Effectiveness of a tiny tuned liquid damper on mitigating wind-induced responses of cylindrical solar tower based on elastic wind tunnel tests

Highlights

• Six types of tiny TLDs with different inner diameters (9, 10, 11, 12, 13 and 14 mm) were designed and manufactured.

• Structural parameters of tiny TLDs were identified to compare them with the theoretical values.

• The effectiveness of TLD on mitigating the wind-induced responses of a solar tower was studied by using wind tunnel tests.

Abstracts

A tiny TLD was specially designed and manufactured to investigate its effectiveness on mitigating the wind-induced responses of a 243-meter-high solar tower by using wind tunnel tests based on an elastic test model. First, an elastic test model of the solar tower was made, and its structural parameters, including natural frequency, the first three mode shapes and structural damping ratio, were identified. Second, six types of tiny TLDs with different inner diameters (9, 10, 11, 12, 13 and 14 ​mm) were designed and manufactured, and the natural frequency and sloshing damping ratio of water in these tiny TLDs were identified to compare them with the theoretical values. The results show the measured and theoretical natural frequencies agree well with each other, while the measured sloshing damping of water is much larger than the theoretical value. Then, a series of wind tunnel tests were carried out to obtain the wind-induced responses of the solar tower. The effectiveness of TLD on mitigating the wind-induced responses of the solar tower was systematically investigated based on a series of parametric studies. The results show the wind-induced responses in the cross-wind and along-wind directions, including the acceleration at the top, the shear and moment at the bottom, can all be significantly reduced by the tiny TLDs with optimized parameters. It seems that the efficiency of the TLDs at the vortex-induced vibration critical wind velocity is significantly higher than that at the design wind velocity. In addition, the parametric studies indicate that the effectiveness of the TLDs is considerably sensitive to the frequency ratio, the height of the TLDs and the mass ratio.

Introduction

Tuned liquid damper (TLD) has become one of the most effective measures to reduce undesirable dynamic responses in civil engineering structures. The TLD is liquid (usually water) confined in a container that uses the sloshing energy of the liquid to reduce structural vibration, which was widely used to reduce wind induced responses (Tamura et al., 1995; Li et al., 2012a; Zhang et al., 2016) due to the advantages of convenient installation, less maintenance and high automatic activation performance (Colucci et al., 2019). Note that the TLD is usually reformed from the water storage devices in high-rise buildings, which basically does not increase or only a low cost.

Many theoretical studies on the mechanical model of sloshing liquid have been carried out to facilitate the design of TLDs. There were two theoretical mechanical models. The first was lumped mass method originally proposed by Graham and Rodriguez (1952), in which the liquid was equivalent to a system composed of a fixed rigid mass and a spring vibrator. Housner (1963) proposed a simplified equivalent model, and Kareem and Sun (1987) studied its effectiveness based on the dynamic stochastic response of structures. However, Li et al. (2012b) and Li and Wang (2012) indicated that there is no exact location for the equivalent masses in the model proposed by Graham and Rodriguez (1952), and a supplementary exact expression for the equivalent model was developed. The second was shallow-water wave theory method (Fujino et al., 1992; Koh et al., 1994; Reed et al., 1998). Most of them were based on the potential flow theory to establish a nonlinear model for different containers.

Previous studies have shown that the sloshing damping of water in conventional TLDs is often significantly lower than the required values (Tait, 2008). To make conventional TLDs more effective, some energy dissipating devices, such as the baffles (Shad et al., 2016; Zahrai et al., 2012), the perforated screens (Cassolato et al., 2011; Molin and Remy, 2013) and the floating plate (Ruiz et al., 2016), were installed in the containers to enhance the sloshing damping. Sakai et al. (1989) proposed a new type device called tuned liquid column damper (TLCD), and some other researchers paid their attentions on the TLCD (Altay and Klinkel, 2018; Balendra et al., 1999; Cammelli et al., 2016; Min et al., 2015; La and Adam, 2018). Another classic modification based on the conventional TLDs was multiple tuned liquid dampers (MTLDs) (Love and Tait, 2015; Tuong and Huynh, 2020; Xu and Shum, 2002). The results showed that it was more effective to reduce structural vibration because the sloshing frequencies of the MTLDs were distributed within a certain range around the natural frequency of the controlled structure. Recently, Pandit and Biswal (2019; 2020) studied the possibility of the TLDs with sloping bottoms to reduce the undesirable responses of structures subjected to earthquakes.

In the previous decades, two main methods, including numerical analyses and full-scale measurements, were often used to study the effectiveness of TLD on mitigating wind-induced responses. Wakahara et al. (1992) numerically carried out an optimized design of a TLD on a high-rise building based on the comfort and serviceability. Tamura et al. (1995) conducted a series of full-scale measurements of wind-induced responses for four buildings, and evaluated the equivalent damping ratios of these buildings with and without TLD. Suduo et al. (2002) numerically studied the effectiveness of the TLCD in reducing the wind-induced response of a long-span bridge, and the results showed the TLCD can significantly reduce the buffeting response and increase the critical flutter wind velocity. Kim and Adeli (2005) numerically compared the effectiveness of the semi-active TLCD and the hybrid viscous fluid damper-TLCD based on a 76-story building subjected to wind loads. Ikeda et al. (2011) and Love et al. (2011) respectively studied the efficiencies of the TLD in reducing the wind-induced responses of wind turbines and seismic isolation structures by using numerical analyses. Ross et al. (2012) studied the reduction of equivalent static wind loads for a lateral-torsional coupled high-rise building installed with a TLD. Wang et al. (2016) proposed an innovative system composed of TLCD and tuned mass damper (TMD) to mitigate the wind-induced responses of high-rise buildings based on numerical analyses.

Wind tunnel tests were seldom used to study the effectiveness of TLD on mitigating wind-induced responses of civil structures due to the difficulty of designing a suitable tiny TLD. Chen and Georgakis (2015) adopted a shaking table to input equivalent acceleration in the test model to simulate the wind-induced responses of a wind turbine with TLD. Chang and Gu (1999) studied the effectiveness of a rectangular TLD in reducing the vortex-induced vibration of a tall building by wind tunnel tests.

In this study, a tiny TLD was specially designed and manufactured to investigate its effectiveness on mitigating the wind-induced responses of a 243-meter-high solar tower by using wind tunnel tests based on an elastic test model. First, an elastic test model of the solar tower was made, and its structural parameters, including natural frequency, the first three mode shapes and structural damping ratio, were identified. Then, six types of tiny TLDs with different inner diameters (9, 10, 11, 12, 13 and 14 ​mm) were designed and manufactured, and the natural frequency and sloshing damping ratio of water in these tiny TLDs were identified to compare them with the theoretical values. Finally, a series of wind tunnel tests were carried out to obtain the wind-induced responses of the solar tower, and the effectiveness of TLD on mitigating the wind-induced responses of the solar tower was systematically investigated based on a series of parametric studies.