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1Technical Report #3

The U.S. Federal Government and private companies have sponsored extensive research to develop, validateand apply human models which can be used to aid in the design of safety features for crash impact protection.The ATB/CVS (Articulated Total Body/Crash Victim Simulator) program has been developed by the Departmentof Defense and the Department of Transportation for the purpose of simulating motor vehicle occupants in acrash, and air crew during escape from aircraft. However, the program can be used to simulate the dynamics ofmany other systems of linked masses. The capabilities of the program includes the representation of safetycomponents including air bags, safety belts, and energy absorbing surfaces. This report addresses the applicationof the ATB program to wheelchair restraint and covers the features and operation of the program. Input data fora validated wheelchair/occupant model in a frontal crash is contained within the report. The model employs aHybrid III anthropometric test dummy seated in the ISO/SAE surrogate wheelchair, which is secured using a 4-point belt tie-down system.

ABSTRACT

RERC on Wheelchair Technology2

INTRODUCTION

A principal impetus for the development ofhuman mathematical models has been to simulate thedynamic response of a vehicle occupant in a crash. TheU. S. Federal Government and private companies havesponsored extensive research to develop, validate andapply human models which can be used to aid in thedesign of safety features for impact protection.

The ATB/CVS (Articulated Total Body/CrashVictim Simulator) program has been developed by theDepartment of Defense and the Department ofTransportation in the United States. The principalpurpose of the program is to simulate motor vehicleoccupants in a crash, and air crew during escape fromaircraft. However, the program can be used to simulatethe dynamics of many other systems of linked masses.

The ATB program is used to create lumped massmodels for simulating the three dimensional motionof sets of connected or disjointed rigid elements. Theprogram uses a hybrid analytical formulation based onNewton’s equations of motion with constraints, but alsoincludes compatibility relationships based on Newton’sthird law. The various body segments are representedby lumped mass elements connected by joints. Eachrigid element is assigned the mass and inertialproperties of the equivalent body segment. The bodysegments are visually represented by ellipsoids whichare also the contact surfaces which demarcate the forceinteractions with the surrounding environment. Theprogram can handle up to 60 segments.

The program incorporates a variety of alternativesfor linking body masses to represent humans or crashdummies. The organizations that distribute theprogram have validated data sets for the crashdummies commonly used in testing.

The capabilities of the program include therepresentation of safety components such as air bags,safety belts, and energy absorbing surfaces. Theaccurate representation of these safety componentsrequires component testing, model validation andexperience.

ATB program version VI-4, released in January1994 by the Armstrong Aerospace Medical ResearchLaboratory, is the current evolution of the Calspan 3-Dmodel and the Crash Victim Simulator Model (CVS)which was initially developed by the Department ofTransportation. These programs have been in use since1970. The source code for the program has beenpublished and is available on disk. ATB version IV-4runs on a 486 PC or workstation. A typical simulationof a frontal crash takes less than 10 minutes.

The development and application of the programis well documented by government reports [1,2,3].

FEATURES OF THE ATB PROGRAM

The ATB program applies Newton’s laws ofmotion to chains of masses linked by joints (i.e., thedummy) which are in a reference frame (i.e., the vehicle)subjected to acceleration. The masses are influencedby forces applied by contacts with the environment(e.g., vehicle surfaces, belts, air bags.)

A typical dummy, made up of 17 segments andconnected by 16 joints, is shown in Figure 1. Thesegments are assigned mass and inertial properties,based on the equivalent body component. These bodysegments are visually represented by ellipsoids, whichalso serve as contact surfaces.

The alternatives for joining segments are depictedin Figure 2. The joints are defined in such a way thatthey can be represented as follows: locked joint; singlepin; a combination of pins connected together (Eulerjoint); ball and socket joint; slip joint (linear motionalong one axis); null joint (allows multiple dummiesor unconnected masses to be simulated.)

The torque characteristics of the joints are specifiedby functions of the character shown in Figure 3. Fiveparameters are used in the specification: the joint stopangle, the energy dissipation function, and the linear,square, and cubic torque coefficients. In addition,friction and damping can be specified. Recentimprovements in joint specification, permit therestoring torque to be specified by contours on aspherical joint surface.

Planes are commonly used to represent vehiclesurfaces. The planes are defined by three pointsspecified relative to a reference coordinate system. Theorder of specifying these points is shown in Figure 4.This figure shows that the coordinates of the points arespecified in order P1, P2, P3. When the right hand ruleis applied, rotating P2 toward P3, the thumb shouldpoint toward the contacting ellipsoid.

External forces are applied to the body surfacesby contacts with planes, ellipsoids and hyperellipsoidswhich represent external surfaces. Planes, specified bythree coordinate points, are commonly used torepresent contact surfaces. The method for determiningthe magnitude, direction and location of ellipsoid toplane contact forces is illustrated in Figure 5. Aperpendicular from the plane to the point of maximumpenetration of the ellipsoid defines the penetrationfunction “d”. This “d” function is used to calculate thenormal and frictional forces, based on force and


displacement relationships provided in the input dataset. The point of application can be specified at theellipse center (point 1), the point of maximumpenetration (point 0), or anywhere in between. T h efunctions for energy dissipation and permanentdeformation are based on “d” and its rate of change.Alternatively, hysteresis can be specified by “R” and“G” factors which produce penetration dependentunloading and reloading characteristics. Friction forcesare applied at the same point as the contact force, butparrallel to the contact surface. Its magnidude isdetermined by the coefficient of friction. The contactforce relationships can be specified as constants,polynomials, tabular data, or combinations of the three.

