FEA Using Ansys
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Transcript of FEA Using Ansys
By ANSYS INC
ANSYS
• Engineering simulation software founded by software engineer John Swanson.
• Developed a range of computer-aided engineering (CAE) Products, it is perhaps
best known for its ANSYS mechanical and ANSYS multiphysics products.
• Ansys mechanical and ANSYS multiphysics software are non exportable analysis
tools.
• These are general purpose finite element modeling packages for numerically
solving mechanical problems, including static/dynamic structural analysis both
linear/non linear), heat transfer and fluid problems
contd...
ABOUT ANSYS
About Analysis
Process of analyzing a structure to the externally applied loads( Pressure, Force, Temperature)
Basic Terminologies-Structural analysis• Stress• Strain• Poisson ratio• Hook's law• Young's modulus• Bending moment• Shear force• Stress strain curve for various materials• Linear• Nonlinear• Isotropic vs. anisotropic vs. orthotropic
Stress
When some external system of forces or loads act on a body, the internal forces (equal and opposite) are set up at various sections of the body, which resist the external forces. This internal force per unit area at any section of the body is known as unit stress or simply stress
Stress, σ = P/A
Strain
When a system of forces or loads act on a body, it undergoes some deformation. This deformation per unit length is known as unit strain or simply a strain. It is denoted by a Greek letter epsilon (ε).
Strain, ε = δl / l δl = ε.l
Displacement
A change in the configuration of a continuum body results in a Displacement. The displacement of a body has two components: a rigid-body displacement and a deformation. A rigid-body displacement consists of a simultaneous translation and rotation of the body without changing its shape or size. Deformation implies the change in shape and/or size of the body from an initial or undeformed configuration to a current or deformed configuration
Shear Stress
When a body is subjected to two equal and opposite forces acting tangentially across the resisting section, as a result of which the body tends to shear off the section, then the stress induced is called shear stress.
Shear stress, τ = Tangential force Resisting area
Shear Strain
When a body is subjected to two equal and opposite forces acting tangentially across the resisting section, as a result of which the body tends to shear off the section corresponding strain is known as shear strain.
Shear Force
In static equilibrium, the internal force has a magnitude equal to opposite in direction and parallel to the cross-section. is called the shear force.
F-Shear Force
BENDING MOMENT
• The bending moment at the cross section of a beam may be defined as the algebric sum of the moment of the forces to the right or left of the section
• The bending moment at the cross section of a beam may be defined as the algebric sum of the moment of the forces to the right or left of the section
DEGRESS OF FREEDOM
• Minimum no of independent co ordinates required to determine completely the positions of all parts of a system at a given instant time
• Minimum no of independent co ordinates required to determine completely the positions of all parts of a system at a given instant time
Young’s modulus And Poisson’s Ratio For Some Materials
Materials Young’s Modulus Poisson’s Ratio
Steel 2.1e5 0.3
Cast Iron 1.20e5 0.28
Wrought Iron 1.90e5 0.3
Aluminium 0.70e5 0.35
Aluminium Alloy 0.75e5 0.33
Brass 1.10e5 0.34
Bronze 1.20e5 0.34
Copper 1.20e5 0.34
Copper Alloy 1.25e5 0.33
Magnesium 0.45e5 0.35
Titanium 1.10e5 0.33
Glass 0.60e5 0.22
Rubber 50 0.49
Concrete 0.25e5 0.15
Truss element
• The truss elements are the part of a truss structure linked together by point joints, which transmit only axial force to the element
• The truss elements are the part of a truss structure linked together by point joints, which transmit only axial force to the element
GLOBAL & LOCAL AXES
GLOBAL :Global axes are defined for the entire
system. They are same in direction for all the elements even though the elements are differently oriented
LOCAL : Local axes are established in an
element. Since it is the element level, they change with the change in orientation of the element. The direction differs from element to element
Need for Analysis
•To reduce product development cycle time
•To reduce the cost of product
•Idle time reduction
•Better design and Alternate materials
•To reduce material wastage
Types of Methods
• Mathematical approach• Physical model• Numerical method
Introduction to FEM & FEA
• FEM-Finite element method• FEA –Finite element analysis
FEM
• Finite element method of structural analysis was created by academic and industrial researches during 1959’s and 1960’s
• Theoretical approach.• Examples Euler's rule, LaGrange method, Newton raphson method, Fourier series
Nature of FEM
• Force method (Forces unknown) Strain energy method Consistent deformation method Matrix flexibility method Clayperons theorem of 3 moments• Displacement method (Displacements unknown) Kanis method Slope deflection method Matrix stiffness method Moment distribution method FEM
FEA
FEA- simulate loading conditions on design &
determine design response to these conditions
The design is modeled using discrete elements called elements
The sum of response of all elements in the model gives the response of design
Problem types in FEA
• Boundary value problem-static and steady state analysis
• Initial value problem-fluid flow• Eigen value problem-Modal analysis, vibration
and natural frequency• Boundary initial value problem-forced
vibration, transient and dynamic analysis
Linear vs. Non linear
• What is linear analysis?• What is non linear analysis?• Types of non linearity• When should we do a non linear analysis?
