Linear Absorber Research Articles

Damping A Passenger Car With A Gyroscopic Damper System

Today, body vibration energy of passenger cars gets dissipated by linear working shock absorbers. A new approach substitutes the damper of a passenger car by a cardanic gimbaled flywheel mass. The constructive design leads to a rotary damper in which the vertical movement of the wheel carrier leads to revolution of the rotational axis of the flywheel. In this arrangement, the occurring precession moments are used to control damping moments and to store vibrational energy. Different damper characteristics are achieved by different induced precession. From almost zero torque output to high torque output, this damper has a huge spread. Next to the basic principal, in this paper an integration in the chassis, including a constructive proposal is shown. A conflict with high torque and high angular velocity leads to a special design. Moreover concepts to deal with all vehicle situations like yawing, rolling and pitching are shown. Since the gyroscope acts in global world coordinate system the movement of the vehicle has to be considered. This leads to a special control of all for systems together regarding different direction of the flywheels angular velocity.

Design and analysis of energy-harvesting shock absorber with electromagnetic and fluid damping

The design and numerical simulation of a linear generator for use in an automobile shock absorber are presented in this paper. The conceived linear generator employs high-performance rare earth permanent magnets with compact size to ensure efficient energy recovery. Finite element analysis and Matlab simulation are utilized to derive the generator configurations for the satisfactory utilization of magnets and optimized functioning. Experimentation was performed on a linear generator prototype and electromagnetic shock absorber to validate the numerical analysis. The numerical model is then utilized in the design of a full-scale energy-harvesting shock absorber with fluid damping and a linear generator. A novel feature of the presented work is the use of fluid amplification to simultaneously achieve energy dissipation and velocity amplification. Fluid amplification does not affect the dynamics of the system and increases the coil velocity by approximately eight times. Smooth variation in damping force, improved fail-safe characteristics, and absence of transmission elements, such as mechanical gears, are additional advantages of the system. Matlab Simscape evaluation is employed to analyze comfort, safety, and energy-harvesting characteristics, which are then compared with that of the conventional fluid shock absorber. Simulation with actual road excitation data indicates that the presented system harvests 15 W of the average power from each wheel. Lastly, the layout for integrating the presented shock absorber in McPherson suspension is discussed.

Damping-induced interplay between vibrations and waves in a forced non-dispersive elastic continuum with asymmetrically placed local attachments

We study the dynamics of a linear, uniform, undamped string under harmonic base excitation, with an attachment consisting of either a spring–dashpot system or a vibration absorber. Mode complexity caused by the local damping of the attachment can lead to coexistence of vibrations and waves in the string. We consider either identical harmonic base motions at both ends or harmonic base excitation at one end. In the case of double harmonic base excitation, it is possible to choose the parameters of the attachment, so that the mode complexity is maximal in one part of the string (leading to travelling waves and elimination of vibrations) and almost zero in the other part (with standing waves or vibration modes). Similarly, for single base excitation, we analytically predict the parameters of the attachment that maximize mode complexity and enhance the interplay of vibrations and travelling waves in the string. Under such conditions, the system acts as a passive vibration confinement device, with induced energy being transmitted through travelling waves to a region where it is confined in the form of standing waves. Our results can be used for predictive design and reveal an unexpected new application of the classical linear vibration absorber.

Heat transfer analysis of an elevated linear absorber with trapezoidal cavity in the linear Fresnel reflector solar concentrator system

This paper describes various aspects of the design methodology and heat transfer calculations for an elevated linear absorber. The absorber is a part of the linear Fresnel reflector solar concentrator system, in which hot fluid is generated. The design of the absorber is an inverted trapezoidal air cavity with a glass cover enclosing a multi tube absorber. In a trapezoidal cavity absorber, a set of linear multi tube absorber with plate (named as “plane surface”) and without plate (named as “tube surface”) underneath are considered. An analytical simulation is done for different gaps between the tubes and for different depths of the cavity. A better design of the absorber is found out to maximize the heat transfer rate supplied to the absorber tube fluid. Also, the experimentally obtained overall heat loss coefficients are compared with the analytical values for the considered arrangements of absorber set up and results are discussed in details.

