The analytical formulations of the velocity and the acceleration of a 2-DOF spherical parallel mechanism are derived by the screw theory. Based on building its dynamics model by the principle of virtual work and recip...The analytical formulations of the velocity and the acceleration of a 2-DOF spherical parallel mechanism are derived by the screw theory. Based on building its dynamics model by the principle of virtual work and reciprocal product of the screw, the equation of the motor moment is obtained. Through the transformation of dynamics model, the configuration space method of the dynamics equation and the corresponding coefficients are presented. Finally, the result of an example shows that the inertia moment and the gravity play a more important role than the coriolis and centrifugal moment, and the former is ten times of the latter in the magnitude. So, the latter can be neglected only when the velocity of mechanism is very slow.展开更多
A study was conducted to investigate the effects of compatibilizers, including Maleic anhydride grafted polypropylene （MA-PP） and maleic anhydride grafted ethylene-propylene-diene copolymer （MA-EPDM）, on wood-flou...A study was conducted to investigate the effects of compatibilizers, including Maleic anhydride grafted polypropylene （MA-PP） and maleic anhydride grafted ethylene-propylene-diene copolymer （MA-EPDM）, on wood-flour/polypropylene （WF/PP） composites. WF/PP composites were prepared by direct extrusion profiles using a twin-screw/single-screw extruder system. DMA analysis showed that the loss factor of composites decreased and the storage modulus improved in the presence of MA-PP, which indicated much better interfacial adhesion between the PP matrix and wood flour filler than in the absence of compatibilizer. Morphological feature based on SEM observation showed that MA-PP and MA-EPDM improved the dispersion of the wood particles in the plastic matrix. MA-EPDM is a soft segment, although it improved the interfacial adhesion, storage modulus decreases with adding of MA-EPDM. As compatibilizer of wood-flour/polypropylene composites, both DMA analysis and SEM feature proved that MA-PP was superior to MA-EPDM.展开更多
Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static me...Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static mechanical behavior of the ballast track in the heavy-haul railway system,numerical simulation models of the ballast bed with USP and without USP are presented in this paper by using the discrete element method(DEM)-multi-flexible body dynamic(MFBD)coupling analysis method.The ballast bed support stiffness test and dynamic displacement tests were carried out on the actual operation of a heavy-haul railway line to verify the validity of the models.The results show that using the USP results in a 43.01%reduction in the ballast bed support stiffness and achieves a more uniform distribution of track loads on the sleepers.It effectively reduces the load borne by the sleeper directly under the wheel load,with a 7.89%reduction in the pressure on the sleeper.Furthermore,the laying of the USP changes the lateral resistance sharing ratio of the ballast bed,significantly reducing the stress level of the ballast bed under train loads,with an average stress reduction of 42.19 kPa.It also reduces the plastic displacement of ballast particles and lowers the peak value of rotational angular velocity by about 50%to 70%,which is conducive to slowing down ballast bed settlement deformation and reducing maintenance costs.In summary,laying the USP has a potential value in enhancing the stability and extending the lifespan of the ballast bed in heavy-haul railway systems.展开更多
As the support mechanism of space-borne antennas,space deployable antenna mechanism belongs to complex multi-closed-loop coupling mechanism,configuration design and dynamic analysis are more difficult than general par...As the support mechanism of space-borne antennas,space deployable antenna mechanism belongs to complex multi-closed-loop coupling mechanism,configuration design and dynamic analysis are more difficult than general parallel mechanism.In this paper,an unequal-length scissors mechanism(ULSM)is proposed by changing the position of the internal rotational joint through a basic scissors mechanism.A scissors hoop-rib truss deployable antenna mechanism(SHRTDAM)is constructed by replacing the parabolic rib with the ULSM.Kinematic analysis of SHRTDAM is conducted,and the degree of freedom(DOF)of the whole antenna mechanism is analyzed based on screw theory,the result showed that it has only one DOF.Velocity and acceleration characteristics of SHRTDAM are obtained by the screw derivative and rotation transformation.Based on Lagrange equation,dynamic model of this mechanism is established,the torque required to drive the mechanism is simulated and verified by Adams and MATLAB software.In addition,a ground experiment prototype of 1.5-m diameter was fabricated and a deployment test is conducted,which demonstrated the mobility and deployment performance of the whole mechanism.The mechanism proposed in this paper can provide a good reference for the design and analysis of large aperture space deployable antennas.展开更多
