Damping Forces Research Articles

Effect of Damping Modeling and Characteristics on Seismic Vulnerability Assessment of Multi-Frame Bridges

ABSTRACT Rayleigh damping is a common method used to model energy dissipation in bridges, but improper damping modeling can develop spurious damping forces and lead to inaccurate results for dynamic analysis and seismic vulnerability assessment. The Rayleigh damping matrix contains mass-proportional and stiffness-proportional parts. To reduce or eliminate possible spurious forces, previous studies suggested using stiffness-proportional damping only and/or using the updated tangent stiffness matrix of the structure instead of the initial stiffness for the Rayleigh damping. The objective of this article is to study the effect of different damping modeling techniques and characteristics on the seismic response of multi-frame box-girder bridges and the resulting fragility curves for vulnerability assessment. Nonlinear time history analysis and incremental dynamic analysis are performed using 3D OpenSees bridge models to develop system and component fragility curves for different damping modeling scenarios. Different sources of uncertainties as related to earthquakes, structural geometries, and material properties are considered. The changes in fragility curves and median fragilities due to the different damping modeling scenarios are discussed. Confidence bounds for the developed fragility curves are presented as well to better understand the effect of damping on the developed fragility curves.

Design of Permanent-Magnet Linear Generators with Constant-Torque-Angle Control for Wave Power

This paper presents a simulation method for direct-drive permanent-magnet linear generators designed for wave power. Analytical derivations of power and maximum damping force are performed based on Faraday’s law of induction and circuit equations for constant-torque-angle control. Knowledge of the machine reactance or the load angle is not needed. An aim of the simulation method is to simplify comparison of the maximum damping force, losses, and cost between different generator designs at an early design stage. A parameter study in MATLAB based on the derived equations is performed and the effect of changing different generator parameters is studied. The analytical calculations are verified with finite element method (FEM) simulations and experiments. An important conclusion is that the copper losses and the maximum damping force are mainly dependent on the rated current density and end winding length. The copper losses are inherently large in a slow-moving machine so special consideration should be taken to decrease the end winding length. It is concluded that the design of the generator becomes a trade-off between material cost versus high efficiency and high maximum damping force.

Experimental and Analytical Investigation of Short Squeeze-Film Damper (SFD) Under Circular-Centered Orbit (CCO) Motion

Modern rotating machines operate at higher shaft speeds, crossing a few bending critical speeds, which often induce large dynamic loads on the bearing supports that may increase the rotor orbital whirl motion. Accurate prediction of squeeze-film damper (SFD) forces is the key issue for designers to arrive at a suitable design. An experimental setup was developed with eccentric shaft to find the damper forces. Submerged type damper with relatively large clearance was considered for the present work. It results in higher gap Reynolds number (Re) which varies from 1.5 to 15 in the present case. Four force sensors are used to measure the damper forces and two eddy current probes were used to measure the damper orbit. Circular-centered orbit (CCO) of eccentricity ratio (e) 0.176 was used in the present work. Theoretical modeling of SFD forces is considered with viscous, inertial, temporal contributions under laminar and turbulent conditions. Modified Reynolds equation with short damper approximation is used to derive the SFD forces for 2π- film. Fourier coefficients of measured forces and displacements are estimated and used to extract the 1× components and phase information. Radial and tangential forces were calculated from the measured total forces to find the contributions of viscous and inertial forces. Experimental forces are compared with theoretically predicted forces and they are in good agreement with the experimental results.

Innovative adaptive viscous damper to improve seismic control of structures

In this paper, a new adaptive viscous damper (AVD) is proposed and required equations are developed to describe its mechanical behavior. As opposed to conventional adaptive devices, the proposed damper is capable of adapting its own mechanical properties without any need for other devices such as sensors, processing unit, actuators, energy supplies, and wired or wireless connections. Eliminating such equipment not only reduces costs, but also removes related time lag and improves the efficiency of the control system. The proposed AVD includes a cylinder filled with viscous fluid and a piston with a nozzle at its head. The passing area of the nozzle is variable and as a result, the device can cover a range of damping coefficients. For non-extreme excitations, the damping coefficient is relatively small and consequently the damping force is reduced. Conversely, when extreme movements occur, the nozzle contracts a bit and generates relatively large control forces in order to protect the main structure efficiently. The mechanical model of the AVD is created in OpenSees and the damper is implemented in a two-story building example subjected to different earthquake records. The results show that compared to a typical viscous device, the proposed AVD can reduce the mean values of displacement, acceleration, and base shear by up to 52.5, 62.9, and 44.4% and increase the energy dissipation by up to 94.3% for extreme cases. Moreover, for non-extreme cases, the AVD shows a more flexible behavior and reduces the unfavorable damping forces.

