Damping Behavior Research Articles

Simulation of van der Waals liquid droplets within a hot air atmosphere using the smoothed particle hydrodynamics method

The mass and heat transfer of van der Waals liquid droplets within a hot air atmosphere in microgravity have been studied using adaptive Smoothed Particle Hydrodynamics by assuming that the gas atmosphere is in contact with a thermal reservoir for a single-component two-dimensional system. A better definition of the diffuse interface between the phases was obtained through the introduction of a Korteweg tensor. As in previous works, the best initial particle distribution was obtained using the process of spinodal decomposition. The temperature obtained from the van der Waals cycle was compared with the temperature that arises from the integration of the conservation laws that contain the heat-flux vector. The calculated temperature profiles are the same for both the liquid and gas phases. The interface satisfies the condition of coexistence between the phases. In addition, the mass and heat transfer rates as well as the decrease of the drop radius were obtained for the three temperatures studied, finding that these are enhanced as the temperature of the reservoir is increased. Finally, it was possible to observe a damped oscillatory behavior of the temperature between the liquid phase and the interface for the first instants of time. We conclude that this is the mechanism by which the areas with lower temperature within the drop are heated before starting the mass transfer between the liquid and the gas phase.

Efficient Tumor Eradication at Ultralow Drug Concentration via Externally Controlled and Boosted Metallic Iron Magnetoplasmonic Nanocapsules.

With the aim to locally enhance the efficacy of cancer nanotherapies, here we present metal iron based magnetoplasmonic drug-loaded nanocapsules (MAPSULES), merging powerful external magnetic concentration in the tumor and efficient photothermal actuation to locally boost the drug therapeutic action at ultralow drug concentrations. The MAPSULES are composed of paclitaxel-loaded polylactic-co-glycolic acid (PLGA) nanoparticles partially coated by a nanodome shape iron/silica semishell. The iron semishell has been designed to present a ferromagnetic vortex for incorporating a large quantity of ferromagnetic material while maintaining high colloidal stability. The large iron semishell provides very strong magnetic manipulation via magnetophoretic forces, enabling over 10-fold higher trapping efficiency in microfluidic channels than typical superparamagnetic iron oxide nanoparticles. Moreover, the iron semishell exhibits highly damped plasmonic behavior, yielding intense broadband absorbance in the near-infrared biological windows and photothermal efficiency similar to the best plasmonic nanoheaters. The in vivo therapeutic assays in a mouse xenograft tumor model show a high amplification of the therapeutic effects by combining magnetic concentration and photothermal actuation in the tumor, leading to a complete eradication of the tumors at ultralow nanoparticle and drug concentration (equivalent to only 1 mg/kg PLGA nanoparticles containing 8 μg/kg of paclitaxel, i.e., 100-500-fold lower than the therapeutic window of the free and PLGA encapsulated drug and 13-3000-fold lower than current nanotherapies combining paclitaxel and light actuation). These results highlight the strength of this externally controlled and amplified therapeutic approach, which could be applied to locally boost a wide variety of drugs for different diseases.

An efficient approach to converting the damping fractal models to the traditional system

The general form of the damping fractal Duffing oscillator is considered in this investigation. In this work, the rank of the damping term is not restricted to half the rank of the inertia force. The classical solution of such fractal models cannot be available except for special cases. Due to the complicated fractal problem, a new approach is developed to make the solution available in each case. The approach depends on the idea of converting the fractal models to the equivalent ones in the traditional space. Numerical calculations showed that there is an agreement with the numerical solution when the fractal of the two scales becomes identical to the continuous space. The calculations showed that the decrease in the rank of the inertia force yields a damping behavior, while the decrease in the rank of the damping force leads to suppression of the damping influence of the inertia force. Further, some stability diagrams are plotted to study the stability behavior.

A Higher-Order Galerkin Time Discretization and Numerical Comparisons for Two Models of HIV Infection.

