Dynamic Response of A Group of Cylindrical Storage Tanks with Baffles Considering the Effect of Soil Foundation

The sloshing in a group of rigid cylindrical tanks with baffles and on soil foundation under horizontal excitation is studied analytically.The solutions for the velocity potential are derived out by the liquid subdomain method.Equivalent models with mass-spring oscillators are established to replace continuous fluid.Combined with the least square technique,Chebyshev polynomials are employed to fit horizontal,rocking and horizontal-rocking coupling impedances of soil,respectively.A lumped parameter model for impedance is presented to describe the effects of soil on tank structures.A mechanical model for the soil-foundation-tank-liquid-baffle system with small amount of calculation and high accuracy is proposed using the substructure technique.The analytical solutions are in comparison with data from reported literature and numerical codes to validate the effectiveness and correctness of the model.Detailed dynamic properties and seismic responses of the soil-tank system are given for the baffle number,size and location as well as soil parameter.

Testing method of rock structural plane using digital drilling

The rock mass consists of rock blocks and structural planes,which can reduce its integrity and strength.Therefore,accurately obtaining the characteristics of the rock mass structural plane is a prerequisite for evaluating stability and designing supports in underground engineering.Currently,there are no effective testing methods for the characteristic parameters of the rock mass structural plane in underground engineering.The paper presents the digital drilling technology as a new testing method of rock mass structural planes.Flawed rock specimens with cracks of varying widths and angles were used to simulate the rock mass structural planes,and the multifunctional rock mass digital drilling test system was employed to carry out the digital drilling tests.The analysis focuses on the variation laws of drilling parameters,such as drilling pressure and drilling torque,affected by the characteristics of prefabricated cracks,and clarifies the degradation mechanism of rock equivalent compressive strength.Additionally,an identification model for the characteristic parameters of rock mass structural planes during drilling is established.The test results indicate that the average difference of the characteristics of prefabricated cracks identified by the equivalent compressive strength is 2.45°and 0.82 mm,respectively.The identification model while drilling is verified to be correct due to the high identification accuracy.Based on this,a method for testing the characteristic parameters of the surrounding rock structural plane while drilling is proposed.The research offers a theoretical and methodological foundation for precise in situ identification of structural planes of the surrounding rock in underground engineering.

Generalized response displacement methods for seismic analysis of underground structures with complex cross section

The response displacement method(RDM)is recommended for the seismic analysis of underground structures in the transverse direction for many codes,including bases for design of structures-seismic actions for designing geotechnical works(ISO 23469)and code for seismic design of urban rail transit structures(GB 50909-2014).However,there are some obvious limitations in the application of RDM.Springs and the shear stress of the soil could be approximately evaluated for the structures having a simple cross section,such as rectangular and circular structures.It is necessary to propose simplified seismic analysis methods for structures with complex cross sections.This paper refers to the idea of RDM and proposes three generalized response displacement methods(GRDM).In GRDM1,a part of the soil surrounding a structure is selected to generate a generalized underground structure with a rectangular cross section,and the same analysis model as RDM is applied to analyze the responses of the structure.In GRDM2,a hollow soil model without a generalized structure is used to compute the equivalent load caused by the relative displacement of the soil,and the soil-structure interaction model is applied to calculate the responses of the structure.In GRDM3,a continuous soil model is applied to compute the equivalent load caused by the relative displacement and shear stress of the soil,and the soil-structure interaction model is applied to analyze the responses of the structure,which is the same as the model used in GRDM2.The time-history analysis method(THAM)is used to evaluate the accuracy of the proposed simplified methods.Results show that the error of GRDM1 is about 20%,while the error is only 5%for GRDM2 and GRDM3.Among the three proposed methods,GRDM3 has obvious advantages regarding calculation efficiency and accuracy.Therefore,it is recommended to use GRDM3 for the seismic response analysis of underground structures that have conventional simple or complex cross sections.

