The Computer Aided Analysis of the Bus Accidents Oriented to the Numerical Simulation of the Injury of the Human Body

Transcription

1 The Computer Aded Analyss of the Bus Accdents Orented to the Numercal Smulaton of the Injury of the Human Body XIAO-YUN ZHANG,XIAN-LONG JIN,JIE SHEN School of Mechancal Engneerng Shangha Jao Tong Unversty No. 800 Dongchuan Road, Shangha CHINA Abstract: - Whle bus accdents tend to draw publc concerns n Chna, much recent research has only focused on the analyses of car accdents due to relatve hgh rates. However, the research dedcated tself to the scope of reconstructng and analyzng traffc accdents nvolvng bus and quas bus vehcle. Thus, the paper here s to represent a comprehensve method for the reconstructon of bus accdents, ntroducng analyss of human body njury as an auxlary approach to verfy the results of smulaton n order to mprove the accuracy of whole judgments, apart from usng the technque of trajectory optmzaton as conventonal reconstructons of car accdents, whch gnore human body njury. Accordng to clncal results and nformaton collectng and concludng from the accdent stes, the studes of body njury, whch work as a knd of feedback n order to check and gude ordnary smulatons, were carred out nvestgatng the severty levels and dynamc response of human body under the gven condtons calculated from common method. Wthn the method, the correspondng modfcatons of modelng, calculatng and smulatng need to be made, relatng to the comparsons between predcted njury parameters and practcal effects on vctms. Through the demonstratons of the reconstructons and analyses of two real-lfe paradgms regardng bus accdent, ths paper ndcates the general routng of the method for common cases. The research looks at applyng two useful numercal reconstructon technques, namely Mult-body body dynamcs and trajectory optmzaton methods. Wth the help of two numercal modelng sklls, prelmnary results ndcate that the combned reconstructon method can reflect the process of bus accdent reasonably well. In comparson wth conventonal methods, the method provdes more relablty as well as accuracy. Key-Words: - bus accdent; accdent reconstructon; njury; occupant knematcs; trajectory optmzaton 1 Introducton The Chnese road traffc has been n a severe condton. For nstance, t s reported that the death toll caused by traffc accdents exceeded one hundred thousand persons each year successvely from 2001 to 2004, wth the fact that 2005 amounted to 9873 persons and 2006 stll resulted to persons. Therefore, the stuatons of the Chnese road traffc need to be mproved n many ways (e.g. makng roads better, and developng vehcle technology). Nowadays, wth the rapd development of the computer and software technques, numercal smulaton and reconstructon technques that orented to the analyss of the traffc accdent have been wdely appled and greatly concerned. However, these current technques have manly been focusng on how to strengthen the safety of small passenger cars, whle gnorng the needs of accdent reconstructon regardng bus, and the structural desgn of bus. In fact, road traffc accdents wth respect to the buses become a common crash type n Chna. The number of cases and deaths caused by accdents of the bus has kept occupyng a large proporton among all the traffc accdents. Besdes, the number of deaths resulted from a sngle accdent s also seen at a hgh level n Chna. Accordng to the record data from the admnstraton of Chnese traffc polce, n 2006, the number of bus traffc accdents was 7421, whch was equal to 11.6% of the total number of the vehcle-crashng accdents. Among others, the number of the sgnfcant traffc accdents, whch resulted to over 10 deaths, even amounted to 26, leadng to 396 people dead and 359 njured n all. ISSN: Issue 5, Volume 10, May 2011

