PC CRASH 6 - ВНТУperlov.vk.vntu.edu.ua/file/1e8e10cd56d0b607bcd4da59aec89be3.pdf · 12 PC-Crash: a simulation program for vehicle accidents Chapter 1: Introduction PC-Crash is

PC CRASH 6.2 A simulation program for vehicle accidents

ANALYSIS & BRIEF MANUAL

Jasper Traets

/department of mechanical engineering

12 PC-Crash: a simulation program for vehicle accidents

Table of contents Chapter 1: Introduction 3 Chapter 2: Possibilities 4

2.1 Vehicles 4 2.2 Environment of the accident 15 2.3 Sequences 20 2.4 Trajectories 24 2.5 Pedestrians 26 2.6 Occupants 28 2.7 Crash Simulation 29 2.8 Collision Optimizer 31 2.9 Output (reports, diagrams and animations) 32

Chapter 3: Brief manual: example of a crash simulation 34 3.1 Description 34 3.2 Simulation with 2 small cars 34 3.3 Simulation with a small and a larger car. 41 3.4 Comparison of the 2 simulations 44

Recommendation 45 References 46

/department of mechanical engineering 2


Chapter 1: Introduction PC-Crash is a powerful program for the simulation of motor vehicle accidents, covering many different accident situations. It takes advantage of the latest hardware and software developments, which allows increasingly complex calculations to be performed on personal computers. PC-Crash contains several different calculation models, including an impulse-momentum crash model, a kinetics model for realistic trajectory simulations, and a simple kinematics model for time-distance studies. For maximum versatility, PC-Crash simulation results can be viewed and outputted in scale plan and elevation views, 3D perspective view, and in numerous diagrams and tables. At the moment the program PC-Crash is not in use by the research field vehicle safety of the department of mechanical engineering at the TU in Eindhoven. A study to the possibilities and the working of PC-Crash is necessary to determine whether the program is a useful addition to the research field. This report is a result of that study, including a brief manual for a simulation of an accident.



Chapter 2: Possibilities In this chapter all the possibilities and options of the program PC Crash will be discussed. In some cases, when there’s a lot of information about a certain feature, is referred to one of the manuals of PC Crash.

2.1 Vehicles

2.1.1 Selecting a vehicle In PC-Crash there are a two main ways to select a vehicle for the simulation.

1. From a database In PC-Crash there are a few databases integrated:

Figure 2.1 Vehicle database Canadian Specs Database - Cars and light trucks in North America ADAC95 - Yearly European database, this one from 1995 Vyskocil - Former European database, including trucks

and motorcycles DSD - New European standard database DSD Japan - New Japanese standard database The DSD databases contain a lot of vehicle information. The year of manufacture and vehicle type can be specified to make searching easier


12 PC-Crash: a simulation program for vehicle accidents 2. Custom vehicles

It’s also possible to import custom vehicles into PC-Crash. The following type of vehicles/objects belong to this category:

- Vehicles that are not in one of the databases (like large trucks, trailers, etc.)

- Vehicles from the database that are edited (vehicle settings changed) - Objects like walls, trees or something like that. - Multibody pedestrians and (motor)cycles.

Instead of editing an existing vehicle from the database you can also create your own (new) custom vehicle.

2.1.2 Vehicle settings The vehicle settings dialog box is divided in a few parts which will be discussed below:

1. Vehicle geometry

Figure 2.2 : Vehicle geometry In this part you can change the whole geometry of the vehicle. This consists of dimensions (like length, width, height, wheelbase, front overhang and track) but also type of vehicle, number of axles, weight, C.G.


12 PC-Crash: a simulation program for vehicle accidents and moments of inertia (yaw, roll, pitch) properties belong to the vehicle geometry. The possibility to activate ABS belongs also to this part.

2. Suspension

Figure 2.3: Vehicle suspension properties For each wheel of the vehicle the stiffness and damping can be specified. There are 3 default levels to choose from: stiff, normal or soft. In these cases the static spring compression is resp. 10, 15 and 20cm. Furthermore you can define parameters for vehicle body to ground impacts in case of a rollover. The parameters to define are friction between vehicle body and the ground, coefficient of restitution and stiffness (deformation of the car body due to its static weight).


