Field of Invention:
The present invention provides a novel tuned combined liquid damper (TCLD) for damping and vibration control of civil structural works and also other mechanical places where vibration control is necessary. It is a new type passive vibration control device which works on the principle of sloshing of the liquid combined with the nonlinear relative liquid motions to mitigate structural vibration.
Background of the art:
In almost all the world's skyscrapers, there is a unique device protecting the building from strong lateral motion due to wind and earthquakes. It is known as vibration absorbers or vibration dampers. There are many conventional technologies to control the vibration of a structure, such as the Tuned Mass Damper (TMD), the Tuned Liquid sloshing Damper (TLD), and the Tuned Liquid-Column Damper (or TLCD). etc. Among them, TLD and TLCD have been more effective than TMD.
The performance of TLCD and TLD have been investigates by many researchers and they have been used in a wide variety of applications as a passive or semi active structural devices. Sakai et al, (1989) proposed the nonlinear mathematical expression of the TLCD and carried out experiments to validate the analytical model. Later many authors used the linearized equation of motion to investigate the effectiveness of the TLCD to suppress the structural vibration using frequency domain analysis. Won et al. (1996) have examined seismic performance to identify the critical design parameters of TLCD for flexible structures using time-domain analysis. Banerji et al. (2000) have studied the performance of TLDs under real earthquake excitations and gave a brief idea of design guideline of rectangular TLDs under real earthquake excitations. The play of liquid sloshing frequency has an important role to obtain the performance of TLD. It has been proved experimentally (Sun et al. 1989). Yu et al. (1999) modeled a rectangular TLD as an equivalent TMD with nonlinear stiffness and damping. Later Lee et al. (2011) evaluated the seismic response of structures using a new bi-directional tuned column and sloshing damper; instead of using two independent dampers in two orthogonal directions, one damper which can control two different orthogonal vibration modes simultaneously is used. Rozas et al, (2015) introduced a new type bi-directional tuned liquid column damper for reducing seismic response

of buildings in two perpendicular axes, which acts as two independent and orthogonal TLCDs, but due to its configuration its requires less liquid than two equivalent independent TLCDs.
The structure can be damped either by passive methods, in which case no power supply is required, or by active methods, which do require a power supply. The present invention is a passive type vibration control system of structure, and it does not require an external power source to operate, which makes it very economical and easy to design, install and maintain. Some passive liquid dampers in the prior art are:
KR20100039952 discloses a tuned liquid column damper having an adjustable fluid damping, for vibration attenuation of structures. This invention adjusts the damping properties of a TLCD by adding various types of control means like air chambers. This device is only a type of Tuned Liquid Column Damper, and it does not combine the effect of TLD with the TLCD in a single container.
CN104294955 discloses a Dual tuned liquid damper cylinder, which is basically a U-shaped Tank filled with liquid (generally water). It's apparatus comprises of only a U-shaped Tank, horizontal sliding means, lower level spring, orifice and liquid. The tank is not fixed with the structure, so maintenance cost will be higher due to damage in the components by wear and tear. Also this device is only a type of Tuned Liquid Column Damper, and it does not combine the effect of TLD with the TLCD in a single container.
CN103541458 discloses a liquid damping fluid column with a combination of tuned liquid damper; including tanks, baffles fixing and adjusting means, elastic support and transfer means. This device is single water tank, which have the benefits of liquid damping but this is not a combined device. The container is not fixed with the structure, but it is hinged with elastic supports.
WQ2014046549 A1 discloses a Pendulum type Liquid Column Damper (PLCD) which is basically a partly liquid filled U-Tube container hinged to a building structure so it can move like a pendulum relative to a building structure. This device is a type of passive vibration controlling device, but as because this device is not fixed with the building, it requires larger space to perform oscillations, and requires higher maintenance cost. This device does not combine the TLCD and TLD in one container, so space utilisation is less efficient.

