Past investigations of the hydrodynamic forces on vertical columns have generally been based on rigid structure assumptions.The effects of structural flexibility and geometry characteristics on the hydrodynamic force ...Past investigations of the hydrodynamic forces on vertical columns have generally been based on rigid structure assumptions.The effects of structural flexibility and geometry characteristics on the hydrodynamic force distribution are not well understood.In this study,fluid-structure interaction models are developed for numerical analyses.This modeling technique is verified with an experimental test in the literature using both circular and rectangular cross-sections.A series of material elasticities that present structural properties ranging from rigid to flexible is then used to conduct analyses.This finding indicates that an increase in structural flexibility can decrease the impact force to some extent,but this effect is limited.A concrete bridge pier with fluid flow impact can be considered rigid when it is fixed at the bottom.After that,the effects of the initial downstream water height and the width of water tank on the hydrodynamic force are thoroughly investigated.The results demonstrate that the increase in the downstream water height with a constant upstream water height corresponds to a decreased force.Moreover,the vertical column results in a blockage effect on the fluid flow.The greater the blockage effect,the higher the hydrodynamic force.The blockage effect from the vertical column can be neglected when the tank width is greater than eight times the structural cross-section diameter.展开更多
The demand for lightweight and multifunctional surface structure in high-end equipment is steadily growing.The harmonization between flexibility and electromagnetic tunability has become a significant subject for stea...The demand for lightweight and multifunctional surface structure in high-end equipment is steadily growing.The harmonization between flexibility and electromagnetic tunability has become a significant subject for stealth morphing aircraft.This paper presents a microwave absorbing structure based on the kirigami configuration,aiming at improving the conformality with the negative Poisson’s ratio characteristic and expanding the radar stealth range with tunability.A precise electromagnetic reflectivity model of the impedance surface was established by the inversion method,and an integrated optimization algorithm was employed to optimize the structural parameters based on numerical analysis.Specimens composed of thermoplastic polyurethane elastic colloids and resistive materials were prepared to assess the in-plane mechanical tensile and electromagnetic absorption performances through experimental methods.The results indicate that the original absorption band spans 6.2-11.1 GHz,shifts to 8-18 GHz with stretching at a panel rotation angle of 16°,and remains nearly constant for further stretching.The specimens adhere to complex curved surfaces well in experiments and maintain the electromagnetic absorption performance compared with flat surfaces.This research offers a valuable reference for designing electromagnetic stealth structures that are highly stretchable and adjustable.展开更多
The pushover method for underground structures is a seismic analysis method featured by high calculation accuracy and a simple implementation process.The method has been widely used in seismic design and other related...The pushover method for underground structures is a seismic analysis method featured by high calculation accuracy and a simple implementation process.The method has been widely used in seismic design and other related scientific research;however,the influence of different soil-structure flexibility ratios on the accuracy of this method is still not well understood.In this study,we select the cross-section structures beneath the Daikai subway station as the research object and establish 12 finite element analysis models with different soil-structure flexibility ratios using ABAQUS.All models are computed by the dynamic time-history method or the pushover method.Furthermore,the dynamic time-history solution result is taken as the standard solution,and the precision and application of the pushover analysis method are discussed based on the parameters of peak interlayer displacement and peak internal force of the middle column section.The results show that the soil-structure flexibility ratio has a significant influence on the calculation accuracy of the pushover method,and the calculation accuracy of this method is the most ideal when the soil-structure flexibility is equal to 1.The research results can provide significant references for the seismic design of underground structures or the improvement of simplified seismic analysis methods.展开更多
Inspired that the neck structure can stabilize the head from body movements and external dynamic vibration by the role of intervertebral disc and surrounding muscles,a novel multi-layer structure with nonlinear elasti...Inspired that the neck structure can stabilize the head from body movements and external dynamic vibration by the role of intervertebral disc and surrounding muscles,a novel multi-layer structure with nonlinear elastic components is proposed in this paper.The proposed structure is expected for loading the weight of the end effector and isolating bending vibration with lowfrequency in the range of 0.1 Hz to 1 Hz.First,considering the loading,the potential energy,restoring force,and structural configuration in axial direction are defined.Then,the dynamical restoring force and stiffness for bending are modelled for different structural parameters and configurations after the axial weight.According to the functions of the proposed structure required in applications including loading capacity and bending vibration isolation effectiveness,design criteria are carried out.Due to the realization of high-order quasi-zero stiffness property,the effective isolation band for bending vibration can be extended from about 0.08 Hz.In addition,based on the proposed design criteria,the constructed multi-layer structure displays remarkable dynamical stabilization effectiveness in ultralow frequency band.The proposed structure not only provides the biological explanations for car sickness,nausea,and airsickness of humans,but also solves the bottleneck techniques in bioinspired nonlinear isolation structural design for transverse dynamical stabilization,which has remarkable potential applications in the fields of mechanical arm,sensors in satellite etc.展开更多