12 PC-Crash: a simulation program for vehicle accidents 3. Occupants and cargo

Figure 2.4: Occupants and cargo Here you can define the mass of the occupants and the cargo, if present. The weight of the occupants is applied at the same height as the center of gravity. For the front occupants this load is applied 15% of the wheelbase in front of the vehicle mid-point, for the rear occupants 20% of the wheelbase behind the vehicle mid-point. The roof cargo load is placed directly above the center of gravity and 0.3m (1 foot) above the vehicle height. For the trunk cargo this place is in the middle of the vehicle at height of the center of gravity and 10% of the wheelbase behind the rear axle. Due to the load of occupants and cargo, the vehicle’s center of gravity, vehicle’s mass and all the moments of inertia will change. The program automatically calculates the new values. The moments of inertia are corrected with the following formula:

Iloaded = Iempty (mloaded/mempty)



4. Rear brake force

Figure 2.5: Rear brake force In this part you can modify the curve, which represents the proportion of rear brake force (qh, vertical axis) to the front brake force (z, horizontal axis). This is done by modification of (one of) the following 3 parameters: - Phi: slope of the first line - z1: the point where the slope changes - m: slope of the second line

Modification of the curve is possible by entering the correct values for those 3 parameters or by shifting the curve with the mouse. This part is by the way only relevant if a C.G. height is entered! If done, automatically a distribution curve is created.


12 PC-Crash: a simulation program for vehicle accidents 5. Vehicle shape

Figure 2.6: Vehicle shape

The shape of the selected vehicle can be adjusted in this dialog box. In the default settings there’s a choice between Sedan, Hatchback or Van. Moreover it’s possible to enter custom dimensions. If no DXF or IDF shape (discussed later) is used, this shape will be shown in the 3D window. It’s also used for collisions with multibody systems and for calculations with the rollover model.



6. Trailer

Figure 2.7: Trailer In this dialog box it’s possible to modify all trailer parameters. In the drop down boxes you can select the correct trailer for each tow vehicle. Furthermore the type of trailer (unsteered, steered or semi-trailer), the drawbar length (distance between hitch and front trailer axle) and the hitch overhang (overhang of the hitch outside the rear bumper of the tow vehicle) are defined here. In case of a 3D simulation, also a hitch height should be entered.

For the moment transfer about the axes (x, y, and z) of the hitch a few parameters can be changed: - S0: Constant frictional torque - Phi 0: Offset value from o0. If rotation between tow vehicle is > Phi 0 +

Phi min or <Phi 0 – Phi min, then the linear increasing S is applied. If Phi 0 = 0, S is symmetrical for positive and negative rotations.

- Phi min: Angular rotation of the trailer about the hitch with respect to Phi 0 at which torque S starts

- S: Linearly increasing resistive torque about the specified axis, starting at Phi 0 + Phi min



2.1.3 Tire model In this section tire parameters can be defined. Besides selecting and changing the tire size and (if desired) selection of dual tires (with additional spacing parameter), this holds that you can define and adjust the used tire model. Two different models are included in PC-Crash and will be discussed below:

a) Linear tire model

Figure 2.8 Linear tire model

The only adjustable parameter in this model is the maximum lateral slip angle. The maximum slip angle is specified for a friction coefficient of µ = 1. If a lower coefficient of friction is specified, this maximum angle will be lower too. With a coefficient of friction of 0.8 and a specified maximum lateral slip angle of 10 °, the maximum tire slip angle will be 8°. At this angle the maximum lateral tire force of 80% of the normal force is reached. More specific information about this model can be found in the PC Crash Operating Manual [1].


12 PC-Crash: a simulation program for vehicle accidents b) TM-Easy tire model

Figure 2.9: TM Tire model

In this dialog box the longitudinal and lateral parameters can be specified for each wheel separately. If the box ‘parameters for all wheels’ is checked the parameters will be same for all wheels. The adjustable parameters are: - Fmax: peak frictional force value. Default value = 1. - Smax: slip value at which Fmax occurs. - Fslip: sliding frictional force value. Default value = 0.8. - Sslip: slip value at which Fslip occurs. - FOp: Slope of the tire model curve at the origin



2.1.4 Other vehicle related settings In this part some other vehicle related settings will be discussed. It handles about specific settings, which won’t be used very often.

1) Engine/Drive train

Figure 2.10 : Engine drivetrain dialog box The engine power curve characteristics, transmission and differential ratios can be specified here. The maximum engine power in hp and the corresponding engine speed can be entered in the dialog box. The resulting torque curve can be viewed and modified in the Engine Torque Diagram tab. This modification consists of selection of a standard curve (normal, sport, diesel or turbo diesel) or shifting points on the curve manually. The maximum vehicle speed (in combination with the available horsepower) is necessary, to calculate the air resistance at this maximum speed. Also maximum engine speed (rpm) and efficiency (a normal value is 70 tot 90%) is specified in this part. The next selection has to deal with the drive mode. The available types are front wheel drive, rear wheel drive and 2 types of four-wheel drive (front/rear 50/50 or 30/70). Finally the number of gears and the gear ratios can be specified in the text boxes. Automatically the maximum vehicle speed for each gear is shown.



