information from the AN.At the receiver,a new detection scheme that detects across two adjacent timeslots is also proposed.With imperfect CSI,the secrecy rate of the proposed scheme is derived over Rayleigh fading channels in order to investigate the performance.Moreover,based on the secrecy performance analysis,the lower bound of the ergodic secrecy rate(ESR),the corresponding closed form of the lower bound,and the approximated expression are also derived.The simulation results verified in this paper prove that the proposed scheme with imperfect CSI can achieve satisfactory performance.展开更多
The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanica...The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanical,aerospace,marine,and civil engineering applications due to their ability to enhance bending stiffness with minimal additional weight.Under high loads or stress concentrations,localized structural failures can initiate global buckling in stiffened panels.This study investigates how such defects affect the critical buckling load,stiffness,and thickness of stiffened panels.Two finite element analyses were conducted:a linear analysis to identify the initial buckling mode and a nonlinear analysis using the Riks algorithm in Abaqus CAE,incorporating localized imperfections.The simulations show that material and geometric defects can reduce buckling resistance depending on their severity.展开更多
Based on the theoretical representation of piezoelectric quasicrystal,a generalized dynamic model is built to represent the transmission of wave aspects in surface acoustic pulse nano-devices.Surface elasticity,surfac...Based on the theoretical representation of piezoelectric quasicrystal,a generalized dynamic model is built to represent the transmission of wave aspects in surface acoustic pulse nano-devices.Surface elasticity,surface piezoelectricity,and surface permittivity help to include the surface effect,which equals additional thin sheets.It is shown that,under certain assumptions,this generalized dynamic model may be simplified to a few classical examples that are appropriate for both macro and nano-scale applications.In the current work,surface piezoelectricity is used to develop a theoretical model for shear horizontal(SH)waves where it contains the surface piezoelectricity theory and a linear spring model to quantitatively and qualitatively explore SH waves in an orthotropic piezoelectric quasicrystal layer overlying an elastic framework(Model I),a piezoelectric quasi-crystal nano substrate,and an orthotropic piezoelectric quasicrystal half-space(Model II).The theoretical model stimulates the numerical results,which establish the critical thickness.As the piezoelectric layer’s thickness gets closer to nanometres,surface energy must be included when analyzing dispersion properties.Furthermore,the effects of surface elasticity and density on wave velocity are investigated individually.The authors establish a parameter,precisely the ratio of the physical modulus along the width direction to along the direction of wave travel.The surface effect’s impact on the general char-acteristics of piezoelectric structures is seen as a spring force acting on bulk boundaries.Analytical presentation of frequency equations for both symmetric and anti-symmetric waves pertains to the case of an electrical short circuit in Model II.The project aims to analyze SH waves in orthogonal anisotropic,transversely isotropic piezoelectric layered nanostructures,providing a practical mathematical tool for surface effects analysis and adaptability to other wave types,including Rayleigh waves and acoustic surface waves.展开更多
The uplink massive multiple-input multiple-output(MIMO)status update system is very concerned about information freshness performance,especially for some central control Internet of Things(IoT)applications.In this con...The uplink massive multiple-input multiple-output(MIMO)status update system is very concerned about information freshness performance,especially for some central control Internet of Things(IoT)applications.In this context,age of information(AoI),as the metric of information freshness,gets more and more recognition,and simultaneously,the status packet blocklength plays an important role in improving the information freshness.In this work,we firstly consider a case with perfect channel state information(CSI)at the base station(BS),and derive the closed-form expression of the average AoI by using the Shannon theory.Guided by this,we obtain the tradeoff relationship among the status packet blocklength,transmission time and transmission failure probability.Accordingly,we optimize the status packet blocklength to minimize the average AoI.Then,we consider a more practical case with finite blocklength and imperfect CSI at the BS.In this case,we exploit pilot sequence to assist channel estimation,and derive an approximated closed-form expression of the average AoI according to short packet communication theory.It is found that increasing pilot block-length can improve the accuracy of channel estimation but reduce the frequency of status updates.Hence,we jointly optimize the pilot blocklength and status packet blocklength to improve the AoI performance.Extensive simulation results validate that the proposed methods can achieve almost the same performance as the exhaustive search methods.展开更多
