In general, the seismic response analysis in earthquake engineering assumes that the vibration parameters of the target and the contact surface of the external media are identical,i. e., single point input. However, e...In general, the seismic response analysis in earthquake engineering assumes that the vibration parameters of the target and the contact surface of the external media are identical,i. e., single point input. However, earthquake energy has an attenuation phenomenon in wave propagation,so a wide range of soil slopes and the external medium contact surface of different input points on motion are not identical. If we consider single point input only, it may not correspond with reality, so it is necessary to carry out research on multi-point input methods. Based on the 2-D slope model,single-point input and multi-point input are performed respectively to analyze and compare their similarities and differences in the perspectives of the characteristics of seismic response of soil layer and plastic zone distribution to provide a reference for the seismic design of slopes. The results show that in the perspective of soil seismic response analysis,the peak acceleration output and peak velocity output under multi-point input are greater than the peak values under single point input at the same monitoring point,the peak appearing time is also earlier than that of the single point input; in terms of the plastic zone distribution,the multi-point effect is manifested as the presence of more obvious tensile shear failures; in the perspective of safety coefficient,the safety coefficient under each multi-point input is smaller than that of single point input,a difference of about 7 % or so. In summary,multi-point input is more reasonable and practical than single point input,so multi-point input should be considered in seismic design.展开更多
This study investigates the impact of welding heat input on weldments of modified 9Cr-1Mo(P91)steel,a high-strength material that requires high-energy welding processes like submerged arc welding.In the as-welded cond...This study investigates the impact of welding heat input on weldments of modified 9Cr-1Mo(P91)steel,a high-strength material that requires high-energy welding processes like submerged arc welding.In the as-welded condition,P91 steel welds primarily consist of untempered martensite,which transforms into tempered martensite during post-weld heat treatment(PWHT).Electron spectro-scopy analysis reveals the presence of M_(23)C_(6) and MX carbonitride precipitates at grain boundaries.Increasing the heat input leads to greater quantities of precipitates in the prior austenite grain boundaries,which can affect material properties.Weldment hardness profiles exhibit modest improvements,while ultimate tensile strength and toughness decrease with higher welding heat input,poten-tially due to the formation of a ferritic phase.Residual stress distributions are noticeably influenced by the welding heat input level.展开更多
To analyze the correlation between the input energy parameters(V_(E))and typical intensity measures(IMs)of offshore ground motions,based on 273 earthquake events recorded by the K-NET in Japan,892 offshore ground moti...To analyze the correlation between the input energy parameters(V_(E))and typical intensity measures(IMs)of offshore ground motions,based on 273 earthquake events recorded by the K-NET in Japan,892 offshore ground motion records with moment magnitudes from 4.0 to 7.0 were used in this study.Residuals obtained through a ground motion model were calculated and analyzed for the correlation between V_(E) and amplitude,duration,frequency content and cumulative IMs.The results indicate that PGV and PGD have strong correlation with the V_(E)(T>0.2 s and T>0.4 s),the duration IMs have weakly negative correlation with the V_(E),Sd_(1) has a strong correlation with the V_(E) in the periods of T>0.4 s,T_(g) has a weak correlation with V_(E) and the cumulative IMs have strong correlation with the V_(E).The parametric predictive equations between typical IMs and V_(E) was proposed,and the differences between the prediction equations from the onshore ground motion records were compared.The differences in parametric predicted equations between offshore and onshore ground motions were confirmed in this study.Proposed correlation equations can be applied to offshore probabilistic seismic hazard analysis and the selection of ground motion records by generalized conditional intensity measures.展开更多
This paper proposes a novel multivalued recurrent neural network model driven by external inputs,along with two innovative learning algorithms.By incorporating a multivalued activation function,the proposed model can ...This paper proposes a novel multivalued recurrent neural network model driven by external inputs,along with two innovative learning algorithms.By incorporating a multivalued activation function,the proposed model can achieve multivalued many-to-one associative memory,and the newly developed algorithms enable effective storage of many-to-one patterns in the coefficient matrix while maintaining the indispensability of inputs in many-to-one associative memory.The proposed learning algorithm addresses a critical limitation of existing models which fail to ensure completely erroneous outputs when facing partial input missing in many-to-one associative memory tasks.The methodology is rigorously derived through theoretical analysis,incorporating comprehensive verification of both the existence and global exponential stability of equilibrium points.Demonstrative examples are provided in the paper to show the effectiveness of the proposed theory.展开更多
Enhancing the stability and performance of practical control systems in the presence of nonlinearity,time delay,and uncertainty remains a significant challenge.Particularly,a class of strict-feedback nonlinear uncerta...Enhancing the stability and performance of practical control systems in the presence of nonlinearity,time delay,and uncertainty remains a significant challenge.Particularly,a class of strict-feedback nonlinear uncertain systems characterized by unknown control directions and time-varying input delay lacks comprehensive solutions.In this paper,we propose an observerbased adaptive tracking controller to address this gap.Neural networks are utilized to handle uncertainty,and a unique coordinate transformation is employed to untangle the coupling between input delay and unknown control directions.Subsequently,a new auxiliary signal counters the impact of time-varying input delay,while a Nussbaum function is introduced to solve the problem of unknown control directions.The leverage of an advanced dynamic surface control technique avoids the“complexity explosion”and reduces boundary layer errors.Synthesizing these techniques ensures that all the closed-loop signals are semi-globally uniformly ultimately bounded(SGUUB),and the tracking error converges to a small region around the origin by selecting suitable parameters.Simulation examples are provided to demonstrate the feasibility of the proposed approach.展开更多