Narrow contact surfaces offer special problemswhen the perpendicular to the maximum penetrationpoint of the ellipse falls outside the contact plane. Thisproblem can be addressed by using an alternative“edge effects” calculation provided by the program orby representing the contact plane with an ellipsoid orhyperellipsoid.

The relationship between “d” and force can bespecified for each allowed contact between an ellipseand a plane, as shown in Figure 6. In addition, threeother parameters can be specified: an inertia spike(which simulates breaking glass), an energy absorbingfunction (R), and a permanent deformation function(G). R and G are defined in Figure 6.

The belt system, shown in Figure 7, is representedby a stretched string which contacts a series of pointson the surface of one or more body segment ellipsoid.For the simplest case (Seat Belt Routine) these pointsare rigidly attached to the body segment ellipsoid. Forthe more general case (Harness Belt Routine) the pointsmove across the surface as determined by anchorlocation, belt tension, belt physical properties, and thelongitudinal and transverse friction coefficient. The beltmay penetrate the body surface, based on the physicalproperties of the body segment ellipsoid. At thebeginning of the simulation, the algorithm simulatesstretching a string between the anchor points and acrossthe ellipsoids. Points in contact with body segmentsare moved to the surface of the segment. Those pointswhich cause the belt to kink are dropped. The algorithmmoves points across the surface, as the simulationprogresses. The point locations are determined byobtaining equilibrium in the stretched string. The pointlocations are recalculated at each iteration, and movedto maintain force equilibrium along the stretched belt.

The basic air bag system is represented by anellipsoid anchored to a reaction surface. The basemodel is a stored gas inflator and an air bag withventing.

A number of special features are included in theprogram to address anticipated requirements of users.These include the following:• Tension element - allows the transmission of

tension only - to simulate muscle,• Flexible element - to simulate neck and spine

elements,• Slip joint - to simulate elements like steering

columns,• Spring-damper element - to simulate alternative

connections,• Wind force application - to simulate aircraft

ejections,• Force and torque application - to permit a time

dependent force or torque to be applied to anyelement,

• Roll-slide friction constraints - to simulate stick-roll motion.

The motion of the vehicle and of individualsegments may be specified in terms of three linear andthree angular displacements, velocities or accelerationswith respect to time. The specification may be eitherwith respect to the inertial axis or to any other segmentwhich has specified motion. This capability is usefulfor simulating vehicle intrusion. Up to nine segmentscan have specified motion.

Figure 8 shows three different coordinate systemsused by the program. A right hand coordinate systemis used in which the Z axis is positive downward. TheX axis is positive forward, and the Y axis is positive tothe right. The acceleration and motion of the vehicleare specified relative to an inertial coordinate system.In general, the vehicle and inertial coordinate systemcoincide at time zero. Each segment has a localcoordinate system with the origin located at the centerof the segment ellipsoid.

The program requires an input data set whichspecifies the human model properties; the motionenvironment; the planes, belts, and air bags whichconstrain the human; the properties of the contacts;the contacts allowed; the initial conditions; and theoutputs desired. The outputs are in three forms -tabular data in ASCII format at specified time steps,binary data at all time steps, and dummy position datasuitable for drawing pictures using the VIEWpostprocessor. Tabular outputs may be obtained forthe time history of linear and angular acceleration,velocity, and accelerations for any specified point onany segment, and all contact, belt and air bag forces.The VIEW postprocessor offers pictures at specifiedtime steps, as shown in Figure 8.

A commercially developed program calledDYNAMAN is based on the ATB program, but offers


enhancements, particularly in ease of use. TheDYNAMAN program contains a preprocessor whichgreatly simplifies the development and modificationof data sets. This preprocessor allows the user to viewthe configuration of the vehicle, dummy, and restraintsystems as the modifications are made. The capabilityincludes routines for positioning the dummy inequilibrium, and for plotting the crash pulse and forcedeformation functions. The postprocessor providestables and graphs of the time history of any of theoutput variables. Pictures and/or animations ofoccupant position with respect to time are also availablefrom the postprocessor. The processor permitsinteractive translation, rotation or zooming of eachimage.

Other enhancements offered by DYNAMANinclude belt retractors with pretensioning, air bag shapeconsisting of both cylindrical and ellipsoidal geometriesthat expand during inflation, and air bag inflation rateswhich can be specified from test data. The forcedeformation functions have additional flexibility,permitting the force to be distributed in the contact area,and allowing individual, rather than combined contactproperties.

The DYNAMAN model is available for PC orwork station. The current version is 3.0, releasedFebruary 1993 [4].