Seismic wave input method for three-dimensional soil-structure dynamic interaction analysis based on the substructure of artificial boundaries

The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the fi nite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave fi eld on the nodes of the substructure composed of elements that contain artifi cial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artifi cial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplifi ed by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verifi ed by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.

The Stress Combination Method for the Fatigue Assessment of the Hatch Corner of a Bulk Carrier Based on Equivalent Waves

The stress combination method for the fatigue assessment of the hatch comer of a bulk carrier was investigated based on equivalent waves. The principles of the equivalent waves of ship structures were given, including the determination of the dominant load parameter, heading, frequency, and amplitude of the equivalent regular waves. The dominant load parameters of the hatch comer of a bulk carrier were identified by the structural stress response analysis, and then a series of equivalent regular waves were defined based on these parameters. A combination method of the structural stress ranges under the different equivalent waves was developed for the fatigue analysis. The combination factors were obtained by least square regression analysis with the stress ranges derived from spectral fatigue analysis as the target value. The proposed method was applied to the hatch comer of another bulk carrier as an example. This shows that the results from the equivalent wave approach agree well with those from the spectral fatigue analysis. The workload is reduced substantially. This method can be referenced in the fatigue assessment of the hatch comer of a bulk carrier.

Numerical Analysis on Neutron Shielding Structure of ITER Vacuum Vessel

The neutron shielding component of ITER （International Thermonuclear Experimental Reactor） vacuum vessel is a kind of structure resembling a wall in appearance. A FE （finite element） model is set up by using ANSYS code in terms of its structural features. Static analysis, thermal expansion analysis and dynamic analysis are performed. The static results show that the stress and displacement distribution are allowable, but the high stress appears in the junction between the upper and lower parts. The modal analysis indicates that the biggest deformation exists in the port area. Through modal superposition, the single-point response has been found with the lower rank frequency of the acceleration seismic response spectrum. But the deformation and the stress values are within the permissible limit. The analysis results would benefit the work in the next step and provide some reference for the implementation of the engineering plan in the future.

Method to analyze wrinkled membranes with zero shear modulus and equivalent stiffness

To solve the problems of divergence,low accuracy and project application of membrane wrinkling analysis,an analysis method of zero shear modulus and equivalent stiffness was proposed.This method is an improvement to the previous method (Method I) of local coordinate transposition and stiffness equivalence.The new method is derived and the feasibility is theoretically proved.A small-scale membrane structure is analyzed by the two methods,and the results show that the computational efficiency of the new method (Method II) is approximately 23 times that of Method I.When Method II is applied to a large-scale membrane stadium structure,it is found that this new method can quickly make the second principal stress of one way wrinkled elements zero,and make the two principal stresses of two-way wrinkled elements zero as well.It could attain the correct load responses right after the appearance of wrinkled elements,which indicates that Method II can be applied to wrinkling analysis of large-scale membrane structures.

An Improved Parameters Extraction Method for Dumbbell-Shaped Defected Ground Structure

The paper presents an improved equivalent circuit parameters extraction method for the dumbbell-shaped defected ground structure (DGS). The new extraction parameters equations are obtained in closed-form expressions, which contain S11 and S21. The DGS unit with center frequency of 5 GHz is designed and fabricated on a TLX substrate with thickness of 1 mm and dielectric constant of 2.55. The circuit simulated results are in good agreement with the measured results. This parameters extraction method can be widely used for the design and analysis of DGS .

Pushover analysis procedure for systems considering SSI effects based on capacity spectrum method

This paper presents a new procedure to transform an SSI system into an equivalent SDOF system using twice equivalence. A pushover analysis procedure based on the capacity spectrum method for buildings with SSI effects （PASSI） is then established based on the equivalent SDOF system, and the modified response spectrum and equivalent capacity spectrum are obtained. Furthermore, the approximate formulas to obtain the dynamic stiffness of foundations are suggested. Three steel buildings with different story heights （3, 9 and 20） including SSI effects are analyzed under two far-field and two near-field historical records and an artificial seismic time history using the two PASSI procedures and the nonlinear response history analysis （NLhRHA） method. The results are compared and discussed. Finally, combined with seismic design response spectrum, the nonlinear seismic response of a 9-story building with SSI effects is analyzed using the PASSI procedures, and its seismic performance is evaluated according to the Chinese ＇Code for Seismic Design of Buildings. The feasibility of the proposed procedure is verified.