The access of massive Internet of Things(IoT)users poses several challenges for Unmanned Aerial Vehicle(UAV)-aided communications,particularly in terms of security and reliability.This paper investigates a secure and ...The access of massive Internet of Things(IoT)users poses several challenges for Unmanned Aerial Vehicle(UAV)-aided communications,particularly in terms of security and reliability.This paper investigates a secure and robust power allocation scheme for UAV-aided IoT Non-Orthogonal Multiple Access(NOMA)downlink networks with a potential eavesdropper,considering imperfect Channel State Information(CSI).Given the noise uncertainty caused by the UAV’s mobility and the statistical channel estimation error,we formulate a robust optimization problem to maximize the total covert rate of all NOMA users,subject to covertness and rate-based reliability constraints.To solve this optimization problem,we first derive the minimum detection error rate and utilize the statistical characteristics(i.e.,the mean and variance of channel gain errors)to obtain the deterministic covertness and reliability constraints,respectively.We then prove that the problem is concave and determine the optimal power allocation algorithm using the Karush–Kuhn–Tucker conditions.Extensive numerical simulations validate the effectiveness of the proposed algorithm and demonstrate its ability to realize more secure and robust UAV-aided IoT systems.展开更多
According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfe...According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfect inspections, thresholds and repeated intervals are concerned in delay-time models. Since the suggestion by the existing delay-time models that the inspections are implemented in an infinite time span lacks practical value, a de- lay-time model with imperfect inspection within a finite time span is proposed. In the model, the nonhomogenous Poisson process is adopted to obtain the renewal probabilities between two different successive inspections on de- fects or failures. An algorithm is applied based on the Nelder-Mead downhill simplex method to solve the model. Finally, a numerical example proves the validity and effectiveness of the model.展开更多
A two-period model is developed to investigate the competitive effects of targeted advertising with imperfect targeting in a duopolistic market. In the first period, two firms compete in price in order to recognize cu...A two-period model is developed to investigate the competitive effects of targeted advertising with imperfect targeting in a duopolistic market. In the first period, two firms compete in price in order to recognize customers. In the second period, targeted advertising plays an informative role and acts as a price discrimination device. The firms＇ optimal advertising and pricing strategies under imperfect targeting are compared with those under perfect targeting. Equilibrium decisions show that, under imperfect targeting, when the advertising cost is low enough, both firms will choose to target ads at the rivals＇ old segments. This equilibrium, which could not exist under perfect targeting, results in two opposite results. When cost is high, the effect of mis-targeting will soften price competition and increase profits; on the contrary, when cost is low enough, it will lead to aggressive price competition and profit loss with the increase of imperfect targeting, so firms may have incentives to reduce the mis- targeting degree.展开更多
The concept of the imperfection sensitive region is given. The advanced stochastic imperfection method is used to research the imperfection sensitive region of single-layer latticed domes. Taking a K6 single-layer lat...The concept of the imperfection sensitive region is given. The advanced stochastic imperfection method is used to research the imperfection sensitive region of single-layer latticed domes. Taking a K6 single-layer latticed dome with a diameter of 50 m as an example, its imperfection sensitive region is made up of the first 12 kinds of joints. The influence of the imperfections of support joints on the stability of the K6 single-layer latticed dome is negligible. Influences of the joint imperfections of the main rib and the secondary rib on the structural stability are similar. The initial deviations of these joints all greatly lower the critical load of the dome. Results show that the method can analyze the structural imperfection sensitive region quantitatively and accurately.展开更多