2 Obvously, the bus accdent has rank tself among the leadng cause of njury, death and dsablty of many people n a sngle traffc accdent and n the meantme, ths typcal vehcle accdents are nclned to be eventful. Therefore, ths knd of crash draws more and more concerns from the publc and authortes at all levels. Impacts nvolvng bus are selected as the accdents of nterest n ths present study, wth the assstance of dfferent computatonal resource. The whole process of a vehcle accdent can be dvded nto three phases: (1) Post mpact - the usual startng pont of the reconstructon whch can be developed dependng on the nformaton obtaned from the accdent scene. (2) Impact - determnaton of the vehcle's mpact speeds, drectons and locaton, and so on. (3) Pre-mpact - decson of speeds and trajectores. The man gudelne of accdent analyss s to fnd out the vehcle moton n collson phase accordng to the vehcle rest poston n post-collson phase, and then the vehcle moton n pre-collson phase, based on collectng, recordng, nvestgatng and analyzng of the accdent scene[1-3]. Vehcle collson analyses and accdent reconstructons have become ncreasngly popular n recent years due to the expandng rate of cvl ltgaton. Because of the defcency of recordng speed nformaton, most of the focus of the vehcle crash reconstructon s on the determnaton of retrevng the pre-mpact velocty. In order to reconstruct the course of an accdent, some methods have been studed and appled n dfferent accdent types. Occupant knematcs s mportant nformaton for forensc experts, accdent analyzers and engneers. Reconstructng occupant knematcs n a real-world accdent usually requres a long smulaton tme. Therefore, mult-body method was developed as an effectve approach to reduce the tme cost of a smulaton of the nteractons between vehcle and occupants. At present, there are manly two common methods n the feld of numercal reconstructon of the road traffc accdent. The frst one s depended on the tre skd marks, whch can depct the movements of vehcle durng the whole process of collson. The other s based on the vehcle's 2-D or 3-D deformaton, whch can be used as mportant nformaton for concludng crash force, momentum, and then velocty accordng to the knowledge of materal characterstc. Nevertheless, the analyss based on the human body njury has not receved ts deserved recognton n the dentfcaton of the traffc accdent. As a matter of fact, the applcaton wth the characterstc of body njury can be very outstandng n dealng wth the coach-nvolved traffc accdent case. Wth the assstance of body njury, the vehcle speed can be analyzed more precsely due to ths knd of auxlary dentfcaton. In the followng passage, two typcal traffc accdents regardng bus were dscussed separately. The vehcle speeds, whch are calculated out n other ways, can get auxlary verfcaton by usng the numercal analyss of the human body njury n the two typcal cases. Generally, there are several smulaton methods presented n accdent analyses, whch can be grouped nto two man types, dynamc methods and analytcal methods. Engneers had tred to combne both methods together to smulate occupant moton nsde vehcle. They appled analytc methods such as momentum-based method to smulate mpact among vehcles, and used dynamc methods such as fnte element method and mult-body dynamcs method to calculate the nteracton between envronment (vehcle or road) and occupants. Usually, the accdent reconstructon method based on the trajectory theory optmzaton reveals traffc accdent through the momentum-based method to reduce the calculaton tme. The analytc method has a capablty of reverse calculaton, whch s helpful to fnd optmum usng smple mpact model. On the other hand, the fnte element method and the multbody dynamcs method could take advantage of both precse contact algorthm and detaled human model to calculate occupant njures. In order to realze the combnaton between trajectory optmzaton method and mult-body dynamcs, t s assumed that equvalent mpulse can replace actual mpact and momentum exchange tme can be determned by engneerng estmaton. However, errors caused by ths estmaton must be taken nto account, and the feasblty of reconstructon by aforesad method should be evaluated further. 2 Mathematcal Model The reconstructon of the accdent nvolvng human body knematcs and vehcle trajectores needs to combne three dfferent methods: momentum-based method to smulate vehcle moton, mult-body dynamc method to evaluate the human body njures, fnte element method to obtan the deformaton parameters at contact surfaces. In ths knd of reconstructon, vehcle dynamcs and human body njures are vrtually seen as nterrelated factors, whch can be used as a potental condton of constran whle nteractng wth each other. ISSN: Issue 5, Volume 10, May 2011

