DEICON uses computation fluid dynamics (CFD) tools to design viscous dampers. The cut-out image shown in Figure 1 (a) depicts the velocity field distribution predicted by the CFD analysis of a ‘laminar flow viscous damper’ . Figure 1(b) shows a snapshot of the same information at the cross-section encircled in Figure 1 (a).
Clear from Figure 1, the large velocity gradient induced by the motion of the plunger in conjunction with the high viscosity of fluid create the desired damping force.
Figure 1 The velocity field (a) and velocity distribution in a cross-section of a ‘laminar flow viscous damper’
The CFD software tool allows the designer to select the proper geometry for the plunger and housing as well as the right fluid so the desired damping coefficient is realized.
Following the design of viscous dampers, they are prototyped and their damping effectiveness verified, experimentally. This is done by subjecting the dampers to periodic motion and measuring their force as well as the displacement. Figure 2(a) shows the experimental set up for measuring damping force and plunger motion of a viscous damper. The two traces in Figure 2(b) depict the measured (blue trace) and the identified (red trace) force vs. displacement of the viscous damper shown in Figure 2(a). Note that the small angle of the oval traces shown in Figure 3(b) points to the viscoelasticity of the liquid used in viscous dampers.
Figure 2 The experimental test set up (a) and the measured force vs. displacement (blue trace) and the identified one (red trace) (b)
Applications
Viscous dampers may be used as a stand-alone damping unit to dampen a single or multiple resonances of an underdamped structure, in conjunction with spring elements in vibration isolation applications, or realization of
tuned mass dampers.
The blue traces in Figure 3 depict the magnitude and phase of frequency response function of an underdamped structure, clearly showing two resonant modes at 6 and 12 Hz. The red traces on the same figure present the same frequency response function after two 'laminar flow viscous dampers' were installed on the structure. Comparison of the blue and red traces in Figure 3 shows the effectiveness of the viscous dampers in dampening both resonant modes.
Figure 3 The experimentally measured frequency response functions of a structure without (blue traces) and with (red traces) viscous damping