The averaged equation of motion for linear acceleration in the BCF swimming mode was derived using the Elongated Body Theory(EBT)through time averaging.An analytical solution for the linear acceleration swimming veloc...The averaged equation of motion for linear acceleration in the BCF swimming mode was derived using the Elongated Body Theory(EBT)through time averaging.An analytical solution for the linear acceleration swimming velocity was obtained,revealing that the average velocity follows a hyperbolic tangent function of time,which can be considered a semi-empirical formula for linear acceleration swimming.The formula’s parameters,such as the steady swimming velocity and the acceleration time constant,can be determined by conducting experiments on linear acceleration,enabling the estimation of drag coefficient,effective added mass,thrust,and drag force.We developed a tensegrity robotic tuna and conducted a linear acceleration experiment.The results confirmed both the averaged equation of motion and its empirical formula,indicating that the formula is not limited by EBT and can be extended to large amplitude swimming and thunniform swimmers with large aspect ratio caudal fins.This provides researchers with an efficient and easy-to-implement method to estimate the swimming thrust and drag forces through linear acceleration experiments,without the need for complex and expensive flow field and force measurement equipment.展开更多
The relationship between forms and forces is one of the main topics of structural morphology. This harmonious coexisting link is very strong for systems in tensegrity state, commonly called ＂tensegrity systems＂. It ...The relationship between forms and forces is one of the main topics of structural morphology. This harmonious coexisting link is very strong for systems in tensegrity state, commonly called ＂tensegrity systems＂. It is currently apparent that, among the tensegrity systems, there also exist cable-bar cells with a discontinuous network of cables. It is possible to design a separate set of cables inside the cable-bar elementary cell and to establish a self-stress state of equilibrium. In this connection, the author of this paper suggested to assume a new Class-Theta tensegrity systems. Each of the basic tensegrity systems termed Class-Theta possesses an external and internal set of tension components. The shape of Greek capital letter 69 （Theta） reflects two sets of such components （two sets of tendons, cables, etc.）. This notation corresponds to Skelton＇s Class-k tensegrity structure. As shown in this paper, the Class-Theta tensegrity cell can exemplify a geometrically and practically useful form for the lightweight and long-span modular structures, mainly but not only in view of civil engineering and architecture.展开更多
A numerical method is presented for the large deflection in elastic analysis of tensegrity structures including both geometric and material nonlinearities.The geometric nonlinearity is considered based on both total L...A numerical method is presented for the large deflection in elastic analysis of tensegrity structures including both geometric and material nonlinearities.The geometric nonlinearity is considered based on both total Lagrangian and updated Lagrangian formulations,while the material nonlinearity is treated through elastoplastic stress-strain relationship.The nonlinear equilibrium equations are solved using an incremental-iterative scheme in conjunction with the modified Newton-Raphson method.A computer program is developed to predict the mechanical responses of tensegrity systems under tensile,compressive and flexural loadings.Numerical results obtained are compared with those reported in the literature to demonstrate the accuracy and efficiency of the proposed program.The flexural behavior of the double layer quadruplex tensegrity grid is sufficiently good for lightweight large-span structural applications.On the other hand,its bending strength capacity is not sensitive to the self-stress level.展开更多
Traditional rigid-body in-pipe robots usually have complex and heavy structures with limited flexibility and adaptability.Although soft in-pipe robots have great improvements in flexibility,they still have manufacturi...Traditional rigid-body in-pipe robots usually have complex and heavy structures with limited flexibility and adaptability.Although soft in-pipe robots have great improvements in flexibility,they still have manufacturing difficulties due to their reliance on high-performance soft materials.Tensegrity structure is a kind of self-stressed spatial structure consisting discrete rigid struts connected by a continuous net of tensional flexible strings,which combines the advantages of both rigid structures and soft structures.By applying tensegrity structures into robotics,this paper proposes a novel worm-like tensegrity robot for moving inside pipes.First,a robot module capable of body deformation is designed based on the concept of tensegrity and its deformation performance is analyzed.Then,the optimal parameters of the module are obtained based on the tensegrity form-finding.The deformation ability of the tensegrity module is tested experimentally.Finally,the worm-like tensegrity robot that can crawl inside pipes is developed by connecting three modules in series.Motion performance and load capacity are tested on the prototype of the worm-like tensegrity robot by experiments of moving in horizontal pipe,vertical pipe,and elbow pipe.Experimental results demonstrate the effectiveness of the proposed design and suggest that the robot has high compliance,mobility,and adaptability although with simple structure and low cost.展开更多