This paper addresses the lane-keeping control problem for autonomous ground vehicles subject to input saturation and uncertain system parameters.An enhanced adaptive terminal sliding mode based prescribed performance ...This paper addresses the lane-keeping control problem for autonomous ground vehicles subject to input saturation and uncertain system parameters.An enhanced adaptive terminal sliding mode based prescribed performance control scheme is proposed,which enables the lateral position error of the vehicle to be kept within the prescribed performance boundaries all the time.This is achieved by firstly introducing an improved performance function into the controller design such that the stringent initial condition requirements can be relaxed,which further allows the global prescribed performance control result,and then,developing a multivariable adaptive terminal sliding mode based controller such that both input saturation and parameter uncertainties are handled effectively,which further ensures the robust lane-keeping control.Finally,the proposed control strategy is validated through numerical simulations,demonstrating its effectiveness.展开更多
The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input ...The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input welding of 400 kJ/cm.With increasing the Ti/N ratio from 2.7 to 5.7,the cuboid nano-sized particles are formed,and their number density increases.The area fractions of ductile intragranular acicular ferrites(IAFs)have the highest value and the area fractions of brittle microstructures of ferrite side plates and upper bainites have the lowest value in TN30 steel.With the Ti/N ratio of about 3.0,the HAZ of steel plate has the best low-temperature toughness.With increasing the Ti/N ratio from 2.7 to 5.7,the PAG sizes after the high-temperature laser scanning confocal microscopy observation decrease linearly with increasing the number densities of nano-sized particles.The PAG size of TN30 steel is between 100 and 150μm,which is conducive to the nucleation of IAFs.展开更多
This paper investigates the secure impulsive consensus of Lipschitz-type nonlinear multi-agent systems(MASs) with input saturation. According to the coupling of input saturation and denial of service(DoS) attacks, imp...This paper investigates the secure impulsive consensus of Lipschitz-type nonlinear multi-agent systems(MASs) with input saturation. According to the coupling of input saturation and denial of service(DoS) attacks, impulsive control for MASs becomes extremely challenging. Considering general DoS attacks,this paper provides the sufficient conditions for the almost sure consensus of the MASs with input saturation, where the error system can achieve almost sure local exponential stability.Through linear matrix inequalities(LMIs), the relation between the trajectory boundary and DoS attacks is characterized, and the trajectory boundary is estimated. Furthermore, an optimization method of the domain of attraction is proposed to maximize the size. And a non-conservative and practical boundary is proposed to characterize the effect of DoS attacks on MASs. Finally, considering a multi-agent system with typical Chua's circuit dynamic model, an example is provided to illustrate the theorems' correctness.展开更多
This paper proposes an adaptive neural network sliding mode control based on fractional-order ultra-local model for n-DOF upper-limb exoskeleton in presence of uncertainties,external disturbances and input deadzone.Co...This paper proposes an adaptive neural network sliding mode control based on fractional-order ultra-local model for n-DOF upper-limb exoskeleton in presence of uncertainties,external disturbances and input deadzone.Considering the model complexity and input deadzone,a fractional-order ultra-local model is proposed to formulate the original dynamic system for simple controller design.Firstly,the control gain of ultra-local model is considered as a constant.The fractional-order sliding mode technique is designed to stabilize the closed-loop system,while fractional-order time-delay estimation is combined with neural network to estimate the lumped disturbance.Correspondingly,a fractional-order ultra-local model-based neural network sliding mode controller(FO-NNSMC) is proposed.Secondly,to avoid disadvantageous effect of improper gain selection on the control performance,the control gain of ultra-local model is considered as an unknown parameter.Then,the Nussbaum technique is introduced into the FO-NNSMC to deal with the stability problem with unknown gain.Correspondingly,a fractional-order ultra-local model-based adaptive neural network sliding mode controller(FO-ANNSMC) is proposed.Moreover,the stability analysis of the closed-loop system with the proposed method is presented by using the Lyapunov theory.Finally,with the co-simulations on virtual prototype of 7-DOF iReHave upper-limb exoskeleton and experiments on 2-DOF upper-limb exoskeleton,the obtained compared results illustrate the effectiveness and superiority of the proposed method.展开更多
The multi-point dynamic aggregation(MPDA)problem is a challenging real-world problem.In the MPDA problem,the demands of tasks keep changing with their inherent incremental rates,while a heterogeneous robot fleet is re...The multi-point dynamic aggregation(MPDA)problem is a challenging real-world problem.In the MPDA problem,the demands of tasks keep changing with their inherent incremental rates,while a heterogeneous robot fleet is required to travel between these tasks to change the time-varying state of each task.The robots are allowed to collaborate on the same task or work separately until all tasks are completed.It is challenging to generate an effective task execution plan due to the tight coupling between robots abilities and tasks'incremental rates,and the complexity of robot collaboration.For effectiveness consideration,we use the variable length encoding to avoid redundancy in the solution space.We creatively use the adaptive large neighborhood search(ALNS)framework to solve the MPDA problem.In the proposed algorithm,high-quality initial solutions are generated through multiple problem-specific solution construction heuristics.These heuristics are also used to fix the broken solution in the novel integrated decoding-construction repair process of the ALNS framework.The results of statistical analysis by the Wilcoxon rank-sum test demonstrate that the proposed ALNS can obtain better task execution plans than some state-of-the-art algorithms in most MPDA instances.展开更多
