A set that is not convex is called a non-convex set. A polygon that is not a convex polygon is sometimes called a concave polygon, and some sources more generally use the term concave set to mean a non-convex set, but most authorities prohibit this usage.
In either case you don't need to deal with the absolute value. A rectified sine wave is a periodic signal with a period equal to half of the full sinusoid, I would write the sine in exponential form and integrate over one period to find the series coefficients.
The solution of these equations is in the form of waves in the +z and -z direction, which for. sinusoidal excitation take the form. V(z) = V+ewt-jgz + V-ewt+jgz) and I(z) = I+e(wt-jgz)+ I+e(wt+jgz) 1 This particular derivation is from Terman, Electronic and Radio Engineering , 4th Ed., McGraw-Hill, 1955,