Recent Submissions
Speciesist bias in AI : a reply to Arandjelović
(2023) Hagendorff, Thilo; Bossert, Leonie; Fai, Tse Yip; Singer, Peter
The elimination of biases in artificial intelligence (AI) applications-for example biases based on race or gender-is a high priority in AI ethics. So far, however, efforts to eliminate bias have all been anthropocentric. Biases against nonhuman animals have not been considered, despite the influence AI systems can have on normalizing, increasing, or reducing the violence that is inflicted on animals, especially on farmed animals. Hence, in 2022, we published a paper in AI and Ethics in which we empirically investigated various examples of image recognition, word embedding, and language models, with the aim of testing whether they perpetuate speciesist biases. A critical response has appeared in AI and Ethics , accusing us of drawing upon theological arguments, having a naive anti-speciesist mindset, and making mistakes in our empirical analyses. We show that these claims are misleading.
Reproduction of transport-induced vibration of paintings based on a multi-channel FxLMS controller
(2023) Gao, Yulong; Ziegler, Pascal; Hartlieb, Eva; Heinemann, Carolin; Eberhard, Peter
Monitoring the vibration of the painting canvas during transport is of great significance to protect paintings from damage. However, limited to the narrow structure of the transport crate, the lack of an inertial reference, and the limitations to attach sensors to the canvas, this is a difficult task. For this reason, based on vibration data measured on the strainer that is easily obtained during transport, this contribution proposes to reproduce these with high accuracy in the laboratory. There, the resulting vibration of the canvas can be conveniently observed in a controlled environment with respect to an inertial reference. A real-time simulation platform based on the multi-channel Filtered- x Least Mean Square (FxLMS) algorithm controls four actuators simultaneously and reproduces the vibration of the strainer obtained from a real transport experiment. The vibration of the canvas is then measured by a laser Doppler vibrometer without contact. The experimental results show that the vibration reproduction system has sufficient reproduction accuracy for the vibration response. Even though some overshoot in the reproduced acceleration can be observed in some cases, the overall reproduction is very good. A long-term reproduction experiment verifies its stable reproducibility. Therefore, the designed vibration reproduction system provides a reference for the unknown canvas response during transport, and further helps art conservators to evaluate the transport process of the painting.
Wake tail plane interactions for a tandem wing configuration in high-speed stall conditions
(2023) Kleinert, Johannes; Ehrle, Maximilian; Waldmann, Andreas; Lutz, Thorsten
In this work, wake-tail plane interactions are investigated for a tandem wing configuration in buffet conditions, consisting of two untapered and unswept wing segments, using hybrid Reynolds-Averaged Navier–Stokes / Large Eddy Simulations (RANS/LES) with the Automated Zonal Detached Eddy Simulation (AZDES) method. The buffet on the front wing and the development of its turbulent wake are characterized, including a spectral analysis of the fluctuations in the wake and a modal analysis of the flow. The impact of the wake on the aerodynamics and loads of the rear wing is then studied, with a spectral analysis of its lift and surface pressure oscillations. Finally, the influence of the position and the incidence angle of the rear wing is investigated. For the considered flow conditions, 2D buffet is present on the front wing. During the downstream movement of the shock, the amount of separation reaches its minimum and small vortices are present in the wake. During the upstream movement of the shock, the amount of separation is at its maximum and large turbulent structures are present accompanied by high fluctuation levels. A distinct peak in the corresponding spectra can be associated with vortex shedding behind the wing. The impingement of the wake leads to a strong variation of the loading of the rear wing. A low-frequent oscillation of the lift, attributed to the change of the intensity of the downwash generated by the front segment, can be distinguished from high-frequent fluctuations that are caused by the impingement of the wake’s turbulent structures.
Service composition in the ChatGPT era
(2023) Aiello, Marco; Georgievski, Ilche
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.
Do RESTful API design rules have an impact on the understandability of Web APIs?
(2023) Bogner, Justus; Kotstein, Sebastian; Pfaff, Timo
Context. Web APIs are one of the most used ways to expose application functionality on the Web, and their understandability is important for efficiently using the provided resources. While many API design rules exist, empirical evidence for the effectiveness of most rules is lacking.
Objective. We therefore wanted to study 1) the impact of RESTful API design rules on understandability, 2) if rule violations are also perceived as more difficult to understand, and 3) if demographic attributes like REST-related experience have an influence on this.
Method. We conducted a controlled Web-based experiment with 105 participants, from both industry and academia and with different levels of experience. Based on a hybrid between a crossover and a between-subjects design, we studied 12 design rules using API snippets in two complementary versions: one that adhered to a rule and one that was a violation of this rule. Participants answered comprehension questions and rated the perceived difficulty.
Results. For 11 of the 12 rules, we found that violation performed significantly worse than rule for the comprehension tasks. Regarding the subjective ratings, we found significant differences for 9 of the 12 rules, meaning that most violations were subjectively rated as more difficult to understand. Demographics played no role in the comprehension performance for violation .
Conclusions. Our results provide first empirical evidence for the importance of following design rules to improve the understandability of Web APIs, which is important for researchers, practitioners, and educators.