A mechanical system for quickfeeding shells in gunboat is particularly analyzed from a dynamic view. SD nonlinear structural simulation is completed by means of dynamic explicit finite element method. Analysis results...A mechanical system for quickfeeding shells in gunboat is particularly analyzed from a dynamic view. SD nonlinear structural simulation is completed by means of dynamic explicit finite element method. Analysis results prove that the mechanical structure is feasible substantially, the material of outer surfaces near striking and overstress position should be improved and measures should be taken to avoid parts high temperature. And all analysis results give a principal theoretical basis for further work.展开更多
A new method is presented to analyze multi-degree-of-freedom (MDOF) dynamic systems subjected to an external shock excitation. A two-degree-of-freedom theoretical system with linear characteristics is exemplified to i...A new method is presented to analyze multi-degree-of-freedom (MDOF) dynamic systems subjected to an external shock excitation. A two-degree-of-freedom theoretical system with linear characteristics is exemplified to illustrate the procedure of this method. The equations of motion of the dynamic system are established via matrix method. The dynamic responses of the dynamic system under an external shock excitation of a half-sine type are obtained by MATLAB and ANSYS. It is proved that the new method is helpful to analyze MDOF dynamic systems.展开更多
The dynamic characteristic analysis model of antenna structures is built,in which the structural physical parameters and geometrical dimensions are all considered as unascertained variables.And a structure dynamic cha...The dynamic characteristic analysis model of antenna structures is built,in which the structural physical parameters and geometrical dimensions are all considered as unascertained variables.And a structure dynamic characteristic analysis method based on the unascertained factor method is given.The computational expression of structural characteristic is developed by the mathematics expression of unascertained factor and the principles of unascertained rational numbers arithmetic.An example is given,in which the possible values and confidence degrees of the unascertained structure characteristics are obtained.The calculated results show that the method is feasible and effective.展开更多
A barrier-free wheelchair robot with a mechanism coupled by wheel and track is presen- ted in this paper. Using the wheelchair, the lower limb disabled persons could be more relaxed to take part in outdoor activities ...A barrier-free wheelchair robot with a mechanism coupled by wheel and track is presen- ted in this paper. Using the wheelchair, the lower limb disabled persons could be more relaxed to take part in outdoor activities whether on flat ground or stairs and obstacles in the city. The wheel- track coupling mechanism is designed and the stability of the bodywork of the wheelchair robot on the stairs is analyzed. In order to obtain the stability of wheelchair robot when it climbs obstacles, centroid projection method is applied to analyze the static stability, stability margin is proposed to provide the stability under some dynamic forces, and the push rod rotation angle in terms of the guaranteed stability margin is given. Finally, the dynamic model of the wheelchair robot based on Lagrange equation is established, which can be a theoretical foundation for the wheelchair control system design.展开更多
We propose a novel rumor propagation model with guidance mechanism in hetero geneous complex networks.Firstly,the sharp threshold of rumor propagation,global stability of the information-equilibrium and information-pr...We propose a novel rumor propagation model with guidance mechanism in hetero geneous complex networks.Firstly,the sharp threshold of rumor propagation,global stability of the information-equilibrium and information-prevailingequilibrium under R_(0)<1 and R_(0)>1 is carried out by Lyapunov method and LaSalle's invariant principle.Next,we design an aperiodically intermittent stochastic stabilization method to suppress the rumor propagation.By using the Ito formula and exponential martingale inequality,the expression of the minimum control intensity is calculated.This method can effectively stabilize the rumor propagation by choosing a suitable perturb intensity and a perturb time ratio,while minimizing the control cost.Finally,numerical examples are given to illustrate the analysis and method of the paper.展开更多
