| 1. |
- Leledakis, Alexandros, 1991, et al.
(författare)
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A method for predicting crash configurations using counterfactual simulations and real-world data
- 2021
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Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575. ; 150
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Tidskriftsartikel (refereegranskat)abstract
- Traffic safety technologies revolve around two principle ideas; crash avoidance and injury mitigation for inevitable crashes. The development of relevant vehicle injury mitigating technologies should consider the interaction of those two technologies, ensuring that the inevitable crashes can be adequately managed by the occupant and vulnerable road user (VRU) protection systems. A step towards that is the accurate description of the expected crashes remaining when crash-avoiding technologies are available in vehicles. With the overall objective of facilitating the assessment of future traffic safety, this study develops a method for predicting crash configurations when introducing crash-avoiding countermeasures. The predicted crash configurations are one important factor for prioritizing the evaluation and development of future occupant and VRU protection systems. By using real-world traffic accident data to form the baseline and performing counterfactual model-in-the-loop (MIL) pre-crash simulations, the change in traffic situations (vehicle crashes) provided by vehicles with crash-avoiding technologies can be predicted. The method is built on a novel crash configuration definition, which supports further analysis of the in-crash phase. By clustering and grouping the remaining crashes, a limited number of crash configurations can be identified, still representing and covering the real-world variation. The developed method was applied using Swedish national- and in-depth accident data related to urban intersections and highway driving, and a conceptual Autonomous Emergency Braking system (AEB) computational model. Based on national crash data analysis, the conflict situations Same-Direction rear-end frontal (SD-ref) representing 53 % of highway vehicle-to-vehicle (v2v) crashes, and Straight Crossing Path (SCP) with 21 % of urban v2v intersection crashes were selected for this study. Pre-crash baselines, for SD-ref (n = 1010) and SCP (n = 4814), were prepared based on in-depth accident data and variations of these. Pre-crash simulations identified the crashes not avoided by the conceptual AEB, and the clustering of these revealed 5 and 52 representative crash configurations for the highway SD-ref and urban intersection SCP conflict situations, respectively, to be used in future crashworthiness studies. The results demonstrated a feasible way of identifying, in a predictive way, relevant crash configurations for in-crash testing of injury prevention capabilities.
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| 2. |
- Leledakis, Alexandros, 1991
(författare)
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Heterogeneity in Car Occupant Safety
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis ultimately aims to enhance occupant protection by incorporating aspects of real-world crash heterogeneity, often overlooked within current safety assessments. By investigating the effects of crash heterogeneity and broadening the comprehensiveness of occupant safety assessments, it seeks to support the development of more effective future vehicle safety systems. Specifically, the thesis focused on developing and applying methods to incorporate a range of heterogeneity aspects—from crash characteristics to occupant posture, anthropometry, and seat adjustments—into vehicle safety assessments. To predict how crash avoidance systems might change the configurations of the remaining crashes, a method using counterfactual simulations was developed. The use of a novel crash configuration definition, along with a purpose-designed clustering method, reduced the number of predicted crash configurations—while being able to maintain coverage of diverse real-world situations. Three crash configurations were selected to be used in the following studies. Non-nominal sitting postures, body sizes, and seat adjustments can influence the occupant’s response during a crash. These aspects were investigated in simulation studies employing numerical Human Body Models (HBMs) and tailor-made analysis methods. The methods focused on quantifying the influence of these aspects (including interaction effects) on the occupant’s response during a crash. Additionally, techniques were developed to streamline the setup and analysis of numerical experiments using HBMs. The application of the methods indicated that autonomous emergency braking systems tend to move the crash locations towards the vehicle’s corners. Additionally, further studies showed that the occupants’ posture, anthropometry, and seat adjustments influenced their kinematic and kinetic crash response. Variations in lower extremity postures had the greatest effect on whole-body response across all tested crash scenarios. For example, in frontal collisions, sitting cross-legged increased pelvic movement, while seat adjustments altered load distributions between the pelvis and the lower extremities. Moreover, occupant characteristics could also induce differences: greater BMI or stature correlated with larger lower extremity loading in frontal impacts. In side impacts, occupants were more sensitive to lateral movement when leaning forward. Furthermore, the influence of individualising the shoulder belt placement on the occupant-to-belt interaction, without changing any other belt parameter, was investigated. The findings revealed that while improved initial belt placement over the shoulder is important, it alone does not guarantee improved seat belt interaction. This approach, by investigating seat belt interaction challenges for occupants with varying characteristics, paves the way for analysing further modifications in belt characteristics towards tailored occupant restraint systems. By incorporating aspects not typically included in current safety assessments, this thesis demonstrates the potential to further enhance assessment for future vehicle safety systems, accommodating a broader range of real-world situations.
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| 3. |
- Leledakis, Alexandros, 1991, et al.