Although the simple adaptive control （SAC） is widely studied both in theory and application in flexible space structure control and other control problems, it is restricted by the almost strictly positive real （ASP...Although the simple adaptive control （SAC） is widely studied both in theory and application in flexible space structure control and other control problems, it is restricted by the almost strictly positive real （ASPR） conditions. In most practical control problems, the ASPR conditions are not satisfied. Therefore, based on the SAC theory, this paper proposes a backstepping simple adaptive control algorithm which suits the system with arbitrary relative degree with no need of parallel feed forward compensa- tor. The proposed control algorithm consists of decomposition of the arbitrary relative degree system into a known subsystem and an unknown ASPR subsystem which are connected in cascade, design of constant output feedback controller for the known subsystem, and implementation of backstepping method and SAC of the unknown ASPR subsystem. Inheriting the characteristics of the SAC, this method can be adaptive online for the parameter uncertainties. Then, the application of the proposed controller to large flexible space structure with collocated sensors and actuators is studied, and the simulation results validate the proposed controller. It is a new strategy to apply the classical SAC to high relative degree plants.展开更多
The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously.Recently researches have focused on the unsteady aerodynamic characteristics of flex...The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously.Recently researches have focused on the unsteady aerodynamic characteristics of flexible wings under passive actuation.However,the unsteady aerodynamic characteristics with the fluid-structure interaction effects in the multi-body active actuation process of morphing airfoil deserve further investigation.In this paper,a fluid-structure coupled simulation method for multi-body flexible morphing airfoil with active actuation subsystem was investigated,and the aerodynamic characteristics during deformation were compared with different skin flexibility,flow field environment,actuation mode and actuation time.The numerical results show that for the steady aerodynamic,the skin flexibility can improve the stability efficiency.In the unsteady process,the change trend of the transient lift coefficient and pitching moment are consistent with those of the active drive characteristics,while the instantaneous lift-drag ratio coefficient is greatly affected by the driving mode and can be improved by increasing the driving duration.展开更多
Non-dominated sorting genetic algorithm II（NSGA-II）with multiple constraints handling is employed for multi-objective optimization of the topological structure of telescope skin,in which a bit-matrix is used as the ...Non-dominated sorting genetic algorithm II（NSGA-II）with multiple constraints handling is employed for multi-objective optimization of the topological structure of telescope skin,in which a bit-matrix is used as the representation of a chromosome,and genetic algorithm（GA）operators are introduced based on the matrix.Objectives including mass,in-plane performance,and out-of-plane load-bearing ability of the individuals are obtained by fnite element analysis（FEA）using ANSYS,and the matrix-based optimization algorithm is realized in MATLAB by handling multiple constraints such as structural connectivity and in-plane strain requirements.Feasible confgurations of the support structure are achieved.The results confrm that the matrix-based NSGA-II with multiple constraints handling provides an effective method for two-dimensional multi-objective topology optimization.展开更多
In the present study,the formula calculating ship impact forces on light wharf structures is presented when the elastic deformation of the hull and the pier structures as well as the nonlinear deformation of the fende...In the present study,the formula calculating ship impact forces on light wharf structures is presented when the elastic deformation of the hull and the pier structures as well as the nonlinear deformation of the fender are taken into account. The ship impact forces are statistically analyzed with the Monte-Carlo method according to the known probability distribution types of random variables.Based on the simulated results, the distribution of ship impact forces which is characterized by bimodal distribution can be expressed as the combining probability density function of beta distribution and normal distribution. The corresponding parameters of the probability density function can be estimated with the maximum likelihood method. The results show that ship impact forces on light wharf structures follow the distribution of type I extreme value.The mean coefficient and variation coefficient are 1.11 and 0.008 respectively during 50 years of design reference period.展开更多
As a special type of novel flexible structures, tensegrity holds promise for many potential applications in such fields as materials science, biomechanics, civil and aerospace engineering. Rhombic systems are an impor...As a special type of novel flexible structures, tensegrity holds promise for many potential applications in such fields as materials science, biomechanics, civil and aerospace engineering. Rhombic systems are an important class of tensegrity structures, in which each bar constitutes the longest diagonal of a rhombus of four strings. In this paper, we address the design methods of rhombic structures based on the idea that many tensegrity structures can be constructed by assembling one-bar elementary cells. By analyzing the properties of rhombic cells, we first develop two novel schemes, namely, direct enumeration scheme and cell-substitution scheme. In addition, a facile and efficient method is presented to integrate several rhombic systems into a larger tensegrity structure. To illustrate the applications of these methods, some novel rhombic tensegrity structures are constructed.展开更多
