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 ...
- 499
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 ...
- 15.2k
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 ...
- 244
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 ...
- 293
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 ...
- 939
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 ...
- 2,656
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 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
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
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
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 ...
- 2,991
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 ...
- 4,900
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)$$
with J as your [kg m^2] inertia, I in [A] amps, and R your friction...at the ...
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3
votes
linearizing a non linear state space equation
The Lagrangian for your 1D pitch system is $\mathcal{L} := T - U$, which is
$$
\mathcal{L} = \frac{1}{2}(mb^2 + Ma^2)\dot{\phi}^2 + \frac{1}{2}J\dot{\theta}^2 + (Ma - mb)g\sin\phi
$$
The Euler-...
- 461
3
votes
Help understanding this dimension sheet
h11 is the tolerance range. There's a standard shaft/hole chart based on dimension/tolerance. (sorry about the images, I've searched on google but cannot find everything on the same image).
h11 is ...
- 355
3
votes
a model of a solid using trusses to approximate internal stresses?
Not only can this be done, but it also is done for concrete structures all the time.
The shear reinforcement in concrete beams is calculated using Mörsch's truss analogy model:
Source
The concrete ...
- 13.1k
3
votes
I’m having trouble converting this orthogonal shape to isometric, I’m only a beginner and would really appreciate some help
Now can you draw it?
Post your attempt in your question.
- 10.9k
2
votes
Accepted
Shear area of atypical section
You can calculate the shear stiffness directly and then get an effective area after the fact if you'd like.
$$A_{shear}=\frac{V}{\gamma_{ave}\,G}$$
You can calculate average shear by averaging over ...
- 1,335
2
votes
Accepted
deformation-dependent damping
I think "viscous" refers to the physical effect that causes the damping - i.e. the viscosity of a fluid. The viscous forces might be a linear or nonlinear function of the velocity, or something more ...
- 12.5k
2
votes
Mathematical modelling of the crank in a two-stroke (diesel) engine
You don't need a differential equation.
Write the kinematics for the piston as
$$\begin{aligned}
x & = r \sin(\varphi) - \ell \sin(\beta) =0 \\
y & = r \cos(\varphi) + \ell \cos(\beta)
\...
- 703
2
votes
How to simulate car acceleration
I don't know if you're still interested in this topic, but it sort of relates to a question I had about modeling acceleration. I might be able to clear up some confusion, though, because I had the ...
- 41
2
votes
How to simulate car acceleration
Real-world torque at standstill:
This is not your main area of concern but needs addressing so that you can then properly deal with the main issue.
Your statement
at t=0 acceleration is ...
- 3,874
2
votes
How to find the angle of deformation in Ansys APDL?
You can easily get the structural rotation around X axis for a given node (N) using the next APDL command: *get,Parameter_output,NODE,N,ROT,X. You can substitute <...
- 131
2
votes
Using a controller for a simple heating system
You shouldn't use a proportional control. The type of controller you describe (switching from 0 to full load and back to 0 almost instantaneously) is called a bang-bang controller. This controller is ...
- 1,210
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