Additional Viscous Damping Research Articles

Damping in masonry arch railway bridges under service loads: An experimental and numerical investigation

This article investigates the damping behavior of masonry arch bridges under service loads extracted from experimental data and provides guidelines on how to emulate this behavior in numerical analysis, particularly in discrete element model applications. First, an experimental campaign is undertaken and vibrations on three masonry arch railway bridges under train loads were monitored. The modal damping ratios from several sensors on each bridge were extracted by isolating the modal component of free decay vibrations which commence immediately after the train leaves the bridge. The modal damping ratios identified under service loads were compared with their counterparts identified under ambient vibrations. The suitability of mass-proportional, stiffness-proportional and Rayleigh damping models in emulating damping in masonry arch bridges was evaluated. In the numerical phase of the study, a single-arch masonry bridge was modeled using mixed discrete continuum approach and a moving load analysis was conducted without applying any additional viscous damping. The results of the numerical analysis indicate that the inherent damping in discrete element models provided by their nonlinear nature can be sufficient to emulate the damping behavior of masonry arch bridges under service loads. The research provided in this article is unique in the sense that it combines an experimental study and a numerical study on damping of masonry arch bridges under service loads. Unlike its counterparts in literature, which use either ambient vibrations or seismic action, damping values are computed under appropriate levels of vibration amplitudes for service loads, which is critical to estimate the modal damping ratios accurately under these loads.

Contribution of fluid viscous dampers on fatigue life of lattice-type offshore wind turbines

Given the recent developments in wind energy generation technology, offshore wind turbines have been widely used to exploit offshore wind energy. Supporting structures of offshore wind turbines play an important role in correct operation of wind turbines and their operational life. Supporting structures will experience millions of lateral load reversals due to wave- and wind-induced vibrations. Because of the stress concentration, more fatigue damages are expected at the structural joints. Supporting structures of offshore wind turbines have commonly small inherent damping and it is believed that because additional viscous damping can reduce structural vibrations and result in less stress concentration at the joints. In this study, vertically oriented fluid viscous dampers are used to increase fatigue life of a full-height Lattice-type Offshore Wind Turbine (LOWT). Obtained results indicated that the use of fluid viscous dampers significantly delayed fatigue failure and increased fatigue life of structural joints by up to 3 times.

Nonlinear wave loads on a stationary cylindrical-type oscillating water column wave energy converter

Based on the potential flow theory, a second-order Higher-Order Boundary Element Method model is developed to simulate hydrodynamic loads and pressure on a stationary cylindrical-type oscillating water column (OWC) wave energy converter. Quadratic pneumatic damping and additional viscous damping are introduced to simulate the effects of the power take-off and the viscous dissipation inside the chamber, respectively. The proposed model is verified against a carefully instrumented scaled experiment. The effects of the chamber geometry and the wave environment on the hydrodynamic loads of the OWC device are then explored using the validated model. The resonance excited by the second-order wave component is observed with the fundamental frequency being half of the natural frequency. This resembles a sloshing mode and leads to a significant increase in hydrodynamic pressure and surge force as well as pitch moment. The effects of the second-order waves cannot be ignored under the action of the low-frequency long waves. In addition, the surge force and the pitch moment are not sensitive to the variation in the orifice opening ratios, while the heave force increases with the opening ratio at a resonant heave frequency.

Using a Tuned-Inerto-Viscous-Hysteretic-Damper (TIVhD) for vibration suppression in multi-storey building structures

This paper explores the use of a novel tuned-inerto-viscous-hysteretic-damper (TIVhD) for reducing the seismic response of multi-storey building structures. The TIVhD is an inerter-based damper device consisting of a linear hysteretic damper connected in series with an inerto-viscous damper. The layout of TIVhD is similar to that of tuned-inerter-hysteretic-damper (TIhD) with an additional viscous damping element in parallel with an inerter. The design is motivated by the fact that most inerter designs cannot completely remove the parasitic damping due to friction, fluid compression, etc. Moreover, the use of linear hysteretic damping is considered to be a more realistic approach when material damping is present. In this paper, the TIVhD is installed between the ground and the first-storey and is tuned by firstly assumed the viscous damping coefficient to be zero. Then the other three parameters are optimised following the tuning procedure of the TIhD that is based on the fixed-point theory with additional fine-tuning procedure by targeting the first vibration mode of the multi-storey structure. The optimum TIVhD parameters are finally obtained using two scenarios: (1) amplifying its viscous damping coefficient and stiffness while keeping the inertance constant; (2) amplifying its inertance and stiffness while keeping the viscous damping constant. Both scenarios are aiming at the same reduction level of that given by the TIhD. Finally, the effectiveness of the TIVhD on reducing the structural response is demonstrated for both harmonic and seismic base excitation cases in the time domain. This has been made possible by a newly developed time domain response of linear hysteretic damping via the Hilbert transform and a time reversal technique.

