Questions tagged [modeling]
Questions about approaches for simulating physical systems or phenomena by building from related understanding and basic principles.
190
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Spalart-Allmaras turbulence model
In this post Alex gives an implementation of the Spalart-Allmaras turbulence model [1, 2]. The example produces reasonable results, as far as I can tell. However, the implementation Alex uses deviates ...
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1
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Extension of: Numerically solving a system of SDE's with Levy noise?
A great answer by Alex is to be found here for my original question: Numerically solving a system of SDE's with Levy noise?
Now Let us perturb this system with time delays so the system is:
\begin{...
- 435
4
votes
1
answer
298
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Implementation of FEM to steady-state coupled fluid flow and heat transfer
This is a steady-state conjugate heat transfer problem (the time-independent version of this problem). The problem is conjugate as the energy equation is being solved in thermally connected solid and ...
- 297
7
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1
answer
238
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Modelling heat transfer in periodically reversing flow
This is a heat transfer problem, which involves reciprocating (fully-reversing) fluid flow over a heated block of solid. The objective is to determine the temperature field in the solid and the fluid ...
- 297
13
votes
2
answers
765
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How to Create Kapitza's Pendulum?
Hi, I have never worked on a project of this kind before. I am having difficulty using Kapitza's Pendulum (inverted pendulum with moving vertical base).
It is hard for me to make the model equations, ...
- 143
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1
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303
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Refining mesh size leads to absurd results for a coupled heat transfer FEM model
I have been recently solving a conjugate heat transfer problem, which involves fully-reversing or reciprocating flow of fluid over a heated block of solid. The problem is 2D and the temperature field ...
- 297
2
votes
1
answer
133
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Directly calculating the cyclic steady state of a time-periodic conjugate heat transfer problem
Context
The following transient problem is the reciprocating (i.e., fully reversing) flow of a fluid $0<x<L, 0<y<d$ over a thick heated block $0<x<L, -e<y<0$ until the system ...
- 297
1
vote
0
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73
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Some conceptual doubts about steady and transient solvers of the NS + energy equations
Recently, I have been solving some transient and steady, flow and heat transfer problems in Mathematica. The transient problem is essentially the reciprocating (i.e., fully reversing) flow of a fluid ...
- 297
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1
answer
405
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Numerically solving a system of SDE's with Levy noise?
Consider this system from the following paper titled: The long-time behaviour of a stochastic SIR epidemic model with distributed delay and multidimensional L´evy jumps
https://arxiv.org/pdf/2003....
- 435
4
votes
2
answers
96
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ParametricPlot for phase field error (case: Predator-Prey Model) [closed]
so I have a task that need to draw a phase field of predator-prey model, but first I tried my lecturer's coding:
...
- 41
0
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0
answers
52
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Modeling Experimental data with a CDF
I have some data plotted above which relates two variables that were derived experimentally. I'm trying to fit a cumulative distribution function to it so that we can take a sample of Y at X. I've ...
- 1,076
1
vote
1
answer
78
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Fitting a sum of three lorentzian based on a dataset
as you can see below, I have developed a code that allows me to fit the present dataset via a Lorentzian. Now what I should do is to develop a sum of three Lorentzians based on this model so that this ...
2
votes
1
answer
178
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Fitting a Lorentzian curve to data
Good morning everyone,
regarding my research "high resolution laser spectroscopy" I would like to fit the data obtained from the experiment with a Lorentzian curve using Mathematica, so as ...
1
vote
0
answers
58
views
How to take a derivative of a function with respect to another function inside the function?
I have these two equations:
...
- 263
4
votes
1
answer
573
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My model has not finished evaluating in more than a day so can't test if it works, what is wrong with it?
Hello I have this modified monocentric city model that I have been working on for a while.
Sorry for the long post, I wanted to add the whole code, because it's all connected.
My suspicion is that it ...
- 263
2
votes
1
answer
182
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The nonlinear state-space model of a spherical pendulum cannot be linearized and cannot be controlled?
I am attempting to model and control a spherical pendulum. I have derived the equations as follows:
...
- 23
0
votes
0
answers
180
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How to plot elements from an array?
