# Lower Velocity Function Constants#

```Lower Velocity Function Constants = {model_name} <floatlist>
```

## Description / Usage#

This card takes the specification of the Lower-wall velocity function for the confined channel lubrication capability, or the lub_p equation. This function specifies the velocity of the Lower channel wall as a function of time. Currently two models for {model_name} are permissible:

 CONSTANT This model invokes a squeeze/separation velocity uniformly across the entire material region, viz. the two walls are brought together/apart at a constant rate. This option requires two floating point values is the velocity component in the x-direction. L/t is the velocity component in the y-direction. L/t is the velocity component in the z-direction. L/t (NOTE: this is usually taken as zero as it is set in the Lower Wall Height Function model) SLIDER_POLY_TIME This model implements a spatially-uniform velocity in the x-direction that is specified as a polynomial in time. The value of time may be scaled by a given scaling factor and the polynomial may have an unlimited number of terms. is the time scaling factor are the coefficients in front of the t^(i-2) term
 ROLL This model invokes a wall velocity which corresponds to a rolling-motion. This model takes nine constants ???? : Roll radius, L. x-coordinate of axis origin, L. y-coordinate of axis orgin, L. z-coordinate of axis origin, L. Direction angle 1 of rotation axis Direction angle 2of rotation axis Direction angle 3of rotation axis Squeeze rate. rotation rate TANGENTIAL_ROTATE This model allows a unique specification of tangential motion in a lubrication shell element. Previous implementations allowed specification only in terms of coordinate direction, but this option can be used to rotate a cylinder. Five floats are required x-comnponent of a vector tangential to the shell. This vector must never be normal to the shell. It is then projected onto the shell. y-comnponent of a vector tangential to the shell. z-comnponent of a vector tangential to the shell. U1, or scalar speed of wall velocity in a direction determined by the cross product ot the tangent vector and the normal vector to the shell. (L/t) U2 scalar speed component in direction normal to U1. (L/t)

## Examples#

Following is a sample card:

```Lower Velocity Function Constants = CONSTANT {v_x= -0.001} {vy=0.00} {vz=0}
```

This card results in an Lower wall speed of -0.001 in the x-direction which is tangential to the substrate, thus generating a Couette component to the flow field.

## Technical Discussion#

For non-curved shell meshes, most of the time they are oriented with the x-, y-, or zplane. This card is aimed at applying a tangential motion to that plane, and so one of the three components is usually zero.