Cornelius Strackeljan
Dr.-Ing. Cornelius Strackeljan
Mehrkörperdynamik (IWTM)
Current projects
Simulating the implantation process of endoprostheses to determine mechanical load in the bones during operation
Duration: 01.01.2022 to 30.06.2025
Modern, shoulder arthroplasties with stemless implants (figure a) help to preserve larger parts of the original bone substance and to reduce potential risks of conventional implants. Their shape allows newly formed bone structures to grow directly through the implant. However, it is not fully explained how an optimal fixation of the implant can be achieved or stimulated.
In this context, the project aims to simulate the mechanical loading in the humerus during the operation using the finite element method. The results are used to investigate whether one or more mechanical parameter, e.g. stresses or elastic/plastic strains, can be correlated with measurement data of cell activity in the bone, which is available in the form of SPECT/CT data.
The derived workflow consists of the following steps:
- Derive the relevant bone geometries as well as the exact location of the implant from SPECT/CT data (figure b) .
- Transform the geometries as well as the measurement data to a reference position for the simulation.
- Generate a finite element model from the data (3D point cloud and corresponding intensity from the CT measurement (figure a) .
- Conduct FEM-Simulation with suitable material models and material data (figure d) .
- Evaluation of the simulation results and correlation with measured cell activity in vicintiy of the implant.
Completed projects
Thermo-hydrodynamic bearing models with increased accuracy
Duration: 01.07.2023 to 31.03.2024
This project builds on two previous publicly founded projects, which focused on detailed models for hyrodynamic bearings to calculate the complex dynamic behaviour of rotors, which are supported by hydrodynamic bearings. In this context, it is essential to simulate the non-linear behaviour of the bearings as accurately as possible. This non-linear bearing behaviour is characterised by non-linear stiffness and damping properties, cavitation processes and a non-linear dependence of the lubricant viscosity on the operating temperature. This modelling is done by transient solving the differential equations, which describe the lubricating film: the Reynolds PDE and the energy equation.
Three aspects are analysed in more detail in the current project:
- Precise calculation of the fluid flow in gap height direction. The velocity of this flow is usually very small because of the small gap heights (order of magnitude: <100 µm), but it can still have a big impact on heat transfer mechanisms in the lubricating film. This is especially true for thrust bearings at high rotational speeds and loads (figure 1). Because there is more heat transfer in gap height direction, more heat is carried over the segment, which means an increased temperature niveau in the lubricating film
- Investigation of the centrifugal term in the Reynolds PDE for thrust bearings, which is often not implemented completely, but only up to the order h³. At high rotational speeds, this can also lead to inaccuracies. In the analysed load cases, the inertial influence is overestimated by up to 15% due to the simplified implementation.
- Investigation of suitable temperature boundary conditions at the segment inlet of hydrodynamic bearings.
Dynamics of exhaust gas turbocharger rotors with coupled radial and axial bearings
Duration: 01.10.2019 to 31.03.2022
The aim of the research project is to improve the existing calculation methodology for high-speed exhaust gas turbochargers (ATL) with hydrodynamic bearings. While the previous project focused on radial bearings in the form of floating bush bearings (shown in blue), the current project addresses the modeling of axial bearings (shown in red; simple and floating disk bearings). The influences of the thrust bearings on the rotor dynamics as a result of their non-linear tilting rigidity and the coupling of the thrust bearings to the radial bearings are to be investigated. This also includes practically relevant counter-rotation excitations, e.g. due to engine vibrations.
The movement of the shaft results in dynamic misalignment of the track disk and, if applicable, the floating disk. The resulting small gaps lead to high shear stresses and thus to a significant heat input into the system. At the same time, there are interactions between the temperatures and the hydrodynamic properties (thermal expansion, viscosity), which is why the transient temperature development of the bearing partners and the oil must be modeled. In addition, radial and axial bearings are connected to each other via the oil supply lines, the influence of which must be recorded thermodynamically and hydrodynamically.
The individual aspects are mapped in a holistic simulation model, which includes rotor, hydrodynamics and thermodynamics, and the underlying differential equations are solved numerically within the framework of time integration, whereby the results of the previous project are consistently developed further.
Ultimately, the reliable simulation of subharmonic vibrations in frequency and amplitude should be made possible, as these cause safety-relevant issues (rubbing processes) as well as having drastic effects on the power loss and service life of the bearings
This text was translated with DeepL