Practical Example: COSMOS Software at Dräger

However, producing an actual prototype for each method costs a lot of time and money. For this reason, Dräger Medical in Lübeck uses the COSMOSWorks and COSMOSFloWorks software packages for the analysis to support its design process. Completely integrated into the SolidWorks 3D CAD system, they provide versatile and fast simulation calculations for virtual prototypes. The world’s leading manufacturer of anaesthesia and intensive medical equipment, Dräger Medical has high demands in terms of the quality of its products. When all said and done, the Lübeck company’s breathing apparatus saves lives. Their convenient anaesthesia stations allow doctors to devote their full attention to the patient (Figure 1). To ensure that the equipment always reflects the most recent advances in breathing therapy and features state of the art operating concepts, Dräger’s designers frequently modify its form and functions. The development time for new equipment is currently around four years, but the board has stipulated that this should be halved to two years in the near future. Figure 1: Dräger Medical has high demands for the quality of its products, in this case the Primus anaesthesia station. Picture: Dräger Medical As a result, time is a crucial factor in the work of Karsten Hoffmann and Uwe Schmid. The two engineers are responsible for the design and development of intensive medical systems and anaesthesia equipment, for which they use SolidWorks, COSMOSWorks and COSMOSFloWorks. Integrated Calculation Brings Significant Time Savings A crucial experience during his work on a new breathing system version led Karsten Hoffmann to recognise the full value of COSMOSWorks. The breathing system on anaesthesia equipment supplies the patient to be anaesthetised with oxygen and the anaesthetic gas. It also absorbs the exhaled carbon dioxide using breathing lime and feeds the circulating gas enriched with oxygen back to the patient. Cost and quality reasons meant that the breathing system was to be produced from plastic rather than aluminium. The new breathing system would consist of the breathing gas block, a valve plate and a cover (Figure 3). The silicon edge seal that sealed the gas ducts from one another was able to compensate for deformation of 0.3 mm. However, with the new plastic material and toggle fasteners, which pressed the cover against the seal, there was a risk that the cover would be bent by more than this amount, meaning that the tightness of the system would no longer be guaranteed. An exact FEM calculation of this bending by an external company provided definite results. However, the problem was that the calculation, including redesign over several iterations, took three months, cost 40,000 DM and resulted in a new solution that placed the fastener at a different position. In the next project, Hoffmann and his team performed the same calculation with COSMOSWorks, which did not involve any redesign. It took them just two afternoons. Karsten Hoffmann explains the benefits: “COSMOSWorks allows us to calculate and compare various possible solutions quickly and without complications during our design process. The alternatives would be to either outsource these calculations or to produce actual prototypes to perform exact measurements. Both of these options are expensive and time consuming. As a result, for many of our possible solutions we would have done without this step and simply relied on our experience.” Another example demonstrates COSMOSWorks’s capabilities in the area of temperature analysis. The patient’s moist breath can condense on the walls of the breathing system. This can mean that the doctor can no longer see the valves or it can impair the function. To prevent this condensation, the designers need to heat the breathing system. The previous version featured a heating contact plate attached on the outside, but on the new unit this did not enable the required temperature of 40 degrees to be reached at the opposite end of the valve plate. Higher heating plate temperatures would have infringed legal regulations stating that plastic parts that can be touched may not be warmer than 70 degrees. This meant that the old solution was totally unacceptable. Hoffmann and his team developed several alternative solutions that increased the thickness of the valve plate, incorporated more material into the design as a heat bridge and included a copper valve plate rather than aluminium. COSMOSWorks proved very advantageous in this testing phase. Producing a prototype for each idea would have been extremely laborious and time-consuming. By contrast, the software performed calculations for each solution and showed that the required contact plate temperature was too high in each case. The final solution was an unconventional idea, in which the heater, rather than being attached externally, was integrated into the valve plate as a heating surface (Figure 2). Figure 2: In the final solution, the heating surface was integrated into the valve plate. Picture: Dräger Medical Digital Thumb Simplifies