Experimental and numerical investigations of a two-body floating-point absorber wave energy converter in regular waves

This paper presents experimental and numerical studies on the hydrodynamics of a two-body floating-point absorber (FPA) wave energy converter (WEC) under both extreme and operational wave conditions. In this study, the responses of the WEC in heave, surge, and pitch were evaluated for various regular wave conditions. For extreme condition analysis, we assume the FPA system has a survival mode that locks the power-take-off (PTO) mechanism in extreme waves, and the WEC moves as a single body in this scenario. A series of Reynolds-averaged Navier–Stokes (RANS) simulations was performed for the survival condition analysis, and the results were validated with the measurements from experimental wave tank tests. For the FPA system in operational conditions, both a boundary element method (BEM) and the RANS simulations were used to analyze the motion response and power absorption performance. Additional viscous damping, primarily induced by flow separation and vortex shedding, is included in the BEM simulation as a quadratic drag force proportional to the square of body velocity. The inclusion of viscous drag improves the accuracy of BEM’s prediction of the heave response and the power absorption performance of the FPA system, which agrees well with experimental data and the RANS simulation results over a broad range of incident wave periods, except near resonance in large wave height scenarios. Overall, the experimental and numerical results suggest that nonlinear effects, caused by viscous damping and interaction between waves and the FPA, significantly influence the system response and power absorption performance. Nonlinear effects were found to be particularly significant when the wave height was large and the period was near or shorter than the resonant period of the FPA system. The study is expected to be helpful for understanding the nonlinear interaction between waves and the FPA system so that the structure of the FPA can be adequately designed.

Analytical and numerical investigation of site response due to vertical ground motion

Owing to the repeatedly observed strong vertical ground motions and compressional damage of engineering structures in recent earthquakes, the multi-directional site response analysis is increasingly critical for the seismic design of important structures, such as nuclear power plants and high earth dams. However, the site response to the vertical component of the ground motion has not been the subject of detailed investigation in the literature. Therefore, in this paper, the vertical site response due to vertical ground motion is investigated by employing both analytical and numerical methods. First, a one-dimensional frequency domain analytical solution, which can be employed for vertical site response analysis in practice, is studied and compared against time domain finite-element (FE) analyses for the two extreme soil state conditions (i.e. undrained and drained conditions). The vertical site response is further investigated with hydro-mechanically (HM) coupled FE analysis, considering solid–fluid interaction. The parametric studies undertaken show that the predicted vertical site response is strongly affected by the parameters characterising the hydraulic phase, namely, soil permeability and soil state conditions, both in terms of frequency content and amplification. The subsequent corresponding quantitative investigation, of the frequency content and amplification function of the vertical site response, shows that depending on the soil permeability the response is dominated by the two types of compressional waves (fast and slow waves). Notably, the parametric studies identify a range of permeability that significantly affects dynamic soil properties in terms of P-wave velocities, damping ratios and vertical site response, and this range is relevant for geotechnical earthquake engineering applications. It is therefore recommended that coupled consolidation analysis is necessary to simulate this effect accurately at such permeability-dependent intermediate transient states between fully undrained and drained conditions. Finally, this work suggests a simple modification of standard total-stress site response analysis to account for vertical ground motion and solid–pore fluid interaction. In order to simulate the attenuation of the response due to solid–pore fluid interaction effects, it is suggested to employ additional HM viscous damping in total-stress analysis, further to the one used to account for hysteretic material damping. This additional viscous damping can be quantified based on the empirical curves proposed in the paper.