Human immunodeficiency virus (HIV) infection affects the immune system, particularly white blood cells known as CD4+ T-cells. HIV destroys CD4+ T-cells and significantly reduces a human's resistance to viral infectious diseases as well as severe bacterial infections, which can lead to certain illnesses. The HIV framework is defined as a system of nonlinear first-order ordinary differential equations, and the innovative Galerkin technique is used to approximate the solutions of the model. To validate the findings, solve the model employing the Runge-Kutta (RK) technique of order four. The findings of the suggested techniques are compared with the results obtained from conventional schemes such as MuHPM, MVIM, and HPM that exist in the literature. Furthermore, the simulations are performed with different time step sizes, and the accuracy is measured at various time intervals. The numerical computations clearly demonstrate that the Galerkin scheme, in contrast to the Runge-Kutta scheme, provides incredibly precise solutions at relatively large time step sizes. A comparison of the solutions reveals that the obtained results through the Galerkin scheme are in fairly good agreement with the RK4 scheme in a given time interval as compared to other conventional schemes. Moreover, having performed various numerical tests for assessing the efficiency and computational cost (in terms of time) of the suggested schemes, it is observed that the Galerkin scheme is noticeably slower than the Runge-Kutta scheme. On the other hand, this work is also concerned with the path tracking and damped oscillatory behaviour of the model with a variable supply rate for the generation of new CD4+ T-cells (based on viral load concentration) and the HIV infection incidence rate. Additionally, we investigate the influence of various physical characteristics by varying their values and analysing them using graphs. The investigations indicate that the lateral system ensured more accurate predictions than the previous model.

Structural dynamic vibration absorber using a tuned inerter eddy current damper

The advantages of eddy current dampers over conventional fluid dampers include the ability to produce resistive forces with no contact between the components wherein damping forces are generated, resulting in a less degradable mechanism. Thus far, the apparent mass effect, referred to as inertance, in an eddy current damper employing rotational motion has not been intentionally applied for vibration control. Therefore, this paper proposes utilizing the inertance effect in an inerter eddy current damper (IECD) to construct a dynamic vibration absorber for the seismic protection of civil structures, termed as the tuned inerter eddy current damper (TIECD). The IECD consists of a ball screw, a conductor, permanent magnets, and a back iron. The gravitational mass of the back iron disk is converted into inertance via the ball-screw mechanism, which amplifies the mass and damping effects of the rotational disk and eddy current, respectively, by converting low-speed translational motion into high-speed rotational motion. An analytical method based on the separation of variables is applied to estimate the eddy current damping force of the IECD at different velocities. Concurrently, a succinct damping model is developed to capture the mechanical behavior of the nonlinear eddy current damping. A series of dynamic tests using a small-scale prototype IECD is then conducted to confirm the feasibility and accuracy of the proposed numerical damping model. Next, an equivalent damping coefficient for eddy current damping is derived under harmonic excitation. Based on a combination of the fixed-point method, the equivalent damping coefficient of the IECD, and complex eigen analysis, an optimal design method for the TIECD is developed. Finally, the effectiveness of the proposed TIECD is validated through a shake table test and a numerical simulation.

Enhanced Dynamic Performance in Hybrid Power System Using a Designed ALTS-PFPNN Controller

The large-scale, nonlinear and uncertain factors of hybrid power systems (HPS) have always been difficult problems in dynamic stability control. This research mainly focuses on the dynamic and transient stability performance of large HPS under various operating conditions. In addition to the traditional synchronous power generator, wind-driven generator and ocean wave generator, the hybrid system also adds battery energy storage system and unified power flow controller (UPFC), making the system more diversified and more consistent with the current actual operation mode of the complex power grid. The purpose of this study is to propose an adaptive least squares Petri fuzzy probabilistic neural network (ALTS-PFPNN) for UPFC installed in the power grid to enhance the behavior of HPS operation. The proposed scheme improves the active power adjustment and dynamic performance of the integrated wave power generation and offshore wind system under a large range of operating conditions. Through various case studies, the practicability and robustness of ALTS-PFPNN method are verifying it by comparison and analysis with the damping controller based on the designed proportional integral differential (PID) and the control scheme without UPFC. Time-domain simulations were performed using Matlab-Simulink to validate the optimal damping behavior and efficiency of the suggested scheme under various disturbance conditions.

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

Performance Improvement of Innovative Shear Damper Using Diagonal Stiffeners for Concentrically Braced Frame Systems

Although concentrically braced frame (CBF) systems enjoy high elastic stiffness and lateral strength, they show a low seismic energy absorption capacity. This dilemma is due to the buckling of CBFs’ diagonal members under compressive loading. To overcome the shortcoming, researchers have proposed the use of dampers to improve the behavior of CBF systems. Among the proposed dampers, the metallic shear damper is the most popular thanks to its suitable performance as well as its economic profit. The main shortcoming of the shear dampers is low stiffness. Therefore, in this article, an innovative approach is proposed to improve the behavior of the shear dampers. Subsequently, strengthening the shear damper with X-stiffeners is proposed, and its behavior is evaluated numerically and parametrically. Results indicate that by adding the X-stiffeners, the ultimate strength and elastic stiffness of the shear dampers are enhanced considerably. However, the properties of the stiffeners do not impact the stiffness in the nonlinear zone. Moreover, the behavior of the dampers is affected by parameters such as the ratio of the strength of the web plate to the flange plates, the ratio of the X-stiffeners to the flange plates, and the ρ factor. To consider the parameters to predict the behavior of the damper, required equations are proposed which demonstrate a good agreement with finite element results.