The present invention can be regarded as a rectangular Tuned Liquid sloshing damper (TLD) and a Tuned Liquid Column Damper (TLCD) combined in one place. Due to its configuration the area required is reduced compared to two independent dampers. The area between the two vertical columns of a TLCD is utilised as a rectangular TLD in this new configuration. So. higher mass of liquid can be incorporated in lesser space by using this new device. The container is fixed with the structure. As the movement of the liquid is relative to the container, the liquids in the TLCD portion and TLD portion of the combined device are not connected internally and so the motions of the fluid in TLCD and TLD portion are independent and they work together but do not influence each other.
Object of the invention:
The object of the invention is to provide a new arrangement to allow a structure to achieve optimal performance when it is subjected to any types of transient shock due to vibration.
And another object of the present invention is to control structural vibration in a cost effective manner.
And another object of the present invention is that it can be used as a bi-directional damper to mitigate structural responses in both the orthogonal directions.
And another object of the present invention is to reduce overall structural vibration for maintaining serviceability condition of the building.
And another object of the present invention is to enhance occupants comfort and safety.

Summary of the invention:
To achieve the foregoing and in accordance with the purposes of the present invention, the present invention provides an arrangement for controlling any structural vibration. It works upon the motion of the liquid in a rigid tank for changing the dynamic characteristics of a structure and dissipating its vibration energy under lateral excitation. It is a new combination of Tuned Liquid sloshing Damper (TLD) and Tuned Liquid Column Damper (TLCD) as shown in Figure 1. However, the unique configuration of the device makes it very much space saving. Thus, the design and installation of this device is also less costly than other types of liquid, damper that allows a structure to achieve optimal performance when it is subjected to any types of transient shock due to vibration. The device is so designed that the natural frequency of the damper (average of the natural frequencies of TLD and TLCD) is tuned with that of the structure. To find out the effectiveness of this new configuration device in controlling structural vibration, a numerical simulation procedure is used. Results show that this new device is very much effective in controlling structural vibrations for different dynamic loads (Sinusoidal loads and Real earthquake loads). Later experiments were carried out to validate the analytical model. The liquid used in the damping devices is generally water.
Brief description of the drawings:
Figure 1 shows the three dimensional view of the new Tuned Combined Liquid Damper (TCLD) where,
1= Tuned Liquid-sloshing Damper (TLD) and
2= Tuned Liquid Column Damper (TLCD)
Figure 2 shows a simplified TCLD -Its Structure system and the equivalent mathematical model where,
1= Tuned Liquid-sloshing Damper (TLD)
2= Tuned Liquid Column Damper (TLCD)and
3= Orifice

Figure 3(a) shows Displacement and Figure 3(b) shows Acceleration response of the structure
with and without TCLD
Figure 4 shows DMF curve of structure with and without TCLD
Figure 8(a) is the elevation-view of the proposed new combined device TCLD
where,
1= Tuned Liquid-sloshing Damper (TLD) and
2= Tuned Liquid Column Damper (TLCD)
Figure 8(b) shows the plan view of the proposed new combined device TCLD
where,
1= Tuned Liquid-sloshing Damper (TLD) and
2= Tuned Liquid Column Damper (TLCD)
Detailed description of the invention:
Current trend in designing and constructing tall buildings is the use of light weight materials and slender structures to achieve a maximum height with a relatively small dead load. The negative side effects of these are high susceptibility to lateral wind and earthquake induced vibrations. The basic idea of most vibration reducing devices is the absorption of a certain, critical part of the input energy thereby reducing the ductility demand of the main structure and thus preventing it from serious structural damage. In recent days Liquid mass dampers have become more popular due to its low implementation cost, easier handling and low maintenance cost, and like other passive devices, they, do not usually interfere with vertical and horizontal load paths. Based on the energy dissipation mechanism, the liquid mass dampers are classified into two groups. Tuned Liquid-sloshing Damper (TLD) and Tuned Liquid Column Damper (TLCD). TLD acts on the principle of liquid sloshing in the tank and dissipates the energy through viscous action of fluid, wave breaking, contamination of free surface, and the geometry of the container and its roughness. TLCD suppresses the input energy by the combined action of the movement of the mass in the U-shaped container, the restoring force on the liquid due to gravity and the damping due to liquid movement through the orifices.

The present invention is a new type vibration controlling device named Novel Tuned Combined
Liquid Damper (TCLD) which combines the effects of TLD and TLCD; both working
simultaneously as a single unit. The device is so designed that the natural frequency of the
combined device TCLD (average of the natural frequencies of TLD and TLCD) is tuned with the
fundamental frequency of the structure. Therefore, by combining the equations of TLD and
TLCD, the governing equations of motion of the system formed by the new combined device
TCLD and the primary structure to be controlled are derived, when both are subject to a base
acceleration. Furthermore a parametric study is conducted to determine the effectiveness of this
new device in controlling structural vibration using a time domain numerical method (The
Newmark-Beta method) to deal with the nonlinearity present in the governing equations. Results
show that this new device is very much effective in controlling structural vibrations induced by
different kinds of dynamic loads(Sinusoidal loads and Real earthquake loads). To experimentally
validate the mathematical model; free vibration test was. conducted on a Single Degree of
Freedom system model, with and without the damper. Finally, an attempt is made to define
appropriate design guidelines of the TCLD for practical usage in reai life applications. The
design also confirms that this new configuration requires very much less space than already
existing other liquid dampers like TLDs and TL-CDs acting individually, which makes this new
device very much cost effective and easy to install in real life applications. The design also
ensures that the TLD portion of the combined device can be used as a bi-directional damper also,
to mitigate structural responses in both the orthogonal directions. This vibration controlling
device can be implemented not only in structures but also in other places where vibration control
is necessary.
To determine the mathematical expression for motions of a TCLD system mounted on a structure
shown in Figure 2, all the forces acting on the system need to be considered. The primary
structure can be modeled as a SDOF system with a mass, stiffness and damping coefficient. Only
the mass of the liquid (generally water) is considered as the mass of the damper and the mass of
the liquid container can be included with the mass of the structure.
The system under investigation can be separated in three substructures; i.e. The Primary structure, TLCD portion and TLD portion. As the movement of the liquid is relative to the container, and the liquids in the TLCD portion and TLD portion of the combined device are not

connected internally; so the motions of the fluid in TLCD and TLD portions respectively are independent and they do not influence each other. For this reason a three degree of freedom system can easily be adopted to describe the equation of motion of the whole system. The relative horizontal displacement of primary structure and the liquid surface displacements in the TLCD and TLD are taken as xs, y1, y2 respectively. For the purpose of the study the TLD is modeled as an equivalent TMD with nonlinear stiffness and damping. The mathematical diagram of the whole system as shown in Fig. 2 depicts the motions of the systems when subjected to ground excitation zb
Equation of motion of TLCD:
As shown in Fig.2, the liquid container will have the same horizontal motion as the structure, when the system is subjected to a ground excitation zb .but the liquid in the tube will experience a relative motion with respect to the tube. The equation of motion of liquid column as given by Sakaietal. (1989) will be

Where ρ is the liquid density in TLCD, A1= Cross Sectional Area Of TLCD B1= Length of the horizontal portion of TLCD, L1= Total length of liquid in TLCD Normalizing the above equation by liquid mass present in the TLCD portion only, i.e. pA1L1

Where is the length ratio. (Length ratio is the length of the horizontal portion of TLCD to
its total length). is the frequency of the liquid in TLCD and the co-efficient of head
loss, is determined using equation given by Wu et al (2005).


Where φ is the blocking ratio of the orifice. Equation of motion of TLD:

Where L2 = Length of the rectangular TLD portion; h2 = Height of water in the TLD ; g = Acceleration due to Gravity
The depth ratio is defined as the ratio of water depth to the tank length of TLD.
The TLD is modeled as an equivalent TMD with nonlinear stiffness and damping, The mass (m2), stiffness (k2), natural frequency (ω2) and damping coefficient (c2) of the equivalent TMD model used in the study is defined by Yu et al.(1999) as. m2 = mass of water present in TLD portion only

Where in Equation is a non-dimensional excitation function where A is amplitude of
excitation and L2 is the tank length in the direction of excitation.
So the equation of motion of the TLD for ground acceleration is given by


Equation of motions of primary structure:
For the vibration due to ground excitation on the combined damper TCLD and structural system, the motion of the ground and the structure induces the liquid motion in the damper, then the combined damper (by simultaneous TLD and TLCD action) will induce a reaction on the structure. The equation of the motion of the structure can be written as

