• Journal of dental hygiene science
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• v.23 no.2
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• pp.176-184
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• 2023

Background: Recently, a piezoelectric ultrasonic scaler based on a feedback control mechanism was introduced for pain relief. This study aimed to investigate the effects of a new ultrasonic scaler in reducing pain and discomfort in adults. Methods: A newly introduced ultrasonic scaler (Master 700^®) was used as the test device and a conventional ultrasonic scaler device (PIEZON^®) was used as the control device. Forty-one healthy adults visited the dental clinic for dental scaling but did not undergo scaling or periodontal treatment within 6 months. Intraoral examinations were performed before scaling and 3 months later; before scaling, both devices were randomly assigned on the left or right side of each dentition (split-mouth model) and scaling was performed by a registered dental hygienist. The levels of pain and discomfort during scaling were evaluated subjectively and objectively using the visual analog scale (VAS) and physiological monitoring of the heart rate (HR), respectively. Time was measured for each device. Results: All clinical indicators, except bleeding on probing, significantly improved with both devices. The treatment times were 7 minutes, 13 minutes (control) and 6 minutes, 59 minutes (test). VAS scores for pain were 4.89±2.12 (control) and 4.58±2.77 (test) points out of 10; for noise, these were 4.68±2.33 (control) and 4.55±2.55 (test), and for vibration, the values were 4.26±2.0 (control) and 4.18±2.48 (test). HR averages were 72.34±3.39 (control) and 75.97±9.78 (test) beats/min. No statistically significant differences were observed between the devices. Conclusion:The pain, discomfort levels, and scaling time of the new piezoelectric ultrasonic scaler did not differ from those of the conventional device. Further research and development are necessary for more prominent pain-relief effects of scaling devices.

• International Journal of High-Rise Buildings
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• v.10 no.3
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• pp.229-242
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• 2021

Dynamic characteristics of tall building structures with double negative stiffness damped outriggers (2NSDO) are parametrically studied using the theoretical formula. Compared with one negative stiffness damped outrigger (1NSDO), 2NSDO can achieve a similar maximal modal damping ratio with a smaller negative stiffness ratio. Besides, the 2NSDO can improve the maximum achievable damping ratio to about 30% with less consumption of an outrigger damping coefficient compared with the double conventional damped outriggers (2CDO). Besides, the responses of structures with 2NSDO under fluctuating wind load are investigated by time-history analysis. Numerical results show that the 2NSDO is effective in reducing structural acceleration under fluctuating wind load, being more efficient than 1NSDO.

• Ocean and Polar Research
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• v.37 no.3
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• pp.235-247
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• 2015

The main purpose of procuring the oceanographic research vessel with state-of-the-art technology is to provide a floating laboratory to conduct field work on the global oceans. The vessel should be properly utilized to locate and evaluate unexplored natural resources as well as to contribute international efforts to better understand and manage global environmental issues. Top priorities in the vessel design are high safety standards, noise and vibration control efficiency, and effective application of research equipment. For the accomplishment of all activities, the vessel length over all should be extended ~100 m with a gross tonnage of ~5,900 ton. In particular, the dynamic positioning system II will essentially operate at sea state 6. The high efficiency emissions reduction system will also be adopted in preparation for entry into force of 3rd exhaust emission control (Tier III). About 130 navigational and scientific instruments will be installed. The final design and model test of the new research vessel were reviewed and completed, respectively, in 2014. Currently, the ship is being built on schedule and expected to be delivered in December 2015. Within the near future, the new vessel will assume the role of carrying out multidisciplinary oceanographic researches of the highest standards in a technologically advanced and environment friendly manner.

• Smart Structures and Systems
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• v.7 no.5
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• pp.365-378
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• 2011

Piezo-based active structural health monitoring (SHM) requires amplifiers specifically designed for capacitive loads. Moreover, with the increase in number of applications of wireless SHM systems, energy efficiency and cost reduction for this type of amplifiers is becoming a requirement. General lab grade amplifiers are big and costly, and not built for outdoor environments. Although some piezoceramic power amplifiers are available in the market, none of them are specifically targeting the wireless constraints and low power requirements. In this paper, a piezoceramic transducer amplifier for wireless active SHM systems has been designed. Power requirements are met by two digital On/Off switches that set the amplifier in a standby state when not in use. It provides a stable ${\pm}180$ Volts output with a bandwidth of 7k Hz using a single 12 V battery. Additionally, both voltage and current outputs are provided for feedback control, impedance check, or actuator damage verification. Vibration control tests of an aluminum beam were conducted in the University of Houston lab, while wireless active SHM tests of a wind turbine blade were performed in the Harbin Institute of Technology wind tunnel. The results showed that the developed amplifier provided equivalent results to commercial solutions in suppressing structural vibrations, and that it allows researchers to perform active wireless SHM on moving objects with no power wires from the grid.

