PropertyRamp Custom Task

A custom task to apply temperature difference to all particles.

Introduction

Various particle properties, such as temperature or concentration, can induce residual stresses. One way to model residual stresses (such a residual thermal stresses) is set particle temperatureat the start of the calculations to a temperature that differs from the stress free temperature. Such an instantaneous temperature change is analogous to impact loading and may cause stress and strain oscillations. To avoid these dynamic effects, it is better to ramp up particle temperature difference by using a thermal ramp by using this custom task.

This task allows you to apply certain particle properties slower to model residual stresses without causes to many dynamic effects. The tasks is called ThermalRamp, because it was originally written only for ramping particle temperature. It has now been extended to also ramp particle concentration (when doing diffusion calculations, pore pressure (when doing poroelasticity calculations, out-of-plane stress (when doing plane stress analysis) or out-of-plane strain (when doing plane strain analysis. The ramp can change all particles the same amount, change them according to a function of position, or change them according to pixels in an image.

A thermal ramp can be used without doing conduction calculations or it can be used in combination with conduction calculations and other thermal boundary conditions. Other ramps can also be used with corresponding boundary conditions. Multiple ramps can be combined to ramp different quantities or to ramp particle values at different times.

Task Scheduling

In scripted files, a ThermalRamp custom task is scheduled by starting with

CustomTask ThermalRamp
Parameter property,(rampProp)
Parameter time,(time)
Parameter start,(start)
Parameter sigmoidal,(style)

In XML files, this task is started using a <Schedule> element, which must be within the single <CustomTasks> block:

<Schedule name='ThermalRamp'>
   <Parameter name='property'>(rampProp)</Parameter>
   <Parameter name='time'>(time)</Parameter>
   <Parameter name='start'>(start)</Parameter>
   <Parameter name='sigmoidal'>(style)</Parameter>
</Schedule>

where the parameters are:

• (rampProp) - This parameter determines which particle property is ramped. The options are:

0. Ramp temperature
1. Ramp out-of-plane stress(zz) for plane stress analysis or strain(zz) for plane strain analysis. A task with this option is not allowed for unless running 2D plane stress or plane strain analyses. This option is used to implement Generalized Plane Stress and Strain.
2. Ramp particle fluid concentration. For diffusion calculations, this option will ramp particle concentration. For poroelasticity calculations, this option will ramp particle pore pressure. A task with this option is not allowed for unless running either diffusion or poroelasticity calculations.

• (time) - Enter the time interval for applying ramp the particle property (in alt time units). This parameter is optional; if omitted, enter ramp value is applied in one time step.
• (start) - Enter the start time for the ramp (in alt time units). This parameter is optional; if omitted, the ramp starts at time zero. The ramp ends at time (start)+(time).
• (style) - Enter 0 or 1 for a linear or sigmoidal ramp. A sigmoidal ramp may reduce dynamic effects at the start and end of the ramp. This parameter is optional; if omitted, the ramp is linear.

The above parameters create a ramp. The next sections explain four different ways to calculate the change in particle property applied during the tamp.

Constant Property Change

To ramp all particles to the same change in selected particle property, use the Delta parameter:

Parameter Delta,(delta)

or in XML files, use:

   <Parameter name='Delta'>(delta)</Parameter>

where

• (delta) - Enter the final property change to apply to all particles (or the magnitude of the change after the ramp is done). The ramp will apply this change incrementally in either at either a linear or a sigmoidal rate (depending on the style parameter setting) during the duration of the ramp. Once the ramp is done, no more changes will be made.

The units for (deltat) depend on property being ramped:

• Temperature - in degrees
• Stress(zz) - in pressure units
• Strain(zz) - in percent strain
• Concentration - in dimensionless concentration potential (and all changes will be constrain particle value to the range 0 to 1)
• Pore Pressure - in pressure units

Position Dependent Property

To apply a position-dependent change to all particles, add the following two commands in scripted files:

Parameter Delta,(delta)
Parameter scale,(function)

or in XML files, add:

   <Parameter name='Delta'>(delta)</Parameter>
   <Parameter name='scale'>(function)</Parameter>

where (delta) is the same as above, but the final change on each particle can be scaled using

• (function) - when this optional parameter is used, the applied (delta) ramp is scaled by any user-defined function of time and particle position. The final change on any particle will be (delta) times the value of (function) evaluated at the particle location.