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16.1.1 What is a Nonlinear Structure
Displacements
Forces
Displacements
Forces
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16.1.2 Causes of Nonlinearities
• Geometric Nonlinearity• Material Nonlinearity• Status Nonlinearity
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Geometric Nonlinearity
Force
Displacement
Moment arm
Forces
Displacements
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Material Nonlinearity
Strain Strain
Stress
Stress
Mild Steel Rubber
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Status Nonlinearity
The contact area depends on the applied force
Force
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16.1.3 Consequences of Nonlinearities
• Principle of superposition no longer applicable
• Solution may depend on loading history
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16.2.1 Equations for a Nonlinear Structure
FDDK
D
K(D)F(D)
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16.2.2 Incremental Method
FDDK
F
Error
Calculated Response
ActualResponse
1
2
3
D
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16.2.3 Newton-Raphson Method
D = D4
F = F4
Actualresponse
1
23
4
D1 D2 D3
F1
F2
F3
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16.2.4 Convergence Criteria in ANSYS
D = D4
F = F4
Actualrespons
e
1
23
4
D1 D2 D3
F1
F2
F3
max
max
005.0
05.0
FF
DD
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16.3.1 Radius of Convergence
D
F
Actualresponse
Do Do
Radius of convergence
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16.3.2 Consistent Stiffness Matrix
• Tangent stiffness• Additional stiffness due to deformation (geometric
change)• Additional stiffness due to stress stiffening• Additional stiffness due to change of loading
direction.
aσuinc KKKKK
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16.3.3 Load Steps, Substeps, and Equilibrium Iterations
Substeps
Time
Load
Load step 2
Load step 1
D = D4
F = F4
Actualrespons
e
1
23
4
D1 D2 D3
F1
F2
F3
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16.3.4 Concepts of Time
• The ends of load steps or substeps can be identified by time.
• For dynamic problem, time is used as a real-world clock.
• For static problem, time is used as a counter.
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16.3.5 Automatic Time Stepping
• For nonlinear problem, the user-input t is used as initial incremental time.
• ANSYS adjusts t automatically according to the convergence behavior of the solution.
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16.3.6 Text Output Information
1
2
3
45
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16.3.7 Graphical Output Information
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16.3.8 Automatic Nonlinear Solution Control
• SOLCONTROL command can be used to activate automatic nonlinear solution control algorithm.
• The default is ON.
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Basic Solution Options
01
02
03
04
05
06
07
08
09
10
SOLCONTROL, Key
ANTYPE, Antype
NLGEOM, Key
TIME, TIME
NSUBST, NSBSTP, NSBMX, NSBMN, Carry
DELTIM, DTIME, DTMIN, DTMAX, Carry
AUTOTS, Key
KBC, KEY
OUTRES, Item, FREQ, Cname
MONITOR, VAR, Node, Lab
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16.4.1 Analysis Type (ANTYPE)
• For nonlinear analysis, only two analysis types applicable: STATIC and TRANS.
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16.4.2 Nonlinear Geometry (NLGEOM)
• NLGEOM turns ON/OFF the effects of geometric nonlinearity.
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16.4.3 Load Step Time (TIME)
• TIME specifies the time at the end of the following load step.
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16.4.4 Number of Substeps (NSUBST, DELTIM)
• NSUBST specifies number of substeps for the following load step.
• DELTIM specifies time for each substep for the following load step.
• The two commands are equivalent, i.e.,
NSUBSTDELTIMTIME
NSUBST, NSBSTP, NSBMX, NSBMN, Carry
DELTIM, DTIME, DTMIN, DTMAX, Carry
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16.4.5 Automatic Time Stepping (AUTOTS)
• AUTOTS turns ON/OFF the functions of auto time stepping.
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16.4.6 Ramped/Stepped Loading (KBC)
0Time
Load
Stepped load
Substeps
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16.4.7 Output Controls (OUTRES)
• OUTRES controls the amount of data stored in Jobname.RST.
OUTRES, Item, FREQ, Cname
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16.4.8 Monitor File (MONTOR)
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Advanced Solution Options
01
02
03
04
05
06
07
08
09
10
11
12
13
EQSLV, Lab, TOLER, MULT
SOLCONTROL, Key1, Key2
NEQIT, NEQIT
CNVTOL, Lab, VALUE, TOLER, NORM, MINREF
NROPT, Option,, Adptky
LNSRCH, Key
PRED, Sskey, --, Lskey
SSTIF, Key
PSTRES, Key
CUTCONTROL, Lab, VALUE, Option
TIMINT, Key, Lab
TINTP, GAMMA, ...NCNV, KSTOP, DLIM, ITLIM, ETLIM, CPLIM
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16.5.1 Equation Solver (EQSLV)
• EQSLV lets you choose the algorithm solving the equations.