Thermal performance of a novel linear cavity absorber for parabolic trough solar concentrator

A novel linear cavity absorber for parabolic trough solar concentrator (PTC) was designed in the present study. The cavity absorber was used for conventional fabrication techniques and its thermal performance was carried out. The theoretical model of thermal efficiency for the cavity absorber has been established and verified by the experimental results. The results revealed that there was an agreement between the model and experiment. Furthermore, the temperature of the working fluid could reach 570K, and the thermal efficiency of the cavity absorber was comparable to that of evacuated tube when the temperature of working fluid was in medium temperature. In conclusion, the thermal performance for the cavity absorber with glass cover and fins was improved.

Influence of temperature on optimum viscoelastic absorbers in cubic nonlinear systems

Recently, viscoelastic materials have been widely used for vibration control due to their efficacy and flexibility in real engineering problems. Their use as constitutive parts of dynamic vibration absorbers requires the investigation of these materials under different operating situations. In the optimal design of the absorbers, it is essential to know how the dynamical properties of the viscoelastic materials change with temperature. In a previous work, the authors presented a methodology to optimally design a linear viscoelastic dynamic vibration absorber to be attached to a cubic nonlinear single-degree-of-freedom system, in a given temperature. In the present work, a study of how temperature variations affect the optimal design of two viscoelastic absorbers, made of distinct materials (neoprene and butyl rubber), is addressed. The mathematical formulation of the problem is based on the concept of generalized equivalent parameters and the harmonic balance method is employed in the solution stage. A cubic nonlinearity in the primary system is considered and the four parameter fractional derivative model of viscoelastic materials is used. Numerical simulations are performed using a recursive equation, in order to find the new characteristics of the absorbers at different working temperatures. The results show that the answer depends not only on the temperature and the material, but also on the magnitude of the excitation load imposed to the system. For a low magnitude of the excitation load, it is verified that the neoprene absorber is less affected by a temperature variation, in terms of its vibration control capabilities. On the other hand, a large magnitude of the load can significantly affect the performance of both considered devices when the working temperature is different from the design temperature.

Performance of a Non Linear Dynamic Vibration Absorbers

AbstractThe most common method of vibration control is the use of the dynamic absorbers. Two types of absorbers can be found: Linear and nonlinear. The use of linear absorbers allows reducing vibration but only at the resonance frequency, whereas nonlinear absorbers attenuate vibration on a wide band of frequency. In this paper, a nonlinear two degrees of freedom (DOF) model is developed. A cubic nonlinearity induced by a gap is considered. The objective of the paper is to characterize nonlinear vibration of the system by applying explicit formulation (EF). An experimental study is performed to validate the numerical results. The jump phenomenon is the principal nonlinear dynamic phenomenon observed on both numerical and experimental investigations.

Experimental validation of a magnetorheological energy absorber design optimized for shock and impact loads

A linear stroke adaptive magnetorheological energy absorber (MREA) was designed, fabricated and tested for intense impact conditions with piston velocities up to 8 m s−1. The performance of the MREA was characterized using dynamic range, which is defined as the ratio of maximum on-state MREA force to the off-state MREA force. Design optimization techniques were employed in order to maximize the dynamic range at high impact velocities such that MREA maintained good control authority. Geometrical parameters of the MREA were optimized by evaluating MREA performance on the basis of a Bingham-plastic analysis incorporating minor losses (BPM analysis). Computational fluid dynamics and magnetic FE analysis were conducted to verify the performance of passive and controllable MREA force, respectively. Subsequently, high-speed drop testing (0–4.5 m s−1 at 0 A) was conducted for quantitative comparison with the numerical simulations. Refinements to the nonlinear BPM analysis were carried out to improve prediction of MREA performance.

Power flow behaviour and dynamic performance of a nonlinear vibration absorber coupled to a nonlinear oscillator

The vibrational power flow characteristics of a two-degree-of-freedom system are investigated to examine the performance of nonlinear absorbers in vibration attenuation of nonlinear primary oscillators. The nonlinearities in the oscillator and those in the absorber are both characterised by cubic restoring and damping forces. Both analytical approximations and numerical integrations are used to obtain time-averaged power flow variables, as well as kinetic energies of the system. Power absorption ratio and the kinetic energy of the nonlinear oscillator are proposed to quantitatively evaluate the effectiveness of nonlinear absorbers with respect to the existing nonlinearities in the oscillator. Comparing with linear absorbers, it is found that softening (hardening) stiffness absorber provides benefits for vibration mitigation of a hardening (softening) stiffness primary oscillator by enhancing power absorption efficiency and reducing the kinetic energy of the oscillator so that the functioning frequency range of the absorber can be enlarged. Nonlinear cubic damping in the absorber is shown beneficial for vibration suppression as the power absorption ratio becomes large at resonance frequencies so that the peak power flow and kinetic energy levels are reduced. The developed model can be conveniently extended to study other types of nonlinearities in the absorber/oscillator. Conclusions and suggestions are provided for applications.