• Earthquakes and Structures
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• v.26 no.5
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• pp.337-348
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• 2024

This paper presents a new seismic isolation design for liquid storage tank (LST). The seismic isolation system includes: LST, flexible membrane, sand mat and rolling seismic isolation devices. Based on the mechanical equilibrium theory, the symmetric concave rolling restoring force model of the isolation device is derived. Based on the elasticity theory and restoring force model of the seismic isolation, a simplified mechanical model of LST with the new seismic isolation is established. The rationality of the seismic isolation design of LST is explored. Meanwhile, the seismic response of the new seismic isolation LST is investigated by numerical simulation. The results show that the new seismic isolation tank can effectively reduce the seismic response, especially the control of base shear and overturning moment, which greatly reduces the risk of seismic damage. The seismic reduction rate of the new seismic isolation storage tanks in Class I, II, and III sites is better than that in Class IV sites. Moreover, the seismic isolation device can effectively control the ground vibration response of storage tanks with different liquid heights. The new seismic isolation LST design provides better isolation for slender LSTs than for broad LSTs.

• Smart Structures and Systems
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• v.26 no.6
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• pp.765-779
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• 2020

Collapse of bridges in recent earthquakes demonstrates the need to deepen the understanding of the behaviour of these structures against seismic actions. This paper presents a highly detailed numerical model of an actual bridge subjected to extreme seismic action which results in its collapse. Normally, nonlinear numerical models have high difficulties to achieve convergence when reinforced concrete is intended to be represented. The main objective of this work is to determine the efficiency of different passive control strategies to prevent the structural collapse of an existing bridge. Metallic dampers and seismic isolation by decoupling the mass were evaluated. The response is evaluated not only in terms of reduction of displacements, but also in increasing of shear force and axial force in key elements, which can be a negative characteristic of the systems studied. It can be concluded that the use of a metallic damper significantly reduces the horizontal displacements and ensures the integrity of the structure from extreme seismic actions. Moreover, the isolation of the deck, which in principle seems to be the most effective solution to protect existing bridges, proves inadequate for the case analysed due to its dynamic characteristics and its particular geometry and an unpredictable type of axial pounding in the columns. This unexpected effect on the isolation system would have been impossible to identify with simplified models.

• International Journal of High-Rise Buildings
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• v.10 no.2
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• pp.93-97
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• 2021

Supplementary damping systems, such as tuned mass dampers (TMDs) and tuned sloshing dampers (TSDs) - also known as tuned liquid dampers (TLDs) - have been successfully employed to reduce building motion during wind events. A design of a damping system consisting of a TMD and two TSDs performing in unison has been developed for a tall building in Taiwan to reduce wind-induced motion. The architecturally exposed TMD will also be featured as a tourist attraction. The dual-purpose TSD tanks will perform as fire suppression water storage tanks. Linearized equivalent mechanical TSD and TMD models are coupled to the structure to simulate the multi-degree of freedom system response. Frequency response curves for the structure with and without the damping system are created to evaluate the performance of the damping system. The performance of the combined TMD-TSD system is evaluated against a conventional TMD system by computing the effective damping produced by each system. The proposed system is found to have superior performance in acceleration reduction. The combined TMD-TSD system is an effective and affordable means to reduce the wind-induced resonant response of tall buildings.

• Journal of Korean Association for Spatial Structures
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• v.12 no.4
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• pp.71-80
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• 2012

Because a smart isolation system cannot be used as a base isolation system for tall buildings, top-story or mid-story isolation systems are required. In this study, adaptability of a smart top-story isolation system for reduction of seismic responses of tall buildings in regions of low-to-moderate seismicity has been investigated. To this end, 20-story example building structure was selected and an MR damper and low damping elastomeric bearings were used to compose a smart base isolation system. Artificial earthquakes generated based on design spectrum of low-to-moderate seismicity regions are used for structural analyses. Based on numerical simulation results, it has been shown that a smart top-story isolation system can effectively reduce both structural responses and isolation story drifts of the building structure in low-to-moderate seismicity regions in comparison with a passive top-story isolation system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.49-56
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• 2022

In this study, numerical simulations for reducing noise between floors in an apartment building was carried out using Active Noise Control (ANC) technology. In order to examine the feasibility of using ANC to reduce noise between floors, accelerometers and microphones for noise collection were installed in the inter-floor noise test facility to measure noise and vibration caused by the impact ball drop test. By using the measured data, Filtered-x Least Mean Square (Fx-LMS) algorithm-based ANC simulations were carried out. In the simulations, after deriving optimal simulation conditions including the adaptive control convergence coefficient, the noise reduction effect was analyzed through numerical simulations using the number of installed accelerometers and speakers as variables. Finally, it was confirmed that the noise between floors could be reduced using ANC technology under limited conditions.

• Journal of Korean Association for Spatial Structures
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• v.11 no.4
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• pp.79-88
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• 2011

Recently, complex-shaped tall buildings represented by 3T(Twisted, Tapered, Tilted) are planed largely. A diagrid structural system is one of the most widely used structural system for complex-shaped tall buildings because of its structural efficiency and formativeness. Plans for tilted tall buildings are largely presented because of beauty of a sculpture and many of buildings use diagrid structural systems. Lateral displacements of tilted tall buildings are induced by not only lateral loads but also self weight. Therefore, reduction of lateral responses of tilted tall buildings is as important as typical tall buildings. In this study, a smart TMD is introduced to reduce seismic responses of tilted diagrid tall buildings and its control performance is evaluated. MR damper is employed for the smart TMD and ground-hook controller is used as a control algorithm for the smart TMD. 100-story tall building is used as an example structure. Control performances of uncontrolled case, controlled case with TMD and controlled case with smart TMD are compared and investigated. Numerical simulation has shown that smart TMD presented good control performance for displacement response but acceleration response was not controlled well.