"act somewhat" is correct and usable in written English.
You can use this phrase when you want to indicate that someone has exhibited a certain behavior, but that it was not too extreme. For example, you could say "Although he was angry, he only acted somewhat aggressively."
The planes act somewhat like the flaps on airplane wings.
Researchers are finding evidence that different synapses of the same neuron act somewhat independently.
She has a background in theater and, yes, puppetry — check YouTube — that has informed her stage act, somewhat to her detriment.
If the dust grains are paramagnetic so that they act somewhat like a magnet, then the general magnetic field, though very weak, can in time line up the grains with their short axes in the direction of the field.
However, the uneven cast of the Peccadillo Theater Company's production, staged earnestly by Dan Wackerman, is more convincing in its lighter moments, making the darker second act somewhat of a letdown.
For most of this four‐ act, somewhat abbreviated version conducted by George Monseur, a plainly green but plainly gifted young man, "La Bohème" went from tune to tune in a simple‐minded but meltingly lyric way.
In a storm, a protected building acts somewhat like a metal cage.
GlaxoSmithKline and Bayer assert that Levitra acts somewhat more quickly than Viagra.
Pedot, which is short for polyethylenedioxythiophene, acts somewhat like a fuse does.
Alternatively, tripartite arbitration boards can be established, with each party appointing its own arbitrator, who acts somewhat as an advocate.
I acted somewhat like a diva when I was involved in music, and I always felt better about myself when I was giving back.
