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| 2. |
- Brolin, Karin, 1974, et al.
(författare)
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Active Child Models for Traffic Safety Research Interim Report 2, October 2013
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The project Active Child Models for Traffic Safety Research is funded by Folksams Forskningsstiftelse. The overall project aim is to increase the safety of child car occupants and thereby reduce the number of traffic induced injuries in 3 to 12 year-old children. The specific aim is to create a computer model of a child that includes active musculature. Based on literature review of child numerical models it was decided to proceed with child multi body models in the MADYMO code (TASS, Rijswijk, the Netherlands). The 6 and 10 year-old child facet models, the Q6, Q10 and Hybrid III 6 year-old ATD models were compared regarding kinematics to experimental data with child volunteers in 1 g braking and steering events. The ATD models did not represent the experimental ATD response. The child facet models represented the child volunteers for about 3-400 ms of the events, and after that behaved cadaver like with much larger head and sternum displacement compared to the volunteers. Then, the child facet model representing the 6 year-old child was chosen to implement muscle activity. Muscle activity was represented by an active spine that applied torques at each vertebral joint in response to joint angle changes in two directions: flexion-extension motions and lateral bending. A partial, integrative and derivative controller governed with input from angular sensors controlled torque actuators. The controller gains were based on adult data and scaled by 50% for a first version of the active child model. Then, an optimization approach was adopted to tune the control gains in the lumbar, thoracic and cervical spine such that head and sternum kinematics would correlate to the mean values from the volunteer braking and steering experiments. The first version of the active child model had a significantly improved biofidelity compared to the original facet model, with shape and magnitude of head and sternum displacements similar to the volunteer data. The optimization created non biofidelic gain combinations, although providing important input to future work. It is necessary to perform a reanalyses of the experimental data in order to have data for powerful performance criteria in future optimizations. Future work is needed to improve the optimization and provide controller gains based on child volunteer data, rather than scaled adult data. Then, the tuned active child model has to be validated to new experimental data sets. A new steering and braking experiment with approximately 1 g acceleration loading was performed during 2013 and will provide a good validation data set. Also, there is a data set with child volunteers in sled test of approximately 4 g that can be used. Then, the active model is suitable to perform parameters studies of how child restraints design, emergency manoeuver characteristics and child posture influences the safety of children in the rear seat.
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| 3. |
- Brolin, Karin, 1974, et al.
(författare)
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Active Spine Modeling Representing a 6 Year-Old Child
- 2014
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Ingår i: 7th World Congress of Biomechanics.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In a car crash, properly restrained forward facing children may sustain head injuries due to contact with the car interior. Emergency events such as braking and steering will influence the kinematics of the child, thereby affecting the child’s interaction with the restraint systems. Volunteer experiments (Stockman et al. 2013) have shown that children around six years of age, properly restrained on a booster cushion, may slip out of the shoulder belt during a 1g emergency event, while older children can maintain their posture better. A numerical human body model of the 6 year-old would be a valuable tool to study and improve the performance of restraint systems in the pre-crash phase. Compared to a crash, an emergency event typically has low g and long duration loading; hence, the muscle activity will influence the kinematics of the child. Therefore, the aim of this work is to develop an active 6 year-old human body model.The 6 year-old facet occupant multi body model in the MADYMO code (TASS, Rijswijk, the Netherlands) was selected. The spine is composed of rigid vertebral bodies connected with spherical joints. Muscle activity was implemented by applying torques at each vertebral joint for flexion-extension and lateral bending. The torque actuators were controlled by proportional, integrative and derivative controllers comparing the current joint angles to an initial posture reference value. The controller gains were based on adult data and scaled by 50% for a first version of the active child model. The resulting active 6 year-old model was used to simulate the volunteer experiments by Stockman et al. 2013. The model was seated on a booster cushion and loaded with the average experimental pulse. The first version of the active child model had a significantly improved biofidelity compared to the original facet model, with shape and magnitude of displacements similar to the volunteer data, see Figure.It is concluded that the first version active 6 year-old model can reproduce this specific emergency event. Future work should focus on controller gain optimization and further validation.
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| 4. |
- Brolin, Karin, 1974, et al.
