c01_ansys_11
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Chapter 1 Introduction to FEA and ANSYS After completing this chapter, you will be able to: • Understand the basic concepts and general working of FEA. • Understand how FEA helps ANSYS to solve the problems. • Understand the advantages and limitations of FEA. • Understand the types of analysis. • Understand the important terms and definitions in FEA. • Start a new file using the ANSYS Product Launcher window. • Understand the ANSYS Output Window. • Understand the Graphical User Interface (GUI) of ANSYS. • Set the analysis preferences and units. • Learn about the database and files in ANSYS. • Learn about saving, resuming, and clearing database. Learning Objectives
Transcript of c01_ansys_11
Chapter 1
Introduction to FEAand ANSYS
After completing this chapter, you will be able to:• Understand the basic concepts and general working of FEA.• Understand how FEA helps ANSYS to solve the problems.• Understand the advantages and limitations of FEA.• Understand the types of analysis.• Understand the important terms and definitions in FEA.• Start a new file using the ANSYS Product Launcher window.• Understand the ANSYS Output Window.• Understand the Graphical User Interface (GUI) of ANSYS.• Set the analysis preferences and units.• Learn about the database and files in ANSYS.• Learn about saving, resuming, and clearing database.
Learning Objectives
1-2 ANSYS for Designers
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INTRODUCTION TO FEAThe finite element analysis (FEA) is a computing technique that is used to obtainapproximate solutions to the boundary value problems in engineering. It uses a numericaltechnique called the finite element method (FEM) to solve boundary value problems. FEAinvolves a computer model of a design that is loaded and analyzed for specific results. Thefinite element analysis was first developed by Richard Courant in 1943. He used the Ritzmethod of numerical analysis and minimization of variational calculus for getting approximatesolutions to vibration systems. Later, the academic and industrial researchers created the finiteelement method for structural analysis.
The concept of FEA can be explained with a small example of measuring the perimeter of acircle. To measure the perimeter of a circle without using the conventional formula, divide thecircle into equal segments, as shown in Figure 1-1. Next, join the start point and endpoint ofeach of these segments by straight line. Now, you can very easily measure the length of straightline, and thus, the perimeter of the circle.
If you divide the circle into four segments only, you will not get accurate results. For accuracy,divide the circle into more number of segments. However, with more segments, the effortrequired will be more. The same concept applies to FEA also, and therefore, there is always acompromise between accuracy and speed while using this method. This makes it an approximatemethod.
The FEA was first developed to be used in the aerospace and nuclear industries, where thesafety of structures is critical. Nowadays, the simplest of the products rely on the FEA fordesign evaluation.
The FEA simulates the loading conditions of a design and determines the design response inthose conditions. The design is modeled using the discrete building blocks called elements.Each element has some equations that describe how it responds to certain loads. The sum ofthe response of all the elements in the model gives the total response of the design.
General Working of FEABetter knowledge of FEA will help you build more accurate models. It will also help youunderstand the backend working of ANSYS. A simple model is discussed here to give you abrief overview of working of FEA.
Figure 1-1 The Circle divided into equal small segments
Introduction to FEA and ANSYS 1-3
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Figure 1-2 Representation of a two-spring assembly
Figure 1-2 shows a spring assembly that represents a simple two-spring element model. Thesetwo springs are connected in series and one of the springs is fixed at the left most endpoint, referto Figure 1-2. The stiffness of the springs is represented by spring constants K1 and K2. Theendpoints of each spring is restricted to the displacement or the translation in the X directiononly. The change in position from the undeformed state of each endpoint can be defined bythe variables X1 and X2. The forces acting on each endpoint of the springs are represented byF1 and F2.
To develop a model that can predict the state of this spring assembly, you can use the linearspring equation given below:
F = KX
If you use the spring parameters defined above and assume a state of equilibrium, the followingequations can be written for the state of each endpoint:
F1 - X1K1 + (X2 - X1)K2 = 0F2 - (X2 - X1)K2 = 0
Therefore,
F1 = (K1 + K2)X1 + (-K2)X2F2 = (-K2)X1 + K2X2
If the set of equation is written in matrix form, the above set of equations will be modified asfollows:
F1 K1 + K2 -K2 X1=
F2 -K2 K2 X2
In the above mathematical model, if the spring constants (K1 and K2) are known and forces (F1and F2) are defined, then you can determine the resulting deformed shape (X1 and X2).Alternatively, if the spring constants (K1 and K2) are known and the deformed shapes (X1 andX2) are defined, then the resulting forces (F1 and F2) can be determined.
This type of spring system may be complicated to define, but they involve most of the keyterminologies used in FEA. These FEA terminologies are listed next.
1-4 ANSYS for Designers
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1. Stiffness Matrix2. Degrees of Freedom3. Boundary Conditions
These terminologies are discussed next.
Stiffness MatrixIn the previous equation, the following part represents the stiffness matrix (K):
K1 + K2 -K2 -K2 K2
This matrix is relatively simple because it comprises only one pair of springs, but it turnscomplex when the number of springs increases.
Degrees of FreedomDegrees of freedom is defined as the ability of a node to translate or transmit the load. In theprevious example, you are only concerned with the displacement and forces. By making oneendpoint fixed, one degree of freedom for displacement is removed from the three possibledegrees of freedom. So, now the model has two degrees of freedom. The number of degrees offreedom in a model determine the number of equations required to solve the mathematicalmodel.
Boundary ConditionsThe boundary conditions are used to eliminate the unknowns in the system. A set of equationsthat is solvable is meaningless without the input. In the previous example, the boundarycondition was X0 = 0, and the input forces were F1 and F2. In either ways, the displacementscould have been specified in place of forces as boundary conditions and the mathematicalmodel could have been solved for the forces. In other words, the boundary conditions helpyou reduce or eliminate unknowns in the system.
NoteThe solutions generated using FEA are always approximate.
The FEA technique needs the finite element model (FEM) for its final solution as it does notuse the solid model. FEM consists of nodes, keypoints, elements, real constants, materialproperties, loading, and boundary conditions.
Nodes, Elements, and Element ShapesBefore proceeding further, you must be familiar with the concepts of nodes, elements, andelement shapes. These concepts are discussed next.
NodesAn independent entity in space is called a node. Nodes are similar to the points in geometryand represent the corner points of an element. The element shape can be changed by movingthe nodes in space. The shape of a node is shown in Figure 1-3.
Introduction to FEA and ANSYS 1-5
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ElementsElement is an entity into which the system under study is divided. An element shape isspecified by nodes. The shape (area, length, and volume) of an element depends on the nodeswith which it is made. An element (triangular shaped) is shown in Figure 1-3.
Element ShapesThe following are the basic shapes of the elements:
Point ElementA point element is in the form of a point and therefore has only one node.
Line ElementA line element has the shape of a line or curve, therefore a minimum of two nodes arerequired to define it. There can be higher order elements that have additional nodes (atthe middle of the edge of the element). The element that does not have a node at themiddle of the edge of the element is called a linear element. The elements with node atthe mid of the edges are called quadratic or second order elements. Figure 1-4 showssome line elements.
Area ElementAn area element has the shape of a quadrilateral or a triangle, therefore it requires aminimum of three or four nodes to define it. Some area elements are shown in Figure 1-5.
