In consequence of rising costs in energy and basic materials there is a demand on light weight constructions especially for on road mobile machineries e.g. cars, trucks and mobile working machines. A mass reduction accompanies commonly with a reduction in stiffness of the construction. Hence, the eigenfrequencies of the system shift down to lower values. If they accord with the operating frequencies undesired oscillation problems occur. To overcome them tuned mass dampers (tmd’s) are usually installed. This approach looks like fighting fire with fire due to the fact that at piece of the reduced weight is added again to remove the vibrations. Here our invention called Fluid Dynamic Absorber (FDA) /2/ ties in. We use a hydraulic transmission as well as an effective inertial system to reduce the weight of tuned mass dampers in a meaningful manner. In this paper the results of a FDA applied at a two mass oscillator as w ell as the results of an equivalent classical tuned mass damper applied at the same oscillator are presented. The FDA attains a weight reduction of approximately 30% compared to the classical one. The second advantage of our invention is the retren chment of the dissipative component (damper). Due to the application of an oscillati ng liquid column pressure losses are integrated into the inertia of the FDA. Hence, the developed system combines the inertia and the dissipative element in one. This is beneficial since most of the research and develo pment activity at tuned mass dampers is related to the dissipation. Several damping systems were published and patented in the last decades: e.g. a solid friction based damper and a fluid damper in /7/, a tuned mass damper using shock absorbers in /6/ and damping with granulate material was published in /4/ and /7/.

The idea to use a hydraulic transmission for tuned mass dampers is based on the hydraulic engine mount. The theory of this kind of machine element and its function are presented in /8/ and /9/. The optimization of stiffness and damping constant of the FDA are based on the theory of /4/. The whole theory of the FDA is presented in /1/.

For the outline of the paper: At first the basic idea of the FDA is pointed out in detail before the describing equations are derived. Based on the mechanical vibrations a two mass oscillator is constructed to compare the efficiency of the FDA compared to a classical tuned mass damper. In the section Results the disposed theories are validated with a test rig. For the test rig a two mass oscillator in the design of a multi storey frame is used.