Interfaces

Available contact algorithms in Radioss are presented in Table 1.

Table 1. Radioss Interfaces Face-to-Face
Type Description Application Contact Treatment
1 & 9 ALE / LAG with sliding Fluid-structure interaction Main-Secondary
2 Tied interface Change of mesh density (solid) Main-Secondary or LM
3 & 5 Contact impact between two parts Use of type 7 is recommended Penalty
6 Contact impact between two rigid bodies User-defined contacts Penalty
7 General purpose contact impact between two parts Solid contact impact at all speeds Penalty or LM
8 Drawbead contact Stamping applications Penalty
10 Similar to type 7, but tied contact Special purpose interface Penalty
11 Impact between two lines For beams, bars or springs Penalty
12 Fluid / fluid contact Fluid to fluid contact Penalty
16 & 17 Contact between nodes to quadratic shape solids and solid-shells or between quadratic shapes Meshes with 8-node or 16-node thick-shell or 20 bricks LM
18 CEL Lagrange / Euler interface Fluid-structure interactions Penalty
22 Lagrange surface and fluid domain Fluid-structure interactions Penalty
The specific interfaces for Radioss ALE/CFD applications are:
  • TYPE1: to contact an ALE part to a Lagrangian part
  • TYPE12: for ALE/Euler bricks to contact moving or fix meshes
  • TYPE18 and TYPE22: to treat fluid-structure interactions

Fluid/Fluid Interface

Interface TYPE12 is designed to connect two non-conforming meshes. Its use is restricted to a main/secondary approach, that is, no more than one main node is connected to a secondary segment.
Note: The main/secondary search algorithm may fail where there are sharp angles. In this case, you must split the interface into several interfaces.

You also might detect an error when the closest main node of a given secondary node does not belong to the segment in front a secondary node. In this case, adjust the mesh locally to avoid ambiguous situations.

The interface is available for quasi-compressibility and compressibility options.

Select Main and Secondary Sides in Fluid/Fluid Interface (Type 12)

Rule 1:

Every secondary node needs a main segment.


Figure 1.

This must remain true when interface is moving.

If a node has no projection on the main surface, the algorithm issues a warning but still works, because the secondary node remains associated to the nearest main segment.

Rule 2:

Every main node must receive contribution from at least a secondary node.


Figure 2.

If a main segment does not have a secondary but its neighbors do, the algorithm still works, because the above rule is satisfied. In principle, it is nevertheless recommended that main segments have at least one secondary node.

You can say that the secondary grid must be finer or equal to the main.

Rule 3:

When compressible, any segment (main or secondary) must be a surface of one and only one ALE brick element.


Figure 3.

Rule 4:

Kinematic conditions on the secondary side are allowed only if consistent with an identical condition on the main side.


Figure 4.

This has to remain true when interface slides.

Fluid/Structure Interaction (ALE/Lagrange Interface)

Three kinds of interfaces are available.

Interface TYPE1

Interface TYPE1 is used to define boundaries between ALE and Lagrange domains. Full slip conditions are applied at the boundary between the two domains, like full sliding wall. Normal material velocities of Lagrange and ALE nodes are equally set.


Figure 5. Fluid-Structure Interaction with Interface TYPE 1

Interface TYPE9

This is an ALE/Lagrange interface with void opening and free surface (that is, if the main and secondary sides are not in contact, there is no interaction between them). An ALE part is defined as secondary and the Lagrangian part is defined as main. The grid velocity is equal to the material velocity in normal direction.

Interface TYPE18 (CEL)

Interface TYPE18 creates contact between Euler/ALE nodes and a Lagrangian main surface. Visco-elastic penalty method is used to impose a relative material (fluid) velocity tangent to the main surface. The grid velocity is not modified by this interface. The interface allows the simulation of the penetration of a Lagrangian part (structure) into an Euler/ALE mesh, for example in the case of ship slamming.

The quality of simulation results using this interface depends strongly on the interface parameters and especially on the stiffness of the interface.

A recommended stiffness factor of the interface for fluid structure interaction problems can be obtained by:(1) S t f a c = ρ ⋅ v 2 ⋅ S e l G a p
Where,
ρ
The (highest) fluid density
v
Velocity of the phenomenon (speed of the sound or higher for supersonic phenomenon)
S e l
Surface of the Lagrangian elements
For aerodynamic problems, the recommendations are:
  • G a p = 1.5 L c with L c being the length of fluid element


    Figure 6.
  • Constant stiffness with K = g ⋅ P ⋅ L c
  • Viscosity related to the interface stiffness:(2) υ s = 2 α ⋅ G a p 2 ⋅ γ P ρ

    With α = 0.5 or α = γ

    P MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaaaa@36CB@ and ρ are the air characteristics


    Figure 7. Fluid-Structure Interaction with Interface TYPE 18
The recommended gap value is equal to 1.5 by the element size.
Note: The interface needs a mesh fine enough to provide appropriate results.