Browsing by Author "Fehr, Jörg"

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Open Access
Accident simulations of a novel restraint safety concept for motorcyclists
(2023) Maier, Steffen; Fehr, Jörg
Open Access
Application of data-driven surrogate models for active human model response prediction and restraint system optimization
(2023) Hay, Julian; Schories, Lars; Bayerschen, Eric; Wimmer, Peter; Zehbe, Oliver; Kirschbichler, Stefan; Fehr, Jörg
Surrogate models are a must-have in a scenario-based safety simulation framework to design optimally integrated safety systems for new mobility solutions. The objective of this study is the development of surrogate models for active human model responses under consideration of multiple sampling strategies. A Gaussian process regression is chosen for predicting injury values based on the collision scenario, the occupant's seating position after a pre-crash movement and selected restraint system parameters. The trained models are validated and assessed for each sampling method and the best-performing surrogate model is selected for restraint system parameter optimization.
Open Access
Cervical muscle reflexes during lateral accelerations
(2023) Millard, Matthew; Hunger, Susanne; Broß, Lisa; Fehr, Jörg; Holzapfel, Christian; Stutzig, Norman; Siebert, Tobias
Autonomous vehicles will allow a variety of seating orientations that may change the risk of neck injury during an accident. Having a rotated head at the time of a rear-end collision in a conventional vehicle is associated with a higher risk of acute and chronic whiplash. The change in posture affects both the movement of the head and the response of the muscles. We are studying the reflexes of the muscles of the neck so that we can validate the responses of digital human body models that are used in crash simulations. The neck movements and muscle activity of 21 participants (11 female) were recorded at the Stuttgart FKFS mechanical driving simulator. During the maneuver we recorded the acceleration of the seat and electromyographic (EMG) signals from the sternocleidomastoid (STR) muscles using a Biopac MP 160 system (USA). As intuition would suggest, the reflexes of the muscles of the neck are sensitive to posture and the direction of the acceleration.
Open Access
Characterisation of an energy absorbing foam for motorcycle rider protection in LS-DYNA
(2021) Maier, Steffen; Helbig, Martin; Hertneck, Holger; Fehr, Jörg
Open Access
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.
Open Access
Correlations of seat pressure distribution and perception of (dis)comfort in autonomous driving to parametrize digital human models
(2024) Reinhard, René; Harant, Monika; Emmerich, Sebastian; Obentheuer, Marius; Fahse, Niklas; Fehr, Jörg; Kleer, Michael; Linn, Joachim
While the driving position in a human-operated car restricts the driver’s body to a certain functional position, dictated by the requirements of observing the surrounding while having all the necessary controls in reach, for highly automated vehicles (SAE level 3 and up), these restrictions are lowered. This new freedom allows to perform non-driving-related tasks along with new seating positions including resting. The current driving simu lator study explores possible correlations between the subjective perception of (dis)comfort and the bodies’ mo tion, tracked by seat pressure mats and motion tracking sensors. The participants were confronted with evasive maneuvers with notable accelerations in lateral direction and yaw angle, while being seated in three different conditions in the driver’s seat inside the driving simulator RODOS®: (1) an alert condition, with their hands on the steering wheel, (2) a hands-free condition, where the seat was still in upright position, but the attention was not necessarily on the road, and (3), a reclined position, lying back in a reclined seat. This work identifies a correlation between the seat pressure distribution and the subjective (dis)comfort and shows its independence to the seating condition.
Open Access
Development and verification of a physiologically motivated internal controller for the open-source extended Hill-type muscle model in LS-DYNA
(2023) Martynenko, Oleksandr V.; Kempter, Fabian; Kleinbach, Christian; Nölle, Lennart V.; Lerge, Patrick; Schmitt, Syn; Fehr, Jörg
Nowadays, active human body models are becoming essential tools for the development of integrated occupant safety systems. However, their broad application in industry and research is limited due to the complexity of incorporated muscle controllers, the long simulation runtime, and the non-regular use of physiological motor control approaches. The purpose of this study is to address the challenges in all indicated directions by implementing a muscle controller with several physiologically inspired control strategies into an open-source extended Hill-type muscle model formulated as LS-DYNA user-defined umat41 subroutine written in the Fortran programming language. This results in increased usability, runtime performance and physiological accuracy compared to the standard muscle material existing in LS-DYNA. The proposed controller code is verified with extensive experimental data that include findings for arm muscles, the cervical spine region, and the whole body. Selected verification experiments cover three different muscle activation situations: (1) passive state, (2) open-loop and closed-loop muscle activation, and (3) reflexive behaviour. Two whole body finite element models, the 50th percentile female VIVA OpenHBM and the 50th percentile male THUMS v5, are used for simulations, complemented by the simplified arm model extracted from the 50th percentile male THUMS v3. The obtained results are evaluated additionally with the CORrelation and Analysis methodology and the mean squared error method, showing good to excellent biofidelity and sufficient agreement with the experimental data. It was shown additionally how the integrated controller allows simplified mimicking of the movements for similar musculoskeletal models using the parameters transfer method. Furthermore, the Hill-type muscle model presented in this paper shows better kinematic behaviour even in the passive case compared to the existing one in LS-DYNA due to its improved damping and elastic properties. These findings provide a solid evidence base motivating the application of the enhanced muscle material with the internal controller in future studies with Active Human Body Models under different loading conditions.
Open Access
Documenting research software in engineering science
(2022) Hermann, Sibylle; Fehr, Jörg
The reuse of research software needs good documentation, however, the documentation in particular is often criticized. Especially in non-IT specific disciplines, the lack of documentation is attributed to the lack of training, the lack of time or missing rewards. This article addresses the hypothesis that scientists do document but do not know exactly what they need to document, why, and for whom. In order to evaluate the actual documentation practice of research software, we examined existing recommendations, and we evaluated their implementation in everyday practice using a concrete example from the engineering sciences and compared the findings with best practice examples. To get a broad overview of what documentation of research software entailed, we defined categories and used them to conduct the research. Our results show that the big picture of what documentation of research software means is missing. Recommendations do not consider the important role of researchers, who write research software, whose documentation takes mainly place in their research articles. Moreover, we show that research software always has a history that influences the documentation.
Open Access
Efficient simulation strategy to design a safer motorcycle
(2023) Maier, Steffen; Fehr, Jörg
This work presents models and simulations of a numerical strategy for a time and cost-efficient virtual product development of a novel passive safety restraint concept for motorcycles. It combines multiple individual development tasks in an aggregated procedure. The strategy consists of three successive virtual development stages with a continuously increasing level of detail and expected fidelity in multibody and finite element simulation environments. The results show what is possible with an entirely virtual concept study - based on the clever combination of multibody dynamics and nonlinear finite elements - that investigates the structural behavior and impact dynamics of the powered two-wheeler with the safety systems and the rider’s response. The simulations show a guided and controlled trajectory and deceleration of the motorcycle rider, resulting in fewer critical biomechanical loads on the rider compared to an impact with a conventional motorcycle. The numerical research strategy outlines a novel procedure in virtual motorcycle accident research with different levels of computational effort and model complexity aimed at a step-by-step validation of individual components in the future.
Open Access
Effiziente Modellierung flexibler Robotersysteme zur Echtzeitsimulation am Beispiel eines Leichtbauroboters
(2025) Hoschek, Sebastian; Rodegast, Philipp; Gesell, Jakob; Scheid, Jonas; Fehr, Jörg
Die Echtzeitsimulation mechanischer Systeme und deren digitale Zwillinge gewinnen in der Industrie zunehmend an Bedeutung. Sie ermöglichen unter anderem die Optimierung von Steuerungsalgorithmen, die Vorhersage des Systemverhaltens und die Implementierung von Regelstrategien in der Automatisierungstechnik. Ein Industriepartner entwickelt derzeit einen mobilen Leichtbauroboter für den Einsatz im Logistikbereich, bei dem die hohe Flexibilität der Struktur zu elastischen Durchbiegungen führt. Um die Genauigkeit und Leistungsfähigkeit des Roboters zu verbessern, ist eine präzise Modellierung dieser elastischen Effekte erforderlich. In dieser Arbeit werden zwei verschiedene Modellierungsansätze für die Echtzeitsimulation untersucht. Der erste basiert auf einer physikalischen White-Box-Modellierung als flexibles Mehrkörpersystem, wobei ein klassisches Finite-Elemente-Modell (FEM) durch Modellordnungsreduktion vereinfacht wird, um eine effiziente Berechnung zu ermöglichen. Der zweite Ansatz verwendet ein Finite-Segmente-Modell, das eine Parameteridentifikation erfordert, um eine realitätsgetreue Abbildung des Systemverhaltens zu gewährleisten. Beide Methoden werden auf den Leichtbauroboter angewendet und hinsichtlich ihrer Vor- und Nachteile verglichen. Wesentliche Kriterien sind dabei der Modellierungsaufwand, die Berechnungsgeschwindigkeit und die Genauigkeit der Simulationsergebnisse. Die Ergebnisse liefern eine Entscheidungsgrundlage zur Auswahl geeigneter Modellierungsmethoden in Echtzeitanwendungen.
