Theoretical and experimental investigations of flexural wave propagation in periodic grid structures designed with the idea of phononic crystals

The propagation characteristics of flexural waves in periodic grid structures designed with the idea of phononic crystals are investigated by combining the Bloch theorem with the finite element method. This combined analysis yields phase constant surfaces, which predict the location and the extension of band gaps, as well as the directions and the regions of wave propagation at assigned frequencies. The predictions are validated by computation and experimental analysis of the harmonic responses of a finite structure with 11 × 11 unit cells. The flexural wave is localized at the point of excitation in band gaps, while the directional behaviour occurs at particular frequencies in pass bands. These studies provide guidelines to designing periodic structures for vibration attenuation.

Hydrothermal Synthesis and Crystal Structure of a Square Grid Coordination Copper(II) Polymer from 1,4-Bis(imidazole-1-ylmethyl)benzene

The title compound [Cu（bix）2（NO3）z·H2P]n 1 （bix = 1,4-bis（imidazole-1-ylme-thyl） benzene） has been synthesized by hydrothermal method. Its crystal structure is of monoclinic, space group P1^- with a = 8.3075（13）, b = 9.4725（13）, c = 10.0192（13） A, α = 91.088（4）, β = 104.063（6）, γ = 101.88（1）, V = 746.5（3） A^3, Z = 1, C28H30N10O7Cu1, Mr = 682.16, Dc = 1.518 g/cm^3, μ = 0.796 mm^-1, F（000） = 353, the final R = 0.0535 and wR = 0.0996 for 2921 observed reflections with I 〉 2σ（I）. Each bix ligand binds two Cu（Ⅱ） ions to form a 2-D（4,4） square grid layer, which is connected by hydrogen bonds showing large channels occupied by solvated water molecules and nitrate anions.

Determination of optimal grid opening width for herringbone water-sediment separation structures based on sediment separation efficiency

The herringbone water-sediment separation structure(HWSSS) was developed to prevent debris flows. This paper mainly focuses on evaluating the sediment separation efficiency of HWSSS in debris flow prevention and determining the grid opening width D, a crucial structure parameter for HWSSS design. Theoretical analysis on the total sediment separation rate Pt reveals that the efficiency of sediment separation is much related with sediment grain size distribution(GSD) and grid opening width. The lower limit of Pt is deduced from the perspective of safety consideration by transforming debris flow into sediment-laden flow. Hydraulic model tests were carried out. Based on the regression analysis of the experimental data, the quantitative relationships between Pt and D and GSD characteristic values were finally established. A procedure for determining optimal grid opening width is proposed based on these analyses. These results are of significance in evaluating sediment separation effect by HWSSS in debris flow prevention and contribute to a more explicit methodology for design of HWSSS.

Analysis of Reflection Characteristics for Foam Filled Grid Structure

The reflection characteristics of gird structures are calculated by the spatial network method in the case of normal incidence plane electromagnetic wave. The numerical result shows that the grid panels without electromagnetic wave absorbing foams are not ideal. However, the absorbing ability can be achieved as low as -25 dBsm from 8 GHz to 12 GHz when the grid cells are filled with foam absorbers. Also it is noted from computation that the foam filled grid structures with larger cell size, higher and thinner ribs will improve the absorbing abilities, which illustrates that they can be used as the effective light-weight stealth structures for aeronautical application.

Unstructured Grid Immersed Boundary Method for Numerical Simulation of Fluid Structure Interaction

This paper presents an improved unstructured grid immersed boundary method.The advantages of both immersed boundary method and body fitted grids which are generated by unstructured grid technology are used to enhance the computation efficiency of fluid structure interaction in complex domain.The Navier-Stokes equation was discretized spacially with collocated finite volume method and Euler implicit method in time domain.The rigid body motion was simulated by immersed boundary method in which the fluid and rigid body interface interaction was dealt with VOS(volume of solid) method.A new VOS calculation method based on graph was presented in which both immersed boundary points and cross points were collected in arbitrary order to form a graph.The method is verified with flow past oscillating cylinder.

Analysis of nonlinear stability and post-buckling for Euler-type beam-column structure

Based on the assumption of finite deformation, the Hamilton variational principle is extended to a nonlinear elastic Euler-type beam-column structure located on a nonlinear elastic foundation. The corresponding three-dimensional （3D） mathematical model for analyzing the nonlinear mechanical behaviors of structures is established, in which the effects of the rotation inertia and the nonlinearity of material and geometry are considered. As an application, the nonlinear stability and the post-buckling for a linear elastic beam with the equal cross-section located on an elastic foundation are analyzed. One end of the beam is fully fixed, and the other end is partially fixed and subjected to an axial force. A new numerical technique is proposed to calculate the trivial solution, bifurcation points, and bifurcation solutions by the shooting method and the Newton- Raphson iterative method. The first and second bifurcation points and the corresponding bifurcation solutions are calculated successfully. The effects of the foundation resistances and the inertia moments on the bifurcation points are considered.

Study on Relation between Industrial Structure and Grid Load in Shanxi Province

The section of electric power is the foundation of national economy. The paper analyzes the relation between industrial structure and grid load in Shanxi province, and finds out that electricity demand and grid load relate linearly to value added of industry. In the end, the paper predicts electricity demand and grid load via the model.

An Overset Grid Method for Fluid-Structure Interaction

An overset grid methodology is developed for the fully coupled analysis of fluid-structure interaction (FSI) problems. The overset grid approach alleviates some of the computational geometry difficulties traditionally associated with Arbitrary-Lagrangian-Eulerian (ALE) based, moving mesh methods for FSI. Our partitioned solution algorithm uses separate solvers for the fluid (finite volume method) and the structure (finite element method), with mesh motion computed only on a subset of component grids of our overset grid assembly. Our results indicate a significant reduction in computational cost for the mesh motion, and element quality is improved. Numerical studies of the benchmark test demonstrate the benefits of our overset mesh method over traditional approaches.

PERTURBATIONAL FINITE VOLUME METHOD FOR THE SOLUTION OF 2-D NAVIER-STOKES EQUATIONS ON UNSTRUCTURED AND STRUCTURED COLOCATED MESHES

Based on the first-order upwind and second-order central type of finite volume (UFV and CFV) scheme, upwind and central type of perturbation finite volume (UPFV and CPFV) schemes of the Navier-Stokes equations were developed. In PFV method, the mass fluxes of across the cell faces of the control volume (CV) were expanded into power series of the grid spacing and the coefficients of the power series were determined by means of the conservation equation itself. The UPFV and CPFV scheme respectively uses the same nodes and expressions as those of the normal first-order upwind and second-order central scheme, which is apt to programming. The results of numerical experiments about the flow in a lid-driven cavity and the problem of transport of a scalar quantity in a known velocity field show that compared to the first-order UFV and second-order CFV schemes, upwind PFV scheme is higher accuracy and resolution, especially better robustness. The numerical computation to flow in a lid-driven cavity shows that the under-relaxation factor can be arbitrarily selected ranging from (0.3) to (0.8) and convergence perform excellent with Reynolds number variation from 10~2 to 10~4.

Research on buffer structure and flow field simulation of swash plate plunger type hydraulic transformer

In order to solve the problem of excessive noise and vibration during the operation of the hydraulic transformer,an optimization method of valve plate damping hole structure is proposed to alleviate the phenomenon of pressure shock.Firstly,the mathematical model of oil pressure gradient in the plunger cavity is established,and the incremental equation of pressure change is derived.Secondly,a kind of buffering structure is proposed,the corresponding relationship between the pressure change and the envelopment angle of the buffering hole and the aperture size is determined by analyzing the oil pressure change curve in the plunger cavity.Finally,the flow field models with buffering holes are established,and the transient simulation of the pressure change process under the optimal solution is carried out with ANSYS software and the flow field pressure distribution contours are obtained.Through the analysis of simulation results,it is concluded that the optimal envelope angle of the three buffer holes ofA-T-B-Ais 5°,and the optimal aperture is 1.8 mm,1.6 mm,and 1.7 mm,respectively.The buffer hole can achieve a better-buffering effect in the range of variable pressure angle[0°,101°].The buffer hole structure can effectively alleviate the pressure shock and reduce the noise level,which lays a foundation for the design and theoretical research of hydraulic transformers.

A NUMERICAL METHOD FOR SIMULATING NONLINEAR FLUID-RIGID STRUCTURE INTERACTION PROBLEMS

A numerical method for simulating nonlinear fluid-rigid structure interaction problems is developed. The structure is assumed to undergo large rigid body motions and the fluid flow is governed by nonlinear, viscous or non-viscous, field equations with nonlinear boundary conditions applied to the free surface and fluid-solid interaction interfaces. An Arbitrary-LagrangianEulerian (ALE) mesh system is used to construct the numerical model. A multi-block numerical scheme of study is adopted allowing for the relative motion between moving overset grids, which are independent of one another. This provides a convenient method to overcome the difficulties in matching fluid meshes with large solid motions. Nonlinear numerical equations describing nonlinear fluid-solid interaction dynamics are derived through a numerical discretization scheme of study. A coupling iteration process is used to solve these numerical equations. Numerical examples are presented to demonstrate applications of the model developed.