This study performs a novel control effi ciency assessment approach that compares performance of optimal control algorithms regarding vibration of tensegrity structures. Due to complex loading conditions and the inher...This study performs a novel control effi ciency assessment approach that compares performance of optimal control algorithms regarding vibration of tensegrity structures. Due to complex loading conditions and the inherent characteristics of tensegrities, e.g. geometrical nonlinearity, the quantization of control effi ciency in active control of tensegrity constitutes a challenging task especially for diff erent control algorithms. As a fi rst step, an actuator energy input, comprising the strain energy of tensegrity elements and their internal forces work, is set to constant levels for the linearquadratic regulator (LQR). Afterwards, the actuator energy of the linear-quadratic Gaussian (LQG) is iterated with identical actuator energy input in LQR. A double layer tensegrity grid is employed to compare the control effi ciencies between LQR and LQG with fi ve diff erent control scenarios. The results demonstrate the effi ciency and robustness in reducing the dynamic response of tensegrity structures, and a theoretical guideline is provided to search optimal control options in controlling actual tensegrities.展开更多
DNA nanotubes(DNTs)with user-defined shapes and functionalities have potential applications in many fields.So far,compared with numerous experimental studies,there have been only a handful of models on the mechanical ...DNA nanotubes(DNTs)with user-defined shapes and functionalities have potential applications in many fields.So far,compared with numerous experimental studies,there have been only a handful of models on the mechanical properties of such DNTs.This paper aims at presenting a multiscale model to quantify the correlations among the pre-tension states,tensile properties,encapsulation structures of DNTs,and the surrounding factors.First,by combining a statistical worm-like-chain(WLC)model of single DNA deformation and Parsegian's mesoscopic model of DNA liquid crystal free energy,a multiscale tensegrity model is established,and the pre-tension state of DNTs is characterized theoretically for the first time.Then,by using the minimum potential energy principle,the force-extension curve and tensile rigidity of pre-tension DNTs are predicted.Finally,the effects of the encapsulation structure and surrounding factors on the tensile properties of DNTs are studied.The predictions for the tensile behaviors of DNTs can not only reproduce the existing experimental results,but also reveal that the competition of DNA intrachain and interchain interactions in the encapsulation structures determines the pre-tension states of DNTs and their tensile properties.The changes in the pre-tension states and environmental factors make the monotonic or non-monotonic changes in the tensile properties of DNTs under longitudinal loads.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
Conventional manipulators with rigid structures and sti ness actuators have poor flexibility,limited obstacle avoidance capability,and constrained workspace.Some developed flexible or soft manipulators in recent years...Conventional manipulators with rigid structures and sti ness actuators have poor flexibility,limited obstacle avoidance capability,and constrained workspace.Some developed flexible or soft manipulators in recent years have the characteristics of infinite degrees of freedom,high flexibility,environmental adaptability,and extended manipulation capability.However,these existing manipulators still cannot achieve the shrinking motion and independent control of specified segments like the animals,which hinders their applications.In this paper,a flexible bio-tensegrity manipulator,inspired by the longitudinal and transversal muscles of octopus tentacles,was proposed to mimic the shrinking behavior and achieve the variable motion patterns of each segment.Such proposed manipulator uses the elastic spring as the backbone,which is driven by four cables and has one variable structure mechanism in each segment to achieve the independent control of each segment.The variable structure mechanism innovatively contains seven lock-release states to independently control the bending and shrinking motion of each segment.After the kinematic modeling and analysis,one prototype of such bionic flexible manipulator was built and the open-loop control method was proposed.Some proof-of-concept experiments,including the shrinking motion,bending motion,and variable structure motion,were carried out by controlling the length of four cables and changing the lock-release states of the variable structure mechanism,which validate the feasibility and validity of our proposed prototype.Meanwhile,the experimental results show the flexible manipulator can accomplish the bending and shrinking motion with the relative error less than 6.8%through the simple independent control of each segment using the variable structure mechanism.This proposed manipulator has the features of controllable degree-of-freedom in each segment,which extend their environmental adaptability,and manipulation capability.展开更多
基金financial support via the National Natural Science Foundation of China granted No.51275127.