Long Slender Piezo-Resistive Silicon Microprobes for Fast Measurements of Roughness and Mechanical Properties inside Micro-Holes with Diameters below 100 µm

During the past decade, piezo-resistive cantilever type silicon microprobes for high-speed roughness measurements inside high-aspect-ratio microstructures, like injection nozzles or critical gas nozzles have been developed. This article summarizes their metrological properties for fast roughness and shape measurements including noise, damping, tip form, tip wear, and probing forces and presents the first results on the measurement of mechanical surface parameters. Due to the small mass of the cantilever microprobes, roughness measurements at very high traverse speeds up to 15 mm/s are possible. At these high scanning speeds, considerable wear of the integrated silicon tips was observed in the past. In this paper, a new tip-testing artefact with rectangular grooves of different width was used to measure this wear and to measure the tip shape, which is needed for morphological filtering of the measured profiles and, thus, for accurate form measurements. To reduce tip wear, the integrated silicon tips were replaced by low-wear spherical diamond tips of a 2 µm radius. Currently, a compact microprobe device with an integrated feed-unit is being developed for high-speed roughness measurements on manufacturing machines. First measurements on sinusoidal artefacts were carried out successfully. Moreover, the first measurements of the elastic modulus of a polymer surface applying the contact resonance measurement principle are presented, which indicates the high potential of these microprobes for simultaneous high-speed roughness and mechanical parameter measurements.

Magnetic accumulation of kinetic energy from a reciprocating mechanical system for a dynamic behaviour improvement

This paper presents a magnetic means of accumulating kinetic energy from a traversing rod (TR) used to guide yarn during winding processes on rotor spinning machines. A passive magnetic system for accumulating kinetic energy at the reversal points of reciprocating motion is introduced, and its unique repulsive magnetic force is described in relation to the specific traversing-motion characteristic. The magnetic damping force phenomenon and preconditions for its application in the machine are also defined and discussed. We also show magnetic field optimisation by means of pole-piece geometry modification to obtain a magnetic force characteristic that closely approximates the required motion characteristic. Thus, the efficiency of kinetic-energy accumulation at the reversal points of the reciprocating motion of the TR is increased. The utilisation of an eddy-current effect on the accumulator body to apply the magnetic-damping phenomenon for vibration reduction is also described. The results of this work demonstrate the promise of the system using modern rare-earth compound-based magnets applicable not only to the studied traversing system but also to various mechanical devices as a non-contact means of reducing deformation and vibration. The developed and experimentally verified mathematical models presented here represent a useful tool for further optimisation of specific applications in the field of mechanics.

Design and Modeling for 2D Plate Type MR Damper

A two-dimensional magnetorheological damper is developed for the two-dimensional damping requirement in the engineering. The velocity and pressure distribution model of the two-dimensional plate-type damper, also the damping force calculation model are established based on the Navier-Stokes equation. The structural physical parameters are analyzed in theory including the working gap δ, the length a and the width a of the middle slide plate. Experiments have been done to test the damping performance of the two-dimensional plate-type magnetorheological damper on the two-dimensional vibration test-bed, and the effect of the excitation current on the damping performance is analyzed. The experimental results show that the influence of Coulomb damping force on the damping force of magnetorheological damper is great when the appropriate magnetorheological fluid is used. The damping force of magnetorheological damper becomes larger with the increase of excitation current, and the system amplitude is gradually reduced, the maximum reduction of 2.5956 times. It’s confirmed that the design of the two-dimensional plate-type magnetorheological damper is reasonable.

Numerical calculation and experiment of a heaving-buoy wave energy converter with a latching control

Latching control was applied to a Wave Energy Converter (WEC) buoy with direct linear electric Power Take-Off (PTO) systems oscillating in heave direction in waves. The equation of the motion of the WEC buoy in the time-domain is characterized by the wave exciting, hydrostatic, radiation forces and by several damping forces (PTO, brake, and viscous). By applying numerical schemes, such as the semi-analytical and Newmark B methods, the time series of the heave motion and velocity, and the corresponding extracted power may be obtained. The numerical prediction with the latching control is in accordance with the experimental results from the systematic 1:10-model test in a wave tank at Seoul National University. It was found that the extraction of wave energy may be improved by applying latching control to the WEC, which particularly affects waves longer than the resonant period.

