Recent publications
Fatally injured vulnerable road users, especially pedestrians who collided with motorised vehicles, account for 31% of all recorded fatalities in urban traffic in the EU. Autonomous vehicles will improve this situation in the future, reducing the impact of the human factor in critical traffic situations. The development of autonomous driving functions requires simulation environments to train certain behaviours. Consequently, these simulations need well represented vulnerable road users. In this paper, an approach for accurate prediction of pedestrian behaviour at street crossings is presented. The suggested solution involves an agent-based model working with A* pathfinding and risk-based areas, validated by a drone dataset on German road crossings.
The representation of material failure due to wave propagation is essential for the numerical analysis of engineering structures under high dynamic loading. Explicit time integration schemes are well established for this kind of application. In order to realistically model the failure of certain material classes, it is necessary to resolve lower scale features accurately. Concurrent multiscale approaches are therefore well suited to this task. However, they are often complex and computationally demanding. The introduction of interfaces between disparately meshed domains may additionally lead to emerging reflections for waves that contain high frequencies, which the coarse domain cannot resolve. In this article, we compare accuracy, computational efficiency, versatility, and effort for two finite element implementations of concurrent two‐scale schemes. Both offer the possibility of adding a Selected Perfectly Matched Layer (SPML) to dampen incompatible frequencies. One approach is the widely used conventional Lagrange multiplier (LM) approach; the second is a weak staggered (WS) coupling, which was designed to maintain direct solution schemes' efficiency with explicit time integration and diagonal mass matrices. It turns out that, for typical discretizations, the WS coupling achieves an accuracy comparable to the LM coupling but requires fewer computational operations and, relevant for parallel computer architectures, significantly less communication efforts. Adaptive changes of interface topology, for example, due to explicitly resolved cracks crossing the interface, can easily be represented in the WS approach, making it a suitable candidate for the application in scenarios where gross damage is expected.
This paper presents a semi-automated approach for assessing building vulnerability on an urban scale, specifically focusing on floods and heavy rainfall events. The method involves three steps: categorization of buildings using open geodata, development of parametric building models for each category, and probabilistic analysis to generate fragility curves. To overcome the challenge of analyzing individual buildings in a large area, generalized models based on building categories are utilized, reducing computational effort but introducing uncertainties. Probabilistic analyses are conducted by adjusting simulation parameters to address these uncertainties. The approach is applied to a reference area in Berlin as a case study. The results provide valuable insights into the vulnerability of individual buildings within different categories. This research contributes to the field of the vulnerability assessment of buildings by offering a practical and efficient method applicable at an urban scale. It enables informed decisionmaking and the development of risk reduction strategies.
The behavior of road or perimeter protection barriers under vehicle impact are usually investigated based on crash tests and finite element (FE) numerical approaches, which are ether expensive or time-consuming. Several studies have proposed to reduce the computation time of the numerical analysis by substituting the complex FE models of vehicles using simplified mass–spring–damper system models. However, these models have drawbacks since consideration of different vehicle impact angles is difficult and they are unable to correctly simulate the risk of high-speed vehicle collision running over the barrier. In this paper, a new approach is proposed to simulate the collision of vehicles with barriers based on the discrete element method (DEM). Here, to save computation time only a handful of 3D non-spherical particles are used to represent the barrier and vehicle. These particles are generated based on the super-quadric function, which is capable of generating a variety of shapes needed for the model. The contact detection and evaluation are carried out based on discrete function representation of the particles with uniform sampling. The bond between two discrete elements is defined using a nonlinear cohesive beam model since the distance between the elements is relatively large. The simulation results obtained based on this approach are more accurate and complete than the simplified mass–spring models and computationally more efficient than the FE model.
In an online survey, 154 decision-makers from the food industry were asked about resilience management, coping with disruptions, resilience characteristics, resilience dimensions and investment needs in their companies. This article analyses the survey, presents methods for assessing resilience and identifies potential for improvement. 84% of those surveyed responded that their companies had not yet implemented a resilience management system. Of the resilience dimensions, the impact of technology on ensuring the safety, quality and quantity of their products was rated highest, followed by finance. All respondents plan to invest in technology and digitalisation to increase resilience.
