This is a new General Offensive Unit design, an invented class. The Culture enjoys using irony for its own names.
What you're seeing are render tests to find out how to represent the force fields of this Culture ship.
That hypothetical "Bully" class would be set somewhere in the second half of the Culture chronology, before The Hydrogen Sonata. It would be the last iteration prior to Abominator-class Offensive Unit, which would not be radically superior in firepower, but much more capable of handling vast expanses thanks to its ability to split into several parts.
A small series of illustrations will follow to put it into context.