Advanced Manufacturing Research and Collaboration Cluster - Analysis Software

Analysis Software

AMRCC member practitioner of this technology

The Traditional Approach

Traditionally, the product development process has relied on a combination of past experience, basic calculations, and prototype testing. Initially, a design concept was chosen, often heavily influenced by what worked in the past. Next, calculations were made to get some assurance that the design would meet the requirements. Prototype parts were then obtained and tested. Typically, testing identified some needed changes, which then lead to another round of prototypes and testing. When schedule and budget constraints were imposed, the output of the development process was often the first design that passed the tests rather than an optimum design.

Before giving an over view of design by analysis, a review of the methods traditionally used in the product development process would be helpful. Traditionally, the development process has relied on classical structural mechanics and experimental based methods.

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Classical Structural Mechanics

Classical structural mechanics uses mathematical equations to model physical systems. The equations are based on maintaining equilibrium under the applied loads and on maintaining continuity of deformations. This method has the advantage of being relatively straightforward. Equations applicable to many problems are readily available in handbooks, textbooks, and various standards. The calculations can be done quickly at low cost with a calculator or spreadsheet. However, there are several limitations to classical analysis methods. First, equations are only available for relatively simple geometry and loading. In addition, solutions are usually limited to linear, static problems and give only partial results for specific points on the structure. For many real world problems, classical methods are, at best, able to only approximate reality.

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Experimental Methods

Experimental based methods apply the scientific method to the product development process. With this method, a hypothesis is formulated and accepted or rejected based on prototype tests. Experimental methods can provide a better representation of reality and a more complete evaluation of failure modes than is possible with classical analysis methods. However, fabricating prototypes is usually a long and expensive process. In addition, test fixtures and instrumentation must be obtained, set up, and calibrated.

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Design by Analysis

In recent times, theories describing material behavior along with powerful computational tools have been developed. Both of these have led to an analysis technique known as finite element analysis. Incorporating this powerful technology into the product development process can lead to superior designs and to significant reductions in development time and cost.

Finite element analysis is an extension of classical mechanics. Mathematically, a structure is divided into subdivisions called finite elements. The elements have simple geometric shapes for which equilibrium equations can be readily formulated. The equations for each element can be combined using equilibrium of loads and continuity of displacements between elements. External constraints are then applied. The resulting equation system is solved simultaneously for displacements. Stresses are then calculated using laws of material behavior. Finite element analysis can be more accurate then classical methods as complex geometry can be represented exactly. More realistic boundary conditions can be applied and non-linear effects can be included. Unlike classical methods, a complete set of results is obtained for the entire structure. In effect, finite element analysis electronically simulates a prototype test. Thus, much physical prototyping and testing can be avoided reducing development time and cost.

The software currently available for finite element analysis features efficient graphical user interfaces for defining the model, powerful equation solver technology, and extensive results processing capability. In addition, advanced capabilities are also available to aid in tasks such as optimization and probabilistic analysis. Of course, as the physical problem becomes more complex, more capability is required from the software, hardware, and analyst.

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Additional Finite Element Analysis Applications

In addition to linear-elastic stress and deflection analysis, finite element analysis can be used in the following applications:

  • Non-Linear Geometry
    • Contact of multiple surfaces
    • Large deflections, Buckling
  • Non-Linear Materials
    • Plasticity
    • Hyperelasticity (rubber)
    •  Temperature dependent properties
    • Creep
  • Dynamics
    • Modal analysis
    • Harmonic response analysis
    • Random vibration analysis
    • Spectrum analysis
  • Thermal
    • Steady state or transient
    • Conduction, Convection, Radiation
    • Phase change
  • Fluid Flow (CFD)
    • 2D or 3D
    • Steady state or transient
    • Laminar or turbulent flow
    • Compressible or incompressible flow
    • Thermal or adiabatic
    • Newtonian or non-newtonian
  • Electromagnetics
    • Electrostatics
    • Magnetostatics
    • Current conduction
    • Harmonic
    • Transient
  • Acoustics
    • Compressible, non-flowing, inviscid fluids
    • Modal
    • Harmonic
    • Transient


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Finite Element Analysis Examples

The plots below are an example of the complex geometry that can be analyzed using finite element analysis.


Geometry
Finite .Element Representation

Deflection Results Contours

Stress Results Contours


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Considerations for Evaluating FEA software

When evaluating finite element software, the following are important considerations:

  • User friendly interface with efficient graphics display.
  • Robust solution algorithms.
  • Efficient post-processing results.
  • Comprehensive documentation and user training and support.
  • Extensive quality assurance and error notification procedures.


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What is Computational Fluid Dynamics (CFD)?

Computational Fluid Dynamics is the use of a mathematical model to simulate the physics of a flowing fluid. Depending on the software used and its capabilities, CFD can predict the following:

  • Pressure Distribution
  • Velocity Distribution
  • Temperature Distribution
  • Flow Rates
  • Cavitation/Phase Change
  • Body Forces
  • Chemical Reactions
  • Heat Transfer
  • Species Concentrations
  • Mechanical Deformation
  • Flow Path Visualization


The appropriate CFD packages can also simulate time dependant solutions in addition to steady state solutions.