Open Access
EMMA4Drive - Digital human twins for evaluating ergonomics and safety in new mobility solutions
(2022) Linn, Joachim; Fehr, Jörg
Open Access
EMMA4Drive : a digital human model for occupant simulation in dynamic driving maneuvers
(2023) Obentheuer, Marius; Fahse, Niklas; Harant, Monika; Kleer, Michael; Kempter, Fabian; Reinhard, René; Roller, Michael; Björkenstam, Staffan; Fehr, Jörg; Linn, Joachim
About two-thirds of all German workers currently commute to their workplace by car without being able to engage in any meaningful activity. In the future, occupants of autonomous driving vehicles will be able to perform new activities, such as regeneration exercises, working, or consuming entertainment media [1]. This leads to many new challenges in assessing the layout of vehicle interiors, both in terms of comfort and vehicle safety. The goal of the EMMA4Drive project is to further develop the muscle-activated multi-body human model EMMA (Ergo-dynamic Moving Manikin) for use in next-generation partially or fully autonomous driving vehicles. The resulting software prototype EMMA4Drive will be able to analyze and evaluate safety and ergonomics equally during driving maneuvers under dynamic loads as a digital image of the occupant. In the automotive industry, digital human models (DHM) are widely used to simulate the human driver in the early stages of product development. Furthermore, detailed finite element (FE) models of the human body are used to simulate the highly dynamic impact and resulting injuries in the human body in crash simulations [2]. Moreover, DHM based on multibody system (MBS) kinematics are widely applied in reachability investigations and (posture- based) ergonomic assessment of the driver [3]. However, to predict active movement in dynamic driving maneuvers such as cornering, sudden braking, or lane change and pre-crash scenarios, neither FE nor simple MBS kinematic models are applicable. For a more detailed overview on DHMs in this application case, we refer to [4]. In this work, we will present an approach for the enhancement of a multibody based DHM to generate human like motions for a highly dynamic driving simulation. For motion prediction, an optimal control problem (OCP) is set up and solved. A model order reduction (MOR) approach is used to transfer driver seat interaction from detailed FE simulations to the Optimal Control (OC) framework. We use our RODOS driving simulator [5] to validate simulation results (e.g., motions, seat pressure distribution) and to identify OC parameter configurations for motion prediction.
Open Access
Evaluation of a novel passive safety concept for motorcycles with combined multi-body and finite element simulations
(2020) Maier, Steffen; Doléac, Laurent; Hertneck, Holger; Stahlschmidt, Sebastian; Fehr, Jörg
Open Access
Finite element simulations of motorcyclist interaction with a novel passive safety concept for motorcycles
(2021) Maier, Steffen; Doléac, Laurent; Hertneck, Holger; Stahlschmidt, Sebastian; Fehr, Jörg
Open Access
Implementation and validation of the extended Hill-type muscle model with robust routing capabilities in LS-DYNA for active human body models
(2017) Kleinbach, Christian; Martynenko, Oleksandr; Promies, Janik; Häufle, Daniel F. B.; Fehr, Jörg; Schmitt, Syn
In the state of the art finite element AHBMs for car crash analysis in the LS-DYNA software material named *MAT_MUSCLE (*MAT_156) is used for active muscles modeling. It has three elements in parallel configuration, which has several major drawbacks: restraint approximation of the physical reality, complicated parameterization and absence of the integrated activation dynamics. This study presents implementation of the extended four element Hill-type muscle model with serial damping and eccentric force-velocity relation including Ca2+ dependent activation dynamics and internal method for physiological muscle routing.
Open Access
Improved a posteriori error bounds for reduced port-Hamiltonian systems
(2024) Rettberg, Johannes; Wittwar, Dominik; Buchfink, Patrick; Herkert, Robin; Fehr, Jörg; Haasdonk, Bernard
Projection-based model order reduction of dynamical systems usually introduces an error between the high-fidelity model and its counterpart of lower dimension. This unknown error can be bounded by residual-based methods, which are typically known to be highly pessimistic in the sense of largely overestimating the true error. This work applies two improved error bounding techniques, namely (a) a hierarchical error bound and (b) an error bound based on an auxiliary linear problem , to the case of port-Hamiltonian systems. The approaches rely on a secondary approximation of (a) the dynamical system and (b) the error system. In this paper, these methods are adapted to port-Hamiltonian systems. The mathematical relationship between the two methods is discussed both theoretically and numerically. The effectiveness of the described methods is demonstrated using a challenging three-dimensional port-Hamiltonian model of a classical guitar with fluid–structure interaction.