3 Frstly, undetermned parameters of vehcle motons were predefned n the lght of prelmnary judgments n reference to nvestgatons. Then the process of reconstructng vehcle collson through the smulaton of vehcle trajectores was establshed. Some unknown parameters of nterest, nvolvng vehcle dynamcs, were obtaned through the momentum-based approach. Secondly, the outputs from the smulaton of the trajectory optmzaton, n the form of veloctes, acceleratons and orentatons, are ntroduced as the nputs for calculatng human body knematcs and njures. 3D mult-body models were establshed to reflect the nteractons between vehcles and vctms. Then, the movements of human body dynamcs were descrbed accordng to the outputs of vehcle crash smulaton wth momentum-based method. Fnally, n order to verfy the consstency between the smulaton results and the accdent facts, human body njures and deformatons of vehcle were reevaluated accordng to the legal medcal reports and the recordng materals. Accordng to the smulaton dscrepancy wth the practcal effects, Modfcatons for undetermned parameters of vehcle motons, such as ntal veloctes, postons and orentatons, were made. And the new condtons were ntroduced to the frst step of vehcle trajectory optmzaton. The same process of calculatons was carred out as aforesad untl desred results were receved. The Undetermned parameters were solved as the teratve approach was accomplshed. 2.1 Trajectores Optmzaton Method Vehcle-vehcle mpact model can be represented by momentum-based method. A normal-tangental coordnate system s establshed whch orgnates at the mpact center (Fg.1). Fg.1 Impact confguraton The n axs s normal and the t-axs s tangental to the contact plane respectvely. And the followng assumptons are taken[4-6]. (1) Each vehcle has one mass and three degrees of freedom (two translatons and one rotaton). (2) An exchange of the mpact forces between vehcles happen wthn an nfnte small tme step at a sngle pont. (3) The moton of occupants nsde vehcle can t affect vehcle knematcs. Based on the law of conservaton of momentum and the equaton of lnear and angular mpulse momentum, the change of the relatve velocty for both vehcles at the mpact center can be calculated from pre-mpact velocty and normal and tangental mpulse. In ths study, the vehcle movement s analyzed wth the software PC-Crash that s a common commercal tool to reconstruct vehcle-vehcle accdent usng momentum-based collson model. PC-Crash defnes the resttuton coeffcent as rato between resttuton mpulse and compresson mpulse. When the mpulse s separated nto two components, the normal and tangental mpulse can be calculated from: N = N (1 ) C + ε (1) T = μn (2) In EQ (2), the equvalent frcton coeffcent μ can ndcate the collson type. For example, equvalent frcton coeffcent s very low for the sldng mpact n whch mpact force often results n severe rotaton of vehcle and complex occupant knematcs. Due to the fact that all data regardng the accdents were collected from the feld, there s necessarly a degree of uncertanty regardng the precse condtons under whch each accdent took place. Wthout faclty attached to the vehcle nvolved, t s mpossble to know exactly the veloctes of the bus durng collson. The cases presented here have at best an eyewtness account of the accdent, whch s of course useful and necessary, but not scentfcally rgorous. In many accdent stuatons the approxmate locaton where the vehcles collded can be found due to skd or scratch marks, shatter felds or several types of scuffs. If the vehcles have not been moved from ther rest postons when the scene nvestgatons were made, these postons and the movement drectons are consdered as ISSN: Issue 5, Volume 10, May 2011

