Damper Configurations Research Articles

Post-tensioned rocking dissipative timber wall systems: Numerical prediction

Low-damage post-tensioned technologies were born with the aim to obtain structural solutions able to guarantee, in case of seismic events, not only the safeguarding of human life, but also the rapid re-use of the buildings without permanent damage. In this context, structural systems based on rocking dissipative timber walls have been introduced, in which rocking behavior is entrusted to post-tensioned bars, and the dissipative contribution is provided by steel dampers, easily replaceable after an intense seismic event. The paper presents a nonlinear numerical model to predict the response of different configurations of Post-Tensioned (PT)-timber wall systems, particularly useful to support the design phase. More in detail, the geometrical non-linearity due to the rocking behavior of the system and material non-linearities that characterize the dampers are taken explicitly into account. The proposed numerical modelling strategy has been validated on different experimental literature tests performed by non-linear static analyses on both single and double wall systems equipped with different damper configurations. The comparison between numerical and experimental results is performed to demonstrate the effectiveness of the proposed model in predicting the behavior of post-tensioned walls subjected to cyclic loads. Further, parametric analyses have been developed in order to investigate the effect of different parameters, such as wall dimensions, initial post-tensioned force in the bars, number of axial and shear dampers, on the global behaviour of post-tensioned timber systems.

Cyclic model of post-tensioned low damage timber walls with dissipative devices

Post-tensioned rocking dissipative timber wall systems born from the idea to obtain structural solutions able to guarantee, after a seismic event, a rapid re-use of the buildings without permanent damage, as well as to guarantee the safeguarding of human life. In this framework, the rocking of timber walls is entrusted to post-tensioned bars, placed in ad hoc cavities of the panel, while the dissipative contribution is provided by steel dampers, which are sacrificial elements subjected to damage easily replaceable after an intense seismic event. In this context, it can be helpful to have a numerical model in order to support the design phase; indeed, the paper presents a non-linear numerical model of post-tensioned rocking dissipative timber walls able to predict the response of this innovative system. In particular, geometrical and material non-linearities, due to the rocking behavior of the system and to the material that characterize the dampers, are taken explicitly into account. Further, the proposed numerical modelling strategy has been validated on literature experimental campaigns performed on both single and double wall systems, with different damper configurations. The comparison between experimental and numerical cyclic responses are shown in term of global results, i.e. force/displacement curves and post-tension variation of the bars. The comparison demonstrates the effectiveness of the proposed model in predicting the behavior of post-tensioned walls subjected to cyclic loads.

Performance of wire rope damper in vibration reduction of stay cable

This paper systematically investigates the novel application of wire ropes as a damper rather than as an isolator to reduce the wind-induced high-mode vibration of stay cables. Three-direction cyclic loading tests, including tension–compression direction, shear direction, and roll direction, are conducted to clarify the damping behavior of the proposed wire rope damper. The wire rope damper exhibits asymmetric hysteretic characteristics in the tension–compression direction, while the hysteresis loops in the shear and roll directions are symmetrical. A modified normalized Bouc-Wen model is presented to describe the multi-directional hysteretic characteristics of the wire rope damper. An analysis method considering the nonlinear damping behavior is developed in this study to overcome the limitations of the traditional analysis using an equivalent damping coefficient. The proposed analysis method is validated against the physical experiments. The proposed wire rope damper system was installed on the Su-Tong Yangtze River Bridge to reduce the high-mode vortex-induced vibration of the stay cable. The field monitoring data demonstrate that the proposed wire rope damper can significantly reduce the in-plane and out-of-plane vibrations. The effect of the wire rope damper on the cable vibration control is further examined using the proposed analysis method. The finite element results further demonstrate the effectiveness of the wire rope damper in high-mode vibration reduction of stay cables. The features of the wire rope damper, such as multi-directional damping, broadband applicability, and simple configuration, are beneficial to its application in cable vibration control.