Open Access
An improved development process of production plants using digital twins with extended dynamic behaviour in virtual commissioning and control : Simulation@Operations
(2023) Pfeifer, Denis; Scheid, Jonas; Kneifl, Jonas; Fehr, Jörg
The challenges in automation system development are driven by short development cycles and individualization along with resource‐constraints. State of the art solutions do not provide the necessary digital tools to apply model‐based methods in automation engineering to achieve higher performing systems. To overcome these issues this paper presents a novel approach to address some of the current challenges in automation systems development using digital twins with extended dynamic behaviour. The study underscores how dynamic models can be imported through standardised interfaces into virtual commissioning (VC) tools, improving the development process by effectively utilising domain‐specific expertise. The paper highlights how these digital twins enhance not only the VC process but can also be applied to model‐based control methods. Initial experiments showcase the utility of digital twins in calculating dynamic acceleration limits during trajectory planning of CNC control and enhancing feed‐forward control. Further, the importance of parameter identification in achieving accurate system models is stressed. The initial results are promising, and future work aims to combine these methods in an industrial application involving a newly developed, individual lightweight robot, demonstrating the potential for enhanced design, accelerated development, and resource efficiency in automation systems.
Open Access
Improving the accuracy of musculotendon models for the simulation of active lengthening
(2023) Millard, Matthew; Kempter, Fabian; Stutzig, Norman; Siebert, Tobias; Fehr, Jörg
Vehicle accidents can cause neck injuries which are costly for individuals and society. Safety systems could be designed to reduce the risk of neck injury if it were possible to accurately simulate the tissue-level injuries that later lead to chronic pain. During a crash, reflexes cause the muscles of the neck to be actively lengthened. Although the muscles of the neck are often only mildly injured, the forces developed by the neck’s musculature affect the tissues that are more severely injured. In this work, we compare the forces developed by MAT_156, LS-DYNA’s Hill-type model, and the newly proposed VEXAT muscle model during active lengthening. The results show that Hill-type muscle models underestimate forces developed during active lengthening, while the VEXAT model can more faithfully reproduce experimental measurements.
Open Access
Low-dimensional data-based surrogate model of a continuum-mechanical musculoskeletal system based on non-intrusive model order reduction
(2023) Kneifl, Jonas; Rosin, David; Avci, Okan; Röhrle, Oliver; Fehr, Jörg
Over the last decades, computer modeling has evolved from a supporting tool for engineering prototype design to an ubiquitous instrument in non-traditional fields such as medical rehabilitation. This area comes with unique challenges, e.g. the complex modeling of soft tissue or the analysis of musculoskeletal systems. Conventional modeling approaches like the finite element (FE) method are computationally costly when dealing with such models, limiting their usability for real-time simulation or deployment on low-end hardware, if the model at hand cannot be simplified without losing its expressiveness. Non-traditional approaches such as surrogate modeling using data-driven model order reduction are used to make complex high-fidelity models more widely available regardless. They often involve a dimensionality reduction step, in which the high-dimensional system state is transformed onto a low-dimensional subspace or manifold, and a regression approach to capture the reduced system behavior. While most publications focus on one dimensionality reduction, such as principal component analysis (PCA) (linear) or autoencoder (nonlinear), we consider and compare PCA, kernel PCA, autoencoders, as well as variational autoencoders for the approximation of a continuum-mechanical system. In detail, we demonstrate the benefits of the surrogate modeling approach on a complex musculoskeletal system of a human upper-arm with severe nonlinearities and physiological geometry. We consider both, the model’s deformation and the internal stress as the two main quantities of interest in a FE context. By doing so we are able to create computationally low-cost surrogate models which capture the system behavior with high approximation quality and fast evaluations.
Open Access
Modeling, simulation, and vision-/MPC-based control of a PowerCube serial robot
(2020) Fehr, Jörg; Schmid, Patrick; Schneider, Georg; Eberhard, Peter
A model predictive control (MPC) scheme for a Schunk PowerCube robot is derived in a structured step-by-step procedure. Neweul-M² provides the necessary nonlinear model in symbolical and numerical form. To handle the heavy online computational burden concerning the derived nonlinear model, a linear time-varying MPC scheme is developed based on linearizing the nonlinear system concerning the desired trajectory and the a priori known corresponding feed-forward controller. Camera-based systems allow sensing of the robot on the one hand and monitoring the environments on the other hand. Therefore, a vision-based MPC is realized to show the effects of vision-based control feedback on control performance. A semi-automatic trajectory planning is used to perform two meaningful experimental studies in which the advantages and restrictions of the proposed (vision-based) linear time-varying MPC scheme are pointed out. Everything is implemented on a slim, low-cost control system with a standard laptop PC.