• Journal of Magnetics
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• v.22 no.1
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• pp.109-121
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• 2017

Ferrofluids are a special category of smart nanomaterials which shows normal liquid behavior coupled with superparamagnetic properties. One of the earliest and most prospective applications of ferrofluids is in damping, which has prominent advantages compared with conventional damping devices: simplicity, flexibility and reliability. This paper presents the basic principles that play a major role in the design of ferrofluid damping devices. The characteristics of typical ferrofluid damping devices including dampers, vibration isolators, and dynamic vibration absorbers are compared and summarized, and then recent progress of vibration energy harvesters based on ferrofluid is briefly described. Additionally, we proposed a novel ferrofluid dynamic vibration absorber in this paper, and its damping efficiency was verified with experiments. In the end, the critical problems and research directions of the ferrofluid damping technology in the future are raised.

• Smart Structures and Systems
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• v.18 no.2
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• pp.293-315
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• 2016

Seismic isolation is often used in protecting mission-critical structures including hospitals, data centers, telecommunication buildings, etc. Such structures typically house vibration-sensitive equipment which has to provide continued service but may fail in case sustained accelerations during earthquakes exceed threshold limit values. Thus, peak floor acceleration is one of the two main parameters that control the design of such structures while the other one is peak base displacement since the overall safety of the structure depends on the safety of the isolation system. And in case peak base displacement exceeds the design base displacement during an earthquake, rupture and/or buckling of isolators as well as bumping against stops around the seismic gap may occur. Therefore, obtaining accurate peak floor accelerations and peak base displacement is vital. However, although nominal design values for isolation system and superstructure parameters are calculated in order to meet target peak design base displacement and peak floor accelerations, their actual values may potentially deviate from these nominal design values. In this study, the sensitivity of the seismic performance of structures equipped with linear and nonlinear seismic isolation systems to the aforementioned potential deviations is assessed in the context of a benchmark shear building under different earthquake records with near-fault and far-fault characteristics. The results put forth the degree of sensitivity of peak top floor acceleration and peak base displacement to superstructure parameters including mass, stiffness, and damping and isolation system parameters including stiffness, damping, yield strength, yield displacement, and post-yield to pre-yield stiffness ratio.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1346-1354
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• 2018

Quality of the power system depends upon the reliability of its components such as transformer, transmission lines, insulators, circuit breakers and isolators. The transient voltage due to internal or external reasons may affect the insulation level of the components. The insulation level of these components must be tested against these conditions. Different studies, testing of different electrical components against high voltage impulses and different industrial applications rely on the international manufactures for pulsed power generation and testing, that is quite expensive and large in size. In this paper a model of impulse voltage generator with capacitive load of pin type insulator is studied by simulation method and by an experimental setup. A ten stage high voltage impulse generator (HVIG) is designed and implemented for different applications. In this proposed model, the cost has been reduced by using small and cheap capacitors as an alternative for large and expensive ones while achieving the same effectiveness. Effect of the distributed capacitance in each stage is analyzed to prove the effectiveness of the model. Different values of front and tail resistances have been used to get IEC standard waveforms. Results reveal the effectiveness at reduced cost of the proposed model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.6 s.123
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• pp.515-523
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• 2007

As environmental vibration requirements on precision equipments get more stringent, use of pneumatic vibration isolators becomes more crucial and, hence, their dynamic performance needs to be further improved. Dynamic behavior of those pneumatic vibration Isolation tables is very important to both manufacturer and customer as performance specifications. Together with conventional transmissibility, transient response characteristics are another critical performance index especially when movements of components, e.g., x-y tables, of the precision equipments are very dynamic. In this paper, analysis on transient response of a pneumatic vibration isolation table loaded by a mass moving on it is presented. This is a conventional dynamics problem on a rigid body with 6 degree of freedom and a mass with another degree of freedom. How to obtain transient responses of the isolation table is described when the movements of the mass are prescribed relative to the table.

• Earthquakes and Structures
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• v.17 no.2
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• pp.191-204
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• 2019

Near-field earthquake records including long-period high-amplitude velocity pulses can cause large isolation system displacements leading to buckling or rupture of isolators. In such cases, providing supplemental damping in the isolation system has been proposed as a solution. However, it is known that linear viscous dampers can reduce base displacements in case of near-field earthquakes but at the potential expense of increased superstructure response in case of far-field earthquakes. But can non-linear dampers with different levels of non-linearity offer a superior seismic performance? In order to answer this question, the effectiveness of non-linear viscous dampers in reducing isolator displacements and its effects on the superstructure response are investigated. A comparison with linear viscous dampers via time history analysis is done using a base-isolated benchmark building model under historical near-field and far-field earthquake records for a wide range of different levels of non-linearity and supplemental damping. The results show that the non-linearity level and the amount of supplemental damping play important roles in reducing base displacements effectively. Although use of non-linear supplemental dampers may cause superstructure response amplification in case of far-field earthquakes, this negative effect may be avoided or even reduced by using appropriate combinations of non-linearity level and supplemental damping.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.6
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• pp.241-249
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• 2021