NoteIn this chapter, only the basic introduction of element shapes has been covered. The detaileddescription about element types and their usage is given in Chapter 4.
Figure 1-4 The line elements
Figure 1-3 A node and an element
1-6 ANSYS for Designers
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Volume ElementA volume element has the shape of a hexahedron (8 nodes), wedge (6 nodes),tetrahedron (4 nodes), or a pyramid (5 nodes). Some of the volume elements are shown inFigure 1-6.
Areas for Application of FEAFEA is a very important tool for designing. It is used in the following areas:
1. Structural strength design2. Structural interaction with fluid flows3. Analysis of shock4. Acoustics5. Thermal analysis6. Vibrations7. Crash simulations8. Fluid flows9. Electrical analysis10. Mass diffusion11. Buckling problems12. Dynamic analysis13. Electromagnetic analysis14. Coupled analysis
General Procedure of Conducting Finite Element AnalysisTo conduct the finite element analysis, you need to follow certain steps. These steps are givennext.
Figure 1-6 The volume elements
Figure 1-5 The area elements
Introduction to FEA and ANSYS 1-7
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Figure 1-7 FEA through ANSYS
1. Set the type of analysis to be used.2. Create the model.3. Define the element type.4. Divide the given problem into nodes and elements (mesh the model).5. Apply material properties and boundary conditions.6. Derive the element matrices and equations.7. Assemble the element equations.8. Solve the unknown quantities at nodes.9. Interpret the results.
FEA through ANSYSIn ANSYS, the general process of finite element analysis is divided into three main phases,preprocessor, solution, and postprocessor, refer to Figure 1-7.
PreprocessorThe preprocessor is a program that processes the input data to produce the output that is usedas input to the subsequent phase (solution). Following are the input data that needs to begiven to the preprocessor:
1. Type of analysis (structural or thermal, static or dynamic, and linear or nonlinear)2. Element type.3. Real constants.4. Material properties.5. Geometric model.6. Meshed model.7. Loadings and boundary conditions.
The input data will be preprocessed for the output data and preprocessor will generate the
1-8 ANSYS for Designers
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data files automatically with the help of users. These data files will be used by the subsequentphase (solution), refer to Figure 1-7.
SolutionSolution phase is completely automatic. The FEA software generates the element matrices,computes nodal values and derivatives, and stores the result data in files. These files are furtherused by the subsequent phase (postprocessor) to review and analyze the results through thegraphic display and tabular listings, refer to Figure 1-7.
PostprocessorThe output from the solution phase (result data files) is in the numerical form and consists ofnodal values of the field variable and its derivatives. For example, in structural analysis, theoutput is nodal displacement and stress in the elements. The postprocessor processes theresult data and displays them in graphical form to check or analyze the result. The graphicaloutput gives the detailed information about the required result data. The postprocessor phaseis automatic and generates the graphical output in the form specified by the user, refer toFigure 1-7.
Effective Utilization of FEASome prerequisites for effective utilization of FEA from engineers and FEA software arediscussed next.
EngineersAn engineer who wants to work with this tool should have sound knowledge of Strength ofMaterials (for structural analysis), Heat Transfer, Thermodynamics (for thermal analysis), anda good analytical/designing skill. Besides this, he should also have a fair knowledge of advantagesand limitations of the FEA software being used.
SoftwareThe FEA software should be selected based on the following considerations:
1. Analysis type to be performed.2. Flexibility and accuracy of the tool.3. Hardware configuration of your system.
Nowadays, the CAE / FEA software can simulate the performance of most of the systems. Inother words, anything that can be converted into a mathematical equation can besimulated using the FEA techniques. Usually, the most popular principle of GIGO (GarbageIn Garbage Out) applies to FEA. Therefore, you should be very careful while giving/acceptingthe inputs for analysis. A careful planning is the key to a successful analysis.
FEA SoftwareThere are variety of commercial FEA software packages available in market. However, nosoftware has the capability to meet the complete analysis requirements of a design.Therefore, some firms use one or more CAE software depending on their requirements.Some companies also develop their own customized version of commercial software to meettheir requirements provided by the commercial software. Some of the most popular and
Introduction to FEA and ANSYS 1-9
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commercially available FEA software are as follows:
1. ANSYS2. Adina3. Abaqus4. Hypermesh5. NX Nastran6. Cosmos7. NISA8. Marc9. Ls-Dyna10. MSC/Dytran11. Star-CD
Advantages and Limitations of FEA SoftwareFollowing are the advantages and limitations of FEA software:
Advantages1. It reduces the amount of prototype testing; thereby, saving the cost and time involved in
performing design testing.2. It gives graphical representation of the result of analysis.3. The finite element modeling and analysis are performed by the preprocessor phase and
the solution phase, which if done manually, will consume a lot of time and, in some cases,may be impossible to do.
4. Variables such as stress, temperature can be measured at any desired point in the model.5. It helps optimize the design.6. It is used to simulate the designs that are not suitable to prototype testing such as
surgical implants (artificial knees).7. It helps you create more reliable, high quality, and competitive designs.
Limitations1. It provides approximate solutions.2. FEA packages are costly.3. Qualified personnel are required to perform the analysis.4. The results give solutions but not remedies.5. Features such as bolts, welded joints, and so on cannot be accommodated to the model.
This may lead to approximation and errors in the result obtained.6. For more accurate result, more computer space and time are required.
KEY ASSUMPTIONS IN FEAThere are four basic assumptions that affect the quality of the solution and must be consideredfor finite element analysis. These assumptions are not comprehensive, but cover a wide varietyof situations applicable to the problem. Moreover, by no means, do all the followingassumptions apply to all the situations. So, make sure to use only those assumptions that applyto the analysis under consideration.
1-10 ANSYS for Designers
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Assumptions Related to Geometry1. Displacement values will be small so that a linear solution is valid.2. Stress behavior outside the area of interest is not important, so the geometric simplifications
in those areas will not affect the outcome.3. Only internal fillets in the area of interest will be included in the solution.4. Local behavior at the corners, joints, and intersection of geometries is of primary
interest, therefore no special modeling of these areas is required.5. Decorative external features will be assumed insignificant for the stiffness and
performance of the part and will be omitted from the model.6. The variation in mass due to the suppressed features is negligible.
Assumptions Related to Material Properties1. Material properties will remain in the linear region and nonlinear behavior of the material
property cannot be accepted. For example, it is understood that either the stress levelsexceeding the yield point or excessive displacement will cause a component failure.
2. Material properties are not affected by the load rate.3. The component is free from surface imperfections that can produce stress risers.4. All simulations will assume room temperature, unless otherwise specified.5. The effects of relative humidity or water absorption on material used will be neglected.6. No compensation will be made to account for the effect of chemicals, corrosives, wears or
other factors that may have an impact on the long term structural integrity.
Assumptions Related to Boundary Conditions1. Displacements will be small so that the magnitude, orientation, and distribution of
the load remains constant throughout the process of deformation.2. Frictional loss in the system is considered to be negligible.3. All interfacing components will be assumed rigid.4. The portion of the structure being studied is assumed a separate part from the rest of the
system, therefore so that any reaction or input from the adjacent features are neglected.