Seismic retrofit of special truss moment frames using viscous dampers

The special truss moment frame (STMF) is known to provide higher lateral stiffness with relatively less weight as compared to conventional moment resisting frames. In this study the seismic performance of STMF was investigated by fragility analyses and the results were compared with the performance of special moment resisting frames. Then seismic retrofit scheme was proposed by installing a viscous damper in the special segment to meet enhanced seismic performance objective. The required amount of additional viscous damping was determined based on the nonlinear static procedure provided in the ASCE/SEI 41-10. The analysis results showed that the STMF showed larger stiffness and strength but smaller ductility compared with the moment frames, which resulted in similar seismic fragility in both structures. The seismic performance of STMF with viscous dampers in the special segments turned out to meet the desired target performance, and the effect of adding viscous dampers in the seismic fragility was most significant in the complete damage state.

VIV and galloping of single circular cylinder with surface roughness at 3.0×10 4≤ Re≤1.2×10 5

Passive Turbulence Control (PTC) in the form of selectively distributed surface roughness is used to alter Flow Induced Motion (FIM) of a circular cylinder in a steady flow. The objective is to enhance FIM's synchronization range and amplitude, thus maximizing conversion of hydrokinetic energy into mechanical energy by oscillator in vortex-induced vibration and/or galloping. Through additional viscous damping, mechanical energy is converted to electrical harnessing clean and renewable energy from ocean/river currents. High Reynolds numbers ( Re) are required to reach the high-lift TrSL3 (Transition-Shear-Layer-3) flow regime. PTC trips flow separation and energizes the boundary layer, thus inducing higher vorticity and consequently lift. Roughness location, surface coverage, and size are studied using systematic model tests with broad-field laser visualization at 3.0×10 4< Re<1.2×10 5 in the low-turbulence free-surface water-channel of the Marine Renewable Energy Laboratory of the University of Michigan. Test results show that 16° roughness coverage is effective in the range (10°–80°) inducing reduced vortex-induced vibration (VIV), enhanced VIV, or galloping. Range of synchronization may increase or decrease, galloping amplitude of oscillation reaches three diameters; wake structures change dramatically reaching up to ten vortices per cycle. Conversion of hydrokinetic energy to mechanical is enhanced strongly with proper PTC.

Fully coupled dynamic analysis of an earth dam

The paper studies the seismic behaviour of an existing homogeneous earth dam using a fully coupled finite-element effective stress approach in conjunction with a recently developed multi-surface, elasto-plastic constitutive model for structured soils. The model is calibrated using laboratory test results for the embankment material and the foundation soils. The initial state variables (stress, hardening parameters) are determined by simulating a simplified geological history of the foundation soil, dam construction stages and reservoir impounding, prior to the application of the earthquake shaking at the bedrock level. The paper critically reviews the role of the constitutive model parameters, the hysteretic damping introduced by the model and the additional viscous damping parameters in the accumulation of permanent displacements and in the development and subsequent dissipation of excess pore water pressures due to the seismic loading. The analyses, carried out with reference to a set of earthquake records related to different return periods, show that the overall behaviour of the system in terms of displacements is characterised by a more enhanced deformation pattern of the downstream slope as compared with the upstream one. The large plastic strains accumulation induced throughout the shaking is followed by the development of excess pore water pressures inside the dam and the foundation deposit. Nonetheless, the results are indicative of a satisfactory dynamic performance of the dam, even when subjected to severe seismic loading conditions.

Optimization of the power flow extracted from a flexible structure using a control approach

Vibrating energy is a renewable energy that can be used to power wireless transducers. This article presents analytical and numerical results that put forward design parameters for optimizing the energy conversion from mechanical vibration to electrical power with an electromagnetic transducer. The studied structure is a flexible structure using an electromagnetic transducer connected to a resistive feedback loop. This passive harvesting circuit is a simplified representation of the storing system usually including a battery and a rectifying electronic. Here the energy harvesting strategy chosen creates an additional viscous damping on the structure. The numerical model of the generator, including the coupling law, predicts the power transferred between electrical and mechanical energies. For a purely resistive feedback, the study of the harvested energy shows that harvesting and stabilization strategies are different. A simple analytical model, derived from modal synthesis techniques, shows that Jacobi's maximal power transfer theorem can be adapted for multi-physic problems: the electrical and mechanical damping ratios have to be matched to maximize the power transferred. This result is confirmed by experimental measurements. The analytical study also shows that it is possible to use the root locus to choose the two optimal energy harvesting feedback gains and then consequently the harvesting electronic circuit's parameters. Copyright © 2010 John Wiley & Sons, Ltd.

