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# Questions tagged [boundary-conditions]

For questions regarding the choice and/or appropriateness of conditions necessary to model a particular phenomenon with a partial differential equations.

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### Open boundary conditions in time

I want to simulate lattice QFT on lorentzian manifold, for my purposes it's necessary for time dimension to be non-compact. Both dirichlet and neumann boundary conditions are out of question since ...
• 101
1 vote
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### Boundary Conditions on the Inlet and Outlet in a Discontinuous Galerkin framework

In the book Discontinuous Galerkin Method (DGM), Analysis and Applications to Compressible Flow by Vít Dolejší and Miloslav Feistauer, Springer, it is mentionned, in section 8.3.2 that deals with ...
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### How can I apply a mixed boundary condition to a multi-material heat transfer problem using Crank-Nicolson?

I am working on a mixed material model for a melting material and need to enforce both a Dirichlet and Neumann type condition at the interface. Subject to an external surface heat flux at the top of ...
1 vote
35 views

### Imposing higher order finite difference schemes for boundary value problems on a finite interval

I have some questions. I'm going to assume everything is in 1d with a Laplacian operator. If I discretize the Laplacian operator using $p = 2a+1$ grid points with periodic boundary conditions, I ...
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### Symmetry axis boundary condition

I was wondering about the symmetry axis boundary condition in commercial CFD solvers such as ANSYS Fluent. If the problem is the flow through a round pipe or out of a round nozzle, it is natural to ...
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### Solving Poisson's Equation with Periodic Boundary Conditions

So, I've been attempting to design a simple solver for a problem of finding the gravitational potential of a system using Poisson's equation (let's call the potential phi, $\phi$). The goal is that I ...
1 vote
387 views

### Crank Nicolson Method with closed boundary conditions

I want to simulate 1D diffusion with a constant diffusion coefficient using the Crank-Nicolson method. $$\frac{\partial u (x,t)}{\partial t} = D \frac{\partial^2 u(x,t)}{\partial x^2}.$$ I take an ...
• 111
1 vote
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### How can we use the two boundary conditions for the Taylor-Maccoll Equations for Cone Shock Waves?

The Taylor-Maccoll equations below govern the gas dynamics around a supersonic, axially oriented cone. Using the notation from Anderson's Fundamentals of Aerodynamics, which uses a dimensionless ...
302 views

### Why do we use modified pressure in incompressible multiphase solvers with gravity?

The context of my question is two-phase incompressible solvers such as interFoam in OpenFOAM, but I have seen this trick used ...
54 views

### Why is the maximum potential energy greater than the maximum kinetic energy?

I was plotting the energy variation in a mass-spring system. If I define the initial conditions to be at maximum displacement from the origin, the potential energy is plotted correctly but kinetic ...
• 123
1 vote
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### How to include zero flux boundary conditions?

I am trying to solve the following differential equation in the domain of $\theta \in [0, 2 \pi]$ using finite differences scheme: For $0< \theta \leq \pi$ \begin{align} \rho_i^{n+1}=\rho_i^{n}+D\...
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### Boundary value problem solver fails on trivial case

I am trying to solve a boundary value problem on $[0, \infty]$, using scipy's scipy.integrate.solve_bvp and I am seeing that the solutions are not converging even ...
• 33
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### Can successive over-relaxation (SOR) method deal with ill-posed PDE BVP?

Recently, I've been struggling to understand the limitations and capabilities of the successive over-relaxation (SOR) method for boundary value problems which are ill-posed, such as, for instance, ...
• 83
1 vote
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### Convergence stall when solving 2D Poisson PDE with pure Neumann boundaries (finite differences)

I recently started coding a small library of 2D PDE solvers (time dependent and time independent), and my first attempt was a 2D Poisson equation of the form: \nabla(\epsilon\nabla\varphi)=\nabla\...
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### Does DCT diagonalize the FD discretisation of the Laplacian with Neumann boundary conditions?

If one has the Poisson problem (assume $\int_{\Omega} f = 0$ and $\int_{\Omega} u = 0$): \begin{alignat}{3} \Delta u(x) &= f(x), &\quad&x\in\Omega \\ \partial_nu(x) &= 0, &\quad&...
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1 vote
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### How can I define an equipotential surface/volume in FEniCS?

I want to solve electrostatic problem for potential. Charge density and medium permittivity are known, so is the potential of a grounded surface. I know how I can implement that. But I would like to ...
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### How does Tannehill impose boundary conditions when coding the Parabolized Navier Stokes on an Implicit Finite Differences Scheme?

I'm trying to implement the scheme he describes on his book "Computational Fluid Mechanics and Heat Transfer" on Chap.9 and I'm having trouble imposing BC. I don’t get how he imposes them. I ...
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### Applying Stress Boundary Conditions in Commercial Finite Element Analysis Codes

I am trying to replicate a finite element analysis given in a research paper titled On the Detection of Stress Singularities in Finite Element Analysis 1 by G.B.Sinclair et. al. The geometry of the ...
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1 vote