A clear procedure for determining the performance of vehicle security barriers (VSB) will aid event planners and security forces in selecting an appropriate type of VSB and placing it at a safe distance from the crowd. This paper presents a numerical analysis procedure for precisely determining the penetration distance of vehicles running over VSBs in various site conditions. Here, the finite element (FE) method is used in combination with stochastic analysis. The certification crash test results of the VSB are used to verify the FE model by comparing the vehicle’s maximum penetration distance, velocity-displacement curve, and motion sequence of the barrier and vehicle. This verification process ensures the accuracy of the FE model. A sensitivity analysis was conducted to model the impact of parameters such as vehicle impact speed and impact angle. The hazard area was then approximated using the moving least squares method (MLS) to show the vehicle’s penetration behind the VSB.
Zusammenfassung
Akustische Lokalisierung bietet die Möglichkeit, in Innenräumen relativ hohe Lokalisierungsgenauigkeiten von etwa 10 cm zu erreichen. Dies ist besonders vorteilhaft in Bereichen wie Krankenhäusern, wo funk-sensible Umgebungen den Einsatz herkömmlicher Technologien einschränken können. Der Einsatz von Mikrofonanordnungen (Arrays) zur Richtungsschätzung ermöglicht zudem die Reduzierung der Anzahl benötigter Ankerknoten. Dies führt zu einer erheblichen Senkung der Installations- und Betriebskosten. In dieser Arbeit wird ein solches System entworfen, das auf einem rechteckigen Array mit 64 Mikrofonen basiert. Für die beabsichtigte Schmalband-Richtungsschätzung mit mehreren Benutzern sind orthogonale Signale erforderlich. Deshalb werden in dieser Arbeit verschiedene Kandidaten orthogonaler Codes für diesen Einsatz untersucht. Zadoff-Chu-Sequenzen erweisen sich dabei als geeignete Wellenform. In einem Experiment wird die Machbarkeit des Konzepts anhand von drei Quellen demonstriert. Das 95% Konfidenzintervall um den Median der Richtungsabweichung beträgt 0,008 ∘. Die Ergebnisse dieser Arbeit bieten eine Grundlage und ermöglichen die Weiterentwicklung von speziell dünn besetzten Arrays, die die gleichzeitige Schätzung von mehr Quellen als Sensoren erlauben.
A rheological model is proposed that captures the performance loss and properties of a potential subsequent recovery of socio-technical systems subject to arbitrary disruptions. The model facilitates the quantitative assessment of such systems’ resilience. While most models known from the literature describe systems that fully recover from aforementioned load events, the proposed model can capture also permanent performance loss or post disruption improvement. To demonstrate the versatility of the approach for a wide range of the socio-technical system spectrum, the model is applied to three systems: the frequency stability of the continental Europe power grid, flight operations of German airports, and the revenue of the German gastronomic sector. Fitting the proposed two-spring, one-damper, single-degree-of-freedom model to the recorded performance data determines relevant parameters which serve as a quantitative measure of the respective system’s resilience. The small set of model parameters can be associated with relevant resilience dimensions. Variation of these parameters allows to quantitively determine the change of the model’s response to the load events, and thus of the resilience predicted by the model. This allows to identify parameter ranges in which the model predicts, e.g., full recovery of a system, instead of permanent performance loss.