Systematic design of particle dampers for transient vertical vibrations

A multilevel design toolchain is used for the development of particle dampers for vertical transient vibrating structures. Thereby various experimental tests and numerical models are combined. The design toolchain consists of three levels. The first level deals with the micro-mechanical behavior of single particle–particle and particle–wall impacts. The resulting coefficient of restitution is then used on the second level. Within, the second level the properties of vertical vibrated granular matters inside a container under harmonic motion are analyzed. The resulting motion modes and energy dissipation of the granular matter strongly depend on the excitation conditions, i. e. the excitation amplitude and excitation frequency. Multiple analytical formulations for the different motion modes, i. e. solid-like state and collect-and-collide motion mode, are derived to describe the energy dissipation within the particle damper. These analytical descriptions are in good agreement with numerical discrete element simulations. Finally, the third level of the design toolchain deals with designing a damper for a desired structure. The analytical formulations describing the energy dissipation within the particle damper are used to optimize a particle damper configuration for a simple beam-like structure undergoing a vertical transient vibration. The efficiency of the optimized particle damper dissipation is proven experimentally.

Performance Assessment of Hydraulic Micro Relief Valve

Directly operated relief valves often exhibit abnormal or unstable behavior resulting in noise, premature wear, degraded performance, and failure. In this work, an investigation is carried out to assess the role of the hydraulic damper on the poppet element. The article reports the details of the investigation approach, integrating specific experimental tests with lumped-parameter modelling.Starting from a reference layout, the hydraulic behavior of different damper configurations is characterized (ranging from undamped to strongly damped poppets), for pressure and flow-rate conditions typically encountered in micro-hydraulic power packs. Depending on the damper design, the poppet operation ranges from unacceptability (due to noise) to fine-tuned response. The investigation give the chance to highlight how the damper layout impacts on the valve behaviour, in terms of pressure overshoot and settling time and provides the necessary information for relief valve design, modelling and analysis.

NUMERICAL INVESTIGATION OF DYNAMIC RESPONSE CHARACTERISTIC OF DAMPED BRACED TUBE SYSTEM WITH DIFFERENT DAMPED SLIT COMFIGURATION

This paper investigated the dynamic response characteristic with focus on damped slit configuration of damped braced tube systems with oil dampers. According to the results, 1) damped braced tube system has over 10% 1st to 3rd damping ratio, 2) while the displacement and acceleration responses are simultaneously reduced up to maximized 1st mode damping ratio, the acceleration reduction effect may be getting worse after the peak, 3) while uniform damper distribution contributes to better damping performance, centralized damper distribution contributes to better period reduction.

Effects of Mass Attachments on Flutter Characteristics of Thin-Walled Panels

Mass attachments may exist in the design and use of an aircraft panel, such as sensor layout, internal wiring, surface icing, etc. These mass attachments can change the flutter characteristics of the panel in supersonic flight and have important impacts on structural safety. In order to investigate the flutter characteristics of the panel with mass attachments, an assumed mode method is proposed to deal with the changes in the modal properties of the panel structure. Combined with the first order piston theory and p-k method, the flutter velocities and flutter frequencies of the panel under different cases can be obtained in the frequency domain. Firstly, based on the large displacement with a small strain assumption proposed by von Kármán and the proposed assumed mode method, the structural dynamic model of a simply supported panel with mass attachments and artificial dampers is constructed. Then, modal aerodynamic forces of the simply supported panel can be obtained based on first-order piston theory. Finally, flutter equations are transformed into the frequency domain and solved by the p-k method. The results showed that the existence of mass attachments can significantly change the flutter velocities and flutter frequencies of the panel. However, the flutter characteristics of the panel can be enhanced or recovered through some appropriate damper configuration schemes. Calculating the flutter characteristics of thin-walled panels with mass attachments can more accurately simulate real situations during flight, and one can obtain a safer design scheme of thin-walled panels.

