a method to simulate the mr fluid in ansys
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A Method to Simulate the MR Fluid in ANSYS
ZHANG Zheng-xin1,LIU Qian-hui2,HUANG Fang-lin1 (1.School of Civil Engineering,Central South University,Changsha 410075,China; 2.Vocational Technical
College,Guizhou University,Guiyang 550001,China) The magnetorheological fluid(MRF) is consistent with the mechanical properties of
Newtonian fluid when no external magnetic field is present,at this time it can be modeled using
FLUID142 in ANSYS.However,when exposed to a magnetic field,the MRF is also showing
some solid-like characteristics,at present,there is no exactly appropriate element type in ANSYS
to model MRF.This paper presents a method to simulate the mechanical behavior of
magnetorheological fluid subjected to magnetic field in the pre-yield region in ANSYS.The main
idea is devide an MRF element into two coincident elements,one of them has density and
viscosity without shear modulus while another has shear modulus without density and
viscosity.Take a simply supported MRF sandwich beam as an example,comparing the results
with the theoretical analysis and experimental study of Ref.[1],this method can obtain good
results and reasonable conclusion,verified the validity of finite element analysis in this
paper.This kind of method which can be called Coincident Elements Method provides a new way
to model the structures with MRF or MR dampers in ANSYS,and it also has some inspiration for
the future development of related elements in ANSYS.
【Key Words】: magnetorheological fluid yield stress viscosity complex shear modulus
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OPTIMIZATION OF MAGNETO-RHEOLOGICAL DAMPER
Done by
S.DINESH KUMAR (3rd year)
email: sdkmit@gmail.com
contact no:+91 9894999261
S.SHANMUGARAJ (3rd year)
email : shanmu36@gmail.com
contact no: +91 9994410105
DEPARTMENT OF PRODUCTION TECHNOLOGY,
MADRAS INSTITUTE OF TECHNOLOGY
ANNA UNIVERSITY
ABSTRACT:
Magnetorheological Fluid Dampers (MR damper) have provided technology that has enabled
effective semi-active control in a number of real world applications like vibration isolation of
systems etc.
This paper throws light on the design optimization of a high-efficiency magnetorheological
(MR) damper based on the non-dimensional damping coefficients for various damper
geometries to reduce the vibrations in the tool. The MR damper is composed of a core, a wound
coil, and a cylinder-shaped flux return. The core and flux return form the annulus through which
the MR fluid flows. The MR damper was constrained within a cylindrical volume of fixed height
and diameter. Within this volume, candidate geometries were constructed on the basis of the
number of wire coils desired in the valve. These candidate geometries were imported into an
ANSYS magnetic finite element analysis (FEA) routine and the magnetic flux densities
through the MR damper was calculated. We have fabricated and found experimentally that the
magnitude of the vibration has been reduced by 30% than the existing damper.
KEYPOINTS:DAMPING, DESIGN OPTIMIZATION, FINITE ELEMENT ANALYSIS,MR-
DAMPER
CONTROLLABLE FLUID:
Smart fluids are such that they have a low viscosity in the absence of an influencing field, but
become quasi-solid with the application of such a field.
There are two types of controllable fluids.
Magneto rheological fluids (MR fluids).
Electro rheological fluids (ER fluids).
ADVANTAGES OF MR FLUIDS OVER ER FLUIDS:
1. YIELD STRESS:
MR fluids have a yield stress an order of magnitude greater than their ER counterpart
ER fluids yield stress= 2-5 kPa,
MR fluids yield stress =50-100 kPa
2. POWER:
ER and MR fluid devices have similar power requirements of ~ 50 watts. But the voltage and
current requirements for ER fluids and MR fluids are;
ER fluids
Voltage = 2000–5000 Volts
Current = 1–10 m Amps
MR fluids
Voltage = 12–24 Volts
Current = 1–2 Amps.
3. STABILITY:
ER fluids are highly sensitive to contaminants or impurities. Contaminants have little effect on
the MR fluids.
WORKING PRINCIPLE OF MR FLUID:
The magnetic particles contained within the carrier oil are distributed randomly in suspension
under normal circumstances, as in figure 1.1
FIGURE 1.1 MR FLUIDS SHOWING MAGNETIC PARTICLES.
FIGURE 1.2 ALIGNMENTS OF MAGNETIC PARTICLES
When a magnetic field is applied, however, the microscopic particles align themselves along the
lines of magnetic flux, see figure 1.2. When the fluid is contained between two poles, the
resulting chains of particles restrict the movement of the fluid, perpendicular to the direction of
flux, effectively increasing its viscosity.This yield stress is dependent on the magnetic field
applied to the fluid, but will reach a maximum point after which increases in magnetic flux
density have no further effect, as the fluid is then magnetically saturated. MR fluids are also
known to be subject to shear thinning, whereby the viscosity above yield decreases with
increased shear rate.
