ASSOCIATIVE SIZING OF AERONAUTICAL STRUCTURES FROM CATIA V5 TO SAMCEF : APPLICATIONS

TO STATIC AND BIRD IMPACT ANALYSES

A.P. Gonze & J. Verstuyft SONACA S.A.

Abstract : This paper presents an associative chain performing the structural sizing of aeronautical structures. Starting points are a Catia V5 Digital Mock Up parametrized or not, load data’s defined in Excel sheets and a material data base. From these inputs, FEMPAD macro’s are used to build SAMCEF data files, to launch FEM analyses and to write Word result reports. These tools allow to study various aeronautical structures under different solicitations (pressure, temperature, prescribed deformations, bird impact). Methods have been developed in order to build linear (Asef), static non-linear (Mecano) or explicit (Plexus) analyses in a user friendly in-house tool box interfaced with CATIA V5 for geometry and FEM mesh definition.

1. INTRODUCTION The general principle of the work presented here is to build an application around the knowledge and not around a tool. A lot of specific tools are used for the structural sizing of aeronautical structures: Catia V5 for the digital mock up, SAMCEF for Finite Element Analyses, Word for reports, Excel sheets for load definition, in-house tools for stressing. The idea of the application presented here is to keep a strong associativity with the Digital Mock Up using specific tools with as less as possible modifications. An other important guideline is to build a modular tool in order to be able to replace as easily as possible a box by another. All information must be unique and available easily everywhere by all boxes constituting the sizing chain. Finally, the integration of report aspects has been taken into account. The concept is based on the definition of an exchange format as simple as possible in order to connect various old or new programs without a lot of modifications. Two tools are used to power the application. “Fempad” is used to write procedures (“script-like”), to extract FEM results (“samres-like”) and to make variable manipulations or computations (“Excel-like”) in a unique language. “FEMWORD” is used to generate certification reports (Word or HTML) and to write program data files (see Figure 1). FEMWORD allows to parametrize any program performing the fusion between a template file (file in which you find no value but keywords representing the latter and

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some commands allowing to make loops, tests, …) and a neutral file (file in which you identify the links between the keywords and the values).

UFigure 1 : Femword principle These tools allow to build an in-house application fully associative chaining specific high performance software (commercial or in-house) from the digital mock up to certification reports. Current application is divided in four FEMPAD macro’s:

• Generation of FE models

• Generation of loads

• Launch FEM analyses

• Postprocessing

2. FROM CATIA V5 DMU TO SAMCEF MODELS Two kind of models are generated. Firstly, each part are meshed separately and assembled by rivets. These rivets are modelled by bushing elements. The two bushing ends are mapped on shell elements that are to be assembled (Figure 2). Contact between parts is also taken into account. Secondly and more classically, all parts of the structure are modelled with common nodes using volumes, shell and beam elements. These approaches can be mixed. A structure can be made of separated parts and sub-assemblies with common nodes.

UFigure 2: Rivet modelling Figure 3 illustrates the generation of a FE model. A first step is performed in Catia. A surface idealisation is associated to each 3D Catia V5 part. This idealisation can be parametrized like the 3D part. The second step consists to mesh surface idealisations in Catia. Finally, with the help of a CAA development each mesh part is exported into a neutral file containing the mesh definition: nodes, elements, groups and properties. On a second hand, the points constituting the riveting assembly are exported into a neutral file. All these operations are performed in Catia V5 environment and consequently can take the advantages of Catia parametrization if necessary. For a unique model, a non-parametrized approach can be less time consuming.

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The second step is performed by FEMPAD macro’s. An Excel sheet contains the description of the assembly. The sheet contains two kinds of information:

• The part description: list of parts to assemble, part materials (linear, plastic, composite), an optional redefinition of thicknesses, the part colour, …. Materials are addressed by their names (2024T42 for example). The real values of material parameters (Young modulus, …) are defined in a neutral material database.