Decisions ”When we are looking for improvements, it is not a case of exactly calculating results to the nth decimal place. It is all about using the ‘digital thumb’ to identify which of two possible solutions is the better and is the right way for us to go. To do this, we don’t need special expert systems, integrated tools like COSMOSWorks are more than good enough”, stresses Karsten Hoffmann. The Lübeck company also uses the COSMOSFloWorks flow analysis application. Karsten Hoffmann considers it to be of great value as even an experienced designer can make mistakes when it comes to fluid mechanics. “We once calculated how the 45-degree nozzles demanded by the market would change the characteristics of a gas flow compared to straight nozzles. COSMOSFloWorks showed that this tended to cause the gas to flow along the wall of the pipe rather than in the centre of the duct, where the hot wires for the gas flow measurement were attached”, he explained. This falsified the measured results and indicated that the patient was not being fed sufficient gas. Appropriate resistance bodies were incorporated to divert the gas flow back to the centre of the duct behind the angled nozzle. “I would have bet my house on the fact that the pressure drop of only 0.2 mbar for 60 litres with a circular resistance body that COSMOSFloWorks had calculated could not be right. I had expected 2 mbar, but a prototype proved that the software had been right.” Dräger also uses the software to perform flow simulations for two-phase models. For example, in intensive medicine, patients are supplied with air at an increased oxygen concentration, which can lie between 30 and 100 percent. Measurements using the software showed the designers that, with a particular structural mixing chamber design, air and oxygen did not mix but tended to flow to the outlet next to one another (Figure 4). As the aperture for the concentration measurement was right in the boundary layer, this resulted in significant fluctuations in the measured values. Deflection ribs were therefore required in the mixing chamber, and their effects could be calculated and visualised very accurately in COSMOSFloWorks. Figure 4: The software showed that air and oxygen flowed to the outlet alongside each other. Picture: Dräger Medical Finally, Uwe Schmid, an expert in fluid dynamics at Dräger, uses the analysis application for heat transfer, including clarification of the extent to which gas flows heat up the surrounding separating walls. “Unfortunately, COSMOSFloWorks does not yet provide calculations for phase transitions such as evaporation and condensation, but I certainly use the system for all other analytical tasks”, a satisfied Schmid reports. Basic Knowledge Required, Not Expert Knowledge The critical advantage of COSMOSWorks and COSMOSFloWorks lies in their integration into SolidWorks. This allows designers to perform relatively complicated FEM calculations and flow simulations quickly, without the need to change systems or workstations. The time saved allows them to run through more unconventional alternative solutions. The integration solution also avoids any problems with interfaces and corrupt data reading. Finally, separate expert systems, such as conventional CFD (Computational Fluid Dynamics) solutions would require much more sophisticated operation and orientation. Figure 5: Uwe Schmid (l) and Karsten Hoffmann are responsible for the design and development of intensive medical systems and anaesthesia equipment. Picture: Dräger Medical In sharp contrast, COSMOSFloWorks enables engineers to calculate flows without needing to be CFD experts themselves. Nevertheless, the easy operation does not totally replace the need for basic knowledge of fluid mechanics. Uwe Schmid advises: “Designers should always make sure their own model is actually suitable for calculation in a particular application.” He generally recommends evaluating applications using similar issues with known examples and experiments and then verifying the plausibility of the results obtained. Overall, both COSMOS applications were easy for users to learn. Only two or three users had to attend a full training session. All of the others either learned it by self-study or by seeking help from their colleagues. Around fifteen users current use the COSMOS applications. Uwe Schmid considers one particularly useful feature to be the Wizard, which allows the user to make interactive entries. It removes the need for inconvenient searching for material values and simplifies the entry of general conditions. “I always use the Wizard to generate my first model and this is often enough”, says Uwe Schmid. Taking more of an overall view, quick and easy analysis using integrated applications ultimately increases designers’ creativity. Ideas and innovations are more likely to end up in products if their suitability can easily be verified. The use of COSMOSWorks and COSMOSFloWorks not only saves time and costs for producing numerous prototypes, it also makes a significant contribution to the quality of Dräger Medical’s life-preserving equipment.