Why dynamic relaxation doesn’t seem to work at times?

For the analysis of static loading process, such as gravity loading, dynamic relaxation method is commonly used with the keyword “CONTROL_DYNAMIC_RELAXATION”. In addition, two more cards are also necessary, “LOAD_BODY_Z” and “DEFINE_CURVE”, assuming the gravity is in the z-direction.

However, in defining the curve, the value of “SIDR” (the second parameter under the card of DEFINE_CURVE) should be 1 (one). If it is zero (default), then there will be no dynamic relaxation analysis.