Magnetorheological dampers

ABSTRACT:  Magnetorheological fluids (MRF) are increasingly used for the design of dampers in many cases when a given response is critical for desired performance. Some recent examples are self-powered magnetorheological dampers, cable vibration control and wheeled vehicle dampers. Loads of this type can be very big, especially in the case of seismic-dampers as well as in heavy vehicles and aircraft landing gear. This problem can be more efficiently dealt with by using an inverse-problem strategy, where the required performance is specified a priori, and the fluid parameters are changed accordingly by means of a variable magnetic field. The effect on the flow of the time-variation of the parameters of the Herschel-Bulkley constitutive model is analyzed in this paper. In this way, the influence of a varying magnetic field on the unsteady flow of a magnetic fluid is explored. Yield stress, viscosity and power index are assumed time-dependent. In particular, linear variations in time of these parameters are considered, and the case where the yield stress and viscosity oscillate in time is explored in detail. The characteristics of the velocity field are analyzed for different values of the constants that determine the time structure of the constitutive parameters.

This study concerns the modeling of the hysteretic behavior of magnetorheological (MR) dampers. In general, hysteresis is one of key factors influencing the output of such actuators. So far, more attention has been paid to studying the combined hysteretic behavior of MR actuators by observing the relationships between the output (force/torque) and the inputs (current, velocity, and position). However, these devices feature two distinct hysteretic mechanisms: mechanical/hydraulic and magnetic. The mechanical hysteresis is of different nature than the magnetic hysteresis due to the properties of ferromagnetic materials forming the actuator's electromagnet circuit, and these should be split in the modeling process. In the present study, we separate the magnetic hysteresis from the mechanical/hydraulic one by investigating the magnetic flux vs. exciting current relationship of a commercial flow-mode MR damper subjected to sinusoidal current loading and independently of the mechanical excitations. The resulting behavior of the electromagnetic circuit is then examined using the non-linear inductor approach with hysteresis. Total hysteresis is then modeled using a non-linear inductor model in combination with a phenomenological parametric Maxwell type model of the damper.

Magneto Rheological damper is a special type of damper that is filled with Magnetorheological fluids which can be controlled by magnetic field using an electromagnet. These types of smart fluids change their physical properties when subjected to magnetic field and turn into visco-elastic solids in few milliseconds. This property allows the MR damper to be used as a shock absorber by controlling its damping characteristics by changing the intensity of electromagnet. This paper focuses on the various applications of MR dampers in latest technologies.

Abstract: machine building. SUBSTANCE: mount includes support plates, a damper, springs in the form of threads and thread tensioning means. The damper consists of constant magnets. Threads are rigidly fixed on one of the support plates and rigidly attached  to  another support plate by means of thread tensioning means. Distance between support plates is not less than 0.5 of the distance between constant magnet poles. The magnets fixed on one support plate face with their opposite poles the magnet(s) fixed on the other support plate. The magnets fixed on the support plate in a circumferential direction are equally spaced from each other to the distance of not less than 0.5 of the distance between constant magnet poles. As per the first version, the damper of the mount is formed at least with four magnets. At least three magnets are fixed on one of the support plates in a circumferential direction. On the other support plate there fixed is one constant magnet, the axis of which passes through the centre of circle. As per the second version, the damper of the mount is formed at least with six constant magnets. At least three magnets are fixed on each of the support plates in a circumferential direction. Centres of  those  circles are located on one axis, and difference of their diameters is at least 1.0 of the distance  between poles of constant magnet. EFFECT: improving vibration damping efficiency of the mount.

The mitigation of seismic-induced vibrations is essential for the effective protection of buildings and occupants during earthquakes. This especially applies to slender buildings with metallic frames; in this case, the structure’s geometrical layout and relatively low damping properties favor an excessive and potentially catastrophic oscillatory response to a seismic event. Semiactive systems for energy dissipation are among the most commonly used strategies to control this oscillatory response. They offer the right balance between the reliability of passive devices and the versatility and adaptability of fully active systems. In this work, a vibration-suppression system based on dissipative bracings that integrate commercial magnetorheological fluid dampers (MRDs) was designed and validated through experimental tests on a true-scale structural model that was representative of a five-story slender building with a metallic frame. A practical and robust approach was proposed for: (1) The definition of the MRD type in compliance with a predefined mitigation target for seismic-induced accelerations on each floor of the structure; (2) The modeling of the MRDs, contribute to the dynamic response of the structural system. The approach involves a linearized formulation of the characteristic damping curves of the MRDs at different values of the activating current. By relying upon this linearization, a rapidly converging iterative process was set up to simulate the seismic response of the structure in the case of activated or deactivated dampers. The reference structure and the vibration-suppression system were then manufactured and tested on a sliding table, which provided realistic seismic excitation. The good correlation levels between the numerical predictions and the experimental measurements proved the effectiveness of the conceived system and of the approaches that were used for its design and simulation.

