presentation on my helmet design

1. HELMET DESIGN
ENGG30061
Tristan Procida
N0972073
Mechanical Engineering
Nottingham Trent Univeristy

2. Set Up and initial shape created
The design process begins with importing images into
Fusion 360 as a canvas to trace. This will assist as a
guide for keeping within the shape of a helmet when the
main shape is being created. To do this, a quadball is
used. This feature in Fusion 360 allows the user to
manipulate. To make it easier to achieve the desired
shape, setting the three angles of the helmet canvas as
unelectable prevents the images imported from
accidently being selected while edges, vertices and faces
are being selected. In addition, the opacity can be
changed so that the canvas doesn’t completely obstruct
the the quadball.
The shape of a helmet is eventually
reached, and the canvas can be turned
off.

3. Visor cut-out and fillet
modification for enhanced
aerodynamic performance
The initial visor cut out on the helmet is created by creating a sketch on the plane that is the
side view of the helmet. The spline tool, (in combination with turning the canvas back on) is
how the general outline of the cutout is achieved. At the same time, a copy of the original
form is pasted and scaled down slightly as shown in the image, to provide the different layers
that make up the helmet. A similar process is used to cut another section out of the helmet
for the driver to look through. The split tool is used to create a serration between on the
surface of the body, resulting in a new face. This face can then be separately selected and
then deleted. The model of the head can then be unhidden to check if the scaling and
positioning of where the eyes would be line up with the helmet. Further adjustments such as
exaggerated fillets were made as this benefits the aerodynamic function of the helmet which
is demonstrated later in the simulation on Ansys.

4. Visor and appearance
The visor cut out for the outer shell was then
copy and pasted and scaled up while also
using the thicken function to produce the
actual visor. The same thicken function was
used to give the rest of the helmet its structure
and overall shape.
The appearance was then
edited by modifying colour
and material. Yellow was
chosen to provide good
contrast between the visor
and the inner padding that
was to be added later.
A transparent material was chosen for
the visor to imitate what it would look
like and its function in real life.

5. Additional Modifications
A cylinder was created, and then modified to give the
outline of the shape added to the front of the helmet below.
The patch tool was used to close off each end of the
cylinder and then the stich tool was used to make the three
faces become a single body. This body was then mirrored
twice to give the reverse vent below as well as the vents for
the opposite side of the helmet. These bodies were then all
selected and used the combine tool with the cut operation
to use them to create the openings in the front of the
helmet. These extra vents, as well has being an aesthetic
enhancement, will serve the function of enabling better heat
transfer rate seeing as this is where the user will exhale.
Sufficiency of these extra slots will be assessed during the
transient thermal analysis.

6. Final touches and render
Before rendering the final image, a joint was
created between the visor and helmet so that
the visor could revolve and move as a visor
would function on a conventional helmet.
Then, the inner lining was created by pasting
the main initial helmet shape and scaling it
down. Again, fillets were added and the
thicken tool was used. The appearance was
then changed to a different material to
represent the appearance of an actual helmet.
In the sculpt form, a pipe was added along
the perimeter of the cutout, for final details.

7. Computational Fluid Dynamics Set
Up The first steps include importing the
geometry into Ansys and creating an
enclosure around the helmet which tells
Ansys how much air around the helmet to
simulate. Too small and the enclosure will
affect the flow around the helmet, but too
large and Ansys will take too long to
simulate. The chosen dimensions of the
enclosure as shown in the image (right).
The next step was to create named
selections: wall, inlet, outlet and helmet.
After creation they successfully
appeared in the tree outline.

8. Computational Fluid Dynamics Set
Up
Before the mesh was generated the resolution
was increased to 7 from the default, 4. This
allows Ansys to create a finer mesh, so although
taking longer to generate, it means that the final
solutions will be more accurate.

9. Once the simulation is complete, Ansys will be able to produce the drag coefficient of the
helmet. However, first, a necessary piece of data that is required for the formula of the
drag coefficient is the area of the cross section. To do this, the helmet is traced with a
sketch in the front view. The inspect tool can then be used to calculate the area of this
outline as well as the length of the helmet.
Computational Fluid Dynamics
Set Up
These values can then
be entered into Ansys,
ready for simulation.

10. CFD Results
The results
returned a drag
coefficient of
0.27302144 after
1500 iterations.

11. CFD Results – Velocity Magnitude
After solving, an XY plane (offset from the
origin) and XZ plane can be added to
provide a surface to display the result of the
surrounding air when considering the
velocity magnitude. The maximum air
velocity experienced is at the top and
bottom, as well as sides of the helmet at
2.36e+01 m/s.

12. Using path lines is an alternative way to display the
results of the simulation. Through this way of
displaying results, the offset XY can be removed and a
view of the airflow trailing behind the helmet can be
seen to be transitioning from laminar to turbulent.
CFD Results – Velocity
Magnitude

13. CFD Results – Static Pressure

14. Limitations of CFD Simulation
The first point to consider would be that the driver won’t always have their head
at the same angle, and so any changes to their head position while in use will
change the front cross section perpendicular to the flow. This means that for a
more successful simulation, the angle at which the helmet is placed in the
enclosure will have to be changed at any possible angles the driver's neck can
access. This could be a safety concern because if a helmet were to experience a
significantly different drag coefficient at different angles, the driver may
experience injury due to the force applied to their neck and spine. Another
consideration would be that the helmet had to be simplified for the sake of the
simulation as the visor had to be removed and the bottom of the geometry of the
remaining helmet had to be patched as a shaped with an open bottom would
introduce complications if it was to be simulated. Therefore, results from the
simulation are only approximate and can only provide data on the general shape
of the helmet.

