The filter below should grab the source IP:
((?<=Source Network Address: )[0-9.]+)
You can modify the first portion to find and target what value you want, such as "Source Port: " or "Workstation Name: ", and then detail the second portion to grab what follows, whether it be digits, letters, or a mix. I found the following links to be helpful:
Once your tests are successful, add them to Aanval. You'll immediately notice if they're working or not with new data that is imported. The following link also provides some additional helps for filters and Aanval: