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.
This will be usedshortly. The Sine Wave The average value of this waveform is zero. If this waveform represents, say, the current waveform being applied to a battery, thenthere would be no net charge into the battery. The Half-Wave Rectified Waveform (using diodes) This waveform has an average value which is non-zero.