Finite Element Analysis
Viva Questions
FEA Viva Questions
1. What is Discretization?
Discretization means dividing the body (system) into an equivalent system of finite elements with associated nodes and elements. 2. Difference between Mapped and Free Meshing Free Meshing:
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Has no element shape restriction.
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The mesh does not follow any pattern.
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Suitable for complex shaped areas and volumes.
Mapped Meshing:
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Restrict element shapes to quadrilaterals.
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Typically has a regular pattern with obvious rows of elements.
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Suitable only for regular areas and volumes such as rectangles and bricks
3. What is Shape Function?
The shape function is the function which interpolates the solution between the discrete values obtained at the mesh nodes. 4. What is Array?
An array is a systematic arrangement of objects, usually in rows and columns. 5. Good techniques of Geometric modeling
(1) Structural/stress analysis (2) Heat transfer analysis (3) Fluid flow analysis (4) Electric or magnetic potential distribution analysis (5) Biomechanical engineering
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Finite Element Analysis
Viva Questions
6. What is FDM, FEM and BEM Finite Difference Method (FDM): The FDM is generally restricted to simple geometries
in which an orthogonal grid can be constructed; for irregular geometries, a global transformation of the governing equations (e.g., boundary fitted coordinates) must be made to create an orthogonal computational domain. Finite Element Method (FEM): For nonlinear problems the dominance of finite element
methods is overwhelming. The ability to model complex geometries using unstructured meshes and employing elements that can be individually tagged makes the method unique. Boundary Element Method (BEM): For linear problems finite element methods
currently dominate the scene, with boundary element methods posting a strong second choice in selected application areas. The boundary element method is often more efficient than other methods
The BEM only requires the discretization of the boundaries of the problem domai n. It works by constructing a "mesh" over the modeled surface. However, for many problems boundary element methods are significantly less efficient Boundary element formulations typically give rise to fully populated matrices. This means that the storage requirements and computational time will tend to grow according to the square of the problem size. By contrast, finite el ement matrices are typically banded (elements are only locally connected) and the storage requirements for the system matrices typically grow quite linearly with the problem size . 7. Approaches in FEA formulation
(1) Direct equilibrium method (2) Work or energy methods (3) Methods of weighted residuals 8. What is the full form of IGES and DXF? Initial Graphics Exchange Specification (IGES) is a file format which defines a vendor
neutral data format that allows the digital exchange of information among Computeraided design (CAD) systems. AutoCAD DXF (Drawing Interchange Format or Drawing Exchange Format) is a CAD
data file format developed by Autodesk for enabling data interoperability between AutoCAD and other programs.
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Finite Element Analysis
Viva Questions
9. Define “h” and “p” method
The name for the h-method is borrowed from mathematics. The finite element method was originally developed by the work of mathematicians, particularly those who worked in the area of numeric integration. The variable h is used to specify the step size in numeric integration. This variable name carried over into finite element analysis.
The p in p-method stands for polynomial. Increasing the polynomial order of the shape function changes the accuracy of the p-method. This allows a very complex displacement function to be approximated across a large element.
In terms of computing time, the h and p methods will have about the same requirements. In each case you are solving for about the same number of nodes. The hmethod increases the number of nodes by adding more elements. The p-method increases the number of nodes by increasing the order of the shape function. 10. What is post processing?
Post-processing may be defined as the “art of results representation”. Post processing of finite element data generally requests additional software to organize the output.
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Finite Element Analysis
Viva Questions
11. What are global and local coordinates?
A local coordinate system is one in which vertices are specified relative to the object (usually the object's center point) to which they belong. A global coordinate system is one where vertices are specified relative to a single universal center point.
12. Steps in FEA (ANSYS)
The following are the general steps of the finite element method. Step 1 Divide the body into an equivalent system of finite elements with associated nodes and choose the most appropriate element type. Step 2 Choose a displacement function within each element. Step 3 Relate the stresses to the strains through the stress/strain law —generally called the constitutive law. Step 4 Derive the element stiffness matrix and equations. Use the direct equilibrium method, a work or energy method, or a method of weighted residuals to relate the nodal forces to nodal displacements. Step 5 Assemble the element equations to obtain the global or total equations and introduce boundary conditions. Step 6 Solve for the unknown degrees of freedom (or generalized displacements). Step 7 Solve for the element strains and stresses. Step 8 Interpret and analyze the results for use in the design/analysis process.
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Finite Element Analysis
Viva Questions
13. To what does the term Degree of Freedom refer? The term ‘degrees of freedom’ refers to rotations and displacements that are associated
with each node. 14. Full Form of AGMA: AGMA - American Gear Manufacturers Association: comparative analysis between the
ISO and AGMA standards, focused on tooth-root strength, based on the precise FEM modeling of spur and helical gears. 15. Full Form of APDL: APDL (ANSYS Parametric Design Language), a proprietary scripting language
for input and is used for automation. 16. Degree of Freedom in pipe element
Pipe elements are two-node members which allow arbitrary orientation in the 3-D (three-dimensional) X, Y, Z space. The pipe is a general six degree of freedom (DOF) element three global translation and rotational components at each end of the member. 17. Von-mises stress Von Mises stress is a geometrical combination of all the stresses (normal stress in the
three directions, and all three shear stresses) acting at a particular location. Von Mises stress is widely used by designers, to check whether their design will withstand given load condition. Concept of Von mises stress arises from distortion energy failure theory. According to von Mises’s failure criterion, the material under multi-axial loading will yield when the distortional energy is equal to or greater than the critical value for the material. Von Mises stress is useful for materials which classify as ductile. If the Von Mises stress at a particular location exceeds the yield strength, the material yields at that l ocation. If the Von Mises stress exceeds the ultimate strength, the material ruptures at that location. For brittle materials, the Von Mises stress concept isn't applicable. Instead, maximum principle stress (normal stress on the plane at which it is maximum) is what is used to predict failure.
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Finite Element Analysis
Viva Questions
18. What should be the element type for a system of air flow over a car?
Only fluid domain is meshed, no need to mesh the car. The top surface of the car is assumed as a wall. 19. What is variational approach?
The variational method is the more straight forward approach and involves minimizing the potential energy of the system. To illustrate the variational formulation, the finite element equations of the bar will be
derived from the Minimum Potential Energy principle. 20. Minimum Total Potential Energy Formulation
The theorem of minimum potential energy can be stated as: Of all the kinematically admissible displacement functions the actual displacement function is the one that minimizes the potential energy function at stable equilibrium. 21. Steps of wind tunnel simulation
22. Dynamic and Transient Analysis
23. Difference between CST and LST, CST advantage over LST
24. Graph of number of element vs. Iteration
25. Which practical is dynamic analysis in workbook
26. Global Iteration
27. Large Static deflection
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Finite Element Analysis
Viva Questions
28. A softball designing of exercise
29. Reason for Sher Shah bridge failure
The load on bridge was greater than design load of the pillars 30. Column buckling prevention techniques
31. Sphere Modeling
32. What is mesh compatibility?
33. Why we break link element into only one element? For higher accuracy what should be done?
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