2) Wind resistance

Figure 2.11 : Air resistance dialog box The magnitude and point of the resistant force is entered in this part. To make the calculation of the air resistance force possible, a value for cw·A for each side of the vehicle should be specified in the text boxes. The point of force is specified in percentages of the vehicle dimensions. Also the wind parameters (speed, direction and timing) can be entered: - Direction: counterclockwise from the global x-axis. - Strength: in specified units (kph or mph) - Timing: Wind gusts can be specified by dT On and dT off times. For a

steady wind the dT On time should be longer as the simulation time.



2.2 Environment of the accident Everything that has to do with the definition of the environment of the accident is discussed in this part. In this field you can think of the specification the road, placement of vehicles and obstacles and appearance of vehicles, pedestrians and obstacles as well in 2D as 3D.

2.2.1 Scenes To make the simulation as truthful as possible, there can be implemented scene data into PC Crash.2 types of scenes can be distinguished: 2D and 3D. The construction of both types of scenes is discussed below. 2D scene: In general there are 3 ways to get 2D Scene data. The first way is Import a scene drawing. If this drawing is not drawn with meters as units, then the Scale tool should be used. Another way to implement scene data in PC Crash is Import of a scene bitmap image. This bitmap can be a scanned drawing, (aerial) photograph or a PC-Rect photograph. The 3rd way is to Create a scene drawing. Using the different tools in the Draw toolbar, a scene can be drawn complete with road marks, road signs, etc.

Figure 2.12 : Draw toolbar


12 PC-Crash: a simulation program for vehicle accidents An example of a 2D scene is shown below:

Fig. 2.13 Example of a 2D scene drawing This drawing shows a road with a curved part at the (left) end. Road marks are drawn and also the tire marks and end position of the vehicles are drawn on the road surface to make the reconstruction in PC Crash easier. 3D Scene: Here it’s also possible to import a drawing or to create one by yourself, but the construction of a 3D scene is more complex then it is in 2D. It consists namely not only of the construction of the road itself but also of the definition of the elevation, cross slope, ditch angle, ditch profile, radius and width of the road. For all those parameters an adjustable diagram is available in which the desired values can be specified. In the screenshots below a few of those options are shown: Figure 2.14: 3D road object dialog box


12 PC-Crash: a simulation program for vehicle accidents More detailed information about the modification of these parameters can be found in the PC Crash Operating Manual [1] An example of a 3D scene is shown below:

Fig. 2.15 Example of a 3D scene drawing In this picture you can remark the elevation of the road and the ditches beside the road.



2.2.2 Placement of vehicles, pedestrians and obstacles When vehicles (all types), pedestrian and obstacles have been loaded into PC Crash, they have to be placed in the correct (impact) position. This can be done in various ways:

- Tow Truck tool With this tool you can move and rotate the vehicle into the desired position with the mouse.

- Position & Velocity dialog box

In this dialog box (opened fast by pressing F7) the position of the center of gravity can be specified by entering the x, y and (for 3D simulations) z coordinate of C.G. The rotation of the vehicle can also be entered here.

Figure 2.16: position & velocity dialog box



2.2.3 Appearance To get a more realistic appearance of vehicles, pedestrians and obstacles, you can attach a 2D or 3D drawing shape or a 2D bitmap to them. A lot of shapes and bitmaps are standard included in the PC Crash installation directory. It’s also possible to create or edit one. These shapes are not only available for vehicles (cars, trucks, (motor) bikes) but also for pedestrians, walls, trees, etc. An example of the application of these shapes is shown in the picture below. The red car is a VW Golf IV, the blue car a Chrysler PT Cruiser.

Figure 2.17: VW Golf & Chrysler PT Cruiser



2.3 Sequences The motion of objects in PC-Crash can be defined by programmable sequences. Pressing F6 opens the Sequences dialog box. The Start icon represents the point time =0. All sequences before time =0 are placed above this icon, all sequences after time=0 below. There are three categories of sequences: Vehicle/Driver, Points and Friction. Each category will be discussed briefly below. Further details can be found in the PC Crash Operating Manual (Chapter 4: Programming Sequences) [1].

Figure 2.18 : Sequences dialog box

2.3.1. Vehicle/Driver sequence This part consists of 4 different sequences:

- Accelerate - Brake - Reaction - Crash

Accelerate and brake: Accelerate and Brake use the same dialog box and these sequences are used to define all values for acceleration, braking and steering.



Figure 2.19: Accelerate and brake dialog box Parameters to define:

- Lag time: the time it takes to reach the specified brake or acceleration level.