It is the key problem to be solved ror the development of Lagrange analysis bow to ase limited Lagrangian gauges and calculate the main information about the dynamic mechanical property of rock under blasting loading....It is the key problem to be solved ror the development of Lagrange analysis bow to ase limited Lagrangian gauges and calculate the main information about the dynamic mechanical property of rock under blasting loading. This paper, using grey system, sets up a GM (1, 1 ) model relatal wltk characeristic time, and a theoretical analysis about tbe dynamic mechanical property has been carried out.The result of numerical simulation proves that the model is effective and feasible.展开更多
Serious accidents of mine hoists caused by high-speed sliding between friction lining and wire rope are often seen in coal mines.In order to solve this problem,we analyzed the contact characteristics between friction ...Serious accidents of mine hoists caused by high-speed sliding between friction lining and wire rope are often seen in coal mines.In order to solve this problem,we analyzed the contact characteristics between friction lining and wire rope.Then we carried out a dynamic mechanical analysis(DMA) to explain the change in mechanical properties of the friction lining as function of temperature and load frequency and found that temperature has a stronger effect on the mechanical properties than the frequency.We used multiple regression analysis to obtain the thermoviscoelastic constitutive relations of the friction lining.As well we derived the analytic solution for the thermoviscoelastic contact radius and pressure by combining the theory of viscoelastic contact mechanics with thermoviscoelastic constitutive relations.展开更多
The thermodynamic parameters of FRW fire-retardant plywood at different temperatures were measured by dynamic mechanical analysis (DMA) equipment such as storage modulus, loss modulus and loss angle tangent. The influ...The thermodynamic parameters of FRW fire-retardant plywood at different temperatures were measured by dynamic mechanical analysis (DMA) equipment such as storage modulus, loss modulus and loss angle tangent. The influences on the thermodynamic properties of FRW fire-retardant plywood by the FRW fire retardant were analyzed between the FRW fire-retardant plywood and the untreated plywood. The results showed that the transition temperature of FRW fire-retardant plywood’s storage modulus was delayed than the untreated plywood. Its value was also higher than the untreated plywood. Meanwhile the glass transition temperature of plywood treated by FRW fire retardant was raised. FRW fire-retardant plywood could keep the better mechanical performances and ability of deformation-resistance at higher temperature and during longer period than the untreated plywood.展开更多
基金Supported by the National Natural Science Foundation of China (50375071)the Jiangsu Province Key Lab on Digital Manufacture Project (HGDML-0604)~~
文摘The analytical formulations of the velocity and the acceleration of a 2-DOF spherical parallel mechanism are derived by the screw theory. Based on building its dynamics model by the principle of virtual work and reciprocal product of the screw, the equation of the motor moment is obtained. Through the transformation of dynamics model, the configuration space method of the dynamics equation and the corresponding coefficients are presented. Finally, the result of an example shows that the inertia moment and the gravity play a more important role than the coriolis and centrifugal moment, and the former is ten times of the latter in the magnitude. So, the latter can be neglected only when the velocity of mechanism is very slow.
基金This paper was supported by National Foundation of Application of Agricultural Scientific and Technological Achievements (2006GB23600450).
文摘A study was conducted to investigate the effects of compatibilizers, including Maleic anhydride grafted polypropylene （MA-PP） and maleic anhydride grafted ethylene-propylene-diene copolymer （MA-EPDM）, on wood-flour/polypropylene （WF/PP） composites. WF/PP composites were prepared by direct extrusion profiles using a twin-screw/single-screw extruder system. DMA analysis showed that the loss factor of composites decreased and the storage modulus improved in the presence of MA-PP, which indicated much better interfacial adhesion between the PP matrix and wood flour filler than in the absence of compatibilizer. Morphological feature based on SEM observation showed that MA-PP and MA-EPDM improved the dispersion of the wood particles in the plastic matrix. MA-EPDM is a soft segment, although it improved the interfacial adhesion, storage modulus decreases with adding of MA-EPDM. As compatibilizer of wood-flour/polypropylene composites, both DMA analysis and SEM feature proved that MA-PP was superior to MA-EPDM.
基金the project supported by the National Natural Science Foundation of China(Grant No.52372425)the Fundamental Research Funds for the Central Universities(Science and technology leading talent team project)(Grant No.2022JBXT010).
