Explaining "how" to calculate the dynamic force on the agitator is more difficult than providing a value for the conditions described.  Further, "how" the "dynamic force" will be used makes a difference in the suggested safety factors to be applied to the calculated values.
For the purposes of equipment design, the dynamic forces should be calculated based on the motor horsepower and agitator speed, since at some viscosity the motor could be fully loaded.  On that basis, torque will be about 11,000 N-m.  An estimate of the bending load on the shaft and drive is about the same, 10,000 N-m.  Those loads require a 125 mm diameter shaft.
For the purposes designing a support for the agitator, a rigid mounting is necessary.  The support should be designed to handle 2.5 times the calculated torque and 3.0 times the calculated bending load.
If all that is needed is an anticipated operating load for the dimensions and viscosity described, the agitator will require about 33 hp.  That requirement is based on a viscous power number of 360 (for laminar operation), which is multiplied by a factor of 2.2 for the impeller Reynolds number of about 1,000.  The resulting viscous (not turbulent) power number is 780.

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