文摘The averaged equation of motion for linear acceleration in the BCF swimming mode was derived using the Elongated Body Theory(EBT)through time averaging.An analytical solution for the linear acceleration swimming velocity was obtained,revealing that the average velocity follows a hyperbolic tangent function of time,which can be considered a semi-empirical formula for linear acceleration swimming.The formula’s parameters,such as the steady swimming velocity and the acceleration time constant,can be determined by conducting experiments on linear acceleration,enabling the estimation of drag coefficient,effective added mass,thrust,and drag force.We developed a tensegrity robotic tuna and conducted a linear acceleration experiment.The results confirmed both the averaged equation of motion and its empirical formula,indicating that the formula is not limited by EBT and can be extended to large amplitude swimming and thunniform swimmers with large aspect ratio caudal fins.This provides researchers with an efficient and easy-to-implement method to estimate the swimming thrust and drag forces through linear acceleration experiments,without the need for complex and expensive flow field and force measurement equipment.
文摘The relationship between forms and forces is one of the main topics of structural morphology. This harmonious coexisting link is very strong for systems in tensegrity state, commonly called ＂tensegrity systems＂. It is currently apparent that, among the tensegrity systems, there also exist cable-bar cells with a discontinuous network of cables. It is possible to design a separate set of cables inside the cable-bar elementary cell and to establish a self-stress state of equilibrium. In this connection, the author of this paper suggested to assume a new Class-Theta tensegrity systems. Each of the basic tensegrity systems termed Class-Theta possesses an external and internal set of tension components. The shape of Greek capital letter 69 （Theta） reflects two sets of such components （two sets of tendons, cables, etc.）. This notation corresponds to Skelton＇s Class-k tensegrity structure. As shown in this paper, the Class-Theta tensegrity cell can exemplify a geometrically and practically useful form for the lightweight and long-span modular structures, mainly but not only in view of civil engineering and architecture.
基金support of the research reported here by Basic Science Research Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Education, Science and Technology (NRF2010-0019373)
文摘A numerical method is presented for the large deflection in elastic analysis of tensegrity structures including both geometric and material nonlinearities.The geometric nonlinearity is considered based on both total Lagrangian and updated Lagrangian formulations,while the material nonlinearity is treated through elastoplastic stress-strain relationship.The nonlinear equilibrium equations are solved using an incremental-iterative scheme in conjunction with the modified Newton-Raphson method.A computer program is developed to predict the mechanical responses of tensegrity systems under tensile,compressive and flexural loadings.Numerical results obtained are compared with those reported in the literature to demonstrate the accuracy and efficiency of the proposed program.The flexural behavior of the double layer quadruplex tensegrity grid is sufficiently good for lightweight large-span structural applications.On the other hand,its bending strength capacity is not sensitive to the self-stress level.
基金National Natural Science Foundation of China,52005293,Yixiang Liu,U20A20201Yixiang Liu,Shandong Provincial Natural Science Foundation,ZR2020QE152+3 种基金Yixiang Liu,Key R&D Program of Hebei Province,China,20311803DYixiang Liu,Key R&D Program of Shandong Province,China,2021CXGC011304Yixiang Liu,Research Project of the State Key Laboratory of Mechanical Transmissions,Chongqing University,SKLMT-MSKFKT-202118Yixiang Liu,Fundamental Research Funds of Shandong University,2021JCG001,Yixiang Liu.
文摘Traditional rigid-body in-pipe robots usually have complex and heavy structures with limited flexibility and adaptability.Although soft in-pipe robots have great improvements in flexibility,they still have manufacturing difficulties due to their reliance on high-performance soft materials.Tensegrity structure is a kind of self-stressed spatial structure consisting discrete rigid struts connected by a continuous net of tensional flexible strings,which combines the advantages of both rigid structures and soft structures.By applying tensegrity structures into robotics,this paper proposes a novel worm-like tensegrity robot for moving inside pipes.First,a robot module capable of body deformation is designed based on the concept of tensegrity and its deformation performance is analyzed.Then,the optimal parameters of the module are obtained based on the tensegrity form-finding.The deformation ability of the tensegrity module is tested experimentally.Finally,the worm-like tensegrity robot that can crawl inside pipes is developed by connecting three modules in series.Motion performance and load capacity are tested on the prototype of the worm-like tensegrity robot by experiments of moving in horizontal pipe,vertical pipe,and elbow pipe.Experimental results demonstrate the effectiveness of the proposed design and suggest that the robot has high compliance,mobility,and adaptability although with simple structure and low cost.