NBR/CR‐Based High‐Damping Rubber Composites Containing Multiscale Structures for Tailoring Sound Insulation

AbstractHigh‐damping acoustic composites with unique sound insulation feature is reported, demonstrating surprisingly stable soundproof properties over a wide bandwidth of frequency (63–6300 Hz) with good mechanical properties. The extraordinary acoustic properties are attributed to the multiscale synergy of lamellar and hollow structures by multifillers adding. The acoustic composites are designed and fabricated through a low‐temperature one‐time rubber mixing process using nitrile butadiene rubber(NBR), chloroprene rubber (CR) as matrix and mica powder (MP), hollow glass beads (HGB), and montmorillonite (MMT) as multifillers. The soundproof mechanism is discussed in detail. Results indicate that the synergism of damping and sound absorption behaviors in the composition has a considerable impact on the acoustic characteristics, which can be controlled by the blending ratio of NBR/CR matrixes and the multiscale structures of MP/HGB/MMT multifillers. The designed multifillers acoustic composites can adapt to broadband engineering noise control including walls in express train constructions, panels of vessel or aircraft cabins, and large transportation pipelines.

Kinematic model of bulk acoustic wave antenna considering magnetic damping

The bulk acoustic wave (BAW) antenna suffers from eddy current loss as well as magnetic damping loss, which are important factors affecting the performance of the antenna. The Lorentz force generated from piezomagnetic layer during the radiation process of BAW antenna is solved based on the eddy current loss model constructed previously. Then a kinematic model of BAW antenna considering magnetic damping is constructed by introducing the acoustic resonance model. A finite element analysis (FEA) model for magnetic damping behavior of BAW antenna is developed to verify the analytical model. The results from the numerical simulation and the theoretical calculation are in good agreement, which verifies both the analytical model and FEA modeling method. Finally, the resonant displacement of BAW antenna with different thickness ratios of piezoelectric and piezomagnetic layers is studied by the verified kinematic model. It is found that the antenna has the maximum resonant displacement when the thickness ratio is 1:1.

On the experimental scaling and power dissipation of violent sloshing flows

Violent and vertical sloshing flows appear when the fuel tanks of aircraft wings are shaken by air gusts or turbulence. The liquid slosh inside of the tank significantly damps the wing vibrations and its behaviour is still not fully understood. In this paper a simplified version of the problem is tackled, presenting the results obtained in an experimental campaign that investigates the scaling effects and the influence of the most relevant non-dimensional numbers of the problem. Single degree of freedom (SDOF) Froude scaled decay tests are devised in order to study the vertical sloshing problem in an aerospace context establishing relations between the slosh induced damping ratio and three of the most relevant non-dimensional numbers, namely the filling level, density ratio and initial amplitude. The experimental results indicate a maximum damping for a 50% fill level and a positive relationship between the damping ratio with the density ratio. The initial amplitude also increases with the damping ratio up until a threshold amplitude after which the damping starts to decrease. A clear explanation of the liquid induced damping ratio behaviour, confirmed for the three selected scales, is given in terms of two magnitudes: the sloshing force intensity and the phase-shift between this force and the tank motion. These two magnitudes are the key elements behind the physical interpretation of the liquid dissipation in the problem.Finally, the power dissipated by the liquid is calculated and correlated with the liquid slosh damping ratio, the sloshing force intensity and the phase-shift. This correlation shows an equivalency of the damping ratio with the dissipated power.

Characterization of the Fluid Damping in Simplified Models of Pump-Turbines and High Head Francis Runners

In order to satisfy the power demand in the electrical grid, hydraulic turbine units frequently work under off-design operation conditions and pass through transient events. These operation conditions can lead to high vibration amplitudes in the turbine runners, decreasing their useful life, and in some cases to premature failures. To determine and to understand the behaviour of the fluid damping is a relevant topic, because this parameter limits the maximum amplitude in resonance conditions. The runner of some types of turbines, such as reversible pump-turbine and high head Francis turbine, can be modelled as a disk-like structure, due to their similar mode shapes. Because of this, in this work, the fluid damping of a vibrating disk was studied. The disk was submerged in water and was put in a resonant state at different vibration amplitudes. Moreover, this structure was excited at different distances to a rigid surface, in order to analyse the effects of the distance between the runner and the casing. The main effects on the fluid damping were determined and characterized, showing a dependency of the fluid damping ratio on the different parameters.

