Optimization of Radial Fan Impeller Using Finite Element Analysis-report[1]
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OPTIMIZATION OF RADIAL FAN IMPELLER
USING FINITE ELEMENT ANALYSIS
A PROJECT REPORT
Submitted by
KISHORE KANNA.B 40401114020 MOHAMMED MOHAIDEEN.M 40401114033PANDIARAJ.T 40401114039SATHISH KUMAR.K 40401114049
in partial fulfillment for the award of the degree
of
BACHELOR OF ENGINEERING
in
MECHANICAL ENGINEERING
B.S.ABDUR RAHMAN CRESCENT ENGINEERING COLLEGE,
CHENNAI-48
ANNA UNIVERSITY: CHENNAI 600 025
MAY 2005
BONAFIDE CERTIFICATE
This is to certify that the project work entitle “OPTIMIZATION OF
RADIAL FAN IMPELLER USING FINITE ELEMENT ANALYSIS”
is a Bonafide record of the work done by
KISHORE KANNA.B - 40401114020
MOHAMMED MOHAIDEEN.M - 40401114033
PANDIARAJ.T - 40401114039
SATHISH KUMAR.K - 40401114049
Students of B.E., (Mechanical Engineering) of B.S ABDUR
RAHMAN CRESCENT ENGINEERING COLLEGE, Chennai at Ranipet.
During the period from 31-01-05 to 28-02-05.
We wish them all the success in their future endeavour.
For BHARAT HEAVY ELECTRICALS LIMITED
Mr. R.BABU M.Tech (IIT-Madras) Mr.S.PARAMANANTHAM
Deputy Manager (Fans) H.R.D.Officer
BHEL-BAP BHEL-BAP
Ranipet Ranipet
ANNA UNIVERSITY: CHENNAI 600 025
BONAFIDE CERTIFICATE
This is to certify that the project report ‘OPTIMIZATION OF RADIAL
FAN IMPELLER USING FINITE ELEMENT ANALYSIS’ is the
bonafide work of
KISHORE KANNA.B 40401114020MOHAMMED MOHAIDEEN.M 40401114033PANDIARAJ.T 40401114039SATHISH KUMAR.K 40401114049
Who carried out the project work under my supervision.
Dr.R.GANESAN Mr.P.GANESHHEAD OF THE DEPARTMENT INTERNAL GUIDE
DEPARTMENT OF MECHANICAL ENGINEERINGB.S.ABDUR RAHMAN CRESCENT ENGINEERING COLLEGE
CHENNAI-48
VIVA VOCE EXAMINATION
The viva voce examination of this project work submitted by
B.KISHORE KANNA, REGISTER NO: 40401114020
T.PANDIARAJ, REGISTER NO: 40401114039
K.SATHISH KUMAR, REGISTER NO: 40401114049
M.MOHAMMED MOHAIDEEN, REGISTER NO: 40401114033
is held on
EXTERNAL EXAMINER INTERNAL EXAMINAR
ACKNOWLEDGEMENT
AKNOWLEDGEMENT
It is our great pleasure in presenting the project work undergone at Bharat
heavy electrical limited (BHEL), Ranipet.
At this moment we wish to place on record our sincere gratitude to
prof. S.Peer Mohamed, Correspondent and Dr.K.P.Mohamed, Principal, for
their encouragement.
Our sincere gratitude to our Head of the Department Dr.R.Ganesan
and Project coordinator Mr.J.Bhaskaran for providing us with necessary
infrastructure.
Our sincere gratitude to Mr.P.Ganesh, Lecturer who has been a
resource of encouragement and guidance for our project work. We are
indebted towards him for his valuable suggestions and help without which
our project could not have been completed.
We express our sincere gratitude and thanks to Mr.S.Paramananthan,
HRDC Officer, BHEL- Ranipet.
Our sincere gratitude and thanks to our External guide Mr.R.Babu,
Deputy Manager, BHEL-Ranipet.
Our sincere thanks to all the staff members of our department for
their encouragement and guidance.
Last but not least we thank all of our friends who stood by us and
provided the moral support during the preparation of our project work.
ABSTRACT
Increasing cost of consumable materials has put an enormous pressure
on the pricing as well as the profitability of an organization. Therefore
without any compromise on quality, the variable cost has to be reduced. This
demands novel thinking and creativity for constant improvement in design,
resulting in good profits.
In this project work, an attempt has been made to optimize the design
of aerofoil bladed radial fan impeller using finite element analysis (FEA).
The optimization is done using FEA in “ANSYS – MECHANICAL
UTILITY”
In the FEA section, modeling as well as analysis was done using ANSYS
MECHANICAL UTILITY. In this section, the thickness of the every
component of the impeller was reduced and Stiffeners were provided to
curtail the large deflections in the optimized model. Stresses and deflections
were analyzed for the modified and pre modified model.
The results of the optimization were successful as 18.5% savings in net
weight after FEA optimization. So, the material cost is reduced and also the
space occupied. In FEA the stress and deflection analysis were performed
whose results were well within the limits.