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What is the CFD Process?

The CFD process is very similar to that of finite element analysis. There are several steps involved:

  • Create model (either 2-D or 3-D solid)
    • Usually imported from a CAD package
    • May require cleanup, simplification of features
  • Mesh the model
    • Size and type of mesh elements depends on geometry of model and physical phenomena of interest
  • Define boundary conditions
    • Select appropriate physics/conditions to be modeled
    • Select appropriate mathematical models of physics involved
  • Run the simulation
  • Process the results
    • Create desired numerical reports
    •  Create plots and/or graphical images


The time requirements for the CFD process depend on several factors. A simple 2-D model of basic fluid flow may run in minutes on a desktop workstation. At the opposite extreme a complex 3-D model simulating advanced phenomena may require days to solve on a group of 30 dedicated processors.

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What are its benefits?

There are two primary benefits to the use of CFD analysis. First, CFD can reduce development time and expense by allowing a design to be tested, improved, and optimized prior to the purchase of prototypes. Thus the expense of preliminary prototype parts that prove inadequate may be reduced, and the lead time associated with ordering prototypes can be eliminated. Depending on the application, CFD may be able to completely replace prototype testing. Typical variance of a well defined CFD analysis is generally on the order of 10% compared to laboratory tests.

The second major benefit of CFD is that it offers an enhanced understanding of physical phenomena that are difficult to measure or visualize using standard lab tests. For example, flow path visualization allows the identification of recirculation zones where energy is lost from the system. Likewise, careful examination of CFD results can allow a designer or engineer to modify the design to accentuate desired characteristics or minimize unwanted traits.

It should be acknowledged that CFD is not for everything. In some cases lab testing may return results in a matter of minutes where a CFD simulation may need hours to run. (This is especially true if the testing regimen of interest requires multiple conditions, such as varying pressure drops on a valve or pipe that would require multiple CFD analysis.)

Additionally, while not wanting to down play the fact that CFD can offer rough results for a 'quick look' at a concept, it is noted that obtaining accurate results (within 10%) can require considerable refinement of the model. CFD thus lends itself well to product development work where multiple models of very similar geometries and physics will be studied, allowing the time investment required for optimization of the model to be regained.

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What kind of hardware, software, and training are required?

The hardware and software requirements for CFD work will vary widely depending on what is to be studied.

CFD simulations are very demanding in terms of processor and memory requirements, typically requiring dedicated machines. For many applications a high-end desktop workstation will have sufficient capability to run a CFD simulation. The use of multiple processors can significantly reduce the solution time. The largest and most complex simulations can literally require dozens of processors and terabytes of RAM in order to obtain results in a reasonable time period. Keep in mind that the study of time-dependant phenomena will dramatically increase the amount of solving time and computer resources required.

The selection of software is dependent entirely upon the needs of the user. Some common packages are listed in the next section.

Training is also an important part of an effective CFD analysis. Most CFD packages were developed in highly academic settings. While the popularity of CFD in industrial settings is growing, it is typically assumed that those using the software will have an engineering background with a good coverage of fluids. Many CFD suppliers (and third party groups) offer training specific to certain CFD programs. Such training is highly recommended.

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Who are some CFD suppliers?

There are literally hundreds of CFD programs available. Many are highly specialized to narrow applications such as combustion, aerospace, chemical reactions, etc. Some codes are available free of charge or at low costs, while at the opposite extreme some commercial vendors charge in excess of $20,000 a year for a license. When selecting a CFD package the intended application should be considered, along with the level of support offered by the provider.

The following are some of the commercial packages that have been widely advertised:

  • Fluent (Fluent Inc.)
  • Fidap (Fluent Inc.)
  • Polyflow (Fluent Inc.)
  • Icepak (Fluent Inc.)
  • Flotran (Ansys Inc.)
  • Star (Computational Dynamics Ltd.)
  • Algor (Algor Inc.)
  • CFX (AEA Technology)


CFD modules are often available as add-ins to other analysis programs such as finite element analysis packages.

Some users may find it preferable to hire an outside consultant to perform CFD work, thereby avoiding potentially high costs for software, hardware, and training. Several of the providers of commercial CFD packages offer such services. If your company already has an established relationship with a firms that provides consulting and analysis work you may discover that they also have CFD capabilities. Additionally, some commercial CFD providers offer web based versions of their software for an hourly rate.

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AMRCC member practitioner of this technology

The companies listed below, are willing to discuss their hands-on Analysis Software experiences with you. Please feel free to use the email contact feature below to notify them of your interest. You will be contacted by the company's expert with that software to address your questions at their first convenience.

Company: Fisher Controls, LLC, Marshalltown, IA.

Parts Modeled: fluid flow passages, valve plugs, valve cages, pressure retaining castings, actuators, and related components

Types of Analyses: fluid flow, pressure distribution, velocity distribution, multiphase effects, linear and non-linear static, dynamic, thermal, fluid flow and electromagnetic.

Software: Fluent, Gambit, ANSYS

For additional information from this current user, contact: Fisher

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