Generalization of the Den Hartog model and rule-of-thumb formulas for optimal tuned mass dampers

In recent years, the need of improving safety standards for both existing and new buildings against earthquake and wind loads has created a growing interest in the use of the so-called tuned mass dampers, exploited to control, in active or passive way, the dynamic response of structures. To design and optimize tuned mass damper systems, the effective analytical procedure proposed by Den Hartog in his seminal work (Den Hartog, 1985) has been widely adopted over the years, without including damping of the main structure. However, in many cases of engineering interest, the damping of the primary system plays a key role in the overall mechanical response, with the result of an increase in complexity of the related optimization problem, which are in fact solved in the vast majority by means of ad hoc numerical procedures. In the present work, we recover the classical optimization strategy by Den Hartog and generalize it by including the main system’s damping, providing new analytical solutions whose results are consistent with the few ones obtained through alternative mathematical methods by Thompson (1981) and Krenk (2005) and subsequently by Fang et al. (2019). In particular, some closed-form solutions and helpful rule-of-thumb formulas for the optimal setting of the design parameters are derived, by considering two types of incoming excitations, i.e. the force acting on the main mass and the ground motion input, both of interest for engineering applications. Finally, theoretical outcomes are compared with consolidated data from the literature. • Generalization of the Den Hartog model and analytical derivation of optimal tuning frequency ratio and damping of the absorber in Tuned Mass Dampers subjected to force or ground motion inputs. • Definition of rule-of-thumb formulas for design purposes. • Comparison of results from proposed analytical approach and numerical analyses to show advantages and effectiveness of the method, also for design parameters out of classical ranges. • Explicit expressions for optimal Tuned Mass Damper configurations in cases of stochastic ground motion input.

Retrofitting of a Precast Reinforced Concrete Industrial Building Using Friction Dampers Without Stopping Functionality

This paper presents a seismic retrofit of an industrial-type precast reinforced concrete building structure using friction dampers. This project consisted of retrofitting two precast reinforced concrete buildings, of which one of them will be presented here. Precast concrete is one of the most preferred methods of construction for industrial structures due to its low cost, fast construction and availability in rural areas. Unfortunately, most structures constructed before “Specification for Buildings to be Built in Seismic Zones(TBDY 2018)” are not sufficiently engineered and are expected to have poor performance when exposed to a major seismic event. Because stopping the production cost can be tolerated by the owners, a retrofitting technique that can be assembled during normal function of the industrial structures is required. As a result of this requirement, friction dampers are selected as the supplemental energy dissipation device. ASCE 41-17 [10] is employed for the damper design and performance evaluation of the building. Before the damper study, some instability and weak connection problems are solved by some traditional measures of strengthening. The most effective damper configuration and capacities are selected after an iterative trial-and-error linear study using the simplified methods developed by PROMER. Nonlinear push-over analysis are conducted after linear prestudies. Finally, a nonlinear time-history analyses is performed for confirmation of the results. , It is shown that the proposed retrofit scheme satisfies the desired performance goals for both DBE and MCE events. Overall, it is considered that proposed retrofit scheme with dampers provides the optimal solution for the stakeholders of the project from a performance, design, constructability, and economical point of view. Some application photos will be presented and methods are explained in detail in the paper. The friction damper behavior is based on the rotational friction hinge concept

Dynamic response characterization and simplified analysis methods for viscoelastic dampers considering heat transfer

AbstractViscoelastic (VE) dampers are sensitive to temperature, excitation frequency, and strain level. As they dissipate the kinetic energy from earthquake or wind‐induced structural vibrations, their temperature increases from the heat generated, consequently softening their VE materials and lowering their dynamic mechanical properties. Temperature increase can be significant for long‐duration loading, but can be limited by heat conduction and convection which depend on damper configuration. The writers analytically explored such effect on the six different dampers by using their previously proposed three‐dimensional finite‐element analysis method. Results provided better understanding of how heat is generated within the VE material, conducted and stored in different damper parts, and dispersed to the surrounding air. These results also led to characterization of both local (e.g., temperatures, properties, and strain energy density) and global (e.g., hysteresis loops, and stiffness) behavior of VE dampers, and provided a framework for a new simplified one‐dimensional (1D) modeling approach for time‐history analysis. This new proposed 1D method greatly improves the computation time of the previously proposed long‐duration method coupling fractional time‐derivatives VE constitutive rule with 1D heat transfer analysis. Unlike the previous method, it idealizes uniform shear strain and VE material property distributions for computational efficiency, but still simulating non‐uniform temperature distribution along the thickness direction of the VE material. Despite the approximations, it accurately predicts VE damper global responses.