High speed sintering,a new powder-bed fusion additive manufacturing technology,utilizes infrared lights(IR)to intensely heat and melt polymer powders.The presence of defects such as porosity,which is associated with p...High speed sintering,a new powder-bed fusion additive manufacturing technology,utilizes infrared lights(IR)to intensely heat and melt polymer powders.The presence of defects such as porosity,which is associated with particle coalescence,is highly dependdent on the level of energy input.This study investigate the influcence of energy input on porosity and its subsequent effects on the mechanical properties and microstructures of PEBA parts.The parts were manufactured with a variety of lamp powers,resulting in a range of energy input levels spanning from low to high.Subsequebtly,they underwent testing using Archimedes’method,followed by tensile testing.The porosity,mechanical characteristics,and energy input exhibit a strong correlation;inadequate energy input was the primary cause of pore formation.Using the reduced IR light power resulted in the following outcomes:porosity,ultimate tensile strength,and elongation of 1.37%,7.6 MPa,and 194.2%,respectively.When the energy input was further increased,the porosity was reduced to as low as 0.05%and the ultimate tensile strength and elongation were increased to their peak values of 233.8%and 9.1 MPa,respectively.展开更多
An observer-based adaptive backstepping boundary control is proposed for vibration control of flexible offshore riser systems with unknown nonlinear input dead zone and uncertain environmental disturbances.The control...An observer-based adaptive backstepping boundary control is proposed for vibration control of flexible offshore riser systems with unknown nonlinear input dead zone and uncertain environmental disturbances.The control algorithm can update the control law online through real-time data to make the controller adapt to the environment and improve the control precision.Specifically,based on the adaptive backstepping framework,virtual control laws and Lyapunov functions are designed for each subsystem.Three direction interference observers are designed to track the timevarying boundary disturbance.On this basis,the inverse of the dead zone and linear state transformation are used to compensate for the original system and eliminate the adverse effects of the dead zone.In addition,the stability of the closed-loop system is proven by Lyapunov stability theory.All the system states are bounded,and the vibration offset of the riser converges to a small area of the initial position.Finally,four examples of flexible marine risers are simulated in MATLAB to verify the effectiveness of the proposed controller.展开更多
Sandwich structures are vulnerable to multi-point impacts,and such impacts can result in a reduction in residual strength even catastrophic accident.Therefore,the multi-point impact behaviors of PMI foam sandwich stru...Sandwich structures are vulnerable to multi-point impacts,and such impacts can result in a reduction in residual strength even catastrophic accident.Therefore,the multi-point impact behaviors of PMI foam sandwich structure are investigated and studied using experimental and numerical coupled methods.Three impact energy levels and five Distances Between Impact Positions(DBIP)are considered in details,and representative impact characteristics are compared to reveal the association between Compression After Impact(CAI)strength and DBIP.Results indicate that the interference between the multi-point impact events has a dominant effect on CAI strength when DBIP is small,and the variation in bending stiffness induced by the boundary effect is the dominant factor affecting CAI strength when DBIP ranges from 20 mm to 60 mm.In addition,matrix damage represents the primary damage mode in multi-point impact,and the calculated ratio of energy absorbed by the top face sheet and honeycomb core,in relation to the total absorbed energy,serves as a clear indicator of the damage severity experienced by both components.This work is enlightening for the structural design of impact-resistant composites.展开更多
In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm s...In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm separately.Meanwhile,the microstructure and mechanical properties were evaluated to explore the toughening mechanism of weld metal.Results show that a lot of active inclusions are obtained in the weld metal due to the design idea of low carbon and oxide metallurgy,which contributes to the generation of numerous fine and interlocking acicular ferrite.The acicular ferrite volume ratio of weld metal exceeds 60%.Moreover,the impact energy at-40℃ surpasses 115 J and the crack tip opening displacement value at-10℃ is more than 0.2 mm under three heat inputs owing to the role of acicular ferrite,of which 85 kJ/cm is the best.The martensite-austenite constituents are minor in size and the microstructure of the weld metal in reheated zone is dominated by small massive equiaxed ferrite,without impairing the toughness.As the heat input increases,the content of acicular ferrite drops and then rises;the impact toughness and fracture toughness first worsen consequently and then stabilize on account of the dramatic expansion of the proeutectoid ferrite size.展开更多
The evolution of microstructure and local properties near the welding interface is essential for the service safety of dissimilar metal welded joints between nickel-based alloy(NA) and low-alloy steel(LA).In this work...The evolution of microstructure and local properties near the welding interface is essential for the service safety of dissimilar metal welded joints between nickel-based alloy(NA) and low-alloy steel(LA).In this work,NA filler metal was deposited on LA substrate under different heat inputs by tungsten inert gas(TIG) welding.Microstructural characterization and microhardness tests were carried out near the prepared cladding interfaces.Optical and scanning electron microscopes show the lack of evident hardening transition layer along the welding interface.As the heat input increases,the mean hardness of the deposited layer also increases remarkably due to the rising dilution rate.Microstructural characterization shows a significant composition gradient across the cladding interface,but the diffusion gradient is limited to a small range.Under high heat input,a planar grain zone is generated along the interface due to the large temperature gradient across the interface region.展开更多
The welding interface is crucial to the service safety of dissimilar metal weld(DMW)joints between stainless steel(SS)and low alloy(LA)steel.Different status of welding interfaces was prepared by cladding SS consumabl...The welding interface is crucial to the service safety of dissimilar metal weld(DMW)joints between stainless steel(SS)and low alloy(LA)steel.Different status of welding interfaces was prepared by cladding SS consumables to LA steel substrates with different heat inputs via tungsten inert gas arc welding(TIG),followed by a series of microstructural characterizations and hardness tests.Results showed that a hardening and transition layer(TL)would be generated along the welding interface,and the width and hardening degree of the TL would increase with the heat input.Meanwhile,heavy load hardness tests showed that highly severe inhomogeneous plastic deformation and the microcrack would be generated in the interfacial region and the welding interface respectively in the highest heat input sample(1.03 kJ/mm).These results indicate that the increase in heat input would deteriorate the bonding performance of DMW joints.Further microstructural observations showed that the higher hardening degree of the highest heat input sample was mainly attributed to the stronger grain boundary,solution,and dislocation strengthening effects.展开更多
