General Bushing Usage, Preload, Test Data

Hello Community,

We are facing an issue with the use of the General Bushing Element (a non-linear spring, a Bouc-Wen element, and one transfer function in parallel).

We conducted dynamic measurements around an operating point (0.15mm/250N) and obtained values for dynamic stiffness and loss angle. Additionally, we measured a quasi-static force-displacement curve starting from 0 mm and 0 N, extending up to 0.4 mm, thus encompassing the operating point.

When using the parameter identification tool, we achieve a good fit for these two quantities (dynamic stiffness and loss angle) over the frequency range for the three measured dynamic amplitudes. This good fit is obtained whether we enter a linear offset of 0.15 mm in the tool or not, although the values in the tool differ as expected.

However, in our simulation where we replicate the measurements, we encounter higher forces. We attempt to replicate the measurements by first setting the offset (0.15 mm) and then replicating the dynamic measurements (Dispalcement Driven). It is noticeable that setting the offset to 0.15 mm already results in significantly higher forces than in the quasi-static measurement or the resulting non-linear spring. This is likely because the Bouc-Wen part adds a force that increases with amplitude, even at low frequencies.

Our questions revolve around this point:

Where should the offset be defined? Most likely in the identification tool. In the Bushing in the Model Tree, there are also fields for offset and preload. Shouldn't the quasi-static test also be replicable with the Bushing? How else can we reach the operating point? The simulations start in the design position, then gravity acts, and an operating point is established from which the dynamics start. (And force is too high...)

We are interested in how other users handle this General Bushing. How do you manage preload? Where do you account for it? How do you reach the operating point if the path to it is distorted by the Bouc-Wen element? Or is this only an issue for us because we are misinterpreting the help and conducting incorrect static measurements?

Perhaps someone would like to share their experiences and thoughts.

Best regards,

Tobias