4 relable. If skd marks were found on the accdent scene, ntermedate postons of vehcle can be concluded on the post mpact trajectores. Therefore, from the trajectores, valuable nformaton can be collected from the feld n terms of the mpact poston, rest postons and ntermedate postons for accdent stuatons. For each vehcle, these parameters can be specfed [4-6]: P Stop : Vehcle rest poston (coordnates) d : Headng vector at rest poston Stop P mpact : Impact poston and vehcle overlap P Inter, d Inter : One or more ntermedate postons (locaton and headng of the vehcles on the post mpact trajectores) Once these parameters have been specfed for the real accdent, the followng qualty functon can be used to calculate the qualty of the smulaton results. Ths qualty functon defnes the target of the optmzaton process. The assumpton has been made, that the lower the dfference between smulaton results and real accdent data s regardng these values, the closer the smulaton s to the real case. Ths formula s based on the least mean squares, as the qualty functon tends to zero the best match between smulaton and real accdent data has been found, and a smulaton error can be calculated. 2 ( w x ) Q = 2 w 100% (3) The term x of the qualty functon are defned by the dfferences between real accdent data and smulaton results. These factors are normalzed and a weghtng w for each parameter can be specfed to gan more control over the optmzaton process. The qualty functon terms or error estmators x are defned for each car as follows. Postonal errors (stop postons): PStopSm P Stop E Postonal = (4) P P Stop mpact Postonal errors (ntermedate postons): PInterSm P Intre E PostonalInter = P P (5) Inter mpact Headng errors (stop postons): arccos( d Stop d ) StopSm E Headng = (6) π Headng errors (ntermedate postons): arccos( d Inter d ) InterSm EHeadngInter = (7) π As for the optmzaton strateges, several dfferent algorthms lke the Coordnate approach by Gauss-Sedel, the Smplex method, the Gradent and Newton approach, Monte Carlo and Evolutonary methods deal wth the problem of multdmensonal optmzaton. Not all these methods are applcable, because some of these methods need dervatves of the target functon to the nput parameters. Thnkng of the factors of robustness, numercal stablty and hgh progress rates, the Evolutonary method, that s, the genetc algorthm s chosen. In summary, the method of trajectory optmzaton, whch depends on skd marks and scene of accdent feld, s actually acheved by usng the aforesad momentum-based technque. 2.2 Injury Smulaton The mult-body dynamcs method s ntroduced usng MADYMO, one of the most advanced computatonal solutons n the world. The dynamcs response of complex mult-body systems can be smulated. A mult-body system generally conssts of rgd and flexble bodes joned together by knematc jonts (e.g., revolute or translatonal jonts) or force elements (e.g., sprngs and dampers), and the presence of these knematc jonts s defned by means of global and local coordnate reference systems n such a model (Fg.2 (a)). It s suffcently flexble to construct a mult-body model of human body or vehcle wth varous knematc jonts and dscrete bodes of partcular sze and shape (Fg.2 (b)) [7]. Whle MADYMO (Mathematcal Dynamc Model) MADYMO s the world-wde standard for occupant safety analyss and s routnely used by the automotve, avaton, and government ndustres, as well as academc nsttutons, for conductng research on njury bomechancs, our studes focus on ts applcatons n vehcles, motorcycles and bcycles. Ths software uses numercal algorthms (e.g., modfed Euler or Runge-Kutta) to predct the moton of systems of bodes connected by knematc jonts, based on ntal condtons and the nertal propertes of the bodes. Because MADYMO allows ISSN: Issue 5, Volume 10, May 2011