The composite structure with the dielectric elastomer and soft materials is the main form of theactuators in soft robots. However, the theoretical model is hard to obtain due to the nonlinear large deformationof mater...The composite structure with the dielectric elastomer and soft materials is the main form of theactuators in soft robots. However, the theoretical model is hard to obtain due to the nonlinear large deformationof materials. In this paper, a new composite element model is established based on the absolute nodal coordinateformulation. The consistent deformation conditions at the contact interface between two thin plates are deduced.The hyperelastic constitutive model and the dielectric elastomer constitutive model are introduced for the twothin plates. Then the dynamic model is established to study the dynamic behaviors of the composite flexiblestructure with various parameters. The results show that the nonlinear deformation appears obviously whenthe flexible composite plate structure is driven by various voltages, and the warping deformation becomes moreobvious with the increase of the voltage. The width and thickness of the driven thin plate influence the stabilityof the whole structure. With the decrease of the width or thickness, the deformation of the structure is moreconsistent with obvious periodicity, and the control performance is improved. Finally, the structural parametersof the composite structures are optimized to improve the control performance based on the dynamic performance.Additionally, smaller width and thickness parameters are preferred to obtain better performance in the design offlexible actuator of soft robot.展开更多
The local joint flexibility matrix of multibrace tubular joints (uniplanar and multiplanar joints) is defined. The formulation for computing the elements of local flexibility factor matrix of multibrace tubular joints...The local joint flexibility matrix of multibrace tubular joints (uniplanar and multiplanar joints) is defined. The formulation for computing the elements of local flexibility factor matrix of multibrace tubular joints by semi-analytic method is presented in this paper. The stiffening effect of unloaded braces and cross-flexibility between braces are discussed. Using the local flexibility of unibrace joints instead of that of multibrace joints in conventional structural analysis will lead the result to an unsafe side.展开更多
Rotating Space Slender Flexible Structures(RSSFS)are extensively utilized in space operations because of their light weight,mobility,and low energy consumption.To realize the accurate space operation of the RSSFS,it i...Rotating Space Slender Flexible Structures(RSSFS)are extensively utilized in space operations because of their light weight,mobility,and low energy consumption.To realize the accurate space operation of the RSSFS,it is necessary to establish a precise mechanical model and develop a control algorithm with high precision.However,with the application of traditional control strategies,the RSSFS often suffers from the chattering phenomenon,which will aggravate structure vibration.In this paper,novel deformation description is put forward to balance modeling accuracy and computational efficiency of the RSSFS,which is better appropriate for real-time control.Besides,the Neural Network Sliding Mode Control(NNSMC)strategy modified by the hyperbolic tangent(tanh)function is put forward to compensate for modeling errors and reduce the chattering phenomenon,thereby improving the trajectory tracking accuracy of the RSSFS.Firstly,a mathematical model for the RSSFS is developed according to the novel deformation description and the vibration theory of flexible structure.Comparison of the deformation accuracy between different models proves that the novel modeling method proposed has high modeling accuracy.Next,the universal approximation property of the Radial Basis Function(RBF)neural network is put forward to determine and compensate for modeling errors,which consist of higher-order modes and the uncertainties of external disturbances.In addition,the tanh function is proposed as the reaching law in the conventional NNSMC strategy to suppress driving torque oscillation.The control law of modified NNSMC strategy and the adaptive law of weight coefficients are developed according to the Lyapunov theorem to guarantee the RSSFS stability.Finally,the simulation and physical experimental tests of the RSSFS with different control strategies are conducted.Experimental results show that the control law according to the novel deformation description and the modified NNSMC strategy can obtain accurate tracking of the rotation and reduce the vibration of the RSSFS simultaneously.展开更多
The development and rapid usage of numerical codes for fluid-structure interaction(FSI) problems are of great relevance to researchers in many engineering fields such as civil engineering and ocean engineering. This m...The development and rapid usage of numerical codes for fluid-structure interaction(FSI) problems are of great relevance to researchers in many engineering fields such as civil engineering and ocean engineering. This multidisciplinary field known as FSI has been expanded to engineering fields such as offshore structures, tall slender structures and other flexible structures applications. The motivation of this paper is to investigate the numerical model of two-way coupling FSI partitioned flexible plate structure under fluid flow. The adopted partitioned method and approach utilized the advantage of the existing numerical algorithms in solving the two-way coupling fluid and structural interactions. The flexible plate was subjected to a fluid flow which causes large deformation on the fluid domain from the oscillation of the flexible plate. Both fluid and flexible plate are subjected to the interaction of load transfer within two physics by using the strong and weak coupling methods of MFS and Load Transfer Physics Environment, respectively. The oscillation and deformation results have been validated which demonstrate the reliability of both strong and weak method in resolving the two-way coupling problem in contribution of knowledge to the feasibility field study of ocean engineering and civil engineering.展开更多
Due to the shortage of non-renewable energy in the world, China has started to vigorously develop nuclear power construction in recent years. With the introduction of the concept of "modularization" for plan...Due to the shortage of non-renewable energy in the world, China has started to vigorously develop nuclear power construction in recent years. With the introduction of the concept of "modularization" for plant construction, a single nuclear island is divided into several hundred modules for operation. Due to its particularity, nuclear power has put forward more stringent requirements on hoisting technology. The concept of "integral zero deformation" has greatly increased the difficulty of hoisting, especially for large eccentric flexible structures such as cylinder, the control of deformation is of great significance and far-reaching impact on the docking of adjacent modules. Reasonable hoisting technology is a strong guarantee for subsequent safety construction.展开更多