This paper investigates the consensus control of multi-agent systems(MASs) with constrained input using the dynamic event-triggered mechanism(ETM).Consider the MASs with small-scale networks where a centralized dynami...This paper investigates the consensus control of multi-agent systems(MASs) with constrained input using the dynamic event-triggered mechanism(ETM).Consider the MASs with small-scale networks where a centralized dynamic ETM with global information of the MASs is first designed.Then,a distributed dynamic ETM which only uses local information is developed for the MASs with large-scale networks.It is shown that the semi-global consensus of the MASs can be achieved by the designed bounded control protocol where the Zeno phenomenon is eliminated by a designable minimum inter-event time.In addition,it is easier to find a trade-off between the convergence rate and the minimum inter-event time by an adjustable parameter.Furthermore,the results are extended to regional consensus of the MASs with the bounded control protocol.Numerical simulations show the effectiveness of the proposed approach.展开更多
In recent years, cyber attacks have posed great challenges to the development of cyber-physical systems. It is of great significance to study secure state estimation methods to ensure the safe and stable operation of ...In recent years, cyber attacks have posed great challenges to the development of cyber-physical systems. It is of great significance to study secure state estimation methods to ensure the safe and stable operation of the system. This paper proposes a secure state estimation for multi-input and multi-output continuous-time linear cyber-physical systems with sparse actuator and sensor attacks. First, for sparse sensor attacks, we propose an adaptive switching mechanism to mitigate the impact of sparse sensor attacks by filtering out their attack modes. Second, an unknown input sliding mode observer is designed to not only observe the system states, sensor attack signals, and measurement noise present in the system but also counteract the effects of sparse actuator attacks through an unknown input matrix. Finally, for the design of an unknown input sliding mode state observer, the feasibility of the observing system is demonstrated by means of Lyapunov functions. Additionally, simulation experiments are conducted to show the effectiveness of this method.展开更多
Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint ...Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.展开更多
Synapse organizers are essential for the development,transmission,and plasticity of synapses.Acting as rare synapse suppressors,the MAM domain containing glycosylphosphatidylinositol anchor(MDGA)proteins contributes t...Synapse organizers are essential for the development,transmission,and plasticity of synapses.Acting as rare synapse suppressors,the MAM domain containing glycosylphosphatidylinositol anchor(MDGA)proteins contributes to synapse organization by inhibiting the formation of the synaptogenic neuroligin-neurexin complex.A previous analysis of MDGA2 mice lacking a single copy of Mdga2 revealed upregulated glutamatergic synapses and behaviors consistent with autism.However,MDGA2 is expressed in diverse cell types and is localized to both excitatory and inhibitory synapses.Differentiating the network versus cell-specific effects of MDGA2 loss-of-function requires a cell-type and brain region-selective strategy.To address this,we generated mice harboring a conditional knockout of Mdga2 restricted to CA1 pyramidal neurons.Here we report that MDGA2 suppresses the density and function of excitatory synapses selectively on pyramidal neurons in the mature hippocampus.Conditional deletion of Mdga2 in CA1 pyramidal neurons of adult mice upregulated miniature and spontaneous excitatory postsynaptic potentials,vesicular glutamate transporter 1 intensity,and neuronal excitability.These effects were limited to glutamatergic synapses as no changes were detected in miniature and spontaneous inhibitory postsynaptic potential properties or vesicular GABA transporter intensity.Functionally,evoked basal synaptic transmission and AMPAR receptor currents were enhanced at glutamatergic inputs.At a behavioral level,memory appeared to be compromised in Mdga2 cKO mice as both novel object recognition and contextual fear conditioning performance were impaired,consistent with deficits in long-term potentiation in the CA3-CA1 pathway.Social affiliation,a behavioral analog of social deficits in autism,was similarly compromised.These results demonstrate that MDGA2 confines the properties of excitatory synapses to CA1 neurons in mature hippocampal circuits,thereby optimizing this network for plasticity,cognition,and social behaviors.展开更多
基金funded by the Program of China Earthquake Science Data Sharing Platform and the Youth Fund(17404031570521)
文摘In general, the seismic response analysis in earthquake engineering assumes that the vibration parameters of the target and the contact surface of the external media are identical,i. e., single point input. However, earthquake energy has an attenuation phenomenon in wave propagation,so a wide range of soil slopes and the external medium contact surface of different input points on motion are not identical. If we consider single point input only, it may not correspond with reality, so it is necessary to carry out research on multi-point input methods. Based on the 2-D slope model,single-point input and multi-point input are performed respectively to analyze and compare their similarities and differences in the perspectives of the characteristics of seismic response of soil layer and plastic zone distribution to provide a reference for the seismic design of slopes. The results show that in the perspective of soil seismic response analysis,the peak acceleration output and peak velocity output under multi-point input are greater than the peak values under single point input at the same monitoring point,the peak appearing time is also earlier than that of the single point input; in terms of the plastic zone distribution,the multi-point effect is manifested as the presence of more obvious tensile shear failures; in the perspective of safety coefficient,the safety coefficient under each multi-point input is smaller than that of single point input,a difference of about 7 % or so. In summary,multi-point input is more reasonable and practical than single point input,so multi-point input should be considered in seismic design.
