The Envyo application implements an equation parser based on the Shunting yard algorithm, and is available as MIT license [6]. This equation parser is modified to work with common LS-DYNA application variables such as histories, eff. plast. strains, stresses, and more. Variables are declared with the & symbol, and commands are executed in the order of input. The following variables are available:
| &HISV#i |
History variable at position i. |
| &EPS |
Effective plastic strain (the last entry in *INITIAL STRESS SHELL which may have a different meaning than eff. plast. strain). |
| &ELELENGTH |
Element length of the current element. |
| &SIG_IJ |
Components of the 2nd order stress tensor. |
| &SIG_INIT |
Enables initializing a specific stress value - refers to all stress components. |
| exp | Exponent. An alternative input would be e**. |
Example
The following example illustrates the usage of the equation parser. The commands following the additional history are executed in the order of input:
&HISV#4 = abs(&HISV#3-&HISV#2)*0.000467354 &HISV#8 = &HISV#2 &HISV#9 = &ELELENGTH MAX_NUM_HISV = 8
The value of history variable #4 is calculated using the absolute value of history #3 - #2, multiplied by a scale factor. Following these operations, history variable #8 is assigned the value at history variable #2, and the element length is stored at history variable # 9. Nevertheless, only eight history variables is written to the final result file due to MAX_NUM_HISV.