某东南沿海电厂钢结构腐蚀影响因素分析

目的 对比腐蚀环境因子分布和钢结构腐蚀事件分布,分析影响火力发电厂钢结构腐蚀的主要环境因素,探讨火力发电厂钢结构腐蚀的机理。方法 以东南沿海某火力发电厂为例,对电厂厂区进行网格化,利用便携式温湿度计进行逐网格温、湿度监测,逐网格收集结构物表面灰尘,并分析其中氯离子、可溶盐、酸碱含量等,开展腐蚀环境监测。统计从2012年至2022年10年间该电厂每一网格内的腐蚀防护工程,如腐蚀防护器件、装备、材料购置等项目的施工或应用次数。结果 温度、湿度及钢结构表面灰尘中氯离子含量、可溶盐含量、灰尘浸渍水p H等因子受海洋环境、厂区结构分布、生产活动多重原因的影响,随距海距离增加呈带状分布,或围绕生产设施点呈辐射分布。结论 环境因子对钢铁结构腐蚀的影响大小顺序为结构物灰尘含盐量>结构物灰尘浸渍水p H>相对湿度>结构物灰尘氯离子含量>温度。电厂钢结构腐蚀机理为雨水或大气凝结水溶出结构物表面灰尘的可溶性盐,含盐水经涂层缺陷输运至金属表面,成为钢铁腐蚀原电池的离子导路,导致钢结构发生电化学腐蚀。

基于遗传算法的自由曲面单层空间结构网格参数化自动生成及方向优化

自由曲面空间网格结构的力学性能和网格方向之间的联系复杂,难以快速直接地找到最优方向,若对结构网格方向进行多角度建模分析,则存在工作量大且准确性不易保证等问题。为了快速确定自由曲面空间网格结构的最优网格方向,提出一种基于遗传算法的自由曲面空间结构网格方向优化方法,以结构网格方向为优化变量,结合参数化建模软件Grasshopper和有限元分析软件SAP2000实现参数化分析,以结构应变能和结构最大位移两项力学指标作为优化目标,通过最小化目标函数实现结构网格方向优化。通过参数化编程,可实现快速自动优化,并结合工程案例,应用自动优化方法进行网格优化。结果表明:基于遗传算法的自由曲面空间结构网格方向自动优化法具有实用性和高效性,具有较高的工程应用价值。

碳纤维树脂基复合材料回转体的网格结构优化研究

针对复杂回转体的网格结构参数进行优化,以最大载荷质量比为优化目标,筋条几何参数及数量为设计变量,ABAQUS有限元屈曲分析为手段,确定模型结构承载效率的评价指标,进行单因素分析。其中,纵筋数量、纵筋宽度、筋条高度3种因素对模型承载效率影响较为显著。环筋数量与环筋宽度对模型承载效率的影响显著性较低,并结合实际制造条件分析得出用于正交试验的因素范围。利用数理上的正交性原理设计了L_(16)(4^(5))正交表与适用于复杂网格结构的正交试验方案。通过数值模拟,得到16组试验结果,并对试验结果进行极差分析。发现各因素对目标值影响程度的排序均为:纵筋宽度>筋条高度>纵筋数量>环筋数量>环筋宽度,并得出最优参数组合。最后对最优参数组合进行试验验证,找出使用最优参数组合的回转体所能承受最大载荷的理论值与实际值之间的差异,并分析差异出现的原因。

杭州电竞中心结构设计重难点概述

杭州电竞中心内圈主体结构采用钢框架-支撑结构,外圈采用“大倾角梭形斜柱+多段钢折梁框架”,是集承重与抗侧力于一体的结构体系,屋盖采用车辐式索承网格自平衡结构形式。详细介绍了地下结构、中央场馆结构的设计要点,门厅处利用建筑造型空间设计为多段钢折梁与跨层桁架相结合的结构形式;室内二层至三层楼面设计一浮空弧形人行桥,截面形式为薄壁钢箱梁,桥宽2.2m,跨度57m,采用“上挂下支”的稳定结构形式。对整体结构进行了静力弹性、动力弹塑性、振动台试验、典型节点有限元、整体稳定以及局部稳定等系列分析与试验。结果表明:结构在静力荷载和地震作用下强度和刚度均满足规范要求;典型节点极限承载力为荷载设计值的4.17倍;结构整体稳定性安全系数为3.79;斜柱局部稳定安全系数为2.52。合理的设计保证了结构的安全、经济和实用性。

