PASSIVE CONTROL OF VIBRATIONS OF SEISMICALLY ACTIVATED ARCH DAMS WITH TUNED LIQUID COLUMN Gas DAMPERS: PART 1 THEORY

By coupling Tuned Liquid Column Gas Damper (TLCGD) to arch dam, structural damping can be increased considerably. This improvement is badly needed for the retrofit of existing ancient dams that are not verified with the criteria of modern seismic civil engineering codes. The low cost (when compared to an equivalent TMD), passive sealed and modally tuned TLCGD,- making use of the gas-spring effect increases effectively the damping during the steady-state vibrations of lightly damped structures, within the frequency range of application that limits the maximum fluid speed by about 10 m/s. For dynamic analysis of the coupled system during the seismic strong motion phase, modal synthesis is applied for the case of empty reservoir (i.e. at low water level). Hence, neither the hydrostatic pressure nor the hydrodynamic effects in the reservoir are considered, and thus the radiation damping into the water is absent. So it should be the more sensitive case of lowest structural damping to be considered. Also higher natural frequencies are observed when compared to the full or the partially filled reservoir. The structural continuum of concrete dam body and some part of the bedrock foundation is idealized and discretized as an assemblage of finite elements with finite number of degrees of freedom by ANSYS[13]. The equation of motion of an incompressible liquid in the rigid and sealed piping system in normal direction to the mid-plane of the dam body, moving with the dam is described with regard to the piston theory of relative flow and of gas compression by a generalized (nonstationary) Bernoulli equation. Conservation of momentum of the fluid mass yields the control forces. The substructure synthesis of the coupled system is (approximately) studied and the equations of motion are given in matrix form. The dynamic analysis of a seismically activated dam with one TLCGD and one TLCGD in some parallel units attached are studied and the coupled modal equations considering one isolated structural mode are derived and the elements of state space vector for TLCGD with three parallel units are derived. By transferring into state space and following the optimization procedure, the optimal parameters of TLCGD are defined.

کلیدواژه ها:

Liquid absorber ، Structural Damping ، Effective damping