Viscous Damper Management Defined

By Jim O Neal

The improvement of the so called smart fluids and viscous dampers founded on them has enabled considerably more efficient and convenient vibration attenuation possibilities than ever before. This kind of semi-active dampers are already used in many industrial sectors: cars and trucks, washing machines, bridges, constructing structures to name a few. This is as a result of the small size and particularly to the quick regulation potential they give: they usually are controlled in accordance with the precise demands of your shaking system.

This short article presents the core theoretical resolution behind my viscous damper and a few concerns with regard to the study of shake. There are additional scenarios to control the attenuator, but I have identified this one quick and helpful enough. The solution is not my design and it is valid for virtually any viscous damper. I bow to Jeong-Hoi Koo, whose "Groundhook" algorithm or "velocity-based on-off groundhook control" (On-Off VBG) provided in his dissertation I utilized.

Groundhook Rule on Two-Degree-of-Freedom System

The context where the control law is offered is a two-degree-of-freedom mass-spring-damper system. The basic principle of a groundhook control is that the mass whose shake is attenuated, is hooked to the ground with a damping element. The semi-active part is the controlled, viscous damper which is positioned between the vibrating masses. The control law is simple: when the upper vibrating mass is moving upwards and the lower weight down, strain is applied to the viscous damper. This induces a drawing force to the structure weight to the equilibrium situation of the system.

Groundhook Law Made Easy on Single-Degree-of-Freedom System

Nevertheless, due to a presupposition or an approximation, this law is often made simple. In case the velocity of the lower weight is believed to be really small and at the same phase with the vibrating mass constantly, the process might be modelled utilizing a single-degree-of-freedom vibration system. Once the upper moving weight is heading upwards and the lower mass remains still, strain is employed to the viscous damper. That triggers again a pulling force to the structure weight towards the stability situation of the system.

Importance of Understanding Your Shake

In order to acquire the most out of the attenuation possibilities of a viscous damper, it's essential to carefully understand your vibrating system. This means that, it's essential to measure the shake of the object accurately to find out the disturbing frequencies, their amplitudes and the time instant when the wavelengths occur (for instance three seconds from startup).

Only after measuring these, you can come up with how a semi-active viscous damper would solve the situation. Or perhaps you will determine that a classic passive damper is a more feasible solution. Even so, when integrating smart control algorithms on your solution, you should always review the shake system thoroughly.

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