DUMMY DATA FOR THE ATB PROGRAM

For frontal crash simulations, the 50% male HybridIII dummy is normally used. A 50% male Hybrid IIIdummy has been measured for mass, inertial and jointproperties by the Armstrong Aerospace MedicalResearch Laboratory [5]. Based on these measurements,a data set for the ATB program was developed. Thedata set used sophisticated joints which permitted thetorque to vary with azimuth and pitch angles. Theresulting dummy had good inertial and joint biofidelity.However, the shoulder surface did not provide arealistic shape for simulating shoulder belt contact. Thiswas initially corrected by adding a shoulder contactellipse to the upper torso. This additional contactellipse was not plotted by the VIEWII program.Consequently, visualization of the belt interaction wasnot precise. The Hybrid III dummy compiled by theAir Force is shown in Figure 1.

Under a grant from the Centers for DiseaseControl, The University of Virginia modified the AirForce Hybrid III Dummy so that the shoulder ellipsoidwas included as a linked body segment. As aconsequence, the shoulder is visible in the VIEWII plots.The resulting dummy, shown in Figure 9, has 18segments and 17 joints. The joint between the shoulder

and upper torso is locked, so the two segments movetogether, as they do in the Air Force version. The dataset was validated through sled tests using a Hybrid IIIdummy restrained by a three point belt in crashes at 30mph [6]. This dummy data set is designated the CDC/UVA Hybrid III Dummy. Continued research fundedby the National Institute for Disabilities andRehabilitation Research resulted in a validated dummyfor use in a surrogate wheelchair described in ISO draftstandard 10542 for Wheelchair Tie-downs andOccupant Restraints [7]. The data set is referred to asthe NIDRR/UVA Dummy. This dummy uses simplerjoint functions than used in the Air Force Hybrid IIIDummy.

Data sets for smaller and larger dummies can beobtained by using a program named GEBOD. Thisprogram provides data in the input format suitable forinclusion in ATB. The dummy properties are scaled,based on input specifications of height, weight, orpopulation percentile.

ATB PROGRAM OPERATION

The operational configuration of the CVS/ATBProgram is outlined in Figure 10. The ATB44 SimulationProgram is shown in the central block of Figure 10. Theprogram requires an input data set and provides threeoutput data sets. These data sets are identified by theirextension as follows:• .AIN Input file (Unit 5),• .AOU Main output tabular file (ASCII)

(Unit 6),• .TP1 Output for VIEW pictures (ASCII)

(Unit 1),• .TP8 Output for plots and tables (BINARY)

(Unit 8).

It is also possible to separate the data for each ofthe output variables into separate tabular files. Whenthis option is exercised the files carry sequentialextensions; .T21; .T22; .T23;.....Tmn. Other output filesare possible, but not commonly used. See the User’sGuide for the complete documentation of the files.

Output files .TP1 and .TP8 both requirepostprocessors to provide pictures, animation, tablesand graphs. The postprocessor which comes with theprogram is VIEWII, which draws the pictures of thevehicle planes and body segments at each specified timestep. The output data from the .AOU file is formattedtabular ASCII data and can be viewed with a text editorand printed.

To initiate the program follow these steps:• To run the ATB program, version IV4, type

ATBIV4.


• At the first prompt, provide the prefix ofthe .AIN data file.

• At the second prompt provide the prefixdesired for the output files. (It may be thesame as the prefix for the .AIN file.) Adiagnostic file is assigned the same prefixas the .VIN file, and an extension of .VOU.

The VIEWII program provides pictures on thecomputer monitor of the occupant, the safety belts andair bags, and the vehicle at specified time steps. Thesepictures may then be printed using <Print Screen> ormay be stored using a commercially available screengrabber. The stored pictures can be used for animationusing commercially available software.

VIEWII requires two input data files - the .TP1 file,and the .VIN file. The .TP1 file is generated as an outputfrom the ATB program. It is a file in ASCII format whichcontains data for drawing the segments and belts ateach specified time step. The frequency of time stepsavailable in this file is determined by the ATB program.AIN data set. Field NPTR 1 in CARD A.5 determinesthe frequency at which picture files are available in the.TP1 file (see Input Data section for explanation of dataCARD.)

The .VIN file specifies the size, orientation, andcolor of the dummy segments and vehicle planes. Aninput data guide and sample .VIN files, which producepictures for ATB inputs RCRASH.AIN and WC1.AIN,are contained in Appendix C.

To run the post processor, follow these steps:• To run the VIEWII postprocessor, type

VIEWII• At the first prompt, provide the prefixof

the .TP1 file.• At the second prompt, provide the

prefix of the .VIN file.• When the processing is complete, press

<Enter> to view the pictures in sequence.

INPUT DATA FOR ATBIV4

REAR CRASH MODEL RCRASH.AINThe file RCRASH.AIN is contained in Appendix

A. This file illustrates the essential features of an inputdata set for ATBIV4. The data set is organized in 8sections labeled A through H, as described in Figure11. The first section is the A CARDS, which deals withrun control. In the A CARDS, there are several dataelements which are frequently changed by the user.

Space in line A.1a allows the date of the run to bemanually documented. The A.1b and A.1c CARDS

provide two lines of 80 characters for a description ofthe run. The A.4 CARD contains parameters whichcontrol the integration steps and total time duration ofthe run. Referring to the example case, the A.4 cardcontains the numbers; 6 32 .005 .00025 .001 .000125.The number 32 specifies the number of time steps and.005 specifies the duration of the integration time steps(seconds). The product of these two is the length ofthe run - 160 milliseconds for this case. Data will bewritten to the .AOU file at each time step. The integratormay increase or decrease the time step to improveefficiency and accuracy. The number .00025 is the initialintegrator step size. The max and min time steps are.001 and .000125 respectively. The number 6 is thenumber of iterations for the final convergence test ofthe integrator. In general, the only change needed isthe number of time steps, in order to increase ordecrease the duration of the simulation.

