But
===

Calculate added mass [:ref:`R4.07.03 <R4.07.03>`], damping, or stiffness matrices.

The matrices are induced by a perfect, incompressible fluid, at rest or in potential flow, on a 2D, 2D axisymmetric or 3D structure.

The terms of these matrices are calculated on the modal basis of the structure in a vacuum.

The calculation of the terms of the matrices is carried out by solving the equations of LAPLACE in the context of a **thermal analogy**. The calculated temperature plays the role of pressure in the fluid domain. It is therefore necessary to take care to define the fluid material by **thermal** characteristics, and assign a **thermal** model to the part of the mesh that represents the fluid.

Thanks to this operator, it is possible to determine, for example, the matrices added to a bundle of tubes, considered as a single structure immersed in the same fluid.

As part of a calculation by dynamic substructuring, it is also possible to evaluate the mass matrix added on a generalized model.

For systematic uses of this command and to simplify the writing of the command file, we will effectively use the macro command MACRO_MATR_AJOU [:external:ref:`U4.66.11 <U4.66.11>`].

Produces a data structure of type Matr_asse_gene_r.

The following test cases show examples of how to use this operator:


*
    *
        *
            * FDLV100 [:external:ref:`V8.01.100 <V8.01.100>`],


            * FDLV101 [:external:ref:`V8.01.101 <V8.01.101>`],


            * FDLV102 [:external:ref:`V8.01.102 <V8.01.102>`],


            * FDLV103 [:external:ref:`V8.01.103 <V8.01.103>`],


            * FDLV104 [:external:ref:`V8.01.104 <V8.01.104>`],


            * FDLV105 [:external:ref:`V8.01.105 <V8.01.105>`],


            * FDLV106 [:external:ref:`V8.01.106 <V8.01.106>`],


            * FDLV107 [:external:ref:`V8.01.107 <V8.01.107>`],


            * FDLV109 [:external:ref:`V8.01.109 <V8.01.109>`],


            * FDLV110 [:external:ref:`V8.01.110 <V8.01.110>`].