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1.1 Errors within Organizations
Next, we will be sharing the mistakes made by CAE engineers working in di!erent organizations.
Common CAE mistakes
CAE
Engineers
Marketing
Engineers
Managers System
Administrators
HR
CAE Engineers :
1) Submission of a job without the proper checking (should be cross checked by ideally 2 CAE
engineers): Checking the work of someone else is a rather boring and not willingly accepted job. But
it is very important and a job of high responsibility. Checking and rechecking all the details, ensures
good quality and minimal mistakes.
For example, a CAE service providing company submitted a meshing job to their regular client.
Everything was perfect except for the material properties. The analyst at the customer end was used
to error free models being submitted by this CAE team over the years. He blindly started the analysis
without checking the material properties. At a later stage in the design process, a big di!erence was
noticed in the results of the current analysis and the previous one carried out for a similar model.
After checking both the models carefully, the analyst realized the di!erence in the material properties.
Please be careful before submitting your work and check it several times and then ask your colleague
to check it as well. Also, always request that your client check the model in every aspect before starting
the analysis.
2) Import / Export errors : Some of the preprocessors do not export all the elements and boundary
conditions that exist, unless special options are turned on or special translators are used. One CAE
group exported a big mesh model with the template set for a speci"c external solver. Some of the
special elements (RBE3 elements) were not exported due to a translator problem. These were extra rigid
connections and were not resulting in rigid body modes during the free-free check. The analysis was
carried out As-It-Is by an analyst. Based on the CAE results, the CAD engineers released the drawings
and a prototype was prepared. The test results were not satisfactory and further modi"cations were
suggested. Updated CAD data was provided again to the same meshing group. The changes were
local and it was to be carried out on the earlier submitted model. By this time, the CAE group had an
upgraded version of the pre-processing software and the export operation was 100% successful (all
the elements including the ones that were missed earlier were exported properly). The results for the
modi"ed model showed a drastic di!erence when compared to the original. After careful checking and
I Common Mistakes and Errors
This chapter includes material from the book “Practical Finite Element Analysis”. It also has been
reviewed and has additional material added by Matthias Goelke and Gareth Lee.
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comparing the number of elements, the analyst realized that a few rigid elements were missing in the
"rst model. Hundreds of engineers had worked on the job in the mean time (CAD, prototype, testing,
planning etc.). Who is responsible for this delay and cost? Is it the analyst, the service provider, or the
pre-processing software? It’s strongly recommended to import the mesh model before submission to
the client (in a new "le) and apply all of the quality checks as well as compare the number of elements
of each type (like number of tria, quad, rigid, spring, mass etc.).
3) Experienced engineers are the best guides and teachers for newcomers and less experienced
colleagues: CAE engineers are usually highly quali"ed (education wise) and having years of
experience means that a lot of know-how and knowledge is available within the team. The best
teachers for newcomers in any organization are undoubtedly the senior engineers working in the
same group. Software trainers or consultants do not know exactly what is required by the customer.
Every company should encourage and pay special incentives for experienced engineers to share their
knowledge with the newcomers.
4) Meshing is considered as low level work, post graduates and PhDs are reluctant to spend
time on meshing: Sometimes a dangerous trend is observed among post graduates and PhDs. They
feel meshing is a low level job and being highly quali"ed, they should not waste time in such low level
work. A building cannot be built on a weak foundation. Meshing is the foundation of CAE. At least
in the initial years, analysts should be encouraged to mesh the components.
5) CAE engineers are reluctant to visit the shop !oor, testing department, or "eld to study the
manufacturing, functioning, and failures of the components: Just sitting in front of the computer
in an air-conditioned o#ce and submitting nice analysis reports is not going to make the analysis
successful. What is absolutely necessary is to regularly visiting the test department, observing the
components on the structure, and comparing the real life performance with the computer model.
These days, many times a CAE team is located in a di!erent country than the manufacturing and
testing facility. The quality of the CAE work would be much better if there is an opportunity to know
the product, manufacturing process, testing and on "eld behavior.
6) Providing basic training related to data acquisition and testing: At least a basic training on the
data acquisition and testing methods is strongly recommended for CAE engineers.
7) Unnecessary emphasis on modeling the minute details without giving due consideration to
available time, hardware, and software capabilities: Finite Element Analysis is an approximate
approach. Modeling the things to the minute details without giving due consideration to the
capabilities of the available software and hardware could unnecessarily complicate the problem. For
example, when analyzing a structure and the failure is expected at the body, a bolt should not be
simulated by modeling the minute details like threads. Instead a beam element and connections
using rigids in the washer area could adequately model the bolt ( in the linear static domain).