基于等效线性化的SISC隔震框架结构动力响应分析

为探究采用废旧轮胎隔震垫(STP)制成的柱下新型隔震装置(SISC)在村镇框架结构中的隔震效果,通过SAP2000建立隔震与非隔震三层框架结构模型,利用简化计算方法进行初步布置,采用反应谱法及时程分析法对比了隔震前后层间剪力比,并进行了上部结构的动力响应分析。结果表明:简化计算方法、振型分解反应谱法及时程分析法得到的底部剪力比分别为0.4207、0.4091、0.4491;隔震结构较非隔震结构自振周期延长2~3倍,由时程分析法可得隔震结构中上部结构层间位移角、顶层加速度较非隔震结构最大分别降低86.48%、49.26%,均满足规范限值要求,上部结构整体呈现平动;SISC隔震框架结构按照简化计算方法进行SISC初步布置具有可行性,该研究成果为STP隔震体系在村镇框架结构中的实际应用提供参考。

正交异性钢桥面板双轴疲劳性能评估

为精确评估正交异性钢桥面板在双轴应力状态下的疲劳性能,以东营胜利黄河大桥为背景,建立该桥正交异性钢桥面板顶板、U肋、横隔板交叉连接部位焊缝的节段三维有限元模型,采用等效结构应力法对正交异性钢桥面板体系的双轴疲劳问题进行研究;通过模型试验验证正交异性钢桥面板体系的双轴疲劳特性,并进行其构造细节疲劳寿命评估。结果表明:弧形切口起焊点的疲劳裂纹萌生位置在横隔板下方焊趾处,经历裂纹萌生、裂纹稳定扩展和裂纹失效3个阶段,最终失效阶段裂纹形式为Ⅱ型裂纹主导的Ⅰ-Ⅱ型复合裂纹,此为该桥正交异性钢桥面板结构体系的主导疲劳失效模式;顶板焊缝焊趾及弧形切口起焊点焊趾处于双轴应力状态,面内剪切结构应力幅对疲劳应力的影响显著,按单轴疲劳应力进行寿命预测误差较大,按单轴疲劳应力状态对结构进行疲劳寿命设计偏于不安全;基于组合等效结构应力法的计算值与试验值吻合较好,各焊接细节计算得到的最大值下的疲劳裂纹起裂位置均与试验结果一致,按双轴疲劳应力预测疲劳寿命与试验值吻合较好,疲劳寿命评价精确度较高。

含金属内衬复合材料抗爆容器的初始设计方法

针对目前复合材料抗爆容器工程设计方法合理性欠缺现状,基于轻量化思路,结合动力系数法及网格理论提出了可用于含金属内衬复合材料抗爆容器设计的“等代设计法”。采用该方法完成了内径0.5 m、抗爆当量1 kg TNT的复合材料圆筒初始设计,复合材料圆筒的面密度由等效金属圆筒的19.3 g/cm^(2)降低到3.6 g/cm^(2)。在该圆筒内部开展了炸药加载试验,结果表明圆筒设计合理,该设计方法有效,为抗爆容器的轻量化设计提供了新思路。

