2. Methodology#

This chapter describes the methodology used to carry out pipe studies with Salome-Meca.

In this document, we rely on an example of simple modeling (see figure 1) composed of 1D wireframe elements, 2D elements and 3D elements (TEs).

2.1. Geometric construction methodology (module GEOM)#

1D wire elements are used to describe the pipe network consisting of straight elements and bends. To be able to connect the 3D tee later, the wire lines connecting to the tee were modelled by stopping these wire lines at the connection points with the tee.

The 2D elements are generated from a wire section of the line on which the ovalization is to be post-processed. In fact, currently the parameters for the ovalization of 1D elements cannot be visualized in Salome.

The tee at the intersections of the wire lines must be modelled in 3D and meshed in hexahedral (see paragraph 4.2) in order to be able to accurately calculate the stresses at the junctions (pipe, main pipe, incident).

Currently in Code_Aster, there are 1D/3D and 1D/2D fittings but not 2D/3D. It is therefore necessary to go through wire sections at the ends of a tee for connections with elements of the line of different dimensions (2D/3D for example).

_images/1000000000000328000002BC3D476365A542CF81.png

Figure 1: Piping network composed of 1D, 2D, 3D elements

2.2. Preparing the model for calculation (compound and groups)#

Several types of groups of different natures are required for the calculation:

  • 1D objects:

  • groups of 1D elements supporting the 1D meshes corresponding to the same section characteristic.

  • node groups for each boundary condition to be applied during the calculation

  • for pipe modeling, you need to have the starting group of nodes for each wire section to affect characteristic GENE_TUYAU.

  • node group for each node representing an additional component (pumps, valves,…), for which DIS_T or DIS_TR models will be assigned.

  • for each connection of the wireline with an element of a different dimension (1D 2D, 1D 3D links), a group of nodes containing a single node.

  • 3D objects:

  • groups of 3D elements (3D tees for example).

  • 2D objects:

  • groups of 2D faces (3D tee faces for example for 1D 3D connections). For this type of connection, you need a node group containing a single node for the 1D part and a face group for the 3D part. This will affect the « 3D_ TUYAU » keyword and possibly the AXE_POUTRE option.

  • groups of faces supporting 2D pipe elements corresponding to the same section characteristic.

2.3. Mesh construction methodology (Smesh module)#

The recommended method for creating the mesh consists in meshing each object of the same dimension (1D, 2D or 3D) grouped together in the various geometric compounds independently, then to generate for each mesh produced the groups of meshes from the geometric groups created in the geometric groups created in module GEOM previously, and finally to create a mesh compound bringing together the various meshes. This mesh compound represents the output data to be exported in MED format to perform the calculation.

2.4. Main Code_Aster operators for calculation#

The main Code_Aster operators to be used for the assignment of pipe elements and for the connections between elements of different dimensions are:

  • The operator MODI_MAILLAGE [U4.23.04] OPTION ORIE_NORM_COQUE is required in order to orient all the normals of 2D elements in the same direction.

  • The operator CREA_MAILLAGE [U4.23.02] OPTION =” QUAD8_9 “allows you to transform quadratic 2D shell elements with 8 nodes (QUAD8) into quadratic elements with 9 nodes (QUAD9). This transformation is required to be able to use COQUE_3D elements.

  • Each distinct wireline must be subject to an assignment of the orientations of the main axes of the cross sections of the beam elements. You must fill in the direction fields relating to option GENE_TUYAU (operator AFFE_CARA_ELEM [U4.42.01]), which must be applied to the first node of each wireline (requires a node group for each wireline).

  • Use of discrete elements DIS_TR (to take into account the mass and inertia of point elements representing additional components on the line such as valves, valves for example), as well as discrete elements DIS_T (to take into account the only point mass of certain additional components): the creation of groups of nodes is necessary to be able to apply these elements DIS_TR or DIS_T (operator AFFE_MODELE [U4.41.01]).

  • Assigning the wire elements constituting the pipe into pipe elements TUYAU_3M (straight) or TUYAU_6M (curves), (operator AFFE_MODELE [U4.41.01]) .These elements combine both beam kinematics, which describe the overall movement of the pipe line, and shell kinematics, which provide the description of swelling, ovalization, and warping of the cross section.

  • Each change in the characteristics of the elements of the pipe line (diameter, thickness, material, etc.), requires the creation of distinct groups (operator AFFE_CARA_ELEM [U4.42.01]).

  • Modeling of 3D-1D and 2D-1D connections (operator AFFE_CHAR_MECA option LIAISON_ELEM [U4.44.01]):

  • 3D-1D (pipe elements): OPTION 3D_ TUYAU

  • 3D-1D (beam elements): OPTION 3D_ POU

  • 2D-1D (pipe elements): OPTION COQ_TUYAU

  • 2D-1D (beam elements): OPTION COQ_POU