缩尺模型混合模拟试验测量误差分析及试验验证

基于缩尺模型子结构混合模拟试验方法,将正态分布随机数引入测量误差,利用MATLAB和OpenSEES混合编程技术,分别对剪切型模型、弯剪型模型进行了考虑测量误差的子结构混合模拟数值模拟分析。数值模拟结果表明：在满足JGJ/T 101-2015《建筑抗震试验方法规程》的误差范围内,缩尺比为1/2、1/4缩尺模型的测量误差与足尺模型相应测量误差基本相当。在缩尺比例不小于1/4情况下,随着地震峰值加速度增大,总的累积相对差值呈增加趋势;在相同地震峰值加速度作用下,总的累积相对差值随梁柱线刚度比增加呈减少趋势。通过1/2钢框架子结构混合模拟试验,验证了所提出的缩尺模型子结构混合模拟试验方法的精准性和可行性。     

CFD数值模拟的系统误差反馈及其实现

顾了近年来CFD数值模拟的系统误差及不确定度的研究进展，分析了系统误差反馈的基本程序及CFD在通风空调领域应用过程中所遇到的特殊困难，并介绍了CFD数值模拟的系统误差反馈思路。     

多房间建筑室内火灾数值模型的验证

介绍单层多房间建筑室内火灾数值模拟的验证研究。模型的计算值与Luo和Beck的实验结果进行了比较。为了考虑火灾的燃烧的过程，采用Laminar Flamelet方法。多房间建筑内热辐射的计算则使用DOM（discret ordinates method）方法。在验证工作中，最困难的工作是通风不良条件下火灾的模拟。由于在低含氧量的情况下，火焰的燃烧特性并没有得到很好的认识，因此对燃烧模型并没有引入任何的修改，以便保留处理燃烧过程方法的通用性以及便于检验Laminar Flamelet燃烧模型的能力。模拟结果与Luo和Beck的实验值能很好吻合。     

Three-dimensional numerical simulation of a hybrid fresh air and recirculated air diffuser for decoupled ventilation strategy

In conventional mixing ventilation air conditioning system, fresh air which has been polluted by recirculated air is supplied to occupied zone. Therefore, more fresh air which results in energy penalty needs to be supplied in order to keep good indoor air quality (IAQ) and thermal comfort. Some alternatives such as personalized ventilation air conditioning system can address this problem effectively by supplying fresh air directly into occupied zone. However, room layouts and visual effects will be influenced deeply because of extended air ducts. A new approach supplying fresh air directly by utilizing high velocity circular air jet without mixing with recirculated air is introduced. Objective measurements and computational fluid dynamics (CFD) tool are used to evaluate corresponding indoor parameters to verify that it can both supply fresh air into occupied zone effectively and avoid draught rating.     

Post-rehabilitation assessment of a centenary steel bridge through numerical and experimental analysis

This paper presents an experimental and numerical analysis regarding the structural assessment of an existing steel bridge – the Eiffel Bridge – after a recent rehabilitation. The Eiffel Bridge, a centenary road–rail truss bridge, comprising two superimposed decks, was subjected to major rehabilitation works involving the replacement of the top concrete deck, the strengthening of the upper chords of the main truss girders and the replacement of the support bearings. In this context a load test and an environmental test were carried out aiming at the assessment of the new structural condition and the evaluation of the effectiveness of the elements' strengthening. A structural analysis was carried out in order to characterize the most relevant aspects of the structural behavior and to support the discussion of the field results. Particular aspects concerning the main girders' bending, the nature of nodes' rotations, and the response under temperature changes are highlighted. The effectiveness of the strengthening of the top chords is verified based on the strains' measurements. Finally, it is shown that the thorough characterization of the structural behavior enabled the establishment of a reference condition for future assessments of the structure.     

Shaking table test and numerical simulation on a vertical hybrid structure under seismic excitation

A shaking table test of a 12‐story steel/reinforced concrete (S/RC) frame, which is composed of a 4‐story steel frame in the higher part, a 1‐story S/RC frame as a transition story in the middle part, and a 7‐story reinforced concrete (RC) frame in the lower part of the model, has been conducted, and its results are compared with those of a standard 12‐story RC frame to evaluate seismic performance of this S/RC frame. The numerical simulation on such hybrid frame structure has been performed and validated by the above experimental results. It is found that irregular lateral‐stiffness distribution along structural height will not only increase rotation at the joint of boundary between transition story and steel frame or concrete frame but also enlarge rotation at such joint and lead to more obvious rigid deformation in steel frame of S/RC frame, which will undoubtedly intensify bending failure. Meanwhile, acceleration response of the upper steel frame will reach its peak when characteristic site period is near the counterpart of the upper steel frame. Further, the maximum interstory drift under frequent earthquake excitation is at the lower substructure, namely, the RC frame, but this is not the case in rare earthquake situation. When it comes to determining damping ratio for vertical hybrid structure, a general method for engineering, which takes concrete and steel damping ratio for the whole structure analysis and then gets envelopes of these results for design, may yield conservative results. Meanwhile, such method may underestimate responses near the transition story.     

