With a live connection to BW I am unsure how to remove year. My posting date is in the dimensions so I am unable to convert it to a date like you would in an extract and just create a calculated key figure that added a year to 2014 to make it 2015.
But as soon as I try to pull this Date Calc into my chart I get an error message that "tableau cannot connect to the data source" I only get that error message when I try to mess with the dates.
This is what my chart looks like right now:
What is the dimension name that has the Date on your column shelf