Assumptions Related to Fasteners1. Residual stresses due to fabrication, preloading on bolts, welding, or other manufacturing
or assembly processes will be neglected.2. All the welds between the components will be considered ideal and continuous.3. The failure of fasteners will not be considered.4. Loads on the threaded portion of the parts is supposed to be evenly distributed among
the engaged threads.5. Stiffness of bearings, radially or axially, will be considered infinite or rigid.
TYPES OF ANALYSISThe following types of analysis can be performed in FEA software:
1. Structural analysis2. Thermal analysis3. Fluid flow analysis
Introduction to FEA and ANSYS 1-11
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Figure 1-8 Types of structural analysis
4. Electromagnetic field analysis5. Coupled field analysis
Structural AnalysisIn structural analysis, first the nodal degrees of freedom (displacement) are calculated andthen the stress, strains, and reaction forces are calculated from the nodal displacements.The classification of the structural analysis is shown in Figure 1-8.
Static AnalysisIn static analysis, the load or field conditions do not vary with respect to time and therefore, itis assumed that the load or field conditions are applied gradually, not suddenly. The systemunder analysis can be linear or nonlinear. Inertia and damping effects are ignored in structuralanalysis. In structural analysis, the following matrices are solved:
[K] x [X ]= [F]
Where,K = Stiffness MatrixX = Displacement MatrixF = Load Matrix
The above equation is called the force balance equation for the linear system. If the elementsof matrix [K] are a function of [X], the system is known as a nonlinear system. Nonlinearsystems include large deformation, plasticity, creep and so on. The loadings that can be appliedin a static analysis include:
1. Externally applied forces and pressures2. Steady-state inertial forces (such as gravity or rotational velocity)3. Imposed (non-zero) displacements4. Temperatures (for thermal strain)5. Fluences (for nuclear swelling)
The outputs that can be expected from a FEA software given next.
1. Displacements
1-12 ANSYS for Designers
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2. Strains3. Stresses4. Reaction forces
Dynamic AnalysisIn dynamic analysis, the load or field conditions do vary with time. The assumption here isthat the load or field conditions are applied suddenly. The system can be linear or nonlinear. Thedynamic load includes oscillating loads, impacts, collisions, and random loads. The dynamicanalysis is classified into the following three main categories:
Model AnalysisIt is used to calculate the natural frequency and mode shape of a structure.
Harmonic AnalysisIt is used to calculate the response of the structure to harmonically time varying loads.
Transient Dynamic AnalysisIt is used to calculate the response of the structure to arbitrary time varying loads.
In dynamic analysis, the following matrices are solved:
For the system without any external load:[M] x Double Derivative of [X] + [K] x [X]= 0
Where,M = Mass MatrixK = Stiffness MatrixX = Displacement Matrix
For the system with external load:[M] x Double Derivative of [X] + [K] x [X]= [F]
Where,K = Stiffness MatrixX = Displacement MatrixF = Load Matrix
The above equations are called the force balance equations for a dynamic system. By solvingthe above set of equations, you will be able to extract the natural frequencies of a system. Theload types applied in a dynamic analysis are the same as that for the static analysis. Theoutputs that can be expected from a software are:
1. Natural frequencies2. Mode shapes3. Displacements4. Strains5. Stresses6. Reaction forces
Introduction to FEA and ANSYS 1-13
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All the outputs mentioned here can be obtained with respect to time.
Spectrum AnalysisThis is an extension of the modal analysis and is used to calculate the stress and strain due tothe response of the spectrum (random vibrations).
Buckling AnalysisThis type of analysis is used to calculate the buckling load and the buckling mode shape.Slender structures and structures with slender part loaded in the axial direction buckle underrelatively small loads. For such structures, the buckling load becomes a critical design factor.
Explicit Dynamic AnalysisThis type of structural analysis is available only in the ANSYS LS-Dyna program and is used tocalculate fast solutions for large deformation dynamics and complex contact problems.
Thermal AnalysisThermal analysis is used to determine the temperature distribution and related thermalquantities such as:
1. Thermal distribution2. Amount of heat loss or gain3. Thermal gradients4. Thermal fluxes
All the primary heat transfer modes such as conduction, convection, and radiation can besimulated. You can perform two types of thermal analysis, steady-state and transient.
Steady State Thermal AnalysisIn this analysis, the system is studied under steady thermal loads with respect to time.
Transient Thermal AnalysisIn this analysis, the system is studied under varying thermal loads with respect to time.
Fluid Flow AnalysisThis analysis is used to determine the flow distribution and temperature of a fluid. ANSYS/FLOWTRAN program is used to simulate the laminar and turbulent flow, compressible andelectronic packaging, automotive design, and so on.
The outputs that can be expected from the fluid flow analysis are:
1. Velocities2. Pressures3. Temperatures4. Film coefficients
1-14 ANSYS for Designers
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Electromagnetic Field AnalysisThis type of analysis is used to determine the magnetic fields in electromagnetic devices. Thetypes of electromagnetic analyses are:
1. Static analysis2. Harmonic analysis3. Transient analysis
Coupled Field AnalysisThis type of analysis considers the mutual interaction between two or more fields. It is impossibleto solve the fields separately because they are interdependent. Therefore, you need a programthat can solve both the physical problems by combining them.
For example, if a component is exposed to heat, you may first require to study the thermalcharacteristics of the component and then the effect of the thermal heating on the structuralstability.
Alternatively, if a component is bent into different shapes using one of the metal formingprocesses and then subjected to heating, the thermal characteristics of the component willdepend on the new shape of the component and therefore the shape of the component has tobe predicted through structural simulations first. This is called as the coupled field analysis.
IMPORTANT TERMS AND DEFINITIONSSome of the important terms and definitions used in FEA are discussed next.
StrengthWhen a material is subjected to an external load, the system undergoes a deformation. Inturnthe material will offer a resistance against this deformation. This resistance is offered by thematerial by the virtue of its strength.
LoadThe external force acting on a body is called the load.
StressThe force of resistance offered by a body against the deformation is called stress. The stress isinduced in the body while the load is being applied on the body. Stress is calculated as loadper unit area.
p = F/A
Where,p = Stress in N/mm2
F = Applied Force in NewtonA = Cross-Sectional Area in mm2
The material can undergo various types of stresses and that are discussed next.
Introduction to FEA and ANSYS 1-15
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Tensile StressIf the resistance offered by the body is against the increase in length, the body is said to beunder tensile stress.
Compressive StressIf the resistance offered by the body is against the decrease in length, the body is said to beunder compressive stress. Compressive stress is just the reverse of tensile stress.
Shear StressShear stress exists when two materials tend to slide across each other in any typical plane ofshear, on application of force parallel to that plane.
Shear Stress = Shear resistance (R) / Shear area (A)
StrainWhen a body is subjected to a load (force), its length will change. The ratio of the change inlength to the original length of the member is called strain. If the body returns to its originalshape on removing the load, the strain is called elastic strain. If the metal remains distorted,the strain is called plastic strain. The strain can be of three types, namely, tensile, compressive, orshear strain.
Strain (e) = Change in Length (dl) / Original Length (l)
Elastic LimitThe maximum stress that can be applied to a material without producing permanentdeformation is known as the elastic limit of the material. If the stress is within the elastic limit,the material will return to its original shape and dimension, when the external stress is removed.
Hooke’s LawIt states that the stress is directly proportional to the strain, within the elastic limit.