The production industry is challenged to become more flexible and efficient while coping with a variety of disruptive events, such as natural disasters, infrastructure blockages, or economic crises. From the individual station on a production line to the global supply chain, everything is connected, making regulation and control a complex task. Biological molecular processes, such as the metabolism of living organisms or the cell cycle, are also extremely complex processes that can be compared to industrial production processes, both of which involve a series of intermediate steps and products. Thanks to (self‐)regulatory mechanisms that have evolved over time, these biological mechanisms are very efficient and robust in the face of perturbations. This article proposes an explanatory representation of these complex processes, considering both biological and technical aspects. The aim is to facilitate biomimetic transfer of biological regulation mechanisms into the technical domain. It presents concepts for biomimetic regulation of production lines and sourcing strategies and introduces a workflow for generating digital twins. This workflow is inspired by the cell cycle checkpoints, which ensure that only perfect copies of DNA are passed on during cell replication. By leveraging this understanding, the production industry can potentially improve its own processes and efficiency.
Automated and autonomous industrial inspection is a longstanding research field, driven by the necessity to enhance safety and efficiency within industrial settings. In addressing this need, we introduce an autonomously navigating robotic system designed for comprehensive plant inspection. This innovative system comprises a robotic platform equipped with a diverse array of sensors integrated to facilitate the detection of various process and infrastructure parameters. These sensors encompass optical (LiDAR, Stereo, UV/IR/RGB cameras), olfactory (electronic nose), and acoustic (microphone array) capabilities, enabling the identification of factors such as methane leaks, flow rates, and infrastructural anomalies. The proposed system underwent individual evaluation at a wastewater treatment site within a chemical plant, providing a practical and challenging environment for testing. The evaluation process encompassed key aspects such as object detection, 3D localization, and path planning, achieving an average precision of around 0.7662 in the 2D object detection. In addition, specific evaluations were conducted for optical methane leak detection and localization, demonstrating the system’s capability to detect leaks as small as 40 mL min
-1
. Furthermore, acoustic assessments focusing on pump equipment and gas leak localization yielded an absolute localization error of around 50 cm.
Fracture morphology characterization in broken glass panes is crucial for designing laminated safety glass (LSG) in civil engineering. Verifying completely broken LSG systems requires destructive sampling, increasing costs and hindering development. Therefore, to determine the residual load-bearing capacity, the link between the pre-fracture characteristics and the fracture morphology must be known. However, when the crack propagation needs to be directly captured with high-speed imaging, conventional methods are no longer sufficient for detecting cracks. To enable such investigations, we propose a novel machine learning framework for crack segmentation in high-speed imaging that addresses the complexity of glass fracture and minimises the required labour costs. In this study, the crack propagation of a sample was recorded and analysed at 2,000,000 images per second. The results showcase accuracies surpassing 97% while requiring only two labeled images for training, thus streamlining practical implementation. Furthermore, we show the method's robustness to the extent that hyperparameter tuning becomes unnecessary. Instead, we offer guidelines for selecting the most crucial hyperparameters depending on the problem. Our method offers a promising approach for non-linear temporal interpolation of noisy images, with implications for various applications extending beyond glass fracture analysis.
This contribution is intended to provide researchers with a comprehensive overview of the current state-of-the-art concerning real-time 3D reconstruction methods suitable for medical endoscopy. Over the past decade, there have been various technological advancements in computational power and an increased research effort in many computer vision fields such as autonomous driving, robotics, and unmanned aerial vehicles. Some of these advancements can also be adapted to the field of medical endoscopy while coping with challenges such as featureless surfaces, varying lighting conditions, and deformable structures. To provide a comprehensive overview, a logical division of monocular, binocular, trinocular, and multiocular methods is performed and also active and passive methods are distinguished. Within these categories, we consider both flexible and non-flexible endoscopes to cover the state-of-the-art as fully as possible. The relevant error metrics to compare the publications presented here are discussed, and the choice of when to choose a GPU rather than an FPGA for camera-based 3D reconstruction is debated. We elaborate on the good practice of using datasets and provide a direct comparison of the presented work. It is important to note that in addition to medical publications, publications evaluated on the KITTI and Middlebury datasets are also considered to include related methods that may be suited for medical 3D reconstruction.
