INTRODUCTION TO FINITE ELEMENT ANALYSIS

The limitations of human mind are such that it cannot grasp the behavior of its complex surrounding and creations in one operation. Thus the process of subdividing all systems into their individual components or elements, whose behavior is all readily understood and then rebuilding the original system from such components to study its behavior is a natural way in which the engineer, the scientist or even the economist proceeds.
The finite element method is a numerical method, which can be used for the solution of complex engineering problems with accuracy acceptable to engineers.
In 1957 this method was first developed basically for the analysis of aircraft structures. There after the usefulness of this method for various engineering problems were recognized. Over the years, the finite element technique has been so well developed that, today it is considered to be one of the best methods for solving a wide variety of practical problems efficiently.
One of the main reasons for the popularity of the method in different fields of engineering is that once a general computer program is written, it can be used for the solution of any problem simply by changing the input data.
In FEM since the actual problem is replaced by a simpler one in finding the solution we will be able to find only an approximate solution rather than the exact solution. In most of the practical problems, the existing mathematical tools are not even able to find approximate solution of the problem .Thus, in the absence of any other convenient method to find even the approximate solution of a given problem; we have to prefer the FEM.
The digital computer provided a rapid means of performing many calculations involved in FEA. Along with the development of high speed computers, the application of the FEM also progressed at a very impressive rate.




GENERALLY USED COMMANDS IN ANSYS:

 AADD: Adds separate areas to create single area.

 VADD: Adds separate volumes to create single volume.

 ANTYPE: Specifies the analysis type and restart status.

 AOFFST: Generates an area, offset from a given area.

 APLOT: Displays the selected areas.

 VPLOT: Displays the selected volumes.

 KPLOT: Displays the selected key-points.

 AL: generates an area bounded by previously defined lines.

 LSTR: Defines a straight line irrespective of the active co-ordinate system.

 LGEN: Generates additional lines from a pattern of lines.

 VGEN: Generates additional volumes from a pattern of volumes.

 KGEN: Generates additional key-points from a pattern of key-points.

 LSYMM: Generates lines from a line pattern by symmetry reflection.

 VSYMM: Generates volumes from a volume pattern by symmetry reflection

 KDELE: Deletes unmeshed key-points.

 LDELE: Deletes unmeshed lines.

 ADELE: Deletes unmeshed areas.

 VDELE: Deletes unmeshed volumes.

 VDRAG: Generates volumes by dragging an area pattern along a path.

 VROTAT: Generates cylindrical volumes by rotating an area pattern about an axis.

 LSBL: Subtracts lines from lines.

 LDIV: Divides a single line into to two or more lines.

 LFILLT: Generates a fillet line between two intersecting lines.

 LARC: Defines a circular arc.


BASIC ELEMENT SHAPE:
Mostly, choice of the type of element is dictated by the geometry of the body and the number of independent spatial co-ordinates necessary to describe the system .The element may be one, two and three dimensional
When the geometry, material properties and other parameters (stress, displacement, pressure and temperature) can be described in terms of only one spatial co-ordinate, we can use the one dimensional element. Although this element has a cross-sectional area ,it is generally shown schematically as a line segment .When configuration and other details of the problem can be described in terms of two independent spatial co-ordinates ,we can use the two dimensional elements. The basics element useful for the two dimensional analysis is the triangular element. Rectangular and parallelogram shaped elements or quadrilateral (combination of two or four triangular elements) element can also be used.
If the geometry, material properties and other parameters of the body can be described by three independent spatial co-ordinates, we can idealize the body by using three dimensional elements. Tetrahedron element is the basics three dimensional element. Hexahedrogon can also be used advantageously.
The problems that possess axial symmetry like pistons, storage tanks, valves, rocket nozzles fall into this category. For the discritisation of the problem involving curved geometries finite elements with curved size are useful. The ability to model curved boundaries has been made possible by the addition of mid-side nodes.
Finite element with straight sides is known as linear elements, while those with curved sides are called higher order elements.


APPLICATIONS OF FEA IN VARIOUS FIELDS:

FEA is applicable in three major categories of boundaries value problem.
1) Steady state or equilibrium or time independent problems.
2) Eigen values problems.
3) Propagation problem.

APPLICATIONS:
 Mechanical designs;
 Aircraft structures;
 Heat conduction;
 Hydraulics and water resources engineering;
 Nuclear engineering;
 Biomedical engineering;
 Civil engineering structures.