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The missing link in engineering design

   
 
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Engineering design programs normally tackle only one problem at a time - a significant drawback when most real-world design problems involve juggling with many different factors such as cost, weight, strength and noise. OPTIM is a successful attempt to link several design programs and automate their operation, allowing design engineers to concentrate on the more creative parts of the design process.
OPTIM, a collaboration between two SMEs, two university departments and a large aerospace manufacturer, developed the world's first commercial concurrent optimisation system for engineering design. The partners estimate that they have a two-year lead in this technology and expect to be selling licences by early 1997.

Engineering design is a process of synthesis. An engineer planning a new road bridge, for example, must take into account a whole range of interrelated factors such as the bridge's deflection under different loads, its resistance to earthquakes, the building cost and the noise produced by traffic travelling across it. Unfortunately, juggling all these factors at once can be time-consuming and the engineer may not even be sure that the final design will meet all the constraints imposed on it.
The future of engineering design lies in optimisation, a computer technique that allows engineers to be confident that they have found the best possible solution to a particular aspect of the design. By optimising simultaneously for cost, weight, strength and all the other factors that are important to the final design, the engineer can make sure that nothing has been overlooked and that the finished product is indeed the best for the job.
The partners in OPTIM are world leaders in the difficult techniques of concurrent optimisation. They have developed a saleable product that has already created great interest in the aerospace industry and has a promising future in the design of cars, ships and offshore oil platforms.

Closing the loop

Computers can help with many design tasks, yet typical engineering design software takes a narrow, analytical approach that is a long way from the broad view that characterises the best human designers. A structural analysis program, for instance, can calculate the deflection of a bridge but takes no account of costs, road noise or other important factors. Even in its own area of expertise, the program is limited: it can calculate the deflection for a given bridge design, but it cannot design a bridge to match a given deflection.
So if the deflection turns out to be too great, the structural engineer has to adjust the design and run the analysis program again. After a process of trial and error a satisfactory structural design emerges - but by this time the bridge is heavier than originally planned, which upsets the calculations of the costing specialist in the next office. And so the process continues.
The lead partner in OPTIM is SIREHNA, a French company specialising in technology transfer between research and industrial applications in the area of fluid mechanics. SIREHNA recognised that there was an opportunity to use the latest optimisation technology to link all the different analysis programs used in a typical engineering design. Closing the loop by reducing the need for human input to the repetitive parts of the design process would leave engineers free to do what they do best: specifying the overall design envelope and coming up with truly innovative solutions.
The OPTIM project, which started in December 1992, brought together SIREHNA, aircraft manufacturer British Aerospace, Belgian structural analysis software supplier SAMTECH, and two universities. The aerospace laboratory at the University of Liège in Belgium specialises in optimisation of finite-element systems and was in charge of the algorithms for local optimisation. Eindhoven University of Technology in the Netherlands, which has good links with industry, looked after global optimisation.

If it isn't broken, don't fix it

Throughout the project the aim wherever possible was to allow engineers to continue working with their existing analysis software. The core optimisation program, a SAMTECH product known as BOSS/Quattro, does not attempt to take over the work of the analytical packages; instead it simply feeds them with the details of the design and waits for them to calculate their results. Depending on the answers, BOSS/Quattro then adjusts the design and sends the new details back to the analysis packages, a process it repeats until it is satisfied that it has the best design that meets all the engineers' constraints.
BOSS/Quattro communicates with the various analysis programs through a series of purpose-written translation programs or drivers. Because the drivers are small and easy to write, BOSS/Quattro can be adapted to work with almost any existing or future analysis program. The design programs themselves do not need to be altered in any way, so engineers can continue to work with tried and tested software, including programs they have developed themselves.
The algorithms used for the optimisation can be varied to suit the job in hand, or updated as mathematicians develop new optimisation techniques. A good example of this is simulated annealing, an optimisation technique based on stochastic (random) processes. At present, simulated annealing is not widely used with time-consuming analysis programmes because it needs large amounts of computing power, but for the future it promises to increase designers' confidence that they have indeed found a true global optimum.

Think globally, think locally

The optimisation process starts with the objective function and constraints, a mathematical statement of the various factors that are important in the design (strength, weight, cost and so on), and the importance and limits attached to each. Next, the program uses a technique known as sensitivity analysis to find out which of the parameters used to define the design is the most important. Finally comes the optimisation itself, which falls into two types: local and global.
Local optimisation tries to locate 'valleys' in a multi-dimensional plot of the objective function by finding the steepest slopes and following them downhill until it can go no further. Local optimisers are quick and efficient, but cannot be relied on to find the deepest valleys because they may become trapped at the bottom of other, smaller, valleys. Global optimisation is like flying over the terrain in a helicopter: it is easier to find the deepest valleys but the process is time-consuming and needs powerful computers.

First aircraft, then the world

The aerospace industry has been optimising individual design factors, such as the airflow over a wing, for around five years. Aircraft designers are now starting to look seriously at optimising several factors at once, so aerospace was a natural place to start the OPTIM project. By the time the project finished in November 1995, the partners had developed a new approach to the design of transonic aerofoils, optimising the wing shape for drag but also taking into account structural constraints in a way that was simply not possible with previous techniques.
The OPTIM system is also more flexible and cheaper than the previous in-house systems. Since the commercial launch of the system in June 1996 many aerospace companies have shown serious interest.
Naval architects have only recently begun to look at optimising the shapes of ships' hulls to minimise drag, so it will be several years before concurrent optimisation becomes widely used. Nevertheless, the partners expect to be selling the system within six months.
Interest from companies designing offshore structures has also been strong, and further into the future the software may find applications in the automotive industry, for instance in coupling aerodynamic design with acoustics to produce cars that are quieter as well as more fuel-efficient.

 

 

Project Title:  
A shape optimisation tool for multi-disciplinary industrial design

Programmes:
Industrial and Materials Technologies (BRITE-EURAM/CRAFT/SMT)

Contract Reference: BE-5083

Cordis DatabaseFor more information on this project,
go to the CORDIS Database Record

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