Line A.5 contains an array of 36 two digit integers,called NPRT, which controls the output data and files.Only a few are of interest to most simulations. Thefirst four numbers are:2 0 10 2. The first 2 (NPRT 1) specifies the frequencyof output to the .TP1 file. In this case, data for VIEWIIpictures will be saved at each 10 milliseconds. Thenumber 10 (NPRT 3) specifies the frequency that datadealing with integration and convergence will be sentto the .AOU file. NPRT 4 specifies the kind of outputdesired. The number 2 at NPRT 4 provides the data inthe .AOU file. If individual files (.Tnm) of tabular dataare desired as well, use the number 4. See the InputData Manual for all options.

The B CARDS deal with the dummy. Data forvarious dummies has been developed and validatedby others. Validated data sets should be used wherepossible. For the example case, a Hybrid III dummy isused.

The C CARDS specify the acceleration time historyof vehicle crash. Line C.1 provides 80 characters todescribe the crash. Line C.2 contains the followingnumbers: 180. 0. 0. 0. 176. 0.09. For this case, theacceleration has the characteristics of a half sine wave.The direction of the crash pulse is rearward (180degrees), as specified by the first number. The initialvelocity is 176 inches/sec, and the duration of the pulseis .09 seconds. The crash pulse simulates a rear impactwith a 10 mph change in velocity.

The D CARDS specify the contact surfaces on thevehicle. A number of other features, including belts,air bags, and restraining elements can also be specifiedhere. In the example, three planes are specified. Thenumber 3 in line D.1 specifies that three planes will bedefined. The number 6 in line D.1 deals with Hybrid


III dummy data. It indicates that six functions whichdescribe Hybrid III joint torque will be included in theE.7 CARDS.

The three planes are defined in a series of threeD.2 CARDS. The first line of each D.2 CARD containsthe plane number and a 20 character descriptor of theplane. Each plane is then specified by three coordinatepoints, measured relative to the vehicle to which theplane is attached. For the example case, the origin ofthe vehicle coordinate system is at the center of the frontedge of the floorboard. The D.7 CARD is alwaysrequired, even if all values are zero. Non-zero valuesallow motion to be restricted. The positions of thevehicle planes are shown in Figure 12.

The E CARDS provide a library of force deflectionfunctions and coefficients to specify interactionsbetween body segments and contact planes. The firstin the example is the Seat Cushion Force-DeformationFunction. The first line in E.1 provides a functionnumber and a 20 character title. The second linecontains a -6. The negative number signifies thattabular data will be provided to describe the function.The numerical value (6) specifies the maximum valueof the deformation. The third line contains a 9, whichspecifies 9 data points. The following three linescontain the following nine data points: 0.0,0.0 0.5,341.0,62 1.5,87 2.0,105 3.0,110 4.0,125 5.0,150 6.0,1000.It should be noted that if the deformation exceeds 6.0inches, the function will remain constant at 1000. TheE CARDS can also be used to specify constants. TheSeat Cush R (Function 11) is constant at a value of 0.625.Functions 12 through 35 values are also constants.

Up to 50 functions can be included in the E.1CARDS. They serve as a library, and not all of themhave to be used by any given simulation. The end ofthe E.1 CARDS is demarcated by an integer greater than50. In the example, the number 999 marks the end ofthe E.1 CARDS.

The E.7 CARDS, like the E.1 CARDS, provide alibrary of functions. In the example, six joint functionswhich can be used to describe the joints in the HybridIII dummy are included as functions 41 through 46.

The F CARDS specify the contact interactionswhich are allowed. Line F.1 specifies the number ofcontacts which are provided for each plane. A total ofnine contacts are specified. The following nine linescontain ten numbers which describe the properties ofthe interactions. The ten numbers in the first linedesignate the following:

1-Specification for contact with Plane 1 (Seat Cushion)1-Plane 1 is attached to segment 19 (Vehicle)

1-Specification for contact with Segment 1 (Lower Torso)1-Specification for contact with Surface 1 (Lower Torso)1-Apply Force Deformation Function 1 (SEAT CUSH FDF)0-Apply no inertia spike11-Apply R Function 11 (SEAT CUSH R)21-Apply G Function 21 (SEAT CUSH G)31-Apply Coefficient of Friction Function 31 (SEAT CUSH CF)0-Apply no edge effects correction

The above numbers specify the interactionbetween the dummy lower torso, and the seat cushion.It is possible to attach multiple contact surfaces to abody segment. In this case, the contact surface and thesegment surface for the lower torso are identical.

The vehicle segment is automatically assigned anumber of one greater than the number of segmentson CARD B.1. In this case segment 19 is the vehicle.Segment 19 undergoes the motion which is specifiedin the C CARDS.