Where,
ms = Mass of structure; ks= stiffness of structure;
, Natural frequency of structure.
m1= mass of liquid in the TLCD portion.= ρA1L1
Equation of motions of TCLD and structural system combined:
Combining the Equations (10), (2) and (9), the governing equation of motion the new combined device TCLD and structural system subjected to ground excitation zb „ in matrix form can be
written as

In the numerical simulation an algorithm is set to evaluate the stiffness and damping properties of the TCLD for each time step. The amplitude A is taken as the structural displacement for previous time step. This formulation ensures that the properties of the TCLD depends on the

excitation, as the water dissipates more energy through sloshing and wave breaking as the excitation level increases.
Numerical simulation:
A building is modeled as a SDOF structure and TCLD is mounted on top of the primary structure
as shown in.Fig. 2, used for the analysis. The equivalent properties of primary structure are
m5 =2.0x105 kgand ks = 6.5254 x1.06M/m. Damping ratio of structure, ξs =2% .The structure
has a natural frequency f1 =0.909 Hz, which is tuned by the frequency of combined device TCLD (average of natural frequencies of the TLCD and TLD). The tuning ratio (ratio of natural frequency of the damper to that of the structure) is taken unity for this embodiment. The total mass of water present in the combined device TCLD used in this embodiment is 5% of the structural mass; this water is divided in TLCD and TLD portion of the combined device. The combined device was so designed that the TLCD has 3% mass ratio (ratio of mass of water. present in the TLCD portion to the total structural mass) and the TLD has the rest 2% mass ratio (ratio of mass of water present in the TLD portion to the total structural mass). The Length ratio
of TLCD portion, is kept at 0.8, and the Depth ratio of TLD portion is kept
at 0.15, so that the shallow water sloshing theory remains valid.
To find out the effectiveness of the TCLD in controlling structural vibration, the structure was analyzed twice, once with the damping device attached on the top, and again without the device attached, for different dynamic loadings like sinusoidal excitations and different real earthquake excitations. The results accumulated were discussed later in this section.
Sinusoidal excitation:
To know the functionality of the new device TCLD, the ground excitation used in this case is sinusoidal in nature. Assuming a harmonic excitation given by
(12)
Where, A0 is the amplitude of excitation and co is the excitation frequency. Here.the value of A0 is taken as 1 % of Gravitational acceleration.

Fig. 3 shows the displacements and acceleration response of the structure with and without the TCLD when the structure is excited harmonically at the resonance frequency, i.e. when ω/ωs=1. From the figure it can be clearly seen that the TCLD is very effective in controlling displacement and acceleration response of structure due to harmonic excitations at resonance frequency.
The effectiveness of the TCLD for minimizing the peak Dynamic Magnification Factor is shown in Fig. 4, calculated by sweeping the entire excitation frequency range. The absolute maximum structural displacement (|xs|) at each excitation frequency was obtained. Those
maximum amplitudes were divided by the static state amplitude to obtain peak DMF at each frequency. The formula for calculating the peak Dynamic Magnification Factor due to harmonic ground excitation by using Newmark-Beta Linear acceleration method is given as..

Dynamic Magnification factor curve for the structure with and without TCLD is observed in Fig.4. It is observed that the peak of the uncontrolled structure at resonance frequency is divided into two peaks by the TCLD action. But the difference between the heights of the two separate peaks is not much significant, which implies that the tuning ratio of the device chosen for the study is close to optimum value. Overall it can be seen that a properly designed TCLD reduces structural vibration induced by harmonic excitation very effectively in the range of resonance frequency.
Real earthquake excitation:
In real life situations buildings are not directly excited by sinusoidal excitations, so to simulate the effects of TCLD in mitigating structural responses in real life applications like earthquakes, The structure without and with TCLD attached to the top is subjected to past earthquake data of Eastern turkey earthquake (2011), Norcia Italy earthquake (2016), Coalinga Earthquake (1983) and Loma Prieta earthquake (1989).
Details of the selected earthquake ground motion records and their magnitudes in Richter's scale are shown in Table 1, and the time history accelerogram record is shown in Fig. 5