Effects of Elastically Supported Boundaries on Flutter Characteristics of Thin-Walled Panels

In order to investigate flutter characteristics of thin-walled panels with elastically supported boundaries, a method for dealing with the stiffness matrix constraint relationship is developed based on penalty functions. Combined with the first-order piston theory, flutter velocities and frequencies of thin-walled panels with the different cases of elastically supported boundaries are calculated. Firstly, a thin-walled panel is discretized by the finite element method, and springs with real stiffness coefficients are introduced to simulate elastically supported boundaries. Then, the pressure difference between the outer and inner surfaces of the panel and modal aerodynamic expressions are obtained by introducing the first-order piston theory. Finally, flutter equations are obtained in the time domain by combining the structural dynamic equations with the modal aerodynamic forces. Subsequently, they are transformed to the frequency domain at the flutter state. Then, flutter characteristics of the panel are obtained using the U−g method. The results show that the existence of elastically supported boundaries may reduce the flutter velocity and flutter frequency of the panel but can be enhanced and recovered through some appropriate damping configuration schemes. Calculating the flutter characteristics of thin-walled panels under elastically supported boundaries can more accurately simulate real supported situations and result in a safer design scheme for thin-walled panel structures.

Development of natural rubber-bamboo biochar composites for vibration and noise control applications

The present study focuses on the utilization of bamboo biochar (BB) as a filler in natural rubber (NR) composites. This work is the first attempt to investigate the influence of BB loading on the vibration damping and acoustical properties of NR composites. NR-BB composites were prepared according to the ASTM D3182-21a standard. Vibration damping and acoustical properties were examined using the Obrest beam (ASTM E756-05) and four microphone impedance tube (ASTM E2611-19) methods. Noteworthy, the vibration damping ratio or system loss factor (ξ) obtained maximum for the fourth mode of vibration (NR- ξ = 33.19, NR/10BB- ξ = 17.46, and NR/20BB- ξ = 13.50) in the free layer damping (FLD) configurations. However, the sound transmission loss (STL) was enhanced by 8% and 11% compared to NR composites upon adding 10 and 20 phr of BB, respectively. In addition to vibration damping and STL, the loading of BB in the NR matrix positively influenced physical, mechanical, and thermal properties.

Modal Analysis of Non-Conservative Combined Dynamic Systems

Abstract The emergence of the use of mechanical metamaterials for vibration suppression and the creation of frequency gaps in structures require an understanding of the fundament underlying dynamics partial differential equations coupled to ordinary differential equations. Essentially periodic structures consist of a distributed parameter structure connected (embedded) to a series of spring-mass-dampers. Such systems in the past have been studied as combined dynamical systems. This work deals with the modal analysis of non-conservative combined dynamic systems formed by assembling distributed parameter structures and linear, viscously damped, lumped parameter oscillators. The mathematical model of the forced response of such dynamic systems is presented via differential operators. The related non-linear eigenproblem is formulated next and a proper solution is provided. Furthermore, the orthogonality of the eigenfunctions is studied and the completeness of the generated solution space is verified. Coupled modal coordinate differential equations result through modal analysis, thus revealing the non-proportional damping configuration, while the proportional damping conditions are also derived and discussed. The theory is applied to non-conservative Euler–Bernoulli beams subject to different types of boundary conditions and coupled to linear, viscously damped oscillators. A numerical example yields interesting conclusions about the non-proportionality and the applicability of the associated methods to solving the coupled differential equations.