The F.1 Table provides for contacts of the lowertorso and upper legs with the seat cushion, the fourbody trunk segments with the seat back, and the feetwith the floorboard. The F.3 and F.4 lines are alwaysrequired, even when zero. The F.3 CARD is similar tothe F.2 CARD but it is for segment-to-segment contacts.The F.4 CARD provides information on special joints.The F.5 CARD provides information on which jointfunctions are to be applied to which joints on the HybridIII dummy.

The G CARDS provide the initial position of thedummy. Line G.1 provides information for specifyinginitial velocity of segments which is different fromvehicle velocity. Line G.2 specifies the coordinates ofthe dummy lower torso at time zero. Lines G.3 specifythe yaw, pitch and roll angles of the dummy segmentsat time zero. The pitch angles in the table provide aseated dummy, as shown in Figure 12.

The H CARDS specify the output data desired.H.1 provides linear acceleration. In the example, thenumber 4 indicates that 4 different accelerations aredesired. The segments requested are 1, 3, 6 and 19(lower torso, upper torso,head, and vehicle.) CARDSH.2 and H.3 provide similar data on velocity anddisplacement. H.11 provides a calculation of the HeadInjury Criteria (HIC). The data elements available aredescribed in detail in the Input Data Manual.


WHEELCHAIR/OCCUPANT MODEL - WC1.AINThe Wheelchair Model introduces two additional

features into the RCRASH.AIN model. These featuresare the inclusion of belt restraints and of a wheelchair.The wheelchair is specified in the same way as adummy, but it is complicated by the presence of bothsegments and planes. The segments represent the massproperties of the body and wheels, the attachmentpoints of the tie-downs, and the contact geometry ofthe wheels. The planes represent the contact geometryof the wheelchair body surfaces.

An input file (WC1.AIN) for a wheelchairrestrained by four belt tie-downs is listed in AppendixB. A VIEWII plot of the wheelchair and dummy isshown in Figure 13. A 50% male dummy is seated inthe wheelchair and is restrained by a three point beltsystem. The 50% male dummy in this case is a variationof the dummy used in the RCRASH.AIN file. Thevariation is primarily in the joint properties. The jointproperties have been simplified and modified toprovide better agreement with test results.

In the WC1.AIN file, the A CARDS are generallysimilar to the RCRASH.AIN file. The first significantdifference comes in the B CARDS, which specifyproperties of both the 50% male dummy and thewheelchair. The B.1 line specifies 28 segments and 27joints. The first 18 segments and 17 joints specify the50% male dummy in a similar manner to theRCRASH.AIN file. Joint 18 is a null joint, which allowsthe specification of subsequent segments (thewheelchair) which are not joined to the dummy.Segments 19 and 20 specify the wheelchair body, 21through 24 the wheelchair wheels, and 25 through 28the tie-down anchor points.

The body of the chair is specified by segments 19(CHR) and 20 (CHR1). The first number in the linedesignates the weight (lbs) of the chair - in this case 1.0for CHR and 175. for CHR1. The use of two segmentsallows easy adjustment of the body geometry andinertial properties. Segment CHR adjusts the geometryand CHR1 the inertial properties and the center ofgravity.

The three numbers which follow the weight arethe principal moments of inertia (lbs-sec2-in) about thex, y, and z axes. The next three numbers are the x, y,and z semi-axes of the segment contact ellipsoid. Thefinal four numbers allow the center of the contactellipsoid to be different from the center of mass.

The initial position of the dummy and wheelchairis determined by the G.2.A CARDS. For this case, theorigin of the vehicle coordinate system is taken at the

center of the rear edge of the floorboard. The first G.2.Aline shows that the center of the dummy lower torsosegment is located 33.4 in. forward, and 22.66 in. abovethe rear edge of the floorboard. The center of wheelchairsegment CHR is located 27 inches forward and 4.99inches above the rear edge of the floorboard. Bothsegments are centered in the y direction. The locationof the origin of the vehicle and the wheelchaircoordinate systems are shown in Figure 14.

The other segments of the wheelchair are allpositioned relative to the CHR segment. The positionis specified by the joint locations in the B.3 CARDS.Joint A0 specifies the location of CHR1 relative to CHR.Segment CHR1, the 20th (J+1) segment, is connectedby A0, the 19th (Jth) joint. This relationship (J+1segment and Jth joint) is inherent in the dataspecification. The number 19 designates the segment(JNT) to which joint A0 (Jth) connects segment CHR1(J+1). In this case the designation is that segment CHR1is connected to segment CHR by Joint A0. Theremaining joints A1 through A4 (wheels) and ANC1through ANC4 (tie-down anchors) all connect to thesegment CHR.

The number -4 in the A0 row of the B.3 CARDdesignates the kind of joint. The 4 designates a Eulerjoint, and the negative sign indicates that all joints arelocked. In this case, the segment CHR and CHR1 arelocked together. For the wheels, the number 1 in thejoint type position designates a pin joint. In the eventit is desired to lock the wheels, a negative 1 can besubstituted.

The x, y, and z location of the joint on the segment19 (CHR) is specified by the numbers 7.638, 0.0, and-5.197. The three numbers which follow (all zero)designate the location of the joint on the CHR1 (J+1)segment. In this case the center of the CHR1 segmentis located 7.638 inches in front and 5.197 inches abovethe CHR segment. The other numbers in the B.3 CARDpermit specification of angular geometry.

