Questions tagged [simulation]

Simulation is the process of mimicking the behaviour of a real physical process or system using a representative model.

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Questions about implementing an electromagnetism/photonics solver package

I am hoping to start (very slowly) on implementing some form of a computational photonics/electromagnetism package. I know things like Meep, S4, FDTD++, EMPy, and a host of other proprietary/free/...
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3answers
392 views

2D simulation of a particle with different diffusion coefficient in different directions of the particle

How can one simulate diffusion of a particle which has a natural axis and diffusion coefficient of the particle in the direction of the axis is D_1 and in perpendicular to the axis is D_2? Could ...
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1answer
89 views

Multiscale Simulation of random walker

I want to simulate a system of random walkers (called A) with diffusion coefficient equal to D and other systems of random walkers (called type B) with diffusion coefficient equal to 1000 D. Second ...
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2answers
97 views

A program to simulate cellular automaton model

I have worked on mathematical modeling based on differential equations, and now I want to simulate a cellular automaton based on a ...
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1answer
174 views

How do I simulate an open end?

When simulating a partial differential equation describing a physical phenomenon like vibrations on a string, fluid flow in a chamber or quantum wave functions, the most straight-forward way is to ...
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1answer
129 views

GAMS Optimization

I am writing a GAMS program where I am interested in using the value of a variable as a condition inside an another equation. Let's say I have two equations with two variables, $g_1(t)$ and $g_2(t)$, ...
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2answers
77 views

Should energy be conserved in an N-body simulation where particles don't lose energy in collisions?

In an N-body simulation where forces between particles are attractive and particles do not lose energy on colliding with walls or each other, should energy be conserved? How could it be, with total ...
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0answers
284 views

Simulating a Hill-Type muscle model

I'm trying to do biologically based locomotion animation. I have a Hill-Type Muscle Model (see reference 1) that I've implemented in code. I can find the initial lengths of the tendons, then do a ...
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0answers
63 views

Dielectric in an external electric field

I want to numerically solve for electric field of an object in an external electric field. The object has linear displacement field such that its permitivity ($\epsilon$) is constant. The object's ...
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1answer
100 views

Infinite force in simulation [closed]

In physical problems the infinite force is easily implemented by the mathematical form of that force, take $1/r$ as an example, whenever the distance between two particles becomes small the force goes ...
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0answers
63 views

RCWA for Non-Periodic Structure?

I have a quick question regarding Rigorous Coupled Wave Analysis (RCWA) for numerically solving problems (in optics). I am trying to simulate a device which is non-periodic in x, y directions (but is ...
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0answers
249 views

Error in MD simulation with Lennard-Jones potential in C, resulting in a lack of conservation of energy

I'm working on a MD simulation using the Lennard-Jones potential and the Velocity Verlet algorithm. The code compiles and runs, but the energy for each time step is not conserved; it decreases ...
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1answer
120 views

How does Multi Body Dynamics software work for flexible joints?

I need to model a "fishing rod" in 2 dimensions by joining several "rigid sticks" by flexible/elastic joints. The joints act as plate/torsion springs with different spring constants. The "fishing rod" ...
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1answer
394 views

Three body problem in C++

I am in a begginers programming course and we got a little project. I chose to simulate the three body problem using the Euler method. Even though the system is chaotic there are some special cases ...
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160 views

Initial conditions of nbody problem

Note: I have edited the original question to try to be clearer. I'm trying to simulate a gravitational nbody problem with a Barnes-Hut algorithm, in which the bodies start in a homogeneous sphere ...
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1answer
79 views

Convergence Criteria for Two Fluid Flow Solver

Which one of the following is suitable for judging convergence in Two-Fluid Flow Solver? 1) Absolute Residual (L^2-Norm). 2) Relative Residual. 3) Fraction Change in Velocity, Pressure and Volume ...
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1answer
290 views

Mobile robot path following using model predictive control (MPC)

I'am trying to implement a path following algorithm based on MPC (Model Predictive Control), found in this paper : Path Following Mobile Robot in the Presence of Velocity Constraints Principle: ...
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117 views