- Sequence duration: length of the sequence, defined in distance (m or ft,

dependent on the settings in which unit) or in time (s)

- Acceleration/Deceleration: defined by the Pedal Position slider bar or the Acceleration text box above it. It’s also possible to specify the individual factor at each wheel. The brake or acceleration force is distributed evenly among all wheels except: 1) The rear brake force distribution is used in 3D simulations 2) In case of activation of Real Acceleration, the Engine/Drive train

settings are used.

- Steering:

Figure 2.20: Steering dialog box Turning circle: turning diameter of the center of the outside front wheel Steering time: time it takes to steer the vehicle from last steering angle (or zero) to new steering angle.


12 PC-Crash: a simulation program for vehicle accidents Steering angle: steering angle can be specified individually for each wheel. Input is possible by the slider bar or by entering a value in the text boxes.

- Lane change: Lateral offset: total lateral movement Max. lateral acceleration: this value will not be exceeded while the steering wheel angle is being increased at the start of the maneuver. Steering angular velocity: Angular velocity at which the front wheel steering angle is being changed. Lateral steer rise distance: lateral distance (as percentage of the lateral offset) the vehicle moves while the steering angle of the front wheels is being increased. Three default settings are available: Abrupt (4%), Normal (2,5%) and Smooth (1%). Direction: Lane change to the left or to the right. More info about the lane change model can be found in the PC Crash Technical Manual (Chapter 6: Additional models) [2]

Reaction: This sequence is for the definition of a perception-reaction time or distance. During this reaction sequence the brake or acceleration force and steering angle from the previous sequence is applied. Crash: This sequence allows the input of a speed change without using the program’s crash model.

2.3.2 Points 5 different sequence points can be added to the sequence dialog box: Stop This sequence makes the vehicle stop at the end of the previous sequence.

Zero At the position where the Zero sequence is placed, time and distance are set to zero. This only influences the diagrams.

Synchronization Offsets the distance graph for one vehicle from another in the Diagrams window. This should be the first sequence listed under the Start sequence.

Min/Max Velocity Input of minimum and maximum velocities for the sequences following this sequence


12 PC-Crash: a simulation program for vehicle accidents Geometry change Individual location of each wheel can be changed at any time. Useful for modeling horizontal and vertical wheel movement due to damage. Also al flat tire can be modeled this way (in combination with change in tire friction and tire slip angle).

2.3.3 Friction Dry friction The coefficient of friction may be defined for each wheel individually. If no friction sequence is defined, the default setting for the coefficient of friction will be used.

Wet friction When braking on wet roads, commonly a speed-sensitive friction coefficient is the case. The characteristic parameters are calculated using a hyperbolic function, based on the specification of the acceleration at 20 km/h and 80 km/h.

The used equation is: nvnA −⋅⋅

= 22.0µ

Where A and n are the parameters of the hyperbolic function.



2.4 Trajectories As mentioned in the previous part pre-impact and post-impact trajectories can be defined by sequences. With some modification and manipulating of the sequences you can create the desired motion of the vehicle. Another possibility to create a certain trajectory for the vehicles is the creation of a path by the definition of path points. The vehicle follows this path differently depending on whether the normal Kinetics simulation model or the Kinematics simulation model is used. For the Kinetics model holds that the vehicle motion will depend on the laws of physics, the vehicle properties and the driver model parameters. The vehicle will not follow the path exactly, especially not in cases of high speed. In case of application of the Kinematics model the vehicle will follow the specified path at the specified speed, regardless of the laws of physics. With the option Vehicle Anchor Point you can select the point of the vehicle that is anchored to the specified path.

Figure 2.21 : Path & Path anchor More info about the trajectory model can be found in the PC Crash Technical Manual (Chapter 2: The trajectory model) [2]


12 PC-Crash: a simulation program for vehicle accidents Furthermore a driver model can be specified.

Figure 2.22: Driver model The parameters to define are:

- Maximum steering angle A limit on how far the front wheels will steer. The specified value is for the outside front wheel.

- Maximum steering velocity

A limit on how fast the front wheels can be steered. The specified value is again for the outside front wheel.

- Look ahead duration This time is used to calculate a look ahead distance vector. The path model compares the location of the end of this vector with the defined path to determine the current steering angle.

- Driver Model A Fuzzy model or PID-Tangential model can be selected. Detailed information about these models can be found in the PC Crash Technical Manual (Chapter 6: Additional models) [2]



2.5 Pedestrians In PC Crash there are two ways to model pedestrians. The first way is modeling a pedestrian as a simple block-shaped vehicle. This simple way is used for determining pedestrian visibility around other objects in the scene and for time-distance studies. The pedestrian is handled as a custom vehicle and the position and velocity box can be used to specify position and velocity of the pedestrian. A 3D DXF drawing of a pedestrian can be attached to the custom vehicle to make it look more realistic. The second way is using a multibody model for the pedestrian. In this case the model calculates impacts automatically between the individual parts of the multibody model and the vehicle’s exterior. The model reacts to ground and vehicle impact forces and gravity. A multibody pedestrian cannot be made walk or run the way a human body can. Therefore it’s best to start the simulation immediately after impact. If not, the pedestrian will fall down due to gravity prior to being struck. The properties of the multibody model can be modified on different levels.