文摘Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static mechanical behavior of the ballast track in the heavy-haul railway system,numerical simulation models of the ballast bed with USP and without USP are presented in this paper by using the discrete element method(DEM)-multi-flexible body dynamic(MFBD)coupling analysis method.The ballast bed support stiffness test and dynamic displacement tests were carried out on the actual operation of a heavy-haul railway line to verify the validity of the models.The results show that using the USP results in a 43.01%reduction in the ballast bed support stiffness and achieves a more uniform distribution of track loads on the sleepers.It effectively reduces the load borne by the sleeper directly under the wheel load,with a 7.89%reduction in the pressure on the sleeper.Furthermore,the laying of the USP changes the lateral resistance sharing ratio of the ballast bed,significantly reducing the stress level of the ballast bed under train loads,with an average stress reduction of 42.19 kPa.It also reduces the plastic displacement of ballast particles and lowers the peak value of rotational angular velocity by about 50%to 70%,which is conducive to slowing down ballast bed settlement deformation and reducing maintenance costs.In summary,laying the USP has a potential value in enhancing the stability and extending the lifespan of the ballast bed in heavy-haul railway systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.52105035 and 52075467)the Natural Science Foundation of Hebei Province of China(Grant No.E2021203109)+1 种基金the State Key Laboratory of Robotics and Systems(HIT)(Grant No.SKLRS-2021-KF-15)the Industrial Robot Control and Reliability Technology Innovation Center of Hebei Province(Grant No.JXKF2105).
文摘As the support mechanism of space-borne antennas,space deployable antenna mechanism belongs to complex multi-closed-loop coupling mechanism,configuration design and dynamic analysis are more difficult than general parallel mechanism.In this paper,an unequal-length scissors mechanism(ULSM)is proposed by changing the position of the internal rotational joint through a basic scissors mechanism.A scissors hoop-rib truss deployable antenna mechanism(SHRTDAM)is constructed by replacing the parabolic rib with the ULSM.Kinematic analysis of SHRTDAM is conducted,and the degree of freedom(DOF)of the whole antenna mechanism is analyzed based on screw theory,the result showed that it has only one DOF.Velocity and acceleration characteristics of SHRTDAM are obtained by the screw derivative and rotation transformation.Based on Lagrange equation,dynamic model of this mechanism is established,the torque required to drive the mechanism is simulated and verified by Adams and MATLAB software.In addition,a ground experiment prototype of 1.5-m diameter was fabricated and a deployment test is conducted,which demonstrated the mobility and deployment performance of the whole mechanism.The mechanism proposed in this paper can provide a good reference for the design and analysis of large aperture space deployable antennas.
文摘A mechanical system for quickfeeding shells in gunboat is particularly analyzed from a dynamic view. SD nonlinear structural simulation is completed by means of dynamic explicit finite element method. Analysis results prove that the mechanical structure is feasible substantially, the material of outer surfaces near striking and overstress position should be improved and measures should be taken to avoid parts high temperature. And all analysis results give a principal theoretical basis for further work.
文摘A new method is presented to analyze multi-degree-of-freedom (MDOF) dynamic systems subjected to an external shock excitation. A two-degree-of-freedom theoretical system with linear characteristics is exemplified to illustrate the procedure of this method. The equations of motion of the dynamic system are established via matrix method. The dynamic responses of the dynamic system under an external shock excitation of a half-sine type are obtained by MATLAB and ANSYS. It is proved that the new method is helpful to analyze MDOF dynamic systems.
基金the National Defense Science and Technology Research Projects of China (51421060505DZ0155)the National Science Foundation of Shaanxi Province of China (2005A009)
文摘The dynamic characteristic analysis model of antenna structures is built,in which the structural physical parameters and geometrical dimensions are all considered as unascertained variables.And a structure dynamic characteristic analysis method based on the unascertained factor method is given.The computational expression of structural characteristic is developed by the mathematics expression of unascertained factor and the principles of unascertained rational numbers arithmetic.An example is given,in which the possible values and confidence degrees of the unascertained structure characteristics are obtained.The calculated results show that the method is feasible and effective.
基金Supported by State Key Laboratory of Robotics and Systems(HIT)(SKLRS-2010-ZD-04)Capital Medical Development Scientific Research Fund(20092098)
文摘A barrier-free wheelchair robot with a mechanism coupled by wheel and track is presen- ted in this paper. Using the wheelchair, the lower limb disabled persons could be more relaxed to take part in outdoor activities whether on flat ground or stairs and obstacles in the city. The wheel- track coupling mechanism is designed and the stability of the bodywork of the wheelchair robot on the stairs is analyzed. In order to obtain the stability of wheelchair robot when it climbs obstacles, centroid projection method is applied to analyze the static stability, stability margin is proposed to provide the stability under some dynamic forces, and the push rod rotation angle in terms of the guaranteed stability margin is given. Finally, the dynamic model of the wheelchair robot based on Lagrange equation is established, which can be a theoretical foundation for the wheelchair control system design.