• The part interactions: rivet properties, interactions between two Catia groups (contact, strut, lug, …). The user defines the interaction and some assembly properties depending on the interaction type (rivet type, strut area, lug stiffness, …) but the finite element modelling is not user dependent. For example, user will define the rivet type and automatically the bushing stiffnesses will be computed by specific rules like Gruman one taking into account shell thickness and rivet type. It works like SAMCEF macro commands but for more specific applications or for inexistent SAMCEF macro. A major advantage of this approach is that the FE modelling is not user dependent and that the modelling principles can be written by a “method team” ensuring standard models for standardized parts (higher quality and faster availability inside “project teams”).

From the model Excel sheet, from the neutral files (meshes, rivets and properties) and from template data files, a FEMPAD macro generates a Bacon data file. Note that other types of data files (Plexus, Nastran, …) can be generated if template data files are modified and if the FE modelling is adapted. Last but not least, an associative modelling report is created using a FEMPAD macro and a FEMWORD template. Figure 4 illustrates this approach on a structure modelled without rivets. So with a unique Fempad macro it is theoretically possible to generated equivalent data files for different solvers. This process is associative to the Catia V5 CAD, independent on the user, the reactivity with respect to project needs is high and the user has not to know the syntax of the solver.

Neutral Mesh file Neutral

Rivet file

Neutral Material file

FEMPAD MACRO’s

3D

Riveting Assy

2.5D Mesh

Figure 3: FE model procedure

Figure 4: Global channel

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3. FROM EXCEL LOADS TO SAMCEF DATA FILES

Neutral Mesh file

FEMPAD MACRO’s

Figure 5: Load generation Several types of boundary conditions are taken into account: pressure, temperature and imposed displacements (or deformation). The number of cases to process can be as high as several hundreds. Load data’s come from an external source and conveniently these data’s are summarized in Excel sheets. FEMPAD macro’s extract load information from the sheets and mesh information from neutral mesh data files. A procedure creates SAMCEF data files containing element groups and pressure or temperature mappings. A specific macro command is written to impose a mapped deformation on two groups of nodes coming from Catia. A complex system of elements (rigid bodies, distance sensors, …) is automatically written to impose properly the deformation.

4. FEM ANALYSES

FEMPAD MACRO

Figure 6: Run procedure Figure 6 shows the procedure to launch computations. Loadcases are defined in an Excel sheet by combination of temperature, pressure and deformation cases. Safety factors are associated to each case and type of case (limit or ultimate) is described.

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Finally the type of analysis can be linear or non-linear. From these management data’s and from SAMCEF data files containing the mesh and the boundary conditions, a FEMPAD macro launch all required analyses and organize the result files by directories.

5. FROM FEM RESULTS TO WORD REPORTS

FEMPAD MACRO

Figure 7: Postprocessing procedures Figure 7 shows the postprocessing of FEM results. Postprocessing procedures and associated report templates are written by the “method team”. User selects in a sheet the postprocessing that are to be performed. Using the “Samres” functionality of FEMPAD, results are extracted and processed to compute reserve factors. A Word report is created on the basis of the template file.

6. SOME INDUSTRIAL APPLICATIONS Some static and dynamic applications (bird impact) will be presented.

7. CONCLUSIONS This paper presents an integrated structural analysis application including a FE modelling strongly associative to a Catia V5 Digital Mock Up. There is not the least break of associativity between data’s (DMU and Excel data’s) and results (Word reports). Priority has been given more to associativity than interactivity. Not any specific knowledge of specific tools is necessary (syntax, FE modelling, …). The application has been programmed using Fempad and Femword tools. This software allows to write easily procedures covering all needs (“Script-like”, “Excel-like”, “Samres-like”) with an unique langage. It allows to manage any kind of programs if they can be run in batch with formatted input files. This software provide a very powerful tool to automate process and to accumulate the knowledge. The easiness to access every information everywhere is also a key point.

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