Im trying to solve a differential equation for a range of parameters (1->4). I then want to automatically plot a graph for each of those parameters.
...
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0
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530
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6
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4
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429
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Showing that a Hopf bifurcation exists?
I have the following system of ODEs:
dx/dt = a/(1 + z) - Q*z
dy/dt = Qx - qy
dz/dt = qy - cz/(K + z).
Assuming K = 1, Q = q < c, and a = c*(Sqrt[c/Q] - 1), is there a way to use Mathematica to test ...
- 431
11
votes
1
answer
300
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Generating random sequence of integers with ordering constraints
I would like to write a Mathematica routine for generating random musical melodies that obey (some of) the constraints of traditional tonal harmony. For simplicity's sake, I'm interested only in ...
- 1,857
0
votes
1
answer
188
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Can Mathematica do thermal/mechanical analysis of modeled solid systems?
I want to do thermal and mechanical analysis of various parts which may have complicated geometries.
I am contemplating buying SolidWorks because it does this: you model the part and then use their ...
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0
answers
71
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Why is EstimatedProcess so slow for a vector ARProcess?
I'm trying to fit some 4 x N data to a vector auto-regressive model. However, EstimatedProcess is very slow for this. For a 4-th order vector AR process, it takes more than 10 seconds (for N approx. ...
- 276
2
votes
1
answer
76
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select the right numbers based on a condition
I want to optimize my stock portfolio based on three components:
the price of the different stocks
the number to buy of each of the stocks
the expected return of each stock (after 12 months)
For ...
- 2,393
1
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0
answers
71
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Non linear differential equation plot [closed]
Consider the following paper:
https://reader.elsevier.com/reader/sd/pii/S0096300306007715?token=2B98E3B12F1E623C99A0787996469AF36E8EF230F6ED5289EAFB60B64CE79A6ACCF74B946A34F3370C65D4FC99018648&...
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1
answer
379
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Can LearnDistribution learn conditionality?
I would like to apply LearnDistribution to multivariate conditional distributions. Here's a simple artificial example:
...
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19
votes
2
answers
789
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Large deformation of solids
Link to notebook with this question and code
I'd like to understand how large deformations of solid mechanics work and how they are implemented. For this am looking at the following reference problem: ...
- 38.4k
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votes
1
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95
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NDSolve not finding the right solution for a mass hanging of a thread
My NDSolve isn't predicting the right trajectory for one particular case of a problem.
System
Consider a mass vertically hanging by an almost inelastic thread. The ...
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2
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84
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How to model the following system of ODE's in Mathematica with plots of the solution?
Consider the following
(i)
\begin{align}
\frac{d S}{dt} &= -\frac{\beta S I}{N}\\[2ex]
\frac{dI}{dt} &= \frac{\beta S I}{N}
\end{align}
Where $N=S+I$ is the total population.
(ii)
\begin{align}...
- 435
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vote
1
answer
98
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Help with plotting the bifurcation diagram $R_0$ vs $I.$ [closed]
I am working on the paper "A short study of an SIR model with inclusion of an alert class, two explicit nonlinear incidence rates and saturated treatment rate" by Kumar, Nilam and Kishor and ...
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3
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552
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Mass Transport Model
I've asked similar questions before about Mathematica's Mass Transport model. My aim is to model these systems and show how they change by manipulating various parameters.
This time it's the following ...
- 351
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1
answer
573
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Solving time dependent Schrodinger equation for a wavefunction and harmonic oscillator [closed]
How can I obtain a GIF/graph similar to these ones here by solving the time-dependent Schrodinger equation
$$ i\hbar\frac{\partial ψ(x,t)}{\partial t} = -\frac{\hbar^2}{2m}\nabla^2ψ(x,t) + V(x)ψ(x,t)$$...
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Mass Transfer Value
I'm trying to model the following boundary condition using MassTransferValue.
$$
D_A \frac{\partial[A]} {\partial x} + D_B \frac{\partial[B]} {\partial x}+ D_C \...
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votes
2
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400
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How to add an attractive potential (migration term) named component to Mass Transport PDE
Wolfram Mathematica 12.2 now features "Named Partial Differential Equation Terms"
For specific physics fields, relevant PDE terms have been packaged as
components and augmented with ...
