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ANSYS WB and a review of the design metrics in Piaggio: the case of the motor shaft

ansys wb piaggio

I still can remember the time when, looking at a 3D CAD model of an engine block, I would start thinking about the best way to translate it into a PREP7 procedure. I would come up with something to mesh, but the next time I would have to start from scratch again. In those times, beam representations in conjunction with SIFs were the best way to go with crankshafts. Other components required similar efforts.

Things evolved in a continuous fashion, but a discontinuity came when ANSYS changed its face completely with Workbench. At first I thought that dealing with it would have been a dive into a bottomless ocean, just like the first time I met a CONTA174. But I’ve always been a fundamentalist when it comes to new CAE techniques, so I tried to move to WB as quickly as I could and to the maximum possible extent.

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ansys wb piaggio

ansys wb piaggio

And my way of working radically changed: geometry import and meshing issues sharply decreased, and past models could be used as templates for new, similar analyses. This last aspect evolved dramatically with the introduction of WB projects, where bunches of interconnected analyses form now real CAE procedures, laid down with nearly no effort. Such a case happened just a few weeks ago when I came up against a crankshaft simulation. I had to use WB both as stand-alone application and as part of a CAE chain, including MBS and durability analyses.

The simulations I had to perform required both linear and nonlinear models, involving the simulation of neighboring components, in addition to the crankshaft proper. WB allowed me to quickly setup a baseline model: DM fixed a few CAD issues and Mechanical Automatic Contact detection feature greatly speeded up the assembly setup. The CAD interface can sense CAD simplified representations, allowing to perform partial CAD imports, really useful when dealing with big CAD models. Generating all the other models I needed from the baseline one was really easy at a project level, duplicating when a different topology was needed and linking when only different load systems or different analysis types were required.

That way, I could assess both the frictional load transfer capability and the fatigue performance of the crankshaft assembly.

For the former I used nonlinear models, exploiting the WB contact features, whose default settings are much more error-proof than navigating among all the keyoptions and real constants of the good old CONTA family. I could check the functionality of friction couplings with both standard and custom postprocessing quantities. The latter are easily definable with the aid of another WB feature: the Worksheets.

With them you have an overview of your modeling stages in a neat tabular form. You can check the properties of the bodies included in an assembly, of the contact interfaces, or the available postprocessing quantities, to name a few. From a table you can jump to the relevant model element with a simple click. So Worksheets prove to be a nice tool to check what you’ve done.

The fatigue analyses required the computation of load/stress transfer functions and of a Craig-Bampton modal representation [1]. The latter was calculated by means of a simple combination of rigid Remote Displacement features and of a Commands object: no more messing around with CERIGs, since WB did the job totally in the background.

The results of the activity were not only fatigue safety factors and stress distributions; besides them, and above all, a neat trace of what I did has been left both at a Project and System level, in the WB jargon. The next time a similar component will have to be simulated, it will be an update process, not a generation one. Opening the WB project, the modeling procedure will be easily recognizable.

ansys wb piaggio

ansys wb piaggio

In the past the CAE techniques had a hard time trying to be simultaneously fast and accurate; that slowed their integration into the development process of complex systems. I think that WB has been one of the major milestones in overcoming these problems, therefore allowing the simulations to be perceived as standard and required activities.


Articolo pubblicato sulla Newsletter EnginSoft Anno 8 n°1

Roberto Gonella

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