Walking on air
Clarks is one of the major footwear brands of the world and prides itself on a commitment to individual design, comfort, quality and service. To achieve this, the company employs a large footwear development team. Occasionally, the need arises to seek technology input from outside, which is where the Special Projects Division becomes involved. They have a remit to evaluate innovative concepts and seek ways to turn them into workable shoe designs. A recent challenge was to investigate ways of simulating the airflow of Clark’s Active Air range, with a view to improving the design.
Clarks developed Active Air over 20 years ago to provide superior underfoot comfort in men’s shoes. It consists of a network of air channels and chambers in the sole, which allow air to circulate at every step, absorb shock impact as the heel strikes the ground and deliver energy return at the end of every step. This is fundamentally different from the later Nike system, which encapsulates pressurised air within a plastic container underneath the heel. The channels in the Clarks system allow air to wash backwards and forwards beneath the foot, which not only absorbs shock but allows the foot to breath.
In many modern footwear designs, the toe area is almost entirely isolated from the air circulating in the rest of the shoe and there is little chance of that air escaping. The Clarks system provides a mechanism by which damp air sitting forward of the toes can be exchanged with outside air. The aim is to maximise the benefit of the channels in the sole and look at changes to shoe uppers to increase transfer of air between the channels and the outside of the shoe. Simulating the complex flow of air in the sole was a challenge. Clarks had already used computational fluid dynamics (CFD) for injection moulding projects, to simulate gas flow, mould fill, air trapping and colour mixing. In this instance instead of buying in software, CFD consultant CD Adapco Group was hired, as although CFD software is becoming easier to use, there are still specific skills a consultant can bring to bear.
Creating an accurate model of the Active Air shoe involved collecting data on how it would deform as the wearer rolled across it. A well tried Clarks device called a Pedar, was used to take 50 measurements per second of pressures beneath the foot and create a live pressure map. This data was given to the consultants, who applied it to the model in their STAR-CD package, to see how it would deform and how the gas would move around the shoe. The resulting simulations were clear enough for the designers to make changes on screen, rather than construct expensive and time consuming and prototypes. This speeded up the design process, reduced time to market and proved cost effective, as only one CFD package was used throughout the design process. Shoes designed in this way should be in the shops for Spring/Summer 2003.
