三维板壳单元matlab代码

以下是一个简单的三维板壳单元的Matlab代码：

function [Ke] = plate_shell_element(E, nu, h, coords)
% E: 弹性模量
% nu: 泊松比
% h: 板厚度
% coords: 节点坐标

  % 计算板壳单元刚度矩阵
  Ke = zeros(12,12);
  
  % 定义常量
  C1 = E*h^3/(12*(1-nu^2));
  C2 = E*h/(2*(1+nu));
  
  % 计算局部坐标系下的单元刚度矩阵
  Ke_local = [C1, 0, 0, -C1, 0, 0, 0, 0, 0, -C2, 0, 0; ...
              0, C1, 0, 0, -C1, 0, 0, 0, 0, 0, -C2, 0; ...
              0, 0, C1, 0, 0, -C1, 0, 0, 0, 0, 0, -C2; ...
              -C1, 0, 0, C1, 0, 0, 0, 0, 0, C2, 0, 0; ...
              0, -C1, 0, 0, C1, 0, 0, 0, 0, 0, C2, 0; ...
              0, 0, -C1, 0, 0, C1, 0, 0, 0, 0, 0, C2; ...
              0, 0, 0, 0, 0, 0, C2, 0, 0, 0, 0, 0; ...
              0, 0, 0, 0, 0, 0, 0, C2, 0, 0, 0, 0; ...
              0, 0, 0, 0, 0, 0, 0, 0, C2, 0, 0, 0; ...
              -C2, 0, 0, C2, 0, 0, 0, 0, 0, C1, 0, 0; ...
              0, -C2, 0, 0, C2, 0, 0, 0, 0, 0, C1, 0; ...
              0, 0, -C2, 0, 0, C2, 0, 0, 0, 0, 0, C1];
  
  % 计算坐标变换矩阵
  x1 = coords(1,1);
  y1 = coords(1,2);
  z1 = coords(1,3);
  x2 = coords(2,1);
  y2 = coords(2,2);
  z2 = coords(2,3);
  x3 = coords(3,1);
  y3 = coords(3,2);
  z3 = coords(3,3);
  x4 = coords(4,1);
  y4 = coords(4,2);
  z4 = coords(4,3);
  
  x21 = x2 - x1;
  y21 = y2 - y1;
  z21 = z2 - z1;
  x31 = x3 - x1;
  y31 = y3 - y1;
  z31 = z3 - z1;
  x41 = x4 - x1;
  y41 = y4 - y1;
  z41 = z4 - z1;
  
  V = [x21, y21, z21; x31, y31, z31; x41, y41, z41];
  
  V_inv = inv(V);
  
  % 计算全局坐标系下的单元刚度矩阵
  Ke = V_inv' * Ke_local * V_inv;
end

该代码实现了三维板壳单元的刚度矩阵计算，其中参数 `E` 为弹性模量，`nu` 为泊松比，`h` 为板厚度，`coords` 为四个节点的坐标。输出为一个 12x12 的矩阵 `Ke`。该代码假设输入的四个节点按照逆时针顺序给出，且节点在同一平面内。