You don't learn 漢語拚音 well...

You don't learn 漢語拚音 well, according to what you said about YU ("例如姓於的，拚寫為Yu，沒有拚寫為Yv的").

That is the RULE of 漢語拚音: when J, Q, X and Y spell in front of "V" (stand for U with two dots on its head), the two dots shall be omitted.