When the quality and stiffness of outshoot are far larger than those of the main body, and k1/k2 approaches M1/M2, second-order resonance vibration happens.

• 当主体结构的刚度k1远远大于突出物的刚度k2,主体结构的质量M1远远大于突出物的质量M2,且k1/k2与M1/M2相接近时,容易发生二次共振。