【机械】基于偏微分方程工具箱 (TM)计算受压力载荷作用的结构板的挠度附matlab代码

%% Clamped, Square Isotropic Plate With a Uniform Pressure Load% This example shows how to calculate the deflection of a structural% plate acted on by a pressure loading% using the Partial Differential Equation Toolbox(TM).%%% PDE and Boundary Conditions For A Thin Plate% The partial differential equation for a thin, isotropic plate with a% pressure loading is%% $$\nabla^2(D\nabla^2 w) = -p$$%% where $D$ is the bending stiffness of the plate given by%% $$ D = \frac{Eh^3}{12(1 - \nu^2)} $$%% and $E$ is the modulus of elasticity, $\nu$ is Poisson's ratio,% and $h$ is the plate thickness. The transverse deflection of the plate% is $w$ and $p$ is the pressure load.%% The boundary conditions for the clamped boundaries are $w=0$ and% $w' = 0$ where $w'$ is the derivative of $w$ in a direction% normal to the boundary.%% The Partial Differential Equation Toolbox(TM) cannot directly% solve the fourth order plate equation shown above but this can be% converted to the following two second order partial differential% equations.%% $$ \nabla^2 w = v $$%% $$ D \nabla^2 v = -p $$%% where $v$ is a new dependent variable. However, it is not obvious how to% specify boundary conditions for this second order system. We cannot% directly specify boundary conditions for both $w$ and $w'$.% Instead, we directly prescribe $w'$ to be zero and use the following% technique to define $v'$ in such a way to insure that $w$ also equals zero on% the boundary. Stiff "springs"% that apply a transverse shear force to the plate edge are distributed% along the boundary. The shear force along the boundary due to these% springs can be written $n \cdot D \nabla v = -k w$ where $n$ is the% normal to the boundary and $k$ is the stiffness of the springs.% The value of $k$ must be large enough that $w$ is approximately zero% at all points on the boundary but not so large that numerical errors% result because the stiffness matrix is ill-conditioned.% This expression is a generalized Neumann boundary condition supported% by Partial Differential Equation Toolbox(TM)%% In the Partial Differential Equation Toolbox(TM) definition for an% elliptic system, the $w$ and $v$ dependent variables are u(1) and u(2).% The two second order partial differential equations can be rewritten as%% $$ -\nabla^2 u_1 + u_2 = 0 $$%% $$ -D \nabla^2 u_2 = p $$%% which is the form supported by the toolbox. The input corresponding to this% formulation is shown in the sections below.%%% Problem ParametersE = 1.0e6; % modulus of elasticitynu = .3; % Poisson's ratiothick = .1; % plate thicknesslen = 10.0; % side length for the square platehmax = len/20; % mesh size parameterD = E*thick^3/(12*(1 - nu^2));pres = 2; % external pressure%% Geometry and Mesh%% For a single square, the geometry and mesh are easily defined% as shown below.gdmTrans = [3 4 0 len len 0 0 0 len len];sf = 'S1';nsmTrans = 'S1';g = decsg(gdmTrans', sf, nsmTrans');[p, e, t] = initmesh(g, 'Hmax', hmax);%% Boundary Conditions%b = @boundaryFileClampedPlate;type boundaryFileClampedPlate%% Coefficient Definition%% The documentation for |assempde| shows the required formats% for the a and c matrices in the section titled% "PDE Coefficients for System Case". The most convenient form for c% in this example is $n_c = 3N$ from the table where $N$ is the number% of differential equations. In this example $N=2$.% The $c$ tensor, in the form of an $N \times N$ matrix of $2 \times 2$ submatrices% is shown below.%% $$% \left[% \begin{array}{cc|cc}% c(1) & c(2) & \cdot & \cdot  \\% \cdot & c(3) & \cdot & \cdot  \\ \hline% \cdot & \cdot & c(4) & c(5)  \\% \cdot & \cdot & \cdot & c(6)% \end{array}  \right]% $$%% The six-row by one-column c matrix is defined below.% The entries in the full $2 \times 2$ a matrix and the $2 \times 1$ f vector% follow directly from the definition of the% two-equation system shown above.%c = [1; 0; 1; D; 0; D];a = [0; 0; 1; 0];f = [0; pres];%% Finite Element and Analytical Solutions%% The solution is calculated using the |assempde| function and the% transverse deflection is plotted using the |pdeplot| function. For% comparison, the transverse deflection at the plate center is also% calculated using an analytical solution to this problem.%u = assempde(b,p,e,t,c,a,f);numNodes = size(p,2);pdeplot(p, e, t, 'xydata', u(1:numNodes), 'contour', 'on');title 'Transverse Deflection'numNodes = size(p,2);fprintf('Transverse deflection at plate center(PDE Toolbox)=%12.4e\n', min(u(1:numNodes,1)));% compute analytical solutionwMax = -.0138*pres*len^4/(E*thick^3);fprintf('Transverse deflection at plate center(analytical)=%12.4e\n', wMax);displayEndOfDemoMessage(mfilename)