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RTM-Worx User Manual |
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3.1 Entering the Geometry and Properties
3.1.1 Model structure in RTM-Worx In RTM-Worx, a surface model is used to describe the geometry of an object, and each geometry object is automatically subdivided into elements to serve as the mesh for the FEM calculation. The first paragraph gives an overview of the structure of this surface model and the methods available to edit the model are discussed in the remainder of this section.
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List of selected keypoints, used in [Del], [Move], [Copy] and [Apply] commands. The same list is used in the Curve editor. |
[Del] removes selected points. [Add] adds a keypoint at the (x, y, z) coordinates.. | |
(x, y, z) coordinates. Enter coordinates here for new points. Updated when you select a new keypoint (without Shift or Ctrl down). | |
[Move] translates the selected keypoints by the offset (dx, dy, dz). [Copy] creates new points from selected points at the offset (dx, dy, dz). | |
Offset for [Move] and [Copy] commands. If you select a new keypoint, those fields are updated with the old contents of the (x, y, z) edit fields minus the coordinates of the new keypoint. | |
Properties are used to define venting and injection ports. Select the property you want to assign to the currently selected keypoint(s) here. | |
The [Find] command selects all keypoints with specified properties. [Apply] assigns the current properties to all selected Keypoints. |
You can select existing keypoints by typing their numbers in the Keypoints list, or by selecting them by the mouse. Hold down the Shift key when clicking to select multiple keypoints.
If you select keypoints, either by clicking them with the mouse or typing in the keypoint list, the coordinates of the new point are automatically entered in the (x, y, z) edit fields, the (dx, dy, dz) fields are updated with the difference between the old coordinates and the new ones, and the Properties are shown. This automatic updating is not done if:
The [Move] and [Copy] commands are only enabled when the offset (dx, dy, dz) is fully specified and no keypoint already exists at the location defined by the selected point(s) and the offset.
If you add a keypoint, it will receive the current properties. Properties for existing keypoints are only updated if you changed them by issuing the [Apply] command. The [Apply] button will be disabled when there is no difference between the displayed properties and the properties of the selected keypoints.
The [Del] command will delete all selected keypoints with the exception of keypoints that are used as end vertex by a single curve or shared by more than two different curves. Two curves that are connected by the keypoint that is deleted will be merged into one single curve. When the curves are part of a surface boundary, they will only be merged when the boundary contains four or more curves. Otherwise, the curves will not be merged, and the keypoint is not deleted. You can work around this by splitting one of the other boundary curves before you delete the keypoint. Those rules make it safe to delete any keypoint without destroying the topology of the model, although it does not guarantee that the geometry represents a valid object, neither are there any restrictions.
Before you run a simulation, you need to define the location of injection ports. Otherwise, when you start the simulation nothing happens! Venting ports, where resin leaves the mold, can also be defined but are not necessary to run the simulation. You might actually want to use the simulation to determine the location of venting ports and any venting ports already defined may undesirably influence the way the part fills. Any keypoint can be used to define an injection or venting port by simply changing its properties. If you want to put an injection port at a location where you don't have a keypoint, create a keypoint by using the [Split] commands in the Surface and Curve editors and move it to the desired place with the [Move] command in the Keypoint editor. For a venting port, you need to define the moment it opens and when it closes. In addition, for an injection port, the pressure and/or flow rate must be defined (otherwise the injection port will behave like a venting port).
Property | Default | Full name | Remarks |
---|---|---|---|
fA | 0 % | Activate at fraction filled | Filled fraction of mold when port opens. |
fC | 100% | Close at fraction filled | Filled fraction of mold when port closes. |
Pi | 0 Pa | Injection pressure (maximum) | Pressure at injection port. When it is zero, the port behaves like a venting port, unless a non-zero flow rate is specified. |
Qi | 0 m3/s | Flow rate (maximum) | Constant flow rate at injection port. When zero, the port behaves like a venting port, unless a non-zero injection pressure is specified. |
Note that the pressure defined at an injection port is actually the pressure difference between injection port and venting ports. The pressure at the flow front and venting ports is set to zero by RTM-Worx.
When both the injection pressure and flow rate are non-zero, both values act as upper bounds:
A closed injection or venting port (mold filled fraction is smaller than fA or larger than fC) behaves like an ordinary keypoint. If you want to vary pressure and/or flow rate during injection, connect a number of injection ports with connectors (see section 2.4.6) and let them open and close in sequence.
Curves are used to define the boundaries of surfaces and to serve as runner channels, for example to model the delivery system or easy flow paths between fabric reinforcement and mould walls. Curves can be created using the following methods:
You need at least two keypoints to define a curve, but there is no maximum limit to the number of keypoints. If you use more than two keypoints, a cubic spline is automatically fitted through the points. Keypoints on the curve that are not on one of the ends, so called mid-points, cannot be shared with other curves, e.g., you can only connect a spline curve at the ends. If one of the keypoints in the list is already in use by another curve, the [Add] command will automatically split the curve at such keypoints, and if necessary also the existing curve that already used the keypoint.
You can only delete curves that are shared by two surfaces. The surfaces that shared the curve are automatically merged into one surface. When a curve is used by only one surface, or by three or more surfaces it cannot be deleted. You will have to delete the surface(s) first.