This research is concerned with an optimization study of magneto-rheological damper to achieve a satisfying degree of comfort to the passengers without loss of the vehicle stability. This study explains the effect of using magneto-rheological damper in the construction of vehicles seats by using MATLAB-Simulink software to compare between the passive and active damping systems for various excitations with different frequencies. Moreover, the effect of an active system on the vehicles construction is considered.

ABSTRACT: The fluid dynamics of dampers is investigated for the case where the damping fluid flows through passages in which a magnetic field is applied. This is a specific case of a new and promising field of applications that has emerged through the design of devices that take advantage of some properties of the so-called electrorheological fluids and magnetorheological fluids (ERF and MRF). These fluids are created when a base fluid is seeded with very small dielectric or iron particles, so that it reacts to electric or magnetic fields by developing some non-Newtonian characteristics, most prominently a yield stress, viscosity change, and also viscoelasticity. These fluid properties can be controlled through controlling the strength of the electric or magnetic fields. In this paper, a typical damping load is modeled and related to the required flow of a MRF inside the damper. To this end the fluid is modeled as a Bingham fluid with time-varying yield-stress. The analysis here developed makes it possible to determine the magnetic field variation necessary in order to achieve a specific displacement of the damper’s piston. The flow equations are analytically solved for any time-history of the dimensionless fluid’s yield-stress. Main results are some simplified relationships that correlate damping load and magnetic field time-variations. These results aim at providing analytical tools that may facilitate the design of dampers.

Adjustable mass dampers are recently used to reduce seismic vibrations of engineering structures. Function of these types of systems requires a suitable setting of their parameters. In this study, a practical method to design Multiple Tuned Mass Dampers (MTMD) has been proposed to minimize the maximum displacement of roof, acceleration of roof and TMDs displacement to reduce the seismic response of structures. To solve the problem Cuckoo Optimization Algorithm (CMOA) has been used. The results of numerical simulations for a shear frame of ten floors exposed to earthquakes demonstrate that CMOA is able to present appropriate solutions in the form of Parato charts for setting optimal parameters of MTMD, caused by creating a proper compromise between the objective functions in conflict with each other. Eventually, MTMD desirably reduces seismic responses of structures. Also, MTMD performance depends on input quake, TMD mass ratio and the number of TMDs.

In this paper a method is studied to analyze the recovering of optimal damping constant because of temperature increasing in a shock absorber. The increasing on temperature leads to decreasing that constant by mean dynamic viscosity such to modify the dynamic behavior of a 2DOF system built-up by sprung and unsprung mass.
A MagnetoRheological damper was designed according with the desired optimal damping constant once fixed temperature design. It was seen that the increasing of temperature this constant is lost. As MagnetoRheological-Fluids allows us to increase the viscosity, we use a control signal by a state feedback of reduced order to create a such magnetic induction field to recover the optimal damping constant at higher temperature than design on

This paper shows the influence on dynamic behavior of the car when it is equipped with
magneto-rheological dampers controlled by a feedback. The feedback is built up in two ways; the
first is implemented by a switch on/off control that is characterized by the injection of magnetic
field with a constant value. It happens when a certain value of relative speed between the sprung
and unsprung mass is exceeded. The second feedback is characterized by the H-infinity control
which is based on the relative displacement in order to vary the magnetic field signal in a
continuous manner. At the same time the H-infinity control of vehicle is maintained by taking into
account the exceeding of speed signal in order to consider the substantial differences with the
switch on/off control. These differences are evaluated in terms of relative displacement and speed
between the unsprung and sprung mass. The exogenous excitation is the road disturbances which
are introduced as a square wave input in order to emulate those that are commonly encountered on
the road. All simulations and results are performed by MATLab-Simulink and Mathematica.

ABSTRACT: A predetermined flow pattern in a magnetorheological damper providing continuously variable resistance to flow is required for efficient damping of a given load. The required predetermined flow pattern rests on the a priori determination of the constitutive properties of the magnetorheological (MR) fluid determined to generate variable resistance to flow. The inverse problem of constructing the predetermined response of the damper with a specific displacement pattern of the piston in the damper for efficient damping of a given load is solved. The magnetorheological (MR) fluid in the damper is modeled as a Bingham phase change material with time dependent yield stress offering continuously variable resistance to the flow in the piston to achieve the required specific displacement pattern. The governing equations are solved for any time history of the dimensionless yield stress of the fluid which in turn is determined from the imposed response of the damper. Analytical tools developed can be used in optimizing damper performance. The application of the method to resonance mitigation is illustrated.

