The "varying dynamic overturn moment" is also called the "shaft bending load," which is caused by imbalanced hydraulic loads on the impeller.  The torque applied by the impeller and the random motion of the liquid cause lateral (horizontal) loads on the impeller, which creates a bending moment on the mixer shaft and drive.  The magnitude of the lateral load is an empirical force estimate related to the impeller torque and diameter.  Loads have been measured on operating equipment and correlated to impeller type, diameter, and operating conditions.  Both the "dynamic torque" and "varying dynamic overturning moment" may be two to three times the actual measured loads because of the "dynamic" effect.  Most vessel nozzles and support structures would be designed by mechanical engineers based on "static" loads.  If the dynamic effects are not considered, the structures will not be rigid enough and the mixer will move, potentially causing fatigue failures.

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