基于测量的网络生成树拓扑优化

提出一种基于测量的网络生成树拓扑优化算法，可以根据网络上的流量分布动态地调整网络拓扑。仿真结果表明，在网络输入相同时，这种算法可以显著降低网络资源的占用，并可以有效地消除网络上短期流量波动对拓扑稳定性的影响，防止网络拓扑频繁变化。     

基于等几何裁剪分析的拓扑与形状集成优化

提出了将设计和分析、拓扑与形状优化集成的思想,探索了基于等几何裁剪分析的拓扑与形状集成优化设计算法,该方法统一了结构优化的计算机辅助设计、计算机辅助工程分析和优化设计的模型,基于B样条的等几何裁剪分析既能准确表达几何形状,又可以用裁剪面分析方便处理任意复杂拓扑优化问题,由裁剪选择标准确定合理的拓扑结构变动方向,结构变动时无需重新划分网格,设计结果突破初始设计空间的限制,还可方便优化形状。建立了等几何裁剪灵敏度分析的计算方法,给出了等几何裁剪分析拓扑与形状集成优化算法,通过典型实例表明所用方法的正确性和有效性。     

A Multi-Criteria Topology Optimization for Systematic Design of Compliant Mechanisms

This paper attempts to present a new multi-criteria topological optimization methodology for the systematic design of compliant micro-mechanisms. Instead of employing only the strain energy (SE) or the functional specifications such as mechanical efficiency (ME), in this study an alternative formulation representing multiple design requirements is included in the optimization to describe the performance of compliant mechanisms. In most conventional designs, SE is used to only measure the design requirement from the point of view of structures, while ME is usually applied to describe the mechanical performance of mechanisms. However, the design of a compliant mechanism is required to comprehensively consider both the structural and mechanical performance quantities. Displacement, material usage and dynamic response are imposed as three external constraints to narrow the searching domain. In doing so, the multi-criteria optimization problem involving the SE and ME can reasonably embody the mechanical structural characteristics of compliant mechanisms. A sequential convex programming, the method of moving asymptotes (MMA), is applied to solve the topological optimization problem, which can not only ensure numerical accuracy but also both the monotonous and non-monotonous structural behaviors. SIMP model (solid isotropic material with penalization) is used to indicate the dependence of elastic modulus upon regularized element densities. Several typical numerical examples are used to demonstrate the effectiveness of the proposed methodology, and the prototype of a resulting mechanism has also been manufactured to validate the design of the compliant mechanism.     

Distinctions Between Classes of Superconductors Involve Their Degree of Structural Connectivity

A distinction is made between extreme types, such as highT _c cuprates and soft-metal superconductors concerning the extended, relatively exchange frustration-free covalent ring structures (eight-membered) in the former. Phenomenology indicates for cuprates that bond order (BO) effects within a given number of doped bonds can create real space organization of pairs around O super-exchange centers (trijugate position) within a mobile pair kernel. Indications for this postulated new quantum chemical principle have now been found in related electronic crystal behavior by STM. This situation creates small coherence lengths (∼4 atoms) and unusually high pair numbers. For optimal doping, all holes are converted into pairs and these pairs show trends to geometric checkerboard patterns due to characteristic charge-lattice lock-ins, such as configurations withh _op=0.25 orh _op=0.16. Period of BO and the degree of isolation of the planes determineT _c. Doping curves reflect BO events and are roughly predictable from structural data alone. It is suggested that a variety of related materials with large member rings (e.g. C₆₀) follow the relevant BO phenomenology. By contrast, soft metal superconductors (e.g. Pb) are based on 3D close packed structures with small triangular rings in which exchange interactions are frustrated and small. “Normal” BCS isotope effects suggest the operation of phonons in pair formation over extended coherence lengths (>100 atoms). Very small pair numbers are created through phonons.     

三维表面形貌的连通性表征

从集合的角度,运用图像描述方法,提出了三维表面形貌连通性表征的方法,建立了连通数、连通指数的概念以及相应的算法,并结合实际,模拟出一些特征明显的三维表面形貌,确定了评定表面连通性能的基准面,定量分析了表面形貌的连通性随表面高度的变化情况,比较出在传统的表面形貌参数相似的情况下表面连通性能的差异,为表面形貌表征研究开辟了一个新的途径.     

