I got the following problem: 
I want to rename files in the format of "12xy[..].log" to "[...].log". 

My problem is, that some of them have an "a" following the first time and some of them got a "v" - so I cannot use commands, that follow the logic of replacing part of the name up to a certain character. (Like an underscore etc.) 

Is there anyway to rename them quickly? 

Edit: There is always the same prefix of "MD18". So for example there are some files named "MD18v230_SHAPE.log" or another one named "MD18a004_FACES.log" and so forth. I would like to have them named "v230_SHAPE.log" and "a004_FACES.log" 

Thank you in advance!