Mitigation of Rocking and Sliding Motion of a Free-Standing Structure Subjected to Base Excitation Using Coaxial Circular Cylinders Containing Highly Viscous Liquid in Annular Spaces

Volume 8: Seismic Engineering ◽

10.1115/pvp2019-93205 ◽

2019 ◽

Author(s):

Atsuhiko Shintani ◽

Tomohiro Ito ◽

Chihiro Nakagawa

Keyword(s):

Rigid Body ◽

Viscous Liquid ◽

Analytical Model ◽

Circular Cylinders ◽

Base Excitation ◽

Free Standing ◽

Seismic Input ◽

Sliding Motion ◽

Standing Structure ◽

Rocking Motion

Abstract In this study, the effectiveness of coaxial circular cylinders containing a highly viscous liquid in annular spaces for reduction of rocking motion of a free-standing structure is investigated both analytically and experimentally. First, an analytical model of coupled rocking and sliding motions of a free-standing structure, including the coaxial circular cylinders, subjected to seismic input was derived. The free-standing structure was modeled as a free-standing rigid body. The cylinders were attached to the bottom of the rigid body as a damping device. We then experimentally derived the friction coefficients, inertia moments, and a damping coefficient in the rotating direction. Furthermore, using these parameters, the effectiveness of this system in suppressing the rocking motion is investigated analytically. The proposed method was determined to be very effective in suppressing the rocking motion of a rigid body subjected to a seismic input by the experiment.

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Sliding and Rocking Motion Mitigation of a Rigid Body Subjected to Seismic Excitation due to High-Viscous Liquid

Volume 8: Seismic Engineering ◽

10.1115/pvp2016-63140 ◽

2016 ◽

Author(s):

Tomohiro Ito ◽

Hideki Sakurai ◽

Atsuhiko Shintani ◽

Chihiro Nakagawa

Keyword(s):

Rigid Body ◽

Analytical Model ◽

High Viscosity ◽

Test Model ◽

Damping Effect ◽

Gyro System ◽

Sliding Motion ◽

Cylindrical System ◽

Rocking Motion ◽

Suppression System

After the accident at the Fukushima Daiichi Nuclear Power Plant in Japan, it has steadily become more important to ensure the structural integrity of cask systems containing spent fuels or radioactive debris during seismic events. These cask systems are free-standing cylindrical structures and are believed to show rocking and sliding motions at huge seismic excitations. In the worst case, these cask systems can possibly overturn or collide with each other. Therefore, it is very important to reduce the sliding and rocking motions of the cask system in order to avoid subsequent contamination due to radioactive substances. To date, the authors have been studying the response behaviors of these motions, and have developed some types of methods that are effective at mitigating sliding or rocking motions, and confirmed the effectiveness of these methods. A system utilizing coaxial circular cylinders and high-viscosity liquid filled into the annular spaces was developed for the suppression of sliding motion. This system was installed at the bottom end of the rigid body. Previous studies show that liquids with high-viscosity provide a very large added damping effect that causes sliding motion to be suppressed significantly. For the suppression of rocking motion, the authors developed a system that utilizes a gyro system, and confirmed it’s effectiveness both analytically and experimentally. However, the gyro system is slightly complex and requires electric power even during a seismic event. Thus, some passive suppression method is required. On the other hand, the above-mentioned coaxial circular cylindrical system filled with high-viscosity liquid is thought to have a high damping effect on rocking motion, along with suppression of sliding motion. This study investigated the effect of rocking motion suppression due to the above-mentioned coaxial circular cylindrical system that is utilized for the suppression of sliding motion. First, an analytical model that can account for the coupled rocking and sliding motion was established, and then the rocking behavior of a rigid structure coupled with its sliding motion was studied. Next, shaking table tests were conducted by using a fundamental test model. By comparing the analytically obtained rocking motion with that obtained by the test results, the validity of the analytical model was confirmed. Finally, the analytical model was modified for cask systems equipped with a rocking suppression system, and the rocking motion was analyzed to evaluate its effectiveness. The proposed rocking suppression system was found to be very effective in suppressing the rocking motion of the rigid body when subjected to base excitations.

