6. Nature of post-treatment

6.1. Operand OPERATION

♦ OPERATION =

The extraction operation of a quantity field makes it possible to recover the values of one or more components or quantities derived from these components at the post-treatment site points.

In the case of an extraction on a fiel_elem, the values of the components extracted from this field are calculated as follows:

• If the post-processing location is determined by the keyword GROUP_NO, for each node, the components are averaged over all the elements competing in this node. In the case of extracting a field of type ELNO, we obtain the same values by giving the field of type NOEU.

Note:

Averages at field nodes calculated in local guides are only legal if the angles between these coordinates are small. If not, they don’t make sense.

If the post-processing location is defined by GROUP_NO = \((\mathit{GN}\mathrm{1,}\mathit{GN}\mathrm{2,}\mathit{GN}\mathrm{3,}\mathit{GN}\mathrm{4,}\mathit{GN}5)\), the values are averaged across all the elements in the mesh above.

If the post-processing location is set to be the original \(\mathit{N1}\) and end segment \(\mathit{N5}\), the values will be averaged across the hatched elements.

In the case of quadratic elements (presence of middle nodes), the mean at the vertex nodes can lead to greater weights of certain elements (division function) compared to middle nodes which average over 2 elements (therefore of the same weight). We can therefore find ourselves in the presence of oscillations between the values at the vertices and at the midpoints.

This operation is limited to 6 field components at a time. Given a scalar field \(U\) (typically a component of a quantity), the operation “MOYENNE” calculates the following quantities (\(L\) designating the length of the post-processing location \(C\) in question):

MOMENT_0 = \(\frac{1}{L}{\int }_{c}U(s)\mathrm{ds}\)

MOMENT_1 = \(\frac{12}{{L}^{2}}{\int }_{c}U(s)(s-\frac{L}{2})\mathrm{ds}\)

MINIMUM = \(\underset{c}{\mathrm{Min}}U\)

MAXIMUM = \(\underset{c}{\mathrm{Max}}U\)

MOYE_INT = MOMENT_0 - ½ MOMENT_1

MOYE_EXT = MOMENT_0 + ½ MOMENT_1

It is important that the post-treatment site be walked in one direction. If we use a group of nodes, we will take care to reorder the nodes, using the command DEFI_GROUPOPTION “NOEUD_ORDO”, [U4.22.01]. Thus, the curvilinear abscissa is defined from the original node of the group, following the broken line formed by the nodes.

The integrals above are evaluated assuming \(U\) to be linear between two nodes. Thus, by noting \({U}_{i}\) the values of the field at the nodes (numbered by \(i=\mathrm{1,}\mathrm{...},N\)) of abscissa \({s}_{i}\), we have:

\(\text{MOMENT\_0}=\frac{1}{2({s}_{N}-{s}_{1})}\sum _{i=1}^{N-1}({s}_{i+1}-{s}_{i})({U}_{i}+{U}_{i+1})\)

\(\begin{array}{}\text{MOMENT\_1}=\frac{2}{{({s}_{N}-{s}_{1})}^{2}}\sum _{i=1}^{N-1}({s}_{i+1}-{s}_{i})({U}_{i}({s}_{i+1}+{\mathrm{2s}}_{i})+{U}_{i+1}({\mathrm{2s}}_{i+1}+{s}_{i}))\\ -\frac{3}{({s}_{N}-{s}_{1})}\sum _{i=1}^{N-1}({s}_{i+1}-{s}_{i})({U}_{i}+{U}_{i+1})\end{array}\)

| 'EXTREME'


Calculate the MIN, MAX, MINI_ABS, MAXI_ABSd of a reduced field possibly on a list of nodes or meshes, on all components or a list of components.

6.2. Operand MOYE_NOEUD

Keyword allowing you to choose a detailed or averaged impression at one point. This keyword is only significant for quantities such as cham_elem and for operation EXTRACTION.

MOYE_NOEUD = 'OUI'

For each post-treatment point, the displayed value of a component or a deduced quantity is obtained as the average of the values given by each concurrent mesh at this point. The way to average is the same as for the XXXX_NOEU fields calculated by CALC_CHAMP [U4.81.04].

MOYE_NOEUD = 'NON'

The list of values obtained for each mesh competing at the post-treatment point is displayed.