ABSTRACT: Many structures such as automobile bodies, bridges and buildings are subjected to external forces due to the nature of the environment in which they exist. When the external excitation frequency is similar to the structure's natural frequency a resonance effect is generated, increasing the energy and the amplitude of the oscillation, often causing catastrophic situations. This paper presents a method to decrease such resonant oscillations using magnetorheological dampers.

A passive vehicle suspension has constant spring and damper properties that compromise either ride or road holding ability, depending on whether the suspension is designed to be hard or soft. This study examines the implementation of a gear mechanism in a vehicle suspension system to alter its suspension characteristic while keeping the same spring and damper properties. In the study, a rack-and-pinion mechanism was used to modify the suspension force which acted between the sprung and unsprung masses of a quarter vehicle model. The system with proposed suspension layout was modeled mathematically and solved to obtain the vehicle response due to step excitation for various gear ratios. Results indicated that the use of such a mechanism was capable of changing the equivalent suspension force of the system. It was noted that different gear ratios would amplify or reduce the equivalent suspension force, hence emulating a harder or softer suspension setting compared to that of the original suspension. Additionally, it was found that with optimized gear ratio and gear mass, the implementation was capable of overcoming the compromise between the ride and road holding ability associated with conventional passive suspensions, as simultaneous improvement on both criteria was observed.

Link to Full-Text Articles :
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This study investigates the automotive magnetorheological (MR) shock absorber behaviour in conditions of changing temperature. Its temperature-dependent behaviour was quantified between ambient and maximal operating temperatures of the device. Aspects addressed include the temperature dependence of the control coil resistance in the absorber, the influence of operating current level on control coil temperature and the temperature dependence of the absorber force response and energy dissipation in the system. The results of experiments enabled us to evaluate the mechanical performance of the absorber at varied temperatures.

The current research work is directed to study and improve vehicle behavior during crashes. Hence, a crash-pitch controller integrated with Magneto-Rheological (MR) dampers implemented in both vehicle suspension system and front-end structure is designed and studied. The methodology of the work is based on modeling the vehicle dynamical attitude as a half-car mathematical model that is developed with 3 degrees of freedom (DOF), longitudinal, bounce, and pitch. The model is constructed to study the vehicle’s dynamic response in a full-frontal collision against a fixed barrier. Additionally, a fuzzy logic controller is developed to integrate the suspension MR dampers with another set of MR dampers implemented within the vehicle’s front-end structure. Four different vehicle cases were discussed and compared within the simulation results of the developed model. Moreover, the four mentioned cases can be clarified as first free-rolling, second replacing the vehicle’s conventional dampers with MR dampers, third implemented MR dampers within the vehicle’s front-end structure, finally the fourth case through the integration of MR dampers implemented within both front-end structure and suspension system. Hence, the fourth case was implemented through the augmentation of simultaneous crash-pitch controllers. The simulation results showed a noticeable improvement in the front-end structure deformation as it had been reduced. Moreover, the vehicle’s body attitudes had also been improved where pitch angle had been reduced as well as its settling time. Also, pitch acceleration had been reduced which benefits human body exposure.

Modernly, among all smart materials, MR-Elastomer are widely famous in research area for its attractive features such as damping property, shear modulus and very much fast responding characteristics in vibration control. In this review study fabrication process of unstructured and prestructured MRE by not providing and providing magnetic field at the time of curing process of MRE are reviewed. Also different applications are studied in which MRE's are played a vital role. This study evaluates the application of MRE that can be beneficial in terms of vibration control in particular application.

Vibration has been a major constraint in the machining industries as it has catastrophic effects on the machining parameter. Though there have been several attempts made by the researchers each had their own limitations and constraints. In metal cutting, Magnetorheological fluid (MRF) has proved to be effective in vibration suppression when employed as a semi-active damper. MRF is a smart non-Newtonian fluid which has the capacity to alter its viscosity instantaneously on the application of magnetic field. Along with this property and its robust nature they have used in a wide variety of places as a damper. One major limitation is its settling of magnetic particles which are suspended in a non-magnetic fluid. The settling rate will be further aggravated when the current supplied to coil is increased. Increased current will increase the heat produced in the coil which in turn will heat the non-magnetic fluid wherein its viscosity gets reduced. This problem of settling of iron particles can be prevented by adding stabilizers, similarly the size of particles also has an immediate effect on settling. In the current investigation Titanium and Activated carbon was added as stabilizers to magnetorheological fluid and then the viscosity change brought about in the fluid was studied. Further to support and add clarity to the work variable cutting speed and feed test was also performed. From the experimental results it was evident that stabilizers (activated carbon by 0.1% of weight) in MRF has increased the viscosity and thereby aided in an effective turning process of hardened SS410 steel.