文摘This study investigates the impact of welding heat input on weldments of modified 9Cr-1Mo(P91)steel,a high-strength material that requires high-energy welding processes like submerged arc welding.In the as-welded condition,P91 steel welds primarily consist of untempered martensite,which transforms into tempered martensite during post-weld heat treatment(PWHT).Electron spectro-scopy analysis reveals the presence of M_(23)C_(6) and MX carbonitride precipitates at grain boundaries.Increasing the heat input leads to greater quantities of precipitates in the prior austenite grain boundaries,which can affect material properties.Weldment hardness profiles exhibit modest improvements,while ultimate tensile strength and toughness decrease with higher welding heat input,poten-tially due to the formation of a ferritic phase.Residual stress distributions are noticeably influenced by the welding heat input level.
基金National Natural Science Foundation of China under Grant No.52478568National Key R&D Program of China under Grant Nos.2021YFC3100701 and 2022YFC3003503the Nature Science Foundation of Hubei Province under Grant No.2023AFA030。
文摘To analyze the correlation between the input energy parameters(V_(E))and typical intensity measures(IMs)of offshore ground motions,based on 273 earthquake events recorded by the K-NET in Japan,892 offshore ground motion records with moment magnitudes from 4.0 to 7.0 were used in this study.Residuals obtained through a ground motion model were calculated and analyzed for the correlation between V_(E) and amplitude,duration,frequency content and cumulative IMs.The results indicate that PGV and PGD have strong correlation with the V_(E)(T>0.2 s and T>0.4 s),the duration IMs have weakly negative correlation with the V_(E),Sd_(1) has a strong correlation with the V_(E) in the periods of T>0.4 s,T_(g) has a weak correlation with V_(E) and the cumulative IMs have strong correlation with the V_(E).The parametric predictive equations between typical IMs and V_(E) was proposed,and the differences between the prediction equations from the onshore ground motion records were compared.The differences in parametric predicted equations between offshore and onshore ground motions were confirmed in this study.Proposed correlation equations can be applied to offshore probabilistic seismic hazard analysis and the selection of ground motion records by generalized conditional intensity measures.
基金supported by the National Natural Science Foundation of China(Grant Nos.62376105,12101208,and 61906072)the Fundamental Research Funds for the Central Universities(Grant No.2662022XXQD001).
文摘This paper proposes a novel multivalued recurrent neural network model driven by external inputs,along with two innovative learning algorithms.By incorporating a multivalued activation function,the proposed model can achieve multivalued many-to-one associative memory,and the newly developed algorithms enable effective storage of many-to-one patterns in the coefficient matrix while maintaining the indispensability of inputs in many-to-one associative memory.The proposed learning algorithm addresses a critical limitation of existing models which fail to ensure completely erroneous outputs when facing partial input missing in many-to-one associative memory tasks.The methodology is rigorously derived through theoretical analysis,incorporating comprehensive verification of both the existence and global exponential stability of equilibrium points.Demonstrative examples are provided in the paper to show the effectiveness of the proposed theory.
基金National Natural Science Foundation of China(62373102)Jiangsu Natural Science Foundation(BK20221455)Anhui Provincial Key Research and Development Project(2022i01020013)。
文摘Enhancing the stability and performance of practical control systems in the presence of nonlinearity,time delay,and uncertainty remains a significant challenge.Particularly,a class of strict-feedback nonlinear uncertain systems characterized by unknown control directions and time-varying input delay lacks comprehensive solutions.In this paper,we propose an observerbased adaptive tracking controller to address this gap.Neural networks are utilized to handle uncertainty,and a unique coordinate transformation is employed to untangle the coupling between input delay and unknown control directions.Subsequently,a new auxiliary signal counters the impact of time-varying input delay,while a Nussbaum function is introduced to solve the problem of unknown control directions.The leverage of an advanced dynamic surface control technique avoids the“complexity explosion”and reduces boundary layer errors.Synthesizing these techniques ensures that all the closed-loop signals are semi-globally uniformly ultimately bounded(SGUUB),and the tracking error converges to a small region around the origin by selecting suitable parameters.Simulation examples are provided to demonstrate the feasibility of the proposed approach.