In this paper,we present our report on the forced vibration of a bi-layered plate-strip with initial stress resting on a rigid foundation induced by a time-harmonic force.The investigation is carried out according to ...In this paper,we present our report on the forced vibration of a bi-layered plate-strip with initial stress resting on a rigid foundation induced by a time-harmonic force.The investigation is carried out according to the piecewise homogeneous body model with utilizing the three-dimensional linearized theory of elastic waves in initially stressed bodies(TLTEWISB).The materials of the body are chosen to be linearly elastic,homogeneous,and isotropic.The interface between the layers is assumed to be imperfect,and is simulated by the spring-layer model.A similar degree of imperfection on the interface is realized in the normal and tangential directions.The mathematical model for the problem under consideration is designed,and the system of the equations of motion is approximately solved by employing the finite element method(FEM).The numerical results explaining the influence of the parameter that characterizes the degree of corresponding imperfectness on the dynamic response of the plate-strip are presented.In particular,we demonstrate that the distributions of the normal stress become flat,as the normal-spring parameter increases.展开更多
To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerica...To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerical model, and modal analyses were performed. Then, linear buckling analysis,geometric nonlinear stability analysis, geometric nonlinear stability analysis with initial imperfection, and double nonlinear analysis considering material nonlinearity and geometric nonlinearity were discussed in detail to compare the stability performance of the ellipse-like suspen-dome and the single-layer reticulated shell. The results showthat the cable-strut system increases the integrity of the suspen-dome, and moderates the sensibility of the single-layer reticulated shell to initial geometric imperfection. However, it has little influence on integral rigidity, fundamental vibration frequencies, linear ultimate live loads, and geometric nonlinear ultimate live loads without initial imperfection. When considering the material nonlinearity and initial imperfection, a significant reduction occurs in the ultimate stability capacities of these two structures. In this case, the suspen-dome with a lowrise-span ratio is sensitive to the initial imperfection and material nonlinearity. In addition, the distribution pattern of live loads significantly influences the instability modes of the structure, and the uniform live load with full span is not always the most dangerous case.展开更多
The present paper describes experimental investigation on the flow pattern and hydrodynamic effect of underwater gas jets from supersonic and sonic nozzles operated in correct- and imperfect expansion conditions. The ...The present paper describes experimental investigation on the flow pattern and hydrodynamic effect of underwater gas jets from supersonic and sonic nozzles operated in correct- and imperfect expansion conditions. The flow visualizations show that jetting is the flow regime for the submerged gas injection at a high speed in the parameter range under consideration. The obtained results indicate that high-speed gas jets in still water induce large pressure pulsations upstream of the nozzle exit and the presence of shock-cell structure in the over- and under-expanded jets leads to an increase in the intensity of the jet-induced hydrodynamic pressure.展开更多
Servicing is applied periodically in practice with the aim of restoring the system state and prolonging the lifetime. It is generally seen as an imperfect maintenance action which has a chief influence on the maintena...Servicing is applied periodically in practice with the aim of restoring the system state and prolonging the lifetime. It is generally seen as an imperfect maintenance action which has a chief influence on the maintenance strategy. In order to model the maintenance effect of servicing, this study analyzes the deterioration characteristics of system under scheduled servicing. And then the deterioration model is established from the failure mechanism by compound Poisson process. On the basis of the system damage value and failure mechanism, the failure rate refresh factor is proposed to describe the maintenance effect of servicing. A maintenance strategy is developed which combines the benefits of scheduled servicing and preventive maintenance. Then the optimization model is given to determine the optimal servicing period and preventive maintenance time, with an objective to minimize the system expected life-cycle cost per unit time and a constraint on system survival probability for the duration of mission time. Subject to mission time, it can control the ability of accomplishing the mission at any time so as to ensure the high dependability. An example of water pump rotor relating to scheduled servicing is introduced to illustrate the failure rate refresh factor and the proposed maintenance strategy. Compared with traditional methods, the numerical results show that the failure rate refresh factor can describe the maintenance effect of servicing more intuitively and objectively. It also demonstrates that this maintenance strategy can prolong the lifetime, reduce the total lifetime maintenance cost and guarantee the dependability of system.展开更多
