EX NO:1                          INTRODUCTION TO ANSYS

DATE:

ANSYS is a general-purpose finite-element modeling package for numerically solving a wide variety of mechanical problems. These problems include static/dynamic, structural analysis (both linear and nonlinear), heat transfer, and fluid problems, as well as acoustic and electromagnetic problems.

ANSYS finite element analysis software enables engineers to perform the following tasks:

·         Build computer models or transfer CAD models of structures, products, components, or systems.

·         Apply operating loads or other design performance conditions.

·         Study physical responses, such as stress levels, temperature distributions, or electromagnetic fields.

·         Optimize a design early in the development process to reduce production costs.

·         Do prototype testing in environments where it otherwise would be undesirable or impossible (for example, biomedical applications)

FINITE ELEMENT MOTHED CONCEPT:

          The finite element method is defined as the discreatization whole region (model) into small number of elements. These small elements connected to each other of code prints finite element analysis grew out of matrix methods for the analysis of surface. When the wide spread availability of the digital computer made is possible  to solve system of hundreds of simultaneous equation using FEA software link, Nastron, Ansys etc.,

FINITE ELEMENT ANALYSIS GENERAL PROCEDURE:

          The following steps summarize in finite element analysis procedure,

STEP-1

          The continuous is a physical body structure or solid being analyzed. Discretization may be simply described as the process by which the given body is sub divided into an equivalent system of finite elements. The finite elements may be triangles of quadrilateral for two dimensions continuum

          The collection of the element is called finite element mesh. The choice of element type number of elements and density of elements are defeated on the geometry of the domain, the problem to be analyzed.

STEP-2

          The selection of the displacement models representing approximately the actual distribution of the displacement. The three factors selection of a displacement models are,

i.                   The type and degree of displacement model.

ii.                 Displacement magnitude

iii.              The requirements to be satisfied which ensuring correct solution.

STEP-3

          The deviation of the stiffness matrix which consists of the coefficient of the equilibrium  equation derived from the material and geometric properties of an element at nodal points to be applied forces at nodal points,

[k]{q} = {f}

                             [k] → stiffness matrix

                             {q}→ Nodal displacement vector

                             {f}→ Force vector

STEP-4

          Assembly of the algebraic equation for the overall continues modules the assembly of the overall stiffness matrix for the entire body for individual element and the overall global load vector from the element load vector. The next commonly used technique was direct stiffness method.

          The overall equilibrium relation b/w the total stiffness matrix [k], the total force vector {e} and the nodal displacement vector of the entire body {r} can be expressed at [k]{r}={e}.

STEP-5

          The algebraic equations assembled in step4 are solved for continuous displacement in linear equilibrium problems, this is a relatively straight forward application of matrix algebra techniques.

STEP-6

          In this step the strain and stress and computed from the nodal displacements.

TYPES OF ANALYSES:

STRUCTURAL ANALYSES

Structural analysis is probably the most common application of the finite element method. The term structural (or structure) implies not only civil engineering structures such as bridges and buildings, but also naval, aeronautical, and mechanical structures such as ship hulls, aircraft bodies, and machine housings, as well as mechanical components such as pistons, machine parts, and tools.

Types of Structural Analysis

The seven types of structural analyses available in the ANSYS family of products are explained below. The primary unknowns (nodal degrees of freedom) calculated in a structural analysis are displacements. Other quantities, such as strains, stresses, and reaction forces, are then derived from the nodal displacements.

Structural analyses are available in the ANSYS Multiphysics, ANSYS Mechanical, ANSYS Structural, and ANSYS Professional programs only.

You can perform the following types of structural analyses. Each of these analysis types are discussed in detail in this manual.

Static Analysis

It is used to determine displacements, stresses, etc. under static loading conditions. Both linear and nonlinear static analyses. Nonlinearities can include plasticity, stress stiffening, large deflection, large strain, hyperelasticity, contact surfaces, and creep.

Modal Analysis

It is used to calculate the natural frequencies and mode shapes of a structure. Different mode extraction methods are available.

Harmonic Analysis

It is used to determine the response of a structure to harmonically time-varying loads.

Transient Dynamic Analysis

It is used to determine the response of a structure to arbitrarily time-varying loads. All nonlinearities mentioned under Static Analysis above are allowed.

Spectrum Analysis

An extension of the modal analysis, used to calculate stresses and strains due to a response spectrum or a PSD input (random vibrations).

Buckling Analysis

It is used to calculate the buckling loads and determine the buckling mode shape. Both linear (eigenvalue) buckling and nonlinear buckling analyses are possible. 

Explicit Dynamic Analysis

This type of structural analysis is only available in the ANSYS LS-DYNA program. ANSYS LS-DYNA provides an interface to the LS-DYNA explicit finite element program. Explicit dynamic analysis is used to calculate fast solutions for large deformation dynamics and complex contact problems

THERMAL ANALYSIS

A thermal analysis calculates the temperature distribution and related thermal quantities in a system or component. Typical thermal quantities of interest are:

·         The temperature distributions

·         The amount of heat lost or gained

·         Thermal gradients

·         Thermal fluxes.

Thermal simulations play an important role in the design of many engineering applications, including internal combustion engines, turbines, heat exchangers, piping systems, and electronic components. In many cases, engineers follow a thermal analysis with a stress analysis to calculate thermal stresses (that is, stresses caused by thermal expansions or contractions).

How ANSYS Treats Thermal Modeling

Only the ANSYS Multiphysics, ANSYS Mechanical, ANSYS Professional, and ANSYS FLOTRAN programs support thermal analyses.

The basis for thermal analysis in ANSYS is a heat balance equation obtained from the principle of conservation of energy. The finite element solution you perform via ANSYS calculates nodal temperatures, then uses the nodal temperatures to obtain other thermal quantities.

The ANSYS program handles all three primary modes of heat transfer: conduction, convection, and radiation.

Convection:

You specify convection as a surface load on conducting solid elements or shell elements. You specify the convection film coefficient and the bulk fluid temperature at a surface; ANSYS then calculates the appropriate heat transfer across that surface. If the film coefficient depends upon temperature, you specify a table of temperatures along with the corresponding values of film coefficient at each temperature.

For use in finite element models with conducting bar elements (which do not allow a convection surface load), or in cases where the bulk fluid temperature is not known in advance, ANSYS offers a convection element named LINK34. In addition, you can use the FLOTRAN CFD elements to simulate details of the convection process, such as fluid velocities, local values of film coefficient and heat flux, and temperature distributions in both fluid and solid regions.

Radiation:

ANSYS can solve radiation problems, which are nonlinear, in four ways:

·         By using the radiation link element, LINK31

·         By using surface effect elements with the radiation option (SURF151 in 2-D modeling or SURF152 in 3-D modeling)

·         By generating a radiation matrix in AUX12 and using it as a superelement in a thermal analysis.

·         By using the Radiosity Solver method.

FLUID FLOW ANALYSIS

The ANSYS FLOTRAN derived product and the FLOTRAN CFD (Computational Fluid Dynamics) option to the other ANSYS products offer you comprehensive tools for analyzing 2-D and 3-D fluid flow fields. Using either product or the FLOTRAN CFD elements FLUID141 and FLUID142, you can achieve solutions for the following:

·         Lift and drag on an airfoil

·         The flow in supersonic nozzles

·         Complex, 3-D flow patterns in a pipe bend

In addition, you can use the features of ANSYS and ANSYS FLOTRAN to perform tasks including:

·         Calculating the gas pressure and temperature distributions in an engine exhaust manifold

·         Studying the thermal stratification and breakup in piping systems

·         Using flow mixing studies to evaluate potential for thermal shock

·         Doing natural convection analyses to evaluate the thermal performance of chips in electronic enclosures

·         Conducting heat exchanger studies involving different fluids separated by solid regions

Types of FLOTRAN Analyses

Laminar Flow Analysis

In these analyses, the velocity field is very ordered and smooth, as it is in highly viscous, slow-moving flows. The flow of some oils also can be laminar.

