Difference between revisions of "Category:Linear Hydroelasticity"

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<center><math>\begin{bmatrix}F\end{bmatrix}</math> is generalized force vector (fluid forces, gravity forces,...).</center>
 
<center><math>\begin{bmatrix}F\end{bmatrix}</math> is generalized force vector (fluid forces, gravity forces,...).</center>
  
 +
Left-hand side of the global FEM matrix equation represents "dry" (in vacuuo) structure, while the right-hand side includes fluid forces (and coupling between the surrounding fluid and the structure).
  
 
The eigenvalue problem for the "dry" natural vibrations yields:
 
The eigenvalue problem for the "dry" natural vibrations yields:
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<center><math>\begin{bmatrix}k\end{bmatrix} \begin{bmatrix}\xi\end{bmatrix}+\begin{bmatrix}s\end{bmatrix} \begin{bmatrix}\dot\xi\end{bmatrix}+\begin{bmatrix}m\end{bmatrix} \begin{bmatrix}\ddot\xi\end{bmatrix}</math>=<math>\begin{bmatrix}f(t)\end{bmatrix}</math></center>
 
<center><math>\begin{bmatrix}k\end{bmatrix} \begin{bmatrix}\xi\end{bmatrix}+\begin{bmatrix}s\end{bmatrix} \begin{bmatrix}\dot\xi\end{bmatrix}+\begin{bmatrix}m\end{bmatrix} \begin{bmatrix}\ddot\xi\end{bmatrix}</math>=<math>\begin{bmatrix}f(t)\end{bmatrix}</math></center>
  
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to be continued...
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<center><math>\begin{bmatrix}k\end{bmatrix}=\begin{bmatrix}W^T\end{bmatrix}\begin{bmatrix}K\end{bmatrix}\begin{bmatrix}W\end{bmatrix}</math>is the modal stiffness matrix,
 +
<math>\begin{bmatrix}m\end{bmatrix}=\begin{bmatrix}W^T\end{bmatrix}\begin{bmatrix}M\end{bmatrix}\begin{bmatrix}W\end{bmatrix}</math>is the modal mass matrix.</center>

Revision as of 00:35, 14 November 2008

Problems in Linear Water-Wave theory in which there is an elastic body.

Finite Element Method (FEM) can be used to analyze any general 3D elastic structure using linear hydroelastic theory.

local FE [math]\displaystyle{ \Rightarrow }[/math] global FE model

Dynamic equation of motion in matrix form can be expressed as:

[math]\displaystyle{ \begin{bmatrix}K\end{bmatrix}\begin{bmatrix}D\end{bmatrix}+ \begin{bmatrix}S\end{bmatrix}\begin{bmatrix}\dot D\end{bmatrix}+ \begin{bmatrix}M\end{bmatrix}\begin{bmatrix}\ddot D\end{bmatrix}= \begin{bmatrix}F(t)\end{bmatrix} }[/math], where:


[math]\displaystyle{ \begin{bmatrix}K\end{bmatrix} }[/math] is structural stiffness matrix,
[math]\displaystyle{ \begin{bmatrix}S\end{bmatrix} }[/math] is structural damping matrix,
[math]\displaystyle{ \begin{bmatrix}M\end{bmatrix} }[/math] is structural mass matrix,
[math]\displaystyle{ \begin{bmatrix}D\end{bmatrix} }[/math] is generalized nodal displacements vector,
[math]\displaystyle{ \begin{bmatrix}F\end{bmatrix} }[/math] is generalized force vector (fluid forces, gravity forces,...).

Left-hand side of the global FEM matrix equation represents "dry" (in vacuuo) structure, while the right-hand side includes fluid forces (and coupling between the surrounding fluid and the structure).

The eigenvalue problem for the "dry" natural vibrations yields:

[math]\displaystyle{ \begin{bmatrix}K\end{bmatrix}\begin{bmatrix}D\end{bmatrix}+\begin{bmatrix}M\end{bmatrix}\begin{bmatrix}\ddot D\end{bmatrix}=\begin{bmatrix}0\end{bmatrix} }[/math]


If one assumes trial solution as [math]\displaystyle{ \begin{bmatrix}D\end{bmatrix}=\begin{bmatrix}w\end{bmatrix}\,e^{i\omega t} }[/math] then the eigenvalue problem reduces to [math]\displaystyle{ \left( \begin{bmatrix}K\end{bmatrix}-\omega^2 \begin{bmatrix}M\end{bmatrix} \right )\begin{bmatrix}w\end{bmatrix}=\begin{bmatrix}0\end{bmatrix} }[/math]. As a solution of the eigenvalue problem for each natural mode one obtains [math]\displaystyle{ \omega_n }[/math], the n-th dry natural frequency and [math]\displaystyle{ \begin{bmatrix}w_n\end{bmatrix} }[/math], the corresponding dry natural mode.


Generalized nodal displacements vector can be expressed using calculated "dry" structure natural modes:


[math]\displaystyle{ \begin{bmatrix}D\end{bmatrix} }[/math]=[math]\displaystyle{ \begin{bmatrix}W\end{bmatrix}\cdot\begin{bmatrix}\xi\end{bmatrix} }[/math]


[math]\displaystyle{ \begin{bmatrix}W\end{bmatrix} }[/math]=[math]\displaystyle{ \begin{bmatrix}\mathbf{w_1}\,\mathbf{w_2}\,\ldots \end{bmatrix} }[/math] is matrix of dry natural modes, with modes being sorted column-wise,
[math]\displaystyle{ \begin{bmatrix}\xi\end{bmatrix} }[/math]is natural modes coefficients vector.


[math]\displaystyle{ \begin{bmatrix}W\end{bmatrix}^T \begin{bmatrix}K\end{bmatrix} \begin{bmatrix}W\end{bmatrix} \begin{bmatrix}\xi\end{bmatrix}+\begin{bmatrix}W\end{bmatrix}^T \begin{bmatrix}S\end{bmatrix} \begin{bmatrix}W\end{bmatrix} \begin{bmatrix}\dot\xi\end{bmatrix} +\begin{bmatrix}W\end{bmatrix}^T \begin{bmatrix}M\end{bmatrix} \begin{bmatrix}W\end{bmatrix} \begin{bmatrix}\ddot\xi\end{bmatrix} }[/math]=[math]\displaystyle{ \begin{bmatrix}W\end{bmatrix}^T\begin{bmatrix}F(t)\end{bmatrix} }[/math]


[math]\displaystyle{ \begin{bmatrix}k\end{bmatrix} \begin{bmatrix}\xi\end{bmatrix}+\begin{bmatrix}s\end{bmatrix} \begin{bmatrix}\dot\xi\end{bmatrix}+\begin{bmatrix}m\end{bmatrix} \begin{bmatrix}\ddot\xi\end{bmatrix} }[/math]=[math]\displaystyle{ \begin{bmatrix}f(t)\end{bmatrix} }[/math]


[math]\displaystyle{ \begin{bmatrix}k\end{bmatrix}=\begin{bmatrix}W^T\end{bmatrix}\begin{bmatrix}K\end{bmatrix}\begin{bmatrix}W\end{bmatrix} }[/math]is the modal stiffness matrix, [math]\displaystyle{ \begin{bmatrix}m\end{bmatrix}=\begin{bmatrix}W^T\end{bmatrix}\begin{bmatrix}M\end{bmatrix}\begin{bmatrix}W\end{bmatrix} }[/math]is the modal mass matrix.

Subcategories

This category has only the following subcategory.

F

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