“碰上”的英语可以翻译为：un into ...

航行一直很顺利，直到他们碰上了商船的尾流。The ride was smooth until they got into the merchant ship's wake.我一碰上悲伤的事物就难以控制情绪。I overreact to anything sad.很奇怪,我在这儿碰上他了.It is very extraordinary that I should meet him here....