CLPT - Classical Laminated Plate Theory#

Description#

For the CLPT the displacement field components are:

$u, v, w$

And approximated as:

$\begin{split}u = u_0(x, \theta) + z \phi_x(x, \theta) \\ v = v_0(x, \theta) + z \phi_\theta(x, \theta) \\ w = w_0(x, \theta)\end{split}$

where $$u_0, v_0, w_0$$ are the displacements of the shell mid-surface and $$\phi_x$$ and $$\phi_\theta$$ the shell rotations along $$x$$ and $$\theta$$ following the right-hand rule. For the CLPT the rotations are defined as:

$\begin{split}\phi_x = - \frac{\partial w}{\partial x} = -w_{,x} \\ \phi_\theta = - \frac 1 r \frac{\partial w}{\partial \theta} = - \frac 1 r w_{,\theta}\end{split}$

For the ConeCyl implementations the displacement field is approximated and the approximated functions can be separated as:

$\begin{split}u = u_0 + u_1 + u_2\\ v = v_0 + v_1 + v_2\\ w = w_0 + w_1 + w_2\\\end{split}$

where $$u_0$$ contains the approximation functions corresponding to the prescribed degrees of freedom, $$u_1$$ contains the functions independent of $$\theta$$ and $$u_2$$ the functions that depend on both $$x$$ and $$\theta$$.

The aim is to have models capable of simulating the displacement field of cones and cylinders. The approximation functions are the same for both the Donnell’s and the Sanders’ models.

Models#

Below it follows a more detailed description of each of the implementations:

Each model can be accessed using the linear_kinematics parameter of the ConeCyl object. For linear static analysis the most general model is the clpt_donnell_bcn.

For linear buckling analysis the following models should be used for each type of boundary conditions:

clpt_donnell_bc1#

SS1- and CC1-types of boundary conditions, or anything in between by using elastic restrained edges in $$w_{,x}$$ and $$w_{,\theta}$$. The approximation functions are:

$\begin{split}u = u_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{u} \sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{u} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{u} \sin{{b_x}_2} \cos{j_2 \theta} \right) \\ v = v_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{v}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{v} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{v} \sin{{b_x}_2} \cos{j_2 \theta} \right) \\ w = w_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{w}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{w} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{w} \sin{{b_x}_2} \cos{j_2 \theta} \right)\end{split}$

with:

$\begin{split}{b_x}_1 = i_1 \pi \frac x L \\ {b_x}_2 = i_2 \pi \frac x L\end{split}$

The following general form of elastic constraints at the edges is used:

$\begin{split}U_{springs} = \int_\theta r_1 \left( K_{Bot}^u u_{x=L}^2 + K_{Bot}^v v_{x=L}^2 + K_{Bot}^w w_{x=L}^2 + K_{Bot}^{\phi_x} {\phi_x}_{x=L}^2 + K_{Bot}^{\phi_\theta} {\phi_\theta}_{x=L}^2 \right) \\ + \int_\theta r_2 \left( K_{Top}^u u_{x=0}^2 + K_{Top}^v v_{x=0}^2 + K_{Top}^w w_{x=0}^2 + K_{Top}^{\phi_x} {\phi_x}_{x=0}^2 + K_{Top}^{\phi_\theta} {\phi_\theta}_{x=0}^2 \right)\end{split}$

Note that the stiffnesses: $$K_{Top}^u$$, $$K_{Top}^v$$ and $$K_{Top}^w$$ are not used in clpt_donnell_bc1, but since they are required in other implementations, it is convenient to present the general form using all the elastic terms.