Magnetorheological (MR) damper is one of the most advanced application of semi active devices. Its use is increasing day by day due to its huge advantages and wide range of application. The force delivered by MR damper can be varied by changing the viscosity of its internal MR fluids. Till now no details experimental analysis has been accomplished by considering various parameters. In this paper a brief experimental analysis has been investigated with the help of Universal Testing Machine to characterize MR damper. To characterize accurately MR damper has been analyzed experimentally for different stroke length, stroke rate, stroke mode. From the experimental results it is seen that the force delivered by MR damper has a proportional relation with input excitation current, stroke length and stroke rate.

Magneto Rheological Elastomer (MRE) have been the topic of extreme study throughout the previous hardly any decades. They show novel properties or are possible materials for the new-age devices. These elastomers are new engineering materials remembered for the class of dynamic objects its mechanical property can be limited by an exterior magnetic field [3]. They can be used in transduction and the other way around. These two significant properties of magneto rheological (MR) elastomer provide ascend to numerous possible purposes as actuators, transducer, automobile deferment systems, clutches, brakes, vibration isolators, and constraints. This is comparable to the conduct of  as MR liquid system or an electro rheological (ER) system.

This research is concerned with an optimization study of magneto-rheological damper to achieve a satisfying degree of comfort to the passengers without loss of the vehicle stability. This study explains the effect of using magneto-rheological damper in the construction of vehicles seats by using MATLAB-Simulink software to compare between the passive and active damping systems for various excitations with different frequencies. Moreover, the effect of an active system on the vehicles construction is considered.

ABSTRACT A magnetorheological (MR) damper is a promising appliance for semi-active suspension systems, due to its capability of damping undesired movement using an adequate control strategy. This research has been carried out a phenomenological dynamic model of two MR dampers using an adaptive-network-based fuzzy inference system (ANFIS) approach. Two kinds of Lord Corporation MR damper (a long stroke damper and a short stroke damper) were used in experiments, and then modeled using the experimental results. In addition, an investigation of the influence of the membership function selection on predicting the behavior of the MR damper and obtaining a mathematical model was conducted to realize the relationship between input current, displacement, and velocity as the inputs and force as output. The results demonstrate that the proposed models for both short stroke and long stroke MR dampers have successfully predicted the behavior of the MR damper with adequate accuracy, and an equation is presented to precisely describe the behavior of each MR damper.

A passive vehicle suspension has constant spring and damper properties that compromise either ride or road holding ability, depending on whether the suspension is designed to be hard or soft. This study examines the implementation of a gear mechanism in a vehicle suspension system to alter its suspension characteristic while keeping the same spring and damper properties. In the study, a rack-and-pinion mechanism was used to modify the suspension force which acted between the sprung and unsprung masses of a quarter vehicle model. The system with proposed suspension layout was modeled mathematically and solved to obtain the vehicle response due to step excitation for various gear ratios. Results indicated that the use of such a mechanism was capable of changing the equivalent suspension force of the system. It was noted that different gear ratios would amplify or reduce the equivalent suspension force, hence emulating a harder or softer suspension setting compared to that of the origi...

ABSTRACT: A predetermined flow pattern in a magnetorheological damper providing continuously variable resistance to flow is required for efficient damping of a given load. The required predetermined flow pattern rests on the a priori determination of the constitutive properties of the magnetorheological (MR) fluid determined to generate variable resistance to flow. The inverse problem of constructing the predetermined response of the damper with a specific displacement pattern of the piston in the damper for efficient damping of a given load is solved. The magnetorheological (MR) fluid in the damper is modeled as a Bingham phase change material with time dependent yield stress offering continuously variable resistance to the flow in the piston to achieve the required specific displacement pattern. The governing equations are solved for any time history of the dimensionless yield stress of the fluid which in turn is determined from the imposed response of the damper. Analytical tools...