Symbolic Deep Learning for Structural System Identification

Closed-form model expression is commonly required for parametric data assimilation (e.g., model updating, damage quantification, and so on). However, epistemic bias due to fixing the model class is a challenging issue for structural identification. Furthermore, it is sometimes hard to derive explicit expressions for structural mechanisms such as damping and nonlinear restoring forces. Although existing model class selection methods are beneficial to reduce the model uncertainty, the primary issue lies in their limitation to a small number of predefined model choices. We propose a symbolic deep learning framework that alleviates the constraint of fixed model classes and lets the data more flexibly determine the model type and discover the symbolic invariance of the structural system. A design principle for symbolic neural networks has been developed to leverage domain knowledge and translate data to flexibly symbolic equations of motion with a good predictive capacity for new data. A two-stage model selection strategy is proposed to conduct adaptive pruning on network and equation levels by balancing the model sparsity and the goodness of fit. The proposed method’s expressive strengths and weaknesses have been analyzed in several numerical case studies, including systems with nonlinear damping, restoring force, and chaotic behavior. Results from an experimental case study revealed the potential of the proposed method for flexibly interpreting hidden mechanisms for real-world applications. Finally, we discuss necessary improvements to transfer this computational method for practical applications.

Component Test, Fracture Simulation and Experimental Study on Steel and Shear Panel for Seismic Resistance

AbstractThis paper summarizes the experimental campaign carried out for the development of a new steel energy dissipative devices named Slit Dampers (SDs) designed for earthquake protection of structures. SDs consist in shear steel plates with appropriately shaped cut‐out portions of material for allowing maximum spread of plastic deformation along the device and then maximizing the hysteretic dissipative behavior. A total of eighty‐two steel shear plates with different openings and thicknesses are tested to investigate their behavior under cyclic pseudo‐static loading. Six types steel shear plates are studied, including the SD with narrow slits that divide the plate into rectangular links, and the butterfly fuse with a diamond‐shaped opening that create butterfly shape links in the plate. Other varying test parameters are: loading rate, material strength, and the number of in‐parallel damper elements. It is expected that the proposed model can be successfully used to predict the behavior of dampers in real‐world applications.

Vibration and noise analysis of acetoxime modified TiO2 coating over steel alloy

The analysis of vibration over coated sample is required to investigate the vibration and noise damping behaviors of coatings. In this research work, conventional gun spray method is used to coat oxime modified titanium (IV) isopropoxide on steel to find out damping behaviour of coating. The most conventional method modal analysis is used to measure vibration and noise damping of bare and titania coated samples. During vibration test it was observed that a thin coating has improved the vibration and noise damping when compare with bare sample. The surface morphology of coated samples analysis by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX) and Atomic Force Microscopy (AFM) revealed that the coating thickness and composition of coating. The results shows that the modified TiO2 coating deposited over steel alloy by gun spry method is uniform, homogenous, crack free, and having high vibration damping behavior.

In situ damping identification of plant fiber composites using dynamic grid nanoindentation

Damping properties of plant fiber composites have been quite widely investigated based on macroscale techniques. Considering their heterogeneous and hierarchical microstructure, it is also necessary to study their damping behavior at the microscale to provide better insight into the dissipation origins and mechanisms. This article proposes a characterization of the dynamic mechanical properties of flax/GreenPoxy composites at microscale using dynamic grid nanoindentation technique. Two loading protocols are used: the classical Continuous Stiffness Measurement method (CSM) and a new method called Constant Amplitude Measurement method (CAM). Results show experimental protocols (CAM or CSM) do not have significant effect on storage modulus while they significantly affect the loss factor. The grid nanoindentation technique also provides an interesting map of the viscoelastic properties at the microscale in the cross-section of the composites and the damping contribution of the various components are highlighted.