The equation for $$U_{springs}$$ can be written in matrix form, and it will result in an additional term $$[K_e]$$ to the linear stiffness matrix $$[K_0]$$. The new stiffness matrix with the elastic constraints at the edges ($$[{K_0}_e]$$) becomes:

\begin{align}\begin{aligned}[{K_0}_e] = [K_0] + [K_e]\\[K_e] = \int_{\theta} { \left( r_1 [g_{new}]_{x=L}^T [K]_{Bot} [g_{new}]_{x=L}^. + r_2 [g_{new}]_{x=0}^T [K]_{Top} [g_{new}]_{x=0}^. \right) d\theta }\end{aligned}\end{align}

with :

$\begin{split}[K_{Bot}] = \begin{bmatrix} K_{Bot}^u & 0 & 0 & 0 & 0 \\ 0 & K_{Bot}^v & 0 & 0 & 0 \\ 0 & 0 & K_{Bot}^w & 0 & 0 \\ 0 & 0 & 0 & K_{Bot}^{\phi_x} & 0 \\ 0 & 0 & 0 & 0 &K_{Bot}^{\phi_\theta} \end{bmatrix}\end{split}$

and:

$\begin{split}[K_{Top}] = \begin{bmatrix} K_{Top}^u & 0 & 0 & 0 & 0 \\ 0 & K_{Top}^v & 0 & 0 & 0 \\ 0 & 0 & K_{Top}^w & 0 & 0 \\ 0 & 0 & 0 & K_{Top}^{\phi_x} & 0 \\ 0 & 0 & 0 & 0 &K_{Top}^{\phi_\theta} \end{bmatrix}\end{split}$

and the shape functions $$[g_{new}]$$ contains two extra rows that are built from the relations:

$\begin{split}\phi_x = - \frac{\partial w}{\partial x} = -w_{,x} \\ \phi_\theta = - \frac 1 r \frac{\partial w}{\partial \theta} = - \frac 1 r w_{,\theta}\end{split}$

and therefore:

$\begin{split}[g^{\phi_x}] = - \frac {\partial [g^w]} {\partial x} \\ [g^{\phi_\theta}] = - \frac 1 r \frac {\partial [g^w]} {\partial \theta} \\ [g_{new}]^T = \left[ [g^u], [g^v], [g^w], [g^{\phi_x}], [g^{\phi_\theta}] \right]\end{split}$

Observations:

$$\checkmark$$ linear buckling implemented

$$\checkmark$$ linear static implemented

$$\checkmark$$ non-linear analysis implemented

clpt_donnell_bc2#

Planned to simulate the SS2- and CC2-types of boundary conditions (or anything in between). The flexibily in $$v$$ is removed if compared to the clpt_donnell_bc4. Giving:

$\begin{split}u = u_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{u} \sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{u} \cos{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{u} \cos{{b_x}_2} \cos{j_2 \theta} \right) \\ v = v_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{v}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{v} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{v} \sin{{b_x}_2} \cos{j_2 \theta} \right) \\ w = w_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{w}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{w} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{w} \sin{{b_x}_2} \cos{j_2 \theta} \right) \\\end{split}$

The linear stiffness matrix $$[K_0]$$ is changed using the same elastic contraints used for the clpt_donnell_bc1.

Observations:

$$\checkmark$$ linear buckling implemented

$$\checkmark$$ linear static implemented

$$\checkmark$$ non-linear analysis implemented

clpt_donnell_bc3#

Planned for SS3- and CC3-types of boundary conditions (or anything in between). The approximation functions are:

$\begin{split}u = u_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{u} \sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{u} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{u} \sin{{b_x}_2} \cos{j_2 \theta} \right) \\ v = v_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{v}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{v} \cos{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{v} \cos{{b_x}_2} \cos{j_2 \theta} \right) \\ w = w_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{w}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{w} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{w} \sin{{b_x}_2} \cos{j_2 \theta} \right) \\\end{split}$

The linear stiffness matrix $$[K_0]$$ is changed using the same elastic contraints used for the clpt_donnell_bc1.

Observations:

$$\checkmark$$ linear buckling implemented

$$\checkmark$$ linear static implemented

$$\checkmark$$ non-linear analysis implemented

clpt_donnell_bc4#

SS4- or CC4-types of boundary conditions (or anything in between).

