Universität Stuttgart

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Institute: search.filters.UBSInstitut.Institut für Technische und Numerische MechanikSubject: search.filters.subject.600

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    Role of rotated head postures on volunteer kinematics and muscle activity in braking scenarios performed on a driving simulator
    (2022) Kempter, Fabian; Lantella, Lorena; Stutzig, Norman; Fehr, Jörg; Siebert, Tobias
    Occupants exposed to low or moderate crash events can already suffer from whiplash-associated disorders leading to severe and long-lasting symptoms. However, the underlying injury mechanisms and the role of muscle activity are not fully clear. Potential increases in injury risk of non-nominal postures, i.e., rotated head, cannot be evaluated in detail due to the lack of experimental data. Examining changes in neck muscle activity to hold and stabilize the head in a rotated position during pre-crash scenarios might provide a deeper understanding of muscle reflex contributions and injury mechanisms. In this study, the influence of two different head postures (nominal vs. rotation of the head by about 63 ± 9° to the right) on neck muscle activity and head kinematics was investigated in simulated braking experiments inside a driving simulator. The braking scenario was implemented by visualization of the virtual scene using head-mounted displays and a combined translational-rotational platform motion. Kinematics of seventeen healthy subjects was tracked using 3D motion capturing. Surface electromyography were used to quantify muscle activity of left and right sternocleidomastoideus (SCM) and trapezius (TRP) muscles. The results show clear evidence that rotated head postures affect the static as well as the dynamic behavior of muscle activity during the virtual braking event. With head turned to the right, the contralateral left muscles yielded higher base activation and delayed muscle onset times. In contrast, right muscles had much lower activations and showed no relevant changes in muscle activation between nominal and rotated head position. The observed delayed muscle onset times and increased asymmetrical muscle activation patterns in the rotated head position are assumed to affect injury mechanisms. This could explain the prevalence of rotated head postures during a crash reported by patients suffering from WAD. The results can be used for validating the active behavior of human body models in braking simulations with nominal and rotated head postures, and to gain a deeper understanding of neck injury mechanisms.
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    Ride Comfort Transfer Function for the MAGLEV Vehicle Transrapid
    (2018) Zheng, Qinghua; Dignath, Florian; Eberhard, Peter; Schmid, Patrick
    In order to predict the ride comfort for the MAGLEV vehicle Transrapid TR09 for various scenarios, e.g. for higher vehicle speeds than hitherto travelled, a transfer function from the excitations given by the guideway position to the relevant car body acceleration is calculated by two different methods. Method A is based on a mechatronic simulation model of the Transrapid TR09 which describes a two- dimensional lateral cross section of the vehicle. The simulation model consists of a 2D multibody system describing the mechanical part, four network models of the electro-magnets - two levitation magnets and two guidance magnets - and a signal model of each magnet controller. These signal models contain a representation of the authentic C-Code of the control law used within the actual magnet control units within the vehicle TR09. The overall model can be exploited to calculate the accelerations of the car body for given excitations at the interfaces between guideway and vehicle. Moreover, it is possible to generate a model-based transfer function in the frequency domain from the guideway excitations to the car body accelerations. For method B, measurement results of test runs of the Transrapid TR09 at the test track TVE in Northern Germany are exploited which were recorded for vehicle dynamics analysis and ride comfort evaluation in 2009. From these measurement results two characteristic quantities are generated for several different velocities of the vehicle: Firstly, the position of the guideway is reconstructed by using an integration of the absolute accelerations of the magnets and the signals of the magnet's sensors for the air gap. Secondly, the relation between the accelerations at the car body of the vehicle and the guideway position is calculated as a transfer function in the frequency domain. For this, the measurement data and the reconstructed guideway position are both transformed into the frequency domain by a Fast Fourier Transformation (FFT). The resulting transfer function gives the relevant accelerations for the ride comfort for given excitations of the vehicle as calculated by Method A above. The two transfer functions from Method A and B are compared for validation. Then, a smoothed version of the validated transfer function is applied for estimating the ride comfort for travelling scenarios which have not yet been measured in practical operation, e.g. for higher velocities of the vehicle.
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    Dynamic simulation and control of optical systems
    (2018) Störkle, Johannes; Eberhard, Peter (Prof. Dr.-Ing. Prof. E.h.)
    This thesis deals with the simulation-based investigation and control of optical systems that are mechanically influenced. Here, the focus is on the dynamic-optical modeling of vibration-sensitive mirror systems, which are utilized, e.g., in large astronomy telescopes or high-precision lithography optics. The large-area primary mirrors of telescopes typically consist of many individual hexagonal mirror segments, which are positioned with precise sensors and actuators. Furthermore, an adaptive optical unit usually compensates for the optical aberrations due to atmospheric disturbances. In practice, these aberrations are detected, and corrected, within a few seconds using deformable mirrors. However, to further improve the performance of these optical systems, dynamical disturbances in the mechanics, i.e., small movements and deformations of the optical surfaces, must also be taken into account. Therefore, multidisciplinary simulation methods are developed and presented. Based on this, the dynamical-optical system behavior is modeled using model-order-reduced, flexible multibody systems. Hence, the dynamical analysis of the mechanical-optical system can be performed at low computation costs. Thanks to the optical analysis in the time domain and using Fourier-optical concepts, one can also simulate exposure processes. To actively compensate for aberrations due to mechanical vibrations, model-based control strategies are also designed. They are not only demonstrated by means of simulation examples, but also illustrated through a laboratory experiment. The latter is realized with a low-cost test setup for student training using Arduino microcontrollers, position and force sensors, as well as high-speed cameras.
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    Combining knowledge and information - graph-based description of driving scenarios to enable holistic vehicle safety
    (2023) Bechler, Florian; Fehr, Jörg; Neininger, Fabian; Knöß, Stefan; Grotz, Bernhard
    Currently, vehicle safety is based on knowledge from injury values, crash pulses, and driving kinematics which leads to intervention strategies separated into isolated domains of active and passive safety. In this contribution, it is shown how vehicle safety can be approached holistically, allowing for human-centered and scenario-based safety decision-making. For this purpose, information from interior and exterior vehicle sensors can be linked by a mathematical framework, combining the knowledge that is already available in the individual domains. A universal graph representation for driving scenarios is developed to master the complexity of driving scenarios and allow for an optimized and scenario-based intervention strategy to minimize occupant injury values. This novel approach allows for the inclusion of sub-models, expert knowledge, results from previous simulations, and annotated databases. The resulting graph can be expanded dynamically for other objects or occupants to reflect all available information to be considered in case of urgency. As input, interior and exterior vehicle sensor data is used. Further information about the driving situation is subsequently derived from this input and the interaction between those states is described by the graph dynamically. For example, occupant attentiveness is derived from measurable eye gaze and eyelid position. From this quantity, reaction time can be estimated in turn. Combined with exterior information, it is possible to decide on the intervention strategy like e.g. alerting the driver. Physical or data-based functional dependencies can be used to represent such interactions. The uncertainties of the inputs and from the surrogate models are included in the graph to ensure a reliable decision-making process. An example of the decision-making process, by modeling the states and actuators as partially observable Markov decision process (POMDP), shows how to optimize the airbag efficiency by influencing the head position prior to an impact. This approach can be extended by additional parameters like driving environment, occupant occupancy, and seating positions in further iterations to optimize the intervention strategy for occupants. The proposed framework integrates scenario-based driving dynamics and existing knowledge from so far separated safety systems with individual activation logic and trigger points to enable holistic vehicle safety intervention strategies for the first time. It lays the foundation to consider new safety hardware, sensor information, and safety functions through a modular, and holistic approach.
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