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List of selected curves, used in [Del], [Flip], [Break], [Join], [Split] and [Apply] commands. The same list is also used in the surface editor. |
[Del] removes curves and merges surfaces. [Flip] reverses the order of the keypoints on the curve. [Break] turns each curve segment into a straight curve. [Join] merges adjacent selected curves into one spline curve. [Split] generates new keypoints in between existing ones and splits each selected curve in two separate curves. [Add] creates new curves. | |
List of keypoints for the definition of a new curve. This is the same list that is used in the Keypoint editor. | |
Properties are used to define runners or to attach numerical tags. Select the property you want to assign here. | |
The [Find] command selects all curves with specified properties. [Apply] assigns the current properties to all selected curves. |
If you want to approximate a circle or circular arc, use points spaced at 45 degrees or less. The difference between actual radius and the spline approximation will be less than one percent. Note that the accuracy of the spline approximation also depends on the mesh size. If you use a very coarse mesh, the segments of the curve will always be straight lines. Curves will be smoother when a smaller mesh size is chosen.
Any curve can be used as a runner by adding properties. In RTM-Worx three types of runners are available:
All properties have default values. The diameter defaults to zero, which is allowed and effectively causes the runner to be treated as a curve without properties. The properties are listed in the table below.
Property | Default | Full name | Remarks |
---|---|---|---|
H | 0 m | Diameter | Runner diameter and surface thickness are shared edit fields. RTM-Worx remembers the last value used which makes it easier to choose dimensions. |
Vf | 0 % | Fiber volume fraction | Equals (1 - porosity). The porosity times the total volume is the space available for the resin. Always zero for an isothermal runner. |
k11 | 0 m2 | Permeability | The equivalent value for an isothermal runner is D2/32 where D is the inner diameter. |
A connector is a runner element without neither volume nor resistance to flow. You can use it for example to model an exploded view of the part, or to model injection along an edge without having to define the actual feeding system. RTM-Worx does not provide a separate curve type to model connectors, but you can use the RTM runner with properties defined as follows:
You may have to experiment a bit with the values for Vf and K11 to get good results.
Surfaces are used to model the cavity. By assigning a thickness to a surface it becomes a volume that can be filled with resin.
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List of selected surfaces. Used by the [Del], [Flip] and [Split] commands. |
[Del] removes surfaces. [Flip] swaps the front- and backside by reversing the order of the boundary curves. [Split] breaks up a surface into a number of smaller surfaces. [Add] creates a new surface from the list of boundary curves below. | |
List of curves, identical to the one used in the Curve editor control panel. Used to define the boundary of a surface. | |
Properties include the local shell thickness and optionally the reinforcement porosity and permeability. | |
The [Find] command selects all surfaces with specified properties. [Apply] assigns the current properties to all selected surfaces. |
RTM-Worx supports four types of surfaces:
A surface is defined by a closed loop of boundary curves that is defined in the list of curves in the Surface editor. The curves have to be adjacent, e.g. each set of two curves in the list must have a vertex in common. The order in which the curves are listed determines the front- and backside of a surface. The front side is defined as the side for which the boundary curves are listed in counter-clockwise order. Once a surface is created, you can always change this order with the [Flip] command.
In order to calculate the flow through the fabric reinforcement, it is treated by RTM-Worx as a porous medium with anisotropic in-plane permeability. Because the flow is locally treated as two-dimensional, permeability needs to be defined in two perpendicular directions in the surface plane only. For layers of fabric with different properties, the through thickness average must be specified for the fiber volume fraction and both the magnitude and the direction of permeability. If, for example, even numbers of layers that are anisotropic are stacked 0/90 degrees, the resulting reinforcement becomes isotropic with permeability k11 and k22 equal to the average of minor and major permeability of each individual layer. The properties of the RTM-surface are summarized in the following table:
Property | Default | Full name | Remarks |
---|---|---|---|
H | 0 m | thickness | Field is shared with runner diameter in Curve editor to make it easier to enter dimensions. |
Vf | 0 % | Fiber/volume fraction | Equals (1.0-porosity). Always zero for an isothermal shell surface |
phi | 0o | Lay-up angle | Rotation of fabric in-plane relative to the projection of the reference direction. |
k11 | 0 m2 | Major permeability | Permeability in the main direction. The equivalent value for an isothermal shell surface without reinforcement is H2/12, where H is the distance between the mould surfaces. |
k22 | 0 m2 | Minor permeability | Permeability perpendicular to the main direction. Equal to k11 for isotropic fabrics. |
rX, rY, rZ | 1, 0, 0 | Reference direction | (x, y, z) coordinates that defines the direction for the major permeability value, k11. |
The main direction is locally determined on each element by the following procedure:
There are several ways to visualize reinforcement properties to verify the input:
You can combine the shaded plot of fiber/volume fraction with a vector plot of the permeability to view all reinforcement properties at once. It an also be very helpful to plot porosity of permeability in combination with results (filling time or pressure) to interpret the resin flow.
home |
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about this manual |
quick start |
introduction
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philosophy |
getting started |
interface |
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menu and commands |
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mesh generation
simulation
© 1997-2022 Polyworx
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User Manual |
![]() |
![]() |
![]() |
contents |
![]() |
![]() |
about this manual |
![]() |
quick start |
![]() |
![]() |
introduction |
![]() |
![]() |
installation |
![]() |
features |
![]() |
philosophy |
![]() |
getting started |
![]() |
![]() |
interface |
![]() |
![]() |
workspace |
![]() |
menu and commands |
![]() |
viewing the model |
![]() |
![]() |
model and calculation |
![]() |
![]() |
geometry and properties |
![]() |
mesh generation |
![]() |
simulation |
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RTM-Worx Applications |
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RTM-Worx Documentation |
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