CARDS B.4 and B.5 permit the specification of jointtorques, which are not needed for a restrainedwheelchair. CARDS B.6 provides convergence criteriafor joint torque calculations. In some cases, jointcalculations have been found to lose accuracy. Aninteger 1 in NPRT 36 (CARD A.5) employs a joint driftcorrection routine.

The contact planes for the wheelchair simulationare specified in the D CARDS. In this case 10 planesare specified in the D.1 line. The number 2 in the D.1line allows two belt systems to be specified later. Thenumber 6 is for the dummy joint property library,CARD E.7.


characteristics. The third number specifies thepreferred direction of slip. A zero indicates that thebelt may slip along the surface in any direction. For ananchor point, slip is restricted, and a non-zero integer(1) is required.

There are two ways the belt can be permitted toslip. The fourth field specifies the desired alternative.A zero number allows the belt to slip at the referencepoint. The result is that the distance between referencepoints can vary. A non-zero number (1) does not permitthe belt to slip relative to the reference points. In thiscase the distance between reference points ismaintained. In both cases, the slippage or motion overthe surface is permitted, subject to the constraintsimposed by the coefficient of friction, and the belt andsegment deformation properties.

The fifth through ninth field specify the fivesegment properties for reference point interactions.They are: force deformation, inertia spike, R, G, andfriction coefficient. Zero values for fields 5 through 8indicate a rigid segment surface. The integer valuesdesignate functions from the E.1 CARD library. Itshould be noted that friction functions can specifydifferent functions along the belt and transverse to thebelt.

The last three fields (10, 11, and 12) specify the x,y, and z coordinates of the reference point at time zero.It is important to note that these points are in thecoordinates of the segment designated in Field 1. Thefirst and ninth point are located in the vehiclecoordinate system, the second and third points are inthe Segment 4 (UT2) shoulder coordinate system, andthe remaining points are in the Segment 3 (UT1) uppertorso coordinate system. The origin of the segmentcoordinate system is at the center of mass. The pointsshould be specified so that they are approximately onthe ellipse surface. During the zero time step, theprogram adjusts the points so they lie on the surface.However, if the forces on the belt are such as to pull itaway from the surface, the point will be ignored, unlessit is a tie-point or anchor point.

The second line of the point specification containssix fields. The first three fields are used only in caseswhere a no-contact ellipsoid is associated with thereference segment. The last three fields specify thecoordinates of a vector which designates the preferreddirection of slip. This vector is required for anchorpoints and for other points which are restricted fromslipping (non-zero value in Field 3, line 1). The specifiedvector can not be parallel to the normal to the surfaceto which the reference point is attached. If it is, an errormessage advises the need to change the vector.

The floorboard contact planes, numbers 4 and 6,are attached to the vehicle, and are specified relative tothe vehicle coordinate system. All the remaining planesare attached to the wheelchair, and are specified in thewheelchair coordinate system. The origin of thewheelchair coordinate system is at the center ofsegment CHR. The location of CHR relative to thevehicle coordinate system is specified by CARD G.2.A2.

The attachment of planes to segments takes placein the F.1 CARDS. The first row of these cards specifiesthe number of contacts designated for each of the 10planes. The first and second column of the ensuingtable designates the plane and the segment to which itis attached. In this case planes 1,2,3,5,7,8,9, and 10 areconnected to segment 19 (the wheelchair). Planes 4 and6 are connected to segment 29 (the vehicle).

The occupant restraint and wheelchair tie-downsystems are specified in CARDS F.8. CARD F.8.Aindicates that the first restraint system ( occupantrestraint) has 2 belts, and the second (wheelchairtie-down) has 4 belts. CARD F.8.B designated that eachof the two belts in the occupant restraint system has 9points. The F.8.C CARD permits the specification of thebelt properties. The numbers 5, 0, 15, and 24 refer tofunctions which specify force deformation, inertiaspike, R, and G functions from the E.1 CARD library.It should be noted that the force-deformation functionis a force-strain function in the case of belts. Thenumber 0.5 refers to the initial slack (inches) in the belt.

The eighteen lines which follow the F.8.C CARDspecify the location and properties of the nine referencepoints which define the shoulder belt interaction withsegments. Each point requires two lines of data. Thefirst number (29) specifies the segment with which thepoint interacts. It is evident that the first and ninthpoint interact with the vehicle (segment 29). Thesepoints are anchor points for the ends of the belt. Thesecond and third points interact with the UT2 (segment4), the shoulder. The remaining points interact withUT1 (segment 3), the chest.

The second field in the point specification linedesignates the contact ellipsoid associated with thereference point. In most cases it is the same as thesegment ellipsoid (see the discussion for the F.1 CARDSin example RCRASH.AIN.) In the case of the first andlast points the number is zero. These two anchor pointsare associated with the vehicle which has no definedsegment ellipsoid. The zero value assigns a unit spherefor the point interaction.

The third and fourth fields in the pointspecification line provide options regarding belt slip


The second set of F.8.C CARDS provides data forthe lap belt. The second set of F.8.B CARDS specifiesthe number of points (2) for each of the four tie-downbelts. The four sets of F.8.C CARDS which followdescribe the properties of each belt and locations of itstwo anchor points.

