RTM-Worx User Manual
Feature summary

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1.2 Feature Summary

1.2.1  Integrated environment
1.2.2  Definition of model geometry
1.2.3  Model visualization
1.2.4  Mesh generation
1.2.5  Material and resin properties
1.2.6  RTM Simulation
1.2.7  Presentation of results
1.2.8  Database and import filters

[top] 1.2.1 Integrated environment

The RTM-Worx interface is designed as a workspace in which the model of your part is at the center, with all the tools you need to build and change the model, run the simulation and view properties and results located around it. Because the preprocessing (building the model and defining properties), running the simulation and post-processing (viewing results from properties) is integrated, you can work very fast in one single environment without the need to switch between different applications.
The display of your part is most important while available screen space is limited. Therefore, the area occupied by the tools is designed to be as small as possible. Extensive use of bitmaps has been made because they are easier to remember and recognize compared text. Each button, edit field and list box has a text description that pops up if you point at it with the mouse cursor to help you remind you what it does. The bitmaps are also included in the main menu, which helps you to learn their meaning even faster. In addition, context-sensitive help is available for all parts of the interface.

[top] 1.2.2 Definition of model geometry

The geometry of your part has to be known in order to do a filling simulation. In combination with fabric and resin properties this is called the model. In RTM-Worx, three basic objects are used to build up a so called surface model of the geometry:

Keypoints Points that define locations in space and can be assigned properties to function as either injection or venting ports with prescribed pressure and/or flow rate and time of opening and closing.
Curves Lines that connect two or more keypoints to define boundaries of the part. You can assign a diameter (and optionally fabric properties) to turn a curve into a runner to model the resin delivery system or easy flow paths along the edges of the fabric.
Surfaces Regions defined by a closed loop of curves used to model (thin-walled) sections of your part. In addition to the thickness, you can assign fabric properties for RTM like porosity and anisotropic in-plane permeability.

RTM-Worx has a built-in interactive geometry editor you can use to build the model and to change the geometry. It is also possible to read a geometry from drawings or meshes generated by other CAD or FEM applications and edit the geometry with the integrated keypoint, curve and surface editors.
Surfaces are created by selecting the boundary curves, either by clicking them with the mouse or entering curve numbers using the keyboard. Definition of curves is similar, but now you select the keypoints on the new curve. You can split surfaces to generate new curves on a surface, and split curves to generate new keypoints on an existing curve. For new keypoints, you type the coordinates, or you can use the move and copy functions. Deleting points automatically merges curves and deleting curves automatically merges surfaces. Properties are assigned directly to keypoints, curves and surfaces, and you can let RTM-Worx search for objects with identical properties which are then automatically selected.
Note that it is important that all parts of the model are properly connected, because there will be no flow between parts that are not connected to each other. Surfaces are connected where they share a common curve or keypoint, curves are connected when they have a common keypoint.
Each change is immediately displayed. For the calculation, the geometry is subdivided into smaller objects, called elements (line elements on curves and runners and triangular shell elements on surfaces) and nodes (at the vertices of the elements), and the mesh for new or changed objects is automatically (re-)generated. Therefore, you can run another simulation immediately when you made a change to the model. Direct control over mesh generation is provided in the Mesh Generator, where you can set bounds on the size of elements and regenerate the mesh on the whole geometry.

[top] 1.2.3 Model visualization

RTM-Worx provides a very flexible way of displaying the geometry, it's components (keypoints, curves and surfaces), properties and results. It is possible to display the part in a realistic way (more or less comparable to how it actually looks), but to support editing and verifying correctness of the model, the emphasis is on a more symbolic representation. Here is a short list of possibilities:

  • Keypoints can be displayed as colored squares or as 3D spheres. For injection points and venting ports, different colors and 3D symbols are used. You can selectively turn off keypoints separately from injection points. The size of the colored squares and diameter of the spheres is adjustable.
  • Curves are displayed as lines or 3D rods (with user defined symbol diameter). Runners are displayed with their actual diameter. You can selectively turn off ordinary curves and runners.
  • Surfaces can be turned off, displayed as flat surfaces or as 3D volumes when a thickness is assigned.
  • You can display surfaces and runners with their diameter and thickness scaled by a constant to make it easier to view thickness differences.
  • The line elements and triangles that make up the mesh can be shown on curves, runners and surfaces.
  • You can shrink the 3D elements on curves, runners and surfaces by a small amount to get a clearer view of both the geometry and the way it is subdivided by the mesh and to be able to select curves shared by surfaces in a 3D plot that would otherwise be hidden inside the part.

Of course, the colors used to display the model can be changed to your own preferences. Two standard color sets are provided: one for the screen with a black background, and a second set you can use for printing with a white background and some other colors changed to ensure everything will be visible on the light background.
Because the display of the model is three dimensional, a realistic lighting model is necessary. Therefore, a lighting model (ambient and directed light, diffuse and specular reflection) has been used in RTM-Worx to ensure good visibility. Lighting is separated from the colors used in color contour plots. From the large set of possible combinations of parameters in the lighting model, only a small number of settings delivers good results. RTM-Worx provides you with a very intuitive interface to adapt the lighting to your needs without exposing you the implementation details.