折叠交叉立方体的 2-限制性边通度

$h$-限制性边连通度是衡量大型互连网络可靠性和容错性的一个重要参数。设 $G$ 是连通图且 $h$ 是非负整数,如果 $G$ 中存在某种边子集,使得 $G$ 删除这种边子集后得到的图不连通并且每个分支中点的度至少是 $h$,则所有这种边子集中基数最小的边子集的基数称为图 $G$ 的 $h$-限制性边连通度。$n$-维折叠交叉立方体是由 $n$-维交叉立方体增加一些补边后所得。对于此类问题,首先利用 $2$-限制性边连通度作为可靠性的重要度量,对折叠交叉立方体网络的可靠性进行分析,然后得到折叠交叉立方体的 $2$-限制性边连通度,最后证明并确定 $n$-维折叠交叉立方体的 $2$-限制性边连通度等于 $4n-4 (ngeq 4)$。这个结果意味着,为了使 $n$-维折叠交叉立方体不连通且每个分支中没有度数小于 2 的点,至少应有 $4n-4$ 条边同时发生故障。     

具有良好贯通性的颗粒造孔支架的制备及表征

支架孔隙贯通性的研究一直是多孔生物陶瓷的研究重点之一.采用石蜡球作为造孔剂, 在常规的颗粒造孔法制备多孔陶瓷支架的基础上,通过二甲苯处理以便在石蜡球间形成桥联结构, 以扩大颗粒间的接触面积,从而提高多孔陶瓷支架的孔隙贯通性. 借助扫描电镜(SEM)观察陶瓷支架的多孔结构,评价二甲苯处理石蜡球对陶瓷支架孔隙贯通性的改善效果; 采用密度法测定了陶瓷支架的孔隙率并计算其收缩率,并用成骨细胞评价陶瓷支架的细胞相容性. 结果表明,通过二甲苯的处理, 不仅改善了陶瓷支架孔隙的贯通性,而且提高了其孔隙率, 但孔隙率对陶瓷支架的收缩率无明显影响.细胞培养实验显示成骨细胞可进入多孔陶瓷支架内部, 并在材料表面正常生长,贯通性好的多孔陶瓷支架可为成骨细胞生长提供更充分的空间.     

Topology optimization of thermoelastic structures using level set method

This paper describes the topology optimization of thermoelastic structures, using level set method. The objective is to minimize the mean compliance of a structure with a material volume constraint. In level set method, free boundary of a structure is considered as design variable, and it is implicitly represented via level set model. Objective function of the optimization problem is defined as a function of the shape of a structure. Sensitivity analysis based on continuum model is conducted with respect to the free boundary, which suggests the steepest descent direction. A geometric energy term is introduced to ensure smooth structural boundary. Augmented Lagrangian multiplier method is adopted to enforce volume constraint. Numerical examples are provided for 2D cases, considering design independent temperature distribution.     

Topology optimization for submerged buoyant structures

This paper presents an evolutionary structural topology optimization method for the design of completely submerged buoyant modules with design-dependent fluid pressure loading. This type of structure is used to support offshore rig installation and pipeline transportation at all water depths. The proposed optimization method seeks to identify the buoy design that has the highest stiffness, allowing it to withstand deepwater pressure, uses the least material and has a minimum prescribed buoyancy. Laplace's equation is used to simulate underwater fluid pressure, and a polymer buoyancy module is considered to be linearly elastic. Both domains are solved with the finite element method. Using an extended bi-directional evolutionary structural optimization (BESO) method, the design-dependent pressure loads are modelled in a straightforward manner without any need for pressure surface parametrization. A new buoyancy inequality constraint sets a minimum required buoyancy effect, measured by the joint volume of the structure and its interior voids. Solid elements with low strain energy are iteratively removed from the initial design domain until a certain prescribed volume fraction. A test case is described to validate the optimization problem, and a buoy design problem is used to explore the features of the proposed method.     