Visual analysis of interface deformation in multiphase flow
(2023) Straub, Alexander; Karch, Grzegorz K.; Steigerwald, Jonas; Sadlo, Filip; Weigand, Bernhard; Ertl, Thomas
In multiphase flows, the evolution of fluid-fluid interfaces is of interest in many applications. In addition to fluid dynamic forces governing the flow in the entire volume, surface tension determines droplet interfaces. Here, the analysis of interface kinematics can help in the investigation of interface deformation and the identification of potential breakups. To this end, we developed a visualization technique using metric and shape tensors to analyze interface stretching and bending. For interface stretching, we employ the eigenpairs of the metric tensor defined for the deformation rate of the fluid surface. For interface bending, we present a technique that locally captures the interface curvature change in terms of a shape tensor, extracting its principal directions and curvatures. We then visualize interface deformation by combining both representations into a novel glyph design. We apply our method to study multiphase flow simulations with particular emphasis on interface effects. These include the interplay between fluid dynamics and surface tension forces leading to breakup processes following droplet collisions, as well as droplet-droplet interactions of different fluids where Marangoni convection along the surface is explicitly taken into account.
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.
An efficient hp-adaptive strategy for a level-set ghost-fluid method
(2023) Mossier, Pascal; Appel, Daniel; Beck, Andrea D.; Munz, Claus-Dieter
We present an hp-adaptive discretization for a sharp interface model with a level-set ghost-fluid method to simulate compressible multiphase flows. The scheme applies an efficient p-adaptive discontinuous Galerkin (DG) operator in regions of smooth flow. Shocks and the phase interface are captured by a Finite Volume (FV) scheme on a h-refined element-local sub-grid. The resulting hp-adaptive scheme thus combines both the high order accuracy of the DG method and the robustness of the FV scheme by using p-adaptation in smooth areas and h-refinement at discontinuities, respectively. For the level-set based interface tracking, a similar hybrid DG/FV operator is employed. Both p-refinement and FV shock and interface capturing are performed at runtime and controlled by an indicator, which is based on the modal decay of the solution polynomials. In parallel simulations, the hp-adaptive discretization together with the costly interface tracking algorithm cause a significant imbalance in the processor workloads. To ensure parallel efficiency, we propose a dynamic load balancing scheme that determines the workload distribution by element-local wall time measurements and redistributes elements along a space filling curve. The parallelization strategy is supported by strong scaling tests using up to 8192 cores. The framework is applied to established benchmarks problems for inviscid, compressible multiphase flows. The results demonstrate that the hybrid adaptive discretization can efficiently and accurately handle complex multiphase flow problems involving pronounced interface deformations and merging interface contours.
Electrical impedance imaging technology for needle guidance during medical needle insertion procedures
(2024) Liu, Jan; Pott, Peter P. (Prof. Dr. rer. nat. habil.)
Although performed on a daily basis, medical needle insertion procedures are often associated with complications due to incorrect needle positioning. The most common needle insertion procedure is venipuncture for blood collection. In a study of 4,050 patients, bruising and hematoma occurred in 12.3 % of cases. These are the result of only partial penetration of the blood vessel or complete perforation (needle overshoot).
Needle insertion is usually performed manually, highly dependent on the clinician's skill and the patient's physiology. Existing needle guidance methods are either cumbersome and inadequate for routine procedures, or prone to error. This dissertation aims to explore a new imaging technology based on electrical impedance measurements as an alternative to current guidance systems. It is hypothesized that the integration of multiple localized impedance measurements on a needle enables successful tissue identification and spatial localization. This information can be exploited to develop a 3D imaging system that can be used for needle guidance during medical needle insertion procedures.
In this dissertation, the hypothesis is investigated through the exploration of three aspects. The first aspect involves impedance-based tissue identification using medical needles. A bipolar, multi-local (bipolar), and monopolar approach were established and tested. In the bipolar approach, two concentrically placed needles were used as part of a measurement system. Successful tissue identification based on conductivity values was achieved for fat, skin, and blood phantoms. The multi-local approach involved the modification of a hypodermic needle with 12 stainless steel wire electrodes. A system was established to sequentially switch the active measurement electrodes on the needle. The measured impedance values were assigned to the corresponding tissue types using a k-nearest neighbors classification algorithm. Additionally, the monopolar approach was tested in the context of epidural anesthesia. A setup comprising a Tuohy needle and an ECG electrode successfully discriminated between fat and sodium chloride solution, which was used as a substitute for cerebrospinal fluid.
The second aspect deals with the simulative assessment of needle-based impedance measurements. The above configurations were translated into CAD models and integrated into an FEM environment. The FEM simulations were performed to generate impedance data as a potential basis for a classification task. Also, the current density distribution was investigated to define a region of relevant spatial measurement sensitivity. The so-called sensitive volumes could be successfully integrated into the third aspect, which is the development of the needle guidance system.
For the needle guidance system, a graphical user interface was implemented to serve as the user's control and visualization interface. The user interface can be used to control hardware components responsible for switching electrode pairs and measuring impedance. The visualization environment displays the needle during insertion and shows the surrounding tissue types corresponding to the shape of the sensitive volumes. Eventually, the developed system was evaluated for needle guidance effectiveness. An initial study comparing ultrasound guidance with impedance-based guidance was performed with three subjects. Despite the small sample size, the study found that impedance-based needle guidance was preferred due to its intuitiveness and handling, and the efficacy was highly dependent on the classification success rate.