Stress / Strain = Constant (within the elastic limit)
Young’s Modulus or Modulus of ElasticityIn case of axial loading, the ratio of intensity of tensile or compressive stress to thecorresponding strain is constant. This ratio is called Young’s modulus, and it is denoted by E.
E = p/e
Shear Modulus or Modulus of RigidityIn case of shear loading, the ratio of shear stress to the corresponding shear strain is constant.This ratio is called Shear modulus, and it is denoted by C, N, or G.
Ultimate StrengthThe maximum stress that the material withstands when subjected to an applied load is calledits ultimate strength.
1-16 ANSYS for Designers
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Factor of SafetyThe ratio of the ultimate strength to the estimated maximum stress in ordinary use (designstress) is known as factor of saftey. It is necessary that the design stress should be well below theelastic limit and to achieve this condition, the ultimate stress should be divided by a ‘factor ofsafety’.
Lateral StrainIf a cylindrical rod is subjected to an axial tensile load, the length (l) of the rod will increase (dl)and the diameter (φ) of the rod will decrease (dφ). In short, the longitudinal stress will not onlyproduce a strain in its own direction, but will also produce a lateral strain. The ratio dl/l iscalled the longitudinal strain or linear strain, and the ratio dφ/φ is called the lateral strain.
Poisson’s RatioThe ratio of lateral strain to the longitudinal strain is constant, within the elastic limit. Thisratio is called the Poisson’s ratio and is denoted by 1/m. For most of the metals, the value of the‘m’ lies between 3 and 4.
Poisson’s ratio = Lateral Strain / Longitudinal Strain = 1/m
Bulk ModulusIf a body is subjected to equal stresses along the three mutually perpendicular directions, theratio of the direct stresses to the corresponding volumetric strain is found to be a constant fora given material, when the deformation is within a certain limit. This ratio is called the bulkmodulus and is denoted by K.
CreepAt elevated temperatures and constant stress or load, many materials continue to deform butat a slow rate. This behavior of materials is called creep. At a constant stress and temperature,the rate of creep is approximately constant for a long period of time. After this period andafter a certain amount of deformation, the rate of creep increases, thereby causing fracture inthe material. The rate of creep is highly dependent on both the stress and the temperature.
Classification of MaterialsMaterials are classified into three main categories: elastic, plastic, and rigid. In case of elasticmaterials, the deformation disappears on the removal of load. In plastic materials, thedeformation is permanent. A rigid material does not undergo any deformation whensubjected to an external load. However, in actual practice, no material is perfectly elastic,plastic, or rigid. The structural member are designed such that they remain in the elasticconditions under the action of working loads. All the engineering materials are grouped intothree categories that are discussed next.
Isotropic MaterialIn case of Isotropic materials, the material properties do not vary with direction, which meansthat it has same material properties in all directions. The material properties are defined byYoung’s modulus and Poisson’s ratio.
Introduction to FEA and ANSYS 1-17
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Orthotropic MaterialIn case of Orthotropic material, the material properties do vary with direction and thematerial properties are specified in three orthogonal directions. It has three mutuallyperpendicular planes of material symmetry. The material properties are defined by threeseparate Young’s modulus and Poisson’s ratios.
Anisotropic MaterialIn case of Anisotropic material, the material properties vary with the direction. But in thiscase, there is no plane of material symmetry.
INTRODUCTION TO ANSYSWelcome to the world of Computer Aided Engineering (CAE) with ANSYS. If you are a newuser of this software package, you will be joining hands with thousands of users of thisComputer Aided Finite Element Analysis package. If you are familiar with the previousreleases of this software, you will be able to upgrade your designing skills with thetremendous improvement in this latest release.
ANSYS, developed by ANSYS, Inc., USA, is a dedicated Computer Aided Finite ElementModeling and Finite Element Analysis tool. ANSYS is known as the standard in the field ofComputer Aided Engineering. The Graphical User Interface (GUI) of ANSYS enables theuser to work with 3-dimensional (3D) models and also generate results from them. You canperform a variety of tasks ranging from Finite Element Analysis to complete ProductOptimization Analysis using ANSYS.
The following is the list of analyses that you can perform using ANSYS:
1. Structural analysis2. Thermal analysis3. Fluid flow analysis4. Electromagnetic field analysis5. Coupled-field analysis6. Acoustic analysis
SYSTEM REQUIREMENTSThe following are the system requirements to ensure the smooth running of ANSYS on yoursystem:
• System unit: An Intel Pentium 4 or AMD 64, running Microsoft 2000 Professional Edition,Windows XP 32-bit, or Windows XP x64 on it.
• Memory: 512 MB of RAM is the minimum requirement for all applications. However, for64-bit systems, 1 GB of RAM is the minimum requirement.
• Disk drive: 2.2 GB Disk Drive space (Minimum recommended size).• A DVD drive is required for the program installation.• Graphics adapter: Graphics card compatible with the supported operating systems, capable
of supporting 1024x768 High Color (16-bit), and a 17-inch monitor compatible with thistype of graphics card.
1-18 ANSYS for Designers
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Figure 1-9 Starting ANSYS using the ANSYS Product Launcher
• Approximately twice as much swap space as memory is required. And, TCP/IP for thelicense manager.
• Microsoft Internet Explorer 6.0 or higher.
GETTING STARTED WITH ANSYSThere are two modes to run the ANSYS program: Interactive mode and Batch mode.
Interactive ModeThis is the default mode in ANSYS. It allows you to work with menus and dialog boxes(Graphical User Interface), online help, and tools to create models in the graphics window.
Batch ModeIn the batch mode, you can execute a file of commands in the ANSYS program. It is usefulwhen you do not want to interact with the program such as during the solution phase of ananalysis.
Starting a New File Using ANSYS Product Launcher Window
ANSYS Product Launcher is used to run the required ANSYS program or access a modifiedANSYS file. To run the ANSYS Product Launcher on the Windows system, choose Start > AllPrograms > ANSYS 11.0 > ANSYS Product Launcher from the taskbar menu, as shownin Figure 1-9; the ANSYS Product Launcher window will be displayed, as shown in Figure 1-10.
Taskbar Menu: Start > All Programs > ANSYS 11.0 > ANSYS Product Launcher
Introduction to FEA and ANSYS 1-19
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Alternatively, you can run ANSYS by choosing Start > All Programs > ANSYS 11.0 > ANSYSfrom the taskbar menu; ANSYS will start with the last configured product launcher settings. Ifyou have not run the launcher yet, the highest licensed product will run automatically.
The options in the ANSYS Product Launcher window are discussed next.
Default Page of the ANSYS Product Launcher WindowThe options in the default page of the ANSYS Product Launcher window are used to specifythe simulation environment, license, and the add-on modules, refer to Figure 1-11.
Simulation EnvironmentThis drop-down list is used to specify whether you want to run the interactive or the batchinterface. The options available in this drop-down list are:
ANSYS WorkbenchANSYSANSYS Batch
Figure 1-10 The ANSYS Product Launcher window
Figure 1-11 The options in the default page
1-20 ANSYS for Designers
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MFX - ANSYS/CFXLS-DYNA Solver
By default, the ANSYS environment will be selected. If you want to run the file ofcommands, select the ANSYS Batch environment.
LicenseThis drop-down list is used to select the license from the available types. In this textbook,the ANSYS Multiphysics license is used. The ANSYS Multiphysics has the capability tosolve the structural, thermal, CFD, acoustic, and electromagnetic analysis problems.