Figure 2.23 Multibody model dialog box A few important options will be mentioned below.

- Bodies: all parts of the multibody model can be modified, created or deleted. The new moments of inertia are calculated automatically. Furthermore stiffness, restitution and friction for each part can be defined.

- Joints: the joints make a connection between the individual body parts. The state of these joints can be fully free, fully locked or can have a certain stiffness about the x, y or z rotational axes.

- Springs/Dampers: also a spring/damper system can be used to interconnect the individual parts of the multibody model. Again the location and the stiffness and damping coefficients of the system can be specified.


12 PC-Crash: a simulation program for vehicle accidents - Settings: in this section position, rotation and (initial) velocity of the

whole body or individual parts can be entered. Also properties for length, weight, restitution and friction are specified here. Furthermore there’s an option to change the body data. Anthropometrical data are used here to make the data as realistic as possible.

Detailed information about application of multibody models can be found in the PC Crash Operating Manual (Chapter 5: Multibody model) [1].



2.6 Occupants Occupants can be modeled in the same way as pedestrians, as a simple block-shaped model and as multibody model, but also a Madymo® occupant simulation can be performed. The modeling of the occupant as a simple block is only useful to determine the direction an occupant moves relative to the vehicle during an impact. Modeled this way the passenger will follow the vehicle’s motion during normal driving conditions. In case of an event in which the vehicle acceleration exceeds 2g (e.g. a collision), the passenger will move in the proper direction with respect to the vehicle. In case of modeling a passenger as a multibody occupant, the simulation of the multibody movement should be run apart from the car simulation. This is done in the Multibody properties dialog box. The position of the multibody and the time of the simulation should be specified before the simulation of the multibody occupant can be started. The third way to simulate occupant motion is using a Madymo® Occupant Model. In the Occupant Calculation dialog box the acceleration pulse can be chosen, the geometry and stiffness of the seat can be defined and the position and weight of the passenger can be entered. Furthermore information about using an airbag and/or a seat belt, about the kind of impact (side impact or not) and about the use of a pretensioner can be specified. In this part the calculation is also done separately from the car simulation. In Chapter 6 of the PC Crash Operating Manual more information is given about the Madymo ® Occupant Model.



2.7 Crash Simulation The only things lefts to define before the simulation can be runned are some of the crash parameters. This is done in the Crash Simulation dialog box, easily reached by pressing F8.

Figure 2.24 Crash Simulation dialog box The pre-impact velocity is also shown and can still be modified. For each vehicle the Equivalent Energy Speed (EES) is indicated. The following formulas are used:

21

12

2

1

Def

Def

smsm

EESEES

= )1(

2

2

12

2

+=

Def

Def

D

ss

m

EEES

With m1, m2 = mass of each vehicle sDef1, sDef2 = Crush depth of each vehicle ED = Energy lost by both vehicles in collision due to damage An EES value can be defined, in that case the EES value for the other vehicle is calculated with the following formula:

2

112 m

EESmEEES D −=


12 PC-Crash: a simulation program for vehicle accidents The following impact parameters can be defined here:

- Position of the point of impact Can be done by selecting the correct point with the mouse or by entering the coordinates of the point of impact in the text boxes.

- Impact elasticity (by coefficient of restitution OR separation velocity) Defines the elasticity of the impact following Newtonian Crash Hypothesis. Normally this value is between 0 and 1. Default value is 0.1. A negative value for the coefficient of restitution is also possible. In that case one vehicle tears through a portion of another vehicle and no common velocity is reached. Types of impacts where this is the case are offset frontal impacts and lateral curb impacts.

- Orientation of the contact plane The contact plane can be rotated with the mouse or values for phi and psi can be entered in the text boxes to define the position of the contact plane.

- Inter-vehicle contact friction along contact plane.

If the impulse vector is in line with the outside of the friction cone, the specified inter-vehicle friction has limited the impulse angle and inter-vehicle sliding occurs and the contact friction coefficient describes the relation between the normal and tangential components of the impulse vector.

Clicking the button Crash starts the calculation of the simulation. When done, the simulation can be viewed in the main window, using the Simulation Toolbar.