混杂纤维混凝土动态压缩性能试验及数值模拟研究

为了研究钢-聚丙烯混杂纤维混凝土(HFRC)的动态压缩性能及损伤机理,采用分离式霍普金森压杆(SHPB)装置进行了冲击压缩性能试验。试验得到了设计强度为CF50的HFRC和钢纤维混凝土(SFRC)两种材料在四个不同应变率下的应力-应变曲线,并从破坏应力、峰值应变、峰值韧度等方面进行分析,结果表明HFRC的动态力学性能优于SFRC。采用ANSYSLS-DYNA有限元程序,选用HJC本构模型模拟HFRC动态冲击压缩性能,在验证数值模拟精度的基础上重构材料的应力-应变曲线,数值模拟结果与试验结果基本吻合。通过模拟试件的破坏过程,得到了HFRC在动态冲击荷载作用下的损伤演化方式,为材料的动态损伤机理研究提供理论依据。     

Debris flow hazard assessment by combining numerical simulation and land utilization

Debris flow has caused serious human casualties and economic losses in the main earthquake-hit areas affected by the Wenchuan earthquake. As one of the important and effective means of non-engineering disaster mitigation, debris flow hazard assessment is a key issue for the sustainable economic and social development of earthquake-hit areas. This article illustrates a new method to quantify the debris flow hazard by combining debris flow simulated results with different land utilization within the influence area. The Guo Juanyan gully in Dujiangyan city, Sichuan province, China, located in the meizoseismal area of the Wenchuan earthquake, was selected as the study area. The rainfall characteristics, including the rainfall pattern and the 10-min, 1-h, and 24-h critical rainfalls, were fully explored first. Then, the numerical simulation method was applied as a modeling tool to simulate debris flow influence area and final buried depth under rainfall with different return periods. The simulated results under a 100-year return period rainfall were validated based on field measurements. Finally, the debris flow hazard maps under different return periods were overlapped by combining the simulated results and the types of land utilization. The proposed method can enhance the accuracy of debris flow hazard assessment and can be widely used for debris flow mitigation, which has important application value.     

天津某深基坑工程施工监测及数值模拟分析

介绍了天津铜锣湾广场深基坑工程开挖实例。通过对深基坑开挖过程中的支护结构内力、坑周土体水平位移等的现场监测和数值模拟分析,讨论了基坑开挖过程中支护结构受力的特点及其对周围环境的影响,得到基坑周边土体水平位移的变化规律,为考虑施工因素的深基坑开挖及支护结构设计提供了依据。分析表明:土方开挖对基坑周围土体的影响范围约为两倍的开挖深度;开挖过程中土体及围护桩最大位移位置基本上都处于基坑开挖面附近;在基坑施工过程中,应该尽量减小无支撑暴露的时间,加快底板浇注,防止因土体流变而产生过大的位移;对于环梁支撑体系,如果支撑布置不规则,会造成受力不均,容易产生较大的弯矩值,会对环梁支护结构产生不利影响。     

An energy-based partial pushdown analysis procedure for assessment of disproportionate collapse potential

A disproportionate (or progressive) collapse is triggered by localized structural damage that propagates throughout a large portion of a structural system. The current guidelines issued by the US Department of Defense use the alternative path method to assess the vulnerability of a structural system to disproportionate collapse. In this method, the capability of a structure to sustain local damage is evaluated by notionally removing primary load-bearing elements and checking whether the local damage can be absorbed. The assessment can be performed using linear or nonlinear static structural models or a nonlinear dynamic model. Although nonlinear dynamic analysis gives the most accurate results, it is computationally intensive and requires considerable skill to implement properly. In this paper, the vulnerability of three steel frames to disproportionate collapse is assessed using an energy-based nonlinear static pushdown analysis. The predictions are sufficiently close to the results of a nonlinear dynamic time history analysis that the method would be useful for disproportionate collapse-resistant design of buildings with regular steel framing systems.     

数值模拟联合算法及其在润扬大桥可靠度评估中的应用

为了定量研究大跨桥梁在外界随机因素作用下的结构安全性,实现在线状态的可靠度评估,利用可靠度的随机有限元法对润扬大桥悬索桥在正常运营和损伤等多种工况下的结构可靠度进行了数值模拟和可靠度评估。分析中采用蒙特卡罗重要抽样法和中心复合响应面法的联合算法作为数值模拟的基本工具,介绍了联合算法的具体实现途径、随机变量的参数定义并对大跨桥梁基于可靠度指标的评估准则进行了讨论。得到了多个随机变量的概率灵敏度、主要失效模式所对应的可靠度指标及其相应的状态等级。算例分析结果表明,基于随机有限元的可靠度分析方法可以较好地描述大跨桥梁的非线性特征,联合算法的应用提高了可靠度分析的效率和精度,其结果为润扬大桥悬索桥的状态评估和健康监测提供了参考。     