The variation of displacements of structures with time considering time history data of Eastern turkey earthquake (2011). Norcia Italy earthquake (2016). Coalinga Earthquake (1983) and Loma Prieta earthquake (1989), using TCLD and without it are summarized in Fig. 6 and Table 2, which shows the effectiveness of the damper in reducing peak structural responses. The results show that the performance of the TCLD in reducing the peak structural displacement, vary with the nature of the earthquakes, as the nature of the excitation becomes different.
The results confirm that although the performance of the proposed TCLD vary with the nature of the earthquakes, but overall it performs exceptionally well for all earthquakes, by standing out the maximum structural displacements and also rapid response decay. This is very beneficial in real life, by enhancing occupants comfort and safety in flexible building with low intrinsic structural damping.
The variation of acceleration of structures with time considering time history data of the selected earthquakes using TCLD and without the damper are shown in Fig. 7 and Table 3, which shows the effectiveness of the damper in reducing peak structural responses. The results show that the performance of the TCLD in reducing the peak structural acceleration is less significant. This is because the primary structure chosen for the study has relatively large period of oscillation, which have low spectral acceleration associated with it, and controlling it's responses has only a limited influence on the accelerations, as mentioned by Rozas et al (2015).

initial phase, the liquid sloshing is weak, so it can dissipate less energy, but once the strong
liquid sloshing phase starts, the TCLD becomes increasingly effective in controlling the
structural response, as it dissipates more energy through liquid motions.
This phenomenon leads to an understanding that the TCLD may not be much effective in
controlling the peak structural response if the peak is reached within the first few cycles of
vibration, but overall response reduction is more efficient, which is also beneficial in real life
purposes. This phenomenon can be observed in Rectangular TLDs also, as mentioned by Banerji
et al. (2000).
In general liquid dampers with relatively high mass ratio are more effective in suppressing the
structural displacement, as long as the mass of water is small enough in relation to the structure
mass. This is because a larger mass of water should absorb and dissipate more energy through
relative liquid motions. Much higher value of water mass is not effective as they add to the
inertia] load on the structure due to base excitations. Also a higher mass ratio is impractical due
to the higher space requirements in real civil engineering applications.
An Experimental Setup:
To determine of the effectiveness of the proposed damper experimentally, a building is modeled
as a SDOF structure made of steel and a model TCLD is mounted on top of the primary
structure. The arrangement of the steel structure model over the base is shown in the Fig. A.


The steel structure model has a mild steel plate of thickness 10mm so that it acts as a rigid slab of a structure. The load of the slab is transferred first into the beams then into the columns. There are four number of beams and columns of size 6 mm x 6 mmx770 mm. The columns are connected to beams and the slab and the base plate by welding. The equivalent properties of primary structure are: Mass (ms)= 25.5 Kg and Stiffness (ks)=2.4349x103 Kg/m. Free vibration test was conducted on the primary structure without any damper attached with it. to determine the damping ratio of the structure (cs). Natural frequency of the primary structure model is 1.55Hz.
Instrument used are accelerometer, which measures the acceleration of the vibration the base and top of the structure; TRIMEX Acquire data acquisition system. The Tuned Combined Liquid Damper (TCLD) model is made up of glass fiber sheet of 2mm thickness. It consists of one U-shaped TLCD portion and a rectangular TLD portion in between the columns as described in previous section.
The fundamental frequency of the primary structure is tuned by the frequency of combined device TCLD (average of natural frequencies of the TLCD and TLD). The tuning ratio (ratio of natural frequency of the damper to that of the structure) is taken unity for the current study. The total mass of water present in the combined device TCLD used in this study is 5% of the structural mass; this water is divided in TLCD and TLD portion of the combined device. The combined device was so designed that the TLCD has 3% mass ratio (ratio of mass of water present in the TLCD portion to the total structural mass) and the TLD has the rest 2% mass ratio (ratio of mass of water present in the TLD portion to the total structural mass). The Length ratio
of TLCD portion, is kept at 0.7, and the Depth ratio of TLD portion is kept
at 0.13, so that the shallow water sloshing theory remains valid. The details of TCLD model dimensions are given in Table 4.


