• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
Simulating Real World Pedestrian Accidents : PhD Defence
 

Simulating Real World Pedestrian Accidents : PhD Defence

on

  • 610 views

The construction and evaluation of pedestrian accident simulations with a reference C class vehicle are described in detail. The influence of accident conditions and the expected ranges of various ...

The construction and evaluation of pedestrian accident simulations with a reference C class vehicle are described in detail. The influence of accident conditions and the expected ranges of various quantitative pedestrian injury and motion measures are identified. Vehicle impact velocity, pedestrian size and stance have significant influences on these measures. Therefore it is not possible to state, for instance, that under all accident conditions, one vehicle impact location is likely to cause lower injury measures than another is. There is a clear increase in pedestrian measures (e.g. head velocity, HIC, tibia acceleration, knee bending) with a large increase in impact velocity (i.e. 25 to 40 km/h). However, some measures (e.g. HIC) do not necessarily increase with a small increase in impact velocity (e.g. 25 to 30 km/h) because of the new pedestrian motion (e.g. a new head impact location). Large differences exist between the 6 year old pedestrian and adult pedestrian model measures (e.g. larger post head impact motion but smaller HIC and tibia acceleration) and pedestrian stance has a complex influence on all measures with few overall trends.
Pedestrian protection headlamp, bumper system and hood system concepts are developed in biomechanical, analytical and numerical component models. These concepts are used to construct and subsequently benchmark, with pedestrian accident simulations, two modified vehicle models that incorporate different combinations of the technologies. Both the absolute measures and ranges of the measures from the reference vehicle simulations are compared. There are large differences between the pedestrian measures from the reference and modified vehicles but much smaller differences between the modified vehicles. Impacts with the modified vehicles cause the largest differences in pedestrian motion at 40 km/h, for the 6 year old pedestrian, in stance ‘A’, in the early (up to 20 ms) and late (after 140 ms) stages of the accident simulations. Although the modified vehicles reduce pedestrian injury measures for some of the accident conditions, neither of them reduce all measures for all of the conditions. However, significant improvements in experimental sub system measures [EEVC 1998] are achieved with a prototype modified vehicle that incorporates some of the technologies.

