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Multi Cylinder Engine with multiple stroke lengths

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Old   July 16, 2020, 01:40
Default Multi Cylinder Engine with multiple stroke lengths
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Kurt Stuart
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I am trying to setup a simulation of a 3 cylinder engine with 2 different stroke lengths. Is there a way to do this without specifying a wall motion? When setting this up, where should the pistons be in the surface geometry? All at BDC, or???

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Old   July 20, 2020, 09:13
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Aditya Raman
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Hi kstuart,


There are only 2 ways to prescribe boundary motion, either by a user specified motion file or piston motion. For a case with 2 different stroke lengths, you would have to provide the user specified motion for one cylinder. The other 2 cylinders that have the same stroke length, you can use the piston motion option. The piston motion is determined from the data provided in the engine.in file. You must also provide the phase-lag (\varphi) to account for the firing order.



At the start of the simulation, the pistons should all be at BDC.







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Aditya Raman, PhD

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Convergent Science
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Old   July 21, 2020, 00:25
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Kurt Stuart
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Thank you Aditya.

Perhaps you can help with another question.

I have been using Auto-desk Inventor to create my geometry, and then exporting as an STL file.

When doing this there are some options such as binary or ASCII, resolution, ect. I have left these in defaults but changed resolution to high. Is there a preferred setup for this? Is there a Converge document that goes into more detail on the geometry import details. I have had some geometry issues I'm fighting.

Thanks,

Kurt.
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Old   July 22, 2020, 02:45
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Aditya Raman
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We don't have a preferred way as such. Since you are already importing an STL file, it should work well with Studio. For CAD surface preparation however we do recommend the following
  • Higher resolution in areas of sharp curvature (excess triangles increase simulation time while too few triangles may not capture important surface features)
  • Verify that the solid is watertight to avoid open edge errors
  • Ensure that each circle is represented by a sufficient number of vertices to avoid cylindrical shapes that look like prisms

Even if your surface is of high resolution all over, you can perform coarsening of surfaces that do not require additional resolution inside of Studio. For details on Geometry preparation inside Studio, you can refer to Chap 2 sec 3 of CONVERGE Studio Manual. Also some information on surface defects are detailed in CONVERGE user manual chap 5.


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Aditya Raman, PhD

Research Engineer, Applications
Convergent Science
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