$\begin{split}u = u_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{u} \sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{u} \cos{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{u} \cos{{b_x}_2} \cos{j_2 \theta} \right) \\ v = v_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{v}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{v} \cos{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{v} \cos{{b_x}_2} \cos{j_2 \theta} \right) \\ w = w_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{w}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{w} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{w} \sin{{b_x}_2} \cos{j_2 \theta} \right) \\\end{split}$

The linear stiffness matrix $$[K_0]$$ is changed using the same elastic contraints used for the clpt_donnell_bc1.

Observations:

$$\checkmark$$ linear buckling implemented

$$\checkmark$$ linear static implemented

$$\checkmark$$ non-linear analysis implemented

clpt_donnell_bcn#

General approximation function for the CLPT. It allows any type of boundary condition by setting the proper values for the elastic constants.

$\begin{split}u = u_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{u} \sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{u} \cos{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{u} \cos{{b_x}_2} \cos{j_2 \theta} \right) \\ v = v_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{v}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{v} \cos{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{v} \cos{{b_x}_2} \cos{j_2 \theta} \right) \\ w = w_0 + \sum_{i_1=0}^{m_1} {c_{i_1}}^{w}\sin{{b_x}_1} + \sum_{i_2=0}^{m_2} \sum_{j_2=1}^{n_2} \left( {c_{i_2 j_2}}_a^{w} \sin{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_b^{w} \sin{{b_x}_2} \cos{j_2 \theta} +{c_{i_2 j_2}}_c^{w} \cos{{b_x}_2} \sin{j_2 \theta} +{c_{i_2 j_2}}_d^{w} \cos{{b_x}_2} \cos{j_2 \theta} \right)\end{split}$

The linear stiffness matrix $$[K_0]$$ is changed using the same elastic contraints used for the clpt_donnell_bc1.

Observations:

$$\checkmark$$ linear static implemented

$$\times$$ not working for linear buckling

$$\rightarrow$$ non-linear analysis not implemented

clpt_sanders_bc1#

Counterpart of clpt_donnell_bc1 using the Sanders non-linear equations.

Observations:

$$\checkmark$$ linear static implemented

$$\checkmark$$ linear buckling implemented

$$\rightarrow$$ non-linear analysis not implemented

clpt_sanders_bc2#

Counterpart of clpt_donnell_bc2 using the Sanders non-linear equations.

Observations:

$$\checkmark$$ linear static implemented

$$\checkmark$$ linear buckling implemented

$$\rightarrow$$ non-linear analysis not implemented

clpt_sanders_bc3#

Counterpart of clpt_donnell_bc3 using the Sanders non-linear equations.

Observations:

$$\checkmark$$ linear static implemented

$$\checkmark$$ linear buckling implemented

$$\rightarrow$$ non-linear analysis not implemented

clpt_sanders_bc4#

Counterpart of clpt_donnell_bc4 using the Sanders non-linear equations.

Observations:

$$\checkmark$$ linear static implemented

$$\checkmark$$ linear buckling implemented

$$\rightarrow$$ non-linear analysis not implemented

clpt_geier1997_bc2#

Note

NOT RECOMMENDED, implemented for comparative purposes only.

Analogous to the model published by Geier and Singh (1997) (see [geier1997] for more details) for the SS2- and CC2-types of boundary condition. Originally proposed by Khdeir et al. (1989) (see [khdeir1989]). Uses the Donnell’s equations and the approximation functions are:

$\begin{split}u = \sum_{i_2=0}^{m_2} \sum_{j_2=0}^{n_2} \left( {c_{i_2 j_2}}^{u} \cos{{b_x}_2} \cos{j_2 \theta} \right) \\ v = \sum_{i_2=0}^{m_2} \sum_{j_2=0}^{n_2} \left( {c_{i_2 j_2}}^{v} \sin{{b_x}_2} \sin{j_2 \theta} \right) \\ w = \sum_{i_2=0}^{m_2} \sum_{j_2=0}^{n_2} \left( {c_{i_2 j_2}}^{w} \sin{{b_x}_2} \cos{j_2 \theta} \right)\end{split}$

Observations:

$$\checkmark$$ linear buckling implemented

$$\rightarrow$$ linear static not implemented

$$\rightarrow$$ non-linear analysis not implemented