PropertyRamp Custom Task

A custom task to apply temperature difference to all particles.

Introduction

One way to run simulations with initial thermal stresses is set the temperature to all particles at 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.

Thermal ramps can be used for residual stress calculations. Because they create uniform temperature changes they do not lead to any conduction. Thus a ramp can be used without doing conduction calculations or it can be used in combination with conduction calculations and other thermal boundary conditions.

Task Scheduling

In scripted files, a ThermalRamp custom task is scheduled using

CustomTask ThermalRamp
Parameter DeltaT,(deltaT)
Parameter time,(time)
Parameter start,(start)
Parameter sigmoidal,(style)
Parameter "scale (function)"

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

<Schedule name='ThermalRamp'>
   <Parameter name='DeltaT'>(deltaT)</Parameter>
   <Parameter name='time'>(time)</Parameter>
   <Parameter name='start'>(start)</Parameter>
   <Parameter name='sigmoidal'>(style)</Parameter>
   <Parameter name='scale (function)'></Parameter>
</Schedule>

where the are:

• (deltaT) - Enter the final temperature difference (in degrees) to apply to all particles (in degrees). The thermal ramp will change particle temperature from zero to this value over the duration of the ramp.
• (time) - Enter the time interval for applying the temperature difference (in alt time units). This parameter is optional; if omitted, temperate difference is applied in one time step.
• (start) - Enter the start time for the thermal 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 thermal 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.
• (function) - if this optional parameter is used, the applied (deltaT) ramp is scaled by any user-defined function of time and particle position. Note that the (function) must be embedded in the parameter name (e.g., "scale x/40").

A single calculation may using 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.