8) Loyal to speci"c software and a resistance to learn and use new ones: Engineers using a speci"c
software for years, are not willing switch to other one. No commercial software is perfect and every
software has its own plus and minus points. In the service industry, what matters most is the time and
quality of the work. If a speci"c software is good but takes more time in comparison to another one
for some speci"c application, then it is better to use the better one. Sometimes a combination of two
di!erent software works faster. For example, meshing in one software and then performing quality
improvement or remeshing in other. A CAE engineer should be loyal to his/her duty rather then a
speci"c software.
9) Not the CAE engineers but the design engineers are the most important person in the design
chain: CAE Engineers are usually highly quali"ed, paid higher salaries and sometimes it leads to a
superiority complex (that they are the most important people in the design cycle process). But it
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should always be remembered that the Design Engineer is the most important person and the role
of CAE engineer is to provide analysis services to him/her (other service providers are test, purchase,
manufacturing, etc.).
10) While suggesting the modi"cations, no consideration for the manufacturing constraints
and the cost e#ectiveness: Sometimes the CAE engineer gives suggestions which are either not
manufacturable or cost e!ective. For example, it is very easy to increase the thickness of the parts
showing a higher stress, or to suggest that high strength (costly) material should be used, or to
suggest geometry modi"cations without considering the manufacturing constraints. Sometimes CAE
engineers are adamant about their proposals and are not willing to carry out further iterations as per
suggestions from the design or manufacturing engineer.
CAE Marketing Engineers :
1) Accepting jobs beyond their capabilities: Sometimes marketing engineers accept jobs just
because it is from a reputed company or because the volume of work is very large, without giving
due consideration to the capabilities and limitations of their technical team and available software /
hardware.
2) Promising unrealistic time schedule: Sometimes marketing engineers promises to deliver results
in a time span that is not possible with the current strength of the team and the number of software
seats available. Maintaining a strict time schedule with good quality work is necessary and re$ects the
successful marketing of any company. Sweet talking, impressive infrastructure, and other facilities can
create an excellent "rst impression with the client during initial visits, but it will vanish in no time if the
delivery schedule isn’t maintained and the quality of the work is poor.
CAE Managers and Group Leaders:
1) Committing the job without consulting the CAE engineer: In particular, during a visit to the
clients, managers whose domain is not CAE are involved in the meetings and they sometimes commit
to the job without consulting the responsible person.
2) CAE manager / group leader should be someone who has spent several years in the "eld, not
the one who is an expert in another area or a non-technical manager: A CAE experienced manager
understands the problems faced by CAE engineers and is capable of helping them personally when
required. A CAE job is supposed to be a white collar job, but it really requires day and night hard work
and involves lot of mental stress due to tight delivery schedules. The following replies from managers
or group leaders could be very frustrating and demoralize any CAE engineer “don’t ask me, that’s your
job” or “you should know these simple things” or “if you cannot do it we will "nd someone else” or
“I want results and not the problems, don’t come to my o#ce without the results understood!”. …….
CAE Process Management: CAE Process Management is helping organization to capture knowledge
and ensure best practices for CAE. It can be used for CAE load case automation, process guidance, and
process integration. It lets organizations implement standardized CAE processes that automate the
load case setup, interface with CAD, PDM systems, databases, and other IT systems and applications
by capturing the “best practices” as templates. It also helps them retain knowledge, even though
people may quit and leave organizations besides improving productivity and reliability of doing CAE
between di!erently skilled CAE users.
CAE System Administrators:
1) Laziness in "xing computer hardware / software related problems: In a group of 15 CAE
engineers, a minimum of 15 workstations are required. Computers are, after all, machines and bound
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to create problems. It will not be logical to expect the best performance from the team without
providing them good computers and "xing the hardware, software problems immediately. A
knowledgeable and prompt system administer is a very valuable asset for any CAE group.
2) Improper data backup process: One cannot a!ord a data loss at the midpoint or at the project
completion phase. Imagine what the impression of the organization would be if they say to the
client that although the job was almost "nished, the system crashed and we did not have proper
data backup. It is the responsibility of a system administrator and CAE manager to ensure the simple
arrangement for the daily backup and forcing all the users to backup before leaving the o#ce. Another
good practice is to avoid working in on a single "le through out the process. Instead, save the "le with
a di!erent name after every 3 or 4 hours of work is recommended.
HR:
Inconsistent salaries for the same post and same job pro"le: In many (probably all) organizations
the most infamous department is HR. In CAE groups it is common to "nd inconsistent salaries for
the same quali"cation and the same job pro"le. When there is an urgent requirement, HR people
generally o!er higher salaries. When engineers come to know that the newly recruited person has
been o!ered much more than what they are getting, they feel frustrated. Sometimes this results in
HR recruiting one new engineer and as a result, two existing engineers leave.
