shentIntroduction
这篇文章我本人在学习patran/natran 过程中遇到的问题，及后来找到的解决方法，这篇文章也在逐步更新中，希望这篇文档能给那些学习用patran/nastran 的一点帮助。
汽车卡通短片Yuanchongxin Delft
2011/10/31
ebey1
1. THE SOLUTION FOR THE RESIDUAL STRUCTURE AND THE APPLIED LOADS FOR THE CURRENT SUBCASE ARE ZERO.
后来将边界条件由１２３４５６改为１２３，即将位移约束变成simplified supported，就没有此问题了。
2. USER WARNING MESSAGE 4124 (IFS3P)
moqTHE SPCADD OR MPCADD UNION CONSISTS OF A SINGLE SET 在图中用了RB3 的MPC，其中de
pendent node (ux,uy,uz), independent(ux,uy,uz,rx,ry,rz)，有可能是这里的问题。不过这个倒不影响计算结果。
3. 建立夹层结构的有限元网络
对于meshing, sweep can produce the solid element on the basis of the shell element. 另外sweep 下的loft，可以在两个shell mesh 之间，创建solid element. 对于夹层结构的modeling, shell and solid element should share common node. 否则算出来的结果，solid stress 为零。至于如何共用节点，则需用到element 下的sweep 命令。rerved什么意思啊
4. No PARAM values were t in the Control File
不管失败还是成功的f06 文件中，都会出现这句话。这句话是正常的。如果出现结果为０，并且还没有fatal，另一种可能是因为mpc 没有包括全部边界节点，在对夹层结构圆柱进行分析时，发现由于没有完全把边界节点进行displacement 界定，以及没有完全进行mpc 限制，f06 文件中为０，后来改正一下，就好了。
5. RBE3 加载与使用additionally
可以用RBE３进行axial load 的加载，但不能用于bending moment 的加载，曾尝试过，发现f06 文件
中全部为零。后改成直接对边界曲线进行加载，问题解决。对比下将bending moment 加载到曲线和加载到节点上的区别：曲线：bending moment 为40, EIGENVALUE = 2.187715E-02 节点：bending moment 为40, EIGENVALUE = 2.187715E-02 结果完全一样，这说明将载荷加到曲线或曲线上的节点上，得到的结果完全相同。Axial load 加载到RBE３点上和加载到节点上的区别：RBE3：axial load=30, EIGENVALUE = -2.379083E+00 节点：USER FATAL MESSAGE 4683 (LNNRIGL) KDIF MATRIX NEEDED FOR EIGENVALUE ANALYSIS 由此可以看出，对于圆柱体来说，轴向载荷只能依靠rbe３来加载，而弯曲载荷则靠RBE2 加载。出现此问题，还有可能没有载荷加载。另外，奇怪的事，当弯曲载荷施加于平板时，用linear static 分析可以成功，但是用105 计算时却出现4683 的错误。后来将载荷改为轴向压力时，可使上述错误消失。这说明载荷方向不对，也会出现类似错误。那至于圆柱应该如何呢？
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RBE3 的加载，dependent 的dof 应该是123, indepdendent 应该是123456. 不然造成无解。不过有个参考书上正好相反，但用nastran 计算有误。不知为何，这里需要提到的是计算结果与参考书相差为2，现在尚未找出原因。
6. USER
FATAL免费人工翻译
MESSAGE 9050 (SEKRRS)
^^^ RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL. ^^^ USER ACTION: CONSTRAIN MECHANISMS WITH SPCI OR SUPORTI ENTRIES OR SPECIFY PARAM,BAILOUT,-1 TO CONTINUE THE RUN WITH MECHANISMS. 以前也遇到这种情况，这次遇到后，又在一节点加载了位移约束，就解决了。看来这种错误主要是由于约束不够，线性方程组无解造成的。还有可能是没有equivalence，This should solve your problem or reduce the number of failed ratios.有一次就遇到此情况。
7. 常用材料定义对比表
datumMAT1 MAT2 MAT3 MAT8 MAT9
isotropic anisotropic(2) orthotropic(3) orthotropic(2) anisotropic(3) ? U a FORCE entry if you want to define a static, concentrated force at a grid point by 一个点的力specifying a vector. ? U a FORCE1 entry if the direction is determined by a vector connecting two grid points. 两个点的力? U a FORCE2 entry if the direction is specified by the cross product of two such vectors. 以上的乘积
SPC1,42,123456,1,2,3,4,6,7,8,9 42为SID。
reframeSID: load t identification number 载荷序号G: Grid point 加载点CID：Coordinate system identification number 坐标序号F：Scale factor 放大因子Ni：三维方向的微量，由CID 决定例子：FORCE 3 8 0 2000. 1. 0. 0. 加载在节点8 上的力，大小为2000N.向量为<1 0 0>，分析坐标为coord 0. SID=3。Force1 和force2 的例子在《nastran ur good》P142.
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8. MPC
The displacement constrain can affect the output result sharply. When analysis the buckling of the cylinder, I t the top end as <12456>, which means that it can move at z direction. While the bottom is t as 123456, which means fixed. The result is equal to the reference, but the deformation doesn’t remble much. I don’t know why. 1. The mpc is t as RBE3 Dependent 123456 Independent 123 If the RBE3 is changed as Dependent 123 Independent 123456 The obtained Eigenvalue doesn’t alter much. The former is 0.337, the latter is 0.332. 2. The load can add on one side, and the other side is fixed. It is not good to t compressive load at both end, in this ca, the patran is prone to fail. 3. Under compressive load for cylinder, The deformation is not very symmetry,
and some part have abnormal large deformation, I don’t know why now.
9. 关于几个应力的计算方法
von Mis Stress：
Good question. Von Mis Stress is actually a misnomer. It refers to a theory called the "Von Mis - Hencky criterion for ductile failure". In an elastic body that is subject to a system of loads in 3 dimensions, a complex 3 dimensional system of stress is developed (as you might imagine). That is, at any point within the body there are stress acting in different directions, and the direction and magnitude of stress changes from point to point. The Von Mis criterion is a formula for calculating whether the stress combination at a given point will cau failure. There are three "Principal Stress" that can be calculated at any point, acting in the x, y, and z directions. (The x,y, and z directions are the "principal axes" for the point and their orientation changes from point to point, but that is a technical issue.)
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Von Mis found that, even though none of the principal stress exceeds the yield stress of the mat
spen
erial, it is possible for yielding to result from the combination of stress. The Von Mis criteria is a formula for combining the 3 stress into an equivalent stress, which is then compared to the yield stress of the material. (The yield stress is a known property of the material, and is usually considered to be the failure stress.) The equivalent stress is often called the "Von Mis Stress" as a shorthand description. It is not really a stress, but a number that is ud as an index. If the "Von Mis Stress" exceeds the yield stress, then the material is considered to be at the failure condition. The formula is actually pretty simple, if you want to know it: (S1-S2)^2 + (S2-S3)^2 + (S3-S1)^2 = 2Se^2 Where S1, S2 and S3 are the principal stress and Se is the equivalent stress, or "Von Mis Stress". Finding the principal stress at any point in the body is the tricky part.
Octahedral Shear Stress：Hydrostatic Stress：1st, 2nd, and 3rd invariant stress：
Principal Stress：The magnitudes of the two principal stress from the 2D Mohr’s circle method are calculated according the following equations:
Tresca Shear Stress：
Maximum Shear Stress：
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