The hydrogen-bonded organic frameworks(HOFs)as a new type of porous framework materials have been widely studied in various areas.However,the lack of appropriate active sites,low intrinsic conductivity,and poor stabil...The hydrogen-bonded organic frameworks(HOFs)as a new type of porous framework materials have been widely studied in various areas.However,the lack of appropriate active sites,low intrinsic conductivity,and poor stability limited their performance in the field of electrocatalysis.Herein,we designed two 2D metal hydrogen-bonded organic frameworks(2D–M–HOF,M=Cu^(2+)or Ni^(2+))with coordination compounds based on 2,3,6,7,14,15-hexahydroxyl cyclotricatechylene and transition metal ions(Cu^(2+)and Ni^(2+)),respectively.The crystal structure of 2D–Cu–HOF is determined by continuous rotation electron diffraction,indicating an undulated 2D hydrogen-bond network with interlayeredπ-πstacking.The flexible structure of 2D–M–HOF leads to the formation of self-adaption interlayered sites,resulting in superior activity and selectivity in the electrocatalytic conversion of CO_(2) to C_(2) products,achieving a total Faradaic efficiency exceeding 80%due to the high-efficiency C–C coupling.The experimental results and density functional calculations verify that the undulated 2D–M–HOF enables the energetically favorable formation of*OCCHO intermediate.This work provides a promising strategy for designing HOF catalysts in electrocatalysis and related processes.展开更多
Two kinds of neuro-fuzzy gust response alleviation control laws are designed for a flexible large-aspect-ratio wing model. Simulations and comparisons of random gust alleviation using the two control laws are performe...Two kinds of neuro-fuzzy gust response alleviation control laws are designed for a flexible large-aspect-ratio wing model. Simulations and comparisons of random gust alleviation using the two control laws are performed. Based on the better neuro-fuzzy control law,experiments and simulations of sinusoidal gust alleviation using one-control-surface control system and two-control-surface control system are developed. The investigations show that the two kinds of neuro-fuzzy gust response alleviation control laws can alleviate random gust responses effectively. The neuro-fuzzy gust response alleviation control law including a modifying factor is better than the other one without it. Further,the better one has good effects on the sinusoidal gust alleviation at different frequencies and flow velocities. The two-control-surface control system has better effects on gust response alleviation than the one-control-surface control system when the gust is strong. The simulation results agree well with the experimental results. These results can be usefully referenced to the design of actual gust alleviation control systems.展开更多
The component synthesis active vibration suppression method （CSVS） can be applied to suppress the vibration of flexible systems. By this method, several same or similar time-varying components are arranged according...The component synthesis active vibration suppression method （CSVS） can be applied to suppress the vibration of flexible systems. By this method, several same or similar time-varying components are arranged according to certain rules along the time axis. The synthesized command can suppress the arbitrary unwanted vibration harmonic while achieving the desired rigid body motion. The number of the components increases rapidly when the number of harmonic vibration is growing. In this article, the CSVS based on zero-placement technique is used to construct the synthesized command to suppress the multi-harmonics simultaneously in the discrete domain. The nature of zero-placement method is to put enough zeros to cancel system poles at necessary points. The designed synthesized command has equal time intervals between each component and which is much easier to be implemented. Using this method, the number of components increases linearly with the increasing of the number of being suppressed harmonics. For the spacecraft with flexible appendages, CSVS based on zero-placement is used to design the time optimal large angle maneuver control strategy. Simulations have verified the validity and superiority of the proposed approach.展开更多
Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion.Metal-organic framework(MOF)with unique structure flexibility is an ideal material to study the thermal exp...Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion.Metal-organic framework(MOF)with unique structure flexibility is an ideal material to study the thermal expansion.This work adopts the high-resolution variable-temperature powder x-ray diffraction to investigate the structure and intrinsic thermal expansion in Sr-MOF([Sr(DMPhH_(2)IDC)_(2)]_n).It has the unique honeycomb structure with one-dimensional(1 D)channels along the c-axis direction,the a-b plane displays layer structure.The thermal expansion behavior has strong relationship with the structure,ZTE appears in the a-b plane and large PTE along the c-axis direction.The possible mechanism is that the a/b layers have enough space for the transverse thermal vibration of polydentate ligands,while along the c-axis direction is not.This work not only reports one interesting zero thermal expansion material,but also provides new understanding for thermal expansion mechanism from the perspective of the structural model.展开更多
Making use of modal characteristics of the natural vibration of flexible structure to design the oscillating wing aircraft is proposed. A series of equations concerning the oscillating wing of flexible structures are ...Making use of modal characteristics of the natural vibration of flexible structure to design the oscillating wing aircraft is proposed. A series of equations concerning the oscillating wing of flexible structures are derived. The kinetic equation for aerodynamic force coupled with elastic movement is set up, and relevant formulae are derived. The unsteady aerodynamic one in that formulae is revised. The design principle, design process and range of application of such oscillating wing analytical method are elaborated. A flexible structural oscillating wing model is set up, and relevant time response analysis and frequency response analysis are conducted. The analytical results indicate that adopting the new-type driving way for the oscillating wing will not have flutter problems and will be able to produce propulsive force. Furthermore, it will consume much less power than the fixed wing for generating the same lift.展开更多
基金The National Natural Science Foundation of China(No.52222804,U21A20154).
