My sixth research project in 2016 was to carry out the usage of Paraboloidal-tank Tuned Liquid Dampers (PTLD). It's a kind of device consists of several paraboloidal tanks with water partially filled and mounted on the top of the structure. During the earthquake, the sloshing liquid allows to generate anti-phase damping forces that effectively mitigate the vibration of structure due to the effect of inertia.
Comparing to other kinds of dampers, TLD has many advantages:
(1) Easy for installation and maintenance.
(2) Effective in gross cost since the space of water tanks can be combined with the water storage system or the liquid fuel tanks for liquid supply, fire emergency or many other purposes. Without extra loadings will be applied to the structure since it is usually a necessity for a structure system.
(3) Easy to tune the effective parameters such as liquid depth or the tank dimensions under different applications.
(4) It allows to be designed as a multi-directional damper to mitigate the vibration of Multi Degree-of-Freedom (MDOF) structures suffered from wind action and earthquake.
(5) Effective under both small and large-amplitude vibration.
According to these advantages, TLD has already found in many applications, such as satellites (nutation dampers), marine vessels, towers, bridges and tall buildings (TLD can be combined with the water storage system).
Advantages of Using PTLD
Recently, the rectangular and cylindrical TLD are mostly used. However, vortices may occur at the tank corner because the streamline of sloshing fluid is not suitable for the tank shapes. Only a small part of fluid can participate in sloshing and vibration absorption. In addition, standing waves in sloshing fluid are ineffective in energy dissipation, the random motion of breaking wave is the only effective mechanism for dissipating energy.
Hence, I've carried out the usage of paraboloidal-tank TLD which has some benefits:
(1) The tank shape is suitable for the streamline of sloshing fluid, which can avoid the occurrence of vortices and therefore provide 100 % of fluid participates in sloshing and vibration absorption. I can use only a little water to effectively mitigate the vibration of structure.
(2) It has a curved bottom, which means when the water waves propagate from deep to shallow water zones, the wave shoaling will occur as shown in the figure. It means there will be more possibility of breaking wave occurs with energy dissipation.
(3) The turbulence provoked by breaking wave will trigger the fluid rotating around the water tanks, which can effectively disperse the vibration energy of structure in all directions.
First of all, a simple structure model consists of springs and metal plates is used to vibrate horizontally and simulate the motion of a multistory shear building. Secondly, six different curvatures of paraboloidal tanks (Tank A to F) are used as mounted on the top of structure respectively as an array transverse to the direction of structure vibration.
The water will be filled up to the focal plane of each paraboloidal tank under three different mass ratios (MR) of TLD water to structure (0.76 %, 1.01 % and 1.51 %). The excitation amplitudes of structure are 1 and 2 cm respectively.
Moreover, if the fluid rotates in TLD, a streamlined flow-guiding vane will be installed in each tank to direct the fluid rotating in desired directions (as alternately opposite to the neighboring tanks). In order to avoid the lateral displacement of structure provoked by rotating fluid.
In the first experiment, the video shows that when using Tank A, B, C and D, the fluid inside the tanks only goes to and fro in the direction of vibration, the vibration mitigation effects are not significant (Do feel that the vibration of structure can never stop even with TLD installed?)
However, the vibration mitigation effects when using Tank E and F are very significant (you can see the vibration of structure stops in only 5 seconds) since the frequency of sloshing fluid in TLD is close to the vibration frequency of structure.
Firstly, you will see the breaking wave occur, secondly, the fluid is triggered to rotate around the water tank. This kind of mechanism can effectively disperse the vibration energy of structure in all directions so that to dissipate it. It can also generate the larger anti-phase damping forces applied to enhance the vibration mitigation of structure by 5 times!!
In the second experiment, the video shows that after the installation of flow-guiding vanes, the fluid in each pair of the TLD tanks is well controlled to have the opposite directions of rotation. It can effectively reduce the lateral displacement of structure and stabilize the motion.
However, when the unpaired water tanks are used in TLD system, the lateral displacement of structure cannot be avoided even with guide vanes installed in the tanks. Therefore, the utility of paired water tanks with guide vanes for TLD is suggested.
Moreover, streamlining of guide vanes can not only avoid the drag of rotating fluid but can also help enhance the vibration mitigation of structure by 20 %!!
Applications in Civil Engineering
1. Paired TLD can be arranged in a square array and combined with the water storage system.
2. To direct the fluid rotating in desired directions at multi-directional excitation, the curved and streamlined guide vanes must be arranged at four-fold symmetry.
3. As an example, for a 160-meter-tall building equipped with TLD (mass ratio: 0.4 %, frequency ratio: 0.99), four tanks each of 5.8 m in diameter and 1.3 m tall should be used.
You can play the simulation program here
This project was awarded the Grand Award at Intel International Science and Engineering Fair (ISEF) 2016, World Top 100 Regional finalist of Google Science Fair (GSF) 2016 and Young scientist award (top award) at Taiwan International Science Fair (TISF) 2016. If you are interested in my project, you can download the poster here