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1
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0
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110
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2D transient heat equation resolution
I'm writing a code to get the analytical solution mentioned in Sun et al., 2013. I will copy here the passages needed to solve the equation.
The 2D transient heat equation is:
First of all, I set the ...
3
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0
answers
92
views
Graph embedding constrained to a surface?
Have been contemplating it for a while, but did not dare to post as I felt like this must be a major undertaking to implement. Then saw the excellent answers to a recent question RegionPlot3D KnotData ...
- 2,194
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0
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75
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Microcontrollerembedcode unable to connect to Arduino Yun
Hi Mathematica enthusiasts,
I am trying to follow this tutorial off Wolfram reference for microcontrollers
Real Time Data Acquisition
I have an Arduino Yun Rev2 hooked up exactly as it is from the ...
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answer
130
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finding FWHM of a dataset with unknown mathematical equation
I have a dataset. I have plotted using "Listloglinearplot". Now I need to find the FWHM (full width half maxima) of the same, However I dont know which mathematical eqution describes best to ...
- 309
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0
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88
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NDSolve for ODE-PDE Problem
happy holidays,
I am solving a coupled ODE - PDE system -for simplicity all coefficients are taken as 1-. I checked other questions on the issue but couldn't find any suitable answer or comparison.
...
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78
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How to formulate NDSolve[...] for a two-sector SIR model
The following Code aims to simulate the employment effects of a pandemic, drawing on the conventional SIR model. I extended the SIR model with two economic sectors (...
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3
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1
answer
141
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Does mathematica have support for mixture models?
Does Mathematica have support mixture models? Similar to the R language libraries mclust or ...
- 2,450
6
votes
3
answers
1k
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Time dependent Schrödinger equation in 2D
I have the following Schrödinger equation in $2D$:
\begin{cases}
\partial_t \Psi(x,t) = V(x,t) \Psi(x,t) \quad x \in [-10,10]^2\\
\Psi(x,0)=\exp( \frac{1}{2} (-x^2+y^2))
\end{cases}
where the ...
- 401
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votes
1
answer
100
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Equation Plotting
I'm using the mean field theory approximation and the Ising Model for magnetization to come up with the following equation:
m(T) = tanh(m(T)/T)
where T is an ...
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3
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200
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1
vote
1
answer
289
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Smoothing a function after interpolation + trying to fit 3D data into model without accurate prior knowledge
I have a physical problem simulation that generates this data set in the two cylindrical coordinates $(r,z)$ (doesn't include $\phi$ dependence). The data set (see .wdx file) is in the flattened form $...
- 258
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136
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Magnetostatics analysis of Switched Reluctance Motor in Mathematica
Accidentally stumbled upon magnetostatic calculation in Mathematica.
https://www.wolfram.com/language/12/nonlinear-finite-elements/magnetostatics.html?product=mathematica
I would like to ask a ...
- 2,304
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1
answer
132
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2
votes
1
answer
233
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How to Make a Bifurcation plot of a non linear system of ODEs
I am modelling bacterial growth. I have a quite difficult non linear systems of ODE's. I have 2 bacteria that i'm modelling with competition, as wel as transfer to a different place. so there are 2 ...
- 21
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0
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94
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Error in Monte Carlo simulation. Now Random walk (dotted curve) doesn't fit to the analytical curve (dashed curve)
I've been trying to code a kinetic monte carlo simulation for a system of consecutive chemical reactions using a fixed (repaired) code that the user flinty gives me in the last questions I post:
...
- 13
3
votes
1
answer
249
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Stiff System of ODEs: NDSolve Convergence Issues
I have tried to use NDSolve for solving 4th order coupled ODEs problems (see the attached codes). The MMA solver fails to solve this problem.
...
- 1,796
2
votes
1
answer
171
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NDSolve Convergence Issue for Coupled Field Problems
I have tried to use NDSolve to solve a coupled field Eqs (see the attached Codes). The MMA solver seems to failed to converge to the requested accuracy or precision within 100 iterations
...
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