基金supported in part by the National Key Research and Development Program of China under Grant 2023YFA1011803in part by Natural Science Foundation of Chongqing,China under Grant CSTB2023NSCQ-MSX0588+2 种基金in part by the Fundamental Research Funds for the Central Universities,China under Grant 2023CDJKYJH047in part by the National Natural Science Foundation of China under Grant 62273064,Grant 61991400,Grant 61991403,Grant 61933012,Grant 62250710167,Grant 62203078in part by Innovation Support Program for International Students Returning to China under Grant cx2022016.
文摘This paper addresses the lane-keeping control problem for autonomous ground vehicles subject to input saturation and uncertain system parameters.An enhanced adaptive terminal sliding mode based prescribed performance control scheme is proposed,which enables the lateral position error of the vehicle to be kept within the prescribed performance boundaries all the time.This is achieved by firstly introducing an improved performance function into the controller design such that the stringent initial condition requirements can be relaxed,which further allows the global prescribed performance control result,and then,developing a multivariable adaptive terminal sliding mode based controller such that both input saturation and parameter uncertainties are handled effectively,which further ensures the robust lane-keeping control.Finally,the proposed control strategy is validated through numerical simulations,demonstrating its effectiveness.
基金financially supported by the National Natural Science Foundation of China(52474361).
文摘The effects of Ti/N ratio on the number densities of nano particles,the size of the prior austenite grain(PAG)and the toughness of the heat-affected zone(HAZ)of Mg-deoxidized steels were studied after high heat input welding of 400 kJ/cm.With increasing the Ti/N ratio from 2.7 to 5.7,the cuboid nano-sized particles are formed,and their number density increases.The area fractions of ductile intragranular acicular ferrites(IAFs)have the highest value and the area fractions of brittle microstructures of ferrite side plates and upper bainites have the lowest value in TN30 steel.With the Ti/N ratio of about 3.0,the HAZ of steel plate has the best low-temperature toughness.With increasing the Ti/N ratio from 2.7 to 5.7,the PAG sizes after the high-temperature laser scanning confocal microscopy observation decrease linearly with increasing the number densities of nano-sized particles.The PAG size of TN30 steel is between 100 and 150μm,which is conducive to the nucleation of IAFs.
基金supported by the National Natural Science Foundation of China(62373302,62333009)
文摘This paper investigates the secure impulsive consensus of Lipschitz-type nonlinear multi-agent systems(MASs) with input saturation. According to the coupling of input saturation and denial of service(DoS) attacks, impulsive control for MASs becomes extremely challenging. Considering general DoS attacks,this paper provides the sufficient conditions for the almost sure consensus of the MASs with input saturation, where the error system can achieve almost sure local exponential stability.Through linear matrix inequalities(LMIs), the relation between the trajectory boundary and DoS attacks is characterized, and the trajectory boundary is estimated. Furthermore, an optimization method of the domain of attraction is proposed to maximize the size. And a non-conservative and practical boundary is proposed to characterize the effect of DoS attacks on MASs. Finally, considering a multi-agent system with typical Chua's circuit dynamic model, an example is provided to illustrate the theorems' correctness.
基金supported in part by the National Natural Science Foundation of China (62173182,61773212)the Intergovernmental International Science and Technology Innovation Cooperation Key Project of Chinese National Key R&D Program (2021YFE0102700)。
文摘This paper proposes an adaptive neural network sliding mode control based on fractional-order ultra-local model for n-DOF upper-limb exoskeleton in presence of uncertainties,external disturbances and input deadzone.Considering the model complexity and input deadzone,a fractional-order ultra-local model is proposed to formulate the original dynamic system for simple controller design.Firstly,the control gain of ultra-local model is considered as a constant.The fractional-order sliding mode technique is designed to stabilize the closed-loop system,while fractional-order time-delay estimation is combined with neural network to estimate the lumped disturbance.Correspondingly,a fractional-order ultra-local model-based neural network sliding mode controller(FO-NNSMC) is proposed.Secondly,to avoid disadvantageous effect of improper gain selection on the control performance,the control gain of ultra-local model is considered as an unknown parameter.Then,the Nussbaum technique is introduced into the FO-NNSMC to deal with the stability problem with unknown gain.Correspondingly,a fractional-order ultra-local model-based adaptive neural network sliding mode controller(FO-ANNSMC) is proposed.Moreover,the stability analysis of the closed-loop system with the proposed method is presented by using the Lyapunov theory.Finally,with the co-simulations on virtual prototype of 7-DOF iReHave upper-limb exoskeleton and experiments on 2-DOF upper-limb exoskeleton,the obtained compared results illustrate the effectiveness and superiority of the proposed method.
基金supported in part by the National Outstanding Youth Talents Support Program(No.61822304)the Basic Science Center Program of the NSFC(No.62088101)+2 种基金the Project of Major International(Regional)Joint Research Program of NSFC(No.61720106011)the Shanghai Municipal Science and Technology Major Project(No.2021SHZDZX0100)the Shanghai Municipal Commission of Science and Technology Project(No.19511132101).