A Novel Method for Node Connectivity with Adaptive Dragonfly Algorithm and Graph-Based m-Connection Establishment in MANET

Maximizing network lifetime is measured as the primary issue in Mobile Adhoc Networks (MANETs). In geographically routing based models, packet transmission seems to be more appropriate in dense circumstances. The involvement of the Heuristic model directly is not appropriate to offer an effectual solution as it becomes NP-hard issues; therefore investigators concentrate on using Meta-heuristic approaches. Dragonfly Optimization (DFO) is an effective meta-heuristic approach to resolve these problems by providing optimal solutions. Moreover, Meta-heuristic approaches (DFO) turn to be slower in convergence problems and need proper computational time while expanding network size. Thus, DFO is adaptively improved as Adaptive Dragonfly Optimization (ADFO) to fit this model and re-formulated using graph-based m-connection establishment (G-     

Topology optimization of buildings subjected to stochastic wind loads

Traditionally, the main structural system of tall buildings is designed iteratively to resist extreme wind loads, which provides safe, but typically suboptimal building systems. Topology optimization provides a general approach to obtain optimal material layout to carry the required load within specified design constraints. The wind loading on a structure is typically modeled as an equivalent static load or as a spatio-temporal stochastic field. While a few models for stochastic wind excitation are available, these approaches are focused on obtaining samples for time history analyses. In this study the stochastic wind excitation is modeled as a filtered vector white noise; the state space representation of the filter is obtained by solving a regularized optimization problem from known stationary wind power spectral densities. An augmented state space representation is formed by combining the equation of motion for the structure with the excitation filter. The stationary covariances of the structural responses of interest are then obtained by solving the associated Lyapunov equation. Dynamic condensation of the equations of motion is employed to increase the efficiency of the proposed approach. Objective functions for the optimization scheme are defined in terms of the stationary covariance of the response; various objectives are considered corresponding to typical design considerations. An equivalent smooth formulation is employed to solve the non-smooth min–max problem. A gradient-based method is used to update the design variables, while the sensitivities are computed from the solution of an adjoint Lyapunov equation. The proposed topology optimization scheme is illustrated for a tall building subjected to along-wind and across-wind loads. The results presented herein demonstrate the efficacy of the proposed approach for efficient topology optimization of buildings subjected to stochastic wind excitation.     

Bi-Directional Evolutionary Topology Optimization Using Element Replaceable Method

In the present paper, design problems of maximizing the structural stiffness or natural frequency are considered subject to the material volume constraint. A new element replaceable method (ERPM) is proposed for evolutionary topology optimization of structures. Compared with existing versions of evolutionary structural optimization methods, contributions are twofold. On the one hand, a new automatic element deletion/growth procedure is established. The deletion of a finite element means that a solid element is replaced with an orthotropic cellular microstructure (OCM) element. The growth of an element means that an OCM element is replaced with a solid element of full materials. In fact, both operations are interchangeable depending upon how the value of element sensitivity is with respect to the objective function. The OCM design strategy is beneficial in preventing artificial modes for dynamic problems. Besides, the iteration validity is greatly improved with the introduction of a check position (CP) technique. On the other hand, a new checkerboard control algorithm is proposed to work together with the above procedure. After the identification of local checkerboards and detailed structures over the entire design domain, the algorithm will fill or delete elements depending upon the prescribed threshold of sensitivity values. Numerical results show that the ERPM is efficient and a clear and valuable material pattern can be achieved for both static and dynamic problems.     

Topology optimization of geometrically nonlinear structures using an evolutionary optimization method

The topology optimization using isolines/isosurfaces and extended finite element method (Iso-XFEM) is an evolutionary optimization method developed in previous studies to enable the generation of high-resolution topology optimized designs suitable for additive manufacture. Conventional approaches for topology optimization require additional post-processing after optimization to generate a manufacturable topology with clearly defined smooth boundaries. Iso-XFEM aims to eliminate this time-consuming post-processing stage by defining the boundaries using isovalues of a structural performance criterion and an extended finite element method (XFEM) scheme. In this article, the Iso-XFEM method is further developed to enable the topology optimization of geometrically nonlinear structures undergoing large deformations. This is achieved by implementing a total Lagrangian finite element formulation and defining a structural performance criterion appropriate for the objective function of the optimization problem. The Iso-XFEM solutions for geometrically nonlinear test cases implementing linear and nonlinear modelling are compared, and the suitability of nonlinear modelling for the topology optimization of geometrically nonlinear structures is investigated.     

