Development of a validated numerical simulation model for the prevention of flow noise in prostheses

This project is in cooperation with Otto Bock Healthcare Products and is funded by the Austrian Research Promotion Agency (FFG).

Human joints, in particular the human knee, are a masterpiece of evolution, providing a functional, self-healing, low-noise, and damage-tolerant transmission of power into motion. In our daily lives, we rely on our joints with a reassuring naturalness. Unfortunately, accidents occur, rarely but often unexpectedly, resulting in severe limb injuries and requiring amputation as a last resort for survival. For example, 57,637 amputations were recorded in Germany in 2014. In such difficult life situations, technical aids such as prostheses (from Otto Bock Healthcare GmbH, among others) improve life quality. Otto Bock Healthcare Products GmbH advances medical technology in the prosthetics and orthotics business segment. Its main products include the mechatronic knee prostheses C-LEG4, Genium/Genium X3, and Kenevo. These knee prostheses use a controlled hydraulic damping system to support and secure natural walking. Mechatronic prostheses are considered state-of-the-art remedies after amputations and allow people with impairments to regain a certain degree of mobility and comfort in life. Otto Bock is a market leader in high-tech knee prostheses and minimizes the impairment resulting from such accidents.

Modern knee prostheses must meet a wide range of requirements to provide the user with the best possible support in everyday life. The application profile of users requires functionality, while little noise is emitted. Under certain circumstances, however, considerable noise can be generated, which is perceived as a stress factor by the wearer and is perceived as unpleasant by the surrounding people. Health authorities impose limits for approval to minimize this annoying stress factor. Customer satisfaction even drives the company to suffice stricter limits. Therefore, modern knee prostheses meet a wide range of requirements to provide the user with the best possible support in everyday life. In addition to the functional and mechanical properties, the emitted sound level also makes a significant contribution to wearing comfort.

Based on the extensive expertise of the research group Vibroacosutics and Aeroacoustics of the Institute for Fundamentals and Theory of Electrical Engineering in flow acoustics, we have the following research idea: Vision is a flow-vibroacoustic simulation methodology for the identification, systemic analysis, and avoidance of acoustic source hotspots, which will support the development of lower-noise prototypes in the future. Based on this development, it should be possible in the future to optimize the product design concerning acoustics as early as possible, even before expensive and time-consuming prototypes are manufactured. The goal is to find a validated simulation methodology that allows a robust prediction of the noise emissions with minimal computational effort.

The core idea is to develop a computer-aided simulation methodology that, once integrated at Otto Bock (follow-up project), can be used proactively and at an early stage in product development to avoid noise sources (acoustic hotspots). In detail, acoustic hotspots are understood as cavitation zones, turbulence noise, and the acoustic transfer path via the structure (frame, hydraulics, etc.) to the ear/microphone. Based on highly accurate and computationally intensive simulation models, a time-efficient acoustic simulation method is developed. This time-efficient acoustic simulation method will be validated with measurements on the GENIUM series, allowing the findings to be applied to the flow acoustic and vibroacoustic optimization of the design subsequently. The acoustic measurement setup aims to minimize the background noise of the drive units (which are required for the joint movement) on the one hand and to ensure appropriate reproducibility on the other.