ABSTRACT
CONTENTS
CHAPTER PAGE NO
ACKNOLEDGEMENT i
ABSTRACT ii
CONTENTS iii
LIST OF DIAGRAMS vi
LIST OF TABLES vii
LIST OF NOMENCLATURE viii
CHAPTER 1 INTRODUCTION
1.1 Organization Profile 1
1.2 BHEL – Boiler auxiliary plant ranipet 1
1.3 About the Project. 2
1.4 About the Fan 3
1.5 Classification of fans 3
1.6 Advantages of an Aerofoil Bladed Fan 6
1.7 Constructional features of a radial fan 7
1.8 Methods to drive the Fan 8
1.9 Fan specifications 9
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction 10
2.2 Historical Background 10
2.3 What is FEA? 11
2.4 Need for Finite Element Analysis 11
2.5 The Finite Element Method 12
2.6 Concepts of FEA 13
2.7 General procedure for FEA 14
2.8 Applications of FEA 16
2.9 Setting element attributes 16
2.10 Boundary conditions 17
2.11 Material properties 18
2.12 Element type 18
2.13 Fan laws and Efficiency 22
2.14 Stress Analysis 28
CHAPTER 3 INTRODUCTION ANSYS
3.1 Introduction to ANSYS 31
3.2 ANSYS offers 31
3.3 Examples of ANSYS analysis 31
3.4 Choosing the software 32
3.5 Feature selection 33
3.6 Results required for analysis 33
3.7 Solution speed 33
3.8 Hardware availability 33
3.9 Analysis procedure 34
3.10 Procedure for static analysis 35
3.11 Modal analysis 36
3.12 Procedure for modal analysis 37
3.13 Design optimization 38
3.14 Typical examples of optimized designs 38
CHAPTER 4 METHODOLOGY
4.1. Solid model generation using preprocessor 39
4.2. Meshing contours 39
4.3. Meshing of areas 39
4.4. Defining material 40
4.5. Choosing appropriate element for analysis 40
4.6. Attributing equivalent and actual boundary 40
4.7. Solving the problem using solver 40
4.8. Viewing results 41
4.9. Studying the parameters stress and deflection 41
4.10. Modifying the geometry model by reducing the thickness 41
CHAPTER 5 MODELING
5.1 Segment generation 42
5.2 Real constants for the model 43
5.3 Mapped mesh 45
5.4 Generation of fan impeller 46
5.5 Boundary condition 47
5.6 Solution 48
CHAPTER 6 RESULT AND DISCUSSION
6.1 Static analysis 49
6.2 Optimization 49
6.3 Results for fan impeller original thickness 50
6.4 Results for optimized fan impeller 58
CHAPTER 7 CONCLUSION
7.1. Real constants for the model 66
7.2 Weight reduction 67
REFERENCES
LIST OF FIGURES PAGE NO
FIG.1- LINE PLOT OF FAN IMPELLER SEGMENT 42
FIG.2- AREA PLOT OF FAN IMPELLER SEGMENT 43
FIG.3- REAL CONSTANT NUMBERING FOR THE SEGMENT 44
FIG.4- MAPPED MESH OF THE SEGMENT 45
FIG.5-FAN IMPELLER MODEL WITH REAL CONSTANT NUMBERING 46
FIG.6-MAPPED MESH OF THE IMPELLER MODEL 46
FIG.7- CONSTRAINTS AT THE CENTRE 47
FIG.8- MESH OF IMPELLER WITH CONSTRAINTS 48
FIG.9- ORIGINAL FAN IMPELLER DEFLECTION PLOT 50
FIG.10- ORIGINAL FAN IMPELLER STRESS PLOT 51
FIG.11- ORIGINAL BACKPLATE (BOTTOM) DEFLECTION PLOT 52
FIG.12- ORIGINAL BACK PLATE (BOTTOM) STRESS PLOT 52
FIG.13- ORIGINAL BACK PLATE (TOP) DEFLECTION PLOT 53
FIG.14- ORIGINAL BACK PLATE (TOP) STRESS PLOT 53
FIG.15- ORIGINAL BLADE DEFLECTION PLOT 54
FIG.16- ORIGINAL BLADE STRESS PLOT 54
FIG.17- ORIGINAL COVER PLATE DEFLECTION PLOT 55
FIG.18- ORIGINAL COVER PLATE STRESS PLOT 55
FIG.19- ORIGINAL RING DEFLECTION PLOT 56
FIG.20- ORIGINAL RING STRESS PLOT 56
FIG.21- ORIGINAL FLANGE DEFLECTION PLOT 57
FIG.22- ORIGINAL FLANGE STRESS PLOT 57
FIG.23- OPTIMIZED FAN IMPELLER DEFLECTION PLOT 58
FIG.24- OPTIMIZED FAN IMPELLER STRESS PLOT 59
FIG.25- OPTIMIZED BACKPLATE (BOTTOM) DEFLECTION PLOT 60
FIG.26- OPTIMIZED BACK PLATE (BOTTOM) STRESS PLOT 60
FIG.27- OPTIMIZED BACK PLATE (TOP) DEFLECTION PLOT 61
FIG.28- OPTIMIZED BACK PLATE (TOP) STRESS PLOT 61
FIG.29- OPTIMIZED BLADE DEFLECTION PLOT 62
FIG.30- OPTIMIZED BLADE STRESS PLOT 62
FIG.31- OPTIMIZED COVER PLATE DEFLECTION PLOT 63
FIG.32- OPTIMIZED COVER PLATE STRESS PLOT 63
FIG.33- OPTIMIZED RING DEFLECTION PLOT 64
FIG.34- OPTIMIZED RING STRESS PLOT 64
FIG.35- OPTIMIZED FLANGE DEFLECTION PLOT 65
FIG.36- OPTIMIZED FLANGE STRESS PLOT 65
LIST OF TABLES
TABLE 2.1- ELEMENT TABLE 19
TABLE .5.2- REAL CONSTANTS FOR THE MODEL 43
TABLE.6.1- OPTIMIZATION TABLE 49
TABLE.7.1- DIMENSIONS FOR THE MODEL 66
NOMENCLATURE
N - rpm
D - Fan diameter (mm)
µ - dynamic viscosity
Ns - Specific speed
Q - Volume flow rate (m3/sec)
gH - specific energy (J/kg)
P - Pressure rise (pa)
ρ - fluid density (kg/m3)
CHAPTER 1
INTRODUCTION
CHAPTER1
INTRODUCTION
1.1 Organization Profile
M/S. BHARAT HEAVY ELECTRICAL LTD., popularly
known as BHEL is today, the largest engineering and manufacturing
enterprise of its kind among the public sector undertakings in India. The
company provides products, systems and services in the field of energy and
transportation for domestic and export markets.
The company ranks amongst the worlds top 10 organizations
engaged in the manufacturing of power plant equipment. About 50
countries, extending from USA in the west to Australia and New Zealand in
the far east are BHEL’s customers.
1.2 BHEL - BOILER AUXILIARIES PLANT - RANIPET
BHEL – Trichy launched its phase III expansion for
augmentation of manufacturing capacity to 4,000 MW for boilers and
auxiliaries at Ranipet Tamilnadu in 1982.
The product profile of BAP, Ranipet is
Fans – Radial, Axial, Impulse and Axial reaction
Electrostatic precipitators
Air preheater (Regenerative type)
These auxiliaries play a vital role in the thermal power plants.
There are 43 ancillaries established adjacent to the plant .BHEL gives by
way of technical , raw material and quality control procedure , BAP Ranipet
has technical collaboration with M/S K.K.K, West Germany for fans .
BAP at Ranipet provides direct employment to about 3,000
employees and indirect employment of over 10,000 employees. BHEL is
certified with ISO 9001 and ISO 9002 by BVQI.
1.8 About the Project.
This project has been done to predict and give the results of a
Radial fan impeller under physical operating conditions.
The Radial fan impeller is analyzed before the performance
testing and installation. Stress analysis is performed to find the maximum
stress values. These analysis are done by ANSYS.
In this project static and optimization of fan impeller thickness
have been performed during the analysis using the software.
In static analysis the maximum stress, strain values for the
required boundary conditions are found. In optimization, the impeller
thickness is reduced or optimized without changing or violating the
maximum stress values. So that the weight reduces and hence the cost of the
product also reduces.
HARDWARE REQUIREMENTS
Processor : PENTIUM III
CPU speed : 400Mhz
HDD : 20GB
Main memory capacity: 159MB
SOFTWARE REQUIREMENTS
ANSYS 5.4
1.9 About the Fan
A fan is a turbo machine used for energy transfer. It can be defined as a rotating machine with a bladed impeller, which maintains a continuous flow of air (or) gases.
Fans usually consist of a single rotor with or without a stator element and cause a rise in pressure of the flowing fluid.
PRINCIPLE OF WORKING:
The principle involved is that the mechanical energy owing to the rotation of the fan is converted into the fluid energy (in the form of pressure rise).
Fans obviously consume power as they rotate with the help of prime mover and energize the flowing fluid.
1.5 CLASSIFICATION OF FANS:
1.5.1 ACCORDING TO PURPOSE:
1. Primary Air Fan :( PA FAN)
Primary air fans supply the air needed to dry and transport pulverized coal to the furnace of direct-fired boiler.
2. Forced Draught Fan: (FD FAN)
The forced draught fans supply the air-required for the combustion of fuel and normally handle stoichiometric plus excess air required for the satisfactory burning of fuel.
3. Induced Draught Fan: (ID FAN)
The induced draught fans draw the products of combustion from the boiler while creating sufficient draught (negative pressure) in the furnace for balanced draught operation.
1.5.2 ACCORDING TO FLOW OF AIR:
1. Radial Fan:
A radial fan is a one in which the flow enters along the axis and leaves in the radial direction along the blades. It can be used for PA, FD and ID applications.
Based on the configuration of the blade with respect to the direction of rotation of the impeller (AS SHOWN IN THE FIG.) it is called backward curved, forward curved and radial bladed impeller
FIG. 1.1
2. Axial Fans:
An axial fan is a one in which the main flow is along the axis of
rotation both at entry and exit.
2 < 90 2 = 90 2 > 90
Based on the profile these fans are mainly classified into two
types namely,
I Axial Profile Impeller: (AP IMPELLER)
In this type, the impeller has a central hub which is spherical in
nature and has blades with individual shafts located along the periphery.
The hub is a high precision part which is ball turned to get a curved
smooth profile. The individual blades of the impeller are driven with
the help of hydraulic mechanism.
II Axial Non – Profile Impeller: (AN IMPELLER)
In this type, the impeller has a central hub, which is of
hemispherical nature and has blades curved at a fixed angle and welded
to the hub as in case of its radial counterpart.
Both the fans described above have an inlet guide vane (IGV)
and an outlet guide vane (OGV) along with a diffuser at the exit.
AEROFOIL BLADED RADIAL FAN - A GLANCE
An aerofoil bladed radial fan consists of blades, which are
profiled, in an aerofoil shape as shown in the figure below:
FIG .1.2
1.6 Advantages of an Aerofoil Bladed Fan:
a. Since the aerofoil is a profile curved body, it ensures a
smoother flow than a blunt body and hence no flow separation
thereby minimized losses
b. Because of higher efficiency than normal plate bladed impeller
it consumes less power and hence it is economical.
c. An aerofoil bladed fan has the higher half – load efficiency like
an axial fan and the rigidity of that of a radial fan and hence the
combined feature of both.
But the aerofoil bladed is mostly employed as primary air fan.
1.7 CONSTRUCTIONAL FEATURES OF A RADIAL FAN:
The fan as a whole can be divided in to some major sub –
assemblies.
1. SPIRAL CASING:
The spiral casing consists of two parallel sidewalls, spiral wall,
Suction Chamber and inlet cone. It is split horizontally along the shaft
axis plane; if necessary the upper portion will also be vertically split off
at the center so that impeller installation is easy. The inlet cone and the
suction chamber are welded to the sidewalls.
2. IMPELLER:
The impeller is a completely welded structure. It consists of a
center plate (or) back plate, cover plate and blades. The blades are
welded between the back plate and the cover plate. Proper welding
sequence is followed to have minimum distortion.
3. SHAFT:
The shaft is a hollow tube with 2 endpins shrunk-fit at the 2
ends is welded. Torque is transmitted through the fit and the weld is only
for securing purpose. The tube is controlled at the inside diameter. The
shaft ends are machined after welding. A flat split ring is welded on to
the shaft tube for taking up the shaft flange. The complete shaft is
dynamically balanced.
4. BEARINGS:
The impeller is mounted on pillow block bearings. One is a
locating bearing while the other is a non – locating (FREE) bearing. The
bearings are spherical roller type housed in bearing housing. Or the
bearings are of sleeve types that are selected based on the contractual
requirement and or on the basis of the selection requirement.
5. DAMPER ASSEMBLY:
This consists of a single piece casing, damper flaps, damper
bearings and the actuating mechanism. It is welded casing flanged at both
the ends. The bearing pedestals are mounted to the sidewalls by screws.
There are 3 to 5 flaps fixed by screws on to their shafts, which
are supported by pedestals providing dry lubrication. The flat shafts carry
clamping levers and feather keys transmit the adjusting torque and a
linkage connects the individual clamping levers.
6. SEALS:
The sealing for the shaft with the spiral casing consists of a
labyrinth section For axial and asbestos strip for radial sealing. The
asbestos strip ensures that the movement of the spiral casing during hot
conditions relative to the impeller wheel does not attack the fan’s
functioning. The unmachined flanges of the spiral casing are sealed with
asbestos rope.
1.8 Methods to drive the Fan
Various methods are used to the Fan
Prime movers
Electric motors (the most commonly used)
Engines
Turbines (compressed air to steam)
Compressed air jets.
1.8.1Types of motor drives
There are three ways that can be used for an electric motor to drive a Fan:
1. Belt drive
2. Direct drive
3. Gear drive
1.8.2 Types of Electric motors used to drive fans:
1. Three-phase squirrel-cage motors
2. Three-phase wounded-rotor motors
3. Single-phase, single phase induction motors
4. Single-phase, permanent-split-capacitor motors
5. Single-phase, shaded-pole motors
6. Single-phase universal motors
7. Single-phase, inside-out induction motors
1.9 FAN SPECIFICATIONS:
Backward Aerofoil Bladed Fan Application- Primary Air Fan Power- 1500 KW Plant Capacity- 250 MW Fan size- NDZV 20 BAB2 Speed- 1000 rpm Head- 985 mmmw Pressure ~ 9850 Nm/Kg Volume – 50 m3/s Material Used – Naxtra 70
CHAPTER 2
LITERATURE REVIEW
CHAPTER 2
LITERATURE REVIEW
FINITE ELEMENT ANALYSIS (FEA) :
2.1 Introduction:
Finite Element Analysis (FEA) is a computer-based numerical
technique for calculating the strength and behavior of engineering structures.
It can be used to calculate deflection, stress, vibration, buckling behavior
and many other phenomena. It can be used to analyze either small or large-
scale deflection under loading or applied displacement. It can analyze elastic
deformation, or "permanently bent out of shape" i.e., plastic deformation.
Computer is required because of the astronomical number of calculations
needed to analyze a large structure. The power and low cost of modern
computers has made Finite Element Analysis available to many disciplines
and companies.
2.2 Historical Background:
The very basics of the finite element method rose from the
advances in aircraft. It all began with Hrenikoff, in 1941 presenting a
solution to elasticity problems using “the frame work method”. This trend
continued with Courant’s paper based on piecewise polynomial interpolation
in 1943. Turner et al. derived stiffness matrices for truss, beam and other
elements and presented their findings in 1956. But Clough first coined the
term finite element in 1960.
