## C. Organization of an ATILA job

A computation using ATILA is carried out in different steps, all accessible through the supervisor (see Section I.D). This section briefly describes these steps and refers to the corresponding sections for additional information.

### 1. Model Definition

For a given physical problem, the user must define the kindof analysis needed, for example: computation of the static deformation of anelastic structure under a concentrated mechanical load, electricalshort-circuited modal analysis of a piezoelectric ceramic stack, or computationof the transmitting voltage response of a transducer. This type of analysis islinked to solving subroutines described in Chapter ‎V. The user must also choose the type(s) of elements needed to describe the region under study: elastic, piezoelectric, magnetostrictive or fluid elements, bi-dimensional, three-dimensional or axisymmetrical elements, plane stress, plane strain, plate or shell elements, etc.

At this point, a first estimation of the computation sizecan generally be made by estimating the number of nodes, elements, anddegrees-of-freedom. Also at this point, the user must gather all the physicalparameters described in Chapter ‎IV and ensure their accuracy, which determines the accuracy of the final results. This step is essential.

### 2. Mesh Generation

Mesh generation involves the splitting of the aforementionedregion under study into elements. This is accomplished by defining the nodesand by specifying their coordinates in a given order, called node-numberingorder. Then, the elements are described by listing the nodes for each elementin a given order, called topology. Chapter ‎III describes the node coordinates and the topology. A detailed library of elements is presented in Chapter ‎IV.

During the mesh generation, the user can use all the ATILA elements. These elements allow curved line modelingand lower density meshes. However, it is essential to ensure the validity ofthe geometrical aspect of the elements as well as the mesh size. In generalthe maximum permissible size of mesh spacing is related to the smallestacoustic wavelength used.

Mesh generation can be carried out completely by the user. However, in most cases, the structure’s shape allows the use of an automaticmesh generator, which creates node coordinates and element topologies. If using MOSAIQUE, the user has only to define a grosssplitting based on "super elements", and to select for each of them theirautomatic splitting into finite elements. This procedure is described inChapter ‎V. ATILA may also be interfaced to other commercially availablemesh generators (IDEAS, PREFLU, GID, etc.). Please contact the Chairman formore information.

### 3. Data File Preparation

The ATILA data file describes thetype of analysis, the node coordinates, the element topology, the physicalproperties of the materials and the geometrical properties of the elements, theloading and excitation data and the boundary conditions. Chapter ‎III describes the complete data file preparation and must be read carefully. Specific element information can be found in Chapter ‎IV. Finally, when the automatic mesh generation code MOSAIQUE is used, the data entry file can largely be obtainedautomatically. An example of such a data file appears in Part II.

Checking the data file can be done by displaying the meshusing the program WMDES, accessible through the "Drawthe mesh" button on the supervisor (see page 14 for more details). The generated mesh can be seen on the screen or printed out on a graphics printer (with choice of total or partial mesh, and with or without node and element numbering).

### 4. Running a Job

The solver is launched using the supervisor (see page 14 for more details). The solver is the interface to the program that sets the array sizes, calls up the subroutines for reading the data files, computes the elementary matrices, assembles these matrices intoglobal matrices, solves the equations, and stores the results. It creates aresults file and several data files for post-processing.

### 5. Using the Results and Post Processing

An example of a results file is given in Part III. Aftereach run, a file containing the results (frequencies and eigenvectors,displacement and pressure fields, electrical impedance) is available. Ifdesired, specific data are also stored for post-processing. A graphic displayof the distorted structure, the voltage response, the directivity patterns orthe parallel resistance and capacitance plot can be easily obtained by usingthe programs WMDES, WPLOTSV, WPATTERN and WPLOTRPCP now accessible through the supervisor. Animated views of the vibrating structure are alsoavailable with the program ATILANIM. Their use isdescribed in Section ‎I.D.

The user can also utilize WISOVAL to plot contours of constant value (iso-displacements, iso-potentials, iso-pressures,iso-stresses, etc.) on the modeled structure. WISOVAL can be used only if the generation of the PST filewas requested in the input data file.

### 6. Summary

In summary, the next page displays a simple flow chart of anATILA finite-element job. Note that all these steps canbe done using the supervisor; this will be detailed in the next section (seepage 14).