Semi-Active Fluid Viscous Dampers for Seismic Mitigation of RC Elevated Liquid Storage Tanks

The effectiveness of the semi-active control strategies using fluid viscous dampers (SAFVDs) for seismic mitigation of reinforced concrete (RC) elevated liquid storage tanks is investigated. Three control algorithms are employed for regulating the damping coefficient of the SAFVDs: (1) Passive-OFF, (2) Passive-ON, and (3) Clipped Optimal Control (COC). The uncontrolled response of the tank is compared with those installed with SAFVD of different control algorithms. Focus is also placed on various positions of the dampers, viz., dampers installed at alternate levels (Configurations I, II, IV, and V) and at all levels (Configurations III and VI) of the staging. A discrete two-mass model for the liquid and multi-degree-of-freedom system for the staging, installed with the dampers, is developed for the RC elevated liquid storage tanks. The response of the broad and slender tanks is studied, for which the ratios of the height of the liquid to the radius of the container are 0.5 and 2.0, respectively. The time-history response of the elevated tank is evaluated for eight different earthquake ground motions, including near- and far-field earthquakes. A MATLAB code was developed to solve the coupled differential equations of motion of the system using the state-space approach. Key parameters, viz., convective displacement, rigid mass displacement, base shear, overturning moment, and damper force, are evaluated. The results show that all the control systems considered herein are beneficial in reducing the seismic responses. The frequency response function for the uncontrolled and semi-actively controlled liquid storage tank in frequency domain exhibits significant response reduction, highlighting the effectiveness of the SAFVDs. The structural response is effectively controlled using the SAFVDs with Passive-OFF (valve closed) and COC algorithms. The COC algorithm employed in this study is a promising candidate for the seismic mitigation of RC elevated liquid storage tanks using the semi-active control.

Dynamic modeling and analysis of a quad horizontal damper system for transient vibration reduction in top loading washing machine

The transient horizontal vibration of top loading washing machine with large capacity has been more important because of the radius of the inner tub in the washing machine increases proportionally. In this paper, we introduce a new vibration reduction technology, namely, a quad horizontal damper system for reduction of the transient horizontal vibration of top loading washing machine. And analyzes the vibration characteristics of a top loading washing machine with a quad horizontal damper system using Newtonian mechanics. For verification and validation of the established dynamic model, the displacement of an actual top loading washing machine are obtained from six laser sensors attached at the upper part and the lower part of outer tub respectively. Optimal design was carried out to ensure sufficient strength and reliability for each component of the horizontal damper. The damping force of the horizontal damper was also optimized so that the horizontal vibration in the transient state of top loading washing machine was reduced by about 35~45 % more than the conventional top loading washing machine and no abnormal noise was generated at high spin speed.

Semi-active Control to Reduce Lateral Vibration of Passenger Rail Vehicle Using Disturbance Rejection and Continuous State Damper Controllers

In this paper, Bouc–Wen type magnetorheological fluid damper has been used to monitor the ride quality of a prevailing rail vehicle in lateral vibrations. Modelling of the rail vehicle is done in such a manner that it has an entire 9 degrees of freedom by significant considerations of lateral, roll and yaw motions of the car body, rear, and the front chassis. 200 km/h is considered as train speed for tracks with two varying disturbances. A system consisting of multibody in VI-rail software is provided by a track input and ergo, wheel response it obtained. SIMULINK (software) is responsible for the representation of the motions of the wheel as mathematical models. Two different types of analysis are done firstly with conventional passive lateral damper and secondly with semi-active MR lateral damper in subordinate suspension. To diminish lateral vibrations, the disturbance refusal and non-stop state controller algorithms were executed to manage the damper force. Results acquired are in the form of acceleration and displacement of the center of mass of the body under consideration is done by comparing in terms of reduction indices of their vibrations. A significant improvement in the index is seen in which a semi-active lateral damper is mounted. The results show that the proposed system significantly improves both, the vibration attenuation ability and the ride quality of the vehicle.

