Powertrain Modeling

Overview

The steps for Powertrain modeling are as follows:
  1. Import CAD
  2. Create component sets
  3. Defeature CAD as necessary (Optional)
  4. Facet powertrain assembly
  5. Patch openings and review
  6. HX Modeling
  7. Wrap with wrap controls (Assembly by assembly or entire underhood)
  8. Wrapping quality: Check for bridging and that features are captured
  9. Decimate (may not want to decimate too much)

Process

  1. Import associated CAD for the powertrain:


    Figure 1.
  2. Create sets based on analysis:
    • Tools pull down > Create sets of components
    • Model browser > Show/Hide components by sets for further steps
    • Use sets to select component -> by sets


      Figure 2.
  3. Defeature Geometry (Optional):
    • Simplify model to avoid modeling unnecessary features like logos, solid holes, fillets, and so on
    • Find small parts and delete them
      • Use find_smallParts.tcl script
      • Define 10 as threshold to find small parts (Generally nuts and bolts)
      • It will create a set will small parts based on tolerance
      • Right-click Isolate only to review the parts
      • F2 to open delete panel  Select parts to delete
    • Remove logo (Geometry --> Auto cleanup)


      Figure 3.
      • Select logo and surrounding surface
        • Selection does not need to be precise
        • It should cover all logo surfaces and surrounding surfaces
        • You can select all surfaces as well
      • Measure logo height beforehand to define in this utility
        • Simplify parts
    • Solid hole removal


      Figure 4.
      • Use solid hole removal in Geometry ribbon
      • In edit parameters, turn on the option to remove solid hole
      • Define maximum radius as 20 (Choose radius according to selection)
    • Create primitive shapes to model complex parts with cylinder, sphere or block
  4. Tessellate CAD:
    • Once done with geometry editing tool, tessellate the CAD to further work on mesh-based tools like wrapper, hole gap patch, and so on


      Figure 5.
    • Use rigid body mesher to tessellate
    • Define following parameters (for model in mm scale)


      Figure 6.
    • Tips:
      • Change maximum and minimum sizes according to scale of the model and level of details required.
      • Review tessellated mesh
      • Review that tessellation captures original shape as required
      • Review free edges:
        • Tools > Edges > Free edges
      • Delete geometry to make model lighter (Surfaces and Solids)
  5. Patch:
    • Patch complex areas, gaps, solid opening


      Figure 7.
    • Patch openings, solid holes (Mesh pull down > Hole/Gap fill > Hole fill): Here you need to close opening of pipes, solid holes so the wrapper does not go inside parts; if this happens, you get exterior surfaces as wrap results
      1. Switch to Fill mode to “Hole fill”


        Figure 8.
      2. Select all components
      3. Turn on Consider features which will consider solid holes as well.
      4. Define hole width: 100
        1. Measure the hole length you want to close and define it as maximum width
        2. For powertrain and underhood cases start with maximum width as 50
      5. Review patches. Delete patch elements if not required
      6. Manual patch as required by selecting Faces or edges instead of components
    • Close gaps in the model


      Figure 9.
      1. Switch to Fill mode to “Gap fill”


        Figure 10.
      2. Select opposite faces one in each group
      3. Turn on Consider features.
      4. Measure the gap length you want to close and define it as maximum width
    • Cover slots so that they are not exposed to wrapper; they are not useful for analysis


      Figure 11.
      • Switch to Fill mode to “Patch fill”


        Figure 12.
      • Select Nodelist
      • Select nodes which covers shape. For a flat area, 4 nodes should be enough
  6. Model Heat exchanger (HXs):
    • When you are given detailed HXs with fins and tubes, model them using boxes
      1. Create HXs boxes
      2. Delete the fins and tubes
      3. Only retain HX shroud
      4. Do not include HX box components in wrapping
      5. After wrapping, connect HX box and wrapped parts (required for AcuSolve only)
        1. Mesh pull down > Boolean
        2. Select all wrapped components and HX boxes
        3. Define Boxes as master > Boolean
    • Create HX boxes


      Figure 13.
      • Mesh pull down > Hole/Gap Fill
      • Switch to Fill mode to “Patch fill”
      • Switch selection to Nodelist
      • Select four corner nodes which covers fins and tubes
      • Do it for both inlet and outlet
      • Create a side walls using same tool
      • Organize elements in appropriate components
      • Use Tools panel > Translate to enclose HX in corresponding box


        Figure 14.
  7. Wrap setting - Mesh Controls:
    • Define wrapper settings
      • Mesh pull down > Mesh controls
      • Right-click > Adaptive wrap folder > Create > Model
      • Select wrapper type: external wrapper
      • External wrapper for external flow analysis, for example, underhood thermal
      • Cavity wrapper for internal flow analysis, for example, thermal comfort.
      • Select volume definition: All
        • Available options (All/Nth largest/Enclosed by node/Exclude by node) – See the help for more details
      • Select components to be wrapped
      • Define wrapping parameters:


        Figure 15.
    • Tips:
      • Minimum size should be based on the smallest feature length to be captured. (Rule of thumb – minimum size = 1/3rd of smallest thickness)
      • If all gaps are patched using “Hole/gap fill” tool, define gap patch tolerance as minimum size.
        • Defining bigger gap patch tolerance can create bad wrap mesh
        • Define local controls if any other wrapping size is required locally
    • Define Proximity Controls to avoid contacts between selected parts


      Figure 16.
      • Define proximity controls
      • Select all HX, Air filter and neighboring shroud components
      • Define search floor. Any thing less than value will be refined


        Figure 17.
      • Leak Detection to verify if any leaks present in the model with given selection and parameters
        • Define a source node inside the wrapping domain
          • Make sure source node is enclosed properly and not close by any elements
        • Define multiple target nodes outside the volumes.
          • Define many target nodes and distribute them at different location
          • This way you have a greater chance of finding all possible leaks at once


            Figure 18.
        • Run wrapping:
          • Right-click on adaptive wrap folder -> Mesh
          • If leak detection mesh control is defined and there is a leak, it will terminate wrapping with leak path.
  8. Review wrap results:
    • Review wrap results and validate it before tetmeshing. After wrapping, there will be a new assembly creates which will contain wrapped results


      Figure 19.
    • Check intersections:
      • 3d panel > Tetramesh > Select all wrapped components > Check 2d mesh
      • Define intersection tolerance (for mm scale 0.001 and di-hedral angle as 5)
      • Wrapped results mostly will not have any intersection.
      • But sometimes you can see few intersections which can be resolved using 2d panel > Replace
    • Check free edges and t-connection
      • Tools panel > Edges > Select all wrapped components > Free edge/t-connection
      • Wrapped results should not have any free edges/t-connections
    • Analyze volume wrapper has created
      • Use volume_analyser.tcl script
      • Only display wrapped components (either wrapped or remeshed)
      • It will create a sets with possible volumes and you can review each volume as well
  9. Decimation:
    • If solver is uFx/PowerFlow, it is required to have minimum element count for post processing purpose
    • Decimation reduces elements count retaining sharp features intact with minimal geometry deviation


      Figure 20.
      • Use Decimation scripts to coarsen mesh
        • Select components to decimate
        • Define decimation factor: 0
        • 0: Provides least deviation from input
        • 1: Enables maximum possible deviation
        • Define feature angle: 30