Broadband Damping Properties of Particle Dampers Mounted to Dynamic Structures

BackgroundThe background of this work is the classification of the broadband properties of particle dampers (PDs). This broadband characteristic has experienced little systematic investigation in experiments.ObjectiveSo the primary objective of this paper is to find a measure to quantify the broadband damping properties of PDs. Also the demonstration of applicability to technical structures is a desired goal and the experiments provide a sound basis.MethodsThe methods for evaluating the performance of particle dampers and tuned mass dampers target the reduction of vibration amplitudes over the frequency range. The test bench consists of a mechanical frame structure with multiple eigenfreqencies up to 200 Hz harmonically excited with an electrodynamic shaker. From the differences in the dynamic behaviour the performance metric will be derived and evaluated.ResultsAs a result, a dynamic structure is set up as an effective test bench for different damper configurations. Differences of the tested concepts in regard to the dynamic behaviour over a wide frequency range are observed. From the experimental data a performance metric is deduced to quantify these differences.ConclusionThe conclusions drawn from this paper are, that PDs provide high damping over a wide frequency range. Furthermore, with a suitable performance metric this broadband damping properties can be quantified for the use in further development of PDs.

Effective configuration of perforated baffle plate for efficient slosh damping in liquid retaining tanks under lateral excitation

Perforated baffle plates are used as an anti-slosh mechanism in various fields owing to the need for slosh suppression and weight reduction. However, there is an uncertainty in the selection of configuration of perforated baffle plate due to the several influencing parameters for slosh damping efficiency. Therefore, the present study focuses on the development of an efficient slosh damping configuration for the perforated baffle plate. For this, nonlinear dynamic analysis under seismic ground motions with different PGA/PGV ratios has been carried out in the time domain using the concepts of Computational Fluid Dynamics (CFD) in the numerical models of liquid tanks with perforated baffle plates of different configurations. The response of the system under impulsive and convective modes is analysed by observing the free surface elevation, hydrodynamic pressure, turbulence kinetic energy and turbulence eddy dissipation as the response parameters. The study developed an effective baffle configuration for efficient slosh damping, considering the various response parameters.

Characterization of a magnetorheological fluid damper a review

Magnetorheological (MR) fluid technology has gotten a lot of attention in recent years, and as a result, it's become a lot better. Its adaptability has led to fast expansion in a variety of engineering applications, including base isolation of civil structures, car suspensions, and a variety of bio-engineering mechanisms, through its implementation in different MR fluid base devices, particularly in MR dampers. The MR damper is a sophisticated application of a semi-active device that reduces vibration efficiently in both on and off modes due to its control capabilities. The MR damper can create a high damping force while consuming very little power, responding quickly and flexibly, and being simple to build. In view of the rising demand for MR dampers, this paper examines the advantages of these semi-active systems over passive and active systems, the versatility of MR damper applications, and the fabrication of various MR damper configurations, as well as providing an overview of various MR damper models.

Acoustic black hole duct with damping material

Acoustic black holes have a tapering thickness profile to create the idealized phenomenon of zero reflection and transmission. The phenomenon entails wave propagation in an ideal medium where the profile tapers according to the power law shortening the wavelength and decreasing the wave speed. Consequently, the wave’s travel time tends to infinity so that the wave never reaches the end of the acoustic black hole and cannot be reflected or transmitted. For the application of a duct, thin annular rings of inner radii decrease with the power law to control pressure levels. An infinite number of rings and a final cross sectional area of zero is needed to create the ideal case and is impossible to manufacture. A common method to compensate for imperfections is to use damping material, such as in the experiment [El-Ouahabi et al, in International Conference InterNoise 2015 (2015)], though their results did not show that adding damping to the termination made an improvement. This work aims to find which areas of the acoustic black hole duct are most beneficial to add damping to in order to reduce the reflection and transmission coefficients by measuring the properties of different damping configurations. [Approved for Public Release Distribution Statement A.]