2.3 What is FEA?
The finite element analysis is a kind of analysis in which a
complex region defining a continuum is discretized into simple geometric
shapes called finite elements. The material properties and the governing
relations are imposed on these elements and expressed in terms of unknown
values at element corners.
An assembly process duly considering the loading and
constraints, results in a set of equations. Solution to these equations gives us
the approximate behavior of the continuum.
2.4 Need for Finite Element Analysis:
Finite Element Analysis makes it possible to evaluate a detailed
and complex structure, in a computer, during the planning of the structure.
The demonstration in the computer of the adequate strength of the structure
and the possibility of improving the design during planning can justify the
cost of this analysis work. FEA has also been known to increase the rating of
structures that were significantly over designed and built many decades ago.
In the absence of Finite Element Analysis (or other numerical
analysis), development of structures must be based on hand calculations
only. For complex structures, the simplifying assumptions required to make
any calculations possible can lead to a conservative and heavy design. A
considerable factor of ignorance can remain as to whether the structure will
be adequate for all design loads. Significant changes in designs involve risk.
Designs will require prototypes to be built and field-tested. The field tests
may involve expensive strain gauging to evaluate strength and deformation.
With Finite Element Analysis, the weight of a design can be
minimized, and there can be a reduction in the number of prototypes built.
Field-testing will be used to establish loading on structures, which can be
used to do future design improvements via Finite Element Analysis.
2.5 The Finite Element Method:
In general, in the finite element method, a structure is broken
down into many small simple blocks or elements. The behavior of an
individual element can be described with a relatively simple set of equations.
However, there are two general approaches associated with the
finite element method. One approach called the force method uses the
internal forces as the unknown constraints of the problem, while the other,
the displacement method (or) stiffness method uses displacement as the
unknown.
In the finite element method the continuum is discretized into
small inter connected elements called finite elements, and these elements
have a displacement function associated with it. Each inter connected
element is linked, directly (or) indirectly to every other element through
common interfaces including the nodes and boundary line and surfaces. By
using the known stress strain properties of the material making up the
structure, one can determine the behavior of a given node in terms of
properties of every other in the structure. The total set of equations
describing the behavior of each node results in a series of algebraic
equations best expressed in matrix notation.
2.6 Concepts of FEA:
As described earlier the FEA can be used to determine the
stress and deflection of any structure under load.
According to Newton’s II law,
The force on any body due to external load is given by,
F = ma
This under equilibrium conditions the above equation can be represented in
the differential form as,
mä + cå + ka = 0
where,
a = kx
å = dx/dt
ä = d2x/dt2
So,
[m. (d2x/dt2)] + [c. (dx/dt)] + kx = 0
In matrix form is represented as,
[m] * [k] * [δ] = [f]
By solving the above matrix equations with the values given
(or) solved the values for stress and deflection can be determined easily.
2.7 General procedure for FEA:
With the advent of hi-tech computers, the FEA solutions for complex problems are made easy and simple. The general procedure for the FEA is outlined in the form of a flowchart as below:
FLOW CHART. 2.1
Pre – processor
Read the input data and identify the design constraints.Model the continuum.Identify the element type and mesh the model.Define the boundary conditions and load data.
Processor/solution
Compute element stiffness matrices.Assemble element equations.Solve equations for the conditionCompute results.
Pre – processor
Plot the resultsInterpret the results
27.1 Discretization:
It is the process by which a closed form mathematical
expression such as a function (or) a differential (or) integral equation
involving functions, all of which are viewed as having an infinite continuum
of values throughout some domain, is approximated by analogous
expressions that prescribes values at only a finite number of discrete points
(or) volumes in the domain.
2.7.2 Meshing:
A finite element model includes a mesh of nodes and
elements. The best way of creating mesh is to create the part’s geometry,
then generate a mesh on the geometry. Since the finite element model is
associated with the part, any change to the part is automatically reflected in
the nodes and elements of the mesh. Part geometry based meshes are also
used for geometry-based optimization.
There are generally two types of meshes;
1.MAPPED MESH:
It is a kind of mesh in which the points of the mesh are
arranged in a regular way all through the continuum and can be stretched to
fit a given geometry.
2.FREE MESH:
It is a kind of mesh where the points fill the space to be
considered but is not connected with the regular topology. The mesh with an
irregular structure is often referred to as an unstructured (or) free mesh.
FIG. 2.1
DIAGRAMATIC REPRESENTATION OF MAPPED AND FREE
MESH
FREE MESH
MAPPED MESH
2.8 Applications of FEA:
There are several engineering applications of FEA, but some of the notable one’s are mentioned below:
Structural analysis
Structural machines
Aerospace engineering
Solid mechanics and foundation engineering
Rock mechanics and heat conduction
Hydrodynamics and hydraulic engineering
Water resources and nuclear engineering.
2.9 Setting element attributes:
Before generating a mesh of nodes and elements, the element
attributes are to be defined.
Element type
Real constant set
Material Properties set
Element co-ordinate system
2.10 Boundary conditions:
2.10.1 Definition of Boundary condition
Boundary conditions are nothing but the constraints of the model
that is to be analyzed. The constraints may be displacement, inertias, loads
(forces, moments), temperature, fluid velocity, etc., for every model the
boundary conditions are must be specified. Without the impositions of the
boundary conditions, the element and assemblage stiffness matrices, [k] and
[k], are singular; that is, their determinants vanish and their inverse do not
exist.
The physical significance of this is that a loaded body or structure
is free to experience unlimited rigid body motion unless some supports or
kinematic constraints are imposed that will ensure the equilibrium of the
loads. These constraints are the boundary conditions.
2.10.2 Boundary conditions for the model
1.Displacement:
The rotating motor shaft is fixed in the impeller therefore the
displacement on the impeller hole is zero in all degree of freedom.
2.Angular velocity and angular acceleration:
The impeller rotates about the “z” axis at a speed of
1000rpm. Therefore
Angular velocity = (2πN)/60
= 104.7 rad/sec
The angular acceleration is also given as 9810 rad/sec2.
2.11 Material properties:
Once a mesh has been built to describe the domain occupied by
the structure, the rest of the computer model can be built. It is only at this
stage that the description of the physical problem generated in the initial
stage of the analysis process can be related to the computational geometry
described by the mesh of nodes and elements. For each element, its material
properties must be defined together with the boundary conditions on the
faces of the elements, or at the nodes, which form the exterior of the mesh.
It is not necessarily straight forward task to define precisely the
material properties and, frequently, they must be approximated when
compiling the model data for an analysis.
For this model, the constant Isotropic material has been used and
their values are
1.Young’s modulus EX = 21000 kg/mm2
2. Density DENS = 8.002 e-10 mN/mm3
3. Poisson’s ratio NUXY = 0.3
2.12 Element type
Element type used in FEA may be described in terms of their
shape (through the relative positions of its nodes) and degrees of freedom
(possible directions of movements of each node). The element plot and
nodal plot for the model are shown in fig.