基金Project supported by the Guangzhou Science and Technology Project(Grant No.20210202710)Scientific Research Project of Guangzhou University(Grant No.YG2020010)。
文摘We propose a novel rumor propagation model with guidance mechanism in hetero geneous complex networks.Firstly,the sharp threshold of rumor propagation,global stability of the information-equilibrium and information-prevailingequilibrium under R_(0)<1 and R_(0)>1 is carried out by Lyapunov method and LaSalle's invariant principle.Next,we design an aperiodically intermittent stochastic stabilization method to suppress the rumor propagation.By using the Ito formula and exponential martingale inequality,the expression of the minimum control intensity is calculated.This method can effectively stabilize the rumor propagation by choosing a suitable perturb intensity and a perturb time ratio,while minimizing the control cost.Finally,numerical examples are given to illustrate the analysis and method of the paper.
文摘It is the key problem to be solved ror the development of Lagrange analysis bow to ase limited Lagrangian gauges and calculate the main information about the dynamic mechanical property of rock under blasting loading. This paper, using grey system, sets up a GM (1, 1 ) model relatal wltk characeristic time, and a theoretical analysis about tbe dynamic mechanical property has been carried out.The result of numerical simulation proves that the model is effective and feasible.
基金Projects 50875253 supported by the National Natural Science Foundation of China20060290505 by the Research Fund for the Doctoral Program of Higher Education of China+2 种基金107054 by the Key Project of Ministry of Education of ChinaBK2008127 by the Natural Science Foundation of Jiangsu ProvinceCX08B_042Z by the Scientific Innovation Program for Postgraduates in Colleges and Universities of Jiangsu Province
文摘Serious accidents of mine hoists caused by high-speed sliding between friction lining and wire rope are often seen in coal mines.In order to solve this problem,we analyzed the contact characteristics between friction lining and wire rope.Then we carried out a dynamic mechanical analysis(DMA) to explain the change in mechanical properties of the friction lining as function of temperature and load frequency and found that temperature has a stronger effect on the mechanical properties than the frequency.We used multiple regression analysis to obtain the thermoviscoelastic constitutive relations of the friction lining.As well we derived the analytic solution for the thermoviscoelastic contact radius and pressure by combining the theory of viscoelastic contact mechanics with thermoviscoelastic constitutive relations.
文摘The thermodynamic parameters of FRW fire-retardant plywood at different temperatures were measured by dynamic mechanical analysis (DMA) equipment such as storage modulus, loss modulus and loss angle tangent. The influences on the thermodynamic properties of FRW fire-retardant plywood by the FRW fire retardant were analyzed between the FRW fire-retardant plywood and the untreated plywood. The results showed that the transition temperature of FRW fire-retardant plywood’s storage modulus was delayed than the untreated plywood. Its value was also higher than the untreated plywood. Meanwhile the glass transition temperature of plywood treated by FRW fire retardant was raised. FRW fire-retardant plywood could keep the better mechanical performances and ability of deformation-resistance at higher temperature and during longer period than the untreated plywood.
文摘为了研究浇注式沥青胶浆的高温性能及评价指标,采用动态力学分析(DMA)方法,通过动态剪切流变试验,探讨了不同温度、沥青种类、粉胶比对浇注式沥青胶浆高温性能的影响.分析了广义剪切模量与浇注式沥青混合料高温变形之间的相关性,探讨了该指标作为浇注式胶浆高温性能评价指标的适用性,并以车辙深度为控制标准,对广义剪切模量以及60℃条件下的贯入度提出了建议值.结果表明:浇注式沥青胶浆复数剪切模量和相位角受温度、沥青种类、粉胶比因素影响明显;广义剪切模量与混合料永久变形呈良好的线性关系,能作为一种合适的劲度指标评价浇注式沥青胶浆的高温稳定性;60℃条件下,浇注式沥青混合料贯入度指标建议值不大于3.29 mm.