文摘Past investigations of the hydrodynamic forces on vertical columns have generally been based on rigid structure assumptions.The effects of structural flexibility and geometry characteristics on the hydrodynamic force distribution are not well understood.In this study,fluid-structure interaction models are developed for numerical analyses.This modeling technique is verified with an experimental test in the literature using both circular and rectangular cross-sections.A series of material elasticities that present structural properties ranging from rigid to flexible is then used to conduct analyses.This finding indicates that an increase in structural flexibility can decrease the impact force to some extent,but this effect is limited.A concrete bridge pier with fluid flow impact can be considered rigid when it is fixed at the bottom.After that,the effects of the initial downstream water height and the width of water tank on the hydrodynamic force are thoroughly investigated.The results demonstrate that the increase in the downstream water height with a constant upstream water height corresponds to a decreased force.Moreover,the vertical column results in a blockage effect on the fluid flow.The greater the blockage effect,the higher the hydrodynamic force.The blockage effect from the vertical column can be neglected when the tank width is greater than eight times the structural cross-section diameter.
基金supported by the National Key Research and Development of China(Grant No.2022YFB4601901)the National Natural Science Foundation of China(Grant Nos.12122202 and 12302078)the Postdoctoral Innovative Talents Support Program of China(Grant No.BX20230470).
文摘The demand for lightweight and multifunctional surface structure in high-end equipment is steadily growing.The harmonization between flexibility and electromagnetic tunability has become a significant subject for stealth morphing aircraft.This paper presents a microwave absorbing structure based on the kirigami configuration,aiming at improving the conformality with the negative Poisson’s ratio characteristic and expanding the radar stealth range with tunability.A precise electromagnetic reflectivity model of the impedance surface was established by the inversion method,and an integrated optimization algorithm was employed to optimize the structural parameters based on numerical analysis.Specimens composed of thermoplastic polyurethane elastic colloids and resistive materials were prepared to assess the in-plane mechanical tensile and electromagnetic absorption performances through experimental methods.The results indicate that the original absorption band spans 6.2-11.1 GHz,shifts to 8-18 GHz with stretching at a panel rotation angle of 16°,and remains nearly constant for further stretching.The specimens adhere to complex curved surfaces well in experiments and maintain the electromagnetic absorption performance compared with flat surfaces.This research offers a valuable reference for designing electromagnetic stealth structures that are highly stretchable and adjustable.
基金sponsored by the National Natural Science Foundation of China(52008206)the China Postdoctoral Science Foundation(2021M690279)。
文摘The pushover method for underground structures is a seismic analysis method featured by high calculation accuracy and a simple implementation process.The method has been widely used in seismic design and other related scientific research;however,the influence of different soil-structure flexibility ratios on the accuracy of this method is still not well understood.In this study,we select the cross-section structures beneath the Daikai subway station as the research object and establish 12 finite element analysis models with different soil-structure flexibility ratios using ABAQUS.All models are computed by the dynamic time-history method or the pushover method.Furthermore,the dynamic time-history solution result is taken as the standard solution,and the precision and application of the pushover analysis method are discussed based on the parameters of peak interlayer displacement and peak internal force of the middle column section.The results show that the soil-structure flexibility ratio has a significant influence on the calculation accuracy of the pushover method,and the calculation accuracy of this method is the most ideal when the soil-structure flexibility is equal to 1.The research results can provide significant references for the seismic design of underground structures or the improvement of simplified seismic analysis methods.
基金supported by National Natural Science Foundation of China(61125306,91016004)Foundation of Ministry of Education of China(20110092110020,20120092110026)the Post-Doctoral Research Funds(1108000137,3208004602)
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.12122208 and 11972254)。
文摘Inspired that the neck structure can stabilize the head from body movements and external dynamic vibration by the role of intervertebral disc and surrounding muscles,a novel multi-layer structure with nonlinear elastic components is proposed in this paper.The proposed structure is expected for loading the weight of the end effector and isolating bending vibration with lowfrequency in the range of 0.1 Hz to 1 Hz.First,considering the loading,the potential energy,restoring force,and structural configuration in axial direction are defined.Then,the dynamical restoring force and stiffness for bending are modelled for different structural parameters and configurations after the axial weight.According to the functions of the proposed structure required in applications including loading capacity and bending vibration isolation effectiveness,design criteria are carried out.Due to the realization of high-order quasi-zero stiffness property,the effective isolation band for bending vibration can be extended from about 0.08 Hz.In addition,based on the proposed design criteria,the constructed multi-layer structure displays remarkable dynamical stabilization effectiveness in ultralow frequency band.The proposed structure not only provides the biological explanations for car sickness,nausea,and airsickness of humans,but also solves the bottleneck techniques in bioinspired nonlinear isolation structural design for transverse dynamical stabilization,which has remarkable potential applications in the fields of mechanical arm,sensors in satellite etc.