ELEMENT PICTORIAL VIEW TYPE
2-NODED BEAM ELEMENT
1 - D
3 – NODED BEAM ELEMENT
1 – D
3 – NODED TRIANGULAR ELEMENT
2 – D
6 – NODED TRIANGULAR
ELEMENT
2 – D
4 – NODED AREA ELEMENT
2 – D
8 - NODED AREA ELEMENT 2 – D
8 – NODED BRICK ELEMENT 3 – D
4 –NODED PYRAMID ELEMENT
3 – D
TABLE 2.1
ELEMENT TABLE
2.12.1 Element type for the model
For this analysis 4-noded area element (SHELL 63) is used.
SHELL 63 element is well suited for mapped meshing for this model.
Usually for any area of a model can be meshed using 4-noded area element
(SHELL 63) in a uniform manner (mapped meshing). It is a kind of mesh in
which the points of the mesh are arranged in a regular way all through the
continuum and can be stretched to fit a given geometry so that the results
will be more accurate when compared to free mesh results.
2.12.2 Choosing the element type
1.The range of elements and testing the elements:
It is not possible to present a set of universal guidelines to
develop any finite element model as such structural problem and element
type have their own particular features. It is not even possible to give rules
for what appears in packages to be identical element types since their
formulation can be different.
Any test for element behavior should be more complicated than
the situation of a simple rectangular geometry with a constant load, since
simple situations can give a false impression of the convergence
characteristics for realistic problems.
Quadratic elements, be they membrane or solid elements, give
the best compromise between accuracy and efficiency for general use.
When modeling a structural problem that can be classified, as
having bending deformation and the geometry is either flat or curved, then
the preferred choice of elements is always the general shell element.
Curved surfaces should not be modeled using flat elements as the
discontinuity at element boundaries introduces significant error.
2. Using a Hierarchy of elements:
Analysts should develop a model using a step by step approach.
This means that they should start with a simple approximation, say a beam
model, and make it more precise as the finite element modeling progresses.
Never tackle a real problem directly as this is likely to be time consuming
and wasteful of resources. Remember, that more results that are generated
the more effort that will be necessary to check that they are reliable and
relevant.
3. Restricting the dimensions of a problem:
Avoid the use of solid elements to model a problem where the
length in one of the spatial dimensions, for example the material thickness,
is much less than the lengths in the other two dimension.
4. Plate and shell elements:
Plate and shell elements have historically been the most difficult
to use in terms of achieving reliable and cost effective solutions. In
particular these elements in a static analysis do not give an acceptable
solution if the displacement of the nodes normal to the surface of the
material is greater than the thickness of the material.
5. The role of compatibility:
Elements must have the same order, all though one can mix three
sided and four sided elements.
There must be connection between the corner nodes of
neighboring elements and, if present, continuity between the edge nodes of
adjacent elements.
6. Elements of model contact:
Before developing a three dimensioning model for a problem
with contact between different parts, check that the package has three
dimensional contact algorithms.
2.13 Fan laws and Efficiency
2.13.1 Fan laws:
There are certain fan laws that are used to convert the
performance of a fan from one set of variables to another.
1.Conversation of fan performance
Suppose a fan of a certain size and speed has been tested and its
performance has been plotted for the standard air density. We then can
compute the performance of a fan of geometric similarity by converting the
performance data in accordance with these fan laws without running a test
on the other fan. It called as general fan laws.
2.Variation in fan speed
In order to convert the performance of a fan at one speed to
another speed, We take a number of points on the performance graph and
convert the corresponding data for air volume, static pressure, bhp,
efficiency and noise level fro the speed of the graph to the desired speed
using the following rules.
The air volume (cmf) varies directly with the speed
(cfm2/cfm1) = (rpm2/rpm1)
The pressure vary as the square of the speed
(Sp2/Sp1) = (rpm2/rpm1)
The brake horse power varies as the cube of the speed
(bhp2/bhp1) = (rpm2/rpm1)
The efficiency remains constant but, of course, shifts to the new air
volume values.
Variation in fan size
This law is used to convert the performance of one fan to
another fan when they are geometrically similar .
The fan laws for size , however , can be used only if the two
fans are in geometric proportion .
Both fans have the same number of blades .
Both fans have the same blade angles and any other angles on
the fan wheel and fan housing.
If the diameters of the two wheels are D1 and D2 for a size
ratio D2/D1, all other corresponding dimensions of wheel and housing have
the same ratio.
The air volume (cfm) varies has cube of the size. (cfm2/cfm1)
= (D2/D1)3
The pressure vary as the square of the size .
(sp2/sp1) = (D2/D1)2
The bhp varies as the fifth power of the size .
(bhp2/bhp1) = (D2/D1)5
Variation both fan size and fan speed
If both the fan size D and the fan speed (rpm) are varied , the
two sets of rules discussed above can be applied consecutively , in either
sequence .
(cfm2/cfm1) = (D2/D1)3 *(rpm2/rpm1)
(sp2/sp1) = (D2/D1)2 *(rpm2/rpm1)2
(bhp2/bhp1) = (D2/D1)5 *(rpm2/rpm1)3
(ME2/ME1)=1
Variation in Density
This fan law is used when the fan operates at high altitude
where the air density is less , where the fan handles hot or cold air (the air
density is inversely proportional to the absolute temperature) , or where the
fan handles a gas other than air , while the size and speed of the fan remains
constant.
The air volume remains constant
(cfm2/cfm1) = 1
The pressure vary directly as the density ρ
(sp2/sp1) = (ρ2/ρ 1)
The bhp varies directly as the density ρ
(bhp2/bhp1) = (ρ2/ρ 1)
The efficiency remains constant
2.13.2 Fan Efficiency
Fan work can be equated to the system resistance. Fan pressure has
the dimension of work per unit volume. Thus the system resistance may also
be regarded as the work required per unit volume of gas.
Power kw = Q X Ps
Work = force X Distance
Power = force X Velocity
= pressure X Area X Velocity
= pressure X Volume
The ratio of this air power to the power required to drive the fan is
the fan efficiency. The pressure may be total (including the velocity
pressure) or static and resulting efficiencies may also be “total” or “static”.
Selecting a fan of higher efficiency normally results in higher first
cost, but in lower operating cost.
1. Size and type limitations to good efficiency
High operational efficiencies are only achievable with certain types
and sizes of fan; indeed, the definition of “good” and “high” efficiency
depends on the class and quality of the fan being considered.
For a particular type of fan the best efficiencie swill be achieved by
higher specific speed fans of backward curved, backward inclined or aerofoil
bladed design with the fans being medium or large diameter and operating at
Reynolds numbers in excess of 20x105.
Where Reynolds number = (ρuD) / μ
D – Fan dameter
ρ – Fluid density
μ – Dynamic viscosity
2. Specification of fan requirements
Aerodynamic duty:
An important factor in ensuring a successful fan system is the correct
specification of the fan. The starting point in the specification of the fan is
knowledge of flow rate, which the fan (or fans) is required to handle. Often
there will be a range of flow rates over which the fan will be required to
operate and if this range is large it may be necessary to consider employing a
number of fans in parallel.