文摘The dynamics of the moving-with-constant-velocity internal pressure acting on the inner surface of the hollow circular cylinder surrounded by an infinite elastic medium is studied within the scope of the piecewise homogeneous body model by employing the exact field equations of the linear theory of elastodynamics.It is assumed that the internal pressure is point-located with respect to the cylinder axis and is axisymmetric in the circumferential direction.Moreover,it is assumed that shear-spring type imperfect contact conditions on the interface between the cylinder and surrounding elastic medium are satisfied.The focus is on the influence of the mentioned imperfectness on the critical velocity of the moving load and this is the main contribution and difference of the present paper the related other ones.The other difference of the present work from the related other ones is the study of the response of the interface stresses to the load moving velocity,distribution of these stresses with respect to the axial coordinates and to the time.At the same time,the present work contains detail analyses of the influence of problem parameters such as the ratio of modulus of elasticity,the ratio of the cylinder thickness to the cylinder radius,and the shear-spring type parameter which characterizes the degree of the contact imperfection on the values of the critical velocity and stress distribution.Corresponding numerical results are presented and discussed.In particular,it is established that the values of the critical velocity of the moving pressure decrease with the external radius of the cylinder under constant thickness of that.
基金supported by the National Natural Science Foundation of China(Nos.62171469,62071029)。
文摘The estimation of the Number of Sources(NoS)is a significant challenge in signal processing,particularly due to the impact of colored noise on the performance of NoS estimation.This paper proposes a Multidimensional Feature Network(MFNet)which is designed for NoS estimation by extracting features of the sampled received signals and Sampled Covariance Matrix(SCM).The MFNet treats the raw signal and the SCM as two different types of data,and is able to achieve NoS estimation under colored noise and imperfect array.MFNet employs the Gated Recurrent Unit(GRU)to capture sequential information from the original signal data and to construct the Pseudo Covariance Matrix(PCM).Subsequently,various dimensional features,including eigenvalues and the Gerschgorin disk radius,are extracted from both the PCM and SCM,which are then jointly input into the subsequent network.An overall accuracy of 82%can be achieved after network training.The ablation experimental results demonstrate the effectiveness of multiple inputs.And simulation results demonstrate that the proposed MFNet achieves higher estimation accuracy compared to existing algorithms and exhibits greater robustness against colored noise.
基金supported in part by the National Natural Science Foundation of China(No.52467008)Gansu Provincial Depatment of Education Youth Doctoral Suppo Project(2024QB-051).
文摘Addressing the limitations of inadequate stochastic disturbance characterization during wind turbine degradation processes that result in constrained modeling accuracy,replacement-based maintenance practices that deviate from actual operational conditions,and static maintenance strategies that fail to adapt to accelerated deterioration trends leading to suboptimal remaining useful life utilization,this study proposes a Time-Based Incomplete Maintenance(TBIM)strategy incorporating reliability constraints through stochastic differential equations(SDE).By quantifying stochastic interference via Brownian motion terms and characterizing nonlinear degradation features through state influence rate functions,a high-precision SDE degradation model is constructed,achieving 16%residual reduction compared to conventional ordinary differential equation(ODE)methods.The introduction of age reduction factors and failure rate growth factors establishes an incomplete maintenance mechanism that transcends traditional“as-good-as-new”assumptions,with the TBIM model demonstrating an additional 8.5%residual reduction relative to baseline SDE approaches.A dynamic maintenance interval optimization model driven by dual parameters—preventive maintenance threshold R_(p) and replacement threshold R_(r)—is designed to achieve synergistic optimization of equipment reliability and maintenance economics.Experimental validation demonstrates that the optimized TBIM extends equipment lifespan by 4.4%and reducesmaintenance costs by 4.16%at R_(p)=0.80,while achieving 17.2%lifespan enhancement and 14.6%cost reduction at R_(p)=0.90.This methodology provides a solution for wind turbine preventive maintenance that integrates condition sensitivity with strategic foresight.