TYPES OF MR FLUIDS:
Three types of MR fluids manufactured by the LORD Corporation are now commercially
available. MRF- 132LD (oil based), MRF- 240BS (water based) and MRF- 336AG (silicon oil
based). Since the flash point of MRF- 336AG is high (200°C.) we have chosen it for our
optimization process.
INTRODUCTION TO MAGNETORHEOLOGICAL DAMPER:
Magnetorheological Fluid Dampers (MR damper) have provided technology that has enabled
effective semi-active control in a number of real world applications like vibration isolation of
systems under harmonic loading, civil structural vibration reduction, vibration control in washing
machines, and automobiles. MR fluid dampers are similar to conventional viscous dampers
except that the viscous fluid viscosity is controlled by an applied magnetic field.
APPLICATIONS OF MR DAMPER:
o In Skyscrapers and long bridges susceptible to resonance created by high winds
and seismic activity in order to mitigate the resonance effect.
o Dampers are used in machines that are likely in use every day, including car
suspension systems and clothes washing machines.
o A damping system in a building is much larger and is also designed to absorb the
violent shocks of an earthquake.
INTRODUCTION DESIGN OPTIMIZATION OF MR DAMPER:
The design optimization of magnetorheological damper is carried out using a constrained volume
cylindrical geometry with fixed height and diameter. An optimization methodology based on the
non-dimensional damping coefficients for various damper geometries was carried out.
SCHEMATIC OF MR DAMPER:
FIGURE 1.3 SCHEMATIC OF MR DAMPER
METHODOLOGY OF DESIGN OPTIMIZATION:
The framework of the optimization procedure was based on physical design needs. A damper
was considered with a fixed cylindrical volume allotted for a damper.
Parameters Symbol Units
Total Damper length L mm
Diameter of Damper D mm
Height of the coil hc mm
Annual gap D mm
Coil width mm
Bobbin core radius ta mm
Flange height tb mm
Active length LA mm
Viscosity Pa·s
Magnetic Flux Density or Magnetic
BSUM Tesla
Induction
Current Density Js A/m2
Numbers of turns of wires
N turns
Number of wraps NW No unit
Wire diameter dc mm
TABLE 1 VARIOUS PARAMETERS USED IN THE DESIGN OPTIMIZATION
The MR damper was constrained within a cylindrical volume of fixed height and diameter.
Within this volume, candidate geometries were constructed on the basis of the number of wire
coils desired in the valve. These candidate geometries were imported into an ANSYS magnetic
finite element analysis (FEA) routine and the magnetic flux densities through the MR damper
was calculated.
The MR valve was shaped to guide the magnetic flux axially through the bobbin, across the
bobbin flange and fluid gap at one end, through the flux return, and across the fluid gap and
bobbin flange again at the opposite end (figure 1.4).
FIGURE1.4 MAGNETIC FLUX THROUGH MR DAMPER
FIGURE 1.5 ACTIVE AND PASSIVE FLUID LENGTH.
La - Active Fluid length
Lp - Passive Fluid length
The volume of fluid through which the magnetic field passes was defined as the active volume; it
is only within this active volume that MR effects occur. In order to make the valve most
effective, it was desirable to have a high magnetic flux density passing through a large active
volume. However, producing large magnetic fields required large numbers of magnetic coils. An
optimized circuit would maintain a balance between the field produced and power required by
the magnetic coils, and a valve design that would make best use of the field to activate the MR
fluid yield stress.
A viable candidate geometry was one in which the various critical areas though which the
magnetic field passes were the same size. This was necessary to keep the magnetic flux density
constant throughout the circuit, which ensured that one region of the magnetic
circuit did not saturate prematurely and cause a bottleneck effect. There are three critical
areas in the magnetic circuit: the circular cross-section of the bobbin core A1, the annular cross-
sectional area of the flux return A2, and the cylindrical area at the interior of the bobbin flanges
A3.
FIGURE 1.6 MR VALVE GEOMETRY NOMENCLATURE
Thus, the critical areas were defined by,
The volume constraint on the circuit was specified by prescribing maximum values for R and L.
Small changes in the valve gap, d, would drastically alter the performance of different valves, so
a fixed gap was also prescribed to ensure an unbiased evaluation. For these constraints, the
optimized geometry of the valve could be calculated algebraically.
By solving the equations 1,2&3 the resulting equations for ta, tb, la, hc are;
(4)
(5) (5)
La = 2tb (6)
hc = L – 2tb (7)
PROCEDURE FOR CALCULATING THE CANDIDATE GEOMETRY:
For calculating the candidate geometry, the damper height, diameter are fixed i.e. height=21mm,
diameter= 21mm. The fluid gap is also fixed which is equal to 1mm.
By using the equations 4,5,6,7 the various parameters such as ta, tb, hc, La and number of wraps
are calculated for various coil width.
It was noted from equations 4 and 5 that wc was the only variable necessary to characterize the
geometry of the damper. Since radius of the valve, R and the fluid gap width, d are fixed.
A MODEL CALCULATION:
For a coil width of 6mm, the various candidate geometries obtained are:
Bobbin core radius, = 11.6 mm.