The next parameter to be defined is the pressure rise required of the
fan to move the gas through the system. This requires a knowledge of the
layout the system including pipe lengths, pipe diameters and elevations, a
knowledge of all the pipe work components in the system and information
on the properties of the gas being moved, particularly its density and
viscosity. From this it is possible to calculate the pressure losses in the
system.
If the fan duty varies with time then the use of variable geometry or
variable speed is almost certainly economically beneficial in terms of whole
life costs, if the duties of the fan are anticipated to increase with the time e.g.
: - if the output of the process system in which the fan operates is expected
to grow, then it may be possible to commence operation with a reduced
diameter (or reduced width) impeller fitted in to a standard casing and, as the
demand increases, fit the standard impeller. this will generally be preferable
to initially running the fan at a flow rate way below its design condition and
offer advantages of reduced power consumption and reduced bearing loads.
3. Estimation of fan type, size and speed:
Once the flow rate and pressure are known it is possible to derive
some idea of feasible options for the type of fan required. Simple formula
will allow initial estimates to be made of the probable type(s) and size(s),
which are optimum for a particular installation.
The specific speed, Ns, of a fan is a measure of the fan shape or type.
Ns is defined as Ns = [w (Q) 0.5] / (gH) 0.75
Where w is the rotation speed of the fan (rad / sec)
Q is the volume flow rate (m3 / sec)
gH is the specific energy ( J / Kg )
gH = (p / ρ)
Where p is the fan pressure raise – pa
ρ is the fluid density – Kg / m3
Knowing Q and gH, a range of rotational speeds can be assumed.
Typically these will correspond to 2, 4, or 6 pole motor speeds with a wide
choice available for belt driven fans. The value of Ns defines the optimum
fan type for the duty. If Ns is less than about 1.5 the fan will be a centrifugal
machine; if Ns is greater than about 2.5 the optimum fan will be an axial,
between 1.5 and 2.5 the optimum unit would be mixed flow type.
The next stage is to determine the approximate impeller diameter. For
a centrifugal type fan the dia can be estimated from the relationship, Farrant
V2 tip = gH / (0.8 - 0.23 Ns)
And for an axial or mixed flow machine from
D = 2[ gHQ / w3kL ]0.2
Where the loading coefficient, kL, has a value typically in the range 0.01 to
0.08.
It is thus possible to get an idea of the potential speed and dia of the
fan best suited to the duty. If either the speed or dia appears impractical this
may well point to the need to consider multistage fans or a series of fans in
parallel.
For multistage fans the head per stage reduces, thus raising the
specific speed per stage. For fans in parallel the flow per fan decreases thus
increasing the specific speed per unit.
2.14 STRESS ANALYSIS
Stress is defined as "a force tending to produce strain or
tension and to change the form or dimension of a solid", by dictionary. A
common man's understanding of stress is very much different from that of an
engineer. For an engineer
Limit F
Stress = A 0
A
Where, F = Force vector acting on the small area
M
Ever since the invention of Hooks
Law by the famous English Scientist Robert Hook (1935 -1703) analysis of
stress and strain has attracted many brilliant scientific and engineering
minds. Today, the theory is well developed and is widely used. However, a
general analytical calculation for the state of stress and strain in a general
solid is not yet available and is considered impossible to obtain. ' Stress
analysis problems can be solved using two sets of methods, i.e. experimental
and theoretical Hence, many numerical techniques have been developed and
are widely used in the industries for stress analysis. Finite Element Method
(FEM), one of the numerical techniques, was developed in fifties. Today
Finite Element Method is very popular and widely used in industry. Though
the underlying concept was originally introduced by Argyris in 1954-55, it
was supplemented by Turner, Clough, Martin and Toop in 1956. The
method is widely used since the development of high-speed electronic
digital computers and development of numerical methods to handle difficult
mathematical problems. Though the method was originally developed as a
tool for structural analysis, the theory and formulation have been
progressively refined and generalized and the method has been successfully
applied to many other fields like thermal, fluid, vibration, electrostatics,
Electro-magnetism, etc.
2.14.1 NEED FOR STRESS ANALYSIS
After the Industrial Revolution of nineteenth century,
large and complex machines and structures were built to mankind. As the
time passed, new types of machines and structures were built in critical and
demanding applications, requiring high reliability and economy. These
factors in design, under new environment of competition resulted in
application of analytical methods in the solution of engineering problems.
Design is no longer based upon empirical formulae. The importance of
analytical methods combined with laboratory experiments in the solution of
engineering problems has been recognized and accepted by the engineering
community. The conflicting requirements of increased reliability, reduced
cost and improved performance make the task of designer extremely
complicated.Reduced cost means reduced weight. Increased reliability with
reduced weight can be" achieved only on the basis of careful analysis of
stress distribution in the structure and experimental investigation of the
mechanical properties of the materials. Experimental techniques have
become very refined over the years. Similarly, analytical techniques have
become complex and advanced, leading to better understanding of stress
distribution in complicated solids.
CHAPTER 3
INTRODUCTION TO ANSYS
CHAPTER 3
3.1 Introduction to ANSYS
ANSYS is a general purpose finite element computer program for
the solution of structural, heat transfer engineering analysis. ANSYS
solution to capabilities includes: static analysis, elastic, plastic, thermal,
stress, stress stiffened, large deflections, bilinear elements, dynamic
analysis, model, harmonic response, linear time history, non-linear time
history, heat transfer analysis: conduction, convection, radiation, coupled to
fluid flow, coupled to electric flow, structures, magnetics, etc. Analysis can
be made in one, two, or three dimensions, including axisymmetric and
harmonic element options. ANSYS also contains a complete graphics
package and extensive pre and post processing capabilities.
3.2 ANSYS offers
1.tensive capabilities
2.ailability
3.owth and development
4.pport
3.3 Examples of ANSYS analysis
Examples Special options used
1.Laying ocean cable Dynamic, stress stiffening, large
deflection, hydrodynamic forces.
2.Automatic crash studies Dynamic, large deflection, plasticity,
gaps.
3.Evaluation of golf club swing Large rotations, stress stiffening.
4.Railroad tank car Dynamic, Fluid elements, pressure
vessel fatigue evaluation.
5.Piping system evaluation Static, seismic, gaps, large
deflection.
6.Electric furnaces smelting Heat transfer, thermal- electric
elements.
7.Electronic circuit boards & Heat transfer, radiation, static,
microchips thermal stresses.
8.Offshore power plant Multi-level sub structuring statics,
modal, over 1.5 million dofs.
9.Artificial hip prosthesis Statics, orthotropic materials.
10.Turbine Blade analysis Stress-stiffened, modal analysis.
3.4 Choosing the software
The first thing to consider is how knowledge of structural
mechanics might help you and your organization. To explore this, functional
area are related to structural mechanics must be considered. Structural
analysis may be used to determine the linear static stress and displacement in
structures such as vehicle body shell and the engine under operational loads.