15. Thermal Analysis Simulation
Results
The scale on the left shows that the
maximum temperature experienced by the
head is approximately 26 degrees Celsius.
This was experienced at the nose, with
other areas of relatively high temperature
at the chin (approximately 25 degrees
Celsius).

16. Thermal Analysis Simulation
Results
These images show the same simulation but
without the helmet. The distribution of heat is
much easier to observe here.

17. Limitations of Thermal Analysis
Simulation
The simulations is set up with materials that may not be representative of what the helmet
might be exactly made of. So due to the different heat properties of different materials, the
thermal analysis will not give results applicable to all helmets that share this geometry. In this
simulation, the materials used were Polyurethane, Nylon and a custom value for human skin
(which neglects other components of a human head such as the skull, skin, varying thickness
etc.) In addition, the temperature that the wearers head will fluctuate. The same can be said for
the environment of the heat applied to the surrounding air of the helmet, especially in certain
contexts such as motorsports. This means that the set starting temperatures of all involved
geometries will not be representative of real life and results from this analysis can only be
approximate, although should still represent how the shape and vents (as well as other physical
features) can affect the heat retention this particular system. The body representing the head in
this will also not be representative of a real human skull as realistically, skulls have varying
thicknesses which ultimately affect heat transfer.

18. Explicit Dynamic Simulation Set
Up
The first steps was to choose the materials that were to be
used in the simulation from the engineering data sources
provided by Ansys.
The next steps was
to import the step
file of my geometry
with an added
‘curb” which is to
act as the source of
impact. Once done,
the correct
materials could be
assigned to the
correct bodies.

19. Explicit Dynamic Simulation Set
Up
A mesh can be generated
for all four bodies with the
resolution reduced to 3.
This was done to save time
as this simulation is a
lengthy one to run however
this doesn’t negatively
impact the results gathered
from this significantly and a
resolution of this size is
‘Contacts’ under ’connections’ in
the outline is selected to make sure
the contact regions are set up
properly. These include the helmet
to the lining and then the lining to
the helmet. Bodies selected in red
are the contact bodies and blue
indicates it is a target body.

20. Explicit Dynamic Simulation Set
Up
The face displayed was assigned as the fixed
support. This is to prevent any unwanted
movement once we solve for the results. When
looking at the force reaction, the same face was
chosen.
The end time was set to
0.009 seconds as the
point of interest is only
the moments just before
and just after the
impact.
Once prepared, the outline looked like this.

21. Explicit Dynamic Simulation
Results
The simulation is then ran and we
are provided with a heat map
displaying the areas of the most
stress experienced by the helmet.
Intuitively it is at the point of
contact between the helmet and
the concrete block as well as the
corners of the cutout for the users
eyes (near the user’s temple).

22. Explicit Dynamic Simulation
Results
1 2 3
4 5 6
7 8
9

23. Explicit Dynamic Simulation
Results
When looking at the results of the
helmet from this angle, a
limitation of the simulation can
be seen as the lining of the
helmet moves from its starting
position and so this interferes
with the real-life dynamics of an
impact while wearing this helmet.
The graph below each stage of
the crash shows at what point in
time the image is at and
1 2 3
4
5

24. Video of results

25. Explicit Dynamic Simulation
Results
The images display what
stresses the human head would
experience if a helmet wasn’t
to be worn in the same
scenario. We are able to see
that a max stress of 7.2139e7
Pa is reached. Therefore,
although not an optimum
helmet, some protection will
still be achieved.

26. Limitations of Explicit Dynamics
Simulation
The findings of this simulation are limiting as impact is only considered from one direction
when in real scenarios, the driver could be struck from any angle. Moreover, an accident
doesn’t usually just consist of a single impact but rather multiple consecutive ones (if a
driver were to roll around on the floor). This could affect how the helmet responds to
impacts on part of the helmet that are already under stress at that time of a successive
impact. Also as stated before, the material chosen such as concrete, nylon and
polyurethane won’t give sufficient data to draw conclusions on the effectiveness of the
helmet. For example, the driver wont always come into contact with concrete, a lot of the
time it is the vehicle itself that they are driving.

27. In conclusion, the limitations of such a study are too great to make safe assumptions about
the suitability of the helmet for its intended use. Out of the three studies, the most reliable
one (and most beneficial one) will be the CFD as although only looking at a rough geometry
of the original helmet, the details ignored in the simplified version were probably negligible
at the speed the simulation was run at and so the calculated drag coefficient can be expected
to be the approximately the same, and so further modifications to made to the helmet in CAD
can be based off this current drag coefficient for any optimization. With some of the
limitations lying in the materials chosen for the simulation, a wise consideration would be to
look at what potential material the helmet could be made out of. Carbon fiber is a suitable
material for the construction of the helmet. Despite its usually high cost, this shouldn’t be an
issue for the context of the use of the helmet as budgets are usually high in competitive
motorsport environments. This means that competitors are willing to pay anything for the
best in the industry. The features of carbon fibre that outweigh other conventional materials
for helmets (such as fiber glass) include a high strength to weight ratio, which is perfect for
reducing the most amount of weight possible as well as having enough strength for the
safety of the user. (navcomm, n.d.)
Conclusion

28. References
navcomm. (n.d.). Fiber glass or carbon fiber.
Retrieved from navcomm:
https://navcomm.eu/en/content/18-fiberglass-or-
carbon-fiber