Under free vibration test the base of the structure model was fixed. The structure with and without TCLD was excited by giving the same amount of initial displacement of 44.5 mm. The acceleration response with time is measured by attaching accelerometers top of the structure. TRIMEX Acquire data acquisition system is used to acquire and analyze the experimental data with the help of Accelerometer Interface Unit.
To justify the mathematical formulations given in Equation 11, the structure is also analyzed numerically using a time domain method (The Newmark-Beta method) by MATLAB programming to deal with the non linearity present in the governing Equation 11. An algorithm is set to evaluate the stiffness and damping properties of the TCLD for. each time step. The parameters used for the numerical study are identical to those used in the experimental case; so experimental and numerical results can be compared to evaluate the accuracy of the procedure. Assuming a harmonic excitation given by

Where, A0 is the amplitude of excitation and ω is the excitation frequency. For the case of free vibration the value of A0 was taken as zero. An initial displacement of 44.5mm was given as an initial condition in the Newmark-Beta method and initial velocity was taken as zero.
To find out the effectiveness of the TCLD in controlling structural vibration, a set of experiment (Free vibration test) was carried out on the Steel structure model, once with the damping device attached on the top, and again without the device. The same structure was also analyzed numerically with the same structure and damper parameters.

The variation of displacement and acceleration of structure with time, with and without TCLD, for free vibrational test for both experimental and numerical cases are shown in Fig.9 and Fig. 10 respectively.

From Figures. 9 and 10, it can be observed that the motion of the model structure decays very rapidly with TCLD attached on the top of the structure compared to the uncontrolled structure, which signifies the energy dissipating efficiency of the damper. It can also be seen from the

Figures that the Experimental and Numerical results match very closely, which signifies the accuracy of the mathematical formulations and experimental models used in this study.
The energy input to an SDOF system by imparting to it the initial displacement xs(0) and initial velocity xs(0) is given by

At any instant of time the total energy in a freely vibrating SDOF system is made up of two parts, Kinetic energy Ek of the total mass and potential energy equal to the strain energy Ep of deformation in the spring, where

So the total vibrational energy ET at any instant of time is given by the following expression

The total energy for a damped system will always be a decreasing function of time because of energy being dissipated by damping.

Figure. 11: Variation of Total Vibrational Energy of the structure with and without TCLD for free vibration, (a) Total energy with time; (b) Cumulative Percentage of energy dissipation with time

Figure 11 signifies the effectiveness of TCLD in dissipating vibrational energy of structure. The structure with TCLD dissipated almost all of its energy within a very short period of time due to the sloshing of the liquid combined with the nonlinear relative liquid motions inside the damper; while the structure without the damper attached to it, took significantly longer time to dissipate the energy.
The result obtained determines that the device performs very well by reducing structural displacement and accelerations, and also by decaying responses of structure very rapidly in case of free vibration. This signifies that the device is indeed very beneficial for real life usage. because of the fact that oscillations of tall buildings developed by dynamic loads such as earthquakes, may persist long after the event themselves have ceased, which sometimes exceeds serviceability criteria.
An exemplary embodiment 1:
After finding out the effectiveness of the new combined device TCLD, it is required and practically useful to outline some general guidelines of designing the new combined device TCLD that has been found to be effective in mitigating response of a structure subjected to different dynamic loadings. Fig.8 (a) and Fig.8 (b) show the details of the elevation'view and plan view of the new proposed combined device TCLD. The suggested steps of design are as follows:.
1. Determine the natural frequency of the structure. ωsand considering the tuning ratio to be unity, select the fundamental frequency of TLCD portion, ω1. .2. Then compute the total length of water of the TLCD portion, L1, from Equation
3. Again considering the tuning ratio to be unity, seiect the fundamental frequency of TLD portion, ω2. So as ωs = ω1 = ω2.

4. Compute the required tank length for TLD portion, L2, which should be less than L1 from
Equation considering a value of depth ratio, to be as
close to the shallow water depth limit, say 0.15. Then calculate the water depth, h2, in the TLD portion which will be equal to L2Δ. In order to fit the TLD inside the two vertical columns of TLCD, the values of A must be so chosen that the value of L2