[top] 1.2.4 Mesh generation

The geometry model of the part is subdivided into smaller objects, so called elements, which are used in the calculation. In general, increasing the number of elements leads to more accurate simulation results and higher resolution (for example in the approximation of the shape of the flow-front), at the cost of longer calculation times and increased memory requirements. The number of elements is only limited by the amount of RAM available to RTM-Worx. In general you will use 1000 to 10000 elements.
Because line elements are always straight, the smoothness of spline curves depends on the number of straight elements used to subdivide the curve. RTM-Worx always displays the mesh so you can directly see how good the approximation is compared to the actual geometry by visual inspection.
The generation of the mesh is automatically done when the geometry is changed, and only on the surfaces and curves where necessary. The size of the mesh is controlled by specifying upper and lower bounds on the size of the element edges. Buttons are provided to halve and double the element size, generate a course mesh (smallest number of elements possible), a mesh with elements of uniform size (equal to the size of the smallest curve in the geometry) and to generate a default mesh with an upper bound on the element size that equals 10% of the size of the bounding box around the model. In between the upper and lower bounds, a graded mesh is generated where the edge size adapts to the amount of detail in your model, e.g. the size of curves (which is the distance in between keypoints) in the neighborhood of the elements.
For optimal results, the majority of the triangular elements on surfaces should be near to equilateral (sides of equal length and three internal angles of 60 degrees) and obtuse triangles must be avoided. To help you optimize the mesh, the element quality and obtuseness of elements can be displayed in a color contour plot where good (near optimal) elements and bad elements have different colors.

[top] 1.2.5 Material and resin properties

Fabric properties are specified on the surface they apply to, in the surface editor that is used to define surfaces. The following runner and surface types are available in RTM-Worx:

  • Runner. The only property you need to define is the runner diameter.
  • RTM runner. In addition to the diameter, you define the porosity and permeability (UD strands).
  • Shell surface. Thin-walled section without reinforcement. The only property is the thickness.
  • RTM surface: thickness, porosity, major and minor permeability, lay-up angle and reference direction.

There is no separation between geometry definition and the so-called Element Groups found in classical FEM programs. Although Element Groups are a useful concept, and used internally by RTM-Worx, it is not the most intuitive way to define properties. It is however, very useful if you can change the properties of several surfaces of curves together: you might need to use multiple surfaces to approximate a curved section of your part for which one type of reinforcement is used. Therefore, RTM-Worx provides a search capability that allows you to select all curves or surfaces with equal properties with a click on a button. This also solves the problem of having different element groups that have equal properties, or tracking down element groups that are not in use: all the bookkeeping is taken care of automatically.
For an isothermal RTM simulation, the only resin property needed for a simulation is the viscosity.

[top] 1.2.6 RTM Simulation

Once you defined the geometry of your part and assigned all properties, you can run a simulation. The calculation is fast, can be aborted and restarted at the point where it was stopped. When properties are not defined, default values are used (the resin viscosity for example defaults to 1.0, diameters and thickness to 0.0 etc.) and disconnected or impermeable parts of the model are simply not filled. During the simulation, results of specific time instances (snapshots) are saved to the output file. When the calculation has been done, you can walk through all the time steps for which results have been saved to view the entire filling history. The number of times steps to be saved can be adjusted, saving more time steps allows you to see more detail in time but will also increase the size of the project database and slow down loading and saving the project. It is also possible to run the simulation until the mould is full, saving only a moderate number of time steps, then walk through the sequence to a point just before something that interests you happened, and restart the calculation at this point with a small time step to be able to see much detail in time.
You can delete results from the calculation to minimize size of the database and when the geometry or properties are changed, results from the calculation are automatically deleted.

[top] 1.2.7 Presentation of results

For the interpretation of the results of the calculation, you can walk through the filling history (the amount of detail in time depends on the number of time steps that were saved to disk), and view the results using any combination of the following options (in addition to all basic visualization options, see 1.2.3):

  • shaded contour plots of pressure or filling time, or model properties;
  • color contour plots of pressure or filling time;
  • vector plots of velocity (or permeability).

The combination of properties with calculation results (for example a shaded plot of permeability in combination with flow front progression line contours and a velocity vector plot) is important to understand the results, and more important, to identify potential problems and bottlenecks that you want to resolve in order to optimize the RTM process.

[top] 1.2.8 Database and import filters

In RTM-Worx, you work on one project at a time for which all the data is saved in one single database. The database contains the geometry model, properties (lay-up, resin), calculation parameters and current display settings. Each change is automatically saved to the database and commands are provided to copy the database (if you want to use it to try out some changes while you don't want to change the current model), to store the database in an archive file (which is read-only, and can be read by RTM-Worx to provide a common basis to compare several alternative changes to the product and/or process) and to rename or move the database to another location on your hard disk.
If you have a CAD model of your part, or a mesh from another FEM application (structural analysis for example), you can use the Import facility in RTM-Worx to read the files generated by those applications and convert it to a RTM-Worx geometry model. Currently supported file formats are Auto-Cad™ DXF, C-Mold™ mesh (*.MSH), binary STL, SEPRAN mesh and p7 (*.pi7) databases.


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