Suppression of nonlinear vibration system described by nonlinear differential equations using passive controller

In this paper, the linear absorber is proposed to reduce the vibration of a nonlinear dynamical system at simultaneous primary resonance and the presence of 1:1 internal resonance. This leads to a two-degree-of-freedom system subjected to external excitation force. The method of multiple scales perturbation technique is applied throughout to determine the analytical solution up to first-order approximations. The stability of the system near the one of the worst resonance case is studied using the frequency response equations. The effects of the different system and absorber parameters on the behavior of the main system are studied numerically. For validity, the numerical solution is compared with the analytical solution and gets a good agreement. Effectiveness of the absorber ( $$E_{a})$$ is about 800 for the nonlinear vibrating system. The simulation results are achieved using MATLAB programs. At the end of the work, the comparison with the available published work is reported.

Influence of circumferential solar heat flux distribution on the heat transfer coefficients of linear Fresnel collector absorber tubes

The absorber tubes of solar thermal collectors have enormous influence on the performance of the solar collector systems. In this numerical study, the influence of circumferential uniform and non-uniform solar heat flux distributions on the internal and overall heat transfer coefficients of the absorber tubes of a linear Fresnel solar collector was investigated. A 3D steady-state numerical simulation was implemented based on ANSYS Fluent code version 14. The non-uniform solar heat flux distribution was modelled as a sinusoidal function of the concentrated solar heat flux incident on the circumference of the absorber tube. The k–ε model was employed to simulate the turbulent flow of the heat transfer fluid through the absorber tube. The tube-wall heat conduction and the convective and irradiative heat losses to the surroundings were also considered in the model. The average internal and overall heat transfer coefficients were determined for the sinusoidal circumferential non-uniform heat flux distribution span of 160°, 180°, 200° and 240°, and the 360° span of circumferential uniform heat flux for 10m long absorber tubes of different inner diameters and wall thicknesses with thermal conductivity of 16.27W/mK between the Reynolds number range of 4000 and 210,000 based on the inlet temperature. The results showed that the average internal heat transfer coefficients for the 360° span of circumferential uniform heat flux with different concentration ratios on absorber tubes of the same inner diameters, wall thicknesses and thermal conductivity were approximately the same, but the average overall heat transfer coefficient increased with the increase in the concentration ratios of the uniform heat flux incident on the tubes. Also, the average internal heat transfer coefficient for the absorber tube with a 360° span of uniform heat flux was approximately the same as that of the absorber tubes with the sinusoidal circumferential non-uniform heat flux span of 160°, 180°, 200° and 240° for the heat flux of the same concentration ratio, but the average overall heat transfer coefficient for the uniform heat flux case was higher than that of the non-uniform flux distributions. The average axial local internal heat transfer coefficient for the 360° span of uniform heat flux distribution on a 10m long absorber tube was slightly higher than that of the 160°, 200° and 240° span of non-uniform flux distributions at the Reynolds number of 4000. The average internal and overall heat transfer coefficients for four absorber tubes of different inner diameters and wall thicknesses and thermal conductivity of 16.27W/mK with 200° span of circumferential non-uniform flux were found to increase with the decrease in the inner-wall diameter of the absorber tubes. The numerical results showed good agreement with the Nusselt number experimental correlations for fully developed turbulent flow available in the literature.

Numerical investigation of coexisting high and low amplitude responses and safe basin erosion for a coupled linear oscillator and nonlinear absorber system

Over the last half century, numerous nonlinear variants of the tuned mass damper have been developed in order to improve attenuation characteristics. In the present study, the performance of a linear oscillator and an absorber with a strongly nonlinear cubic stiffness is evaluated by using numerical methods. This configuration has been of recent interest due to its capability of wide-band energy absorption. However, high amplitude solutions, which would amplify the response of the system, have been shown to often coexist with the low amplitude solutions. The present research is focused on numerically determining the relative strength of the coexisting solutions. Erosion profiles are presented, quantifying the integrity of the system, i.e. the likelihood of converging to a safe, low amplitude response, and providing an indication of the structural safety of a practical absorber system. The results indicate that the high amplitude solutions not only exist but significantly influence the response of the system within the range of expected operating conditions, particularly at excitation frequencies lower than the natural frequency of the linear oscillator. The erosion profiles indicate a 20–40% increase in system integrity for the case of zero damping compared to a small amount of damping, no significant integrity change when adding a small linear stiffness component to the nonlinear absorber, and no significant change in integrity between the midpoint and extreme of the bi-stable range. Additional higher-period solutions are also discovered and evidence of a chaotic response is presented.