文摘Over-the-air computation(AirComp)enables federated learning(FL)to rapidly aggregate local models at the central server using waveform superposition property of wireless channel.In this paper,a robust transmission scheme for an AirCompbased FL system with imperfect channel state information(CSI)is proposed.To model CSI uncertainty,an expectation-based error model is utilized.The main objective is to maximize the number of selected devices that meet mean-squared error(MSE)requirements for model broadcast and model aggregation.The problem is formulated as a combinatorial optimization problem and is solved in two steps.First,the priority order of devices is determined by a sparsity-inducing procedure.Then,a feasibility detection scheme is used to select the maximum number of devices to guarantee that the MSE requirements are met.An alternating optimization(AO)scheme is used to transform the resulting nonconvex problem into two convex subproblems.Numerical results illustrate the effectiveness and robustness of the proposed scheme.
基金supported by the Ministry of Science and Technology Taiwan under Grant No.MOST 109-2628-E-009-002-MY3.
文摘This study aims to investigate the propagation of harmonic waves in nonlocal magneto-electro-elastic(MEE)laminated composites with interface stress imperfections using an analytical approach.The pseudo-Stroh formulation and nonlocal theory proposed by Eringen were adopted to derive the propagator matrix for each layer.Both the propagator and interface matrices were formulated to determine the recursive fields.Subsequently,the dispersion equation was obtained by imposing traction-free and magneto-electric circuit open boundary conditions on the top and bottom surfaces of the plate.Dispersion curves,mode shapes,and natural frequencies were calculated for sandwich plates composed of BaTiO3 and CoFe2O4.Numerical simulations revealed that both interface stress and the nonlocal effect influenced the tuning of the dispersion curve and mode shape for the given layup.The nonlocal effect caused a significant decrease in the dispersion curves,particularly in the high-frequency regions.Additionally,compared to the nonlocal effect,the interface stress exerted a greater influence on the mode shapes.The generalized analytical framework developed in this study provides an effective tool for both the theoretical analysis and practical design of MEE composite laminates.
基金supported by the Shanghai Shuguang Program(No.18SG36)。
文摘This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary conditions,the system is subject to the combined external lateral loads and internal pulsating fluid excitations.The nonlinear dynamic model is established with the Euler-Lagrange equations and then systematically discretized via the Galerkin method.The multi-scale analysis reveals how material properties and geometric imperfections influence the internal resonance.Particular emphasis is placed on elucidating,through the modal energy analysis,the energy exchange mechanisms between the first two vibration modes.
基金supported in part by the Natural Science Project of Hubei Province under Grant 2023AFB383in part by the Open Foundation of Hubei Key Laboratory for High-Efficiency Utilization of Solar Energy and Operation Control of Energy Storage System under Grant HBSEES202107.
文摘Based on the objective reality of channel estimation error,this paper introduces a novel artificial noise(AN)aided spatial modulation(SM)secrecyenhancing scheme under imperfect channel state information(CSI).In the proposed scheme,SM is used to activate one antenna from the transmit antennas,and the information symbols will be transmitted with the designed AN at each timeslot.By utilizing the legitimate channel’s imperfect CSI,AN is generated across two adjacent timeslots.Because the CSI is known at the legitimate receiver,then it can perfectly cancel the AN.However,the eavesdropper knows nothing of the legitimate channel’s CSI,so it can not recover any useful information from the AN.At the receiver,a new detection scheme that detects across two adjacent timeslots is also proposed.With imperfect CSI,the secrecy rate of the proposed scheme is derived over Rayleigh fading channels in order to investigate the performance.Moreover,based on the secrecy performance analysis,the lower bound of the ergodic secrecy rate(ESR),the corresponding closed form of the lower bound,and the approximated expression are also derived.The simulation results verified in this paper prove that the proposed scheme with imperfect CSI can achieve satisfactory performance.
