索膜結(jié)構(gòu)非線性有限元分析

1、索膜結(jié)構(gòu)非線性有限元分析        【中文摘要】索膜結(jié)構(gòu)的突出特點之一就是外形的多樣性,曲面存在著無窮的可能性,其設(shè)計也迥異于傳統(tǒng)結(jié)構(gòu)。由于索膜結(jié)構(gòu)屬于柔性結(jié)構(gòu),變形后位移很大,所以在計算中必須考慮其幾何非線性。我國在這方面的研究近幾年才開始,尚不夠成熟,相關(guān)書籍也未幾。本文首先扼要先容了索膜結(jié)構(gòu)的國內(nèi)外現(xiàn)狀和薄膜結(jié)構(gòu)的分類及特點,在薄膜結(jié)構(gòu)分類中,張拉索膜結(jié)構(gòu)是應(yīng)用最為廣泛和靈活的一種膜結(jié)構(gòu)類型,這是本文研究的重點。索膜結(jié)構(gòu)的分析是由初始形態(tài)確定、受荷分析和薄膜裁剪這三部分構(gòu)成,這三部分相互聯(lián)系、相互制約。柔

2、性的索膜材僅當(dāng)加以適當(dāng)?shù)念A(yù)應(yīng)力時才具有確定的外形和抵抗外荷載的能力,才能真正成為“結(jié)構(gòu)”,因此初始形態(tài)分析在膜結(jié)構(gòu)設(shè)計中具有非常重要的意義。對于初始形態(tài)分析,現(xiàn)有的研究方法主要有三種,分別是力密度法、動力松弛法和非線性有限元法。這三種方法各有利弊,由于非線性有限元法具有較好的計算精度,所以本文選用了這種方法。其次,現(xiàn)在幾乎所有索膜軟件和理論都是基于空間三角形平面膜單元與空間兩節(jié)點直線桿單元的組合。且該類軟件也為數(shù)未幾,有些軟件功能還不完善。重慶大學(xué)研究生蘇文章(2005)、李仁佩(2006)提出了一種精度較高且計算工作量較小的四節(jié)點等參索單元理論,并成功運用于單索結(jié)構(gòu)和索網(wǎng)結(jié)構(gòu)分析中。本文在此

3、基礎(chǔ)上提出了一種新型的單元組合形式,即四節(jié)點等參索單元與空間三角形平面膜單元組合,其目的是將四節(jié)點等參索單元理論推廣到索膜結(jié)構(gòu)研究分析中。在扼要先容了鋼索和膜材的物理力學(xué)性能后,本文基于空間三角形平面膜單元和四節(jié)點等參索單元的有限元理論,推導(dǎo)了其有限元平衡方程,并組合成索膜結(jié)構(gòu)有限元平衡方程。為了驗證該理論的正確性,本文使用了MATLAB語言,分別編制了兩節(jié)點直線索單元與三角形平面膜單元組合的找形程序(C2M3)和四節(jié)點等參索單元與三角形平面膜單元組合的找形和荷載分析程序(C4M3)。并使用若干算例,進行了兩個程序找形的對比。同時又運用CAFA、3D3S和ANSYS等軟件進行計算與所編程序進行

4、對比,發(fā)現(xiàn)此類單元組合,不僅滿足計算精度,而且還可以降低迭代次數(shù),可以應(yīng)用于工程結(jié)構(gòu)設(shè)計。最后,本文利用C4M3程序研究了索膜結(jié)構(gòu)膜材參數(shù)對結(jié)構(gòu)找形和荷載分析的影響,比如兩個方向預(yù)應(yīng)力比、索的預(yù)拉力與薄膜預(yù)張力之比等因素,得到了關(guān)于索膜形態(tài)和荷載分析的一些結(jié)論和建議。');【Abstract】 One of the outstanding trait of the cable-membrane structure is the diversity of shape, curved su*ce existing infinite possibilities,and the design

5、is quite dissimilar to traditional structure. The structure of cable-membrane is belonging to flexible structure, and have a great displacement after deforming, so we must take geometrical non-linear problem into account when calculating. The relevant researches of this aspect has just begun in thes

6、e years in our country, so it's not fully mature, and we don't have much relevant literatures.This * introduces briefly the domestic and overseas Status quo, and the category as well as traits of the cable-membrane structure at first. Tensile structure is the most widely and freely used styl

7、e of the cable-membrane structure, and it's the keystone of the article. Analysis of the structure is made up of determining initial form, the analysis of bearing load,cutting out of the membrane, and the three parts are correlative and restrict to each other.Only when bringing prestress to bear

8、 on the flexible material of cable-membrane, can it have the definite shape and the capability of bearing external load, can it be the real "structure", so the analysis of initial form have a very important significance in designing the cable-membrane structure. There are three methods of

9、research ,such as force density method, dynamic relaxation method and the nonlinear finite element method to analyze initial form. These three methods each have their own advantages and disadvantages, The nonlinear finite element method have a better precision in calculation, so this article chose i

10、t.Secondly,almost all the software and theory of cable-membrane are based on the combination of the spatial * plane membrane element and the spatial two-node straight-line element. There are not a good many of the quantity of this kind of software, and the function of some software is not perfect. P

11、ostgraduate.Su Wenzhan(g2005) and Li Renpe(i2006) in Chongqing University propose a theory of four-node isoparametric cable element which has a better precision in calculation, at the same time a lower workload ,and succeeds in the analysis of single cable structure and cable net structure. In this

12、* ,a new form of combinatorial element, namely a mixed finite element model combining the four-node isoparametric cable element and the spatial * plane membrane element is presented. The purpose of this * is promoting the four-node isoparametric cable element theory to the research of cable-membrane

13、 structure.After introducing physical and mechanical capability of cable and membrane briefly, this * introduce the finite element theory of the spatial * plane membrane element and the four-node isoparametric cable element, derivate finite element equation, and become the finite element equation of

14、 cable-membrane structure.To validate the validity of this theory, the * uses MATLAB language, respectively establish the program of form-finding and load analysis which is combined two-node straight-line element with * plane membrane element (C2M3), and a similar program which is combined four-node

15、 isoparametric cable element and * plane membrane element (C4M3). This * compares the two programs via certain examples . At the same time the * compares the results which come form CAFA、3D3S and ANSYS with the program which was established by ourselves, finding that this kind of combination not only meet the precision in calculation, but also reduce the number of iterations,and can be used in engineering design.Finally, the * uses C4M3 to research the influence of the membrane's parameter in form-finding and load analysis, such the ratio of pre