RMIT Auto1026: Audi R8 Car Body Design and Analysis with Beam Elements

This presentation details the design and analysis of the Audi R8 car body using beam elements. The study utilizes Altair Hypermesh for pre-processing and NASTRAN for solving modal and frequency response analyses. The car body is modeled using 76 nodal points and 17 different thin-walled box sections. Modal analysis reveals natural frequencies, with the first mode at 42.5 Hz, exhibiting torsional twisting. Frequency response analysis, with single node, in-phase, and out-phase excitations, validates the modal frequencies. The analysis calculates the car body's mass (295.4 kg) and provides insights into its structural behavior under different excitations. The results are visualized using Altair Hyperview, demonstrating the application of CAE tools in automotive engineering.

Slide 1:
Today I am going to present design and analysis of the Car body of Audi R8 model using beam
elements. A modal analysis has been performed to obtain natural frequencies of car’s body-in-
white and a force excitation analysis is performed both in-phase and out-phase to visualize car
body’s frequency response.
Slide 2:
In this slide, I explain the chosen car Audi R8’s body in white which is chosen to perform current
study. Audi R8 is a 2-seater sports car which is made by German car manufacturer Audi and its
model was launched in the year 2006. Its body is built in Aluminum. Till now Audi has launched
3 different versions of this car and it is amongst most famous sports cars around the world. Audi
R8’s body-in-white is shown on this slide which is taken as reference to prepare a CAD model
with closely matching dimensions. The length of the car is approximately 4.4 meters, width is
approximately 1.94 meters, and height is about 1.24 meters. More details about the modeled
body-in-white are discussed in subsequent slides.
Slide 3:
In this slide, model preparation of Audi R8 car model is explained. Using available dimensions
on the CAD model, car body has been modeled. Altair Hypermesh has been chosen as the tool
for pre-processing. A total of 76 nodal points has been defined in hypermesh to outline the car
body. These points define the locations which when connected prepare the car’s skeleton.
Coordinates of 76 points defined in hypermesh are listed here. By carefully connecting the
defined points with linear or straight line bodies as well as curved line bodies, shown model is
obtained. A 3D isometric view, side view, front view and top view are shown here. Since current
analysis utilizes beam elements hence line bodies are used to model the car body.
Slide 4:
To make the car body which comprises of different section, a total of 17 different sections are
prepared and assigned at respective line bodies. List of prepared sections are shown here. All
the sections are defined as thin walled boxes. Each of this section is used at least on a single
line body and some are used for multiple line bodies to make close to reality car model
Slide 5:

Once the section for beam elements are defined, a property is to be defined in Hypermesh to
assign it to respective line body. The material used for entire car body is Aluminum for which
elastic modulus is 72 Gigapascals and density is 2800 kilograms per meter cube. First a
material card is defined in Hypermesh named Aluminum as shown in the first figure. Now 1
property card is prepared corresponding to each section prepared. A total of 17 property cards
are defined corresponding to 17 sections shown on previous slide. When property card is
assigned to respective line body, its mesh size is also defined which is chosen as 10 millimeters
for current study. Once all the property cards are properly assigned, Output car body model is
shown in the figure here. All the views of car body, front, right and top are shown here. Once the
property card is assigned and line body is meshed, It is necessary to check for connectivity of
elements at nodes. For this equivalence check is performed in Hypermesh. After equivalence
check is done, many line bodies were found to be open and they are equivalenced so that entire
car body is connected. Now this model is ready to be taken for next step.
Slide 6:
Prepared car body is checked for its mass and volume. Based on assigned cross-sections and
material density, Hypermesh can calculated mass of each line body and sum them up to give
total mass of entire body in white. After selecting all the elements, the calculated mass of the
car body is 295.4 kilograms as shown in the figure. Now this model is ready to be exported to
run the modal analysis using NASTRAN solver. For this Hypermesh offers an option to export
the prepared model to relevant solver deck. When NASTRAN is chosen, Hypermesh exports
the prepared model in compatible format which is .bdf for current case. After export model is
solved in NASTRAN by using JCL.bdf file which is already provided for this study.
Slide 7:
Once the NASTRAN solver completes the modal analysis, it writes the results in multiple files.
Altair Hyperview software is used here to visualize the results here. Audi R8 car’s body in white
is shown here where coloring is done based on different components of the car model. The file
with extension .op2 is browsed and imported as result in Hyperview to perform post-processing.
Slide 8:
Now we explain the results obtained from modal analysis. The first 6 modes obtained from
analysis are rigid body modes which are neglected and actual natural frequency starts from
mode number 7 which is referred as mode 1 here. The very first natural frequency obtained

