The Envyo application implements an equation parser based on the Shunting yard algorithm and is available as a MIT license [6]. This equation parser has been modified to work with common LS-DYNA application variables such as histories, eff. plast. strains, stresses, temperatures, etc. Variables are declared, using 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 second order stress tensor. |
| &SIG_INIT | Enables initializing a specific stress value that refers to all stress components. |
| &T | Enables modifying temperature initial values or curves stored on nodes. |
| &ADD ELE HISV#i | Element history variable from file i is used. |
| &LookupTable#1 | Lookup table from file i is used. |
| exp | Exponent. An alternative input would be e**. |
| &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 second order stress tensor. |
| &SIG_INIT | Enables initializing a specific stress value that 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, times a scale factor. Following these operations, history variable #8 is assigned the value at history variable #2, and the element length will be stored at history variable #9. Nevertheless, only eight history variables are written to the final result file due to MAX_NUM_HISV.
The temperature stored on nodes as fixed initial values and/or curves as tempertature over time are transferred from Celsius degrees to Kelvin degrees.