High shear rate flow in a linear stroke magnetorheological energy absorber

To provide adaptive stroking load in the crew seats of ground vehicles to protect crew from blast or impact loads, a magnetorheological energy absorber (MREA) or shock absorber was developed. The MREA provides appropriate levels of controllable stroking load for different occupant weights and peak acceleration because the viscous stroking load generated by the MREA force increases with velocity squared, thereby reducing its controllable range at high piston velocity. Therefore, MREA behavior at high piston velocity is analyzed and validated experimentally in order to investigate the effects of velocity and magnetic field on MREA performance. The analysis used to predict the MREA force as a function of piston velocity squared and applied field is presented. A conical fairing is mounted to the piston head of the MREA in order reduce predicted inlet flow loss by 9% at nominal velocity of 8 m/s, which resulted in a viscous force reduction of nominally 4%. The MREA behavior is experimentally measured using a high speed servo-hydraulic testing system for speeds up to 8 m/s. The measured MREA force is used to validate the analysis, which captures the transient force quite accurately, although the peak force is under-predicted at the peak speed of 8 m/s.

Vibration Analysis of a Nonlinear System with a Nonlinear Absorber under the Primary and Super-harmonic Resonances (TECHNICAL NOTE)

Abstract In vibratory systems, linear and nonlinear vibration absorbers can be used to suppress the primary and super-harmonic resonance responses. In this paper, the behavior of a nonlinear system with a nonlinear absorber, under the primary and super-harmonic resonances is investigated. The stiffnesses of the main system and the absorber are cubically nonlinear and the dampers are linear. Multiple time scales method is used to obtain approximate solution of the nonlinear equations of motion. Results show that at primary resonance, a linear absorber can suppress the peak amplitude of the system better than a non-linear one. But under super-harmonic resonance, the vibration amplitude can be more effectively reduced by adding a nonlinear absorber to the vibrating system.

Linear and nonlinear piezoelectric shunting strategies for vibration mitigation

This paper studies linear and nonlinear piezoelectric vibration absorbers that are designed based on the equal-peak method. A comparison between the performance of linear mechanical and electrical tuned vibration absorbers coupled to a linear oscillator is first performed. Nonlinearity is then introduced in the primary oscillator to which a new nonlinear electrical tuned vibration absorber is attached. Despite the frequency-energy dependence of nonlinear oscillations, we show that the nonlinear absorber is capable of effectively mitigating the vibrations of the nonlinear primary system in a large range of forcing amplitudes.

Design and Analysis of a Simple Nonlinear Vibration Absorber

In this work, a system consisting of a main structure with a nonlinear tuned vibration absorber having a hardening spring attached to it is considered. The nonlinearity in the absorber's spring is a cubic nonlinearity and is obtained by attaching two additional, relatively soft, similar linear springs to the absorber's mass. These added springs are attached to the absorber's mass in such a way that they are initially normal to the absorber's displacement axis. The dynamics of main structure and that of the nonlinear absorber are analyzed using the first order harmonic balancing method (HB1) and the results are compared against those of a system composing of a linear vibration absorber attached to a similar main structure. A numerical example is considered. The results obtained are in agreement with the known features of nonlinear absorbers. They showed that the absorber's effective frequency band width is increased when a nonlinear absorber is employed instead of a linear one. The results also showed that the displacement amplitude of the absorber during operation is decreased when using a nonlinear absorber. It is also found that the absorber's effective band width depends on the original length of the added linear springs, that are used to obtain the nonlinearity in the absorber, in such a manner that it increases as the original length of the two springs is decreased.

New Designs of Building Integrated Solar Energy Systems

New solar energy systems with fixed concentrators have been designed to be integrated to buildings and adapt heat and electricity demand. The proposed systems are associated with less tracking requirements and the use of thermal, PV or hybrid PV/T absorbers. In some cases, an additional absorber can receive the diffuse radiation as well as the direct sunlight that is not captured by the main absorber. The simplest design mode of these systems is the flat absorber with flat reflector, which is static or movable to track solar radiation. A second design is the static parabolic or CPC reflector and a third one the Fresnel lens. These concentrators are combined with a primary linear absorber and tracking the converged beam solar radiation. The non-absorbed diffuse radiation and out of focus solar radiation is absorbed by a flat absorber, working as secondary absorber, so that the system to absorb almost all incident solar radiation. Thermal absorbers or photovoltaic strips can be mainly used as primary receivers, while for the concentrators, specular or diffuse reflectors can be applied in mirror type systems and linear Fresnel lenses in lens type systems. Fresnel lenses can be also used for solar control of building atria. In the paper the design and application aspects of the suggested new solar energy systems are presented. Results for flux profile on focal plane and absorber's temperature show the positive effect of the suggested new concentrator - absorber configurations.

Numerical Simulation of a Trapezoidal Cavity Absorber in the Linear Fresnel Reflector Solar Concentrator System

The present article describes the numerical study of heat transfer analysis in a trapezoidal cavity absorber of a linear Fresnel reflector solar concentrator (LFRSC) system. The linear absorber is a part of the linear Fresnel reflector solar concentrator system, in which hot fluid is generated. The absorber is an inverted air cavity with a glass cover enclosing an absorber surface. In the present analysis, a linear multi-tube absorber with and without the absorber plate underneath is considered. The ANSYS workbench package with FLUENT 12.0 version is used to develop the two-dimensional, steady-state, and laminar-flow heat transfer model for a trapezoidal cavity absorber. The models with Boussinesq and non-Boussinesq approximations are used for the numerical analysis and the performance is compared. The heat transfer rate, radiation heat loss, and combined heat loss coefficients are predicted at various absorber surface temperatures and for the absorber surface with ordinary black paint and with selective surface coating. For validation, the present computational model is compared with the analytical values and other reported closed cavity models. A better design of the cavity absorber is found out to maximize the heat transfer rate applied to the absorber tubes for better fluid outlet temperature.

Experimental validation of a magnetorheological energy absorber design analysis

A key challenge when designing linear stroke magnetorheological energy absorbers for high-speed impact is that high piston speeds in linear stroke magnetorheological energy absorbers induce high Reynolds number flows in the magnetic valve of the magnetorheological energy absorber, so that achieving high controllable dynamic range can be a design challenge. So far, the research on magnetorheological energy absorbers has typically assumed that the off-state force increases linearly with piston velocity. But at the higher piston velocities occurring in impact events, the off-state damping exhibits nonlinear velocity squared damping effects. This problem was recognized in our prior work, where it was shown that minor losses are important contributing factors to off-state damping. In this study, a nonlinear analytical magnetorheological energy absorber model is developed based on a Bingham-plastic nonlinear flow model combined with velocity squared dependent minor loss factors. This refined model is denoted as the Bingham-plastic nonlinear flow model with minor losses. From this Bingham-plastic nonlinear flow model with minor losses, an effective design strategy is presented for conventional magnetorheological energy absorbers. The Bingham-plastic nonlinear flow model with minor losses is validated via computational fluid dynamics simulation, so that magnetorheological energy absorber performance can be analytically verified before being manufactured. The magnetorheological energy absorber is fabricated and tested up to an effective piston velocity of 5 m/s by using the high-speed drop tower facility at the GM R&D Center. Comparison of our analysis with measured data is conducted, and the effective design of the magnetorheological energy absorber using the Bingham-plastic nonlinear flow model with minor losses is validated.

Computational study of vortex-induced vibration of a sprung rigid circular cylinder with a strongly nonlinear internal attachment

For a Reynolds number (Re) based on cylinder diameter of 100, and a ratio of cylinder density to fluid density of 10, we investigate the effect of a strongly nonlinear internal attachment on the vortex-induced vibration (VIV) of a rigid circular cylinder restrained by a linear spring, and constrained to move perpendicularly to the mean flow. The variational multiscale residual-based stabilized finite-element method used to compute approximate solutions of the incompressible Navier–Stokes equations about the moving cylinder is coupled to a simple model of a “nonlinear energy sink” (NES), an essentially nonlinear oscillator consisting of a mass, a linear damper, and a strongly nonlinear spring. The NES promotes nearly one-way transfer of energy to itself from the primary structure (the cylinder), resulting in reduction of the amplitude of the limit-cycle oscillation by as much as 75%, depending on the parameters characterizing the NES. Various mechanisms of nonlinear interaction of the NES with the cylinder undergoing VIV are discussed. Although no optimization of the NES is performed in this work, we demonstrate capacity for passive suppression of VIV and compare the performance of the NES to the tuned linear absorber of equal mass.