The H CARDS are specified in the same way asfor the RCRSAH.AIN example. In CARD H.1, fourlinear acceleration outputs are designated. The secondand third fields determine the reference segment(0=inertial) and the segment number (20=CHR1) forwhich the acceleration is measured. The 4 through 6fields specify the x, y, and z coordinates in the segmentreference frame of the point at which the accelerationis to be measured. H.2 CARDS provide similarspecification for linear velocity and displacement.

The program permits four options for specifyingthe crash pulse. Example RCRASH.AIN applied thefirst option - a half sine pulse. The WC1.AIN exampleuses the second option - tabular unidirectionaldeceleration. Other options permit six degree offreedom in acceleration or velocity. In all options,deceleration (negative acceleration) is treated aspositive in the input data supplied in the C CARDS.

The first two fields in the C.2 CARD designate theazimuth and elevation angle of the unidirectionalacceleration vector. In Example WC1.AIN, both arezero, signifying a zero degree frontal crash. The thirdfield is the initial velocity (528 in/sec). The ninth fieldspecifies the number of time points at whichacceleration data will be supplied. Fields 10 and 11contain the first time step (0.0) and the interval betweentime steps (.005 sec), respectively. Following the C.2line are the 41 acceleration data points, beginning withthe first (0.0). Twelve data points per line with a formatof F6.0 are required. The acceleration value at the lastdata point will be continued for the duration of thesimulation.

ACKNOWLEDGEMENTS

The work of Dr. Louise Obergefell of theArmstrong Aerospace Medical Research Laboratoryhas been invaluable in providing many of theillustrations used in describing the ATB program. Dr.T. Shams of GESAC provided valuable early work inmodeling wheelchairs using the DYNAMAN model.Dr. E. Sievika and his colleagues at the University ofVirginia have added significantly to the modeling andvalidation of both dummies and wheelchairs. Theadvancements of all these researchers is recognized andappreciated.

DATA AND MODEL SOURCES

Recently, more user friendly input and outputprocessors have been developed for the CVS/ATBmodel. The DYNAMAN series provides an inputprocessor which permits rapid viewing and editing ofdata. The output processor uses both the .TP1 and the.TP8 files and provides plots, tables of data, and picturesof dummy motion. The dummy motion can be easilyexamined from different angles.

Data for the modeling of humans and theirinteraction with the environment are available from avariety of databases. The Crash Analysis Center at TheGeorge Washington University, 20101 Academic Way,Ashburn, VA, 22011-2604, maintains a film and datalibrary of more than 15,000 crash tests conducted bythe Department of Transportation. Other computerprograms and databases to assist in developing inputdata were summarized by Digges [8].

The sources of the present programs should becontacted for new developments. The sources are:ATB - AL/CFBV, Bldg 441, 2610 Seventh St. WrightPatterson AFB, Ohio, 45433DYNAMAN - GESAC, Rt 2 Box 339A, KearneysvilleW.Va, 25430

REFERENCES

1. Fleck, J., and Butler, F., “Validation of the Crash VictimSimulator, DOT HS-806 279, 280, 281, and 282; 1981.

2. Obergefell, et.al., “Articulated Total Body ModelEnhancements”’ Vol 1 through 3, AAMRL-TR-88-007, Feb1988.

3. Armstrong Aerospace Medical Research Laboratory,“Input Description for the Articulated Total Body Model,”AAMRL Document. AAMRL, Wright Patterson AFB, Ohio,1994.

4. GESAC, “Dynaman User’s Manual, Version 3.0", 1993.

5. Kaleps, et.al., “ Measurement of Hybrid III DummyProperties and Analytical Simulation Data BaseDevelopment”, AAMRL-TR-88-005, Feb 1988.

6. Sieveka, et.al., “Impact Injury Simulation Research”’Wayne State Symposium on Biomechanics of Impact, April,1991.

7. Shaw, G., Lapidot, A., Scavinsky, M., Schneider, L., andRoy, P., “Interlaboratory Study of Proposed Compliance TestProtocol for Wheelchair Tiedown and Occupant RestraintSystems”, SAE 942229, November, 1994.

8. Digges, K., 1988. Occupant/Vehicle Crash Models andData Bases Maintained by the National Highway TrafficSafety Administration. 1988 IRCOBI ConferenceProceedings, IRCOBI Secretariat, 109 Ave. Salvetore Allende- 69500 Bron, France. pp 149-158.


Segments

1-LT 7-RLL 13-RLA2-MT 8-RF 14-R3-UT 9-LUL 15-LUA4-N 10-LLL 16-LLA5-H 11-LF 17-LH6-RUL 12-RUA

JOINT

1-P

2-W

3-NP

4-HP

5-RH

6-RK

7-RA

8-LH

9-LK

10-LA

11-RS

12-RE

13-RW

14-LS

15-LE

16-LW

JNT

1

2

3

4

1

6

7

1

9

10

3

12

13

3

15

16

4

15

1

RIGHT LEFT

Joint J connects segmentJ+1 to segment JNT.

5

16

16

1714

13

13

12

1

6

78

12 3 15

Figure 1. Standard Body Set up

9

1011

5

6

7

8

9

10

2

2

11 1443


Figu

re

2Joi

nt

Typ

esF

igur

e 2.