Add-on Modules AreaThe check boxes in this area are used to select the add-on modules. The two add-onmodules available in this area are ANSYS DesignXplorer (-DVT) and VT Accelerator(-VTA).
NoteIn this textbook, you will deal with the structural and thermal analyses. Therefore, you need toselect the ANSYS option from the Simulation Environment drop-down list and the ANSYSMultiphysics option from the License drop-down list.
File Management TabThe options in this tab are used to set the working directory and assign a name to a job. Theseoptions will vary depending on the simulation environment you select. The options in this tabare shown in Figure 1-12.
Working DirectoryAll the ANSYS files are stored in the working directory. To set the working directory,choose the Browse button; the Browse for Folder dialog box will be displayed. Select therequired folder and choose the OK button; the selected folder will become the workingdirectory for all the files saved by ANSYS unless and until you change it.
Job NameEnter the file name in the Job Name edit box. This filename will be used for all filesgenerated in ANSYS. You can assign the job name maximum up to 32 characters.
Customization/Preferences TabThe options in this tab are used to customize the working environment and are shown inFigure 1-13. These options in this tab will vary depending upon the simulation environment.
Figure 1-12 The File Management tab
Introduction to FEA and ANSYS 1-21
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Memory AreaSelect the Use custom memory settings check box from this area; the options in this areawill be activated.
Total Workspace (MB)This spinner is used to set the memory for running the ANSYS. By default, the valueis 512 MB, which is enough for most of the analysis work.
Database (MB)This spinner defines the portion (in MB) of the total memory that the database willuse. By default, its value is 256 MB.
Custom ANSYS ExecutableThis option is used to start a customized ANSYS executable file.
Additional ParametersThis option is used to set the parameter values at the ANSYS start-up.
ANSYS LanguageThis drop-down list is used to specify the translated language file. By default, the en-usoption is selected from this drop-down list, which implies that the US English language isset as the default language.
Graphics Device NameThis drop-down list is used to set the graphics device. By default, win32 will be selectedfor the Windows system. Select the 3D option from the drop-down list, if a graphics deviceis installed on your system.
Figure 1-13 The Customization/Preferences tab
1-22 ANSYS for Designers
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High Performance Computing Setup TabThe options in this tab are used to launch and run ANSYS by sharing memory with multipleprocessors, or run ANSYS with proper MPI configuration. If you are running ANSYS on astand-alone system, use the default options from this tab.
The MFX - ANSYS/CFX Setup TabThis tab will only be activated when you select MFX - ANSYS/CFX option from the SimulationEnvironment drop-down list. The options in this tab are used to run ANSYS and CFX withtheir proper licenses.
Saving and Loading the Launcher ConfigurationYou can save or load a specific launcher configuration. To save the specific launcherconfiguration, choose Profiles > Save Profile from the menu bar; the LauncherProfile - Save dialog box will be displayed. Enter the configuration name in the Name editbox and choose the Save button from the same dialog box; the configuration will be saved.
To load a specific configuration, choose Profiles > Load Profile from the menu bar; theLauncher Profile - Load dialog box will be displayed. Select the required configuration fromthe Profiles area and choose the Load button from this dialog box; the selectedconfiguration will be loaded.
To rename or delete a profile or to set a profile as the default profile, choose Profiles >Manage Profiles from the menu bar.
After setting all options in the ANSYS Product Launcher window, choose the Run buttonfrom it; the ANSYS 11.0 Output Window and the ANSYS Multiphysics Utility Menu window(ANSYS session) will be displayed.
ANSYS 11.0 OUTPUT WINDOWThe ANSYS 11.0 Output Window, shown in Figure 1-14, runs along with the ANSYSMultiphysics Utility Menu window (ANSYS session). If you close the output window, theANSYS Multiphysics Utility Menu window (ANSYS session) will also be closed.
It gives the information on how ANSYS interpreted the user’s input. The ANSYS 11.0Output Window also receives text output from the program.
Introduction to FEA and ANSYS 1-23
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ANSYS MULTIPHYSICS UTILITY MENU WINDOW (ANSYSSESSION)The Graphical User Interface (GUI) of ANSYS is shown in Figure 1-15. It is the easiest way tocommunicate with the ANSYS program. In this textbook, you will follow the GUI method tosolve the problems. Various menus and toolbars in ANSYS session are discussed next.
Utility MenuIn ANSYS, the menu bar is called as the utility menu. It contains the file control, plot, plotcontrol, and many other options. This menu is very important in ANSYS GUI.
Conventions Used in the Utility MenuThe following are the conventions used in the utility menu, refer to Figure 1-16.
Dialog BoxIf you choose an option that has three dots (...) after it, a dialog box will be invoked.
Graphical PickingIf you choose an option with a plus sign (+) after it, then you will be prompted to selectthe entities from the graphics area.
Figure 1-14 The ANSYS 11.0 Output Window
1-24 ANSYS for Designers
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SubmenuIf you choose an option that has an arrow symbol (>) after it, a submenu will be displayed.
ActionIf you choose an option that has a blank space after it, an action will be performed.
Figure 1-15 The ANSYS session
Figure 1-16 Conventions used in the Utility Menu
Introduction to FEA and ANSYS 1-25
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Main MenuThe Main Menu is arranged in a tree-like structure with various colors to indicate the level ofthe tree structure, as shown in Figure 1-17. This structure depicts a step-by-step approach tothe analysis. It contains the tools to create the model and perform the analysis.
In the Main Menu, the options having a square symbol at their left, indicate that a dialogbox will be invoked when you choose them. If you choose an option that has an arrowsymbol at its left, then you will be prompted to select entities from the graphics area.
Graphics AreaIn the graphics area, you can build the model, apply the load, show the results, and postprocessthe counters and graphs. It is just like the drawing area in other CAD software packages withthe only difference that in this graphics area, you can view the result in counters and graphs.If you right-click in the graphics area, a shortcut menu will be displayed, as shown in Figure 1-18.The shortcut menu contains the options for adjusting the graphics window display, setting theview, and zooming the model in the graphics area.
Figure 1-17 The Main Menu
Figure 1-18 The shortcut menu used to adjust the graphics window properties
1-26 ANSYS for Designers
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Standard ToolbarIt contains the most commonly used tools such as New Analysis, Open Analysis File, SaveAnalysis, and so on. The Standard toolbar is shown in Figure 1-19.
ANSYS Command PromptThe ANSYS command prompt allows you to enter the commands. The format of the commandwill be displayed dynamically when you type it, as shown in Figure 1-20.
Command Window IconThis button is used to float the ANSYS command prompt. You can resize thecommand prompt and also change its position by using this button. To restore it to theoriginal position, choose the Close button from the command window. The floating
ANSYS command prompt is shown in Figure 1-21.
Raise Hidden IconWhile working on ANSYS, sometimes the dialog box will hide behind the ANSYSUtility Menu window (ANSYS session). Choose the Raise Hidden button to displaythese hidden dialog boxes. Figure 1-22 shows the hidden dialog box and Figure 1-23
shows the raised dialog box.
