请教几个概念，请高手知道

pyyp2

小弟新手，请教几个小问题哈
1. FE displacement results are most accurate at the nodes.
   Strains are most accurate when determined at the Gauss Points.这句话怎么解释，具体啥意思？
》For derivatives, Gauss points are usually the superconvergence points. For displacement, it might happen that the nodal points are the superconvergence points.

2.In the inter-element terms, natural (non-essential ) boundary conditions are eliminated by imposing equilibrium at the nodes in the direct assembly process.
  In the inter-element terms, the essential conditions are usually imposed only after the global stiffness matrix is assembled. 这句咋解释，还有这个自然边界条件是啥？
>Natural boundary conditions are related to derivatives and can used directly to form the load vector. Essential boundary conditions are not related to derivatives. They are something like displacement, temperature, and so on. To enforce this type of boundary conditions, penalty method is usually employed after forming the global stiffness matrix.
3. 在求刚度矩阵的时候，会用到 weak form吗，我看都是直接BDB积分直接出来了，weak form 在求刚度里面用不到，还是只在通过控制方程求解的时候才用到。
谢谢各位哈，初学者，轻拍哈。
>First we have strong form which is the partial differential equation. Then we have discrete form where everything is still continuous. Next we introduce the discrete form based on the weak form from which we get the finite element formulation.

minwell2008

围观,表示不会

pyyp2

顶贴啊 不要沉啊！！

ckf

表示 不会  围观 继续等 答案。。。

sunkaibf

对问题1 的理解是:
我们使用位移法求出的位移就是节点的,而应力应变是对于积分点而言的,就是高斯点.

hiiamcl999

围观，求高手出现！

yymaverick

有限元一般基于位移法，单元位移是通过节点位移插值的，插值函数即为单元形函数。有限元求解的平衡方程一节点位移为基本未知量，因此节点位移是精确的。理论上通过形函数和节点位移可以得到单元内任一点的位移和位移梯度，从而得到应变，由应变得到应力往往需要在单元内积分，且常使用数值积分，通常采用高斯积分，因此涉及到高斯点的应力和应变。