CFD implementation in software [closed]

I've been learning CFD theory for 4 months (which includes FEA, FDM AND FVM) and now I want to start running simulations. As a novice to CFD software, I would appreciate some advice on where to start, ...
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1answer
164 views

Methods for solving $x'=Ax+b$ for small, sparse, singular $A$

I am in the process of building a robotics physics engine. I have been using the Linear ODE $x' = Ax + b$ for the core of my physics integration, but have never found a really good solution method for ...
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3answers
837 views

Simple Simulation Examples in Computational Fluid Dynamics

I would like to incorporate a CFD topic in a project I currently have. The deadline is a little less than a month from now. Basically, what I would like to do is solve some equations and simulate ...
2
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1answer
300 views

Help understanding and implementing fast multipole method for N-body

I've been trying to understand the Fast Multipole Method but not really getting anywhere. It seems like the fastest mainstream N-body simulation algorithm, and I would like to implement it in an ...
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1answer
83 views

$(1+x^M)^{1/M}$ need to be able to calculate any order derivatives vs. $x$ and $M$ for $x\ge 0$ and $M\gt 2$

cannot delete my own question, so I try to overwrite it instead...
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63 views

Solving a nonlinear problem with CDF

I'm trying to solve this problem: $\begin{cases} \partial_t E=-k\left([f(\rho)-i.\left[\delta+\frac{1}{2}a\left[\dfrac{\nabla^2_{\bot}}{4}+1-\rho^2\right]\right]]E - 2CP\right)\\ \partial_t P=-\...
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3answers
811 views

What do C, C++ and Java have that Fortran 2003 don't? [closed]

As you may know, Fortran is widely and longly (?) used in science. I've heard a lot of people saying that we natural scientists should all migrate to C++ or Java. I've seen people increasingly ...
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1answer
68 views

Is it common or to use objects for calculation of pair interactions in physics and chemistry simulations?

When simulation atoms, molecules, colloids, autc., are there programs that define each interacting unity as an object in the OOP sense? In my own case, I've been simulating magnetic nanoparticles in ...
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2answers
152 views

Is model-view-controller useful pattern useful to build scientific simulation programs?

I work with scientific simulation, but what I like the most in programming is creating graphical user interfaces and 2D or 3D outputs to visualize the evolution of the simulations. I know most input ...
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2answers
3k views

Simple java gravity simulation

I'm trying to write a class that uses Newton's law of Gravitation to work out the field of a planet. I've tested my code by inputting values for Earth, for purely vertical motion, so I should get g = -...
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1answer
382 views

How to model the mixing of two fluids in a container?

In the context of a research project of mine, I am faced with the difficult task of modeling the mixing of two fluids in a container. I would like to achieve the following: Given a container (...
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0answers
35 views

Limitations of particle in cell method for high density plasma

Are there any limitations of particle in cell (PIC) method for high density plasma? To be more specific, is modeling of a narrow channel of high density plasma possible or are there any limitations ...
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1answer
336 views

Finite difference scheme for 2D sound propagation

I am simulating the sound wave propagation in non-rectangular and asymetric spaces using finite-difference method. I presume linear acoustics equations to be enough (i.e. $\Box p = 0$, $\Box \vec{v} = ...
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2answers
2k views

Good desktop PC for molecular dynamics simulations

I want to build a new desktop PC for MD simulations of relatively simple protein/carbohydrate systems using mainly GROMACS and Amber force field. No ab initio or QM-MM simulations are intended for now....
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787 views

BiCopter simulation in Matlab

I derived a bicopter dynamical model with two servos and two BLDC motors. And now am trying to simulate it using Matlab. As base for simulation I used this paper and this code Unfortunately, the ...
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0answers
53 views

Software to simulate behavioral economic models?

I am looking for a way to simulate behavioral economic models to illustrate the effects of changing parameters. I am familiar with statistical analysis (especially R), but I only have few programming ...
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1answer
113 views

Solve implicit ODE numerically in orbit simulation

I'm trying to plot the orbit of a compact binary star system where general relativistic effects become important. I'm using post-Newtonian approximation and I want to solve the orbit numerically based ...
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1answer
824 views

How to calculate divergence and vorticity from a velocity field using finite elements

I am in the process of writing a finite element solver for the Navier-Stokes equations and am having trouble computing things like the divergence and vorticity correctly. Currently to compute the ...
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2answers
366 views

Implementing the pressure correction method using finite elements

Ok so I am nearing the completion of my finite element Navier-Stokes solver that uses the $\theta$-method for time stepping and the pressure correction method for the pressure. I am following the ...
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0answers
365 views

ANSYS Fluent: Defining External Force on a Cell Zone [closed]

I am using ANSYS Fluent 15 to simulate a case of fluid flow. In my case, I have three cell zones in my simulation, let's call them top, middle and bottom. My requirement is to put a vertical constant ...
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1answer
565 views

Pressure projection method boundary conditions

When using the pressure projection method to solve the incompressible Navier-Stokes equations do we apply Neumann boundary conditions for pressure only where there are associated no-slip velocity ...
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1answer
111 views

CFD turbulence modelling mean pressures vs peak pressures

I have been experimenting with using Autodesk CFD to investigate facade/ cladding pressures on a (rectangular) building, comparing results with cladding/ facades pressures pressures from design codes ...
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1answer
382 views

How to initiate spirals in this model?

I am trying to reproduce Tang & Othmer paper which is related to excitations and oscillations in G-protein model in Dictyostelium discoideum, an amoeba species. The mathematical model in the paper ...
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2answers
116 views

Can other running processes harm the performance of my simulation?

I don't have an high-end machine on which run my simulation (Python + C extensions, based on numpy for calculations) Thus I intend to run the program on my PC, for several hours. I won't use the ...
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2answers
145 views

Relationship between FEM solutions of PDE with different spatial resolutions

I use FEM to simulate deformations of elastic objects for animation applications in computer graphics. The governing equation is generally with the form: $$ \mathbf{M}\ddot{\mathbf{u}} +\mathbf{C}\dot{...
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0answers
104 views

Conservation at grid interface in adaptive mesh refinement

I am using adaptive mesh refinement to solve one dimensional inviscid Burgers equation. However I am facing some difficulty to handle grid interfaces which are not uniform (coarse-fine grid interface)....
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2answers
1k views

GPU-enabled Lattice Boltzmann solvers?

Is anybody aware of any GPU-enabled Lattice Boltzmann solvers (preferably on C++/OpenCL and open-source) that would be recommended? I have found Advanced Simulation Library, but it seems to be very ...
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1answer
354 views

How to generate movie of the simulation done in LAMMPS? [closed]

I simulated nanowire deformation using LAMMPS and visualized it using VMD in Centos 6.5. But I'm not able to generate .jpg image file or the simulation movie. How can I proceed??
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2answers
538 views

Should a colorbar have constant values throughout a simulation?

The default option for matplotlib's pcolormesh (also true for VisIt and I think also true for Matlab) is to allow the maximum and minimum of a colorbar vary. Which ...
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1answer
623 views

Hypersonic flow in Fluent

I am working in my graduating project about the hypersonic flow, particularly the properties of the air behind a strong shock wave, I try to do a simulation for that process in Fluent but I don't know ...
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2answers
425 views

Simulating a Simple Pendulum - Increasing amplitude on each swing?

I am trying to animate a dampened pendulum using RK4 for a highschool project. The equations that describe the dampened system are as follows: (from http://www.maths.tcd.ie/~smurray/Pendulumwriteup....
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1answer
392 views

Surface charge boundary conditon for Poisson-Boltzmann solver

I want to set up a surface charge boundary condition for the simulation of semiconductor and electrolyte interface. The 2D-Poisson example and surface charge boundary condition are shown in following ...
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2answers
532 views

How to interpret/convert density in 2D simulations?

Density has units of $kg/m^3$. In simulations often scaling is done to deal with non-dimensional values, so the physical density is converted to the non-dimensional density so that it can be used in ...