Figure 2.25 Simulation toolbar



2.8 Collision Optimizer Collision Optimizer is a tool to determine pre-impact speeds and other parameters, based on the defined rest and/or intermediate positions. Three algorithms are available for the optimizing process: Genetic, Linear and Monte Carlo. The Linear algorithm is only applicable to impact velocity and point of impact. For the Genetic and Linear algorithms, each parameter is optimized in two phases, starting with the higher step width, before the next parameter is optimized. The parameters to optimize are:

- Impact velocity - Point of impact (in the x-y-plane) - Point of impact z-coordinate - Contact plane (angel phi) - Pre-impact directions (pre-impact heading angles) - Vehicle positions - Restitution - Contact friction

The Monte Carlo algorithm works different. Here 100 iterations are performed, using random values for the selected optimization parameters. More information about the algorithms used in Collision Optimizer can be found in the PC Crash Operating Manual (Chapter 3) [1] and PC Crash Technical Manual (Chapter 4) [2]. For each vehicle the following values can be defined:

- Velocity range limits - EES - Weighting of distance and angular errors for the rest and intermediate

positions - Weighting of EES

The results of an optimization can be presented in a report or in diagrams. Example of such a report: Optimizer report: Iterations: 122 (87 < 10.0 %) Error limit: 10.0 % Velocity ranges: v1: 49.0 - 52.0 km/h v2: 15.0 - 25.0 km/h Pre-impact directions: 1: 0.1 - 4.1 ° 2: 97.3 - 101.3 ° Move Point of Impact: x: 1.88 - 1.98 m y: 0.10 - 0.20 m z: 0.00 - 0.00 m Impact parameters: Coefficient of restitution (e) : 0.10 - 0.10 Contact friction 1.00 - 1.00 Rotate Contact Plane: 98.8 - 98.8 °



2.9 Output (reports, diagrams and animations) After a simulation is done, the results can be presented in 3 different ways The first way is to collect all the data in a report. For each vehicle the values for the vehicle settings and impact parameters for as well the pre-impact as the post-impact situation are presented. In the Report Settings can be selected which parameters in which way are mentioned in the report. The next way to present the results is by diagrams. In PC Crash a lot of different diagrams can be generated out of the data created by the simulations: Vehicle:

- Velocity - Distance v. time - Heading - Yaw angular velocity - Steering angle - Brake factors - Coefficient of friction - Tire normal forces - Tire lateral forces - Tire brake forces - Acceleration Figure 2.26: Distance-Time-Velocity diagram - Roll angle - Roll angular velocity - Pitch angle - Pitch angular velocity - Tire overall slip - Tire rpms - Trailer hitch force

Multibody systems For the next parameters for each of the 16 components of the multibody (pedestrian) model 4 values (in x, y and z direction plus resultant) can be displayed (except for Energy)

- Distance - Velocity - Acceleration - Rotation angle - Angular velocity - Angular acceleration - Energy (kinetic) - Contact forces - Spring forces

Figure 2.27 : Head & Neck Acceleration diagram


12 PC-Crash: a simulation program for vehicle accidents Collision Optimizer:

- Velocities - Point of impact - Restitution, contact friction - Pre-impact directions - Pre-impact positions

Madymo diagrams: - Displacements - Velocity - Acceleration - Forces - Torques

It’s also possible to define your own position for a sensor and display the results in a diagram. This is done by the option Sensor signals. The third and last way to display results is by an animation. After running the simulation, a movie can be rendered in the 3D Window (opened by pressing F9). Camera and light source settings should be defined to become a good view. Also for the rendering of the movie a few settings can be defined, like dimensions, camera position and sort of compression. Furthermore importing of Madymo® data is possible, so a Madymo® simulation (specially a Madymo occupant simulation) can also be displayed in the 3D Window.

Figure 2.28 : 3D Window The picture above shows how the start of a simulation can look in the 3D Window.


12 PC-Crash: a simulation program for vehicle accidents Chapter 3: Brief manual: example of a crash simulation In this chapter a crash simulation is worked out step by step to give an idea of the working method in PC Crash. There should be mentioned that this is a very simple case, just to show the most important steps.

3.1 Description The compatibility of cars in car accidents is an actual issue in the vehicle safety research field. Therefore compatibility will be the subject of this case. The results of a collision between two cars of a small type will be compared with the results of a collision between a car of a small type and a car of a larger type. For the cars of the small type a Renault Clio (1994) is chosen. For the car of the larger type a Jeep Grand Cherokee (1993) is chosen. Maybe this choice looks a bit strange, but the reason for the selection of those cars is, that there’s a DXF-patch available for these cars to make them look more realistic in the simulation. The type of collision is a frontal impact with ± 40% offset. Both vehicles have a speed of 50 km/h.