ABSTRACT Magnetorheological fluids (MRF) are increasingly used for the design of dampers in many cases when a given response is critical for desired performance. Some recent examples are self-powered magnetorheological dampers, cable vibration control and wheeled vehicle dampers. Loads of this type can be very big, especially in the case of seismic-dampers as well as in heavy vehicles and aircraft landing gear. This problem can be more efficiently dealt with by using an inverse-problem strategy, where the required performance is specified a priori, and the fluid parameters are changed accordingly by means of a variable magnetic field. The effect on the flow of the time-variation of the parameters of the Herschel-Bulkley constitutive model is analyzed in this paper. In this way, the influence of a varying magnetic field on the unsteady flow of a magnetic fluid is explored. Yield stress, viscosity and power index are assumed time-dependent. In particular, linear variations in time of these parameters are considered, and the case where the yield stress and viscosity oscillate in time is explored in detail. The characteristics of the velocity field are analyzed for different values of the constants that determine the time structure of the constitutive parameters.

ABSTRACT Magnetorheological (MR) fluid is a suspension of small iron particles, where, in the presence of a magnetic field, the solid particles arranged themselves as deformable chains. The deformation of the chain structure can be performed in three common modes known as flow mode, shear mode and squeeze mode. Among the three, the flow and shear modes have been widely investigated and used in commercial applications. Nevertheless, limited focus has been given to the combination of both modes. Furthermore, the existing combination between the flow and shear mode has been always defined at the same effective area, which is commonly known as the shear-flow mode. This paper provides a new perspective of mixed mode by arranging in series the different modes in the same MR cell. In order to manifest the theoretical model, an effective area representing the shear-flow mode is positioned separately with another effective area of the pure flow mode. The magnetic circuit design is validated by using the finite element method in 2D simulation. Moreover, the simulated results of magnetic flux density in the MR fluid are used to predict the force produced by the flow and shear-flow modes. The fabricated cell is tested under quasi-static loading and the results are compared with those that were predicted. It can be concluded that, to a certain extent, the obtained experimental results have been successfully predicted by the proposed model.

Magnetorheological (MR) fluid is a suspension of small iron particles, where, in the presence of a magnetic field, the solid particles arranged themselves as deformable chains. The deformation of the chain structure can be performed in three common modes known as flow mode, shear mode and squeeze mode. Among the three, the flow and shear modes have been widely investigated and used in commercial applications. Nevertheless, limited focus has been given to the combination of both modes. Furthermore, the existing combination between the flow and shear mode has been always defined at the same effective area, which is commonly known as the shear-flow mode. This paper provides a new perspective of mixed mode by arranging in series the different modes in the same MR cell. In order to manifest the theoretical model, an effective area representing the shear-flow mode is positioned separately with another effective area of the pure flow mode. The magnetic circuit design is validated by using ...

ABSTRACT:  Flow of magnetorheological (MR) fluids in dampers is investigated. The MR fluid flows through narrow passages in the damper subject to a magnetic field applied across the passages. The inverse problem of the determination of the required constitutive properties of the MR fluid together with the corresponding flow pattern for the efficient damping of a given load is solved. The fluid is modeled as a Bingham plastic with time-varying yield-stress. Flow is governed by the continuously adjustable constitutive parameters of the MR fluid which are determined to generate variable resistance to flow to dampen the selected load efficiently. The method developed leads to the determination of the magnetic field variation necessary to achieve a specific displacement of the piston in the damper. The governing equations are solved for any time history of the dimensionless yield stress of the fluid. Relationships that correlate damping load and magnetic field time variations are obtained. The analytical tools developed are helpful in damper design.

ABSTRACT: The fluid dynamics of dampers is investigated for the case where the damping fluid flows through passages in which a magnetic field is applied. This is a specific case of a new and promising field of applications that has emerged through the design of devices that take advantage of some properties of the so-called electrorheological fluids and magnetorheological fluids (ERF and MRF). These fluids are created when a base fluid is seed with very small dielectric or iron particles, so that it reacts to electric or magnetic fields by developing some non-Newtonian characteristics, most prominently a yield stress, viscosity change, and also viscoelasticity. These fluid properties can be controlled through control of the electric or magnetic fields’ strength. In this paper, a typical damping load is modeled and related to the required flow of a MRF inside the damper. To this end the fluid is modeled as a Bingham fluid with time-varying yield-stress. The analysis here developed makes it possible to determine the magnetic field variation necessary in order to achieve a specific displacement of the damper’s piston. The flow equations are analytically solved for any time-history of the dimensionless fluid’s yield-stress. Main results are some simplified relationships that correlate damping load and magnetic field time-variations. These results aim at providing analytical tools that may facilitate dampers’ design.

A method to model and minimize resonant structural oscillations using magnetorheological dampers is presented. The response of the magnetorheological fluid flowing in a circular tube under a pressure gradient to the applied variable magnetic field is tailored to determine the optimum stress field in the fluid to mitigate resonance effects. Mathematics Subject Classification. 76 · 35 · 41.