(författare)
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Development of an Active 6-Year-Old Child Human Body Model for Simulation of Emergency Events
- 2015
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Ingår i: 2015 IRCOBI Conference Proceedings - International Research Council on the Biomechanics of Injury. ; :IRC-15-74, s. 689-700
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Konferensbidrag (refereegranskat)abstract
- One contributing factor to head injury in restrained child occupants is pre‐crash maneuvers andactive child human body models (HBMs) can be useful tools to design pre‐crash interventions with child safety infocus. This paper implemented postural control in the MADYMO human facet occupant model of a 6‐year‐oldchild using feedback controlled torque actuators. Control parameters were tuned and the active HBM wascompared to experimental data from braking and steering events with child volunteers. The head and sternumdisplacements of the active HBM were within one standard deviation of the experimental data, while theoriginal HBM did not capture the volunteer kinematics at all. By predicting biofidelic child kinematics, thedeveloped model shows potential as a useful tool for the automotive industry to study the protective propertiesof restraint systems in pre‐crash scenarios. For autonomous steering events, it was illustrated that the shape ofthe acceleration pulse highly influences the peak head displacements of child occupants. This is an aspect thatneeds to be considered when autonomous interventions are designed, to ensure the safety of short forwardfacing child occupants.
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| 5. |
- Brolin, Karin, 1974, et al.
(författare)
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Safety of children in cars: A review of biomechanical aspects and human body models
- 2015
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Ingår i: IATSS Research. - : Elsevier BV. - 0386-1112. ; 38:2, s. 92-102
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Forskningsöversikt (refereegranskat)abstract
- The protection of children in motor vehicle crashes has improved since the introduction of child restraint systems. However, motor vehicle crashes remain one of the top leading causes of death for children. Today, computer-aided engineering is an essential part of vehicle development and it is anticipated that safety assessments will increasingly rely on simulations. Therefore, this study presents a review of important biomechanical aspects for the safety of children in cars, including child human body models, for scenarios ranging from on-road driving, emergency maneuvers, and pre-crash events to crash loading. The review is divided into four parts: Crash safety, On-road driving for forward facing children, Numerical whole body models, and Discussion and future outlook.The first two parts provide ample references and a state-of-the-art description of important biomechanical aspects for the safety of children in cars. That children are not small adults has been known for decades and has been considered during the development of current restraints that protect the child in the crash phase. The head, neck, thorax, and pelvis are body areas where development with age changes the biomechanics and the interaction with restraint systems. The rear facing child seat distributes the crash load over a large area of the body and has proved to be a very efficient means of reducing child injuries and fatalities. Children up to age 4. years need to be seated rearward facing for optimal protection, mainly because of the proportionally large head, neck anthropometry and cartilaginous pelvis. Children aged 4 up to 12. years should use a belt positioning booster together with the vehicle seat belt to ensure good protection, as the pelvis is not fully developed and because of the smaller size of these children compared to adults. On-road driving studies have illustrated that children frequently change seated posture and may choose slouched positions that are poor for lap belt interaction if seated directly on the rear seat. Emergency maneuvers with volunteers illustrate that pre-crash loading forces forward-facing children into involuntary postures with large head displacements, having potential influence on the risk of head impact. Children, similar to adults, benefit from the safety systems offered in the vehicle. By providing child adaptability of the vehicle, such as integrated booster cushions, the child-restraint interaction can be further optimized. An example of this is the significant reduction of lap belt misuse when using integrated boosters, due to the simplified and natural positioning of the lap belt in close contact with the pelvis. The research presented in this review illustrates that there is a need for enhanced tools, such as child human body models, to take into account the requirements of children of different ages and sizes in the development of countermeasures.To study how children interact with restraints during on-road driving and during pre- and in-crash events, numerical child models implementing age-specific anthropometric features will be essential. The review of human whole body models covers multi body models (age 1.5 to 15. years) and finite element models (ages 3, 6, and 10. years). All reviewed child models are developed for crash scenarios. The only finite element models to implement age dependent anthropometry details for the spine and pelvis were a 3. year-old model and an upcoming 10. year-old model. One ongoing project is implementing active muscles response in a 6. year-old multi body model to study pre-crash scenarios. These active models are suitable for the next important step in providing the automotive industry with adequate tools for development and assessment of future restraint systems in the full sequence of events from pre- to in-crash.
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| 6. |
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| 7. |
- Gras, Laure-Lise, 1985, et al.
(författare)
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Active Child Models for Traffic Safety Research, Interim Report 1, October 2012
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The project Active Child Models for Traffic Safety Research is funded by Folksams Forskningsstiftelse. The overall aim is to increase the safety of child car occupants and thereby reduce the number of traffic induced injuries in 3 to 12 year-old children. This will be done by creating a computer model of a child that includes active musculature. The model will be used to reproduce emergency manoeuvres with biofidelic response at low acceleration levels. Literature on child safety has been reviewed with a main focus on child numerical models. Very few child models exist and for most of them, their response is validated against Anthropometric Test Devices (ATDs) certification corridors and not paediatric data. Models of children and child sized ATDs are either finite element or multi body models. Finite element models are more likely to predict injuries and contacts, whereas multi body models can preferably be used to reproduce kinematics in long duration events like emergency manoeuvres. Because of this, it has thus been decided to first work with child multi body models in the MADYMO code (TASS, Rijswijk, the Netherlands). The models that will be studied are the 6 and 10 year-old child facet models and the Q6 and Hybrid III 6 year-old ATDs available in MADYMO as well as the 6 year-old pedestrian model previously developed by Jikuang Yang at Chalmers University of Technology. Simulation activities have been planned and the models’ responses will be analysed and compared with kinematics data of child volunteers in emergency manoeuvres and sled tests. Then, based on their performance, one model will be chosen to implement active musculature. Extra experimental data for tuning and validation of the model may be required. As a consequence, new experiments on child volunteers are planned, including the acquisition of muscular activity. The model response will be compared to those results. Based on the active child multi body model capability to reproduce pre-crash events, it will be discussed and decided in January 2013 whether to continue with a multi body model or start the same process with a finite element model. In the long term, the active child model will be used to reproduce both pre-crash and in-crash events and help understanding the protective principles of forward facing children and how they interact with current and future vehicle safety systems and child restraints.
