Vehicle Collision Objects Setup

Owned by Kimberly Liu
Last updated: Aug 23, 2021
7 min read

Overview

This page explores the parameters defining the nature and behaviour of collision objects in our impact analysis. The goals of this investigation are listed below.

  • Gain a better understanding of the real-life representation of the collision objects in order to accurately model their behaviour in collision scenarios

  • Verify the size, geometry and material of collision objects and ensure they meet ASC regulations

  • Re-evaluate contact types and fixed supports used in the current simulation setup

  • Propose new simulation setups that can model the behaviour of the chassis and collision objects more realistically

  • Ensure models are sufficiently constrained and can be solved by running test cases in Ansys

1.0 ASC Regulations Regarding Collision Objects

Relevant regulations and figures are listed below.

1.1 Collision Object Specifications Based on ASC Regulations

Specifications for collision objects based on regulation are summarized in the table below.

Collision Object

Ref. ASC Regulation

Area of Contact

 

Real-Life Representation

Collision Object

Ref. ASC Regulation

Area of Contact

 

Real-Life Representation

Front bar

10.3.A.8

100 mm x 600 mm

(350 mm above ground)

Bumper (see F.3.3)

Side bar(s)

10.3.A.8

100 mm x 600 mm

(350 mm above ground)

Bumper (see F.3.3)

Top Object (“pucks”)

10.3.A.8

150 mm diameter

Ground (rollover)

Walls (Rollover Analysis)

F.3.3

Not specified

Ground

 

1.2 Current Collision Objects Setup:

This page summarizes all collision scenario cases: MS14 Simulations Overview

Sample CAD model with chassis and collision objects: https://workbench.grabcad.com/workbench/projects/gcwijX10VhtEeZ8mtyGdmiV5BQItzO7K-9PXmyIs5vRPFL#/file/544822163

 

Information on our current collision objects setup is summarized in the table below.

Object

Dimensions

Material

Notes

Object

Dimensions

Material

Notes

Front Bar

100 mm x 1850 mm

All collision objects are currently structural steel.

  • Wider than the specified 100 mm x 600 mm in regs (10.3.A.8)

  • Jason noted that there is no width specified in Figure 1 of F.3.3. He increased the width to a reasonable value and there hasn’t been any issues with previous submissions.

  • The average width of a car is 6-6.5 ft which is ~1830-1980 mm. Therefore a width of 1850 mm seems reasonable.

Side Bar

Top Objects (“Pucks”)

150 mm diameter

  • simulations have been run for this in a separate (corrupted?) file

Walls (rollover analysis)

2000 mm x 2000 mm

  • dimensions are large enough to span the chassis

  1. We should consider adding and running simulations involving the following objects/scenarios:
    1) Front and side 100 mm x 600 mm objects *
    2) Top “puck” objects.

    Note: there is a separate file (named “extra sims”?) that already includes these objects, but the simulation file has been corrupted.
    * location of this shorter bar is important (centered? offset?)
  2. We should also investigate material selection for the collision object to more accurately model the behaviour of the real objects they represent.

    For example, the bars representing bumpers can be either steel or alumnum.

2.0 Ansys Contact Types and Behaviours

Ansys Contact Types and Explanations - Mechead.com

The current model set up uses the Bonded contact type between collision objects and the chassis tubes.

A table summarizing contact types in ansys is shown. More details on the options are summarized in the drop down below.

2.1 Bonded

  • default configuration and applies to all contact regions (surfaces, solids, lines, faces, edges)

  • no sliding or separation between faces and edges (think glued)

  • contact area doesn’t change with loading

  • linear solution

2.2 No Separation

  • cannot separate objects, but can slide

  • nodes in contact are bonded to the target surface

2.3 Frictionless

  • can separate and slide

  • standard unilateral contact - gaps can form between the bodies depending on loading

  • non-linear solutions - area of contact changes with loading

  • model should be well constrained

2.4 Frictional

  • can separate and slide with resistance ( modelled with shear stresses)

2.5 Rough

  • can separate, no sliding

  • does not close any gaps

  1. We should use the Frictionless contact type between the collision objects (bars, pucks, walls) and chassis.

    This constraint models basic unilateral contact and will allow for deformation of both bodies and gaps to form between them. However, we should be careful with sliding. Additional constraints are required to fully contain the movement of the chassis and ensure the simulation can be solved.

3.0 Model Setup

3.1 Existing Set-up

See this page for details on the current Ansys Workbench Setup: MS14 Workbench Setup

  • “11. Add fixed support to the back face of your impact object”

  • “12. Add acceleration to your model, in the direction away from the impact object. For every G of force you want to simulate, add 9.8m/s^2 to acceleration (i.e. for 5Gs, acceleration should be 49m/s^2).”

