Adaptive control of damaged structures by using smart tunable liquid column gas damper considering dynamic soil–structure interaction

Liquid column dampers are adjusted based on the characteristics of the host structure and the type of external forces. It is assumed in most studies that the structure is rigidly connected to the ground, and the characteristics of the structure are invariant during external excitations. The performance of passive dampers may lose, or structural displacements may be increased by changing these conditions. This study presented a new method to find the optimal control forces for structures equipped with smart tuned liquid column gas damper (TLCGDs), considering variable characteristics of the structure and the soil–structure interaction. The proposed method calculates the gas pressure inside the columns by regularly adjusting and updating the frequency and damping of the TLCGD. The unknown or changed soil–structure characteristics are estimated by a system identification method, and damper parameters are determined through an optimization algorithm. The method was tested on 3- 9- and 10-story shear buildings under harmonic and earthquake excitation. According to the results, the smart damper more effectively reduced the structural displacement.

RMS Control of Response of Jacket Structure Using Tuned Liquid Column Ball Gas Damper Under Random Ocean Waves

Jacket structures are one of the most important offshore structures for extracting oil and gas. The fatigue life is affected due to the continuous dynamic wave force experienced by the structure. Generally, the structure is designed so that the dynamic response is small, which increases the cost. So, controlling its response is a good alternative to increase its life span. In this work, a simplified jacket structure under a random sea state is controlled for its response using a tuned liquid column ball gas damper (TLCBGD). The jacket structure in a water depth of 60m is modeled in a surge degree of freedom. The parameters of TLCBGD are optimized using a genetic algorithm for achieving better control in response quantities. For the analysis purpose, the wave is considered stochastic and presented by Pierson–Moskowitz (PM) spectrum of significant wave height 10m. In such a case, the jacket structure response can be presented using the root mean square (RMS) values obtained from the Lyapunov technique. Based on the random vibration analysis theory, the Lyapunov method can be employed to obtain the RMS of the system driven directly without solving the governing differential equation. This method requires the system to be driven by white noise. So, in this study, filters are developed to get the required narrow banded ocean spectrum. It is noticed that the response quantity is highly sensitive to the filter parameters. This is because a slight change in excitation parameters and a change in filter parameters near the system’s natural frequency affect the response significantly. Further, it is seen that the use of the genetic algorithm for tuning the TLCBGD gives very good control on the response quantity of the jacket structure.

Numerical Investigation on Static and Rotor-Dynamic Characteristics of Convergent-Tapered and Divergent-Tapered Hole-Pattern Gas Damper Seals

To study the influence of taper seal clearance on the static and rotor-dynamic characteristics of hole-pattern damper seals, this paper develops three-dimensional transient computational fluid dynamic methods, which comprise single-frequency and multi-frequency elliptical orbit whirl model, by the transient solution combined with a mesh deformation technique. Through the investigations, it is illustrated that: (1) In the present paper, the leakage rates of convergent-tapered hole-pattern damper seals are less than divergent-tapered hole-pattern damper seals for the same average seal clearance, and the maximum relative variation reaches 16%; (2) Compared with a constant clearance hole-pattern damper seal, the maximum relative variation of the rotor-dynamic coefficients is 1,865% for nine taper degrees in this paper; (3) Convergent-tapered hole-pattern damper seals have smaller reaction forces and effective damping coefficient, larger cross-over frequency, and direct stiffness coefficient, while divergent-tapered damper seals have the opposite effects; (4) Divergent-tapered hole-pattern damper seals alleviate the rotor whirl because of a larger effective damping coefficient when the rotor system has large natural frequency and small eccentricity. Convergent-tapered damper seals provide both sealing and journal bearing capabilities at the same time, and are more advantageous to the stability of the rotor system when rotor eccentricity is the main cause of rotor instability.

Study of Offshore Jacket Platform Attached With Tuned Liquid Column Gas Damper

With increase in need of energy, scarcity of natural resources also increases. Need for energy has led the people to move into the ocean since they contain abundant natural resources. Offshore platforms play a major role in exploring and exploiting these resources. Jacket platform being a fixed offshore jacket platform is used in water depths 300 to 400 m. The study of behavior of these offshore structures is vital part in the design since they are subjected to dynamic loading of waves, wind, earthquake, ice etc. These structures in hostile environment are subjected to heavy loads. There is need for controlling the response of these structures. This can be achieved by providing external dampers. There are various dampers available to control the response of structures. Tuned liquid dampers (TLD)s and Tuned Liquid Column Damper (TLCD)s use liquid inside to tune its frequency to natural frequency of structure. Tuned Liquid Column Gas Damper (TLCGD) is latest version of dampers. It has a unique flexibility of tuning frequency compared to all other dampers. In the present study, jacket platform is modeled as Multi degree of freedom (MDOF) system. At later stage, for simplistic analysis, MDOF system is reduced to SDOF system using static condensation. Performance of TLCGD for both the systems is compared. Airy’s wave theory is used for wave force excitation. Equations of motions for Jacket platform models attached with TLCGD are developed and solved using Newmarks β method in MATLAB. TLCGD is found to be very flexible in tuning the frequency and maximum reductions in response, 21.3% and 23.14% are observed at 0.3 MPa for MDOF and SDOF systems respectively. Work done shows that the results for MDOF and SDOF are comparable and hence, jacket as SDOF can be used for analysis for reducing the complexities.