Abstract Summary
Due to its low prime costs and stable dynamic behavior, the tuned liquid column damper (TLCD) has been a reliable structural vibration control device since its first adoption for civil engineering structures. The TLCD can mitigate lateral vibrations in uniaxial direction. It consists of two vertical tubes, which are connected by a horizontal conduit and filled with a Newtonian liquid. Besides this prominent uniaxial version, a cross shaped TLCD was also originally proposed which has received less attention so far. This version is established by combining two uniaxial TLCDs in a crossed configuration to form a central joint, where horizontal conduits of both TLCDs are connected and allow liquid passage. Thanks to its layout, the cross shaped TLCD can control lateral vibrations in all transverse directions regardless of the excitation angle. The main reason for its neglected application has been the lack of an appropriate mathematical model. The authors derived the desired model after discovering a mathematical formulation, which couples the liquid deflection in each tube and reduces the damper to a single degree of freedom system. This new representation covers not only the uniaxial and cross shaped TLCDs, but also all omnidirectional TLCDs with star shaped layouts consisting of n>2 tubes. Based on this mathematical model, the authors introduced a semi active frequency tuning mechanism. For this purpose, a test bench, and a prototype of an omnidirectional TLCD were developed and experimental studies conducted. Best performance was observed by dividing the tubes in multiple cells which can be activated and deactivated by actuator driven valves. This approach allows us to modify the area of the tubes yielding a change in the natural frequency of the damper. To estimate the system states of the experimental setup based on the measured liquid deflections in the tubes and the vibration acceleration of the test bench, a moving horizon estimator was developed. Experiments were conducted on the test bench to assess the accuracy of the mathematical model and the semi active frequency tuning. The present contribution summarizes these theoretical and experimental development steps in a collective manner and reports the validation of the damper on a 28 m steel tower. In this recent study, the authors designed and built a second prototype based on the identified structural parameters. Initial tests were conducted on the prototype using the previously developed test bench to identify the damper properties before its installation on the real world structure. Subsequently, the damper and two linear actuators were mounted at the top of the structure, allowing user defined excitation of the structure, and thus simulating different vibration scenarios on the structure. An accelerometer was used to record the structural response in lateral directions. Both the omnidirectional control and semi active frequency tuning capabilities of the damper were investigated together with further state observer approaches. Compared to the case without damper, the measured response of the tower was mitigated independent of the orientation of the damper. Furthermore, using the semi active mechanism, the damper’s restoring force was further optimized.