(författare)
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Influence of an Individualised Shoulder Belt Position for Diverse Occupant Anthropometries on Seatbelt Interaction in Frontal and Side Impacts
- 2023
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Ingår i: Conference proceedings International Research Council on the Biomechanics of Injury, IRCOBI. - 2235-3151. ; , s. 639-664
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Konferensbidrag (refereegranskat)abstract
- This simulation study investigated the influence of individualised shoulder belt position on seatbelt interaction and occupant kinematics in two frontal and one far side impact, considering the variability of occupant anthropometry and sitting postures. Morphed Human Body Models, positioned as front passengers, were simulated in 132 setups. For every occupant, an individualised shoulder belt position configuration was created by changing the D-ring mounting location, aiming for a mid-shoulder belt fit. A “traditional belt” configuration was also tested, with the D-ring mounted on the B-pillar. The initial belt's placement over the occupant's shoulder was influential; however, it may not necessarily lead to an overall improved seatbelt interaction as a single parameter. Different occupants were associated with different seatbelt interaction challenges. Tall occupants with low Body Mass Index (BMI) were more likely to slide out of the shoulder belt, while short low-BMI occupants were more likely to submarine. The early torso to pelvis retention balance and the torso’s axial rotations were identified as the main mechanisms behind those observations. The study identified seatbelt interaction challenges for different occupant groups and could facilitate the analysis of additional changes in belt characteristics towards individualised occupant restraint systems.
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| 4. |
- Leledakis, Alexandros, 1991
(författare)
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Pre-Crash and In-Crash Car Occupant Safety Assessment
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tens of millions are annually injured in Road Traffic Accidents (RTAs) worldwide, while the estimated number of RTA fatalities amounted to 1.35 million in 2016. In Europe, car occupants hold the largest share (48%) of fatalities among all road users. The high fatality and injury numbers motivate the work of enhancing road traffic safety. A holistic safety assessment approach, considering both the pre- and the in-crash phase of a crash, has the potential to enhance real-world occupant protection evaluation, as well as facilitate the development of effective countermeasures. In standardized car occupant safety assessments, occupant surrogates of standardized anthropometries are employed in standardized postures, with the seat adjusted to a single predefined position. The vehicle is then subjected to predefined crash configurations with meticulously described impact points and angles. In contrast, real-world traffic crashes involve occupants of different shapes and sizes, who adjust the position of the seat and their posture on the seat differently, and the vehicles are subjected to diverse crash configurations (multiple impact locations, impact directions, and speed combinations). The overall aim of this thesis is to develop and apply methods, spanning from the pre-crash to the in-crash phase, capable of evaluating and enhancing the real-world occupant protection of future vehicles. The introduction of crash-avoidance systems has the potential to alter the crash configurations that future vehicles will be exposed to. A method for predicting crash configurations has been developed in this thesis and applied to highway driving, and urban intersection crashes. Performing counterfactual simulations of digitized real-world crashes, with and without the addition of a conceptual Automatic Emergency Braking system, provides a prediction of the remaining crashes. The use of a novel crash configuration definition, along with a purpose-designed clustering method, facilitates the reduction of the number of predicted crash configurations without sacrificing coverage of the diverse real-world situations. Three predicted crash configurations, representative of urban intersection crashes, were further analyzed during the in-crash phase. A Human Body Model was positioned in a wide range of occupant postures identified from the literature. The findings suggest that the lower extremity postures had the largest overall influence on the lower extremities, pelvis, and whole-body responses for all crash configurations. In the evaluated side-impacts, leaning the torso in the coronal plane affected the torso and head kinematics by changing the interaction with the vehicle’s interior. Additionally, in far-side impacts supporting the occupant’s arm on the center console resulted in increased torso excursions. Moreover, the upper extremity responses were consistently sensitive to posture variations of all body regions.
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| 5. |
- Leledakis, Alexandros, 1991, et al.
(författare)
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The influence of car passengers’ sitting postures in intersection crashes
- 2021
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Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575. ; 157
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Tidskriftsartikel (refereegranskat)abstract
- Car passengers are frequently sitting in non-nominal postures and are able to perform a wide range of activities since they are not limited by tasks related to vehicle control, contrary to drivers. The anticipated introduction of Autonomous Driven vehicles could allow “drivers” to adopt similar postures and being involved in the same activities as passengers, allowing them a similar set of non-nominal postures. Therefore, the need to investigate the effects of non-nominal occupant sitting postures during relevant car crash events is becoming increasingly important. This study aims to investigate the effect of different postures of passengers in the front seat of a car on kinematic and kinetic responses during intersection crashes. A Human Body Model (HBM) was positioned in a numerical model of the front passenger seat of a midsize Sports Utility Vehicle (SUV) in a total of 35 postures, including variations to the lower and upper extremities, torso, and head postures. Three crash configurations, representative of predicted urban intersection crashes, were assessed in a simulation study; two side impacts, a near-side and a far-side, respectively, and a frontal impact. The occupant kinematics and internal loads were analyzed, and any deviation between the nominal and altered posture responses were quantified using cross-correlation of signals to highlight the most notable variations. Posture changes to the lower extremities had the largest overall influence on the lower extremities, pelvis, and whole-body responses for all crash configurations. In the frontal impact, crossing the legs allowed for the highest pelvis excursions and rotations, which affected the whole-body response the most. In the two side-impacts, leaning the torso in the coronal plane affected the torso and head kinematics by changing the interaction with the vehicle's interior. Additionally, in far-side impacts supporting the upper extremity on the center console resulted in increased torso excursions. Moreover, the response of the upper extremities was consistently sensitive to posture variations of all body regions.
