It is difficult to solve the structural problems related to agricultural engineering,due to the wide ranges of the means of related variables and complex structural shapes.For these reasons,discrete models are require...It is difficult to solve the structural problems related to agricultural engineering,due to the wide ranges of the means of related variables and complex structural shapes.For these reasons,discrete models are required that are able to replace or simplify solid structure components used in traditional analysis methods.Therefore,the objective of this study was to develop a regular truss structure model that behaves the same way as a solid structure.It was assumed that if a unit element consists of truss elements with each hinge at the end of the element and the size of the element is infinitesimal,the stress distribution and displacement field will be constant throughout the domain of the unit element.Additionally,the behavior of the truss element was assumed to be in a linear state in a two-dimensional plane.The law of energy conservation,based on the theory of elasticity,was applied to determine the equilibrium conditions between discretized and solid elements.The restrictive condition that we obtained revealed that applications are limited to only ideal elastic materials with a Poisson’s ratio of 1 to 3.The volumetric ratio of the equivalent truss to the continuum structures was 3:1,regardless of the size or number of the mesh.To calculate the internal stress and strain of the unit element,the geometric relationships of each truss member,which has its own role against different stress directions,were used.The calculated von Misses stresses were used to verify this model.Stress concentrations,as explained based on Saint Venant’s principle,were also observed in the equivalent truss structure model.The main stress paths,indicating the areas where reinforcement bars should be placed,were successfully shown without the requirement that each element be transformed in the direction of principal stress;this was done by eliminating elements with only compressive and near-zero stresses.展开更多
We consider H（curl, Ω）-elliptic variational problems on bounded Lipschitz polyhedra and their finite element Galerkin discretization by means of lowest order edge elements. We assume that the underlying tetrahedral...We consider H（curl, Ω）-elliptic variational problems on bounded Lipschitz polyhedra and their finite element Galerkin discretization by means of lowest order edge elements. We assume that the underlying tetrahedral mesh has been created by successive local mesh refinement, either by local uniform refinement with hanging nodes or bisection refinement. In this setting we develop a convergence theory for the the so-called local multigrid correction scheme with hybrid smoothing. We establish that its convergence rate is uniform with respect to the number of refinement steps. The proof relies on corresponding results for local multigrid in a H^1 （Ω）-context along with local discrete Helmholtz-type decompositions of the edge element space.展开更多
Capacity analysis is a fundamental and essential work for evaluating the performance of cognitive wireless mesh network （CWMN） which is considered a promising option for the future network. Power control is an effic...Capacity analysis is a fundamental and essential work for evaluating the performance of cognitive wireless mesh network （CWMN） which is considered a promising option for the future network. Power control is an efficient way to avoid interference and improve capacity of wireless mesh networks. In this paper, a quantitative result of the per-node average throughput capacity of CWMN with power control is deduced for the first time, which is much helpful for understanding the limitations of CWMN. Firstly, under the large-scale channel fading model and protocol interference model, a closed-form expression for the maximum channel capacity of each node with power control is presented, under the constraint that the interference tolerated by the primary users （PUs） does not exceed a threshold. And then, with the deduced channel capacity result, the per-node average throughput capacity of CWMN is derived based on two regular topologies, i.e. square topology and triangle topology. The simulation results indicate that the capacity is effectively improved with power control, and affected by topology, tolerated interference threshold, the number of cognitive users （CUs） and primary users （PUs）.展开更多
基金We acknowledge that this work was supported by the research grant of Chungbuk National University in 2013.
文摘It is difficult to solve the structural problems related to agricultural engineering,due to the wide ranges of the means of related variables and complex structural shapes.For these reasons,discrete models are required that are able to replace or simplify solid structure components used in traditional analysis methods.Therefore,the objective of this study was to develop a regular truss structure model that behaves the same way as a solid structure.It was assumed that if a unit element consists of truss elements with each hinge at the end of the element and the size of the element is infinitesimal,the stress distribution and displacement field will be constant throughout the domain of the unit element.Additionally,the behavior of the truss element was assumed to be in a linear state in a two-dimensional plane.The law of energy conservation,based on the theory of elasticity,was applied to determine the equilibrium conditions between discretized and solid elements.The restrictive condition that we obtained revealed that applications are limited to only ideal elastic materials with a Poisson’s ratio of 1 to 3.The volumetric ratio of the equivalent truss to the continuum structures was 3:1,regardless of the size or number of the mesh.To calculate the internal stress and strain of the unit element,the geometric relationships of each truss member,which has its own role against different stress directions,were used.The calculated von Misses stresses were used to verify this model.Stress concentrations,as explained based on Saint Venant’s principle,were also observed in the equivalent truss structure model.The main stress paths,indicating the areas where reinforcement bars should be placed,were successfully shown without the requirement that each element be transformed in the direction of principal stress;this was done by eliminating elements with only compressive and near-zero stresses.
基金supported in part by China NSF under the grant 60873177by the National Basic Research Project under the grant 2005CB321702
文摘We consider H（curl, Ω）-elliptic variational problems on bounded Lipschitz polyhedra and their finite element Galerkin discretization by means of lowest order edge elements. We assume that the underlying tetrahedral mesh has been created by successive local mesh refinement, either by local uniform refinement with hanging nodes or bisection refinement. In this setting we develop a convergence theory for the the so-called local multigrid correction scheme with hybrid smoothing. We establish that its convergence rate is uniform with respect to the number of refinement steps. The proof relies on corresponding results for local multigrid in a H^1 （Ω）-context along with local discrete Helmholtz-type decompositions of the edge element space.
基金supported by the National Science & Technology Major Project of 2011ZX03001-005-02the National Natural Science Foundation of China (61272516, 61272518, 61170275)the China-Canada Project (2010DFA111320)
文摘Capacity analysis is a fundamental and essential work for evaluating the performance of cognitive wireless mesh network （CWMN） which is considered a promising option for the future network. Power control is an efficient way to avoid interference and improve capacity of wireless mesh networks. In this paper, a quantitative result of the per-node average throughput capacity of CWMN with power control is deduced for the first time, which is much helpful for understanding the limitations of CWMN. Firstly, under the large-scale channel fading model and protocol interference model, a closed-form expression for the maximum channel capacity of each node with power control is presented, under the constraint that the interference tolerated by the primary users （PUs） does not exceed a threshold. And then, with the deduced channel capacity result, the per-node average throughput capacity of CWMN is derived based on two regular topologies, i.e. square topology and triangle topology. The simulation results indicate that the capacity is effectively improved with power control, and affected by topology, tolerated interference threshold, the number of cognitive users （CUs） and primary users （PUs）.