文摘The multi-point dynamic aggregation(MPDA)problem is a challenging real-world problem.In the MPDA problem,the demands of tasks keep changing with their inherent incremental rates,while a heterogeneous robot fleet is required to travel between these tasks to change the time-varying state of each task.The robots are allowed to collaborate on the same task or work separately until all tasks are completed.It is challenging to generate an effective task execution plan due to the tight coupling between robots abilities and tasks'incremental rates,and the complexity of robot collaboration.For effectiveness consideration,we use the variable length encoding to avoid redundancy in the solution space.We creatively use the adaptive large neighborhood search(ALNS)framework to solve the MPDA problem.In the proposed algorithm,high-quality initial solutions are generated through multiple problem-specific solution construction heuristics.These heuristics are also used to fix the broken solution in the novel integrated decoding-construction repair process of the ALNS framework.The results of statistical analysis by the Wilcoxon rank-sum test demonstrate that the proposed ALNS can obtain better task execution plans than some state-of-the-art algorithms in most MPDA instances.
基金This work was financially supported by the National Natural Science Foundation of China(No.52275333).
文摘High speed sintering,a new powder-bed fusion additive manufacturing technology,utilizes infrared lights(IR)to intensely heat and melt polymer powders.The presence of defects such as porosity,which is associated with particle coalescence,is highly dependdent on the level of energy input.This study investigate the influcence of energy input on porosity and its subsequent effects on the mechanical properties and microstructures of PEBA parts.The parts were manufactured with a variety of lamp powers,resulting in a range of energy input levels spanning from low to high.Subsequebtly,they underwent testing using Archimedes’method,followed by tensile testing.The porosity,mechanical characteristics,and energy input exhibit a strong correlation;inadequate energy input was the primary cause of pore formation.Using the reduced IR light power resulted in the following outcomes:porosity,ultimate tensile strength,and elongation of 1.37%,7.6 MPa,and 194.2%,respectively.When the energy input was further increased,the porosity was reduced to as low as 0.05%and the ultimate tensile strength and elongation were increased to their peak values of 233.8%and 9.1 MPa,respectively.
基金financially supported by the Sichuan Science and Technology Program(Grant No.2023NSFSC1980)。
文摘An observer-based adaptive backstepping boundary control is proposed for vibration control of flexible offshore riser systems with unknown nonlinear input dead zone and uncertain environmental disturbances.The control algorithm can update the control law online through real-time data to make the controller adapt to the environment and improve the control precision.Specifically,based on the adaptive backstepping framework,virtual control laws and Lyapunov functions are designed for each subsystem.Three direction interference observers are designed to track the timevarying boundary disturbance.On this basis,the inverse of the dead zone and linear state transformation are used to compensate for the original system and eliminate the adverse effects of the dead zone.In addition,the stability of the closed-loop system is proven by Lyapunov stability theory.All the system states are bounded,and the vibration offset of the riser converges to a small area of the initial position.Finally,four examples of flexible marine risers are simulated in MATLAB to verify the effectiveness of the proposed controller.
基金Supported by the National Key R&D Program of China(2023YFB3709602,2023YFB3709603)National Natural Science Foundation of China(12372141)the Key R&D Program in Shaanxi Province(2024GH-ZDXM-27).
文摘Sandwich structures are vulnerable to multi-point impacts,and such impacts can result in a reduction in residual strength even catastrophic accident.Therefore,the multi-point impact behaviors of PMI foam sandwich structure are investigated and studied using experimental and numerical coupled methods.Three impact energy levels and five Distances Between Impact Positions(DBIP)are considered in details,and representative impact characteristics are compared to reveal the association between Compression After Impact(CAI)strength and DBIP.Results indicate that the interference between the multi-point impact events has a dominant effect on CAI strength when DBIP is small,and the variation in bending stiffness induced by the boundary effect is the dominant factor affecting CAI strength when DBIP ranges from 20 mm to 60 mm.In addition,matrix damage represents the primary damage mode in multi-point impact,and the calculated ratio of energy absorbed by the top face sheet and honeycomb core,in relation to the total absorbed energy,serves as a clear indicator of the damage severity experienced by both components.This work is enlightening for the structural design of impact-resistant composites.
基金the Major Science and Technology Innovation Project of Shandong Province(No.2019JZZY020239)。
文摘In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm separately.Meanwhile,the microstructure and mechanical properties were evaluated to explore the toughening mechanism of weld metal.Results show that a lot of active inclusions are obtained in the weld metal due to the design idea of low carbon and oxide metallurgy,which contributes to the generation of numerous fine and interlocking acicular ferrite.The acicular ferrite volume ratio of weld metal exceeds 60%.Moreover,the impact energy at-40℃ surpasses 115 J and the crack tip opening displacement value at-10℃ is more than 0.2 mm under three heat inputs owing to the role of acicular ferrite,of which 85 kJ/cm is the best.The martensite-austenite constituents are minor in size and the microstructure of the weld metal in reheated zone is dominated by small massive equiaxed ferrite,without impairing the toughness.As the heat input increases,the content of acicular ferrite drops and then rises;the impact toughness and fracture toughness first worsen consequently and then stabilize on account of the dramatic expansion of the proeutectoid ferrite size.
文摘The evolution of microstructure and local properties near the welding interface is essential for the service safety of dissimilar metal welded joints between nickel-based alloy(NA) and low-alloy steel(LA).In this work,NA filler metal was deposited on LA substrate under different heat inputs by tungsten inert gas(TIG) welding.Microstructural characterization and microhardness tests were carried out near the prepared cladding interfaces.Optical and scanning electron microscopes show the lack of evident hardening transition layer along the welding interface.As the heat input increases,the mean hardness of the deposited layer also increases remarkably due to the rising dilution rate.Microstructural characterization shows a significant composition gradient across the cladding interface,but the diffusion gradient is limited to a small range.Under high heat input,a planar grain zone is generated along the interface due to the large temperature gradient across the interface region.
