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1.
二维混凝土随机骨料模型研究   总被引:69,自引:0,他引:69  
为研究二维混凝土随机骨料的投放算法、为混凝土宏观强度分析研究提供依据,将混凝土考虑为由粗骨料和水泥砂浆胶体构成的复合材料,确定了以面积为标度的骨料侵入判断准则和凸多边形骨料生成方式,在此基础上形成二维混凝土随机骨料投放算法。同其他方法相比,建立的"凸型"骨料随机投放算法简单,更易于推广到三维空间。最后给出了骨料随机投放的二维数值混凝土模型和一个简单的混凝土不均质特性分析实例,以说明该文算法的有效性。  相似文献   

2.
随机凹凸型骨料在混凝土细观数值模型中配置算法研究   总被引:4,自引:0,他引:4  
混凝土细观结构随机骨料数值模型的建立及其损伤破坏力学分析,可为混凝土宏观强度分析研究提供依据.适于满足各类指定的骨料级配曲线,针对任意形状、大小的骨料颗粒的生成与投放过程提出了一种改进算法,突破了传统凸形骨料的投放限制,使细观数值模型更接近于混凝土试件断面的实际.具体实现过程中,基于计算机图形学多边形重叠判断及区域填充算法,来消除预投放骨料间的交叠现象.此外,利用粒径极值比来控制骨料形状.还提出骨料颗粒投放过程的用户微干预方法,比较传统完全随机法,提高了投放的成功率及效率.算例验证了骨料的实际投放效果.  相似文献   

3.
随机骨料投放的分层摆放法及有限元坐标的生成   总被引:5,自引:0,他引:5  
为了提高混凝土细观力学预处理过程中骨料投放效率,提出了一种随机骨料的投放方法。基于混凝土随机骨料生长方式,提出了骨料投放的分层摆放法。采用状态矩阵法的判别准则,判别空间中任意一点与骨料凸多边形/凸多面体的位置关系,实现了二维平面/三维空间有限元网格坐标的生成。结果表明,与现有方法相比,该方法可节省CPU时间,具有极高效率。这为实现大规模数值细观混凝土预处理,提供了有力的工具。  相似文献   

4.
大体积混凝土随机骨料数值模拟   总被引:23,自引:4,他引:23       下载免费PDF全文
在细观力学基础上将混凝土考虑为粗骨料、砂浆及它们之间的黏结层组成的三相复合材料.针对大坝等大体积全级配或三级配混凝土,骨料含量比较高(60%-70%)的特点,提出了一种新的高效投放算法,通过一次性随机投放形成同种骨料的所有三角形基骨料,然后在此基础上随机延凸,生成任意形状的随机骨料.与通常的圆形骨料只有2个随机数相比,该生成算法中每个骨料一般需要7个以上随机数,同时该方法的生成效率和骨料含量明显高于其他多边形骨料的生成算法.采用大型通用有限元软件MARC对东江拱坝三级配混凝土试件的单向轴拉破坏过程进行了全过程数值模拟,数值模拟计算结果与试验结果接近.  相似文献   

5.
为了研究混凝土细观力学现象,对混凝土力学行为进行数值模拟,采用二维细观结构数值模拟骨料随机投放,为进行混凝土有限元细观力学分析提供了数值结构模型.采用matlab软件建立了混凝土骨料随机投放模型,其中考虑混凝土为由骨料、砂浆及二者之间的黏结界面组成的三相复合材料,在投放过程中,以骨料面积比例为基本参数、黏结界面厚度取骨...  相似文献   

6.
为了研究混凝土的降阶多尺度方法动态力学特性,模拟随机形状和大小的凸多面体骨料,并考虑了骨料的随机结构和位置,建立了混凝土三维细观仿真模型,通过单轴静态压缩仿真对模型进行了验证.根据细观尺度下混凝土的实际结构,对动态SHPB冲击载荷作用下的混凝土进行仿真模拟,得到了不同入射速度下的实验数据.结果表明,仿真结果与实验结果吻合较好,多尺度方法可以将细观尺度特征和宏观尺度动态力学行为联系在一起,验证了多尺度方法的有效性,在混凝土各相力学性能方面,降阶均匀化方法相比细观尺度模型提高了计算效率.  相似文献   