The present work describes the characterization of two different granular materials, a fine cohesive and a coarse cohesionless
soil, with regard to their behavior under high-rate loading. The conditions range from quasi-static ( 105 s −1 ) to dynamic
strength ( 102 s −1 ) using a standard press and a Split-Hopkinson Bar (SHB) with a triaxial pressure cell. Furthermore, shock
compression ( 105 s −1 ) is investigated in a newly developed plate impact capsule. The experimental data is used to parameterize
both types of soils with two different dynamic material descriptions, a simple model with Drucker–Prager Strength and
p-α EOS and, partly extending from there, a model with piecewise linear dependencies for both volumetric compaction and
strength. The reproduction quality of both material models is quantitatively assessed using Finite Element simulations of the
dynamic tests and discussed. They can potentially serve in future numerical analyses of complex transient dynamic events,
such as explosively-driven ground shock or high-velocity penetration into the soil.
Introduction
Anterior cruciate ligament (ACL) reconstruction remains associated with the risk of re-rupture and persisting rotational instability. Additional extraarticular anterolateral stabilization procedures stabilize the tibial internal rotation and lead to lower ACL failure rate and improved knee stability. However, data for additional stabilization of tibial external rotation is lacking and the importance of an anteromedial stabilization procedure is less well evaluated. Aim of this study is to investigate the influence of an extraarticular anteromedial stabilization procedure for the stabilization of the tibial external rotation and protection of the ACL from these rotational forces.
Methods
Internal and external rotations of the tibia were applied to a finite element (FE) model with anatomical ACL, posterior cruciate ligament (PCL), lateral collateral ligament (LCL), medial collateral ligament (MCL) and intact medial and lateral meniscus. Five additional anatomic structures (Anteromedial stabilization/anteromedial ligament, AML, augmented superficial medial collateral ligament, sMCL, posterior oblique ligament, POL, anterolateral ligament, ALL, and popliteal tendon, PLT) were added to the FE model separately and then combined. The force histories within all structures were measured and determined for each case.
Results
The anteromedial stabilization or imaginary AML was the main secondary stabilizer of tibial external rotation (90% of overall ACL force reduction). The AML reduced the load on the ACL by 9% in tibial external rotation which could not be achieved by an augmented sMCL (-1%). The AML had no influence in tibial internal rotation (-1%). In the combined measurements with all additional structures (AML, ALL, PLT, POL) the load on the ACL was reduced by 10% in tibial external rotation.
Conclusion
This study showed that an additional anteromedial stabilization procedure secures the tibial external rotation and has the most protective effect on the ACL during these external rotational forces.
This paper presents an investigation into the design of ammonia tanks for long-duration and high-pressure blast loads. The focus is on cylindrical steel tanks that apply as outer pressure-tight containers for double-walled tanks storing refrigerated liquefied gases. Based on limited empirical data, it is known in the tank industry that these tanks can withstand an explosion pressure up to a peak overpressure of approximately 10 kPa and 100 ms positive load duration. However, there is a growing need to design tanks for higher peak overpressures in order to establish a higher safety standard and accommodate unforeseen future requirements. This paper explores the concept of adapting established steel tank designs to handle high-pressure and long-duration overpressure due to blast events. Numerical analysis is conducted on a representative steel tank geometry subjected to a triangular blast load of 30 kPa with a 300 ms positive load duration. Various load application and calculation options are analyzed numerically. Considering the challenging nature of analyzing tank structures under blast load, the paper addresses controversial aspects discussed in the literature and presents a suitable analysis concept for a deflagration blast scenario for cylindrical tanks. The results provide insights into the expected structural behavior of the tank under high-pressure and long-duration overpressure. The main finding is that the calculation method developed in this study demonstrates the feasibility of utilizing steel tanks in scenarios involving long-duration and high-pressure blast loads. Furthermore, the paper provides recommendations to guide future studies in this area. The findings have implications for the design and construction of tanks in critical infrastructure and offer valuable insights for engineers and researchers in this field, improving safety standards and ensuring adaptability to future utilization concepts.