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Mitigation of Sliding Motion of a Cask-Canister by Fluid-Structure Interaction in an Annular Region

ASME 2011 14th International Conference on Environmental Remediation and Radioactive Waste Management, Parts A and B ◽

10.1115/icem2011-59208 ◽

2011 ◽

Author(s):

Tomohiro Ito ◽

Yoshihiro Fujiwara ◽

Atsuhiko Shintani ◽

Chihiro Nakagawa ◽

Kazuhisa Furuta

Keyword(s):

Equations Of Motion ◽

Fluid Structure Interaction ◽

Shaking Table ◽

Annular Region ◽

Test Model ◽

Free Standing ◽

Fluid Structure ◽

Structure Interaction ◽

Sliding Motion ◽

Standing Structure

The cask-canister system is a coaxial circular cylindrical structure in which several spent fuels are installed. This system is a free-standing structure thus, it is very important to reduce sliding motion for very large seismic excitations. In this study, we propose a mitigation method for sliding motion. Water is installed in an annular region between a cask and a canister. The equations of motion are derived taking fluid-structure interaction into consideration for nonlinear sliding motion analyses. Based on these equations, mitigation effects of sliding motions are studied analytically. Furthermore, a fundamental test model of a cask-canister system is fabricated and shaking table tests are conducted. From the analytical and test results, sliding motion mitigation effects are investigated.

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Study on Vibration Mitigation of Connected Cabinets Storing Electronics Subjected to Seismic Input Using Elasto-Plastic Damper

Volume 9: Seismic Engineering ◽

10.1115/pvp2020-21395 ◽

2020 ◽

Author(s):

Atsuhiko Shintani ◽

Takuma Yoshida ◽

Chihiro Nakagawa ◽

Tomohiro Ito

Keyword(s):

Rigid Body ◽

Seismic Wave ◽

Power Plants ◽

Rigid Bodies ◽

Single System ◽

Maximum Acceleration ◽

Worst Case ◽

Seismic Input ◽

Entire Plant ◽

Rocking Motion

Abstract This paper deals with the motion of coupled cabinets containing electronics subjected to seismic input. In power plants, chemical plants, etc., several rectangular cabinets containing important electronics are always lined up in the control center. These electronics are necessary for the control of the entire plant; thus, when they are damaged, the entire plant cannot be controlled, and a serious accident may occur. These cabinets are frequently put directly on the floor. Thus, it is perceived that in the worst case, cabinets may turn over by rocking motion during earthquakes and electronics may break. Moreover, even when the cabinets do not overturn, there is a concern about a large acceleration applied to the internal electronics due to the seismic waves. Hence, the need to develop methods that can reduce rocking motion and prevent electronics damage simultaneously. First, we consider the single cabinet with electronics. The cabinet is modeled as a rotating rigid body around its corner. The internal electronics are modeled as a rigid body moving in the translational direction in the cabinet. This system is referred to as single system. We input a seismic wave to the single system and investigate the rocking angle of the cabinet and the acceleration of the electronics in the cabinet. Consequently, we consider the adjacent cabinets connected by an elasto-plastic damper containing electronics. The cabinets are modeled as rotating rigid bodies. The internal electronics are modeled as rigid bodies moving in the translational direction in the cabinets. The whole system is known as a connected system. The elasto-plastic damper has bilinear hysteretic characteristics and can absorb the energy of earthquake inputs. We input the same seismic wave to the connected system to obtain the rocking angle of cabinets and the acceleration of electronics in the connected system. In these simulations, it is assumed that cabinets do not collide with each other. Then, we investigate the effect of the parameters of the elasto-plastic damper suppressing the rocking angle of the cabinets and the acceleration of electronics. Finally, we compare the maximum rocking angle and the maximum acceleration of the single system with that of the connected system and consider an ideal method to reduce the rocking angle and the acceleration simultaneously.