大跨度钢屋盖轮辐式索桁架结构施工方法与数值模拟

轮辐式张拉结构通过张拉柔性拉索形成刚度,抵抗结构所承受的外荷载。为保证柔性结构张拉成型全过程安全可靠、张拉完成后满足设计要求,对施工过程各阶段进行数值模拟和计算分析,确定合理的施工方案。采用有限元软件ANSYS建立济南市黄河体育中心钢屋盖轮辐式索桁架整体分析模型;通过等效降温法对轮辐式拉索施加预拉力,得到不同施工阶段整体结构力学响应;对索桁架结构展开形态分析,使索构件实际内力与设计拉力吻合。研究表明,采用等效降温法可实现对大跨度钢屋盖轮辐式拉索预拉力的模拟,整体结构在各施工阶段的力学响应满足安全性要求。

电动挖掘机落物保护装置拓扑优化设计

针对某型电动挖掘机的乘员防护,提出使用基于等效静态载荷法的拓扑优化方法设计落物保护装置(Falling Object Protective Structures,FOPS)。首先,使用基于位移等效原则的等效静态载荷法,将动态非线性碰撞过程简化为多工况条件下的静态非线性变形过程。随后,提出使用加权系数法,将动态非线性拓扑优化简化为多工况条件下的静态非线性拓扑优化,可显著提高拓扑优化的计算速率和收敛性。最后,基于拓扑优化结果设计FOPS,并按照GB/T 17771—2010进行仿真试验分析。结果表明,新设计的FOPS无须额外加强即可满足乘员落物保护要求,且FOPS的总质量减轻了49.8 kg,这对降低工程机械的采购和使用成本,以及满足节能减排具有积极意义。

基于均匀化拓扑优化的轻质多孔结构等效方法

通过拓扑优化设计得到的孔洞结构,往往不规则,甚至过于复杂、难于加工、多数需要进行二次设计,为了避免二次拓扑优化求解过程复杂、效率低、耗时长,甚至出现不收敛、棋盘格、灰色单元等情况,提出一种基于均匀化拓扑优化的轻质多孔结构等效方法。该方法首先需对研究结构进行初次拓扑优化,提取拓扑优化后的关键性能参数如应变能、最大应力、最大位移等。然后依据上述提取的参数作为后续寻求结构等效的条件。基于能量均匀化方法求解出与拓扑优化后等效的微结构。将等效微结构阵列得到的周期排列结构即为轻质多孔等效结构。最后对拓扑优化结构和轻质多孔等效结构进行有限元分析对比,验证此方法的可行性。结果表明:轻质多孔等效结构与初始拓扑结构相比,其综合性能基本不变,但因轻质多孔结构的规则性使得加工难度大大降低。

基于非线性方法的核级双层容器及支承结构热棘轮效应研究

核级双层容器承担一回路压力边界和一回路冷却剂“纵深防御”包容的双重安全功能,是高温反应堆本体常用的一种结构形式。然而内层容器在瞬态工况下温度变化剧烈,内外层容器之间导热性能差,内外温差大,热棘轮效应是可能的重要失效机制。本文通过建立核级双层容器及支承结构轴对称有限元模型,使用非线性方法分析其在热-机循环载荷作用下温度、应力和应变的响应,研究棘轮效应分布的规律和特征。结果表明:热棘轮效应显著,是该类容器的主要失效模式;热棘轮敏感区域分布具有多点式的特点,在内外层容器不同部位均有涉及;危险区域的塑性应变累积行为主要出现在循环温度载荷的降温阶段,应变增量随循环次数的增加逐步稳定。结论指出热棘轮效应是核级双层容器结构设计必须关注的重点问题,所建立的非线性分析方法是解决该问题的有效手段。本研究可为核级双层容器热棘轮分析以及一回路工况参数优化设计和应变监测测点布置提供重要方法指导。

