39
votes
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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14
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 ...
- 13.1k
7
votes
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
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
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, ...
- 13.1k
6
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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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 ...
- 12.5k
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:
$$...
- 1,831
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 ...
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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 ...
- 1,951
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 ...
- 2,646
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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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
How to simulate car acceleration
The crucial thing here is that for IC engines torque is some function of RPM and so you need to consult the torque curve for a given engine to do any sort of meaningful modelling.
This is also ...
- 15.2k
3
votes
Accepted
How to model a sheet metal nut in SolidWorks?
You might be interested in Smart Components / Smart Features. This technique will associate parts with features.
As for the naming, we call those "Press Nuts", or more generically "Press Hardware"
- 99
3
votes
What do these sigma subscripts represent?
Wood is anisotropic. Its mechanical properties are different in different directions relative to the grain of the wood.
The R, L and T suffixes probably refer to the radial, tangential, and ...
- 12.5k
3
votes
Accepted
Two dimensional plasticity with radial return
Let's look at this problem mathematically a la Simo.
Let stress tensor ($\boldsymbol{\sigma}$) and its deviator ($\boldsymbol{s}$) in plane stress space be
$$
\boldsymbol{\sigma} = \left[\sigma_{11}...
- 1,443
3
votes
What program to implement mathematical models?
"Numerical Recipes" is probably what you need the most. It contains tons of useful scientific/numerical computation codes. It's a book, but I believe it was also available online.
Apart from that, ...
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3
votes
Accepted
Failure of N.R.T.L method to model Phenol / Methylcyclohexane / Toluene system in AspenPlus. Why?
At moderate temperatures and pressure NRTL should be a good option provided that the binary interaction parameters are correct.
You need to check:
Whether the binary interaction parameters for your ...
- 335
3
votes
Accepted
Modelling gas desorption from a still solution (e.g. a beer)
In perfectly stagnate gas systems, transport of a component through a gas collapses to diffusion of the component through the gas. In this case, $k_L a \propto (D / \delta)^n$ where $D$ is diffusion ...
- 2,878
3
votes
Parametric equations for fan blades
For propellers, one usually has blade reference lines called generator lines. They can be parametrically defined in terms of blade number, skew, rake, hub dia, tip dia. If the generator lines are the ...
- 4,597
3
votes
Viscoelasticity and Hyperelastic model, history and difference
Let's look at some (very rough) definitions:
1) Viscoelasticity = elastic behavior that changes if the rate of application of the load is changed or, if the load is kept fixed, the change in the ...
- 1,443
3
votes
Accepted
Viscoelasticity and Hyperelastic model, history and difference
The hyperelastic and viscoelastic material models are both constitutive relations that relate:
Stress and strain, in the case of hyperelasticity.
Stress, strain and strain rate, in the case of ...
- 398
3
votes
Modeling the torque of a real motor
Your general model for an electric motor could be for example, as follows.
$$J \phi ''(t)=\text{I} \tau -R \phi '(t)$$
with J as your [kg m^2] inertia, I in [A] amps, and R your friction...at the ...
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