Figure 1-19 The Standard toolbar
Figure 1-20 The ANSYS Command Prompt
Figure 1-21 The floating ANSYS Command Window
Introduction to FEA and ANSYS 1-27
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Figure 1-22 The hidden dialog box
Figure 1-23 The raised dialog box
1-28 ANSYS for Designers
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Reset PickingThis button is used to reset the picking menu and clear the selection in the graphicarea. Also, the dialog box from which the picking menu is invoked will get closed.Figure 1-24 displays a model in which some of the nodes are selected and Figure 1-25
displays the same model after choosing the Reset Picking button.
Contact ManagerThis button is used to invoke the Contact Manager dialog box, as shown inFigure 1-26. This dialog box is used to create and manage the contact pairs.
ANSYS ToolbarThis toolbar contains the shortcuts of the most frequently used commands and functions. Thistoolbar allows you to create your own tool menu. By default, four ANSYS tools are available inthis toolbar. You will learn more about customizing the ANSYS Toolbar in later chapters.
Model Control ToolbarThis toolbar contains the tools for panning, rotating, and zooming the model. You can alsochange the view of the model using this toolbar. The Model Control toolbar is shown inFigure 1-27.
Figure 1-26 The Contact Manager dialog box
Figure 1-25 The same model after choosing theReset Picking button
Figure 1-24 Model in which some of the nodesare selected
Introduction to FEA and ANSYS 1-29
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User Prompt InformationThis is a prompt area. The instructions for the user will be displayed in this area. It givesinstructions about what to do next.
Current SettingsIn this area, the current attribute settings are displayed such as material, element type, realconstant number, currently active coordinate system, and section number.
SETTING THE ANALYSIS PREFERENCES
Before proceeding to perform an analysis, you need to specify the type analysis you want toperform (Structural, Thermal, Fluid, and so on). This will be the first step in any analysisprocess. To set the analysis preferences, choose Preferences from the Main Menu; thePreferences for GUI Filtering dialog box will be displayed, as shown in Figure 1-28. Thisdialog box is divided into two parts, one showing the individual disciplines and other, thediscipline options.
Figure 1-27 The Model Control toolbar
Main Menu: Preferences
1-30 ANSYS for Designers
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DisciplinesThe disciplines are arranged according to the types of analysis that can be carried out inANSYS. Select the required discipline by selecting the check box on the left side of thedisciplines area. In this textbook, you will learn about the structural and thermal analysis. So,we need to select the Structural and Thermal check boxes only.
Discipline OptionsThe Discipline options area contains two types of solution methods for solving the structuralproblems in ANSYS: h-Method and the p-Method Struct.
h-MethodBy default, this radio button is selected. The h-method can be used for doing any type ofanalysis and requires a finer mesh than the p-method. In this textbook, we will use h-Methodoption to solve the analysis related problems.
p-Method StructThe p-method struct is used only for linear structural static analysis and gives accurate resultswith the coarse mesh. The p-Method Struct option provides the user specified degree ofaccuracy.
Specify the disciplines and their discipline options by selecting the required radio buttonprovided on the left of each option. Next, choose the OK button to exit the dialog box.
Figure 1-28 The Preferences for GUI Filtering dialog box
Introduction to FEA and ANSYS 1-31
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UNITS IN ANSYS
ANSYS is unit independent. It does not prompt you to specify units while carrying out theanalysis. It simply does the calculation of the data fed into it. It is the responsibility of the userto be consistent with the units used in the analysis.
Following are some of the quantities and their respective units used in this textbook.
Length = Millimeters (mm)Mass = Kilogram (kg)Time = Seconds (s)Temperature = Celsius (oC)Force = Newton (N)Pressure = N/mm2
Stress = N/mm2
NoteYou can specify the SI or British units for material property libraries, which will be discussedin Chapter 4.
However, the /Units command is used to remind you to use the consistent set of units. Thiscommand can only be accessed from the ANSYS command prompt, not through the UtilityMenu and the Main Menu. To set the SI system of units, type /UNITS, SI at the ANSYScommand prompt and press the ENTER key; the units will be set automatically.
To set angular units for the variables, choose Parameters > Angular Units from the UtilityMenu; the Angular Units for Parametric Functions dialog box will be displayed, as shownin Figure 1-29.
By default, the Radians RAD option is selected from the Units for angular drop-down list,which indicates that the current angular unit is radians. Select the Degrees DEG option fromthe drop-down list to specify the angular units as degrees.
Command Prompt: /UnitsUtility Menu: Parameters > Angular Units
Figure 1-29 The Angular Units for Parametric Functions dialog box
1-32 ANSYS for Designers
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OTHER IMPORTANT TERMS RELATED TO ANSYSThe other important terms related to ANSYS, common options in ANSYS, and the working ofthese options are discussed next.
Dialog BoxesVarious options available in any ANSYS dialog box is given next.
Inputs to be SpecifiedThe input to the ANSYS dialog box can be provided through text entry, check boxes, radiobutton, option button, single selection list, multiple selection list, two columns selection list, atabbed box, or a tree structure. If you do not enter values in the edit boxes, they will beassumed to be zero (0). For example, in the Create Keypoints in Active Coordinate Systemdialog box, as shown in Figure 1-30, if you choose the Apply button without entering anyvalues in the edit boxes, a keypoint will be created at 0,0,0 location in the active coordinatesystem.
Action ButtonsThe action buttons in the dialog box include OK, Apply, and Cancel.
OKIf you choose this button, the corresponding action will be performed and the dialogbox will be closed.
ApplyThis button allows you to perform the action without closing the dialog box.
CancelThis button is used to exit the dialog box without performing the action.
Graphics DisplayThe graphics display options in ANSYS are used to change the geometry display, resultdisplay, and graph display. The geometry display includes display of nodes, elements, keypoints,and so on. The result display includes temperature or stress contours.
Figure 1-30 The Create Keypoints in Active Coordinate System dialog box
Introduction to FEA and ANSYS 1-33
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The Plot and PlotCtrls menus from the Utility Menu are used to control the display of theobjects.
Plot MenusThe Plot menu, as shown in Figure 1-31, is used to display the nodes, elements, keypoints,lines, areas, and volumes. The Multi-plot option is used to plot all entities mentioned above.
PlotCtrls MenusThe PlotCtrls menu, as shown in Figure 1-32, is used to control the view and style of graphicsdisplay. The PlotCtrls menu can be used to perform the following tasks:
1. Changing the color scheme of ANSYS.2. Changing the default component color.3. Changing graph colors.4. Changing the boundary condition colors.5. Pan, zoom, and rotate the model.6. Add symbols and annotations.7. Animate a particular result.8. Capture an image.9. Number the keypoints, elements, and so on.
Figure 1-31 The Plot menu Figure 1-32 The PlotCtrls menu
1-34 ANSYS for Designers
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Panning, Zooming, and Rotating the ModelIn ANSYS, the front view is the default view and the Z axis is pointed normal to the screen. Youcan pan, zoom, and rotate the model using the keyboard and mouse as explained below:
1. Press and hold the CTRL key and the left mouse button, and then drag the mouse to panthe model. Refer to Figure 1-33.
2. Press and hold the CTRL key and the middle mouse button, and then drag the mouse tozoom and spin the model. Refer to Figure 1-33.
3. Press and hold the CTRL key and the right mouse button, and then drag the mouse torotate the model. Refer to Figure 1-33.
Dividing the Graphics AreaSometimes, you need to divide the graphics area into two, three, or four parts. To do so,right-click in the graphics area and choose the Graphics Properties > Window Layout fromthe shortcut menu; the Multi-Plotting dialog box will be displayed. Depending upon thedivisions required, select the required radio button from the Window Layout area. Choose theApply and then the OK button. Figure 1-34 shows the graphics area divided into four divisions.
NoteThe graphics area must contain atleast one geometric entity before dividing it.
Figure 1-33 Panning, Zooming, and Rotating the model
Introduction to FEA and ANSYS 1-35
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The Pan-Zoom-Rotate Dialog Box
The Pan-Zoom-Rotate dialog box is used to manipulate the view of the model on the screen.To invoke this dialog box, invoke the Pan-Zoom-Rotate tool from the Standard toolbar.Alternatively, you can choose PlotCtrls > Pan Zoom Rotate from the Utility Menu; thePan-Zoom-Rotate dialog box will be displayed, as shown in Figure 1-35.
Active WindowThe Window drop-down list is used to activate any one window or all windows at once. Onceyou activate the window, all the operations (Pan-Zoom-Rotate) are initiated in the active window.
Views AreaThe buttons in this area are used to set the view (in which the model is viewed) in the activewindow. The options in this area are shown in Figure 1-35.
Zooming Options AreaThe buttons in this area are used to zoom the model in the active window. These buttons arediscussed next.
Figure 1-34 The graphics area divided into four divisions
Toolbar: Standard > Pan-Zoom-RotateUtility Menu: PlotCtrls > Pan Zoom Rotate
1-36 ANSYS for Designers
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ZoomThis button is used to zoom the area trapped in the square, which is created by firstspecifying the center and then the size of the rectangle. The enclosed portion will then bezoomed and displayed again.
Box ZoomThis button is used to zoom the area trapped in the square, which is created by specifyingtwo corners. The zoom portion will then be displayed again.
Back UpThis button is used to undo the zooms created earlier using the Pan-Zoom-Rotate dialogbox. You can undo up to five zooms in each active window.
Win ZoomThis button is used to zoom the area trapped in the square, which is created by firstspecifying one corner point and then the edge. The aspect ratio of the window willremain unchanged.
Figure 1-35 The Pan-Zoom-Rotate dialog box
Introduction to FEA and ANSYS 1-37
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Panning and Zooming Options AreaThe buttons in this area are used to pan and zoom the model in the active window. The arrowbuttons are used to pan the model up or down, and left or right. The dot buttons are used tozoom the model in or out.
Rotating Options AreaThe buttons in this area are used to rotate the model about the positive or negative X, Y, andZ screen coordinates in the active window. The origin of the screen coordinate axis is locatedat the center in each window.
Rate SliderThe Rate slider is used to control the amount of pan, zoom, and rotation. The rate varies from1 to 100.
Dynamic ModeThis check box is used to pan, zoom, or rotate the model dynamically. Select this check boxand use the mouse buttons to dynamically pan, zoom, or rotate the model. The functions ofthese mouse buttons are discussed next.
Left Mouse ButtonPress the left mouse button and drag the mouse to pan the model.
Middle Mouse ButtonPress the middle mouse button and drag the mouse to zoom and spin the model.
Right Mouse ButtonPress the right mouse button and drag the mouse to rotate the model.
Action Buttons AreaThe buttons in this area are used to perform different actions. These buttons are discussednext.
FitThis button is used to zoom the active window such that all the entities can be displayedwithin the window.
ResetThis button is used to display the default orientation of the active view. Also, it zooms thewindow such that all the entities can be displayed within the window.
CloseThis button is used to close the dialog box.
HelpThis button is used to invoke the Release 11.0 Documentation for ANSYS window.
1-38 ANSYS for Designers
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Graphics PickingGraphics picking is used to locate or retrieve the entities like nodes and keypoints using theleft mouse button. In ANSYS, there are three types of graphics picking operations.
1. Locational picking2. Retrieval picking3. Query picking
These operations are discussed next.
Locational PickingLocational picking is used to locate the coordinates of nodes and keypoints. Figure 1-36 showsthe Create KPs on WP dialog box that is used for locational picking. The different areas inthis dialog box are discussed next.
Pick Mode AreaThe radio buttons in the pick mode area are used to pick or unpick an entity or a location. ThePick radio button is selected to pick a point from the graphics area. The Unpick radio buttonis selected to deselect the selected point. The right mouse button is used to toggle betweenpick and unpick. The mouse pointer converts into an up arrow, while picking and into downarrow, while unpicking.
Figure 1-36 The Create KPs on WP dialog box
Introduction to FEA and ANSYS 1-39
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Pick Status AreaThis area gives the counts of the picked entities. Also, it gives information about the minimumand maximum number of times that a point can be picked.
Picked DataThis area gives information about the workplane and the global cartesian coordinates of thepicked items.
Keyboard Entry OptionsThis area is used to specify a known coordinate location during locational picking. Forexample, while applying load, you need to press the ENTER key after specifying the coordinatelocation for picking.
Action Buttons AreaThe buttons in this area have been discussed earlier.
Retrieval PickingRetrieval picking is used to pick the existing entities for operations such as applying loads,meshing, applying degrees of freedom, and so on. Figure 1-37 shows the Apply U,ROT onKPs dialog box that is used for retrieval picking. You can either select the individual entitiesby selecting the Single radio button, or you can use the following options for picking theentities:
Figure 1-37 The Apply U,ROT on KPs dialog box
1-40 ANSYS for Designers
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BoxDrag a rectangle around the entities; the entities inside the rectangle will be selected.
PolygonCreate a polygon by picking the points in the graphics area; the entities inside thepolygon will be selected.
CircleClick in the graphics area to specify the center of the circle center. Next, press and holdthe left mouse button and drag the mouse to specify the diameter of the circle; the entitiesinside the circle will be selected.
LoopThis radio button is used to pick only the lines and areas. The complete set of lines orareas within the continuous loop are picked.
Choose the Pick All button to select all entities in the graphics area.
Query PickingQuery picking is used to display the specified items from the database. There are two types ofquery pickers, Model query picker and Results query picker and these are explained next.
Model Query Picker
The model query picker allows you to display the information about the picked entities. Italso provides information about force per unit area, angle between lines, and so on. Toinvoke the model query picker, choose List >Picked Entities + from the Utility Menu;the Model Query Picker dialog box will be displayed, as shown in Figure 1-38.
Select the entities for query and choose the Apply button; the KLIST Command windowwill be displayed, as shown in Figure 1-39. This window contains information about theselected entities. If you select the Generate 3D Anno check box, the 3D annotationattached to the model with help of leader will be displayed in the graphics area.
Results Query Picker
The results query picker allows you to review the results for specific points on the model.To invoke the results query picker, choose General Postproc > Query Results from theMain Menu.
Using Mouse Buttons for PickingYou can use the mouse buttons for picking points/XY nodes in various ways that are givennext.
Utility Menu: List >Picked Entities +
Main Menu: General Postproc > Query Results
Introduction to FEA and ANSYS 1-41
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Figure 1-39 The KLIST Command window
Figure 1-38 The Model Query Picker dialog box
1-42 ANSYS for Designers
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The left mouse button is used to pick or unpick an entity.The middle mouse button is used to perform an action.The right mouse button is used to toggle between the pick and unpick modes.