基于等效结构应力法的高强钢焊接结构低温主S-N曲线

现有的疲劳S-N曲线已不再适用于北极的低温环境,为了评估北极海洋工程设备材料的低温疲劳寿命,有必要建立金属结构尤其是焊接结构的低温疲劳S-N曲线。本文基于等效结构应力法,计算出Q690高强钢管环焊缝的主S-N曲线,并通过共振疲劳试验对该方法进行了验证。在此基础上,结合大量的高强钢焊接结构试验结果,将温度敏感因子c引入到低温疲劳主S-N曲线的推导中,首次建立了基于低温金属焊接结构的主S-N曲线,并对文献中的疲劳S-N试验数据和ASME中的修正方法进行了对比和验证。结果表明,等效结构应力法能够较准确地计算出焊缝疲劳S-N曲线,推导出的金属焊接结构低温主S-N曲线与试验曲线吻合较好,能够满足低温地区工程要求,可为高强钢焊接结构在北极地区低温环境中的广泛应用提供理论指导。该方法可以为金属焊接结构的低温疲劳研究节省大量的成本,减少非标准试验操作造成的不必要的误差。这对北极海洋工程设备的设计、安全运行和疲劳评估具有重要意义。

多点点焊件疲劳寿命分析

根据ST12钢的双点及三点拉剪电阻点焊试件的恒幅疲劳测试结果,分别使用缺口应力法和等效结构应力法进行疲劳寿命预测。在使用缺口应力法时,按试件的实际尺寸和国际焊接学会(International institute of welding, IIW)推荐标准,分别建立了双点和三点拉剪试件的三维实体有限元模型进行弹性应力分析,从有限元分析结果提取von Mises最大应力变化值,结合IIW推荐标准中的S-N曲线对试件进行疲劳寿命分析预测;在使用结构应力法时则采用梁壳混合单元进行有限元应力分析,并且根据主S-N曲线进行疲劳寿命预测。结果表明,在低周疲劳范围内,缺口应力法和等效结构应力法预测的结果相对于试件的实际寿命有较好地相关性,其中等效结构应力法的结果更接近实验寿命结果。

基于等效静态载荷法的多相材料结构动态拓扑优化设计

为了满足多相材料结构动态性能要求,提出一种基于等效静态载荷法的多相材料结构动态拓扑优化设计方法。采用序列固体各向同性料插值模型惩罚刚度矩阵和质量矩阵,以多个动载荷作用的多相材料结构总动态柔顺度最小化为优化目标,以结构质量和成本为约束条件,构建多相材料结构动态拓扑优化模型,利用等效静态载荷法将多相材料结构动态拓扑优化问题转化为多工况下的多相材料结构静态拓扑优化问题,以降低灵敏度分析的复杂程度;采用移动渐近线算法求解多相材料结构动态拓扑优化问题。数值算例结果表明所提方法是有效性的,与传统的拓扑优化方法相比,基于等效静态载荷法的多相材料结构动态拓扑优化求解时间节省了75%,大大提高了计算效率;与单相材料拓扑优化结果相比,多相材料结构动态拓扑优化设计获得的结构具有更好的动态性能。

独立式桥墩防撞结构防撞性能研究

为了解独立式桥墩防撞结构(由钢管混凝土立柱、钢横梁等结构组成)抵御船舶撞击的能力,并选取合适的结构方案,以广州明珠湾大桥为背景进行研究。采用显式动力软件LS-DYNA建立船舶与独立式桥墩防撞结构计算模型,分析立柱间距4.8 m且不设防撞套箱(方案1)、立柱间距6.7 m且不设防撞套箱(方案2)、立柱间距6.7 m且设防撞套箱(方案3)3种独立式桥墩防撞结构方案在3000 DWT船舶中心碰撞和偏心碰撞下的结构动力响应和船舶损伤。结果表明:在中心碰撞下,方案2较方案1能有效减少撞击时迎撞立柱的位移和轴向拉力峰值,提高了独立式桥墩防撞结构的防护性能和承载能力,方案3的防撞套箱能起到缓冲消能的作用;在偏心碰撞下,方案3防撞套箱的旋转能够使船舶远离桥墩,保护桥墩和拱脚下弦杆不受船舶的撞击作用,具有良好的导向能力。设防撞套箱的独立式桥墩防撞结构已在广州明珠湾大桥中应用。