Torsional vibrations in beams are damped by discrete, axial viscous dampers in configurations constituting bimoments. The bimoments act on warping displacements and partial restraining of warping suggests the inclusion of a flexibility parameter, calibrated from numerical results. Correcting for distortion is incorporated in a similar manner. The use of the governing differential equation with calibrated parameters as an alternative to a full complex analysis by a FE model is justified by an example. It is demonstrated that the differential equation determines the damped frequencies and damping ratios with great accuracy. Significant damping ratios of the lowest torsional mode are obtained.