1.2 Modeling and Visualization:
While the above summary re$ects errors and mistakes from an organizational point of view, the
following high level summary is about modeling and visualization errors. During the analysis, the
FEM solver will report Warnings and Errors. While warnings can be considered as hints e.g. element
quality is bad, errors cause the analysis to stop. Errors may be related to extremely distorted elements,
missing material properties, rigid body modes due to insu#ciently de"ned constraints etc.
The below listed modeling pitfalls can be considered as “appetizers” with the intention to make
you think (and worry) more about the model set-up. More in depth details regarding the di!erent
modeling pitfalls are provided in the remaining chapters of this book.
Geometry simpli"cation
In many cases it is appropriate or even required to simplify the imported geometry in order to
achieve a better mesh quality. For instance, the required minimum element size must be not
smaller than x millimeters. In order to solve this (project) related requirement, small "llets may
be replaced by sharp edges, as shown in the images below. Even though this simpli"cation was/
is requested, keep in mind that your FEM model now “deviates” from the initial geometry.
Meshing
What kind of elements are you using in your model? Why are using this element type? Did you
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use this element type before?
You may mesh a thin walled 3D structure with 3D elements such as hexahedral or tetrahedral
elements, or you may mesh the same structure with respect to its midsurface using 2D elements
(trias or quads).
Model meshed with 3D elements
Model meshed with 2D elements
Aside from the “decision” of whether to use 2D or 3D elements, there are other “uncertainties” (or
even errors) related to the di!erent numerical characteristics of quad versus trias and hexahedral
versus tetrahedral elements (see the Chapters on 2D and 3D meshing).
Another modeling error may be related to element size. The ultimate objective or aim is that the
modeling results are independent of mesh size. Typically you need to re-run the analysis based
on a "ner mesh to check for convergence of the simulation results. As a rule of thumb, areas of
interest should be meshed "ner (smaller element size).
Of utmost importance is the element quality. Keep in mind that the elements not only “re$ect”
the CAD model, but eventually the analysis is based on the "nite elements. Hence, any deviation
from the ideal element shape (e.g. perfect quadrilateral shape in case of a quad element)
introduces numerical errors. The magnitude of which is generally di#cult to assess.
In the model shown below some elements are not coupled to each other (i.e. duplicated nodes
exist), hence the mesh is locally incompatible. The area along the edge where the elements are
not coupled is marked in red.
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Still, the FEM program does not prompt any warning or error messages as this may be an intended
model behavior. If the mesh is not intentionally detached (and the model is not checked for
free edges) then this model error may remain unknown until the results are fully checked and
understood. As shown in the contour plot below, the displacements are not continuous across
some parts of the mesh.
Also, keep in mind the orientation of the element normals. In the image below, a simple plate
subjected to bending is shown. The stress contour plot (at the base of the elements Z1) reveals
a sudden change of its sign from bending (positive) to compression (negative).
The following "gure helps to understand this situation. In the green area Z1 is located at the
top of the plate (tension) while in the blue area Z1 is located at the lower side of the element
(compression).
Material
Inconsistencies in your unit system represent another likely source of error, i.e. mixing millimeters
with meters, kilograms with tons, etc. Be especially cautious if you need to convert properties
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from one system to another (e.g. pound-force lbf to Newton). There will be no warning message
associated with any typos, except the “typo” will cause the entire model to “collapse” during
analysis.
Boundary conditions and loads
Errors are extremely prone with applying boundary conditions and loads as discussed in the
Chapter on Boundary Conditions and Loads. To be mentioned exemplarily, a modeling error
may be introduced into the model by applying the constraints (or forces) to what is named
temporary working nodes (in HyperMesh displayed as yellow nodes).
As the temporary nodes (yellow nodes in the image above) are not the same as "nite element
nodes, it may happen that the structure is not constrained or loaded as intended. “Ideally”, this
may lead to rigid body modes (error message) or to questionable results due to an improperly
constrained or loaded model.
Visualization
The blitheness that the analysis went through after struggling around with the model, may lower
your attention regarding details while looking at the results. Quite often, especially while you
are new to FEM, one becomes blinded by contour plots. Hence, always check the magnitude
of displacements and stresses in the "rst step. Despite a reasonable looking displacements (or
stress) contour plot, you may see displacement values in the order of 104 mm (small displacements
assumed) or stresses far beyond 1000 MPa (linear elastic material).