boil, ferment, seethe, uproar, breed
涌 centers on liquid or energy rising up forcefully: boiling, seething, fermenting, or a noisy uproar. The breeding sense extends the idea of something multiplying or swelling from within.
涌 combines 氵 (water) with 甬, which likely contributes the sound and the idea of gushing or springing forth. The character originally depicted water welling up.
Water 氵 on the left and 甬 on the right: picture a hot spring where water bubbles up and seethes, creating an uproar as it boils over.
For ユウ, imagine you watching a pot boil over: you -> ユウ, and the water seethes up.