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1. Preparations in StudioTools

In order for the analysis to be possible in I-DEAS, the model must be prepared in a certain way in StudioTools. The model of the wheel must obey the following points:
  • Watertight: The model may not have any gaps between components, e.g. a gap between a spoke and the rim is unacceptable, regardless of how small it may be.
  • Hub: The wheel must have a hub, that is a hole in the center of the wheel, which mounts to an axle. The reason for this requirement is that we will constrain this hub in I-DEAS to not move while forces are acting on the wheel.
  • Tireless: The model we will be analyzing is the wheel without the rubber tire. Hence, you must be able to remove the tire from the wheel in your model.
  • Correct dimensions: The wheel must be dimensioned properly before importing in I-DEAS. You need not model the wheel in the right dimensions right away - you can scale the wheel at the point in time before exporting it.

The following outlines all the necessary steps taken in StudioTools to model, prepare, and finally export the wheel in Figure 1.1.

Figure 1.1
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Figures 1.2 through 1.5 show the cross-section of the example wheel before the revolve tool has been applied to create the final surface. Note that the continuous line of the cross-section has been divided into 4 separate pieces - this step is necessary to create separate surfaces for the wheel, as opposed to one complete surface.

Figure 1.2 highlights the hub, which must be a separate surface, as the hub's surface will be used to apply a displacement constraint in I-DEAS.

Figure 1.2
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Figure 1.3 highlights two separate lines that will generate the two surfaces between the hub and the outside rim. If you intend to create a wheel with spokes, this surface is unnecessary - instead, you will be filling the space with cylinders or the such (for spokes). Otherwise, if you intend to create a wheel with a solid surface between hub and rim, or trim out holes from this surface, make sure that the two originating lines are separate as outlined in Figure 1.3.

Figure 1.3
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Figure 1.4 highlights the 2 separate outside portions of the wheel's rim. These lines have been separated so that the highlighted lines in Figures 1.3 and 1.5 are separate.

Notice that all corners, except the ones on the inside hub have been rounded. You will see later that sharp corners are especially prone to structural instability.

Figure 1.4
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Figure 1.5 finally highlights a line which, when revolved, generates a surface that will interface with the rubber tire. This surface needs to be separate, as we will apply a pressure force on it.

Figure 1.5
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Figure 1.6 highlights the curve that produces a torus-like shaped tire. While it is not used in the analysis, the tire is included in the model at this point, as it may help in visualizing the wheel.

Figure 1.6
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Figure 1.7 shows the curves on either side of the wheel, which will be used to cut out holes in the region between the hub and the rim.

Figure 1.7
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The result of revolving all lines and cutting out the holes is depicted in Figure 1.8.

Figure 1.8
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We now clean the model for further preparations. First, construction history is deleted from the model, as it will be inconsequential for I-DEAS. Then, all originating curves, as well as the rubber tire are removed from the model, leaving behind the surfaces of the bare wheel.

Figure 1.9
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The rim surface that interfaces with the rubber tire is presently one complete object. We will be applying a force to the wheel on this surface in I-DEAS, but it is not realistic to apply the force to the entire surface, as not all portions of it are equally exposed to the force. Figure 1.10 shows a diagram of the translation of pressure from the street to the rubber tire further to the rim of the wheel.

Figure 1.10
We will need to divide the surface so as to separate the portion to which the force is applied.

We construct two lines as shown in Figure 1.11. Each line should be spaced 1/3 of the rim's width from the center. You should consider using Duplicate Object with attribute Scale X = -1 in order to mirror the first line about its pivot, which has been placed in the center of the wheel.

Figure 1.11
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Figure 1.12 shows the lines with respect to the 3D model. Note that the lines must not necessarily be placed above the wheel. When projecting the lines, their position along the Z axis is inconsequential.

Figure 1.12
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Project the lines onto the wheel.

Important: Make sure not to project in the Perspective view, but rather in the view shown in Figure 1.11. The resulting Curves on Surface are shown in Figure 1.13. Notice how the lines were projected onto the top AND bottom portions of the rim surface. Because we are only interested in a separate bottom surface, you may wish to use the tool COS under the Pick menu to select the two Curves on Surface in the top region, and delete them.

Figure 1.13
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The surfaces are now divided using the tool Trim/Divide under Surface Edit. The two white crosses in Figure 1.14 denote the separation between the surfaces.

Figure 1.14
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Finally, the bottom surface has been separated, as shown in Figure 1.15.

Figure 1.15
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Figure 1.16 shows the shaded version of Figure 1.15. It may help to shade the model before exporting it, so as to visually analyze the structure for any problems, such as missing surfaces.
Important: Make sure that the wheel is the only object in the scene before exporting. You do not want to export any additional objects.

Figure 1.16
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As the last step in preparing the model, we must ensure that the model is dimensioned correctly. Highlight the side view window, and inspect the status bar in the upper left corner, as circled in Figure 17. From here, you can find out what the current units are, and what each grid square corresponds to. In the case of Figure 17, the units have been set as cm and each grid square has a side of 1 unit, i.e. 1cm. Counting the number of grid squares that the wheel is occupying, we find that the wheel has a diameter of 46cm, which is a realistic size. If your wheel does not have realistic dimensions, e.g. 50 meters diameter, you must re-scale. For this, group the components of the wheel, and use the Scale tool to re-scale the wheel.

Figure 1.17
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To save the model as a file type that is recognized in I-DEAS, go to the File menu, and select the box next to Save as.

Figure 1.18
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Under File Formats choose the file format STEP. STEP is the international STandard for the Exchange of Product Model Data, which has been developed by the International Standards Organization (ISO) in conjunction with American, European, and Asian businesses and government agencies to implement a standard for transferring electronic data. You will find that STEP is commonly available among CAD/CAM/CAE software packages, while the StudioTools WIRE format is proprietary to Alias|Wavefront software packages.

Figure 1.19
Leave all available options set to their defaults, and click Save.

Figure 1.20
Give your model a name, and save it. The file extension stp will be added automatically, so you merely have to type in the name of your model file.

Figure 1.21
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