文摘The welding interface is crucial to the service safety of dissimilar metal weld(DMW)joints between stainless steel(SS)and low alloy(LA)steel.Different status of welding interfaces was prepared by cladding SS consumables to LA steel substrates with different heat inputs via tungsten inert gas arc welding(TIG),followed by a series of microstructural characterizations and hardness tests.Results showed that a hardening and transition layer(TL)would be generated along the welding interface,and the width and hardening degree of the TL would increase with the heat input.Meanwhile,heavy load hardness tests showed that highly severe inhomogeneous plastic deformation and the microcrack would be generated in the interfacial region and the welding interface respectively in the highest heat input sample(1.03 kJ/mm).These results indicate that the increase in heat input would deteriorate the bonding performance of DMW joints.Further microstructural observations showed that the higher hardening degree of the highest heat input sample was mainly attributed to the stronger grain boundary,solution,and dislocation strengthening effects.
基金supported in part by the National Natural Science Foundation of China(51939001,61976033,62273072)the Natural Science Foundation of Sichuan Province (2022NSFSC0903)。
文摘This paper investigates the consensus control of multi-agent systems(MASs) with constrained input using the dynamic event-triggered mechanism(ETM).Consider the MASs with small-scale networks where a centralized dynamic ETM with global information of the MASs is first designed.Then,a distributed dynamic ETM which only uses local information is developed for the MASs with large-scale networks.It is shown that the semi-global consensus of the MASs can be achieved by the designed bounded control protocol where the Zeno phenomenon is eliminated by a designable minimum inter-event time.In addition,it is easier to find a trade-off between the convergence rate and the minimum inter-event time by an adjustable parameter.Furthermore,the results are extended to regional consensus of the MASs with the bounded control protocol.Numerical simulations show the effectiveness of the proposed approach.
基金supported by the National Science Foundation of China(Nos.62271293,61903238)the Natural Science Foundation of Shandong Province,China(No.ZR2021MF035)the Social Science Planning Project of Shandong Province,China(No.22CYYJ13).
文摘In recent years, cyber attacks have posed great challenges to the development of cyber-physical systems. It is of great significance to study secure state estimation methods to ensure the safe and stable operation of the system. This paper proposes a secure state estimation for multi-input and multi-output continuous-time linear cyber-physical systems with sparse actuator and sensor attacks. First, for sparse sensor attacks, we propose an adaptive switching mechanism to mitigate the impact of sparse sensor attacks by filtering out their attack modes. Second, an unknown input sliding mode observer is designed to not only observe the system states, sensor attack signals, and measurement noise present in the system but also counteract the effects of sparse actuator attacks through an unknown input matrix. Finally, for the design of an unknown input sliding mode state observer, the feasibility of the observing system is demonstrated by means of Lyapunov functions. Additionally, simulation experiments are conducted to show the effectiveness of this method.
文摘Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.
基金supported by the National Natural Science Foundation of China(82001203,82173819,81871012,and 81571263)the Scientific Research Fund of Zhejiang Provincial Education Department(Y201839276)+3 种基金the Scientific Research Foundation of Zhejiang University City College(X-202103)the R&D Project of Zhejiang(2022C03034)the Natural Science Foundation of Zhejiang Province(LQ23C090001)a Canada Research Chair Award(P2018-0246).
文摘Synapse organizers are essential for the development,transmission,and plasticity of synapses.Acting as rare synapse suppressors,the MAM domain containing glycosylphosphatidylinositol anchor(MDGA)proteins contributes to synapse organization by inhibiting the formation of the synaptogenic neuroligin-neurexin complex.A previous analysis of MDGA2 mice lacking a single copy of Mdga2 revealed upregulated glutamatergic synapses and behaviors consistent with autism.However,MDGA2 is expressed in diverse cell types and is localized to both excitatory and inhibitory synapses.Differentiating the network versus cell-specific effects of MDGA2 loss-of-function requires a cell-type and brain region-selective strategy.To address this,we generated mice harboring a conditional knockout of Mdga2 restricted to CA1 pyramidal neurons.Here we report that MDGA2 suppresses the density and function of excitatory synapses selectively on pyramidal neurons in the mature hippocampus.Conditional deletion of Mdga2 in CA1 pyramidal neurons of adult mice upregulated miniature and spontaneous excitatory postsynaptic potentials,vesicular glutamate transporter 1 intensity,and neuronal excitability.These effects were limited to glutamatergic synapses as no changes were detected in miniature and spontaneous inhibitory postsynaptic potential properties or vesicular GABA transporter intensity.Functionally,evoked basal synaptic transmission and AMPAR receptor currents were enhanced at glutamatergic inputs.At a behavioral level,memory appeared to be compromised in Mdga2 cKO mice as both novel object recognition and contextual fear conditioning performance were impaired,consistent with deficits in long-term potentiation in the CA3-CA1 pathway.Social affiliation,a behavioral analog of social deficits in autism,was similarly compromised.These results demonstrate that MDGA2 confines the properties of excitatory synapses to CA1 neurons in mature hippocampal circuits,thereby optimizing this network for plasticity,cognition,and social behaviors.