基金National Natural Science Foundation of China(10902003)
文摘Although the simple adaptive control （SAC） is widely studied both in theory and application in flexible space structure control and other control problems, it is restricted by the almost strictly positive real （ASPR） conditions. In most practical control problems, the ASPR conditions are not satisfied. Therefore, based on the SAC theory, this paper proposes a backstepping simple adaptive control algorithm which suits the system with arbitrary relative degree with no need of parallel feed forward compensa- tor. The proposed control algorithm consists of decomposition of the arbitrary relative degree system into a known subsystem and an unknown ASPR subsystem which are connected in cascade, design of constant output feedback controller for the known subsystem, and implementation of backstepping method and SAC of the unknown ASPR subsystem. Inheriting the characteristics of the SAC, this method can be adaptive online for the parameter uncertainties. Then, the application of the proposed controller to large flexible space structure with collocated sensors and actuators is studied, and the simulation results validate the proposed controller. It is a new strategy to apply the classical SAC to high relative degree plants.
基金supported by the National Natural Science Foundation of China(Nos.52192633,11872293)the Natural Science Foundation of Shaanxi Province,China(No.2022JC-03)。
文摘The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously.Recently researches have focused on the unsteady aerodynamic characteristics of flexible wings under passive actuation.However,the unsteady aerodynamic characteristics with the fluid-structure interaction effects in the multi-body active actuation process of morphing airfoil deserve further investigation.In this paper,a fluid-structure coupled simulation method for multi-body flexible morphing airfoil with active actuation subsystem was investigated,and the aerodynamic characteristics during deformation were compared with different skin flexibility,flow field environment,actuation mode and actuation time.The numerical results show that for the steady aerodynamic,the skin flexibility can improve the stability efficiency.In the unsteady process,the change trend of the transient lift coefficient and pitching moment are consistent with those of the active drive characteristics,while the instantaneous lift-drag ratio coefficient is greatly affected by the driving mode and can be improved by increasing the driving duration.
基金supported by the National Natural Science Foundation of China(Nos.50905085 and 91116020)the National Science Foundation for Post-doctoral Scientists of China(No.2012M511263)
文摘Non-dominated sorting genetic algorithm II（NSGA-II）with multiple constraints handling is employed for multi-objective optimization of the topological structure of telescope skin,in which a bit-matrix is used as the representation of a chromosome,and genetic algorithm（GA）operators are introduced based on the matrix.Objectives including mass,in-plane performance,and out-of-plane load-bearing ability of the individuals are obtained by fnite element analysis（FEA）using ANSYS,and the matrix-based optimization algorithm is realized in MATLAB by handling multiple constraints such as structural connectivity and in-plane strain requirements.Feasible confgurations of the support structure are achieved.The results confrm that the matrix-based NSGA-II with multiple constraints handling provides an effective method for two-dimensional multi-objective topology optimization.
基金supported by the National High Technology Research and Development Program of China(863 Program,Grant No.2007AA11Z130)
文摘In the present study,the formula calculating ship impact forces on light wharf structures is presented when the elastic deformation of the hull and the pier structures as well as the nonlinear deformation of the fender are taken into account. The ship impact forces are statistically analyzed with the Monte-Carlo method according to the known probability distribution types of random variables.Based on the simulated results, the distribution of ship impact forces which is characterized by bimodal distribution can be expressed as the combining probability density function of beta distribution and normal distribution. The corresponding parameters of the probability density function can be estimated with the maximum likelihood method. The results show that ship impact forces on light wharf structures follow the distribution of type I extreme value.The mean coefficient and variation coefficient are 1.11 and 0.008 respectively during 50 years of design reference period.
基金supported by the National Natural Science Foundation of China (10732050)Tsinghua University (2009THZ02122)the National Basic Research Program of China (973) (2010CB631005)
文摘As a special type of novel flexible structures, tensegrity holds promise for many potential applications in such fields as materials science, biomechanics, civil and aerospace engineering. Rhombic systems are an important class of tensegrity structures, in which each bar constitutes the longest diagonal of a rhombus of four strings. In this paper, we address the design methods of rhombic structures based on the idea that many tensegrity structures can be constructed by assembling one-bar elementary cells. By analyzing the properties of rhombic cells, we first develop two novel schemes, namely, direct enumeration scheme and cell-substitution scheme. In addition, a facile and efficient method is presented to integrate several rhombic systems into a larger tensegrity structure. To illustrate the applications of these methods, some novel rhombic tensegrity structures are constructed.