Also, optimization may be required to produce body shells with a given
displacement for the minimum material thickness.
To find out which of the available packages may be used, a list of
requirements that the software should meet must be produced. More often
than not, no single package will meet all the requirements, but several
packages will meet some of the requirements.
3.5 Feature selection
The geometry of the structures that may need to be analyzed. This
will show whether a package is needed that can solve problems in two or
three dimensions.
3.5.1 Coupling requirements to other software
In some cases there may be a need to link structural results to heat
transfer simulations or even to fluid flow software. There may be a
requirement to send the results to a proprietary post-processor or to some
other display software, so that software must have interfaces.
3.5.2 The size of the simulation problem
Here something about the number of nodes and elements that a
typical mesh contains needs to be known, together with the number of
degree of freedom that is to be calculated. This information helps to
determine the storage requirements of the programs in terms of both primary
and secondary storage.
3.6 Results required for analysis
Stresses, strains and displacements, possibly as a function of
time.
3.7 Solution speed
Many things affect the time that it takes to produce the
solution. Clearly, this depending on the processing speed of the hardware
used, but it also depends on the structural solver itself.
3.8 Hardware availability
If there is a restriction on the make or type of computer or
graphics terminal that the software can be run on, this should be noted.
3.8.1 The following are some of the requirements that are related to the
software
Quality assurance (QA)
User friendliness
User support
Current users
3.9 Analysis procedure
3.9.1 Static analysis
A static analysis calculates the effects of steady loading conditions
on a structure, while ignoring inertia and damping effects such as those
caused by time varying loads. A static analysis can, however, include steady
inertia loads such as gravity and rotational velocity, and time – varying loads
that can be approximated as static equivalent loads (such as the static
equivalent wind and seismic loads commonly defined in many building
codes ).
3.9.2 Loads in a static analysis
Static analysis is used to determine the displacements,
stresses ,strains, and forces in structures or components caused by loads that
do not induce significant inertia and damping effects.
Steady loading and response conditions are assumed that is ,the
loads and the structure’s response are assumed to vary slowly with respect to
time .The kinds of loading that can be applied in a static analysis include:
Externally applied forces and pressures
Steady- state inertial forces (such as gravity and rotational
velocity)
Imposed (non-zero) displacements
Temperatures (for thermal strain)
Fluences (for nuclear swelling)
3.10 Procedure for a static analysis
3.10.1 The procedure for a static analysis consists of three main steps:
1.Build the model
2.Apply loads and obtain the solution
3.Review the results
The overall equilibrium equations for linear structural static analysis are:
[K] {u} = {F}
OR [k] {u} = {Fq} + {Fq}
N
Where: [K] = total stiffness matrix = ∑ [Ke] M=1
{u} = nodal displacement vector
N = number of elements
[Ke] = element stiffness matrix
{Fq} = total applied load vector
{Fr} = reaction load vector
1.Build the model:
To build the model, define the element types, element real
constants, material properties, and the model geometry.
2.Apply loads and obtain the solution:
In this step, the loads (boundary conditions) are defined and the
solution is obtained.
3.Review the results:
After the solution is completed, the post-processing step gives
the results of the static analysis.
Primary data available
Nodal displacements (UX, UY, UZ, ROTX, ROTY,
ROTZ)
Derived data available
Nodal and element stresses
Nodal and element strains
Element forces
Nodal reaction forces
Etc.,
3.11 Modal analysis
Modal analysis is used to determine the vibration characteristics
(natural frequencies and mode shapes) of a structure or a machine
component while it is being designed. it also can be a starting point for
another, more detailed, dynamic analysis, such as a transient dynamic
analysis, a harmonic response analysis, or a spectrum analysis.
3.11.1 Uses of modal analysis
Modal analysis is used to determine the natural frequencies and
mode shapes of a structure. The natural frequencies and mode shapes are
important parameters in the design of a structure for dynamic loading
conditions.
Modal analysis can be made on a pre-stressed structure, such as
spinning turbine blade. Another useful feature is modal cyclic symmetry,
which allows you to review the mode shapes of cyclically symmetric by
modeling just a sector of it.
3.12 Procedure for modal analysis
3.12.1 The procedure for a modal analysis consists of four main steps:
1. Build the model
2. Apply the loads and obtain the solutions
3. Expand the modes
4. Review the results
3.12.2 Assumptions and restrictions
Valid for structural and fluid degrees of freedom(DOFs)
The structure has constant stiffness and mass effects.
There is no damping.
The structure has no time varying forces, displacements, pressures, or
temperature applied (free vibration).
The equation of motion for an undamped system, expressed in matrix
notation using the above assumptions is:
[M] {u} + [K] {u} = {0}
3.13 Design optimization
Design optimization is a technique that seeks to determine an
optimum design. By “optimum design” all the specified requirements are
met with a minimum expense of certain factors such as weight, surface area,
volume, stress, cost, etc. in other words, the optimum design is usually one
that is as effective as possible.
Any aspect of the design can be optimized: dimensions (such as
thickness), shape (such as fillet radii), placement of supports, and cost of
fabrication, natural frequency, material property and so on.
An optimum design can be defied as the best possible design
satisfying a specific objective and a set of constraints imposed by the
specifications or by the design problem itself.
3.14 Typical examples of optimized designs are:
Design of aircraft, aerospace and automotive structures for
minimum weight.
Design of machines, components, frames, and mechanisms,
handling devices etc., for minimum cost.
Design of pumps, turbines, compressors, engines, and etc.,
for maximum efficiency.
CHAPTER 4
METHODOLOGY
CHAPTER 4
METHODOLOGY
4.1. Solid model generation using preprocessor:
In ANSYS there are three stages. They are pre-
processor, solution and post processor. So before doing analysis, the
geometry of the model should be created. Modeling is done in ANSYS
through pre-processor. There we have lot of option through which the
geometry of the model is created.
4.2. Meshing contours:
After generation of the solid model using pre-
processor, the model should be meshed properly. That is the model should
be disecritised into number of small elements. For meshing of the model, we
should generate meshing contours. That is the lines of the geometry should
be properly divided. So that we can easily mesh the model otherwise without
the contours the mesh won’t be proper and we can’t solve it.
4.3. Meshing of areas:
After generation of contours for proper meshing we
should go for meshing of the model. There are two types of meshing. They
are free mesh and mapped mesh. So in free mesh we can solve it and get the
results but it won’t be accurate.
So for accurate results, we have to go for mapped mesh.
So if we did line element sizing (lesize) properly we get mapped mesh.
4.4. Defining material:
So after completing modeling and meshing we have to
define the material of the model. So there are different properties which will
define a material that is density, young’s modulus, Poisson’s ratio. For
different materials this values are different. By using these properties the
material can be define in pre-processor.
4.5. Choosing appropriate element for analysis:
The basic concept of FEA is to discritise the model into
finite number of smaller elements. There are different element types
available in ANSYS pre-processor. Based on the model the element types
vary. We have to choose a appropriate element for analysis.
