Q: Why is the shape of the geometry not displayed on the Viewer of VA-FDTD INTERFACE?
A: Please download and install the DirectX end-user runtime from the Microsoft Download Center.
Q: Why does it take quite a long time to display the shape of the geometry with the Viewer of VA-FDTD INTERFACE?
A: If the number of surfaces exported by the shape modeler is large, it takes a long time to display the shape. The software is able to handle a few thousand surfaces. Please be patient to view the shape.
Q: What number should I enter for Time Skip in the Discretization tab of VA-FDTD INTERFACE?
A: For Time Skip, please enter the number of time steps to be skipped for each group. For example, when the time interval is set to 7[ms] and Time Skip of a group is set to 5, updating for the group is carried out every 35[ms]. When considering a homogeneous medium discretized with a uniform mesh, set the Time Skip to 1. When considering multiple media in which the phase velocities are quite different or considering a homogeneous medium discretized with a nonuniform mesh, the computational cost can be reduced by estimating the stable time intervals for each group and setting the appropriate Time Skips.
Q: Why am I not able to setup PMLs on VA-FDTD INTERFACE?
A: PMLs cannot be set except for the plane perpendicular to the axis. Additionally, please make sure that all of the surface normals are outward with respect to the space to be analysed. In order to set PMLs more correctly, apply all other boundary conditions first followed by PMLs.
Q: Can I set a boundary with a certain boundary condition inside a PML by VA-FDTD INTERFACE?
A: Yes, but be careful because a little bit complicated operation is required. One way is to divide the PML into two or more. In other words, you can divide the original target space into the multiple appropriate ones, then create PMLs after setting some surfaces with a certain boundary condition. For example, noise_barrier_*****Hz.fdi included in VA-FDTD EXAMPLES creates a fixed boundary inside the PML in this way. Another way is to create a boundary surface protruding the space beforehand to be analysed by a SHAPE MODELER. If you set a certain boundary condition such as a fixed boundary condition on this surface and then create PMLs containing the surface, the boundary condition set on the surface is effective even in the PML. In this case, it is necessary to prefix "%" to the group name of the surface. For details, refer to "Specification of shape file" in the help.
Q: How is the space discretized when the total length is indivisible by the spatial interval set by VA-FDTD INTERFACE?
A: For example, if you discretize a 5.1[m] long space with 1[m] interval, 6 cells will be created. In this case, the space of the total length of 6[m] will be analysed, so the result can be different from that of 5.1[m]. If you want to obtain a result for a total length of 5.1[m], discretize the whole space with 0.1[m] interval, or 1[m] interval from 0 to 5[m] and 0.1[m] interval from 5 to 5.1[m].
Q: When I click the "Search" button on the MDS Parameters tab in VA-FDTD INTERFACE, why are the results different each time?
A: Since the optimization is based on random initial values, the results are different each time. Please repeat the search over and over until you get satisfying results.
Q: Is it possible to set multiple point or line sources on VA-FDTD INTERFACE?
A: Unfortunately, it is possible to set only one point or line source. If you want to set multiple point or line sources or want to reproduce plane waves, you can implement them yourself by modifying the FORTRAN VA-FDTD SOLVER source files.
Q: Why does It take a long time to write the FDS file with VA-FDTD INTERFACE?
A: The time required for writing the FDS file is proportional to the product of the number of surfaces output by the shape modeler and the number of cells to be discretized. When the shape includes a curved surface, the number of surface elements increases. Additionally, if the target maximum frequency is high, the number of cells increases. In that case, it may take several hours or even days to export the FDS file. The software is able to handle a few thousand surfaces and about 10 million cells.
Q: What does the number displayed by VA-FDTD CHECKER mean?
A: When "Material" is selected, it means the number added 1 to the Group number in VA-FDTD INTERFACE. In the case of "PML Material", the PML identification number is meant, and in the case of "PML Depth", the depth of the PML layer counted from the edge of the target space is displayed. For "Boundary", the value set by VA-FDTD INTERFACE is displayed. Fixed Boundary is "2", Free Boundary is "3", and so on. The values correspond to each condition is displayed. The positive or negative of the value indicates whether the left(lower) or right(upper) side of the target space. "Bound. Const." shows the identification number of the constant set on the boundary.
Q: I have more memory than Required Memory displayed in VA-FDTD INTERFACE and VA-FDTD SOLVER, but why do I still get an error that memory is not enough when calculating with VA-FDTD SOLVER?
A: The Required Memory is just an approximate value. Since the calculation by VA-FDTD SOLVER may sometimes require a larger one than the displayed one. If you encounter the error, use a computer with a larger memory or discretize the space with a coarse mesh.
Q: Why does the results diverge when a PML is set to a surface of solid?
A: Even the results of radiation_bend_1khz.fdi and radiation_long_1khz.fdi included by EXAMPLES in Download will diverge from the solid PMLs if the Maximum Time is increased. The cause of this issue has yet to be identified. The stabilization of these calculations needs further studies.
Q: I do not have MATLAB, how can I see a time response at a receiver?
A: Using the ParaView output, it is possible to display the time response of an arbitrary point in ParaView. Please check ParaView help for more details.


If you have any questions or comments, please contact Masahiro Toyoda (toyoda_at_kansai-u.ac.jp) by email (please change "_at_" to "@"). Additionally, please write "VA-FDTD:" at the beginning of the subject of the email. Please note that I may not be able to respond to all of the emails. Sorry in advance.

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