基金Natural Science Foundation of Zhejiang Province under Grant No.LQ19E080013the International Scientific and Technological Cooperation Projects of Shaoxing University under Grant No.2019LGGH1005
文摘This study performs a novel control effi ciency assessment approach that compares performance of optimal control algorithms regarding vibration of tensegrity structures. Due to complex loading conditions and the inherent characteristics of tensegrities, e.g. geometrical nonlinearity, the quantization of control effi ciency in active control of tensegrity constitutes a challenging task especially for diff erent control algorithms. As a fi rst step, an actuator energy input, comprising the strain energy of tensegrity elements and their internal forces work, is set to constant levels for the linearquadratic regulator (LQR). Afterwards, the actuator energy of the linear-quadratic Gaussian (LQG) is iterated with identical actuator energy input in LQR. A double layer tensegrity grid is employed to compare the control effi ciencies between LQR and LQG with fi ve diff erent control scenarios. The results demonstrate the effi ciency and robustness in reducing the dynamic response of tensegrity structures, and a theoretical guideline is provided to search optimal control options in controlling actual tensegrities.
基金Project supported by the National Natural Science Foundation of China(Nos.12172204,11772182,11272193,and 10872121)the Program of Shanghai Municipal Education Commission(No.2019-01-07-00-09-E00018)the Natural Science Foundation of Shanghai of China(No.22Z00142)。
文摘DNA nanotubes(DNTs)with user-defined shapes and functionalities have potential applications in many fields.So far,compared with numerous experimental studies,there have been only a handful of models on the mechanical properties of such DNTs.This paper aims at presenting a multiscale model to quantify the correlations among the pre-tension states,tensile properties,encapsulation structures of DNTs,and the surrounding factors.First,by combining a statistical worm-like-chain(WLC)model of single DNA deformation and Parsegian's mesoscopic model of DNA liquid crystal free energy,a multiscale tensegrity model is established,and the pre-tension state of DNTs is characterized theoretically for the first time.Then,by using the minimum potential energy principle,the force-extension curve and tensile rigidity of pre-tension DNTs are predicted.Finally,the effects of the encapsulation structure and surrounding factors on the tensile properties of DNTs are studied.The predictions for the tensile behaviors of DNTs can not only reproduce the existing experimental results,but also reveal that the competition of DNA intrachain and interchain interactions in the encapsulation structures determines the pre-tension states of DNTs and their tensile properties.The changes in the pre-tension states and environmental factors make the monotonic or non-monotonic changes in the tensile properties of DNTs under longitudinal loads.
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Supported by National Natural Science Foundation of China(Grant Nos.51705066,51805128)Sichuan Science and Technology Program(Grant No.2019YFG0343)Fundamental Research Funds for the Central Universities of China(Grant Nos.ZYGX2019J041,ZYGX2016KYQD137).
文摘Conventional manipulators with rigid structures and sti ness actuators have poor flexibility,limited obstacle avoidance capability,and constrained workspace.Some developed flexible or soft manipulators in recent years have the characteristics of infinite degrees of freedom,high flexibility,environmental adaptability,and extended manipulation capability.However,these existing manipulators still cannot achieve the shrinking motion and independent control of specified segments like the animals,which hinders their applications.In this paper,a flexible bio-tensegrity manipulator,inspired by the longitudinal and transversal muscles of octopus tentacles,was proposed to mimic the shrinking behavior and achieve the variable motion patterns of each segment.Such proposed manipulator uses the elastic spring as the backbone,which is driven by four cables and has one variable structure mechanism in each segment to achieve the independent control of each segment.The variable structure mechanism innovatively contains seven lock-release states to independently control the bending and shrinking motion of each segment.After the kinematic modeling and analysis,one prototype of such bionic flexible manipulator was built and the open-loop control method was proposed.Some proof-of-concept experiments,including the shrinking motion,bending motion,and variable structure motion,were carried out by controlling the length of four cables and changing the lock-release states of the variable structure mechanism,which validate the feasibility and validity of our proposed prototype.Meanwhile,the experimental results show the flexible manipulator can accomplish the bending and shrinking motion with the relative error less than 6.8%through the simple independent control of each segment using the variable structure mechanism.This proposed manipulator has the features of controllable degree-of-freedom in each segment,which extend their environmental adaptability,and manipulation capability.