Statistics

Views

Total Views
610
Views on SlideShare
599
Embed Views
11

Actions

Likes
1
Downloads
3
Comments
0

2 Embeds 11

http://www.linkedin.com 9
https://www.linkedin.com 2

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment
  • Good morning, today I would like to present my research topic which is: Pedestrian accident simulation & protection technology evaluation My presentation is split into these topics, beginning with the scope of the pedestrian problem & ending with my recommendations for future research .............. ------------------------------------------------------------------------------------------------------------------
  • Pedestrian safety is an important societal issue . pedestrian fatalities are decreasing in USA/Europe/Japan but still too high . --------------------------------------------------------------------------------------------------------------- Pedestrians are a major road user fatality group in accident statistics, no. 1 in Japan & also a vulnerable road user group . --------------------------------------------------------------------------------------------------------------- Since the 1980’s research organisations have been developing PP test methods . In recent years the car industry has also become involved in developing these methods. There are two test methods that are being used to develop vehicles : The first is based on the WG17 test requirements , not obligatory & being used by an independant body to generate EuroNCAP PP scores for general public information The second is a revised version of the WG17 test requirements that has been developed by the car industry & for 2005 is part of an industry volunteery agreement to improve pedestrian protection ---------------------------------------------------------------------------------------------------------------
  • I have categorised different approaches to find solutions into a framework . The objective of all pedestrian safety research is to improve pedestrian protection & all areas of our society need to contribute to solutions . --------------------------------------------------------------------------------------------------------------- The car industry is one of the contributors & does this through vehicle design & technology improvements There are 2 approaches to identify the most effective improvements ---------------------------------------------------------------------------------------------------------------- On the left we have pedestrian accident simulation in this approach a pedestrian surrogate is used to recreate real world accidents On the right we have sub system test procedures where the accident is broken down into separate impact events & tests this is the basis for the EuroNCAP & ACEA test procedures In order to understand the global behaviour of pedestrian surrogates & vehicles it is necessary to characterise their component behaviour --------------------------------------------------------------------------------------------------------------- On the left we have human limb & joint characterisation in which, studies of the human knee, neck or bone injury mechanisms are made & on the right is vehicle component characterisation where the impact properties of single vehicle components are studied --------------------------------------------------------------------------------------------------------------- The final approach is pedestrian accident statistics & case studies where real world measures drive & indicate the effectiveness of pedestrian research as can be seen in the feedback loop I will now consider my approach in the context of these possible approaches . ---------------------------------------------------------------------------------------------------------------
  • I chose to create a variety of models & methodologies to understand what happens between pedestrians & vehicles during an accident & then APPLY these to create & develop unique PP technologies ---------------------------------------------------------------------------------------------------------------
  • I chose to create a variety of models & methodologies to understand what happens between pedestrians & vehicles during an accident & then APPLY these to create & develop unique PP technologies ---------------------------------------------------------------------------------------------------------------
  • At the end of my research I created an overall methodology that brings together all the models & methods in a framework that is being used to design, develop & evaluate PP technologies in Ford This methodology is guided by & supports the corporate strategy & targets . --------------------------------------------------------------------------------------------------------------- The first aspect of this is a reference vehicle without PP technologies The key elements include; vehicle model construction & validation : at a component level using a systematic testing & modelling methodology & at a vehicle level using sub system impactor test results vehicle model PP evaluation : using sub system impactors & a matrix of accident simulations --------------------------------------------------------------------------------------------------------------- The second aspect concerns modified vehicles with technologies A similar procedure is used with additional steps for evaluating technologies An understanding of the reference vehicle performance is combined with knowledge of real world pedestrian accident studies & a patent search to create technology concepts Biomechanical & analytical models are used to describe & refine the concepts with simplified DoE numerical models for initial technology optimisation . Vehicle models & prototypes can be created with this set of technology models & final optimisation undertaken with a reduced matrix of accident simulations --------------------------------------------------------------------------------------------------------------- The final aspect of the methodology concerns the development & maintenance of CAE tools & accident studies & benchmarking against the reference vehicle & EuroNCap . & real world accident reconstruction to assess in use performance . ---------------------------------------------------------------------------------------------------------------
  • Now I would like to highlight a few of the activities within this methodology A reference vehicle & a set of accident simulation conditions were created There were various aspects to the accident simulation models : a rigid vehicle rear end was constrained to X axis motion under 1g deceleration from an initial velocity of 25, 30, 35 or 40 km/h the main vehicle structure had no constraints except the initial velocity & like the rest of the vehicle model was positioned 70 mm below its ride height to simulate brake dive validated vehicle components were attached to this structure & meshed accourding to mesh quality guidelines & separate component rig test results finally, 1 of 16 humanoid models (4 sizes & stances) were statically positioned in front of the vehicle at one of 2 impact locations ---------------------------------------------------------------------------------------------------------------- The matrix of accident simulation conditions is shown here. The upper bound on vehicle impact velocity is set to the same level as [EEVC 1998] & the lower bound just below the lowest speed limit in Europe 2 impact locations are specified at the most flexible part of most bumper systems; the vehicle centreline Y0 & in next to the crash longitudinal Y500 where the bumper is rigidly mounted . Based on the results of our IRCOBI paper 1g deceleration & a ride height drop of 70 mm (with no pitch) are applied to simulate braking. To reduce the number of simulations only the validated 50th percentile model is used at all 4 vehicle impact velocities ---------------------------------------------------------------------------------------------------------------
