Electronic – Rectifier ripple voltage formula

The problem I see with your schematic is that you have two ground references. Your AC power supply is grounded, as well as D2 cathode. And the bridge rectifier DC output rail's ground is in fact the anode of D2 (even though not shown), the cathode of D3 being the positive (Vcc). Also note that your load R1 is connected between these two points. Now, am I missing a point or are both the anode and cathode of D2 grounded (D2 shorted)?

2*Vsecondary/Pi - Vk or as you put it 0.636*Vac - Vk.