An onomatopoeia and standalone word in its own right, uuueeeee is used to exclaim great pleasure, surprise or awe.
For creative purposes or to accentuate the excitibility of the moment, variable counts of both "U"s and "E"s are acceptable beyond the standard 3-to-5 ratio. Uuueeeee is a very organic word, and can be modified and even capitalized if the situation merits.

When you eat dirt for the first time and leave your family to build a shack in the woods