Property Change from Image Data

An alternative method for ramping up particle change is to ramp to any distribution of particle values as represented within a bit mapped file. In scripted files, a ThermalRamp custom task for file input adds the following parameters

Parameter file,(bmpFileName)
Parameter width,(width)
Parameter height,(height)
Parameter xorigin,(xO)
Parameter yorigin,(yO)
Parameter zlevel,(zO)
Parameter flipped,(flipped)
Parameter DeltaMin,(deltaMin)
Parameter DeltaMax,(deltaMax)

In XML files, this task is scheduled using a <Schedule> element, which must be within the single <CustomTasks> block:

   <Parameter name='file'>(bmpFileName)</Parameter>
   <Parameter name='width'>(width)</Parameter>
   <Parameter name='height'>(height)</Parameter>
   <Parameter name='xorigin'>(xO)</Parameter>
   <Parameter name='yorigin'>(yO)</Parameter>
   <Parameter name='zlevel'>(zO)</Parameter>
   <Parameter name='flipped'>(flipped)</Parameter>
   <Parameter name='DeltaMin'>(deltaMin)</Parameter>
   <Parameter name='DeltaMax'>(deltaMax)</Parameter>

where

• (bmpFile) is the full or relative path name to a BMP file. The file must be an uncompressed, gray-scale, BMP file with 8 or less bits per pixel. The most useful is an 8-bit file with 256 levels of gray.
• (width) and (height) specify the width and height for the image, but there are several ways to specify them.
• (xO), (yO), and (zO) give the (x,y,z) coordinate for the origin of the image when mapped to the grid or mesh in length units. The (zO) coordinate is only needed for 3D calculations and gives z value for each 2D slice of the x-y plane of the data.
• (flipped) is 0 (default) or 1; if it is 1, the origin will move to the upper-left corner of the image with y increasing in the downward direction and x increasing to the right. This change will flip the image in the y direction in the analysis compared to the image graphics.
• (deltaMin) and (deltaMax) map gray values 0 and 255 to a property change. All other gray values are linearly interpolated between these values.

In other words, the property change applied to particles replaces the (delta) parameter above with

      (delta) [math]\displaystyle{ = (deltaMin) + {\bigl((deltaMax)-(deltaMin)\bigr) g\over 255} }[/math]

where g is the average gray value over the domain of the particle. This change is applied incrementally (linearly or sigmoidally) over the duration of the ramp.

Property Change from Image Blocks

Alternatively, the particle temperature can be determined for ranges of intensity by the same method that bit mapped files can be used to assign particle material type. This method is done by replacing (deltaMin) and (deltaMax) with one or more map commands. In scripted files, the new commands are:

Parameter "map #1 #2",(delta)
Parameter "map #1 #2",(delta)

or in XML files, they are:

   <Parameter name='map #1 #2'>(delta)</Parameter>
   <Parameter name='map #1 #2'>(delta)</Parameter>

where

• #1 and #2 are a range of gray scale values (from 0 to 255 with #2 ≥ #1). These values must be embedded in the text of the parameter name, which must begin in "map" (e.g., "map 20 75").
• (delta) is temperature difference to apply to all particles under regions within the gray scale range specified by #1 and #2.

Unlike the previous section, this method selects (delta) by the most prominent matched range under the particle domain and not by the average gray value. This method is actually identical to method used to assign material types in a BMPRegion Command. Because the methods are the same, one could use the same image to assign material types and property ramps and this method would let you pick a different property values for each material type.

Multiple Thermal Ramps

A single calculation may use multiple thermal ramps and the resulting temperature changes will be sum of all ramp values. This feature can be used to increase and then decrease temperature or even to have overlapping ramps.