文摘The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanical,aerospace,marine,and civil engineering applications due to their ability to enhance bending stiffness with minimal additional weight.Under high loads or stress concentrations,localized structural failures can initiate global buckling in stiffened panels.This study investigates how such defects affect the critical buckling load,stiffness,and thickness of stiffened panels.Two finite element analyses were conducted:a linear analysis to identify the initial buckling mode and a nonlinear analysis using the Riks algorithm in Abaqus CAE,incorporating localized imperfections.The simulations show that material and geometric defects can reduce buckling resistance depending on their severity.
文摘Based on the theoretical representation of piezoelectric quasicrystal,a generalized dynamic model is built to represent the transmission of wave aspects in surface acoustic pulse nano-devices.Surface elasticity,surface piezoelectricity,and surface permittivity help to include the surface effect,which equals additional thin sheets.It is shown that,under certain assumptions,this generalized dynamic model may be simplified to a few classical examples that are appropriate for both macro and nano-scale applications.In the current work,surface piezoelectricity is used to develop a theoretical model for shear horizontal(SH)waves where it contains the surface piezoelectricity theory and a linear spring model to quantitatively and qualitatively explore SH waves in an orthotropic piezoelectric quasicrystal layer overlying an elastic framework(Model I),a piezoelectric quasi-crystal nano substrate,and an orthotropic piezoelectric quasicrystal half-space(Model II).The theoretical model stimulates the numerical results,which establish the critical thickness.As the piezoelectric layer’s thickness gets closer to nanometres,surface energy must be included when analyzing dispersion properties.Furthermore,the effects of surface elasticity and density on wave velocity are investigated individually.The authors establish a parameter,precisely the ratio of the physical modulus along the width direction to along the direction of wave travel.The surface effect’s impact on the general char-acteristics of piezoelectric structures is seen as a spring force acting on bulk boundaries.Analytical presentation of frequency equations for both symmetric and anti-symmetric waves pertains to the case of an electrical short circuit in Model II.The project aims to analyze SH waves in orthogonal anisotropic,transversely isotropic piezoelectric layered nanostructures,providing a practical mathematical tool for surface effects analysis and adaptability to other wave types,including Rayleigh waves and acoustic surface waves.
基金supported by National Natural Science Foundation of China (Grants No. 62122094 and No.62171464)
文摘The uplink massive multiple-input multiple-output(MIMO)status update system is very concerned about information freshness performance,especially for some central control Internet of Things(IoT)applications.In this context,age of information(AoI),as the metric of information freshness,gets more and more recognition,and simultaneously,the status packet blocklength plays an important role in improving the information freshness.In this work,we firstly consider a case with perfect channel state information(CSI)at the base station(BS),and derive the closed-form expression of the average AoI by using the Shannon theory.Guided by this,we obtain the tradeoff relationship among the status packet blocklength,transmission time and transmission failure probability.Accordingly,we optimize the status packet blocklength to minimize the average AoI.Then,we consider a more practical case with finite blocklength and imperfect CSI at the BS.In this case,we exploit pilot sequence to assist channel estimation,and derive an approximated closed-form expression of the average AoI according to short packet communication theory.It is found that increasing pilot block-length can improve the accuracy of channel estimation but reduce the frequency of status updates.Hence,we jointly optimize the pilot blocklength and status packet blocklength to improve the AoI performance.Extensive simulation results validate that the proposed methods can achieve almost the same performance as the exhaustive search methods.