Topology optimization of continuum structures for natural frequencies considering casting constraints

A method for the topology optimization on the natural frequency of continuum structures with casting constraints is proposed. The objective is to maximize the natural frequency of vibrating continuum structures subject to casting constraints. When the natural frequencies of the considered structures are maximized using the solid isotropic material with penalization (SIMP) model, artificial localized modes may occur in areas where elements are assigned with lower density values. In this article, the topology optimization is performed by the bi-directional evolutionary structural optimization (BESO) method. The effects of different locations of concentrated lump mass, different volume fractions and meshing sizes on the final topologies are compared. Both two and four parting directions are investigated. Several two- and three-dimensional numerical examples show that the proposed BESO method is effective in achieving convergent solid–void optimal solutions for a variety of frequency optimization problems of continuum structures.     

基于连通性转换的三维多面体快速变形

研究了连通性转换方法,并将其应用于多面体快速变形.采用优先权控制函数控制模型特征,且可以实现点和边的同步处理.通过预先安排连通性转换提高了变形速度,通过解一个稀疏线性方程组缩短变形片的嵌入时间.之后,矫正特征点以及边界处理得到平滑变形序列.用该方法和传统变形方法分别演示了三维多面体模型的变形实例,并对实验结果和相关数据进行了分析比较.实验结果表明,该变形方法可快速实现平滑变形.     

Topology optimization of material‐nonlinear continuum structures by the element connectivity parameterization

The application of the element density‐based topology optimization method to nonlinear continuum structures is limited to relatively simple problems such as bilinear elastoplastic material problems. Furthermore, it is very difficult to use analytic sensitivity when a commercial nonlinear finite element code is used. As an alternative to the element density formulation, the element connectivity parameterization (ECP) formulation is developed for the topology optimization of isotropic‐hardening elastoplastic or hyperelastic continua by using commercial software. ECP varies the stiffness of zero‐length linear elastic links that connect design domain‐discretizing finite elements. Unloading was not considered. But the advantages of ECP in material‐nonlinear problems were demonstrated: considerably simple analytic sensitivity calculation using a commercial code and simple link stiffness penalization regardless of nonlinear material behaviour. Copyright © 2006 John Wiley & Sons, Ltd.     

Topology optimization of structures under multiple load cases using a fiber-reinforced composite material model

This paper presents a method to optimize the topology of structures under multiple load cases with stress constraints. Fiber-reinforced orthotropic composite is employed as the material model to simulate the constitutive relation of truss-like continua. The fiber densities and orientations at the nodes are taken as design variables. First, for each load case, the fiber orientations are aligned with the orientations of principal stress and the fiber densities are adjusted according to the strains along the fiber orientations. Then, to optimize the structure, the fiber densities and orientations under multiple load cases are determined by constraining its elastic matrix to approach the elastic matrix of the optimum structures defined for each single load case. Finally the member distribution in the optimal structure is suggested by the continuous lines formed according to the fiber densities and orientations. Several examples are presented to demonstrate the effectiveness of the proposed approach.     

HARQ Optimization for PDCP Duplication-Based 5G URLLC Dual Connectivity

Packet duplication (PD) with dual connectivity (DC) was newly introduced in the 5G New Radio (NR) specifications to meet the stringent ultra reliable low latency communication (URLLC) requirements. PD technology uses duplicated packets in the packet data convergence protocol (PDCP) layer that are transmitted via two different access nodes (ANs) to the user equipment (UE) in order to enhance the reliability performance. However, PD can result in unnecessary retransmissions in the lower layers since the hybrid automatic retransmission request (HARQ) operation is unaware of the transmission success achieved through the alternate DC link to the UE. To overcome this issue, in this paper, a novel duplication-aware retransmission optimization (DRO) scheme is proposed to reduce the resource usage induced by unnecessary HARQ retransmissions. The proposed DRO scheme can minimize the average channel use while satisfying the URLLC requirements. The proposed DRO scheme derives the optimal HARQ retransmission attempts for different ANs by solving a nonlinear integer programming (NLIP) problem. The performance of the proposed DRO scheme was evaluated using MATLAB simulation and is compared to the existing 5G HARQ support schemes. The simulations results show that the proposed DRO scheme can provide a 14.71% and 15.11% reduced average channel use gain compared to the selective data duplication upon failure (SDUF) scheme and latency-aware dynamic multi-connectivity algorithm (LADMA) scheme, respectively, which are the existing 5G PD schemes that use HARQ.