5 us to quantfy dverse loadng condtons to the body through the use of ther famly of valdated crash test dummes and human models, such analyses were performed and the results were nterpreted n an appled, scentfc manor n our study. Furthermore, MADYMO has a database of human body models developed by TNO (Netherlands Organsaton for Appled Scence Research) and EEVC (European Expermental Vehcles Commttee) nclude Hybrd III dummy and human models n ths software, whch s very sutable for reconstructng accdents nvolvng humans. Besdes, these human models are avalable to smulate human body njures n varous knds of accdents. The consderatons of human knematcs n accdent should be dvded nto two parts: vehclevehcle contacts and human nvolved contacts. In order to analyze human knematcs and ts nteracton wth envronment, 3D mult-body models of vehcle together wth humans and the ground n the accdents should be establshed. These mult-body models are composed of ellpsods and rgd bodes. The outer surfaces of vehcles and human bodes are descrbed usng planes, cylnders, elastc ellpsods and facet surfaces. The ellpsodto-ellpsod and ellpsod-to-plane contact algorthms are used to calculate the nteractons between human models and envronments apart from those between vehcles and roads. As shown n Fg. 3, the moton of vehcle can be defned by the locaton of orgn and the orentaton of the local CS (coordnate system) relatve to the ground reference space CS by specfyng the X, Y and Z components. A planar jont, of whch descrbe the 2D moton of vehcle C.G. wth 2 translatonal DOFs and the yaw moton wth one rotatonal DOF, s used to connect these two CS together. (a) (b) Fg.2 The mult-body system of bodes connected by knematc jonts Fg.3 Two coordnate systems Translatonal moton and yaw rotaton acceleraton derved from vehcle crash smulaton are used as nputs for smulatons of human knematcs. Because the aforementoned momentum-based method consders the exchange of the mpact forces between vehcles occurrng wthn an nfnte small tme, the nputs can t provde the tme hstory sgnal n the mpact phase. In order to re-create the equvalent acceleraton nstead of the actual acceleraton, momentum exchange tme s ntroduced to descrbe the wdth of the equvalent rectangular mpulse sgnal. The equvalent acceleraton s equal to the mpulse dvded by the momentum exchange tme. An = N ( m t) (8) At = T ( m t) (9) Generally, the total momentum exchange tme n a real world collson s 40~80 ms. Therefore, t s necessary to prove the feasblty of the above smplfcaton for forensc applcaton [8-11]. 3 Real-world Accdent Applcaton A method of combnng the trajectores optmzaton method and the mult-body dynamcs method was presented to reconstruct human body knematcs. Ths method can be appled to answer the queston what are the ntal speeds and orentatons of ISSN: Issue 5, Volume 10, May 2011

6 vehcles n the traffc accdents. In ths paper, the knematcs of the dummes n the smulaton was comparable wth that n the real-world case n terms of restng postons, human body njures, and mpact locatons. The error resultng from momentum exchange tme s unavodable due to the lmt of the couplng method. Ths study had tred to estmate the effect of momentum exchange tme n a real-world accdent reconstructon. The study showed the relablty of the concluson could be valdated wthn a reasonable range of momentum exchange tme, whch s very helpful for forensc applcaton. Comparng wth legal medcal report and other nformaton, the feasblty of ths concluson was reasonably proved. Furthermore, by evaluatng the ntegral smulaton results of collson wth respect to realtes, the relablty of applcaton wth the couplng method was fully confrmed. rght occptal regon, hematomas on the left thorax and medal sde of rght femur and abrasons on the left sde of the head. The fatal njury was bran contuson. Besdes, there was no fracture n hs extremtes of lmbs. Fg.5 Accdent scene 3.1 Bref Introduce and the Smulaton Model of Case 1 A Volvo publc bus was eastbound whzzng through an ntersecton on an Aprl mornng, when there was a young man, who had got strke by the vehcle, southbound tryng to walk across the street just on the east of crosswalk, all of a sudden. The bus smashed nto pedestran at the surface of rght front corner. And then the pedestran was knocked down on the road and ded at the scene. Accordng to the scene nvestgaton, t was on a dry and sunny mornng, and