Effects of design and seismic parameters on horizontal displacement responses of sloped rolling‐type seismic isolators

The influences of design parameters, including sloping angles of bearing plates and friction damping forces, together with seismic parameters, including corner periods and effective peak accelerations that are usually used for characterizing a design response spectrum, on the maximum horizontal displacement responses of sloped rolling-type seismic isolators are numerically discussed in this study. Because the seismic isolators feature the constant acceleration control (or zero postelastic stiffness) performance, the equivalent linear model conventionally adopted in the equivalent lateral force procedure might not be adequate for predicting their maximum horizontal displacement response under a given seismic demand. Therefore, considering a small number to a large number of coefficients, several statistics-based empirical formulas that are able to approximate their maximum horizontal displacement response are proposed. Not only the accuracy but also the conservative property of the proposed empirical formulas are discussed by comparing their predictions with the nonlinear response history analysis results. To efficiently determine the horizontal displacement capacity of sloped rolling-type seismic isolators during the preliminary design stage, the statistics-based empirical formula considering a reasonable number of coefficients is recommended.

Adaptive Structural Control of Floating Wind Turbine with Application of MR Damper

Abstract Floating wind turbine has become the most promising technology for deep-sea wind power generation. Therefore, some means to reduce the structural load for stabilizing the wind turbine has been developing. In this paper, a semi-active structural control is realized by replacing the damper in passive TMD with the magnetorheological (MR) damper. The damping force of the MR damper can be changed by altering the voltage applied to it. A simple and convenient control method is designed, which includes adaptive control force design and retrogression controller. The simulation results show that the semi-active control method has a good damping effect, which mitigates much of the structural load with respect to the passive structural control.

Study of vertical seismic isolation technique with nonlinear viscous dampers for lateral response reduction

In a vertical seismic isolation (VSI) system, an individual structure is partitioned in a vertical isolation plane into two dynamically different substructures interconnected by a mechanism. In this way, response reduction is expected in each substructure when compared to the original non-partitioned structure. In this study, the features of an SDOF with nonlinear viscous dampers (NVDs) subjected to harmonic loading have first been investigated, and a criterion has been proposed for evaluating their seismic behavior by comparing to that of linear viscous damper (LVD) based on damper force capacity. Then, by using a set of earthquakes with a wide range of dominant periods, and conducting a series of nonlinear time history analyses, the application of NVDs in the VSI has been thoroughly studied in regard to substructure displacement and acceleration response reduction. In these analyses, the interaction effect of isolation ratios and link parameters on response control of the VSI system was explored. The investigation of NVDs was carried out equating the viscous damper force in different velocity exponents with the corresponding LVD. Results did not indicate a preferable performance of NVDs over an LVD. Yet, employing appropriate link parameters proportional to mass and stiffness ratios could lead to satisfactory levels of seismic response reduction in cases of both types of dampers.

Real-time Damper Force Estimation of Vehicle Electrorheological Suspension: A NonLinear Parameter Varying Approach

This paper proposes a nonlinear parameter varying (NLPV) observer to estimate in real-time the damper force of an electrorheological (ER) damper in road vehicle suspension system. First, a nonlinear quarter-car model equipped with the dynamic nonlinear model of ER damper is presented, which captures the main behavior of the suspension system. The estimation method of the damper force is developed using a NLPV observer whose objectives are to minimize the effects of bounded unknown road profile disturbances and measurement noises on the estimation errors in the H∞ framework. Furthermore, the nonlinearity coming from damper model (and considered in the observer formulation) is handled through a Lipschitz condition. The observer inputs are given by two low-cost sensors data (two accelerometers data from the sprung mass and the unsprung mass). For performance assessment, the observer is implemented on the INOVE testbench of GIPSA-lab (1/5-scaled real vehicle). Both simulation and experimental results demonstrate the effectiveness of the proposed observer in terms of the ability of estimating the damper force in real-time and of minimizing the effects of measurement noises and road disturbances.

Analitycal study of viscous damper parameters at a simple reinforced concrete frame

The energy dissipation process in the structure is caused by the earthquake load can be done by using bracing, base isolation and damper system. Damper is a device that is able to transform one form of energy into another form of energy. When a structure is experiencing vibration then the damper system can transform the energy from mechanical energy to other forms of energy. Viscous damper gives the damper force highly determined by the damping coefficient and relative velocity. In determining the capacity of the viscous damper is strongly influenced by several parameters of the damper consisting of the period of natural structure (T), damping coefficient (C), stiffness (K), relative velocity (V), and relative velocity coefficient (α). So that viscous dampers can reduce enormous earthquake energy significantly. In this paper, by using ground motion of Imperial Valley, the largest of damper force results obtained is 5.062 kN at T=0.128 s and and α=0.1, the smallest of story drift results obtained is 0.087 mm at T=0.128 s and α=0.1, and the largest of relative velocity results obtained is 107.6 mm/sec at T=0.621 s and α=1.5.

