Strumming Effect

Dear Sir/Madam,

 

I am writing a piece of music (my score is MDCA). And I have a stack of notes that I would like to play the sound of an acoustic guitar. I would like to play this stack of notes fast and separately. So I used the notation "Down Stroke" under Tab. But it sounded like my stack of notes were played simultaneously, which was not the effect that I would like to create.