Pressure penetration loading

A single slave-node-based penetration criterion is used. Fluid will penetrate into the surface between the contacting bodies from one or multiple locations, which are exposed to the fluid, until a point is reached where the contact pressure is greater than the specified critical value, cutting off further penetration of the fluid.

When the fluid pressure penetration criterion is satisfied, the fluid pressure is applied normal to the surfaces. If the full current fluid pressure is applied immediately, the resulting large changes in the strains near the contact surfaces can cause convergence difficulties. For large-strain problems severe mesh distortion can also occur. To ensure a smooth solution, the fluid pressure is ramped up linearly over a time period from zero pressure penetration load to the full current magnitude.

You can specify the time period taken for the fluid pressure penetration load to reach the full current magnitude on newly penetrated surface segments. If the accumulated increment size, measured immediately after the penetration, is greater than the penetration time, the full current fluid pressure penetration load will be applied; otherwise, the fluid pressure on the newly penetrated surface segments is ramped up linearly to the current magnitude over the penetration time period, possibly over a number of increments. When the penetration time is equal to 0, the current fluid pressure is applied immediately once the fluid pressure penetration criterion is satisfied. The default penetration time is chosen to be 0.001 of the total step time. The penetration time is ignored in a linear perturbation step.

PRESSURE PENETRATION, PENETRATION TIME=n

Interaction module: Create Interaction: Pressure penetration; Penetration time: n

The fluid can penetrate from either one or multiple locations of the surface. You must identify a node or node set on the slave surface of the contacting bodies that defines where the surface is exposed to the fluid pressure. In two dimensions if the master surface is not an analytical rigid surface (see Analytical rigid surface definition), you must also identify a node or node set on the master surface that defines where the surface is exposed to the fluid pressure. You can specify multiple nodes or node sets if multiple locations of the surface are exposed to the fluid. These nodes or node sets are always subjected to the pressure penetration load if they are on the slave surface, regardless of their contact status. The fluid then starts to penetrate into the surface between the two contacting bodies from these nodes or node sets.

You must define the reference magnitude of the fluid pressure. You can define the variation of the fluid pressure during a step by referring to an amplitude curve. By default, the reference magnitude is applied immediately at the beginning of the step or ramped up linearly over the step, depending on the amplitude variation assigned to the step (see Defining an analysis).

The fluid pressure penetration load will be applied to the element surface based on the pressure penetration criterion at the beginning of an increment and will remain constant over that increment even if the fluid penetrates further during that increment. A nodal integration scheme is used to integrate the distributed fluid pressure penetration load over an element in two dimensions, while in three dimensions Gauss integration scheme is used; the variation of the distributed fluid pressure over an element will be determined by the load magnitudes at the element's nodes.

PRESSURE PENETRATION, AMPLITUDE=name

Interaction module: Create Interaction: Pressure penetration; Amplitude: name

PRESSURE PENETRATION, OP=MOD (default)

PRESSURE PENETRATION, OP=NEW

Interaction module: Interaction Manager: select interaction, Edit

Interaction module: Interaction Manager: select interaction, Deactivate

To account for the asperities on the contacting surfaces, a critical contact pressure, below which fluid penetration starts to occur, is introduced. The higher this value, the easier the fluid penetrates. The default value of the critical contact pressure is zero, in which case fluid penetration occurs only if contact is lost.

In three dimensions the surfaces of the elements at the front of the penetrated nodes can have only ramped-down pressure loadings. In two dimensions the surfaces of the elements at the front of the penetrated nodes can have either zero or ramped-down pressure loadings.

PRESSURE PENETRATION, WETTED FRONT=NODE (default)

PRESSURE PENETRATION, WETTED FRONT=MID ELEMENT

Perturbation analyses can be performed from time to time during a fully nonlinear analysis by including linear perturbation steps between the general analysis steps. With the exception of the static LCP perturbation procedure, contact conditions are not allowed to change during a linear perturbation step; the fluid will not penetrate further into the surface and remains as it was defined in the base state. Even in the case of a static LCP perturbation procedure, where the contact status at the end of the perturbation analysis can be different from the base state, the portions of the contact surfaces where the fluid pressure acts remain frozen at the base state. The fluid pressure magnitude applied in the previous general analysis step, however, can be modified during a linear perturbation analysis step. In matrix generation (see Generating matrices) and steady-state dynamic analyses (direct or modal—see Direct-solution steady-state dynamic analysis and Mode-based steady-state dynamic analysis) you can specify both the real (in-phase) and imaginary (out-of-phase) parts of the loading.

PRESSURE PENETRATION, REAL (default)

PRESSURE PENETRATION, IMAGINARY

Interaction module: Create Interaction: Pressure penetration; Fluid Pressure (Real) 

Interaction module: Create Interaction: Pressure penetration; Fluid Pressure (Imaginary) 

Each slave surface subjected to pressure penetration loading must be continuous and cannot be a closed loop. Pressure penetration loading cannot be used with a node-based slave surface. The pressure penetration load applied at any increment is based on the contact status at the beginning of that increment. You should, therefore, be careful in interpreting the results at the end of an increment during which the contact status has changed. Small time increments are recommended to obtain accurate results.

When pressure penetrates into contacting bodies between an analytical rigid surface and a deformable surface, no pressure penetration load will be applied to the analytical rigid surface. The reference node on the analytical rigid surface should, therefore, be constrained in all directions. To account for the effect of fluid pressure penetration loads on the rigid surface, the analytical rigid surface should be replaced with an element-based rigid surface.

When fluid with different pressure loads penetrates into an element simultaneously from multiple locations on a surface, the maximum value of the fluid pressure loads is applied to the element.

In large-displacement analyses pressure penetration loads introduce unsymmetric load stiffness matrix terms. Using the unsymmetric matrix storage and solution scheme for the analysis step may improve the convergence rate of the equilibrium iterations. See Defining an analysis for more information on the unsymmetric matrix storage and solution scheme.

Only solid, shell, cylindrical, and rigid elements are supported for three-dimensional pressure penetration.