here is 42.5 hertz. For the purpose of plotting, the displacements are scaled by one thousand.
As seen in the first mode animation, the mode shape is torsional twisting. Entire car body is
moving together which shows that all the nodes are connected to each other and there are no
loose connection. The second mode is shown on the right hand side. Second mode’s natural
frequency is calculated to be 43.3 hertz. The mode shape is shown in the animation. Similar to
first mode, all the displacements are scaled by one thousand for this mode as well. This mode
shape is flexible bending mode.
Slide 9:
Third mode is shown in the animation on the left hand side. Its natural frequency is calculated to
be 59.8 hertz. Displacements are shown after scaling by one thousand. This mode shape is
chassis and cabin torsion mode. Fourth mode is shown on the right hand side. The natural
frequency obtained is 63.6 hertz which again by shape is looking to be bending mode.
Slide 10:
Another 3 modes taken out from post-processing are shown here. Mode 5 is shown in first
animation on this slide. Natural frequency obtained is 65.3 hertz. Mode 6 is shown as second
animation on this slide. Natural frequency obtained is 85.5 hertz. Mode 7 is shown at the bottom
most animation for which natural frequency is 94.6 hertz.
Slide 11:
After the modal analysis is completed and natural frequencies are obtained. A frequency
response function is performed on the car’s model. This analysis differs from modal analysis.
Here an external excitation force is applied and scale dynamically to obtained frequency
response of the system which can be compared with natural frequencies of the car body.
To perform this, a few more pre-processing steps are performed. The Hypermesh is used again
to renumber all the nodes of the car body. The total number is nodes in the model is 5855. After
renumbering is done, selected 6 nodes are renumbered starting from 6001 till 6006 as shown in
the figure above. Node 6001 and node 6002 are used to apply force excitations and output
response is taken at rest of the nodes. Once these changes are made, a solver deck for
NASTRAN is again exported from Hypermesh.
This analysis is performed in 3 different excitations. First excitation is single node excitation. It is
applied at node 6002. The file provided for single node excitation is used for this analysis. In
that, original node definition was used starting from 4001 which is changed to 6001 and so on

as per current model. The frequency response of single node excitation is shown here. The first
peak corresponds to frequency of about 42 hertz which was also the very first natural frequency
of the car model from modal analysis.
After single node, in-phase and out-phase analysis is performed. For in-phase excitation, force
is applied at 2 nodes in the same direction while for out-phase excitation, force is applied in
opposite direction. In-phase excitation is analysed for lateral bending of the structure and Out-
phase excitation is applied for analysing torsional bending of the structure.
Results obtained from analysis are plotted in Altair Hyperview. The Acceleration is taken as
output at the nodes and plotted in Decibal 20 here in these graphs. For both in-phase and out-
phase, first peak obtained is corresponding to first natural frequency which is 42.5 hertz. In-
phase shows further peaks which correspond to other mode shapes of the car body obtained in
modal analysis. Both in-phase and out-phase response is observed to be in sync for some of
the nodes while opposite for others. This concludes the results obtained from this study.
Slide 12:
As presented for this study, here are the conclusions. Altair Hypermesh can be used for post-
processing with beam elements and NASTRAN can be used to obtain solution for both modal
as well as frequency response. Audi R8 car’s body-in-white is simulated and analyzed in the
current study with beam elements and 17 different cross-sections to make its shape. Total
calculated mass of the body is 295.4 kilograms. Obtained natural frequencies of the car body
are listed here. A frequency response analysis is also performed for 3 different excitation
methods namely single node, in-phase and out-phase. The first peak of output response verifies
the first modal frequency obtained from the analysis.
THANKS !