This paper proposes a novel three-dimensional(3D)isolation system for facilities and presents the numerical simulation approach for the isolated system under earthquake excitations and impact effect using the OpenSees...This paper proposes a novel three-dimensional(3D)isolation system for facilities and presents the numerical simulation approach for the isolated system under earthquake excitations and impact effect using the OpenSees(Open System for Earthquake Engineering Simulation)software frame work.The 3D isolators combine the quasi-zero stiffness(QZS)system in the vertical direction and lead rubber bearing in the horizontal direction.Considering the large aspect ratio of the isolated facility,linear viscous dampers are designed in the vertical direction to diminish the overturning effect.The vertical QZS isolation system is characterized by a cubic force-displacement relation,thus,no elements or materials can model this mechanic behavior in the existing finite element software.This study takes advantage of the open source feature of the OpenSees to create a new material to represent the mechanic properties of the QZS system.Then the user-defined material is combined with the rubber isolator element to model the 3D isolator.Considering different soil types and input magnitudes,six sets of natural seismic records and artificial waves and half sine pulses are selected as the input excitations.A finite element model for the 3D isolated facility is established based on the combined element and the simulation is performed to calculate the time history response.The numerical simulation reveals the flexibility of the OpenSees to deal with new engineering problems,and the results prove that the new 3D isolation system can have an optimal isolation effect in both horizontal and vertical directions.The maximum acceleration response at the top of the facility is below the target limit,and the maximum deformation and the overturning motion of the isolation system can be controlled in a safe range.展开更多
Performance of the LSFD method is compared with conventional FD schemes. Generally, 9-point stencils for 2D cases and 27-point stencils for 3D cases are used for the approximation of the first and second order derivat...Performance of the LSFD method is compared with conventional FD schemes. Generally, 9-point stencils for 2D cases and 27-point stencils for 3D cases are used for the approximation of the first and second order derivatives obtained with conventional central difference schemes. When the same stencils are used, explicit LSFD formulations for approximation of the first and second order derivatives are presented. The LSFD formulations are actually a combination of conventional central difference schemes along relevant mesh lines. It has been found that LSFD formulations need much less iteration steps than the conventional FD schemes to converge, and the ratio of mesh spacing in the x and y directions is an important parameter in the LSFD application, with a great impact on stability of LSFD computation.展开更多
The sedimentation of slender particles with different densities in stagnant Newtonian fluid was studied Different from former studies based on the concept of sphericity, the drag coefficient of slender particles is qu...The sedimentation of slender particles with different densities in stagnant Newtonian fluid was studied Different from former studies based on the concept of sphericity, the drag coefficient of slender particles is quantitatively correlated with the orientation and Reynolds number based on the particle cylindrical diameter With the aid of Galileo number,the particle cylindrical diameter, the proposed correlation represents very well the experimental data with aspect ratios, orientations, particle material and fluid properties in wide展开更多
基金The authors acknowledge the financial support from National Natural Science Foundation of China(Grant No.51878502).
文摘This paper proposes a novel three-dimensional(3D)isolation system for facilities and presents the numerical simulation approach for the isolated system under earthquake excitations and impact effect using the OpenSees(Open System for Earthquake Engineering Simulation)software frame work.The 3D isolators combine the quasi-zero stiffness(QZS)system in the vertical direction and lead rubber bearing in the horizontal direction.Considering the large aspect ratio of the isolated facility,linear viscous dampers are designed in the vertical direction to diminish the overturning effect.The vertical QZS isolation system is characterized by a cubic force-displacement relation,thus,no elements or materials can model this mechanic behavior in the existing finite element software.This study takes advantage of the open source feature of the OpenSees to create a new material to represent the mechanic properties of the QZS system.Then the user-defined material is combined with the rubber isolator element to model the 3D isolator.Considering different soil types and input magnitudes,six sets of natural seismic records and artificial waves and half sine pulses are selected as the input excitations.A finite element model for the 3D isolated facility is established based on the combined element and the simulation is performed to calculate the time history response.The numerical simulation reveals the flexibility of the OpenSees to deal with new engineering problems,and the results prove that the new 3D isolation system can have an optimal isolation effect in both horizontal and vertical directions.The maximum acceleration response at the top of the facility is below the target limit,and the maximum deformation and the overturning motion of the isolation system can be controlled in a safe range.
基金supported by the National Natural Science Foundation of China (Nos. 10872005, 10532010)
文摘Performance of the LSFD method is compared with conventional FD schemes. Generally, 9-point stencils for 2D cases and 27-point stencils for 3D cases are used for the approximation of the first and second order derivatives obtained with conventional central difference schemes. When the same stencils are used, explicit LSFD formulations for approximation of the first and second order derivatives are presented. The LSFD formulations are actually a combination of conventional central difference schemes along relevant mesh lines. It has been found that LSFD formulations need much less iteration steps than the conventional FD schemes to converge, and the ratio of mesh spacing in the x and y directions is an important parameter in the LSFD application, with a great impact on stability of LSFD computation.
文摘The sedimentation of slender particles with different densities in stagnant Newtonian fluid was studied Different from former studies based on the concept of sphericity, the drag coefficient of slender particles is quantitatively correlated with the orientation and Reynolds number based on the particle cylindrical diameter With the aid of Galileo number,the particle cylindrical diameter, the proposed correlation represents very well the experimental data with aspect ratios, orientations, particle material and fluid properties in wide
