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All of it can be simulated to a certain level of precision - given enough computing power AND correct experimental values for all the parameters. The tricky bit without tests is to get experimental values for eg. the thermal conductivity of Plutonium at TPa of pressure. Experimental tests can also only validate something to a certain level of precision - ...

23

To some extent this answer is echoing things that @Martin said... but from my own point of view. In my experience of (Monte Carlo) simulation, the model you implement captures your knowledge of the physics of the situation; and if your knowledge is "perfect", your calculation, with sufficient compute power at your fingertips, will also be "perfect". ...

11

I think anyone who says "there's no need to do experiments, we can simulate everything!" either: Doesn't know what they're talking about Is trying to sell snake oil Is a scientific fraud trying to push pseudoscience as actual science I have never seen a serious, honest scientist claim that simulation is sufficient substitute for empirical evidence, even ...

5

You can simulate everything to certain precision, but there is at least one aspect that remains unsimulated: reality. What I mean are the following points: When you want to calculate anything a little bit more complicated, at some point, you will use approximations. There are always good reasons for making certain assumptions, neglecting terms and ...

4

This is, unfortunately, not a simple task in general. My experience on non-reflecting boundary conditions is for the Navier-Stokes equations, but you should be able to do a similar approach for your system. As you noted, a fixed boundary ($u=0$) will lead to one type of wave while a free boundary ($\partial u/\partial x = 0$) leads to another wave. What you ...

4

To find the global minima of a function in a configuration space using Monte Carlo methods there are two main approaches simulated annealing and parallel tempering. Simulated annealing Simulated annealing is single Markov chain starting at high temperature for global exploration. The system is then evolved via Monte Carlo update whose criteria for ...

3

According to conservation of momentum, the center of mass of a system cannot accelerate without external forces. In other words, if the center of mass starts out at rest (which is generally a good procedure in simulations), then it should always stay at rest. It is normal for numerical errors to introduce deviations, but the motion you are seeing looks ...

2

A infinite barrier of potential reflects the fact the particle cannot enter a certain region of space. Solving the Langevin equation with such a barrier means that you have to find a way to state that the particle cannot enter the domain, but you also have to describe what happens at the boundary, because several scenarios are possible : the particle stops ...

2

I love the quote "Nobody believes an analysis except the person who did it. Everybody believes a test except the person who did it." Both simulation and test have serious shortcomings. You can't do many tests because they are expensive. Simulations do not incorporate all the physics. It is easy to decide incorrectly that some effect is not important and ...

2

This may not be what you're looking for, but don't forget the non-immediate impact of nuclear weapons. Simulations can only go so far to simulate fallout, persistent radiation, flow of radioactive particles through the nearby area, environmental impact, sociological impact, etc. They're also going to have trouble trying to simulate every possible target ...

1

Smoothed particle hydrodynamics (SPH) is a fluid simulation approach that has been initially developed for astrophysics fluids (galaxies, nebula, exploding stars...), showing huge range of possible "densities", and embedded in ambient vacuum. see https://en.wikipedia.org/wiki/Smoothed-particle_hydrodynamics

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I assume that friction is an external velocity dependent force in your simulation code. Since you have such external forces, your total energy, total angular momentum, total momentum are likely not to be conserved. In your case, the friction is a phenomenological external force, but similar behavior could also be simulated with a large particle, moving in a ...

1

Here may not be a complete answer, but it may give you (and me) some hints and perhaps some alternative solution. Euler's scheme should not work, even for the deterministic equation where noise is set to zero. This is because in Euler's scheme, one always requires $\Delta t$ small so that the $\Delta x$ is small. When $\Delta x$ is large, one runs into the ...

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