3.2 Simulation with 2 small cars First of all the accident environment should be specified. By pressing the Draw

Toolbar button the draw toolbar becomes visible. Choose the Generate road

element option . Now the parameters for a road section can be defined: Length: 50 m The tab Width, Lanes should be filled in as in the image below:

Figure 3.1 Road section dialog box


12 PC-Crash: a simulation program for vehicle accidents On the General tab the colors and the dashing dimensions should be defined: Check Filled Use the default colors Length and distance: 4m By selecting OK the road section is displayed on the screen:

Figure 3.2 Road section The view can be adjusted by selecting Scale in the status bar in the main window or by using the zoom and pan buttons. These options can also be found in the menu Graphics.

The next step is selecting the vehicles. The database is entered by clicking or via the menu Vehicle – Vehicle database. If desired it’s also possible to load a custom

vehicle by selecting the Load Custom Vehicle button or via File – Import – Custom vehicle. In this case the database is used to select the vehicles. For this simulation the Renault Clio 1.4 – 55 kW, 04.1996-06.1998 is selected from the database twice. The only thing that has to be changed in the vehicle settings is the C.G. height. Fill in a value of 0.55m for the C.G. height of both vehicles. By entering a value for the C.G. height the simulation becomes a 3D simulation. The moments of inertia for roll and pitch are calculated automatically. For the other settings the default values are used.


12 PC-Crash: a simulation program for vehicle accidents Now the vehicles can be positioned in the impact position. The width of both cars is 1.63m. With a 40% offset, the y-distance between the C.G. of the cars should be about 0.815 + 0.815 - 0.65 = 0.98m. Open the Position & velocity (F7) dialog box and enter the following values:

Figure 3.3 Position & Velocity dialog boxes To get a realistic appearance, a Vehicle DXF will be attached to the vehicles. The Vehicle DXF dialog box is opened via the menu Vehicle – Vehicle DXF.

Figure 3.4 Vehicle DXF dialog box Select File – Plan View – Load DXF... and locate the DXF file. This file can be found in the directory ../PCCrash/3DDXF/idf/. The file is named 1994 RENAULT Clio.idf. Select this file for both cars and make sure that the file is valid for the whole simulation, so set valid from to –999 s to ensure this.


12 PC-Crash: a simulation program for vehicle accidents The dialog box should look like this after the selection of the DXF files:

Figure 3.5 Vehicle DXF dialog box after selection It’s possible to add more drawings to this box, for example a drawing of the deformed situation. This deformed drawing can also be created by the user by checking the box Edit drawing. Next step is the definition of the backward motion of the vehicles. As explained in the part about about sequences ther can be defined be all sorts of motion (forward, backward, with or without steering). Here a simple straight backward motion will be defined. The Reaction sequence is set on a time of 1 s. The first Deceleration sequence is set this way (for both vehicles):

Figure 3.6 Brake dialog box The sequence duration is set to a (low) value of 5m, because in that case the vehicles will stay on the defined road section.



Clicking the backward button shows the backward motion of the vehicles. This results in the following situation:

Figure 3.7: situation after backward simulation

Lock this backward path by pressing the Lock backwards path button when this situation is reached.

Press stop button to get the vehicles back in impact position.

Open the simulation dialog box by clicking the traffic light button :

Figure 3.8 Simulation dialog box


12 PC-Crash: a simulation program for vehicle accidents The settings in the dialog box should be like in the picture on the previous page. Now the settings for the crash and the post-crash motion can be defined. Settings for the post-crash motion are defined in the second Deceleration sequence in the Sequence dialog box (entered by pressing F6):

Figure 3.9 Brake dialog box For this sequence full braking is defined by moving the switch for Pedal Position to the maximum right postion. Brake factors are calculated automatically. After the defining the post-crash motion, it’s time to define crash motion. For this the Crash Simulation dialog box is needed. This dialog box is opened by pressing F8 or via Impact – Crash Simulation.

Figure 3.10: Crash simulation dialog box


12 PC-Crash: a simulation program for vehicle accidents Select the Move Point of Impact checkbox, and click on a arbitrary spot in the mainscreen to select the point of impact automatically. If desired, it’s possible to edit the automatically defined point of impact by modification of the values in the text boxes.

Make sure the vehicles are in initial impact position (if not, press ). Start the calculation of the impact parameters by clickin Crash in the Crash simulation dialog box.

Now press the Simulate forward button to start the dynamic forward simulation. Similar to the backward situation, lock the end position by pressing

the Lock forward path button The following situation should be visible:

Figure 3.11: situation after forward simulation To watch the complete dynamic simulation, press the stop button to get back to

the initial impact position. By clicking hte Simulate backwards button , the vehicles will go to the defined start positions of the simulation. By clicking the

Simulate forward button now, the complete simulation is shown.


