Hello, Kwon Ki Poong-- and welcome to English Forums! Some look at this as a subject-less and verb-less clause: We swim along [as/though we are] fully aware of dangerous under-currents . Because we can complete the idea with the pure copula 'be', we could look at 'aware' as a subject complement (a predicate adjective modifying 'we'), but since we can front the phrase– Fully aware of dangerous under-currents, we swim along – we should consider it an adverbial modifying the whole main clause.
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