若向量\( \overrightarrow{a}\)，\( \overrightarrow{b}\)满足：\(| \overrightarrow{a}|=1\)，\(( \overrightarrow{a}+ \overrightarrow{b})⊥ \overrightarrow{a}\)，\((2 \overrightarrow{a}+ \overrightarrow{b})⊥ \overrightarrow{b}\)，则\(| \overrightarrow{b}|=\) ______ ．