asphalt was used for makng the road surface. The rest postons of the pedestran and the bus are shown n the post accdent scene map, as shown n Fg. 4 and Fg. 5. Also, two long skd marks of front wheels were found on the road. No serous damage was found on the vehcle of accdent except that the glass near the lower rght corner of the wndsheld cracked, as shown n Fg.6. Fg.4 After-accdent stuaton map The vctm was male, 20, 175 cm n heght, about 70 kg n weght, whch s almost lke the 50th human model provded n software MADYMO. Detaled clncal examnaton of the vctm revealed that the accdent manly resulted n mpact over the Fg.6 Vehcle damages The above post accdent data from nvestgatons ndcate that the left sde of the pedestran was struck by the rght left corner of the bus. Then, hs head ht the wndscreen and the thorax contacted the front hood. Because pedestran was always shot along the orgnal drecton of the vehcle and then turned toward ground n the flat-front vehcle accdent, the contact wth the ground s beleved to be the cause of the bruses on vctm rght occput. In ths case, the mpact speed s an unknown prmary parameter of nterest. Accordng to the accdent data and the wtness, the bus s estmated to launch an emergency brake just before the mpact. There are some other ntal condtons that can be obtaned from the accdent data, for example the orentaton of the pedestran, pedestran walkng speed, and pedestran stance pror the mpact. Therefore, the objectve of the accdent reconstructon s to fnd the optmum value of vehcle mpact speed, whch can help to reproduce the mpact locaton and pedestran njures by multbody smulaton. The reconstructon of the vehcle-pedestran accdent s performed wth mult-body dynamc smulaton software MADYMO. MB models of full ISSN: Issue 5, Volume 10, May 2011

7 crash feld are developed for the case, ncludng pedestran, vehcle and ground. The vehcle model has only a translatonal DOF n the drecton of straghtforward moton. Its outer surfaces of vehcle front hoods are generated by rgd fnte element mesh, whch are fxed on a rgd body presentng the total mass of the vehcle. Ths rgd mesh can not only allow for relatve quck computaton but provde a detaled stffness descrpton of geometrcally contact. The contact characterstcs of the front of bus are estmated from publc lteratures. The 50th TNO pedestran model s used to smulate the vctm n ths case. Before smulaton, n order to reproduce the njures and the vehcle damage correspondng well wth the scene data, the dummy s postoned for mpact on the left sde of hs body. The dummy remans n a walkng posture wth the mpacted secton to the foremost poston and the arms n a natural stance. Also, the pedestran s gven an ntal velocty of 1m/s. A frcton coeffcent s appled to pedestran-to-vehcle contact at 0.3 and pedestran to ground contact at 0.7. The vehcle s assumed to have a deceleraton of 0.7g when brakng on the dry asphalt road. 3.2 Bref Introduce and the Smulaton Model of Case 2 An IVECO bus was turnng left on a suburb concrete road, on a dry and sunny mornng n September. Because of the vson blockage resulted from road curve, the bus entered opposte lane and collded wth a FAW heavy truck comng aganst t. The rest postons of both vehcles are shown n the after accdent stuaton map. Accordng to the skd marks, the truck drve had braked before mpact. After the collson, the truck pushed the bus back for about 1.2m. The expert examnaton of the vehcles after the accdent showed that the two vehcles had collded head-on wth each of ther front left parts. The frontal coverage of the truck amounted to about 1.4m (total vehcle wdth 2.5 m). Longtudnal deformaton of the front axs of the truck amounted to about 40cm. The IVECO bus was severely damaged over ts entre front porton, more severely on the drver s sde. Longtudnal deformaton of the bus s about 4 m (total vehcle length 6 m). In ths case, there are one and twenty occupants n the truck and the bus, respectvely. As result of the crash, one occupant n the truck and seven occupants n the bus ded on the accdent scene. None of the passengers on the bus