2.0 Literature Review
2.1 Vibration Isolation

In engineering, vibration causes damage, failure and destruction of a structure. Vibration on structure either building or machine, must be avoid, get rid or minimize them. Vibration is any motion that repeats itself after an interval of time described by Rao in “Mechanical Vibrations” 1. In engineering field, vibrations are commonly found in rotating machineries. Ormondrovd and Hartog 2 said that Dynamic Vibration Absorber (DVA) also known as Tuned Mass Damper (TMD) has been physically proven to reduce mechanical vibration. In this paper, TMD will be used. The TMD has been studied for many decades as mentioned by Warburton 3. Tuned Mass Damper typically comprise of a mass, spring, and a damping element which normally attached to the vibrating main system. Tuned Mass Damper will reduce any undesirable vibration. In vibration control, vibration absorber are classified into two categories which is passive and active according to Rivin 4. The semi-active dampers however, are like improved version of passive energy dissipating technology as they integrate adaptive systems to increase effectiveness and intelligence. Passive systems are used to attenuate structural vibrations induced mostly by natural phenomenon such as earthquake and wind excitation. According to Elias and Matsagar 5, the most famous passive systems are friction control devices, fluid viscous dampers, seismic base isolation, tuned liquid dampers, and tuned mass dampers. The one TMD or Single TMD was originated since the attempt made by Frahm in 1909 6. Then, TMD was improvise with variance of optimum design approach in order to reduce vibration by Ormondroyd and Den Hartog 7. TMD are basically tuned near or frequencies associated with low order modes and can improve overall damping. The equations of motion for a single degree of freedom (SDOF) structure and multi-DOF structure with the TMD mechanism are expressed as,

Ms{x¨s} + Cs{x? s} + Ks{xs} = {Ft} (1)

where Ms, Cs, and Ks are the mass, damping, and stiffness matrices of the structure.
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In the present study, TMD is counted for the control of vibration mode of a generic system. For example, an external actions such as wind and earthquake excites a structure which causes vibration to the main structure. The mechanical model of TMD system as shown in Fig. X where, single degree of freedom is represented by the main system. Then, the mechanical parameters are introduced

Type equation here.

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2.1.1 Passive Tuned Mass Damper

Passive TMDs has been proven by many researchers which is effective in attenuating the vibration of a structural system caused by an external excitation. In high rise buildings, passive TMD are widely used such as in John Hancock Building in Boston equipped with a TMD consisting of two 2.7 x ?10?^5 kg (300 ton) 8. In Taiwan, the tall building Taipei 101 equipped with a 660 tons of TMD ball which equals to 0.24% of the building weight. According to Tamboli 9, the TMD is intended to reduce service-level accelerations at upper levels by about 40%. Research done by Lin, Hu, et al. 10 showed that TMD can reduce seismic responses by as much as 60%. They also conclude that passive TMDs are better in attenuate the vibration amplitude of acceleration than displacement. Lievens, Lombaert, et al. 11 stated that TMD is defined by its mass m, stiffness k and damping c, and characteristics. They presented that TMD performs satisfactorily in uncertain circumstance. Lee, Nian, et al. 12 presented passive vibration control using DVA to reduce vibrations in turning operation. Moradi et al. 13 also presented TVA or known as TMD to suppress vibration in boring manufacturing process.

Figure XX : Time response of system before (left) and after (right) absorber is applied.
Fig XX shows that the absorber reduces the absolute value of the real part of transfer function of the dynamic system. In civil engineering, tall structures are equipped with TMD to protect the structures against forces induced by natural phenomenon such as strong winds and earthquake. Thus, TMDs are being studied widely to counter force induced by earthquake which can cause structural collapse and fatal. Passive vibration absorber Performance of TMD on structural collapse due to earthquakes was studied by Domizio et al. 14 which showed that TMD was able to increase the safety margin of a 4-story steel frame building induced by 8 near-fault earthquakes. An investigation done by Okhovat et al. 15 on TMD for seismic response reduction of Tehran tower with 170m height shows that TMDs are very sensitive for detuning. The effectiveness of TMD on structural response were evaluated by using both peak and normed-based evaluation. In Chile, Garrido and Sarrazin 16 presented the effectiveness of TMD for earthquake to protect Chilean buildings.

Fig XXX 15

The case was studied by considering 2 DOF systems for a database of 132 acceleration which corresponding to seven Chilean earthquakes of magnitude larger than 7.0. Two responses were then calculated as shown in flowchart in Figure XX. However, they stated that the detuning is not relevant if the frequency of TMD is between 95% and 105% of the optimum frequency. Rofooei 17 presented the performance of TMD in reducing the damage in 2-D concrete structural models. The structural models was tested to seven earthquake records with different intensities. The results shows that TMD has efficiently mititgates the damage index for the 8-story model. However, for larger intensities, the TMD does not show any performance due to detuning. Nawrotzki 18 reported in retrofitting of structures with TMD reduces the structural responses about 25% – 40%. The results showed a significant reduction of the structural responses in terms of displacements, accelerations and internal stresses. Effect of torsional response such as rotation of building presented by Khante and Nirwan 19 showed a reduction in displacement, rotation, base shear and bending moment when a passive TMD is applied to the structure. The results showed that TMD has substantial energy absorption capability. As studied by Lin et al. 20, they discovered the effectiveness of TMD on a stochastic structural buildings was more efficient to mitigate the dynamic responses induce by wind rather than earthquake. They stated TMD was more effective in reducing the vibration amplitude of acceleration than displacement. In terms of dissipating energy into primary system criterion, as eloquently stated by Greco and Marano 21 TMD gives a great reduction in terms of energy dissipation. With optimum parameters, the energy criterion gives greater ?_opt^TMDvalues. On the opposite, ?_opt^TMD is larger if the displacement criterion is take on. As depicted in Fig XX, the time history showed the consistency of TMD selected with best optimum design in displacement and energy dissipated criterion.

Fig XX: Time history of displacement and dissipated power for the system without TMD and with TMD optimized by two criteria 21
Meena et al. 22 studied on vibration control using TMD by using approaching methodology of STMD and MTMD. They claimed that the number of TMDs does not have much effect on the optimum tuning frequency and the effectiveness of MTMD. In aerospace engineering, a segmented mirror telescope requires a very tight tolerances in terms of alignment. In this case, Yingling and Agrawal 23 studied on application of TMD in SMT due to its simplicity in implementation and effectiveness on targeting specific modes. The study resulted in reduction of vibration amplitudes by 80% and wavefron error (WFE) by a factor of 5.

Arctic pipeline with one TMD per span Fig. XX 24

In present, an application of TMD in pipeline was one of the application in passive TMD. To overcome the oscillation induced by wind to the pipeline. As shown in Fig XX, every span of the pipeline was installed TMD to attenuate the vibration. Although the frequencies are small (which are all below 5Hz) the vibration cycles can cause failure at pipeline joints according to Hart et al. 24. A study by Farzampour and Asl 25 in performance of TMD in vibration response control of base excited structures shows that active TMD leads to appropriate response reduction. In 8-story building active TMD responded a noticeable reduction as shown in Fig XX

Fig XX :
It is showed that in eight-story shear building, ATMD shows highly limited story drift and shear regarding the strong ground motions; however, application of PTMD leads to slight reduction in story drift and shear. Despite the cost of ATMD, it shows a great reduction in vibration suppression. It is concluded that ATMD leads to appropriate response reduction.

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