38
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From an engineering point of view what are the downsides of a too accurate model?
Beware of overfitting. A more accurate model of gathered data from a system may not be a better predictor of future behavior of a system.
The above image shows two models of some data.
The linear ...
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27
votes
From an engineering point of view what are the downsides of a too accurate model?
The most obvious downside is cost, all engineering projects have a finite budget and spending more money than you need to is clearly a bad thing not to mention wasting time.
There can also be more ...
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13
votes
From an engineering point of view what are the downsides of a too accurate model?
There are a few reasons.
From a purely pragmatic perspective, it's due to time constraints. The requisite time to solve a model increases far, far faster than the level of precision, and whichever ...
- 13k
8
votes
Accepted
Sending out a 12d Civil Design Model
Before I start, let me disclose that I don't know a lot about the details of infrastructure projects or your file format, but I think the general considerations are fairly universal.
There are a ...
- 4,511
7
votes
Can two different modeling programs be used to confirm the results of each other?
Yes, getting a second opinion can be useful. This is done routinely in weather forecasting where exact solutions are unknown, and there is some judgement about how to apply various factors.
There ...
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7
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From an engineering point of view what are the downsides of a too accurate model?
An extremely accurate model may require a prohibitive amount of input data. It might be possible to generate an excellent model of weather systems, for example, by taking as input the position and ...
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6
votes
Is a distributed load in two parts equal to a full distributed load?
Splitting a uniform load into separate pieces that are still continuous will have no effect. This is frequently done.
As far as your question about bending in HE and EB, there shouldn't be any ...
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6
votes
Meshing of complex geometrical domains
While the other guys explained the theoretical framework behind meshing, the practice is markedly different and it is not at all automatic in industries where quality of mesh is of utmost importance ...
- 95
6
votes
Can two different modeling programs be used to confirm the results of each other?
I write this from the perspective of an engineer who develops simulation software.
I think the practice described is bad, and I recommend you do not use two different softwares to "confirm" the ...
- 986
6
votes
Differential equations of a (simplified) loading bridge
Kinematics and dynamics
Those are the steps to solve problems of this nature.
Analize the kinematics of the system.
$\hspace{5.em}$ $_{o}\vec{r}_{OP}$ = $_{o}\vec{r}_{OR}$ + $_{o}\vec{r}_{RP}$
$\...
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6
votes
Accepted
How do you model a real-life truss in structural analysis software?
The most common way to model this structure is as follows (ignore the fact that the proportions are a bit off):
So, all of the diagonals are pinned-pinned. You'll notice in the schematic, however, ...
- 13k
5
votes
Accepted
Differential equations of a (simplified) loading bridge
My guess is that you probably need another differential equation for the angular movement, that will involve the inertia, such as:
$$m_G l^2 \ddot{\varphi} = m_G g l \sin(\varphi)$$
which yields:
$$...
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5
votes
Accepted
Modelling splashing water in FEA
This may be only a partial answer since I don't have any idea what to do for the Young's modulus of the fluid.
Consider the paper Dynamic Pressures on Accelerated Fluid Containers by G. W. Housner. ...
- 3,587
5
votes
Adding a lubricant to an already lubricious material, how is CoF affected?
You can't calculate friction coefficients this way. At the atomic-scale level, the friction coefficient depends on the interactions of the two materials across the interface. If you measure the ...
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5
votes
From an engineering point of view what are the downsides of a too accurate model?
"Too accurate" is not monotonic. It can actually create an illusion of fidelity which makes you think it's worth pumping more money into the simulation. This becomes very important when you're ...
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4
votes
Can two different modeling programs be used to confirm the results of each other?
I think this is a good practice overall.
By using two different softwares, you may be able two avoid two kind of errors:
1) errors that come from an inaccurate software (which should not be ...
- 149
4
votes
Accepted
Is a distributed load in two parts equal to a full distributed load?
I would expect the modeling as a single load to be accurate. Force per linear area is the same expressed either way. You could look at a linear load on a single beam and just add more points of ...
- 321
4
votes
Accepted
How do I use FEM to derive the torsional constant of an arbitrary shape?
You can find an implementation of a finite element used in computation of arbitrary shape section torsional constant here:
http://projects.ce.berkeley.edu/feap/elmt11.f
I don't see any reference in ...
- 56
4
votes
Accepted
connectedness between the output voltage and input voltage
You can write two ODEs describing the relationship, and that would be in the time-domain. Alternatively you could describe things in the frequency domain and get the relationship as a transfer ...
- 1,901
4
votes
How to define Knurl on drawing?
It looks to me like your guess was pretty good. The required information is only the type of knurl, the extents of the knurl, and the pitch. It is conventional to show the representative pattern, but ...
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4
votes
How to define Knurl on drawing?
The (European) standard for knurls is DIN 82. The standard includes a proposed drawing representation as well. Its intention is to describe hand gripping aid knurls. As Ethan48 says, for fitting you ...
4
votes
How I can compute cutting processes with continuum mechanics?
Real-world engineering example
To my knowledge there are no simple analytical methods of determining whether an object such as a sword can cut cleanly through any arbitrary object. In manufacturing ...
4
votes
Accepted
polar moment of inertia for compound shape
Without looking up all the formula's for you, the approach to this problem is rather simple. Find the polar moment of a solid cylinder, and subtract off the
polar moment of the holes.
For the off ...
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4
votes
Matrix Calculation
Your numbers are right. You are just confused about matrix multiplication. See https://en.wikipedia.org/wiki/Matrix_multiplication (or any linear algebra textbook):
For matrix multiplication, the ...
- 2,626
3
votes
Accepted
Discontinuity in mechanism simulation: is the mechanism jammed or is my analysis wrong?
If you plot the x values of OP and HP, they cross zero, which seems unphysical.
Looking more closely, you are doing your rotations backwards, i.e. you are doing our rotations in +theta whereas you ...
- 1,035
3
votes
Modelling splashing water in FEA
Section 2.1.14 of the Abaqus Example Problems Manual is 'Water sloshing in a baffled tank', which might be useful (even if you don't use Abaqus at your own institution, the manuals are hosted by many ...
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3
votes
How do I use FEM to derive the torsional constant of an arbitrary shape?
This is a problem which is usually solved in books on elasticity theory. The underlying math is based on the solution to the Laplace PDE.
If you do a Google search for Larry J. Segerlind's book "...
- 312
3
votes
FEM modal analysis computing displacements
As modal analysis is performed in the frequency domain, your modes and amplitudes are also in the frequency domain.The modal amplitudes ($q_i$) are scaled by the same amount as the applied load. If ...
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3
votes
Is a distributed load in two parts equal to a full distributed load?
Adding just a slight notion:
Your experience would always expect the beam HE to buckle, because it is a Eulerian buckling beam (don't know if it's also called like this in English).
The numeric only ...
- 111
3
votes
Accepted
System model for motor controlled inverted pendulum with rotating motor body (used in camera stabilizer application)
There's a couple questions you can ask:
Can you control the signal? If not, then it's either a noise or disturbance input.
Is it affecting your system (plant), or is it affecting your measurements? ...
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