Turbulent Flow Analysis

Turbulent flow analyses deal with problems where velocities are high enough and the viscosity is low enough to cause turbulent fluctuations. The two-equation turbulence model in ANSYS enables you to account for the effect of the turbulent velocity fluctuations on the mean flow.

Laminar and turbulent flows are considered to be incompressible if density is constant or if the fluid expends little energy in compressing the flow. The temperature equation for incompressible flow neglects kinetic energy changes and viscous dissipation.

Thermal Analysis

Often, the solution for the temperature distribution throughout the flow field is of interest. If fluid properties do not vary with temperature, you can converge the flow field without solving the temperature equation. In a conjugate heat transfer problem, the temperature equation is solved in a domain with both fluid and non-fluid (that is, solid material) regions. In a natural convection problem, the flow results mainly or solely from density gradients brought about by temperature variations. Most natural convection problems, unlike forced convection problems, have no externally applied flow sources.

Compressible Flow Analysis

For high velocity gas flows, changes in density due to strong pressure gradients significantly influence the nature of the flow field. ANSYS uses a different solution algorithm for compressible flow.

Non-Newtonian Fluid Flow Analysis

A linear relationship between the stress and rate-of-strain cannot describe many fluid flows adequately. For such non-Newtonian flows, the ANSYS program provides three viscosity models and a user-programmable subroutine.

Multiple Species Transport Analysis

This type of analysis is useful in studying the dispersion of dilute contaminants or pollutants in the bulk fluid flow. In addition, you can use multiple species transport analysis for heat exchanger studies where two or more fluids (separated by walls) may be involved.

Free Surface Analysis

Free surface analyses deal with problems involving a unconstrained gas-liquid surface. You can use this type of analysis to solve two dimensional planar and axisymmetric problems such as flow over a dam and tank sloshing.

DYNAMIC ANALYSIS:

          ANSYS LS-DYNA combines the LS-DYNA explicit finite element program with the powerful pre- and postprocessing capabilities of the ANSYS program. The explicit method of solution used by LS-DYNA provides fast solutions for short-time, large deformation dynamics, quasi-static problems with large deformations and multiple nonlinearites, and complex contact/impact problems. Using this integrated product, you can model your structure in ANSYS, obtain the explicit dynamic solution via LS-DYNA, and review results using the standard ANSYS postprocessing tools.

LOADS:

The word loads in ANSYS terminology includes boundary conditions and externally or internally applied forcing functions, examples of loads in different disciplines are:

Structural: displacements, forces, pressures, temperatures (for thermal strain), gravity

Thermal: temperatures, heat flow rates, convections, internal heat generation, infinite surface

Magnetic: magnetic potentials, magnetic flux, magnetic current segments, source current density, infinite surface

Electric: electric potentials (voltage), electric current, electric charges, charge densities, infinite surface

Fluid: velocities, pressures

Loads are divided into six categories: DOF constraints, forces (concentrated loads), surface loads, body loads, inertia loads, and coupled-field loads.

• A DOF constraint fixes a degree of freedom (DOF) to a known value. Examples of constraints are specified displacements and symmetry boundary conditions in a structural analysis, prescribed temperatures in a thermal analysis, and flux-parallel boundary conditions.
• A force is a concentrated load applied at a node in the model. Examples are forces and moments in a structural analysis, heat flow rates in a thermal analysis, and current segments in a magnetic field analysis.
• A surface load is a distributed load applied over a surface. Examples are pressures in a structural analysis and convections and heat fluxes in a thermal analysis.A body load is a volumetric or field load. Examples are temperatures and fluences in a structural analysis, heat generation rates in a thermal analysis, and current densities in a magnetic field analysis. Inertia loads are those attributable to the inertia (mass matrix) of a body, such as gravitational acceleration, angular velocity, and angular acceleration. You use them mainly in a structural analysis.
• Coupled-field loads are simply a special case of one of the above loads, where results from one analysis are used as loads in another analysis. For example, you can apply magnetic forces calculated in a magnetic field analysis as force loads in a structural analysis.