Effect of Seawater Exposure on Impact Damping Behavior of Viscoelastic Material of Pounding Tuned Mass Damper (PTMD)  
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1 Institute of Road and Bridge Engineering, Dalian Maritime University, Dalian 116023, China; [EMAIL_ADDRESS]  
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2 Department of Mechanical Engineering, BITS Pilani K K Birla Goa Campus, Zuarinagar, Goa 403726, India 2  
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3 Department of Mechanical Engineering, University of Houston, Houston, TX 77004, USA 34 Correspondence: [EMAIL_ADDRESS] (D.P. ); [EMAIL_ADDRESS] (S.C.M.H. ); Tel: +91-832-2580246; Tel: +1-713-743-4498  
shortcomings that limit their applications, including expensive machinery cost, difficulty in installation and susceptibleness to marine growth or storm damage [11]. Another low cost yet effective VIV suppression equipment is the pipe in pipe in pipe (PIP) system [11; 12; 13]. The PIP system utilizes a specially designed soft spring and a dashpot to replace the traditional hard centralizer. Therefore, the inner pipe and the outside pipe can work together to resist the dynamic excitations. Many other systems share a similar vibration problem with the pipeline structure that is slender and has low damping [14], with the vibration control of such systems having received significant attention [15; 16; 17]. The commonly used vibration control methods can be classified as active control [18; 19; 20], semi-active control [21; 22; 23], passive control [24; 25; 26; 27] and hybrid control [28]. In general, passive vibration control, especially the tuned mass dampers (TMD) and impact dampers, have been extensively studied and are widely used in various structures due to their simplicity and effectiveness [29; 30; 31]. The TMD is a classical dynamic absorber, which can reduce the motion of the primary structure by generating an inertial force of the same frequency but opposite phase. TMDs are frequently implemented with energy dissipation components, such as viscous dampers [32], friction dampers [32; 33], eddy-current components [17; 31], etc. However, these devices often demand continuous maintenance to ensure the presence of the designed damping, which is impossible in some extreme circumstances, such as the subsea environment [34]. Another drawback of the TMD is the detuning effect: when the frequency of the TMD shifts away from the optimum value, the vibration control effectiveness will be dramatically decreased [17]. Compared with the TMD, the impact damper is easy to implement and maintenance free, with a relatively wide band of effective frequencies. Hence, the impact damper can be a complementary energy dissipating element for the TMD. In previous studies, a novel damper that integrates the TMD and the impact damper with the help of the viscoelastic material was proposed and is named the bounding tuned mass damper (PTMD). The schematic of the PTMD is illustrated in Figure 1. As shown in the figure, the PTMD consists of two components: a classical tuned mass damper (TMD) and a delimiter covered with the viscoelastic material. Because of this TMD-delimiter configuration, the PTMD combines the two vibration control mechanisms of the classical TMD and the impact damper. Thus, when there is only a slight vibration of the primary structure, the tuned mass (\(m_{2}\)) will vibrate freely between the two delimiters like a TMD, absorbing the kinetic energy from the primary structure (\(m_{1}\)). When the motion of the primary structure exceeds a certain level, the tuned mass will pound on the delimiter and the PTMD will dissipate energy as an impact damper. From previous studies, the PTMD has been verified to be highly effective in reducing the vibration of buildings [35; 36; 37; 38; 39; 40], bridges [41; 42], transmission towers [43; 44], offshore platforms [45; 46], traffic signal poles [47; 48] and subsea pipeline structures [49; 50; 51; 52; 53].