was wearng a seatbelt except the drver. Accordng to the vdeo montor recordng by the polce, the truck s speed pror to the mpact s about 52 km/h and ts brakng condton s known. So, the task of the reconstructon s to estmate the speed of the bus before mpact. Based on mult-body dynamc method, the combnaton of two scaled smulaton model s appled to ths case: vehcle-vehcle mpact model and vehcle nteror-occupant mpact model. The outputs of the latter model, ncludng occupant knematcs and njures, are used to valdate the results from the vehcle-vehcle mpact model. Frstly, n vehcle-vehcle mpact smulaton, the movements of the two vehcles are analyzed n PC- Crash. Then, usng MADYMO, the crash dynamcs of vehcles from PC-Crash are used as nputs for occupant knematcs smulaton. The models of vehcle-vehcle mpact smulaton are avalable from vehcle database n PC-Crash. Its stffness based mpact model s used whch provdes lnear stffness functon for calculatng the contact forces between two vehcles. The outer geometry of the vehcles s presented by 3D DXF vehcle shape, whch s very useful for calculatng the locaton and drecton of contact force. The occupant sttng at the rght-most seat of the second last row sustaned the fracture of lumbar spne. Because the vehcle nteror space around ths seat s almost undamaged, the lumbar spne force of the above occupant s selected as the reference for valdatng the mpact speed n occupant knematcs smulaton. The MB model of the occupant and the vehcle nteror are showed n Fg.7. Fg.7 Occupant and vehcle nteror model n MADYMO The model of the vehcle nteror s made of several ellpsods, ncludng the seats and the floor. A TNO 50th percentle facet occupant model s used. The outer surface of the facet occupant model s descrbed by about 2000 trangular elements connectng about 1000 nodes defned as a null materal. In ths model, the vertebrae of lumbar, thoracc and cervcal spne are generated by rgd bodes connected by free jonts wth lumped jont ISSN: Issue 5, Volume 10, May 2011

8 restrant model, of whch the geometres are each descrbed by a sngle ellpsod. ELLIPSOID-FE contact s used to smulate vehcle nteror-occupant nteracton. The contact stffness characterstcs are referred to the relatve research. 3.3 Injury Analyss of the Two Case Case 1 The mpact velocty s calculated to be 29 km/h. Fg.8 shows that the reconstructon results correspond well wth the accdent data n terms of mpact pont and rest poston. (e) t=400ms (a) t=20ms (f) t=2000ms Fg.8 Reconstructon results Also, some pedestran njury outcomes are lsted n Table 1 and shown n Fg.9 and 10. The njury crtera used n ths case nclude HIC36, ASA20, max shear force and max lateral torque of rght lower extremty. (b) t=50ms Fg.9 Lateral torque of left lower extremty (c) t=100ms (d) t=300ms Fg.10 Shear force of left lower extremty ISSN: Issue 5, Volume 10, May 2011

9 Table 1 Pedestran njury analyss of Case 1 Body regon Autopsy results Injury crteron value Tolerance level Head Fatal njury HIC36= , 50% prob. of AIS 3+ Chest No serous njury VC=0.1m/s 1m/s, 50% prob. of AIS 3+ ASA20=2.3g 46g, 50% prob. of AIS 3+ Left upper leg No fracture max lateral torque 195Nm 430Nm, 50% prob. of fracture max shear force 2340N 6300N, 50% prob. of fracture Left lower leg No fracture max lateral torque 200Nm 285Nm, 50% prob. of fracture max shear force 2040N 4000N, 50% prob. of fracture Case 2 Wth the above-mentoned known condtons, PC-Crash optmzes vehcle speed based on both vehcles ntermedate and rest postons and rotatons. The mpact velocty of the truck and the bus were calculated to be 25 and 50 km/h, respectvely. The truck s velocty before brakng s 62 km/h. The total trajectory of two vehcles s shown n Fg.11. (b) t=100 ms Fg.12 Movement of the occupant at 0, 50, 100 ms after mpact Fg.11 Calculated trajectory of the two vehcles The lnear acceleraton and angular velocty of the bus C.G. are outputted for the next smulaton. Then, the occupant knematcs s calculated as shown n Fg.12 and 13. Accordng to these results, the lumbar spne manly sustaned compress force durng the accdent. The max axal force between the 2nd and 3rd lumbar vertebra (Fg.14) exceeds the tolerance level 2kN from some prevous research. So, the smulaton corresponds well wth the fact that the occupant sustaned the fracture of lumbar spne. Fg.13 Status of the spnes at 100 ms after mpact Fg.14 Axal Lumbar force durng the accdent (a) t=50 ms 4 Concluson The analyss ndcates that the selectve applcaton of mult-body dynamcs smulatons and the ISSN: Issue 5, Volume 10, May 2011