ANSYS Database and FilesThe ANSYS database and files are discussed next.
DatabaseThe ANSYS database is used to store the input and the result data in the memory. The inputdata includes model dimensions, material properties, the loading data, and so on. The resultdata contains displacements, stresses, strains, reaction forces, and so on.
FilesDuring the process of analysis, the ANSYS writes and reads several files. The format of thesefiles is Jobname.ext. These components of the file name are discussed next.
Jobname
It is the name that is given in the ANSYS Product Launcher of ANSYS. The default nameis File. You can change the jobname in an ANSYS session also. To change the jobname,choose File > Change Jobname from the Utility Menu; the Change Jobname dialog boxwill be displayed, as shown in Figure 1-40. Enter the new jobname in the Enter newjobname edit box and choose the OK button from the dialog box.
ExtensionIn ANSYS, different file extensions are used to identify the contents of a file. For example,db is used for database. The following are some main file extensions used in ANSYS.
*.logThis file contains the history of every command used during a session.
*.errThis file contains a listing of all the errors and warnings encountered during a session.
Figure 1-40 The Change Jobname dialog box
Utility Menu: File > Change Jobname
Introduction to FEA and ANSYS 1-43
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db and dbbThe database file (db) is a read-only file. When you save a read-only db file, the existingread-only file is saved to a dbb file. You cannot save the read-only db file the secondtime because this process will attempt to write over the dbb file, which ANSYS doesnot allow.
*.rst, *.rth, *.rmg, and *.rflThese are the result files that contain the result data calculated by ANSYS. Theresult files are read-only. These files are discussed below:
*.rstSaves the structural result file.
*.rthSaves the thermal result file.
*.rmgSaves the magnetic result file.
*.rflSaves the flotran result file.
NoteIf you start a second session with the same jobname in the same working directory, then ANSYSwill overwrite the old *.log and *.err files.
Saving the File
The save operation copies the database from memory to a file called the database file (db). Tosave the file, choose the SAVE _DB button from the ANSYS Toolbar. Alternatively, you canchoose File > Save as Jobname.db from the Utility Menu to save the file.
Resuming the File
The resume operation restores the database from the db file into the memory. The resumeoperation is used as an undo tool. It restores the database into the memory from the lastsaved database file (db). To resume a file, choose the Resume_DB button from theANSYS Toolbar. Alternatively, you can choose File > Resume Jobname.db from the UtilityMenu to remove a file.
ANSYS Toolbar: SAVE _DBUtility Menu: File > Save as Jobname.db
ANSYS Toolbar: RESUME_DBUtility Menu: File > Resume Jobname.db
1-44 ANSYS for Designers
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Clearing the Database
This operation is used to clear the old database and start a new one. It is similar to restartingANSYS. To clear the database, choose File > Clear & Start New from the Utility Menu; theClear Database & Start New dialog box will be displayed, as shown in Figure 1-41.
Choose the OK button from this dialog box; the Verify window showing a warning that theold database will be deleted will be displayed. Choose the YES button to start a new database.
Some Basic Steps in General Analysis ProcedureEvery analysis involves some basic steps, which are as follows:
1. Preliminary Decisions2. Preprocessing3. Solution4. Postprocessing
The preprocessing, solution, and postprocessing have been discussed earlier in this chapter.
Preliminary DecisionsA successful analysis of any geometry depends on accurate planning, which includes takingthe following decisions:
Figure 1-41 The Clear Database and Start New dialog box
Utility Menu: File > Clear & Start New
Tip. It is recommended to save the database as you progress through an analysis.And, you must save the database before attempting the following operations:
a. Boolean operationb. Meshing operationc. Solving an analysis
Introduction to FEA and ANSYS 1-45
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Analysis TypeFirst of all you need to decide the type of analysis to be performed, that is structural,thermal, fluid flow, electromagnetic field, or coupled-field analysis.
What to ModelNext, you need to decide the type of model required to define a geometry. The solidmodeling in ANSYS is discussed in the next chapter.
Element TypeThis is an important aspect and determines the element characteristics. The elementtypes are discussed in the later chapters.
Points to Remember while Performing an Analysis1. Create each analysis project in a separate working directory.2. Assign different jobnames to differentiate between various analyses.3. Do not delete the files created by ANSYS after the analysis is over.4. Keep on saving the database at regular intervals.5. Save the database before performing complicated operations such as boolean and meshing.6. You cannot open the db files created in ANSYS 11.0 with ANSYS 10.0 or an earlier version.
ANSYS Help
To invoke the help window, choose Help > Help Topics from the Utility Menu; the Release11.0 Documentation for ANSYS window will be displayed, as shown in Figure 1-42.
Also, every dialog box in ANSYS contains the Help button. On choosing this button, the helprelevant to that particular dialog box will be displayed in the Release 11.0 Documentation forANSYS window. The ANSYS help window is divided into two parts: Navigational window andDocument window. The Navigational window contains the Contents, Index, Search, andFavorites tabs. The Document window contains the help information related to the topicselected in the Navigational window. In the help window, you can get help on the ANSYScommands, element types, analysis procedure, and so on.
Utility Menu: Help > Help Topics
1-46 ANSYS for Designers
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Exiting ANSYS
To exit ANSYS, choose the QUIT button from the ANSYS Toolbar or choose File > Exit fromthe Utility Menu; the Exit from ANSYS dialog box will be displayed, as shown in Figure 1-43.Select the appropriate radio button from the list of options given and choose the OK button.The options in this dialog box are discussed next.
Figure 1-43 The Exit from ANSYS dialog box
ANSYS Toolbar: QUITUtility Menu: File > Exit
Figure 1-42 The Release 11.0 Documentation for ANSYS Window
Introduction to FEA and ANSYS 1-47
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Save Geom+LoadsIf you select this radio button and choose the OK button, only the geometry and the loads willbe saved.
Save Geo+Ld+SoluThis radio button is used to save the geometry, loads, and the solution.
Save EverythingThis check box is used to save everything, which including the geometry, loads, solution,graphs, results, and so on.
Quit - No Save!This radio button is used to exit the ANSYS session without saving the database.
Select any one of the above radio buttons according your requirement and choose the OKbutton; the ANSYS session will be closed.
Answer the following questions and then compare them to those given at the end of thechapter:
1. Finite Element Analysis is an approximate method. (T/F)
2. The shape of an element can be changed by moving the nodes of the element in the space.(T/F)
3. The elements that have the nodes at the middle of the element edge are called linearelements. (T/F)
4. The models that have holes or sharp corners need to be densely meshed in those areas toget better results. (T/F)
5. In ANSYS, the top view is the default view for displaying a model. (T/F)
6. You cannot open the db files created in ANSYS 11.0 with ANSYS 9.0 or an earlierversion. (T/F)
7. In the __________ analysis, the nodal degrees of freedom (Displacement) are calculated.
8. The __________button is used to raise the hidden dialog box.
9. The __________menu is used to display the nodes, elements, keypoints, lines, areas, andvolumes.
10. The__________file contains all the errors and warnings encountered during a session.
Self-Evaluation Test
1-48 ANSYS for Designers
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Answers to Self-Evaluation Test1. T, 2. T, 3. F, 4. T, 5. F, 6. T, 7. Structural, 8. Raise Hidden, 9. Plot, 10. *.err
