Model solutions

The most basic issues governing what is possible in computer aided engineering (CAE) are the continued improvement in software technology and the increase in hardware capacity, which allows the simulation of many more complex real-world problems.

The key words here are 'real' and 'world'. For a long time, finite element analysis (FEA) technology used complex structural equations to approximate structural interactions that we couldn't solve any other way. This severely limited us regarding hardware, and because the capacity wasn't there, it also held back our software technology ambitions.

Now hardware is less of an issue. Machines can never be fast enough, but modern hardware has allowed us to develop much more ambitious and 'real-world' software solutions. And even quite complex analyses can be performed at the very early stages of design — where most of the development money is committed.

The whole field of multiphysics has opened up thanks to today's hardware. Multiphysics in an FEA software context refers to the simultaneous combination of multiple physical CAE models from different disciplines — such as fluids, structures, thermal and even chemical domains — to predict device behaviour or whole system response rather than discrete component behaviour.

Aircraft wing flutter and underwater shock effects on marine structures, for example, can be simulated using the discipline. fluid-structural interaction (FSI) is a branch of multiphysics that studies the effects of fluid flow on structures and subsequent interactions.

The primary fields that interact across the different domains are pressures in fluids and displacements in structures. Problems where thermal effects are significant also involve an additional temperature field in both domains.

As more physical effects are included and the need arises for more sophisticated software solutions, more hardware capacity is also required to solve the complex problems which increase in line with the numbers of variables.

In addition there are secondary fields, such as piezoelectric effects in the structural domain and cavitation effects in the fluid domain, that contribute indirectly to fluid/structure interaction.

There are various ways to solve these — the partitioned approach providing the most general-purpose technique. In

FEA software a partitioned or co-simulation approach can be used to solve complex FSI analyses by coupling the FEA solver to external computational fluid dynamics (CFD) solvers.

In this way Abaqus and the external solver run concurrently and solve structural and fluid equations independently while exchanging converged solutions at the fluid-structure interface.

Perfect, seamless communication between FEA and CFD is critical in a coupled approach because the programs are commonly running on remote systems or different hardware in the same location. This takes place with either an independent coupling or a direct-coupling interface.

The recently-introduced Simulia multiphysics program from Abaqus supports both. Deciding which to use depends on how far the analysis needs to go to get the desired results — in other words, good old fashioned engineering know-how.

An independent coupling interface such as MpCCI (the Meshbased parallel Code Coupling Interface), from Germany's

allows you to link Abaqus to your favourite CFD code. The interface also works with Star-CD from

and Fluent from

. This approach also helps foster collaboration between existing FEA and CFD engineering groups, as well as software companies.

The Abaqus Simulia Direct Coupling Interface (DCI) provides a tighter integration between Abaqus and certain third-party CFD solvers, without requiring additional software components.

This approach is useful for FEA groups that need to solve FSI problems on their own. The direct coupling became available with Abaqus Version 6.7 and works with AcuSolve CFD software from Acusim.

recent acquisition of pioneerSOLUTIONS has provided another way of resolving the multiphysics/multidiscipline conundrum. this, together with MSC's SimEnterprise open Services Oriented Architecture (SOA) means that the company can deliver an all-inclusive platform for multidiscipline simulation. Through its Open CFD approach MSC is the first company to deliver an all-in-one common user environment through the SimEnterprise simulation platform that covers fluids applications such as fluid flow, heat transfer, aerodynamics and climate control.

According to chief executive Bill Weyand: 'Today there are over 40 CFD solver tools on the market, all creating separate models. This is an outdated and costly approach. Customers want to work with CFD in a single, multidiscipline environment, with a common and consistent work environment across all the disciplines, enabling them to drive innovative products to market faster.'

Fitting into the SimEnterprise strategy, by complementing its simulation-based design paradigm with abstract modelling for CFDFluidConnection, is

OpenCFD product. This combination not only extends SimEnterprise to be CFD compliant, but also provides a single-user interface covering a range of disciplines.

'We have successfully used FluidConnection for years to automate our development process and CFD simulations,' said Suffolk groundcare specialist

senior technician Jose Nazario. 'This integration will open a variety of multi-disciplinary solutions important to reliably predict our products' performance in different environments,' he added.

This best-in-class approach to CFD breaks the commonly-used disconnected one-off analyses and exploits the SimXpert and SimEnterprise investments in common data model, common user environment, knowledge capture and re-use, and multidisciplinary solutions.

Pioneer's FluidConnection is already proven in major automotive, commercial and heavy machinery applications and is recognised as 'best practice' by several industry leaders. It is now deliverable in SimEnterprise and will be available as a SimXpert workspace early next year.

It is unclear whether these trends will help to get the historically 'hard-to-use' CFD tools into the hands of more designers and engineers.

Sophisticated tools such as FluidConnection and Simulia multiphysics will still be the preserve of specialists for some time.

But CFD for the masses really begins and ends with such software as COSMOS FloWorks, and the many relatively low-cost CFD codes. And as more sophisticated, traditional vendors increase their user ability the landscape could change dramatically.

CFD has always been, and continues to be, a complex problem to work with and solve, but the use of FluidConnection shows a desire by the industry to offer a 'full-service' solution for a wider variety of users.