Line body analysis in ANSYS

Introduction to Fluid Analysis

Flow simulations are widely used in engineering applications ranging from flow around airplane wings and hydraulic turbines to flow in blood vessels and other circulatory systems. We may gain a better understanding of the motion of fluid around objects as well as the fluid behavior in complex circulatory systems by conducting fluid analysis.

Computational fluid dynamics (CFD) simulation complements experimental testing, helps reduce cost and turnaround time for design iterations, and has become an indispensable tool whenever practical design involving fluids is required.

In fluid dynamics, the motion of a fluid is mathematically described using physical quantities such as the flow velocity u, flow pressure p, fluid density ρ, and fluid viscosity ν. The flow velocity or flow pressure is different at a different point in a fluid volume. The objective of fluid simulation is to track the fluid velocity and pressure variations at different points in the fluid domain.

CFD is useful in a wide variety of applications and here we note a few to give you an idea of its use in industry.  The simulations shown below have been performed using the FLUENT software.  CFD can be used to simulate the flow over a vehicle. For instance, it can be used to study the interaction of propellers or rotors with the aircraft fuselage.  The following figure shows the prediction of the pressure field induced by the interaction of the rotor with a helicopter fuselage in forward flight. Rotors and propellers can be represented with models of varying complexity.

The temperature distribution obtained from a CFD analysis of a mixing manifold. This mixing manifold is part of the passenger cabin ventilation system on the Boeing 767. The CFD analysis showed the effectiveness of a simpler manifold design without the need for field testing.

Bio-medical engineering is a rapidly growing field and uses CFD to study the circulatory and respiratory systems. The following figure shows pressure contours and a cutaway view that reveals velocity vectors in a blood pump that assumes the role of heart in open-heart surgery. 

CFD is attractive to industry since it is more cost-effective than physical testing. However, one must note that complex flow simulations are challenging and error-prone and it takes a lot of engineering expertise to obtain validated solutions.

Aircraft design was traditionally based on theoretical aerodynamics and wind tunnel testing, with flight-testing used for final validation. CFD emerged in the late 1960's. Its role in aircraft design increased steadily as speed and memory of computers increased. Today CFD is a principal aerodynamic technology for aircraft configuration development, along with wind tunnel testing and flighttesting.

State-of-the-art capabilities in each of these technologies are needed to achieve superior performance with reduced risk and low cost.

The application of CFD to reduce the drag of a wing by adjustment of pressure gradient by shaping and by suction through slotted or perforated surfaces. The drag of an aircraft can be reduced in a number of ways to provide increased range, increased speed, decreased size and cost, and decreased fuel usage. The adjustment of pressure gradient by shaping and using laminar boundary-layer control with suction are two powerful and effective ways to reduce drag. This is demonstrated with a calculation method for natural laminar flow (NLF) and hybrid laminar flow control (HLFC) wings.

The application of CFD to ground-based vehicles, in particular to automobile aerodynamics development. The use of CFD in this area has been continuously increasing because the aerodynamic characteristics have a significant influence on the driving stability and fuel consumption on a highway. Since the aerodynamic characteristics of automobiles are closely coupled with their styling, it is impossible to improve them much once styling is fixed. Therefore, it is necessary to consider aerodynamics in the early design stage.

CFD also finds applications in internal flows and has been used to solve real engineering problems such as subsonic, transonic and supersonic inlets, compressors and turbines, as well as combustion chambers and rocket engines.

UNDERSTANDING THE PROBLEM

You can save lots of time and money if you first spend a little time with a piece of paper and a pencil to try to understand the problem you are planning to analyze. Before initiating numerical modeling on the computer and generating a finite element model, it is imperative that you develop a sense of or a feel for the problem. There are many questions that a good engineer will ask before proceeding with the modeling process: Is the material under axial loading? Is the body under bending moments or twisting moments or a combination of the two? Do we need to worry about buckling? Can we approximate the behavior of the material with a two-dimensional model? Does heat transfer play a significant role in the problem? Which modes of heat transfer are influential? If you choose to employ FEA,  " back-of-the-envelope" calculations will greatly enhance your understanding of the problem, in turn helping you to develop a good, reasonable finite element model, particularly in terms of your selection of element types.

Some practicing engineers still use finite element analysis to solve a problem that could have been solved more easily by hand by someone with a good grasp of the fundamental concepts of the mechanics of materials and heat transfer. To shed more light on this very important point, consider the following examples.

A BRIEF HISTORYOF THE FINITE ELEMENT METHOD AND ANSYS.

The finite element method (FEM) is a numerical technique that can be applied to obtain solutions to a variety of problems in different engineering branch. Steady state, transient, linear, or nonlinear problems in stress analysis, vibrational, heat transfer, fluid flow, electrical and electromagnetism problems may be analyzed with finite element methods. The origin of the modern finite element method may be traced back to the early 1900s when some investigators approximated and modeled elastic continua using discrete equivalent elastic bars. However, Courant (1943) has been credited with being the first person to develop the finite element method.

In a paper published in the early 1940s, Courant used piecewise polynomial interpolation over triangular subregions to investigate torsion problems. 

The next significant step in the utilization of finite element methods was taken by Boeing in the 1950s when Boeing, followed by others, used triangular stress elements to model airplane wings. Yet, it was not until 1960 that Clough made the term finite element popular. During the 1960s, investigators began to apply the finite element method to other areas of engineering, such as heat transfer and seepage flow problems. Zienkiewicz and Cheung (1967) wrote the first book entirely devoted to the finite element method in 1967.

 In 1971, ANSYS was released for the first time. ANSYS is a comprehensive general-purpose finite element computer program that contains more than 100,000 lines of code. ANSYS is capable of performing static, dynamic, vibrational, heat transfer, fluid flow, and electromagnetism analyses. ANSYS has been a leading FEA program for well over 45 years. The current version of ANSYS 17.0 has a completely new look, with multiple windows incorporating a graphical user interface (GUI), pull-down menus, dialog boxes, and a tool bar. Today, you will find ANSYS in use in many engineering fields, including aerospace, automotive, electronics, and nuclear. In order to use ANSYS or any other "canned" FEA computer program intelligently, it is imperative that one first fully understands the underlying basic concepts and limitations of the finite element methods. 

ANSYS is a very powerful and impressive engineering tool that may be used to solve a variety of problems. However; a user without a basic understanding of the finite element methods will find himself or herself in the same predicament as a computer technician with access to many impressive instruments and tools, but who cannot fix a computer because he or she does not understand the inner workings of a computer!