7.
应用 "被占领区域剔除"的思想,对原有的混凝土骨料三维随机分布的数值模型进行改进,提出了一种新的混凝土骨料三维随机分布数值模型建立的方法,并基于弹性损伤本构关系,采用双折线损伤演化模型描述混凝土细观各相弹性损伤退化,用弹性模量的折减程度来反映混凝土试件在加载过程中的损伤程度.对混凝土圆柱体试件进行了数值模拟计算,并依据混凝土破坏过程图比较了数值模拟的破坏过程与CT试验结果,发现试件破坏时裂纹的萌生、扩展过程与CT观测到的过程具有相似性,表明该模型较好地模拟了混凝土的不均匀性与各向异性,证明建立该模型的方法是可行的.  相似文献   

8.
基于改进随机骨料模型的混凝土细观断裂模拟   总被引:10,自引:0,他引:10  
为了更好地研究混凝土的力学性能和破坏机理,该文在已有细观力学模型的基础上,发展了高效的骨料投放方法及单元筛分准则.基于连续介质力学的方法,采用弹性损伤本构关系描述混凝土细观各相材料力学行为,建立了随机骨料数值模型及相应的细观单元参数选取方法.以多组不同骨料分布的Petersson三点弯曲梁为例,分析和探讨了混凝土的破坏机理.结果表明,该数值模型能较好地模拟混凝土I型断裂拉伸破坏全过程,与试验结果表现出良好的一致性.  相似文献   

9.
为了验证数值试验方法生成混凝土随机骨料模型的合理性,首先采用效率较高的伪随机函数蒙特卡罗方法模拟多级配混凝土随机分布并生成随机骨料空间分布几何模型,然后根据骨料平面分布图中像素的差异以及分形几何学中的盒维数采用数字图像算法对其随机性的合理性进行研究.结果表明,采用蒙特卡罗方法投放的混凝土骨料的随机分布具有分形特征,且随...  相似文献   

10.
在细观层次上,把混凝土看作是由水泥砂浆、骨料及二者之间的界面组成的复合材料,应用渐变网格剖分方法对随机投放的骨料、界面和水泥砂浆进行网格剖分,删除多余节点,重新排列节点顺序,生成三维随机骨料分布的细观有限元数值模型.利用该模型分别进行了混凝土的单轴拉伸、压缩、劈拉和梁弯曲等数值试验,分析了不同界面参数、不同砂浆损伤参数、不同加载形式对混凝土试件的变形特点、破坏形式以及承载能力的影响,探讨了混凝土宏观力学性能(如应变软化和剪胀等性质)的细观机制.  相似文献   

11.
Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.  相似文献   

12.
何延凌 《科技信息》2008,(4):258-258
Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women's language from these perspectives: pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women's language, more attention should be paid to language use in social context. What's more, the linguistic phenomena in a speaking community can be understood more thoroughly.  相似文献   

13.
There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.  相似文献   

14.
The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3~4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰~ -7.8‰, PDB) and matrix dolomites (-6.6‰~ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084~0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078~0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.  相似文献   

15.
理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。  相似文献   

16.
王慧 《科技信息》2008,(10):240-240
Wuthering Heights, Emily Bronte's only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.  相似文献   

17.
The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.  相似文献   

18.
In the 19th century the society was controlled by men, and women were just appendants of them, they had not any rights and freedom. But Jane was an exception, she showed some characteristics of early feminist. Jane showed her characteristics of feminism in three aspects: rebellion, equality, and independence. These characteristics were helpful to her success, and feminism is the only way out for women of that time.  相似文献   

19.
As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.  相似文献   

20.
1 Rise of studies on climate change's effects on biodiversity
Until the 1980s, climate change and biodiversity were studied as two independent disciplines for more than a century. In 1992, the Ecological Society of America's annual report named climate change, biodiversity, and the sustainable ecological system as the three major global environmental issues of the twenty-first century [1].  相似文献   

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