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16.5.2 Time Step Prediction Based on Contact Status
(SOLCONTROL)
• The second key of SOLCONTROL command is to ask ANSYS to adjust time steps according to contact status.
SOLCONTROL, Key1, Key2
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16.5.3 Number of Equilibrium Iterations (NEQIT)
• NEQIT specifies the number of iterations beyond which ANSYS would start another “attempt”.
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16.5.4 Convergence Criteria (CNVTOL)
• CNVTOL overrides the default convergence criteria.
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16.5.5 Newton-Raphson Option (NROPT)
(a) Full Method (b) Modified Method (c) Initial Method
NROPT, Option,, Adptky
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16.5.6 Line Search (LNSRCH)
• LNSRCH turns ON/OFF the “line search” algorithm in ANSYS.
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16.5.7 Predictor (PRED)
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16.5.8 Adaptive Descent (NROPT)
NROPT, Option,, Adptky
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16.5.9 Stress Stiffening (SSTIF, PSTRES)
• SSTIF/PSTRES turns ON/OFF the computation of stress stiffness (K) and storing on file.
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16.5.10 Cutback Control (CUTCONTROL)
• CUTCONTROL specifies the conditions in which ANSYS would decrease time step during auto time stepping.
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16.5.11 Time Integration Effects (TIMINT, TINTP)
• TIMINT turns ON/OFF transient effects.
• The parameter GAMMA of TINTP command can be used to introduce a “numerical damping”.
TIMINT, Key, Lab
TINTP, GAMMA, ...
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16.5.12 Stop Control (NCNV)
• NCNV specifies the stop (failure) conditions of the computation.
NCNV, KSTOP, DLIM, ITLIM, ETLIM, CPLIM
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16.5.13 Terminating an Analysis
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16.5.14 Restarting an Analysis
• An analysis terminated normally can be restarted.
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16.6 Exercise: Hyperelastic Planar Seal
ANSYS- TOPICS
Static analysis• Analysis of a structure for various loads under static condition i.e.
component under rest when loads are applied
ExamplesHolding devices-Clamp or fixture analysis
Types Linear analysis Non linear analysis
Dynamic analysis• Analysis of a structure for various loads under
Dynamic condition i.e. component is in motion when loads are applied or time varying loads
ExamplesSuspension systems of a vehicle
Types Linear analysis Non linear analysis
Structural analysis-Design consideration
• Change design• Alternate material
Thermal analysis
• To determine the temperature distribution occurring in the model
Modes of heat transferConductionConvectionRadiation
Basic terminologies-thermal analysis
• Coeff of thermal expansion• Heat transfer coefficient• Thermal conductivity• Heat generation (Q)• Thermal flux
Structure Idealization
• Process of discritization of a structure into element and nodes
• Infinite no of D.O.F to Finite D.O.FTypes of discritization Natural Artificial
FEM
• Nodes• ElementsTypes of elements1D-Line element(Min 2 nodes)2D-Plane element (Area-Min 4 node)3D-Solid element (Volume-min 8 nodes)
EXAMPLES FOR FINITE ELEMENT
ONE DIMENSIONAL ELEMENTS :TRUSS ELEMENTSBAR, BEAM ELEMENTS
TWO DIMENSIONAL ELEMENTS :TRIANGULAR ELEMENTSRECTANGULAR ELEMENTS
THREE DIMENSIONAL ELEMENTSTETRAHEDRAL ELEMENTSHEXAHEDRAL ELEMENTS
Stages
• Preprocessing• Solution• Postprocessing
Meshing-Importance & drawbacks
• Why should we mesh• Element quality• Problems associated with meshing
Basic terminologies meshing
• Aspect ratio• Skewing• Warp ageTypes of refinementH refinementP refinement
H and P versions
H and P improve the accuracy of the fem
In h versions the order of polynominal approximation for all elements kept constant and the no of elements increased.
In P version the no of elements are maintained constant and the order of polynominal approximation of element is increased
FEM/ANSYS
Section1:StructuralBy completing this section you will learn basic structural analysis using ANSYS.
Section 3:Fluid MechanicsBy completing this section you will learn basic structural analysis using ANSYS.
Section 4: VibrationBy completing this section you will learn basic vibration analysis using ANSYS.
List of other CAE softwares• Msc Nastran• Patran• Ls dyana• Addams• Comsol• Fluent• gambit• Star CD• Hyper form• Pam crash• Mat lab• ANSA