Damping of micro- and nanocellulose reinforced PA610 composites and influences of moisture absorption

Composites consisting of bio-based polyamide 610 (PA610) reinforced with micro- and nano-cellulose were manufactured by melt compounding followed by injection molding. The resulting composites had fiber sizes ranging from nanoscale to 100 µm at 2.5 %, 5 % and 10 % fiber mass fractions. These composites were mechanically characterized by tensile tests followed by scanning electron microscopy to examine the tensile fracture surface. The primary focus of the work was the damping behavior of these nanocomposites, which was found to be substantial. Damping was characterized using the damping ratio extracted from the measured decay of mechanical vibrations. Cellulose nanocrystal-reinforced PA610 at 10 % mass fraction was found to produce a 210 % increase in damping ratio compared to control PA610. Larger fiber sizes and lower mass fractions resulted in smaller, but significant, increases in damping. Comparison to cellulose reinforced polypropylene composites showed that PA610/cellulose composites produced significantly greater relative damping. Additionally, since both cellulose and PA610 are hydrophilic materials, a study was made on the effects of moisture absorption on the damping. It was found that the pronounced effect of the filler on damping was diminished by absorbed moisture and did not return after removing moisture from the samples. The origin of the damping increase and the effects of moisture were discussed in the article.

Kathmandu Basin as a local modulator of seismic waves: 2-D modelling of non-linear site response under obliquely incident waves

SUMMARYThe 2015 Mw 7.8 Gorkha, Nepal earthquake is the largest event to have struck the capital city of Kathmandu in recent times. One of its surprising features was the frequency content of the recorded ground motion, exhibiting a notable amplification at low frequencies (<2 Hz) and a contrasting depletion at higher frequencies. The latter has been partially attributed to the damper behaviour of the Kathmandu basin. While such weak high-frequency ground motion helped avoiding severe damage in the city, the catastrophic outcomes of earlier earthquakes in the region attest to a contrasting role of the Kathmandu basin as a broad-band amplifier, in addition to possible source effects. Given the possibility of future strong events in the region, our main objective is to elucidate the seismic behaviour of the Kathmandu basin by focusing on site effects. We numerically model 2-D P–SV wave propagation in a broad frequency band (up to 10 Hz), incorporating the most recent data for the Kathmandu basin geometry, soil stratigraphy and geotechnical soil properties, and accounting for the non-linear effect of multidimensional soil plasticity on wave propagation. We find that: (1) the Kathmandu basin generally amplifies low frequency ground motion (<2 Hz); (2) waves with large incidence angles relative to vertical can dramatically amplify the high frequency ground motion with respect to bedrock despite the damping effect of soil non-linearity and (3) the spatial distribution of peak ground motion amplitudes along the basin is highly sensitive to soil non-linearity and wave incidence (angle and direction), favouring larger values near the basin edges located closer to the source, as observed during the 2015 event. Our modelling approach and findings can support the ongoing resilience practices in Nepal and can guide future seismic hazard assessment studies for other sites that feature similar complexities in basin geometry, soil stratigraphy and dynamic soil behaviour.

An Investigation on Energy Harvesting Behavior of an Array Piezoelectric Coupled Disc Damper.

In order to make full use of the vibration energy in the process of attenuating vibration, an array piezoelectric coupled disc damper is developed, which works by converting part vibration energy into electrical energy. The piezoelectric damper is made of a pair of piezoelectric coupled discs built in a case cylinder. Its energy harvesting behavior is studied by a series of forced-vibration experiments and simulations. The influences of some factors, such as the excitation frequency, substrate thickness, the size of the piezoelectric patch, the paste form of the piezoelectric patch and the load resistance, on the energy harvesting behavior of the damper are analyzed and concluded. The experimental results show that the maximum peak-to-peak voltage and average power from one piezoelectric patch with an inner diameter of 35 mm, an outer diameter of 80 mm, and a thickness of 1 mm can reach up to 163 V and 161 mW, respectively. This research provides a practical piezoelectric damper attenuating harmful vibration by converting them into useful electric power, and the corresponding theoretical models are derived to predict its electrical output.

Analysis of size effects on thermoelastic damping in the Kirchhoff’s plate resonator under Moore–Gibson–Thompson thermoelasticity

Nanoresonators with ultra-high resonant frequency have found useful applications as electromechanical systems in today’s time. This current work presents an analytical technique for measuring thermoelastic damping (TED) and dynamic behavior of micro/nano Kirchhoff plate resonators using Moore–Gibson–Thompson (MGT) generalized thermoelasticity theory. Modified couple stress theory (MCST) is employed here to take into account the size effect for micro/nano plate. This work comprehensively evaluated the frequency shift and normalized attenuation in the micro plate resonator in the frame of the recently introduced MGT thermoelasticity theory to obtain the closed-form analytical expression for quality factor (QF). The outcomes are compared with the corresponding results of classical continuum theory and classical thermoelasticity theory. Finally, the influence of various parameters including size effects on TED in micro plate resonators has been investigated by carrying out the numerical computation of the present analytical results for different materials. Several important points are highlighted.