  • This is a list of some of my observations for all accident conditions I chose a total of 10 numerical accident simulation measures, these included Impact timing in which I categorised impact events into: pelvis to vehicle face, shoulder to hood & head to hood or windscreen CMD my own measure of composite maximimum displacement Head trajectory Head velocity HIC Pelvis acceleration Knee shear & bending Tibia acceleration & leg fracture location & timing It was difficult to identify any trends that were consistent for all conditions & there were several possible reasons for this, including: Humanoid model limitations (e.g. shoulder & pelvis stiffness & mobility) Vehicle model limitations (e.g. Windscreen material model) Some trends simply do not exist as previously published Although there are model limitations I favour the latter because the simulations have clearly identified the importance of so many factors for example , HIC does not always increase for small velocity increases because the head impact location on the hood changes & unlike previous publications there is a variable stiffness hood In addition, global & detailed animation sequences were used to observe the whole pedestrian accident sequence & structural collapse details . As shown on the next slide these provided more insight into the injury mechanics & revealed potential pedestrian protection solutions ----------------------------------------------------------------------------------------------------------------
  • Visual examination of the vehicle structure clearly reveals what is happening & what design changes might alleviate certain loading conditions ............ In this case the way in which the stiff bumper beam & unsupportive spoiler cause large knee & lower leg bending can be clearly seen This also shows the importance of simultaneously considering the interaction of multiple injury mechanisms & vehicle components In a later slide I will show how some pedestrian protection technologies reduced this problem ---------------------------------------------------------------------------------------------------------------
  • It is possible to identify the main pedestrian body regions & vehicle body regions. & then the relationship between them There is a clear diagonal relationship between pedestrian and vehicle regions. This helps to prioritise the regions & link these priorities with possible solutions . In terms of vehicle regions it can be seen that the bumper is always impacted & has the potential to cause highest societal costs . The hood & fenders follow because they cover such a large vehicle area . Next comes the engine bay , related to the hood but more difficult to change Finally, vehicle face , windscreen & windscreen surround because the vehicle face pedestrian friendly in aerodynamic vehicles & windscreen & surround difficult to change From the pedestrian body regions perspective The largest number of vehicle regions influence the neck & head because head contact might occur in many places. The knee & head are the most commonly injured & cause high societal costs knees are difficult to repair & head injuries are serious & may lead to death. --------------------------------------------------------------------------------------------------------------- From the perspective of a potential solutions there are many patents concerning the hood & fenders the least for the windscreen and windscreen surround . If one considers the highest priority combinations. These include knee injuries caused by the bumper head injuries caused by the hood and, to a lesser extent, lower body injuries caused by the vehicle face . These are the main injuries addressed by the PhD research ---------------------------------------------------------------------------------------------------------------
  • I created a total of 6 patents or patent applications These cover bumper systems, headlamps & hood systems. --------------------------------------------------------------------------------------------------------------- The first application covers different bumper fascia & foam geometry’s to lower the stiffness centre away from the knee & reduce tibia acceleration . & in the second application there is a bumper undertray that incorporates a V shape front deformation zone that allows controlled support for the lower leg whilst reducing tibia acceleration --------------------------------------------------------------------------------------------------------------- On the top application the headlamp lens cover sidewall has slots in it & on the bottom application the sidewall has an S shaped cross section in both cases the objective is to reduce the dynamic headlamp stiffness --------------------------------------------------------------------------------------------------------------- In the left application the hood latch platform box is eccentrically mounted with a shear pin With sufficient pedestrian impact force the shear pin fails & allows the box to rotate & this is transferred into the hood bump stops & into upward & rearward hood motion . In the right hand application the cooling pack and GOR move in a predefined motion Controlled by mounting points & mounting releases This motion transferred to upward and rearward hood motion In both cases, the adult pelvis or child abdomen loading is reduced whilst using the impact energy to increase the hood clearance I developed these concepts further in biomechanical , analytical , & numerical DoE models to construct partly optimised numerical component models as shown in the next slide. ---------------------------------------------------------------------------------------------------------------
  • Biomechanical models can be used identify potential real world injury mechanisms based on boundary conditions & likely geometric impact locations & be a common language with accident investigators --------------------------------------------------------------------------------------------------------------- Analytical models can be used to understand the basic technology mechanics & assist in creating a common language with designers & suppliers with relative numerical values --------------------------------------------------------------------------------------------------------------- Simplified numerical DoE models may be used to systematically undertake a more detailed examination of key technology factors --------------------------------------------------------------------------------------------------------------- & used to create partly optimised component numerical models ......................... That can be incorporated into the complete modified vehicle models as shown on the next slide ---------------------------------------------------------------------------------------------------------------