3.2 Proposed Set-up

See slide 3 in the attached slides in section 4.0 below.

3.3 Old Notes on Proposed Set-up:

There are 3 main iterations for each collision scenario.

V1 - evaluate the effect of the contact type parameter ONLY

V1.2 - change fixed supports on collision body

V2 - potentially change the frame of reference - accelerate the chassis into the fixed object instead

V3 - evaluate the material choice

note: accelerating objects into chassis is simpler. chassis is a more complex structure so it is easier to keep it fixed, ie simulation is more likely to converge this way

 

3.2 Front/ Side Bar Collisions Setup

Case 1: Front/Side Bars

V1

V1.2,1.3

V2

V3

Case 1: Front/Side Bars

V1

V1.2,1.3

V2

V3

Accelerating/Fixed Body

  • fixed chassis, object accelerates (all bodies accelerate?)

  • same as V1

  • fixed object, accelerating chassis

  • pick V1 or V2

Fixed Support

  • fixed support/point on the back end of chassis

  • bottom 2 tubes on c-plane

  • 2-previously suggested we should constrain the side faces to allow for bowing. does this make sense if its supposed to represent a bumper?

  • 3-consider making the collision object longer to model a full vehicle? add fixed support on far end → more deformation (energy absorption)

  • pick V1 or V1-2 or V1-3

  • pick V1 or V1.2

Contact Type

  • Frictionless

Constraints (motion) “Displacement”

  • object can only move forward into the chassis

  • chassis can only move forward into the object

  • pick v1 or v2

Object Material

  • Steel

  • aluminum

Loading

  • 5G

Changes from Previous Set-up

  • contact type (bonded → frictionless)

  • contact type (bonded → frictionless)

  • fixed supports

  • frame of reference and fixed supports

  • material

 

3.3 Rollover (Wall) Collisions Setup

Case 2: Rollover Walls

V1

V2

V3

Case 2: Rollover Walls

V1

V2

V3

Accelerating/Fixed Body

  • fix chassis, accelerate object into chassis

  • fix object, accelerate chassis into object

  • pick V1 or V2

Fixed Support

  • fixed support/point on the back end of chassis

  • fix back end of collision object

  • pick V1 or V2

Contact Type

  • Frictionless

Constraints (motion)

  • object can only move towards the chassis (move normal to contact face of collision object)

  • chassis only moves normal to the contact face of collision object

  • pick V1 or V2

Object Material

  • Steel

  • Steel

  • explore others? do some research on formula sae sims tutorials?

Loading

  • 5G

Changes from Previous Set-up

  • contact type (bonded → frictionless)

  • frame of reference and fixed supports

  • material

 

3.4 Top (Pucks) Collision Setup

Case 3: Rollover Pucks

V1

V2

V3

Case 3: Rollover Pucks

V1

V2

V3

Accelerating/Fixed Body

  • fix object

  • Accelerate chassis into object

  • pick V1 or V2

Fixed Support

  • fixed support/point furthest away on the chassis

  • fix back end of collision object

  • pick V1 or V2

Contact Type

  • Frictionless

Constraints (motion)

  • object can only move towards the chassis (move normal to contact face of collision object)

  • chassis only moves normal to the contact face of collision object

  • pick V1 or V2

Object Material

  • Steel

  • explore?

Loading (magnitude and direction)

  • 5g down

  • 1.5g sideways

  • 4g backwards

Changes from Previous Set-up

  • contact type (bonded → frictionless)

  • frame of reference and fixed supports

  • material

4.0 Simulation Results

https://docs.google.com/presentation/d/1M3C-9bhbgHqtGNw2gmPNj2dSemw7HNtHhgXArRNWh2c/edit#slide=id.geabf25bd74_0_114

5.0 Conclusions and Next Steps

  • In general, the “DOF errors” kept appearing on different tubes of the chassis in UX, UY and UZ. 

    These tubes were constrained (fixed or displacement constraint) in order to help with convergence. However, this method was not efficient as the errors continued to show up in other areas. 

    Eventually, this method led to a point where constraining elements any further would lead to inaccurate modelling in the behaviour of the chassis. (i.e. fixing all tubes will allow the sim to solve)

  • Due to limited time constraints, the convergence issues that arise from the non-linear contacts were not able to be resolved.

  • Moving forward, it is best to continue using the bonded contact type only.

6.0 Other Resources: