‘Unstoppable shifts’ solve hardest problems

Developments at the leading edge are helping design engineers. Tom Shelley reports.

Computer aided design of 3D geometry is considered to be more or less a solved problem and major advances are being made in the simulation of the real world performance of virtual products, including composites. On the other hand, data management and ensuring knowledge of all relevant information by the right people remains a nightmare, but progress is being made.

This was the strong message that came out of this year's Dassault UK PLM forum. Philippe Forestier, one of the original founders of Dassault Systèmes spoke of the "Unstoppable shifts" caused by urbanisation and the need to better manage resources and world food supplies and improve global health.

He argued that there is a growing gap between companies that are making full use of information technologies to advance their businesses in the face of these pressures, and those that do not, advancing the embracers at the expense of the others. On the CAD front, Forestier said that Dassault is "Still spending tons of money" to make the tools more user-friendly.

The company continues to talk about "Lifelike" experiences and as an example, he showed a walk through up an open staircase on the outside of an oil platform, to access some crucial control cabin. We pointed out to Alain Floutier, that to be truly lifelike it should not just simulate of going up the stairs on a nice sunny day above a calm sea, but should be able to reproduce what it might be like to attempt to perform the task in the teeth of a gale above stormy seas.

In the light of such considerations, the design team might then decide to reposition the staircase within the main elements of the structure in order that it could be used safely under such circumstances. He responded that the simulation could be made much more realistic, but would require, "More time and effort", which is why his company is spending money to try to make the process of generating simulations easier.

While geometry and visual appearance may be solved problems, designing component parts with optimum properties requires taking their manufacturing method into account. This is especially true of parts made of composite. John Cox from Dassault Systèmes observed that in such cases, "By the time you have designed the part, you have designed the manufacturing process."

One of the first companies to realise this was Rolls-Royce, and we were given just some idea of how complicated this process can be by Darren James, design technology leader for making aero engine fan blades. He described something of the process of designing carbon fibre reinforced organic matrix fan blades with titanium edges for what he described as a new "Trent 500" sized engine.

The titanium edges are to improve damage tolerance against bird strike, but the bulk of the blades are carbon fibre because of all the advantages this material gives in terms of reduced weight and out of balance forces, and improved vibration and fatigue resistance and imperviousness to corrosion. The shape is somewhat complex, with double curves and changes in thickness to give optimum performance properties in the engine.

In order to do this, it has to be made of "Quite a few hundred" plies, each of which is of a slightly different size and shape to the one beneath it, and each of which has to be specified in terms of material, direction, rosette and position in the stacking sequence. The design process makes use of Catia V5 and Abaqus and SCO3, bespoke code developed by Rolls Royce, in order to undertake the finite element analysis.

These latter codes enable static analysis either 'smeared', looking at bulk properties or ply by ply. In addition, LS-Dyna is used to undertake impact modelling. The team is currently evaluating Catia V6 because, according to James, "It improves collaborative working." Finite element analysis capabilities for analysing aircraft type composite structures and computational fluid dynamics continue to be improved, according to Alain Prior of Dassault Systèmes.

Problems were encountered during the development of both the Boeing 787 and the Airbus A380, and Prior observed that both companies, "Have realised since that it would have been better to do the advanced analysis up front", instead of subsequent to the failures of physical tests. He said that, "A lot of progress has been made with regard to non-linear behaviour, damage behaviour and the detection of damage.

Physical test results are getting very close to the results of computer modelling and increasingly, modelling is being accepted as design validation, as long as modelling methods have been validated by physical experiment.

On the data management front, Forestier made it clear that Dassault is still pushing its secure social networking software 3D Swym as an aid to collaboration and knowledge sharing, but when we asked how many companies had implemented it, Forestier told us that it was still only in serious use by the 9,000 users within Dassault Systèmes, but many other companies were "Interested" including non traditional Dassault Systèmes customers such as in insurance.

Furthermore, the company was hoping to sell it for use by, "Communities within the European Union." The problem of providing easy access to complex bodies of information is, however, being tackled in a different manner by the Systems Engineering Innovation Centre SEIC), which is a collaboration between Loughborough University and BAE Systems.

Steve Hinsley of BAE Systems, seconded to SEIC, explained how he is concerned with not just the mockup model of products but the whole lifecycle management process, now identified as CADMID, standing for, Concept, Analysis, Demonstration, Manufacture, In-Service and Disposal. If a project is governed by large numbers of documents, regardless of whether these are paper or electronic, this leads, according to Hinsley, to an overall "implicit" project lifecycle model which only exists as a whole in people's minds.

Unfortunately, everyone will then have a different version of this model which leads to confusion. There therefore needs to be an "Explicit" model to which everyone has access. One of the areas of problem and confusion is the need to refer to standards, which often run to thousands of pages and are not totally understood by anyone.

Darren Clowes, an engineering doctorate student at the SEIC has been tasked with taking the Technical Datalink 16 standard (MIL STC 6016C), which in its D version is more than 8,800 pages long, and transform it into something on a computer that users can access and discover what they need to know. Ignorance of the details within standards is no excuse for things going wrong, especially if lawyers get involved, and failure to follow them exactly can cost companies a great deal of money.

Clowes said that this particular standard is available either as a hard copy document, with "Lots of inconsistencies", such as cross references that lead to dead ends, or a PDF version which at first sight, appears to have blue hyperlinks, but which in fact only uses the colour blue to highlight certain facts. A project started to put this into computer form in 2005, which Clowes joined in 2007.

The data has been entered using the Eclipse Modelling Framework, which is open source, and allows the construction of a web based format which outputs in natural language. Tools started to be rolled out to customers in 2009. When we asked if the same approach could be applied to other vast and difficult to penetrate sets of documentary regulations, such as the Machinery Directive or the 22 volumes of regulations and procedures used by London Underground, Clowes responded positively.

Design Pointers
• Modelling using 3D geometric CAD is largely considered to be a solved problem, although there is still much work required to make it quicker and easier to use
• In composite component design, design for manufacture is an integral part of the design process
• Tools for simulating the performance of composites are much improved, and, validated by experiment, they are increasingly being accepted as proof of the integrity of a design
• Managing data, particularly where it concerns access and comprehension of complex standards, regulations and requirements remains a problem, but progress is being made

Author
Tom Shelley

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