12 PC-Crash: a simulation program for vehicle accidents At this point all calculations are done and the results can be displayed in reports, diagrams and animations. To get a good idea of the differences between the 2 types of simulations done in this example (namely a simulation of a collision between 2 small cars and a simulation of a collison between a small and a larger car), the results will be compared after both simulations have been done. This comparison will be discussed in part 3.4 of this report.

3.3 Simulation with a small and a large car. r To run the simulation with a larger car instead of one of the small cars, only a few things have to be changed. First of all one of the small cars has to be replaced by the large one. Open the Vehicle database again, select the large vehicle (Jeep Grand Cherokee 4.0 – 194 PS) and change the vehicle no. to 2. :

Figure 3.12 : Selecting the Jeep Grand Cherokee as second vehicle Off course the DXF file of the vehicle should be changed too. The vehicle DXF dialog box is opened in the same way as in the previous part (Vehicle – Vehicle DXF) and the new DXF file for the Jeep is selected. In the Vehicle setting the C.G. heigth for the Jeep should be entered. For this value 0.75m is chosen. (A value betwen the values for a small car and a light truck) The definition of the new impact position is a bit more complex then in the previous simulation because of the different width of the vehicles. The width of the Clio is 1.63m, the width of the Grand Cherokee is 1.84m. So the y-distance between the C.G. of the vehicles will be 0.815 + 0.92 – 0.65 = 1.085m The first vehicle will remain in the same position as before. Only the position of the second vehicle (Jeep) will be changed.



Figure 3.13 Position & Velocity dialog boxes The position and velocity are set, the next step is defining the sequences. Only the sequences for the new vehicle have to be set in the same way as in the 2 small cars case, so a first Decelerate sequence with a duration of 5m and a second Decelerate case with full braking. The backward simulation gives the following result:

Figure 3.14 : Situation after backward simulation


12 PC-Crash: a simulation program for vehicle accidents With the same working method as in the previous case the backward simulation is locked and the crash and post-crash simulation are done.

Figure 3.15: Crash simulation dialog box Define the point of impact again and the forward simulation can be calculated by pushing the Crash button. Run the simulation by pushing the Simulate forward button and lock the forward path.

Figure 3.16: Situation after forward simulation


12 PC-Crash: a simulation program for vehicle accidents The simulation from start to end point can be done in the same way as in the

previous case ( , , ) Differences in the end position are already clearly visible , but the results and differences will be discussed in the next part.

3.4 Comparison of the 2 simulations First of all the end positions of the vehicles can be compared:

Figure 3.17 End positions The small car becomes a larger displacement and rotation in the simulation with the larger car. This is off course an expected result. To check if this result is in harmony with the reality, the result of the PC Crash simulation can be compared with the results of a real crash test (a movie or a report or something like that). The diagrams are not clear enough to get a representative comparison, because of some noise in the results and the small simulation time, especially the small post-crash simulation time. Furthermore displaying of the diagrams in this report will make the report only more extensive and only a little bit more information will be provided. To view the results of the simulations (reports, diagrams and animations), the project files and some resulting animations of the two simulations are added to this report. Filenames including Compatibility1 refer to files of the simulation with the 2 small cars, filenames including Compatibility2 refer to files of the simulation with a small and a larger car.


12 PC-Crash: a simulation program for vehicle accidents Recommendation The goal of the study to the possibilities and the working of PC-Crash was to determine whether the program is a useful addition to the research field. It’s a very extensive program with a lot of possibilities to make the simulation as close to the reality as possible. Some of those possibilities are exact definition of the accident environment (not only the dimensions of the road but also properties like friction), accurate definiton of vehicle movements, good appearance due to 2d&3D patches and calculation of collision parameters with rest and intermediate positions as input (Collision optimizer). This study is done on the basis of some given examples and a number of custom made simulations. Especially for cases where a lot of data are known (e.g.from police reports and declarations of persons concerned and witnesses) the accident can be simulated and reconstructed very well. So my opinion is that this program surely could be a useful addition to the study program.



References [1] PC Crash, a simulation program for vehicle accidents. Operating Manual.

English. Linz, October 2001 [2] PC Crash, a simulation program for vehicle accidents. Technical Manual.

English. Linz, October 2001 [3] PC Crash, a simulation program for vehicle accidents. Example Manual.

English. Linz, August 2001


Documents

PC CRASH 6 - ВНТУperlov.vk.vntu.edu.ua/file/1e8e10cd56d0b607bcd4da59aec89be3.pdf · 12 PC-Crash: a simulation program for vehicle accidents Chapter 1: Introduction PC-Crash is