Experimental study and numerical simulation for a storehouse fire accident

Full-scale experiment and numerical simulations are carried out on a shelf fire in a storehouse to study the ignition manner, the fire spread and the combustion characteristics. A computational fluid dynamics (CFD) model of fire-driven fluid flow, FDS (Fire Dynamics Simulator), is used to solve numerically a form of the Navier–Stokes equations for fire. Ignition manner experiments with both cigarette ends and lighter are conducted first. Then a full-scale experiment on a shelf fire is performed. The temperatures are measured and the fire growth and spread process is analyzed. A numerical model is used to simulate the experiment; the temperatures, fire growth and heat release rate are studied. In numerical simulations, the grid size resolution is analyzed. The experimental results of temperatures and the fire growth and spread process are compared with the results of numerical simulations. It shows that the numerical results are in good agreement with the experimental results. The chimney effect is also observed in both the experiment and the simulation. These useful data can be helpful in the numerical reconstruction of the whole storehouse fire accident.     

沉淀池的三相流数值模拟

采用FLUENT中多相流Mixture模型对辐流式沉淀池内流场、悬浮物浓度场进行模拟,经分析认为不同粒径的颗粒可设置为不同的相,据此实现了对沉淀池的三相流数值模拟。     

垃圾场施工开挖监测及数值模拟分析

通过对某垃圾场施工开挖过程的长期监测,得到了垃圾场开挖过程的变形特性,并对施工开挖效应进行了有限元数值模拟,通过实测数据与数值模拟结果的对比,证明了有限元模型的正确性,进一步分析了土层参数对于垃圾场变形的影响。     

某仓库火灾实验与数值模拟对比

采用FDS模拟某仓库火灾,并与实验结果比较温度曲线和火灾蔓延过程。在仓库中放置三层金属货架,分打火机和烟头两种引燃方式和不同点火位置进行实验。模拟与实验得到的温度曲线相似度很高。250s前模拟与实验得到的火灾蔓延过程比较相似,250s后由于纸箱倒塌,模拟结果出现延迟。合理摆放货物的情况下烟头引燃仓库火灾的可能性较小。     

Estimation of an efficiency factor for a greenhouse: a numerical and experimental study

An analytical expression for instantaneous thermal efficiency (η_i) of a greenhouse in terms of design and climatic parameters has been derived by considering the energy balance equations for different components of the greenhouse. The present analysis can be used for testing the suitability of greenhouses of different sizes and shapes for given climatic conditions. Numerical computations for determination of instantaneous thermal efficiency (η_i) and greenhouse efficiency factor (F′) have been carried out for a typical greenhouse. Parametric studies have also been carried out to predict the performance of the system. Experimental validation has also been reported for a climatic condition of Delhi. It is observed that:o

1. 1. there is a fair agreement between theoretical and experimental observations, and
2. 2. the instantaneous thermal efficiency (η_i) increases with increase of relative humidity (γ) due to less evaporation as expected.

     

吸收边界条件下平面SH波散射的数值模拟

建立了在无限区域内求解任意形状散射体对SH波散射的数值模拟方法。采用一种新的吸收边界条件对Sommerfeld辐射条件进行近似，这种吸收边界条件具有解耦特性，不但简化了计算，且近似程度较高。数值计算结果与解析结果的比较表明了此方法具有良好的吸收效果。     

充气锚杆数值单元的建立与分析

为了研究充气锚杆的受力特征及相应参数对于锚杆锚固力的影响,利用数值方法建立了充气锚杆的计算模拟单元,分别改变锚杆充气长度和充气压力,得到相应锚固力的变化规律,结果表明:随着橡胶膜长度的增大,锚杆的极限锚固力不断增大,二者符合线性关系;由于橡胶膜充气压力的不同,导致了不同的极限锚固力,锚杆极限锚固力与充气压力之间的关系,以及锚杆达到极限锚固力所需的位移与充气压力之间的关系,均可用线性方程进行描述。     

Rotation errors in numerical manifold method and a correction based on large deformation theory

Numerical manifold method (NMM) is an effective method for simulating block system, however, significant errors are found in its simulation of rotation problems. Three kinds of errors, as volume expansion, stress vibration, and attenuation of angular velocity, were observed in the original NMM. The first two kind errors are owing to the small deformation assumption and the last one is due to the numerical damping. A large deformation NMM is proposed based on large deformation theory. In this method, the governing equation is derived using Green strain, the large deformation iteration and the open-close iteration are combined, and an updating strategy is proposed. The proposed method is used to analyze block rotation, beam bending, and rock falling problems and the results prove that all three kinds of errors are eliminated in this method.     

Anisotropic properties of shale and its impact on underground structures: an experimental and numerical simulation

Bulletin of Engineering Geology and the Environment - In this study, the anisotropic properties, including strength, deformation, AE response, and failure pattern of Hunan shale were investigated...