56. Net panel

The identification tag for this tutorial is PDS-ABP. Pregenerated input files for this tutorial are found in the folder named PDS-ABP in the provided tutorial input files.

56.1. Tutorial overview

This tutorial covers:

  • Creating a net panel
  • Net panel edge and node constraints
  • Defining drag coefficients for nets
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Fig. 56.1 Net panel

56.2. Creating a net panel

  • Create a new project.

Note

  • A finite-element net DObject contains nodes and elements. The nodes of a net panel are defined as shown in Fig. 56.2.
  • Edges of a panel (Edges 0,1,2,3) are defined as shown in Fig. 56.2.
  • The edges of the net are coloured for identification in the PST visualization window. Edge 0 = Red, Edge 1 = Blue, Edge 2 = Green, Edge 3 = White.
  • Create a net DObject.
  • Define its initial state using the panel option according to Fig. 56.3. Set node (0,0)’s position at (0,0,0) m.

Note

  • The net properties can be adjusted using the DNetPanel feature in the feature library.
  • Change the $FilamentCount property to 50 of the DNetPanel feature.

Note

  • The filament count corresponds to the inverse of the half mesh size. A filament count of 50 (number of net strands per meter) corresponds half mesh size of 20 mm.
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Fig. 56.2 Net panel edge and node definition

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Fig. 56.3 Tutorial net panel schematic

56.3. Defining drag coefficients

Note

  • By default, nets in ProteusDS have the $FluidCoefficientReData property activated to account for Reynolds number variation of drag coefficient for netting twines. This property will automatically be inserted into the net input file with the creation of a new net DObject.
  • Navigate to the library and click on the reynoldsDependentNetDragData default created $FluidCoefficientReData feature.

Note

  • The default listed Reynolds number and drag coefficient data is based on the variation of drag coefficient for a circular cylinder. This data is used as a multiplication factor to the constant netting drag coefficient, $CDc.
  • Change the $CDc value in the DNetPanel feature to 1.05.

Note

  • The Reynolds number drag coefficient data will be scaled by 1.05 for each netting twine. Typical $CDc values for nets are between 1.0-1.1.
  • At every time step in a simulation, the Reynolds number is calculated at each node based on local flow velocity, filament diameter, and fluid properties. That Reynolds number is used to determine the corresponding intermediate drag coefficient from the $FluidCoefficientReData feature. That intermediate drag coefficient is then multiplied by the CDc property in the DNetPanel feature to produce the final drag coefficient used for drag force calculations.

56.4. Edge Constraints

  • Set all of the edge constraints (e.g. $Edge0Static) to 1.
  • Add a current velocity in the Y direction ($CurrentHeading 90) of 1 m/s.
  • Run a simulation for 10 seconds and watch the deflection of the net.

Note

  • Note that the edges of the net do not move.
  • View the net in engineering mode. Note that the constrained nodes (edges) are shown in in red.

56.5. Node constraints

  • Remove the edge constraints and set all of the node constraints (e.g. $Node00Static) to 1.
  • Run a simulation for 10 seconds and watch the deflection of the net.

Note

  • Note that the corner nodes are constrained.

56.6. Combined edge and node constraints

  • Remove all constraints on the net.
  • Set edge 0 to be static and node (M,0) and node (M,N) to be static.
  • Run a simulation for 10 seconds and note how the net responds to the combined constraints.

56.7. Adding an ExtMass to a net

Note

  • To efficiently model a clump weight attached to a net an $ExtMass can be used.
  • Remove all constraints on the net.
  • Set edge 0 to be static.
  • Add an ExtMass clump weight to the library with the following properties:
// Fluid loading
$CD 1
$CA 0.5
$FluidLoadingMode 1

// Mechanical
$Diameter 1
$Density 2000

// Type
$ExtMassType 0
  • Add the following $ExtMass lines to the net panel input file:
$ExtMass clump 0 10
$ExtMass clump 20 10
  • Run a simulation for 10 seconds and visualize the effect of the clump weights on the net.