Design and Experimental Validation of an H∞ Observer for Vehicle Damper Force Estimation

Abstract The real-time estimation of damper force is crucial for control and diagnosis of suspension systems in road vehicles. In this study, we consider a semi-active electrorheological (ER) suspension system. First, a nonlinear quarter-car model is proposed that takes the nonlinear and dynamical characteristics of the semi-active damper into account. The estimation of the damper force is developed through an H∞ observer whose objectives are to minimize the effects of bounded unknown road profile disturbances and measurement noises on the estimation errors of the state variables and nonlinearity through a Lipschitz assumption. The considered measured variables, used as inputs for the observer design, are the two accelerometers data from the sprung mass and the unsprung mass of the quarter-car system, respectively. Finally, the observer performances are assessed experimentally using the INOVE platform from GIPSA-lab (1/5-scaled real vehicle). Both simulation and experimental results emphasize the robustness of the estimation method against measurement noises and road disturbances, showing the effectiveness in the ability of estimating the damper force in real-time.

Magnetic spring effect on the force characteristics of the electromechanical magnetic liquid damper

The effect of a magnetic spring is observed in electromechanical devices with limited pole sizes. Simultane-ous changing of the system magnetic conductivity after a relative displacement of the poles causes mag-netic tension forces. These forces in electromechanical magnetic fluid dampers have their own specific characteristics which have not been studied before. All this requires studying the effect of a magnetic spring on the damper power characteristics, estimating the effect of the properties of a magnetorheological suspension on the magnetic spring strength, nature of its change and combination of the action of magnetic forces and viscosity resistance to the piston movement. To do that, it is important to analyze the effect of a magnetic spring in statics, at a slow movement of the piston and its dynamic oscillations. The studies were based on the theory of natural experiment and methods of processing experimental results. We have obtained and analyzed dependences of the resistance force of the electromechanical magnetic fluid damper for different vibration frequencies and magnetic inductions. The effect of magnetic spring forces on the damper power characteristic has been investigated. It has been found how the damper resistance force is affected by the magnetic and hydrodynamic components. The use of a damper with alternating elements with high and low magnetic conductivities makes it possible to change the strength characteristic of electromechanical magnetic fluid dampers. The proportion of the force controlled by the magnetic field reaches 75 % of the total effort. The use of the magnetic spring effect allows increasing the damping efficiency at small amplitudes and vibration frequencies. Increasing the magnetic properties of a magnetorheological suspension enhances the effect of a magnetic spring if the piston is non-magnetic, and weakens it if it is a magnetic one. When the magnetic induction rises, the effect of the magnetic spring increases. By changing the initial piston position, it is possible to obtain an asymmetrical power characteristic, for example, without using valves and spools, to increase the rebound force and to reduce the compressive force. If there are no moving parts, the damper reliability increases.

Observer-based Robust Control for Dynamic Positioning of Large-Scale Heavy Lift Vessels

Abstract With the growing demand of large-scale heavy lift vessels in the deep-sea offshore construction works, high performance of Dynamic positioning (DP) systems is becoming ever crucial. However, current DP systems on board of heavy lift vessels do not consider model uncertainty (typically arising from mooring forces). In this paper, an observer-based robust controller is designed that can tackle model uncertainty in hydrodynamic damping and mooring forces, environmental disturbances as well as can filter out the high-frequency vessel movement. Closed-loop system stability is analytically established in terms of uniformly ultimately boundedness. In addition, several key performance indicators are provided for tuning the performance of the controller. The effectiveness of the proposed control framework is studied in simulation with a crane-vessel system.

Developing a novel haptic device for non-rigid computer graphic objects utilizing unmanned aerial vehicles

In this paper, we propose a novel haptic device consisting of a Parrot quadcopter AR Drone 2.0 that delivers force-feedback to users when they press on the surface of the drone in the vertical direction. This drone haptic device will free users from any cumbersome devices which were utilized in previous haptics systems and allow them to sense kinesthetic feedback coming from the drone which in turn renders computer graphic objects, for example, a virtual box. Specifically, this system performs damped harmonic oscillation force motion on users’ hands and fingers. The oscillation function is implemented on the drone whenever users nudge the drone down. Overall, we evaluated the system with ten subjects, and results show the effectiveness of using damping oscillation motion to provide force-feedback delivered from the drone.