Experimental verification of electromagnetic multiple tuned mass dampers for energy harvesting and structural control

AbstractThis paper proposes electromagnetic (EM) multiple tuned mass dampers (MTMDs), hereafter referred to as EM‐MTMD system, for decreasing the vibration responses of high‐rise buildings under earthquake excitations. The EM damper substitutes the traditional fluid damper, enabling the proposed system to convert each TMD unit's vibration energy into electrical energy that can be harvested. Moreover, the system applies a rotary EM damper to ensure the energy dissipation device achieves a long stroke. Each TMD's damping coefficient can be easily adjusted without changing the EM damper configuration. We established a mathematical model of the EM‐MTMD system and derived its theoretical formula. Subsequently, we developed an optimal design method that considers inertance of EM damper for the EM‐MTMD system. For verifying the vibration control performance of the EM‐MTMD system, a model structure with long vibration period (3.53 s) and weight of 6 tons was manufactured to simulate the fundamental modal vibration of a 38‐story building. A prototype three‐unit EM‐MTMD system with a total mass ratio of 2% of the model structure was then designed and implemented to verify the system's dual functions of energy harvesting and vibration control. In shaking table tests, the EM‐MTMD system components were tested first; the model structure was then combined with the EM‐MTMD system and tested extensively to demonstrate the system's effectiveness in controlling the building structure's vibration and generating electrical energy under earthquake excitations. The test results indicated that the EM‐MTMD system can simultaneously decrease building responses effectively under real earthquake excitations and generate power.

Insights into instability of friction-induced vibration of multi-degree-of-freedom models

This study addresses a fundamental problem of linear friction-induced vibration (FiV), the intriguing role of damping on the instability of FiV in the form of mode-coupling. Two well-known classic 2-degree-of-freedom (DoF) slider-belt models are revisited, and a 4-DoF slider-belt model considering different damping configurations in the slider and the belt is investigated. Since proportional damping is very rare in reality, non-proportional damping is given much attention in this paper.Firstly, the analytical solutions of bifurcation boundary of the critical coefficients of friction of the classic 2-DoF models are derived, which show the subtle role of damping clearly and theoretically explain and clear misunderstandings and confusions on the phenomenon about the drop of the stability boundary from that of the undamped system caused by adding non-proportional damping. Secondly, a further increase of non-proportional damping is found to improve the stability and even bring higher degree of stability than increasing proportional damping (which is a new finding). Thirdly, the influences of the different damping distributions among the system components on the stability of the 4-DoF slider-belt model are explored. The evolution of the bifurcation boundary indicates the importance of the ratio of the horizontal to the vertical damping in the slider and in the belt. For some non-proportional damping values, the bifurcation boundary fluctuates, which could exhibit local optimal values of the ratio of damping in different directions of a system component and can be exploited in design against FiV. These findings are valid for general linear second-order dynamic systems with an asymmetric stiffness matrix.

Dynamic response of dry cask storage systems for spent nuclear fuel to near field blast loading

Dry storage casks are the most common form of spent nuclear fuel (SNF) storage in the United States. An explosion near a spent nuclear storage facility poses a serious public risk due to the potential of radioactive leakage. In this study, for the first time, the structural performance of vertical steel–concrete-steel sandwich (SCSS) and reinforced concrete (RC) casks under blast loading scenarios is studied using explicit finite element simulations considering material and geometric nonlinearity and strain rate effects. The response of the cask is investigated in terms of stress levels, deformations, and peak accelerations. The conventional weapons (CONWEP) model was used to induce a blast load on the structure at varying blast charges. The accelerations experienced by the canister and the fuel assemblies, which are critical for design are estimated. The inherent vibration damping characteristics of the cask are evaluated, and a novel damper configuration is proposed to improve the energy dissipation capacity of the system. The results showed that the general integrity of the cask could be preserved in the presence of a thick reinforced concrete layer. However, due to the lack of a damping mechanism, the blast wave can propagate through the system and result in very large accelerations in the canister and the fuel assemblies. Results also revealed that the SCSS configuration has a more ductile response compared to the RC design. The results of this study could be used for the safety evaluation and design optimization of current casks in service and other cylindrical composite containment structures.