The conception of ballistic personal protective equipment requires a comprehensive understanding of the human body’s response to dynamic loads. The objective of this study is to develop rib bone surrogates enhancing new anthropomorphic test devices for personal protective equipment evaluation at high dynamic impacts. These are fabricated with additive manufacturing and compared to post-mortem human subjects (PMHS) data from literature. The 5th rib of the finite element Global Human Body Model Consortium (GHBMC) male 50th percentile (M50) model was extracted and transferred to a CAD model. This CAD model was divided into 30 sections with specific cortical bone thicknesses in all directions (caudal, cranial, cutaneous and pleural) from an equivalent rib of an M50 PMHS. Three different additive manufacturing technologies (direct metal laser melting, fused filament fabrication and multi jet modeling) were used to reproduce the M50 PMHS 5th rib surrogate. A total of 57 specimens were dynamically (500 mm/s) loaded to failure in a bending scenario imitating a frontal thoracic impact. Force, displacement, stiffness, and energy at failure were determined. Also, the strain distribution using 3D digital image correlation was recorded and compared to PMHS data from literature. The rib surrogates show deviations from the PMHS characteristic values. Nevertheless, there are also common characteristics in key variables to certain age groups of the PMHS data, which will facilitate the further development and improvement of adequate surrogates for a more realistic representation of the human body’s response to high dynamic loads.
Nanoparticles are known to enable the modification of the properties of the material they are integrated into. In the context of ballistic protection, previous works have demonstrated that graphene and Montmorillonite (MMT) particles included in high‐density polyethylene (HD‐PE) and used as a matrix enable an increase in the ballistic performance, of consolidated woven aramid fabrics. Furthermore, the ballistic performance has been reported to be influenced by the in‐plane shear properties of the impacted materials. In this context, quasi‐static and high‐rate in‐plane shear tests have been conducted on two types of reinforcements, aramid, and carbon woven fabrics, consolidated by a high‐density polyethylene matrix enriched by graphene, MMT and a mix of graphene and MMT nanoparticles. The conducted investigations provide for the first time in the literature the results of high‐rate in‐plane shear tests on aramid woven reinforcement consolidated with nanoparticle‐enriched and not enriched high‐density polyethylene composites. Despite the use of the same reinforcement and enriched matrix material as in previous works of literature, no significant differences in terms of in‐plane shear behavior have been observed for any of the different types of nanoparticles integrated into the matrix. Nevertheless, the obtained results demonstrate a clear strain rate sensitivity of the tested materials.
Highlights
Aramid and carbon fabrics were consolidated with nanoparticle‐enriched HD‐PE
Quasi‐static and high‐rate in‐plane shear tests were conducted
No influence of the nanoparticles could be identified
A clear strain‐rate sensitivity could be identified for both composites
Very high cycle fatigue (VHCF) experiments are limited in practice due to their long testing times. In ultrasonic fatigue test (UFT) systems, the cyclic oscillation is applied using resonance at 20 kHz with a pulse and pause sequence. However, determining optimal pulse durations to achieve minimal testing time and avoid thermal-induced fatigue damage in fiber-reinforced polymer composites remains a challenge. In this work, several fatigue experiments, temperature analyses, and digital light optical microscopy were carried out to evaluate the influence of pulse duration on the fatigue behavior of a carbon-fiber fabric reinforced in polyether-ketone-ketone (CF-PEKK) composite. A shorter pulse duration with the same pulse-pause ratio as the longer pulse duration is proposed for higher stress amplitudes to avoid any thermal influence during mechanical fatigue without altering the underlying fatigue damage mechanisms. K E Y W O R D S 20 kHz, carbon-fiber-reinforced polymers, energy dissipation, pulse-pause ratio, self-heating effect, ultrasonic fatigue testing, very high cycle fatigue Highlights • The current pulse-pause ratio = 1:6 leads to effective test frequency of $3000 Hz. • Fatigue strength of the composite is independent of ultrasonic pulse duration. • Short pulse duration leads to mechanical fatigue across all cyclic amplitudes.
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Address
Freiburg, Germany
Head of institution
Prof. Dr.-Ing. habil. Stefan Hiermaier