基金the National Natural Science Foundation of China(No.51775345)。
文摘The composite structure with the dielectric elastomer and soft materials is the main form of theactuators in soft robots. However, the theoretical model is hard to obtain due to the nonlinear large deformationof materials. In this paper, a new composite element model is established based on the absolute nodal coordinateformulation. The consistent deformation conditions at the contact interface between two thin plates are deduced.The hyperelastic constitutive model and the dielectric elastomer constitutive model are introduced for the twothin plates. Then the dynamic model is established to study the dynamic behaviors of the composite flexiblestructure with various parameters. The results show that the nonlinear deformation appears obviously whenthe flexible composite plate structure is driven by various voltages, and the warping deformation becomes moreobvious with the increase of the voltage. The width and thickness of the driven thin plate influence the stabilityof the whole structure. With the decrease of the width or thickness, the deformation of the structure is moreconsistent with obvious periodicity, and the control performance is improved. Finally, the structural parametersof the composite structures are optimized to improve the control performance based on the dynamic performance.Additionally, smaller width and thickness parameters are preferred to obtain better performance in the design offlexible actuator of soft robot.
文摘The local joint flexibility matrix of multibrace tubular joints (uniplanar and multiplanar joints) is defined. The formulation for computing the elements of local flexibility factor matrix of multibrace tubular joints by semi-analytic method is presented in this paper. The stiffening effect of unloaded braces and cross-flexibility between braces are discussed. Using the local flexibility of unibrace joints instead of that of multibrace joints in conventional structural analysis will lead the result to an unsafe side.
基金Supported by the Applied Basic Research Program of Liaoning Province,China(No.2023JH2/101300159)the National Natural Science Foundation of China(No.52275090).
文摘Rotating Space Slender Flexible Structures(RSSFS)are extensively utilized in space operations because of their light weight,mobility,and low energy consumption.To realize the accurate space operation of the RSSFS,it is necessary to establish a precise mechanical model and develop a control algorithm with high precision.However,with the application of traditional control strategies,the RSSFS often suffers from the chattering phenomenon,which will aggravate structure vibration.In this paper,novel deformation description is put forward to balance modeling accuracy and computational efficiency of the RSSFS,which is better appropriate for real-time control.Besides,the Neural Network Sliding Mode Control(NNSMC)strategy modified by the hyperbolic tangent(tanh)function is put forward to compensate for modeling errors and reduce the chattering phenomenon,thereby improving the trajectory tracking accuracy of the RSSFS.Firstly,a mathematical model for the RSSFS is developed according to the novel deformation description and the vibration theory of flexible structure.Comparison of the deformation accuracy between different models proves that the novel modeling method proposed has high modeling accuracy.Next,the universal approximation property of the Radial Basis Function(RBF)neural network is put forward to determine and compensate for modeling errors,which consist of higher-order modes and the uncertainties of external disturbances.In addition,the tanh function is proposed as the reaching law in the conventional NNSMC strategy to suppress driving torque oscillation.The control law of modified NNSMC strategy and the adaptive law of weight coefficients are developed according to the Lyapunov theorem to guarantee the RSSFS stability.Finally,the simulation and physical experimental tests of the RSSFS with different control strategies are conducted.Experimental results show that the control law according to the novel deformation description and the modified NNSMC strategy can obtain accurate tracking of the rotation and reduce the vibration of the RSSFS simultaneously.
文摘The development and rapid usage of numerical codes for fluid-structure interaction(FSI) problems are of great relevance to researchers in many engineering fields such as civil engineering and ocean engineering. This multidisciplinary field known as FSI has been expanded to engineering fields such as offshore structures, tall slender structures and other flexible structures applications. The motivation of this paper is to investigate the numerical model of two-way coupling FSI partitioned flexible plate structure under fluid flow. The adopted partitioned method and approach utilized the advantage of the existing numerical algorithms in solving the two-way coupling fluid and structural interactions. The flexible plate was subjected to a fluid flow which causes large deformation on the fluid domain from the oscillation of the flexible plate. Both fluid and flexible plate are subjected to the interaction of load transfer within two physics by using the strong and weak coupling methods of MFS and Load Transfer Physics Environment, respectively. The oscillation and deformation results have been validated which demonstrate the reliability of both strong and weak method in resolving the two-way coupling problem in contribution of knowledge to the feasibility field study of ocean engineering and civil engineering.
文摘Due to the shortage of non-renewable energy in the world, China has started to vigorously develop nuclear power construction in recent years. With the introduction of the concept of "modularization" for plant construction, a single nuclear island is divided into several hundred modules for operation. Due to its particularity, nuclear power has put forward more stringent requirements on hoisting technology. The concept of "integral zero deformation" has greatly increased the difficulty of hoisting, especially for large eccentric flexible structures such as cylinder, the control of deformation is of great significance and far-reaching impact on the docking of adjacent modules. Reasonable hoisting technology is a strong guarantee for subsequent safety construction.