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Study on the Rocking Motion Suppression of a Structure subjected to Seismic Excitation due to Highly Viscous Liquid of Coaxial Circular Cylinders

The Proceedings of Conference of Kansai Branch ◽

10.1299/jsmekansai.2018.93.713 ◽

2018 ◽

Vol 2018.93 (0) ◽

pp. 713

Author(s):

Masahiro FUJINO ◽

Atsuhiko SHINTANI ◽

Tomohiro ITO ◽

Chihiro NAKAGAWA

Keyword(s):

Viscous Liquid ◽

Seismic Excitation ◽

Circular Cylinders ◽

Rocking Motion ◽

Motion Suppression

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Study on the Control of Displacement for Base Isolation Systems Utilizing High-Viscous Liquid (Effects of Eccentricity)

Volume 8: Seismic Engineering ◽

10.1115/pvp2013-97072 ◽

2013 ◽

Author(s):

Tomohiro Ito ◽

Naoto Nishimatsu ◽

Atsuhiko Shintani ◽

Chihiro Nakagawa

Keyword(s):

Viscous Liquid ◽

Structural Integrity ◽

Shaking Table ◽

Annular Space ◽

Spent Fuel ◽

Free Standing ◽

Worst Case ◽

Sliding Motion ◽

Damping Effects ◽

Isolation Systems

In Japan, ensuring the structural integrity of cask systems during seismic events is becoming increasingly important. Cask systems, which are free-standing cylindrical structures that contain spent fuel assemblies, are considered as sliding isolation systems. Thus far, analytical studies conducted by the authors have already indicated that cask systems subjected to strong seismic motions, undergo large sliding motions, and in the worst case, may collide with one another. Therefore, reducing the sliding motions of casks to avoid mutual collisions and consequent contamination of radioactive substances is critical. To suppress sliding motions for very heavy free-standing structures such as cask systems, the authors proposed a sliding motion suppression system that uses high-viscous liquid and coaxial circular cylinders. This system is installed at the bottom end of the structure and the annular space is filled with a high-viscous liquid. A previous study showed that high-viscous liquid in annular spaces provides added damping effects of considerable magnitude, and thus allows the sliding motion to be suppressed. In this study, the added damping effects of the annular space liquid are clarified using a fundamental testing device for various liquid viscosities, ratios of diameters for the inner and outer cylinders, and eccentricities of the inner cylinder. Moreover, shaking table tests are conducted to confirm that the added damping effects suppress excessive displacement.

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Effects of a Gyroscope in Reducing Rocking Motion of a Rigid Vessel Coupled With Inner Structure Subjected to a Base Excitation

Volume 8: Seismic Engineering ◽

10.1115/pvp2009-77137 ◽

2009 ◽

Author(s):

Kazuhisa Furuta ◽

Tomohiro Ito ◽

Atsuhiko Shintani

Keyword(s):

Coming Out ◽

Nuclear Power ◽

Outer Cylinder ◽

Rotational Frequency ◽

Seismic Excitations ◽

Free Standing ◽

Worst Case ◽

Standing Structure ◽

Rocking Motion ◽

Active Substances

Many spent fuels coming out of the nuclear power station are planned to be stored in the special site in Japan until they are reprocessed. In this site, the spent fuels are installed in a cylindrical container called canister. The canister, in tern, will be installed in the outer cylinder called cask that is a free-standing structure. When this system is subjected to strong seismic excitations, sliding or rocking motion will be induced. And, in the worst case, the cask may collide to each other or overturn. Therefore, it is very important to reduce sliding and rocking motions of the cask in order to avoid the consequent contamination of radio active substances. The authors have already reported the studies on the sliding and rocking motions of the cask subjected to a seismic excitation that contains a vibration system in it, and clarified the effects of the vibration of the inner canister. It was shown that the inner canister gives very large influences on the sliding and rocking motions of the outer cask. In this study, we applied a gyroscope at the top of the outer cask for reducing rocking motion of the cask. The effects of the gyroscope are studied for various excitation frequencies, excitation amplitudes and the structural dimensions of the gyroscope such as weight and rotational frequency. It is found that the gyroscope is very effective for reducing rocking motions of the cask-canister system subjected to seismic excitations.

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