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| 6. |
- Leledakis, Alexandros, 1991, et al.
(författare)
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The Influence of Occupant's Size, Shape and Seat Adjustment in Frontal and Side Impacts
- 2022
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Ingår i: Conference proceedings International Research Council on the Biomechanics of Injury, IRCOBI. - 2235-3151. ; 2022-September, s. 549-584
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Konferensbidrag (refereegranskat)abstract
- The sensitivity of occupant kinematic and kinetic crash responses to anthropometric and seat adjustment variation was investigated by performing frontal- and side-impact simulations with a family of morphed Human Body Models (HBMs). The HBM family included variations of shape and size, accounting for stature, Body Mass Index (BMI) and sex. A global sensitivity analysis method was developed and applied. Increased BMI was associated with increased spinal and extremity loading in the HBM for all evaluated impacts. Increasing the stature resulted in a consistent increase in lower extremity loading. The fore-aft seat position influenced the head and torso speed relative to the vehicle interior. Furthermore, in high-severity frontal impacts, adjusting the seat position rearwards altered the load path, increasing the HBM pelvic and lumbar spine loading in favour of reducing the lower extremity forces, and vice versa when the seat was positioned forward. The results from this study highlight potential occupant protection challenges and trade-offs, and can be used to enhance protection, considering occupant anthropometric diversity and seat adjustment variation.
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| 7. |
- Wågström, Linus, 1977, et al.
(författare)
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Integrated Safety: Establishing Links for a comprehensive virtual tool chain
- 2019
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Ingår i: 26th International Technical Conference on the Enhanced Safety of Vehicles (ESV).
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Konferensbidrag (refereegranskat)abstract
- As technologies for injury prevention and crash avoidance both contribute to injury reduction in car crashes, tools predicting the combined effect of all safety features are needed. This study aims at establishing a computer simulation methodology including two important elements for assessing this combined effect. The first element describes the states of the involved vehicles or objects at crash initiation regarding positions, orientations and velocities as parameters used for crash evaluation. The second element focuses on the car occupant, enabling computationally efficient prediction of occupant position transfer during pre-crash maneuvers. An extended aim is to demonstrate how data flows between these elements in an example case study. Real-world data from the Volvo Cars traffic accident database (VCTAD) was used as the basis for pre-crash simulations involving two cars, with and without a conceptual autonomous emergency braking (AEB) function. For cases in which the crash was not avoided by the AEB function, the crash configuration was identified. A simplified occupant kinematics model (SOCKIMO) was developed and applied to these remaining crashes, supporting the selection of crash situations to be analyzed in detail. The SAFER human body model (HBM) was used for simulation of the occupant response, providing information on pre-crash kinematics as well as the occupant crash response. As a result, a novel crash configuration definition for estimating the consequences of car crashes based on preceding events was established. The Volvo parametric crash configuration (VPARCC) definition can be used as a link between pre-crash and crash simulation tools as well as for illustrating sets of real-world accident data and how these change based on maneuvers preceding a crash. SOCKIMO results demonstrated occupant kinematics similar to those of volunteers, and the subsequent simulations using the SAFER HBM showed considerable changes in occupant crash response based on pre-crash vehicle kinematics. The VPARCC definition can also be applied to collision objects such as trucks or vulnerable road users. The developed SOCKIMO can be used to filter out cases from large crash data sets to be further analyzed with detailed models such as finite element active HBMs. By applying the more detailed HBM, the effects of avoidance maneuvers on occupant kinematics relevant for injury prediction can be evaluated. This approach would not be possible using simplified occupant models only (due to the lack of details) or by using detailed models only (due to the large simulation effort). The presented methodology for estimating combined safety performance can be used for transferring output from pre-crash simulations to input for crash simulations. The feasibility of combining the individual elements of this methodology was demonstrated in an example case where autonomous emergency braking led to a large change in the crash configuration and was predicted to introduce substantial occupant pre-crash excursion. In this example case, it was shown that the present A-HBM tool is able to cover the complete sequence from pre-crash maneuvers to crash in one single simulation.
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