Communication facilities play an essential role in disaster situations. Therefore, communication facilities need to have structural and functional safety during and after earthquakes. Recently, technology for partial seismic isolation has been increasing to protect data facilities and communication equipment installed in buildings from earthquakes. However, excessive displacement may occur in the seismic isolator during an earthquake due to the resonance between the building and the seismic isolator having long-period characteristics, which may cause overturning and separation of the installed equipment. In this study, analytical and experimental studies were conducted to evaluate the safety of seismic isolators installed in high-rise buildings. It was confirmed that damages might occur in buildings' seismic isolator, with resonance characteristics of less than 1 Hz.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.2974-2988
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• 2022

Implementation of component isolation in nuclear industry is challenging due to gaps in research and the lack of specific guidelines. In this study, parameters affecting component-level isolation of advanced reactor vessels are identified based on a representative numerical model with explicit consideration of nonlinear soil-structure interaction (SSI). The objective of this study is to evaluate the effectiveness of, and to identify potential limitations of using conventional friction pendulum bearings to seismically isolate vessels. It is found that slender vessels or components are particularly vulnerable to rotational accelerations at the isolation interface, which are caused by rotation of the sub-structure and by excitation of higher modes in the horizontal direction of the seismically isolated system. Component isolation is found to be more effective for relatively stiffer vessels and at sites with stiff soil. Considering that conventional isolators are deficient in resisting axial tension, it is observed that the optimum location for supporting a component to achieve seismic isolation, is at a cross-sectional plane passing through the center of mass of the vessel. These findings are corroborated by numerous simulations of the response of seismically isolated reactor vessels at different nuclear power plant sites subject to a variety of ground motions.

• Earthquakes and Structures
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• v.23 no.1
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• pp.87-100
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• 2022

Limiting the displacement of seismic isolators causes a pounding phenomenon under severe earthquakes. Therefore, the ASCE 7-16 has provided minimum criteria for the design of the isolated building. In this research the seismic response of isolated buildings by Triple Friction Pendulum Isolator (TFPI) under the impact, expected, and unexpected mass eccentricity was evaluated. Also, the effect of different design parameters on the seismic behavior of structural and nonstructural elements was found. For this, a special steel moment frame structure with a surrounding moat wall was designed according to the criteria, by considering different response modification coefficients (RI), and 20% mass eccentricity in one direction. Then, different values of these parameters and the damping of the base isolation were evaluated. The results show that the structural elements have acceptable behavior after impact, but the nonstructural components are placed in a moderate damage range after impact and the used improved methods could not ameliorate the level of damage. The reduction in the RI and the enhancement of the isolator's damping are beneficial up to a certain point for improving the seismic response after impact. The moat wall reduces torque and maximum absolute acceleration (MAA) due to unexpected enhancement of mass eccentricity. However, drifts of some stories increase. Also, the difference between the response of story drift by expected and unexpected mass eccentricity is less. This indicates that the minimum requirement displacement according to ASCE 7-16 criteria lead to acceptable results under the unexpected enhancement of mass eccentricity.

• Journal of Korean Association for Spatial Structures
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• v.22 no.1
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• pp.25-32
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• 2022

The seismic behaviors of the arch structure vary according to the rise-span ratio of the arch structure. In this study, the rise-span ratio (H/L) of the example arch structure was set to 1/4, 1/6, and 1/8. And the installation angle of the seismic isolator was set to 15°, 30°, 45°, 60° and 90°. The installation angles of the seismic isolator were set by analyzing the horizontal and vertical reaction forces according to the rise-span ratio of the arch structure. Due to the geometrical and dynamic characteristics of the arch structure, the lower the rise-span ratio, the greater the horizontal reaction force of the static load, but the smaller the horizontal reaction force of the dynamic load. And if the seismic isolator is installed in the direction of the resultant force of the reaction forces caused by the seismic load, the horizontal seismic response becomes small. Also, as the installation angle of the seismic isolator increases, the hysteresis behavior of the seismic isolator shows a plastic behavior, and residual deformation appears even after the seismic load is removed. In the design of seismic isolators for seismic response control of large space structures such as arch structures, horizontal and vertical reaction forces should be considered.

• Structural Engineering and Mechanics
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• v.87 no.5
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• pp.405-418
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• 2023

This study focused on the effectiveness of seismic isolation technique in case of a reinforced concrete structure with soft story defined as the stiffness irregularity between adjacent stories. In this context, a seismically isolated 3-story reinforced concrete structure was analyzed by gradually increasing the first story height (3.0, 4.5, and 6.0 m). The seismic isolation system of the structure is assumed to be composed of lead rubber bearings (LRB). In the analyses, isolators were modeled by both deteriorating (temperature-dependent analyses) and non-deteriorating (bounding analyses) hysteretic representations. The deterioration in strength of isolator is due to temperature rise in the lead core during cyclic motion. The ground motion pairs used in bi-directional nonlinear dynamic analyses were selected and scaled according to codified procedures. In the analyses, different isolation periods (Tiso) and characteristic strength to weight ratios (Q/W) were considered in order to determine the sensitivity of structural response to the isolator properties. Response quantities under consideration are floor accelerations, and interstory drift ratios. Analyses results are compared for both hysteretic representations of LRBs. Results are also used to assess the significance of the ratio between the horizontal stiffnesses of soft story and isolation system. It is revealed that seismic isolation is a viable method to reduce structural damage in structures with soft story.