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Simulations & Solvers

FDTD, Low-Frequency, Neuron, Mode-Matching, Flow, Acoustics, etc...

244 Topics 734 Posts

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  • FDTD, Low-Frequency, Neuron, Mode-Matching, Flow, Acoustics, etc...

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    11 Topics
    28 Posts
    AntoninoMCA
    @KK The titration procedure provides a scaling factor that must be applied to the stimulation source (incident E-field, input current, or voltage applied at electrode pairs) in order to initiate an action potential in a fiber or neuron. Here are some examples depending on the stimulation source: Source: Incident E-field (e.g., induced by TMS) Assume the incident electric field is 1 V/m, and the titration procedure yields a titration factor, tf. The threshold E-field is therefore tf [V/m]. If this 1 V/m field results from a coil current rate of change dI/dt = A [A/s], then the threshold dI/dt required is A × tf [A/s]. Source: Applied voltage Let the applied voltage across an electrode pair be V = V₀. This value is also used as the Dirichlet boundary condition in low-frequency (LF) simulations. If the titration factor is tf, the threshold voltage becomes V₀ × tf [V]. Source: Applied current Let the applied current to an electrode pair be I = I₀, typically derived from LF simulations via a current flux integrator. With a titration factor tf, the threshold current is I₀ × tf [A]. The titration factor tf is a dimensionless number that gains physical meaning when applied to the relevant stimulation quantity (electric field, voltage, or current). @LJ was suggesting the correct course of action. I hope this clarification is helpful!
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    Removing error

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  • S

    This topic is deleted!

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  • A

    Problens with Sim4Life demo

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    V
    Dear Sim4Life developers, I have came across the same problem and cannot update materials database due to the Russian words within a pathway. Is it possible to solve this problem by directing Sim4Life to search for materials in another pathway? Thank you a lot in advance, Valeriia
  • S

    how to get the temperature exactly at the end of simulation time?

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  • S

    What is time step factor and critical time step in thermal simulation

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    SylvainS
    Have you found an answer to your question already? If not, I would encourage you to read the corresponding sections in Sim4Life's user manual: 2.8.2 Thermal Simulation Settings 2.5.1.1.2 Numerical Stability (this is in the FDTD section, but the same criteria apply in the thermal solver)
  • K

    Simulation progress is stuck at 0% "Queued"

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    SylvainS
    If there is a message such as "Job Finished", this probably means that the job is not really "stuck" at 0% but that it simply failed, for some reason. You might get additional information by looking at the Console (View -> Console) or by looking at the log file from the solver itself (this is a file ending with _Input.log in the Results folder of the project). The latter is also visible from within Sim4Life using the Task Manager (click at the bottom right of Sim4Life to open it).
  • jmtyszkaJ

    aXware FDTD solver and Nvidia driver version

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  • A

    Simulate EM wave with known power output

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    A
    That solved the problem, thank you very much!
  • S

    Homogeneity of E-filed map in plane wave simulation

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    S
    Right. Thank you very much for your explanation and comments.
  • M

    LF magneto static vector potential solver

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    SylvainS
    Your approach is the correct one. There are a few caveats that could explain the discrepancies in the results (one should, of course, obtain the same current flux between anode and cathode regardless of the method used): the surface used to compute the flux should intersect with all field lines between anode and cathode, once, and only once. An example might be a plane that cuts through the head, with one electrode on each side. Another possibility is to create a box that encloses one electrode. In your example, with the sponge, I think you might have current entering from one side and leaving through the other and would actually have expected a total flux of zero. the surface needs to be correctly discretized. For that, try to reduce the Minimum Edge Length property of the surface in the Explorer tree (after drag & drop), then Refresh Viewers, until the Total Flux value stops changing I am not sure what happens if the surface is also a boundary condition for the J field (as in the case of your electrode). Maybe there are some discretization issues there. In all cases, it often helps to visualize the flux of J on your chosen surface, by using the Surface Viewer I hope this helps
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    Capacitor in EM FDTD

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    SylvainS
    For FDTD simulation, you will need to excite the plates by joining them with a wire (use the Sketch -> Lines tool), as if you were building a circuit. Leave a small interval open somewhere so that you can insert an edge source.
  • S

    The standard deviation of a parameter

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    SylvainS
    Hi Saya, "parameters" are by definitions input by the user. Their values, as well as their standard deviation or any other statistics, can therefore not be "found" by the program itself. Maybe it would be clearer if you could provide an example. best regards
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    This topic is deleted!

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    This topic is deleted!

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  • R

    EM simulation - Diverging simulation

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    R
    @Sylvain Thank you. I will try your suggestions.
  • S

    Point sensor makes the simulation diverge?

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    S
    Thanks for your help.
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    This topic is deleted!

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  • M

    CPU usage

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    SylvainS
    By default, the LF solver use a single core of the CPU, so the total CPU usage can appear quite low if you have several cores. In the "Solver" settings of the simulation, you can choose to use more than 1 core. This relies on the MPI library to parallelize the workload between different CPU cores. The speedup you gain with MPI depends on many parameters, including discretization of the computational domain (e.g. number of grid cells) and hardware specs (e.g. available RAM). The only reliable way to know is to try on a few representative examples, with different number of CPU cores. Note that the MPI parallelization requires specific license tokens. If you try and it fails with licensing errors, you can always request a trial license for this feature.
  • S

    Volume average of SAR value

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    SylvainS
    To get a meaningful answer to this kind of question, you would need to provide more detailed information: such as screenshots (you can copy/paste images into your posts), formula, numbers, etc...
  • R

    Assigning boundary conditions to an arbitrary object

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    PeterStijnmanP
    I think that it would not be possible since you can only assign conductivity values for the voxels. Not the edges of the yee cell where the E-fields are computed. This basically means the absorbing boundary gets avaraged and won't work as you would want.