Joi

nt T

ypes


Cou

lom

b

Torq

ue

S1θ

Vis

cous

ramp

V3

V2

ω, Angular Veloctity

ω, Angular Veloctity

V1ω

S1θ+S2(θ-SS) +S3(θ-SS) 32

S1θ+S4[S2(θ-S5) +S3(θ-S5) ]32

θ, Joint Angle (deg)

S5

Figure 3. Joint Torque Functions

13Technical R

eport #3

Figure 4. Positi ve Side of PlaneFigure 4. Positive Side of Plane

RE

RC

on Wheelchair Technology

14

Figure 5. Plane-SEgment ContentsFigure 5. Plane- Segment Contents


.

INTERIAL SPIKEBASE

RELOADUNLOAD

AtAc

F(X)

X X X

R= ATAc + At

R = O; all energy absorbed

G = X permX max

G = 1; no elastic response

PERM MAX

Figure 6. Functions (E CARDS)

t

INERTIAL SPIKE


Figu

re 7

. T

he H

arne

ss B

elt


Figure 8. Coordinate Systems

.

.

X

YZ

Y

Z

X

VEHICLE

Z LOCAL

LOCALRight

Forward

DownY

Z

X

Gravity

INERTIALX

Y


Figure 9. Hybrid III Dummy

SEG NR SEG JOINT NR JOINTJNT NR JNT SEG

1 LT FREE NONE

2 MT 1 P 1 LT

3 UT1 2 W 2 MT

4 UT2 3 CU 3 UT1

5 NK 4 NP 4 UT2

6 HD 5 HP 5 NK

7 RUL 6 HR 1 LT

8 RLL 7 RK 7 RUL

9 RF 8 RA 8 RLL

10 LUL 9 LH 1 LT

11 LLL 10 LK 10 LUL

12 LF 11 LA 11 LLL

13 RUA 12 RS 4 UT2

14 RLA 13 RE 13 RUA

15 LUA 14 LS 4 UT2

16 LLA 15 LE 15 LUA

17 RHD 16 RW 14 RLA

18 LHD 17 LW 16 LLA

Joint J connects segment J+1 to segment JNT.


Figure 10. ATB Inputs and Outputs

.

CONTROL.VIN

ATB.TP1 VIEW II

DATA.AIN

ATB.TP8GRAPHICS

GRAPHSATB.Tmn

TABLES

ATB.AOU

ATB44

TABULAR OUTPUT

PICTURES

SEG NR SEG JOINT NR JOINTJNT NR JNT SEG

1 LT FREE NONE

2 MT 1 P 1 LT

3 UT1 2 W 2 MT

4 UT2 3 CU 3 UT1

5 NK 4 NP 4 UT2

6 HD 5 HP 5 NK

7 RUL 6 HR 1 LT

8 RLL 7 RK 7 RUL

9 RF 8 RA 8 RLL

10 LUL 9 LH 1 LT

11 LLL 10 LK 10 LUL

12 LF 11 LA 11 LLL

13 RUA 12 RS 4 UT2

14 RLA 13 RE 13 RUA

15 LUA 14 LS 4 UT2

16 LLA 15 LE 15 LUA

17 RHD 16 RW 14 RLA

18 LHD 17 LW 16 LLA

Joint J connects segment J+1 to segment JNT.


INPUT DATA REQUIREMENTS

A. RUN CONTROL

B. OCCUPANT DESCRIPTION

C. VEHICLE MOTION

D. CONTACT DEFINITIONS

E. FUNCTIONS

F. ALLOWED CONTACTS

G. INITIAL CONDITIONS

H. TlME HISTORY SPECIFICATIONS

Figure 11. ATB Data Requirements


Figure 12. Rear Crash Model

.

.

Y

Z

X

VEHICLE

RightForward

DownY

Z

X

Gravity

INERTIAL

X

ZY


Dummy & Wheelchair Connections

SEG SEG JOINT JOINT JNT JNT SEGNR NAME NR. NAME NR. NAME1 LT FREE NONE2 MT 1 Pelvic 1 LT3 UT1 2 Waist 2 MT4 UT2 3 Chest 3 UT15 NK 4 Neck 4 UT26 HD 5 Head 5 NK7 RUL 6 Hip-R 1 LT8 RLL 7 Knee-R 7 RUL9 RF 8 Ankle-R 8 RLL10 LUL 9 Lip-L 1 LT11 LLL 10 Knee-L 10 LUL12 LF 11 Ankle-L 11 LLL13 RUA 12 Shoulder-R 4 UT214 RLA 13 Elbow-R 13 RUA15 LUA 14 Shoulder-L 4 UT216 LLA 15 Elbow-L 15 LUA17 RHD 16 Wrist-R 14 RLA18 LHD 17 Wrist-L 16 LLA19 CHR 18 Null NONE20 CHR1 19 CG Locator 19 CHR21 WH1 20 Axel- LR 19 CHR22 WH2 21 Axle-RR 19 CHR23 WH3 22 Axle-LF 19 CHR24 WH4 23 Axle-LR 19 CHR25 ANC1 26 Anchor-LR 19 CHR26 ANC2 25 Anchor-RR 19 CHR27 ANC3 26 Anchor-LF 19 CHR28 ANC4 27 Anchor-RF 19 CHR

Figure 13. Wheelchair/ Dummy Model

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