  • There were 2 modified vehicle models - ‘d1’ on the left & ‘d2’ on the right . Both of these incorporated the bumper undertray & dual density foam but ‘ d1 ’ also featured deformable headlamps & ‘ d2 ’ a mechanically deployed hood The bumper & undertray provided leg & knee support but since the headlamp & hood technologies were incompatible 2 vehicle models were necessary . ---------------------------------------------------------------------------------------------------------------- Based on the results of the matrix of reference vehicle accident simulations a reduced matrix of modified vehicle simulations was created 2 humanoid models were used - the 6 year old child & 50th percentile The 50 th percentile pedestrian model was validated against a cadaver study & the 6 year old exhibited significantly different & extreme behaviour whilst being more sensitive to vehicle design changes There were 2 vehicle velocities - 25 & 40 km/h but the benefits of the bumper & headlamp technologies are clearer at 40 km/h Therefore, ‘ d1 ’ was only assessed at 40 km/h. However, ‘ d2 ’ incorporated the hood technology & to fully deploy the hood required a minimum amount of impact energy . Therefore the ‘ d2 ’ was assessed at both 25 km/h & 40 km/h 2 vehicle impact locations , Y0 and Y500, were retained because the design differences still applied Finally, only 2 stances ‘A’ & ‘C’ were used because they both provided the most useful & robust data stance ‘ A ’ maximised the local impact energy transferred into the vehicle front it is an extreme stance stance ‘ C ’ led to fewer model problems with the vehicle & pedestrian interaction & is a more likely real world stance -------------------------------------------------------------------------------------------------------------------
  • This is a list of some of my observations for the benchmarking accident conditions As with the reference vehicle it was difficult to identify trends & for similar reasons to those mentioned previously . In order to make more sense of the results the range & absolute reference vehicle results for all accident conditions were compared to the absolute results from the modified vehicle simulations A significant difference was defined as a modified vehicle result that fell outside of the expected range for a larger number of accident conditions In general, global pedestrian motion differences were difficult to see particularly between ‘ d1’ & ‘ d2 ’ but there were differences in the early & late stages of the pedestrian accident & between the reference & modified vehicles As might be expected ‘ d2 ’ had a large influence on many results, for example CMDY because the complete vehicle front geometry changed during the impact. Also, many of the lower body measures , for example knee shear & tibia acceleration were similar for ‘ d1 ’ & ‘ d2 ’ because they had identical bumper systems The bumper technologies reduced knee shear & tibia acceleration for most cases but interestingly knee bending was not consistently lower as with the reference vehicle The small increase in HIC for the 50th pedestrian was surprising & as mentioned previously may be caused by many factors Pelvis acceleration was inconsistent across all cases & this may have been caused by known humanoid pelvis construction limitations As with the reference vehicle & shown on the next slide detailed animation sections provided more insight into the injury mechanics ----------------------------------------------------------------------------------------------------------------
  • Here we can see how the modified headlamps, bumper & undertray reduce the knee shear & leg bending when compared to the outline from the equivalent reference vehicle simulation Irrespective of any problems in determining measurement trends between beneficial & detremental technologies animations like this allow a subjective assesment of whether a technology is likely to be beneficial In this case it is clear how the combination of headlamp, bumper & undertray technologies work together to keep the legs straighter than the reference vehicle ---------------------------------------------------------------------------------------------------------------
  • A new methodology has been created (& is now being applied at Volvo) to understand the complexity of the pedestrian & vehicle interaction & design, develop & evaluate PP technologies Bumper, headlamp & hood PP technologies have been created by applying the new models & methods One of these methods used pedestrian accident simulations to benchmark a reference vehicle against modified vehicles Benchmarking is hindered by complex injury measure trends & possibly by humanoid & vehicle model limitations Further full vehicle optimisation in accident simulations is required to minimise all injury measures for each technology The potential benefits of the technologies have also been demonstrated in other types of models (e.g. simplified DoE) & tests (e.g. WG17 tests), that are specified in the methodology ---------------------------------------------------------------------------------------------------------------
  • The humanoid models require a revised pelvis new shoulder & thorax mobility more geometrically representative legs & further accident case study validation Some of the changes are already underway or planned Consideration must be given to the sensitivity of injury measures to vehicle changes & their significance in real world accidents . A potential research area is pedestrian pre impact motion The vehicle models should be improved in a number of areas the choice of windscreen material model non rigid engine modelling component validation of the bumper, undertray & headlamp technologies Potential research areas include application of the methodology to another vehicle vehicle suspension modelling The technologies require a more complete investigation of functional requirements e.g. crash, durability, cost. further technology optimisation in the complete vehicle accident simulations It is important to connect the development of this research with what actually happens in real world accidents something that I was not able to do as fully as planned BUT I have created accident reconstruction forms for pedestrian simulations & these should be the basis for collecting new & detailed accident cases for the ULTIMATE VALIDATION ........................
  • The humanoid models require a revised pelvis new shoulder & thorax mobility more geometrically representative legs & further accident case study validation Some of the changes are already underway or planned Consideration must be given to the sensitivity of injury measures to vehicle changes & their significance in real world accidents . A potential research area is pedestrian pre impact motion The vehicle models should be improved in a number of areas the choice of windscreen material model non rigid engine modelling component validation of the bumper, undertray & headlamp technologies Potential research areas include application of the methodology to another vehicle vehicle suspension modelling The technologies require a more complete investigation of functional requirements e.g. crash, durability, cost. further technology optimisation in the complete vehicle accident simulations It is important to connect the development of this research with what actually happens in real world accidents something that I was not able to do as fully as planned BUT I have created accident reconstruction forms for pedestrian simulations & these should be the basis for collecting new & detailed accident cases for the ULTIMATE VALIDATION ........................

Simulating Real World Pedestrian Accidents : PhD Defence Simulating Real World Pedestrian Accidents : PhD Defence Presentation Transcript