4.6. Attributing equivalent and actual boundary:
After discritising and defining material of a model, we
have to apply the boundary conditions and the loads wherever we required
for the analysis. First, constraints should be applied. So wherever required,
the degrees of freedom should be arrested. After applying constraints, the
loads are applied on nodes or element for the analysis.
4.7. Solving the problem using solver:
Solution is the second stage in ANSYS where the solution
of the given problem is done. So here we won’t do anything the solution
module generate the element matrices and find the stress and deflections
according to the parameters we applied.
4.8. Viewing results:
The results are viewed in post-processor. Where the stress
and deflection can be plotted on the screen. So different colours are plotted
for different stress value. We can view both the maximum and minimum
stress.
4.9. Studying the parameters stress and deflection for existing design:
The above steps are done for the original design and stress
value and deflection for original design can be studied.
4.10. Modifying the geometry model by reducing the thickness:
After studying the stress and deflection for original design.
The stress and deflection for modified design should be studied. The design
is modified by reducing the thickness. Then all the above steps followed for
finding the stress and deflection value.
Finally the results of the original and modified design
should be should be compared in order to obtain a optimized design.
CHAPTER 5
MODELING
CHAPTER 5
MODELING
5.1 SEGMENT GENERATION:
First the segment of the radial fan impeller is created
using ANSYS preprocessor .The created segment is shown below in fig 1.
Area plot for the created segment using ANSYS preprocessor is shown
in the fig 2
COMPONENT ORIGINAL REALCONSTANT VALUES (mm)
MODIFIED REALCONSTANTVALUES (mm)
BACKPLATE(BOTTOM)
25 18
BACKPLATE(TOP)
15 10
BLADE 5 3.15
COVERPLATE 12 8
RING 30 15
FLANGE 80 45
5.2 REAL CONSTANTS FOR THE MODEL:
The table 5.1 shows the real constants for various
components of the original and optimized fan impeller model.
Thicknesses of the various component of impeller are ploted in different
colours which is shown in fig 3.
A1- Back Plate (Bottom)
A2- Back Plate (Top)
A3- Bade
A4-Cover Plate
A5- Ring
A6- Flange
5.3 MAPPED MESH:
Mapped mesh is generated for the model which is shown in fig 4.
Element type used for meshing the model is SHELL
ELEMENT (ET, 1, 63).
5.4 GENERATION OF FAN IMPELLER:
Fan Segment created is copied to 360 degrees along y-
axis with 12 segments (including original) so the fan impeller model is
generated which is shown in fig 6
5.5 BOUNDARY CONDITION:
DISPLACEMENT:
The rotating motor shaft is fixed in the impeller
therefore displacement on the impeller hole is zero in all degree of freedom.
ANGULAR VELOCITY AND ANGULAR
ACCELERATION:
The impeller rotates about the z-axis at a speed of 1000
rpm.Therefore angular velocity=2∏n/60=104.7 rad/sec(105)
Angular acceleration also 9810 rad/sec2.
5.6 SOLUTION:
After completing modeling and giving boundary
conditions the problem has to be solved using the ANSYS-SOLUTION
utility.In the solution utility all the element matrices are formed and it is
solved to find the stress and deflection for the applied boundary condition.
CHAPTER 6
RESULTS AND DISCUSION
CHAPTER 6
RESULTS AND DISCUSSIONS
6.1 STATIC ANALYSIS:
The stress distribution and the deflection of the
impeller are found. The stress distribution and the deflection plot for the
various components of the impeller are plotted in the figures.
6.2 OPTIMIZATION:
For the original fan impeller the stress value is
4.274kgf/mm2 and deflection is .0678mm.The blade in the impeller has the
maximum stress of 4.274kgf/mm2.
COMPONENTS
ORIGINAL FAN OPTIMIZED FAN
STRESS
Kgf/mm2
DEFLECTION
mm
STRESS
Kgf/mm2
DEFLECTION
mm
FAN IMPELLER 4.274 0.0678 5.822 0.09945
BACKPLATE(BOTTOM)
1.284 0.0126 1.291 0.016396
BACKPLATE(TOP)
2.318 0.03426 2.593 0.041143
BLADE 4.274 0.0678 5.822 0.099455
COVER PLATE 2.852 0.0526 3.091 0.064076
RING 2.927 .04845 3.159 0.057363
FLANGE .58453 .00198 .681387 .002394
TABLE .6.1
6.3 RESULTS FOR FAN IMPELLER WITH ORIGINAL
THICKNESS:
6.4 RESULTS FOR OPTIMIZED FAN IMPELLER:
CHAPTER 7
CONCLUSION
CHAPTER 7
CONCLUSION
In this work, an attempt has been made to increase the Fan
efficiency by optimizing the thickness of the various components in the fan
impeller, and analyzing the stress distributions in them. Optimization of the
thickness of the parts of impeller leads to decrease in weight of the Fan
Impeller, and in turn the power required for driving the fan decreases. Pre -
stress conditions are applied to this model, therefore the strengthening and
weakening of the impeller is predicted.
COMPONENT ORIGINAL IMPELLER THICKNESS (mm)
OPTIMIZED IMPELLER THICKNESS (mm)
Back plate(Bottom)
25 18
Back plate(Top)
15 10
Blade 5 3.15
Cover plate 12 8
Ring 30 15
Flange 80 45
7.1. DIMENSIONS FOR THE MODEL:
TABLE.7.1
7.2 WEIGHT REDUCTION:
After optimizing the thickness of the Fan impeller the weight
of the Fan Impeller is reduced.
Existing weight of the Fan Impeller=10 tones
=10,000 kg
After optimizing
% of weight reduced in the =18.5%
Fan Impeller
Amount of weight saved = (18.5/100)*10,000
= 1850 kg.
= 1.85 tones
Cost of steel/kg = Rs.300
In the BHEL-RANIPET there are about 12 Fans made per
year.
Total cumulative weight saved = 12*1850
= 22200 kg
= 22.2 tones
Total cumulative cost saved per year = 22200*300
= Rs. 66,60,000
REFERENCES
REFERENCES
1. John F.Abel, Chandra Kant S Desai (1987), ‘Introduction to the Finite
Element Method’- CBS Publishers and distributors, New Delhi.
2. Kalyanmoy Deb (2000), ‘Optimization for engineering Design’-
Prentice hall of India (p) Ltd, New Delhi.
3. Krishnamoorthy C.S. (1994), ‘Finite Element Analysis’ -Tata
McGraw-Hill publishing company, New Delhi
4. Robert D.Cook, David S. Malkus, Michael E.Plesha (1989), ‘concepts
and applications of finite element analysis’- John Wiley& Sons,
Singapore.
5. Thirupathi R.Chandrapatla, Ashok D.Belegundu (1997), ‘Introduction
to finite elements in Engineering’- Prentice hall of India (p) Ltd,
New Delhi.
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