基金supported in part by the National Natural Science Foundation of China(No.62403500)in part by the Hubei Provincial Natural Science Foundation,China(No.2023AFB202)+4 种基金in part by the Fundamental Research Funds for the Central Universities,South-Central Minzu University,China(No.CZQ23016)in part by the Chunhui Program of Ministry of Education(No.HZKY20220331)in part by the Research Start-up Funds of South-Central Minzu University,China(Nos.YZZ18006,YZY23001)in part by the Fund for Academic Innovation Teams and Research Platform of South-Central Minzu University,China(Nos.XTZ24003,PTZ24001)in part by the Research Matching Grant Scheme from the Research Grants Council of Hong Kong。
文摘The access of massive Internet of Things(IoT)users poses several challenges for Unmanned Aerial Vehicle(UAV)-aided communications,particularly in terms of security and reliability.This paper investigates a secure and robust power allocation scheme for UAV-aided IoT Non-Orthogonal Multiple Access(NOMA)downlink networks with a potential eavesdropper,considering imperfect Channel State Information(CSI).Given the noise uncertainty caused by the UAV’s mobility and the statistical channel estimation error,we formulate a robust optimization problem to maximize the total covert rate of all NOMA users,subject to covertness and rate-based reliability constraints.To solve this optimization problem,we first derive the minimum detection error rate and utilize the statistical characteristics(i.e.,the mean and variance of channel gain errors)to obtain the deterministic covertness and reliability constraints,respectively.We then prove that the problem is concave and determine the optimal power allocation algorithm using the Karush–Kuhn–Tucker conditions.Extensive numerical simulations validate the effectiveness of the proposed algorithm and demonstrate its ability to realize more secure and robust UAV-aided IoT systems.
基金Supported by the National Natural Science Foundation of China(61079013)the Natural Science Fund Project in Jiangsu Province(BK2011737)~~
文摘According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfect inspections, thresholds and repeated intervals are concerned in delay-time models. Since the suggestion by the existing delay-time models that the inspections are implemented in an infinite time span lacks practical value, a de- lay-time model with imperfect inspection within a finite time span is proposed. In the model, the nonhomogenous Poisson process is adopted to obtain the renewal probabilities between two different successive inspections on de- fects or failures. An algorithm is applied based on the Nelder-Mead downhill simplex method to solve the model. Finally, a numerical example proves the validity and effectiveness of the model.
基金The National Natural Science Foundation of China(No.71371050)
文摘A two-period model is developed to investigate the competitive effects of targeted advertising with imperfect targeting in a duopolistic market. In the first period, two firms compete in price in order to recognize customers. In the second period, targeted advertising plays an informative role and acts as a price discrimination device. The firms＇ optimal advertising and pricing strategies under imperfect targeting are compared with those under perfect targeting. Equilibrium decisions show that, under imperfect targeting, when the advertising cost is low enough, both firms will choose to target ads at the rivals＇ old segments. This equilibrium, which could not exist under perfect targeting, results in two opposite results. When cost is high, the effect of mis-targeting will soften price competition and increase profits; on the contrary, when cost is low enough, it will lead to aggressive price competition and profit loss with the increase of imperfect targeting, so firms may have incentives to reduce the mis- targeting degree.
文摘The concept of the imperfection sensitive region is given. The advanced stochastic imperfection method is used to research the imperfection sensitive region of single-layer latticed domes. Taking a K6 single-layer latticed dome with a diameter of 50 m as an example, its imperfection sensitive region is made up of the first 12 kinds of joints. The influence of the imperfections of support joints on the stability of the K6 single-layer latticed dome is negligible. Influences of the joint imperfections of the main rib and the secondary rib on the structural stability are similar. The initial deviations of these joints all greatly lower the critical load of the dome. Results show that the method can analyze the structural imperfection sensitive region quantitatively and accurately.
基金supported by Research Fund of Kastamonu University under project number KUBAP-01/2016-4.
