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.

In scripted input files, the commands are:

ThermalRamp (diff),<(time)>
RampStart (start time)

In XML input files, the command, which must be in the <Thermal> block is:

<Isothermal time="(time)" start="(start time)">(diff)</Isothermal>

where

• (diff) is the final temperature difference to apply to all particles in degrees C (or K) after the ramp is completed.
• The optional (time) is the total time (in alt time units) to reach the final temperature difference. Enter a time less than zero to apply the entire temperature difference on the first time step. The default is to ramp in one step. It is usually better to ramp the temperature difference over a finite time determined by wave speed of the materials in the model.
• The optional (start time) is the time (in alt time units) to start the thermal ramp; the default is to start at time zero.

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.