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| 8. |
- Gras, Laure-Lise, 1985, et al.
(författare)
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Evaluation of 6 and 10 Year-Old Child Human Body Models in Emergency Events
- 2017
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203 .- 1932-6203. ; 12:1, s. e0170377-
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Tidskriftsartikel (refereegranskat)abstract
- Emergency events can influence a child’s kinematics prior to a car-crash, and thus its interaction with the restraint system. Numerical Human Body Models (HBMs) can help understand the behaviour of children in emergency events. The kinematic responses of two child HBMs–MADYMO 6 and 10 year-old models–were evaluated and compared with child volunteers’ data during emergency events–braking and steering–with a focus on the forehead and sternum displacements. The response of the 6 year-old HBM was similar to the response of the 10 year-old HBM, however both models had a different response compared with the volunteers. The forward and lateral displacements were within the range of volunteer data up to approximately 0.3 s; but then, the HBMs head and sternum moved significantly downwards, while the volunteers experienced smaller displacement and tended to come back to their initial posture. Therefore, these HBMs, originally intended for crash simulations, are not too stiff and could be able to reproduce properly emergency events thanks, for instance, to postural control.
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| 9. |
- Gras, Laure-Lise, 1985, et al.
(författare)
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Hyper-elastic properties of the human sternocleidomastoideus muscle in tension
- 2012
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Ingår i: Journal of the Mechanical Behavior of Biomedical Materials. - 1751-6161 .- 1878-0180. ; 15, s. 131-140
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Tidskriftsartikel (refereegranskat)abstract
- Numerical models of the human body require realistic mechanical properties of the muscles as input, but, generally, such data are available only for animals’ muscles. As a consequence, the aim of this study was to identify the hyper-elastic behavior of the human sternocleidomastoideus muscle in tension using different constitutive laws. Ten sternocleidomastoideus muscles were tested in vitro. The hyper-elastic behavior was modeled with an exponential law and a hyper-elastic constitutive law studied analytically. The latter was also studied with an inverse approach using a subject-specific, finite-element model of each muscle. The three approaches were compared statistically. From these laws and methods, the shear modulus μ (4 to 98 kPa) and the curvature parameter α (17 to 52) were identified. Both the analytical and finite-element approaches gave parameters of the same order of magnitude. The parameters of the exponential and hyper-elastic laws were linked thanks to simple linear equations. Our results evidence that the hyper-elastic tension behavior of human sternocleidomastoideus muscle can be described using a simple model (exponential) considering basic geometric features (initial length and cross-sectional area).
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| 10. |
- Gras, Laure-Lise, 1985, et al.
(författare)
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Tensile tests on a muscle: Influence of experimental conditions and of velocity on its passive response
- 2012
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Ingår i: 2012 IRCOBI Conference Proceedings - International Research Council on the Biomechanics of Injury. ; , s. 515-523
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Konferensbidrag (refereegranskat)abstract
- Muscle mechanical properties are necessary to improve numerical models of the human body. They have been assessed for animal muscles in studies performed in various experimental conditions. These different experimental protocols may have an influence on muscle response. The aim of this study was thus to evaluate the effect of testing conditions as well as velocity on the passive response of a muscle. Tensile tests at 1 mm.s -1, 10 mm.s -1 and 100 mm.s -1 were performed on a dog muscle in ambient conditions, immersion in 22°C saline solution and immersion in 35°C saline solution. Maximum load Fmax and final stiffness K were measured. The influence of velocity and of experimental conditions on these parameters was studied statistically. The parameters were not very sensitive to changes in velocity (increase of 5% for Fmax between 1 mm.s -1 and 100 mm.s -1). Nevertheless, they were sensitive to experimental conditions (decrease of 25% for Fmax between ambient conditions and immersion in heated saline solution). Consequently, the experimental conditions have an influence on muscle passive response and must be taken into account in the definition of the mechanical properties used in modeling.
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