文摘In this paper,we present our report on the forced vibration of a bi-layered plate-strip with initial stress resting on a rigid foundation induced by a time-harmonic force.The investigation is carried out according to the piecewise homogeneous body model with utilizing the three-dimensional linearized theory of elastic waves in initially stressed bodies(TLTEWISB).The materials of the body are chosen to be linearly elastic,homogeneous,and isotropic.The interface between the layers is assumed to be imperfect,and is simulated by the spring-layer model.A similar degree of imperfection on the interface is realized in the normal and tangential directions.The mathematical model for the problem under consideration is designed,and the system of the equations of motion is approximately solved by employing the finite element method(FEM).The numerical results explaining the influence of the parameter that characterizes the degree of corresponding imperfectness on the dynamic response of the plate-strip are presented.In particular,we demonstrate that the distributions of the normal stress become flat,as the normal-spring parameter increases.
基金The National Key Technology R&D Program of China(No.2012BAJ03B06)the National Natural Science Foundation of China(No.51308105)+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the Fundamental Research Funds for the Southeast University(No.KYLX_0152,SJLX_0084,KYLX_0149)
文摘To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerical model, and modal analyses were performed. Then, linear buckling analysis,geometric nonlinear stability analysis, geometric nonlinear stability analysis with initial imperfection, and double nonlinear analysis considering material nonlinearity and geometric nonlinearity were discussed in detail to compare the stability performance of the ellipse-like suspen-dome and the single-layer reticulated shell. The results showthat the cable-strut system increases the integrity of the suspen-dome, and moderates the sensibility of the single-layer reticulated shell to initial geometric imperfection. However, it has little influence on integral rigidity, fundamental vibration frequencies, linear ultimate live loads, and geometric nonlinear ultimate live loads without initial imperfection. When considering the material nonlinearity and initial imperfection, a significant reduction occurs in the ultimate stability capacities of these two structures. In this case, the suspen-dome with a lowrise-span ratio is sensitive to the initial imperfection and material nonlinearity. In addition, the distribution pattern of live loads significantly influences the instability modes of the structure, and the uniform live load with full span is not always the most dangerous case.
文摘The present paper describes experimental investigation on the flow pattern and hydrodynamic effect of underwater gas jets from supersonic and sonic nozzles operated in correct- and imperfect expansion conditions. The flow visualizations show that jetting is the flow regime for the submerged gas injection at a high speed in the parameter range under consideration. The obtained results indicate that high-speed gas jets in still water induce large pressure pulsations upstream of the nozzle exit and the presence of shock-cell structure in the over- and under-expanded jets leads to an increase in the intensity of the jet-induced hydrodynamic pressure.
基金supported by the National Defence Preresearch Foundation of China(Nos.51327020105,51304010206)
文摘Servicing is applied periodically in practice with the aim of restoring the system state and prolonging the lifetime. It is generally seen as an imperfect maintenance action which has a chief influence on the maintenance strategy. In order to model the maintenance effect of servicing, this study analyzes the deterioration characteristics of system under scheduled servicing. And then the deterioration model is established from the failure mechanism by compound Poisson process. On the basis of the system damage value and failure mechanism, the failure rate refresh factor is proposed to describe the maintenance effect of servicing. A maintenance strategy is developed which combines the benefits of scheduled servicing and preventive maintenance. Then the optimization model is given to determine the optimal servicing period and preventive maintenance time, with an objective to minimize the system expected life-cycle cost per unit time and a constraint on system survival probability for the duration of mission time. Subject to mission time, it can control the ability of accomplishing the mission at any time so as to ensure the high dependability. An example of water pump rotor relating to scheduled servicing is introduced to illustrate the failure rate refresh factor and the proposed maintenance strategy. Compared with traditional methods, the numerical results show that the failure rate refresh factor can describe the maintenance effect of servicing more intuitively and objectively. It also demonstrates that this maintenance strategy can prolong the lifetime, reduce the total lifetime maintenance cost and guarantee the dependability of system.