10 combnaton of usng both mult-body dynamcs modelng and trajectory optmzaton s an effectve method for reconstructng real-lfe bus-nvolved traffc accdents. The results concde well wth the records provded by traffc polce and the conclusons of nvestgatons gven by legal medcal experts n the terms of vehcle skd length, estmated vehcle trajectory durng crash, vehcle stop state after collson and parameters of body njures. The methods appled n the research, whch ntegrate the trajectory optmzaton nto mult-body dynamcs analyss, prove to be effcent and effectve n the reconstructons of bus accdents due to the reducton of tme cost and more accurate smulaton results correspondng to the practcal stuaton of the accdent scene. The results of the current study also show that the vctm s njury parameters can be ntroduced to assst n verfyng the mult-body dynamcs and trajectory optmzaton as feedback. Prelmnary works shows that some mprovements need to be made to these models n order to mprove the accuracy of the smulatons by substtutng well-shaped fnte element models of some parts of the nteror ornaments for mult-body ones. The study presented n ths paper can also be developed as a helpful approach n desgnng the nteror decoratons of vehcles for occupant safety n the future. In summary, the real-lfe bus accdent has been nvestgated n ths study. And we successfully extend a collecton of selectve combned methods nto the feld of the road traffc accdent nvolvng bus mpact n the research. Further more, the man dsadvantage of usng a sngle Mult-body dynamcs analyss s that there perhaps exst varetes of possbltes that common sngle method can not dstngush one from another on the ground of the lack of condton lmts of smulatons. However, f evaluatons of vctm njury parameters and trajectory optmzaton can be ncorporated nto the orgnal Mult-body dynamcs analyss, the results of smulatons wll be more accurate and relable. Acknowledgements The authors gratefully acknowledge the support from the Natonal Natural Scence Foundaton of Chna (No , , ). References: [1] Zhang X Y, Jn X L and Q W G. Vehcle Crash Accdent Reconstructon Based on the Analyss 3-D Deformaton of the Auto-body. Advanced n Engneerng Software, Vol.39, No.6, 2008, pp [2] Zhang X Y, Jn X L and L Y Y. Improved Desgn of the Man Energy Absorbng Automotve Parts Based on Traffc Accdent Analyss. Materal & Desgn, Vol. 29, No.2, 2008, pp [3] Zhang X Y, Jn X L and Q W G. Parallel Computng wth Doman Decomposton for the Vehcle Crashworthness Smulaton. Vehcle System Dynamcs, Vol.45, No.11, 2007, pp [4] Stephan H, Moser A. Accdent reconstructon methods. Vehcle System Dynamcs, Vol. 47, No.8, 2009, pp [5] Steffan H. Pc-Crash Techncal Manual verson 6.2, Lnz, Austra, [6] Moser A, Steffan H. Automatc optmzaton of pre-mpact parameters usng post-mpact trajectores and rest postons. SAE paper980373, [7] TNO. Madymo utltes manual verson 6.2, Delft, Netherlands, [8] Shen J, Jn X L, Zhang X Y. Smulated Evaluaton of Pedestran Safety for Flat-front Vehcle. Internatonal Journal of Crashworthness, Vol. 13, No.3, 2008, pp [9] Guo L, Jn X L, Zhang X Y. Study of njures combnng computer smulaton n motorcyclecar collson accdents. Forensc Scence Internatonal, Vol. 177, No.2-3, 2008, pp [10] Shen J, Jn X L. Improvement n numercal reconstructon for vehcle pedestran accdents. Proceedngs of the Insttuton of Mechancal Engneerng, Part D: Journal of Auto moble Engneerng, Vol. 222, No. 1, 2008, pp [11] Shen J, Jn X L. Reconstructon of pedestranvehcle accdent usng sequental lnear programmng optmzer. Internatonal Journal of Crashworthness, Vol. 12, No. 6, 2007, pp ISSN: Issue 5, Volume 10, May 2011