附加阻尼控制下风电机组机网耦合载荷建模及分析

针对附加阻尼控制下风电机组机械载荷问题,开展风电机组机网耦合载荷建模及载荷特性分析研究。采用FAST与Matlab/Simulink软件联合方法,建立综合考虑机组机械特性和电气特性的并网风电机组机网耦合载荷模型。采用所建模型开展附加阻尼控制对机组机械载荷影响的仿真分析,并复现附加阻尼控制下风电机组机械系统与电力系统的机网共振现象。结果表明,所建模型能够表征附加阻尼控制下风电机组机械系统与电力系统的耦合互作用,系统低频振荡会导致机组关键结构出现明显振动载荷,且系统振荡频率与机组机械结构固有振动频率接近时两者共振会急剧加大机组振动载荷。

不均匀积雪致大跨网架结构局部损伤分析

网架结构管球连接处局部损伤是此类结构的重要安全隐患。在风致雪漂移引起的不均匀积雪荷载作用下,局部损伤会加剧,最终导致结构局部破坏。因此很有必要分析不均匀积雪荷载作用下带伤服役网架结构局部损伤劣化情况。采用CFD数值模拟技术,以一正放四角锥网架结构为研究背景,分析了在90°风向角、12 m/s风速下,持续降雪24 h中网架结构屋面不均匀积雪分布的变化情况,并建立可表征网架结构管球连接处存在裂纹损伤的多尺度模型,分析了网架结构节点存在不同裂纹尺寸局部损伤时,不均匀积雪致网架结构局部损伤劣化程度。结果表明:网架结构风致积雪不均匀程度非常显著,而且当网架结构管球连接处存在局部裂纹损伤时,在降雪中后期,有管球连接损伤的节点大多都出现了不同程度的裂纹扩展,节点为最不利分布的穿透型裂纹时,裂纹扩展最大为15.64 mm。说明在持续特大降雪这种极端荷载作用下,带伤服役网架结构局部损伤将进一步加剧,危及结构使用安全。

地震作用下网架结构失效模式的判定方法

利用增量动力分析方法,采用多段梁单元对无缺陷网架、考虑节点几何缺陷网架、杆件几何缺陷网架以及综合考虑节点和杆件几何缺陷的网架整体结构在地震作用下的响应进行了研究。对比表明:综合考虑节点和杆件几何缺陷会加速网架结构的失效进程,施加几何缺陷没有改变网架在同一地震激励下的失效模式。从结构响应的角度,根据网架结构特征点加速度位移曲线、位移时程曲线以及网架塑性杆件比例,提出了地震作用下判别网架结构失效模式的具体标准:若网架跨中位移时程曲线发生明显跳跃,网架塑性杆件占比较小且小于一定限值,可判定网架发生动力稳定失效。若网架跨中位移时程曲线无明显跳跃但逐渐发散,且网架塑性杆件占比较高并大于一定限值,可判定网架发生强度型失效。

喷水推进器进水流道格栅流固耦合特性研究

为了研究格栅部件对喷水推进船舶效率的影响,本文拟采用流固耦合的数值计算方法系统地对格栅表面受力及其强度特性进行计算,结合有限元方法和流固耦合理论,以STARCCM+和ABAQUS软件为工具,根据目前已知的格栅剖面设计方法,对目前格栅的剖面形式进行改进,形成新型对称剖面形式的格栅。基于上述计算流体力学与流固耦合计算方法对其进行周围流场、结构静力强度、结构动力强度进行计算与分析。结果表明:对称形式的格栅剖面对于降低格栅的变形与应力水平有一定的帮助,采用新型对称形式的剖面结构使格栅总体变形模式发生了变化,但是最大变形位置与最大应力出现在格栅的位置未发生明显变化,新型对称剖面形式格栅具有比较好的静强度与动强度特性,各栅条均匀承受流体载荷。

城市中压配电网雪花格式网架结构初探

为适应新型电力系统建设需求,提出一种适合国情的雪花格式网架结构。首先,总结国内外典型城市中压配电网结构的特征与优缺点;然后,结合天津已有网架结构,提出雪花格式网架结构及其构建方法;其次,分析测算雪花网结构的负荷转移能力、可靠性与效率效益水平;最后,从结构形式、适合场景等方面给出雪花网结构与花瓣结构等的综合对比情况。结果表明,雪花格式网架结构具有一定综合比较优势,可为中压配电网远景目标网架规划提供指导。