Getting the real part of a expression

Question

I'm trying to get the real part of a expression, but I failed. It looks like this.

Does anyone have a solution?

By the way, it is quite weird because when I simplify this:

Mathematica returns the right answer, but I can't tell the big difference between the two expressions.

Here is my code:

vectorVr = Array[Subscript[vr, #] &, 9];
vectorVi = Array[Subscript[vi, #] &, 9];
$Assumptions = Join[vectorVr, vectorVi] ∈ Reals;

FullSimplify[
  (0.` + 0.0576` I) 
    (I Subscript[vi, 1] - I Subscript[vi, 4] + Subscript[vr, 1] - Subscript[vr, 4]) (-I Subscript[vi, 1] + I Subscript[vi, 4] + Subscript[vr, 1] - Subscript[vr, 4]) 
  // Expand // Re]

Answer 1

Use ComplexExpand

vectorVr = Array[Subscript[vr, #] &, 9];
vectorVi = Array[Subscript[vi, #] &, 9];
$Assumptions = Join[vectorVr, vectorVi] \[Element] Reals;

(0.` + 0.0576` I) (I Subscript[vi, 1] - I Subscript[vi, 4] + 
      Subscript[vr, 1] - Subscript[vr, 4]) (-I Subscript[vi, 1] + 
      I Subscript[vi, 4] + Subscript[vr, 1] - Subscript[vr, 4]) // 
   ComplexExpand // Re // Simplify

(*  0  *)