Flange height, tb = 11.6/2 = 5.7mm.
Coil height = 9.5mm,
No of wraps= 7
Total number of windings = 91.
Similarly, candidate geometries obtained for various coil widths calculated are given below
Wc Ta Tb Hc Wraps N
4 12.7 6.355 8.29 4 44
5 12.1 6.1 8.86 5 60
6 11.6 5.7 9.5 7 91
7 10.9 5.46 10 8 104
TABLE 2 VALUE OF VARIOUS PARAMETERS
FINITE ELEMENT ANALYSIS USING ANSYS:
Due to structural symmetry, the MR damper will be analyzed as a 2D axi-symmetrical
model in ANSYS.
FIGURE1.7 SCHEMATIC AXISYMMETRIC MODEL OF
THE MR VALVE
The main dimensions of the valve are of Dcore, Lcore, Din, Dout, Lactive, Lreturn and g, where
Dcore = diameter of bobbin shaft
Lcore = length of bobbin shaft
Din = inner diameter of the valve
Dout = outer diameter of the valve
Lactive = active core length
g = 0.5mm, fluid gap
Lreturn = thickness of flux return
(Dout - Din)/2 - g
ASSUMPTIONS MADE IN THE ANALYSIS:
Assumptions of ANSYS magnetic analysis are given below.
The element lies in a global X-Y plane
Y-axis is the axis of symmetry for axi-symmetric analysis
An axi-symmetric structure was modeled in the +X quadrants
The only active degrees of freedom are the magnetic vector potential (AZ)
There is no flux leakage. i.e. flux parallel boundary condition is used.
ELEMENTS USED IN THE ANALYSIS
The element used in our analysis is magnetic vector, Quad 4 node 13 (plane 13)
PLANE13 has a 2-D magnetic, thermal, electrical, piezoelectric and structural field capability.
PLANE13 is defined by four nodes with up to four degrees of freedom per node. The element
has nonlinear magnetic capability for modeling B-H curves or permanent magnet
demagnetization curves.
FIGURE1.8 ELEMENT DESCRIPTIONS
MATERIAL PROPERTIES:
1.MR FLUID:
For MR fluid the material properties include relative permeability , magnetic flux density (B),
magnetic field intensity (H) which are chosen from B-H curve of MR fluid.
FIGURE 1.9 THE PLOT OF B-H CURVE FOR MRF 336AG.
s.no Properties Unit Symbol Value
1. Relative Permeability
No unit r 5
2. Magnetic Flux density
Tesla B 0.8,0.9
3. Magnetic Field Intensity
KA/m H 150,200.
TABLE 3 MATERIAL PROPERTIES OF MR FLUID:
2. STEEL:
s.no Properties Unit Value
1. Relative Permeability (r)
No unit 1000
2. Magnetic Flux density(B)
Tesla 1.25,1.45
3. Magnetic Field Intensity(H)
A/m 600,1000.
. MATERIAL PROPERTIES OF COIL AND INSULATION:
The coil and insulation is assumed to have relative permeability of 1.
BOUNDARY CONDITION:
A perimeter boundary condition is applied to obtain a “flux parallel” field solution. This
boundary condition assumes that the flux does not leak out of the iron at the perimeter of the
model.
LOAD CONDITION:
The current density (JS) identified using the formula given in equation (8) was applied over the
coil area. For a 2-D analysis, only the Z component of JS is valid, a positive value indicates
current flowing in the +Z direction in the planar case and the –Z (hoop) direction in the
axisymmetric case.
(8)
Results and Discussions:
After analysis using ANSYS software, the magnetic flux densities for various coil width was
obtained and shown on the table 5.
COIL WIDTH (mm) MAGNETIC FLUX DENSITY (Tesla)
3 0.823
4 1.1
5 1.715
6 0.35
TABLE5 MAGNETIC FLUX DENSITY FOR VARIOUS COIL WIDTHS.
FIGURE 1.11 FLUX DENSITY VS COIL WIDTH.
From the graph the flux density increases as coil width increases. It reaches a maximum value of
1.715 for a coil width of 5mm and then it decreases. The design for which the maximum flux
density is reached gives the optimized design.
The 3 dimensional view of optimized MR damper is shown in the figure 4.13.
The assembled view is shown in figure 1.12.
FIGURE1.12 THE DRAFT FOR THE OPTIMIZED
DESIGN
CONCLUSION:
An optimized magnetorheological damper was designed using volume constrained
optimization methodology with the help of ANSYS software. The optimized design of MR
damper has a magnetic flux density of 1.715 Tesla for a coil width of 5mm and number of wraps
of 7.
The results obtained for optimized MR damper was compared with the results of existing MR
damper. The result shows that the optimized damper has more vibration suppression capability
compared with the existing damper.
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Characterization, and Devices, "Journal of Intelligent Material Systems and Structures, Vol. 7,
March 1996, pp. 123-130.
4.Choi Y T andWereley N M 2002 Comparative analysis of the time response of
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