A review of adverse effects of damping in seismic isolation

AbstractIn this paper the question of possible adverse effects of damping in seismic isolation because of higher mode response is investigated by means of simple models with a few degrees of freedom (DOF). In particular the second mode response of a 2 DOF system is examined in detail for both viscous and hysteretic (e.g. friction or elastoplastic) damping devices. Qualitative and approximate quantitative estimates are obtained by neglecting the influence of the modal coupling terms, due to viscous damping or friction forces, on the first mode response. It is shown that additional viscous damping has a diminishing effect on base displacement, storey shear force and floor spectra values in the vicinity of the first mode resonance. However, a significant amplification of the floor spectra values near the higher mode frequencies may occur. In accordance with the results of previous works, compared with the viscous damping case, hysteretic damping amplifies moderately the first storey shear force and significantly the upper storeys shear force. It also results, in a much more pronounced amplification of the floor spectral values than viscous damping, in the vicinity of the higher eigenfrequencies. However, the higher modes' response is milder if a realistic velocity dependence of the friction coefficient is taken into account. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Robustness of base‐isolated high‐rise buildings under code‐specified ground motions

AbstractThe robustness of base‐isolated high‐rise buildings is investigated under code‐specified ground motions. Friction‐type bearings are often used in base‐isolated high‐rise buildings to make the natural period of those buildings much longer. While additional damping can be incorporated into every story in passive controlled structures with inter‐story type passive members, that can be incorporated into the base‐isolation story only in the base‐isolated building. This fact leads to the property that, as the number of stories of the building becomes larger, the damping ratio reduces. This characteristic may cause some issues in the evaluation of robustness of base‐isolated high‐rise buildings. The purpose of this paper is to reveal the robustness of base‐isolated high‐rise buildings. A kind of inverse problem for the target drift in the base‐isolation story is formulated in order to determine the required quantity of additional viscous damping. It is demonstrated numerically that, as the base‐isolated building becomes taller, the damping ratio becomes smaller and the ratio of the friction‐type bearings in the total damping becomes larger. This may lead to the conclusion that base‐isolated high‐rise buildings have smaller robustness than base‐isolated low‐rise buildings. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Retrofit of seismically isolated structures for near-field ground motion using additional viscous damping

Recent earthquakes have shown that a large magnitude, long period pulse is often prevalent in ground motion records at sites within a few kilometres of the active fault during an earthquake. Near-field earthquake ground motion containing forward directivity effects can result in a larger response in flexible structures, such as seismically isolated structures, compared to that predicted for conventional ground shaking. Hence, a study was performed on a number of generic seismically isolated structures designed to the 1997 Uniform Building Code, as well as a case study on the William Clayton building in Wellington, to determine the impact of near-field ground motion. In optimising the performance of the buildings for both near-field and original "design level" earthquakes, it is concluded that linear viscous dampers added to the existing isolation systems are effective in controlling the response during large magnitude near-field earthquakes with minimal impact on the design response. Additional viscous damping is more effective than hysteretic damping in limiting isolator displacements while also preventing an increase in base shear and floor accelerations for far-field "design level" earthquakes.

점성감쇠기를 이용한 비대칭.비탄성구조물의 내진보강

본 연구에서는 평면 비대칭건물의 비탄성 변위를 주어진 목표까지 제한하기 위하여 필요한 추가적인 감쇠량을 구하는 방법에 관하여 연구하였다. 이를 위하여 먼저 비대칭구조물의 항복 후 거동을 분석하고 구조물에 발생하는 연성도 요구량을 이용하여 필요한 등가 감쇠비를 유도하였다. 이러한 방법을 지진하중을 받는 5층 비대칭구조물에 적용하였다. 시간이력해석 결과와의 비교에 따르면 제안된 방법에 따라 점성감쇠기를 설치한 경우 주어진 지진하중에 대하여 약변 및 강변 모두 만족할만한 거동을 보이는 것으로 나타났다. A procedure for figuring out proper amount of additional viscous damping required to keep the inelastic deformation of a plan-wise asymmetric structure within a given target performance point was developed. To this end the behavior of an asymmetric nonlinear structure after yielding is investigated. Then a formula for the required amount of equivalent damping was derived based on the ductility demand of the structure. The procedure was applied to a five-story asymmetric structure subjected to an earthquake load. According to the comparison with the results from the dynamic time-history analysis, the structure with viscous dampers installed in accordance with the proposed procedure showed satisfactory seismic performance in both the stiff and the flexible edges.