基金financially supported by the National Natural Science Foundation of China(nos.21971012,61933002,21601015,21625102,21674012,and 81601549)the National Key Research and Development Program of China(2020YFB1506300)Beijing Institute of Technology Research Fund Program for Young Scholars。
文摘The hydrogen-bonded organic frameworks(HOFs)as a new type of porous framework materials have been widely studied in various areas.However,the lack of appropriate active sites,low intrinsic conductivity,and poor stability limited their performance in the field of electrocatalysis.Herein,we designed two 2D metal hydrogen-bonded organic frameworks(2D–M–HOF,M=Cu^(2+)or Ni^(2+))with coordination compounds based on 2,3,6,7,14,15-hexahydroxyl cyclotricatechylene and transition metal ions(Cu^(2+)and Ni^(2+)),respectively.The crystal structure of 2D–Cu–HOF is determined by continuous rotation electron diffraction,indicating an undulated 2D hydrogen-bond network with interlayeredπ-πstacking.The flexible structure of 2D–M–HOF leads to the formation of self-adaption interlayered sites,resulting in superior activity and selectivity in the electrocatalytic conversion of CO_(2) to C_(2) products,achieving a total Faradaic efficiency exceeding 80%due to the high-efficiency C–C coupling.The experimental results and density functional calculations verify that the undulated 2D–M–HOF enables the energetically favorable formation of*OCCHO intermediate.This work provides a promising strategy for designing HOF catalysts in electrocatalysis and related processes.
基金National Natural Science Foundation of China(90716006)
文摘Two kinds of neuro-fuzzy gust response alleviation control laws are designed for a flexible large-aspect-ratio wing model. Simulations and comparisons of random gust alleviation using the two control laws are performed. Based on the better neuro-fuzzy control law,experiments and simulations of sinusoidal gust alleviation using one-control-surface control system and two-control-surface control system are developed. The investigations show that the two kinds of neuro-fuzzy gust response alleviation control laws can alleviate random gust responses effectively. The neuro-fuzzy gust response alleviation control law including a modifying factor is better than the other one without it. Further,the better one has good effects on the sinusoidal gust alleviation at different frequencies and flow velocities. The two-control-surface control system has better effects on gust response alleviation than the one-control-surface control system when the gust is strong. The simulation results agree well with the experimental results. These results can be usefully referenced to the design of actual gust alleviation control systems.
文摘The component synthesis active vibration suppression method （CSVS） can be applied to suppress the vibration of flexible systems. By this method, several same or similar time-varying components are arranged according to certain rules along the time axis. The synthesized command can suppress the arbitrary unwanted vibration harmonic while achieving the desired rigid body motion. The number of the components increases rapidly when the number of harmonic vibration is growing. In this article, the CSVS based on zero-placement technique is used to construct the synthesized command to suppress the multi-harmonics simultaneously in the discrete domain. The nature of zero-placement method is to put enough zeros to cancel system poles at necessary points. The designed synthesized command has equal time intervals between each component and which is much easier to be implemented. Using this method, the number of components increases linearly with the increasing of the number of being suppressed harmonics. For the spacecraft with flexible appendages, CSVS based on zero-placement is used to design the time optimal large angle maneuver control strategy. Simulations have verified the validity and superiority of the proposed approach.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.22071221 and 21905252)the Natural Science Foundation of Henan Province,China(Grant No.212300410086)。
文摘Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion.Metal-organic framework(MOF)with unique structure flexibility is an ideal material to study the thermal expansion.This work adopts the high-resolution variable-temperature powder x-ray diffraction to investigate the structure and intrinsic thermal expansion in Sr-MOF([Sr(DMPhH_(2)IDC)_(2)]_n).It has the unique honeycomb structure with one-dimensional(1 D)channels along the c-axis direction,the a-b plane displays layer structure.The thermal expansion behavior has strong relationship with the structure,ZTE appears in the a-b plane and large PTE along the c-axis direction.The possible mechanism is that the a/b layers have enough space for the transverse thermal vibration of polydentate ligands,while along the c-axis direction is not.This work not only reports one interesting zero thermal expansion material,but also provides new understanding for thermal expansion mechanism from the perspective of the structural model.
基金National Natural Science Foundation of China(10432040, 90716006)
文摘Making use of modal characteristics of the natural vibration of flexible structure to design the oscillating wing aircraft is proposed. A series of equations concerning the oscillating wing of flexible structures are derived. The kinetic equation for aerodynamic force coupled with elastic movement is set up, and relevant formulae are derived. The unsteady aerodynamic one in that formulae is revised. The design principle, design process and range of application of such oscillating wing analytical method are elaborated. A flexible structural oscillating wing model is set up, and relevant time response analysis and frequency response analysis are conducted. The analytical results indicate that adopting the new-type driving way for the oscillating wing will not have flutter problems and will be able to produce propulsive force. Furthermore, it will consume much less power than the fixed wing for generating the same lift.
