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    • Rahul Ponginan

      Please click here for a short but important announcement   03/26/17

      Dear Users Our Commercial and Academic users around the world can use these same forums here as before i.e. the Altair Support Forum , Commercial users from India with solver queries can go to the Solver Forum for India Commercial Users , Academic Users from India and AOC India Participants are requested to go to the Forum for India Academic Users and AOC India Participants , We will be tending to all queries in all the forums promptly as before, thank you for your understanding. 

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  2. Hey Tinh, Thanks for the reply man. Would it be possible for you to post screen shots illustration where I can find the above options you have suggested? I tried to look around but not able to figure out where 1D detailed mode representation.
  3. I finally managed to get some results for the version with pcont but they don't make any sense neither...
  4. Today
  5. Hi In panel bar2 click review and click to beam elems to see its syst Or switch 1d representation to detail mode
  6. No, it does not separate node of cbush and quad elem. So you dont need to equivalence them. You can confirm this by panel f10>1d>free nodes => will highlight cbush nodes not equivalenced
  7. Dear Community, my name is Lennart, I am a composites engineering student from Germany and I have started working with Optistruct/Hypermesh full-time since a few weeks. I am trying to get ahold of composite optimisation. Optistruct is only partially able to compute composite parts. it appears that I am very limited in the design of more complex parts. What I am looking for in particular is a way to not only design plies in flat structures, but rather tows and roving in 3D parts, for example a scaffold of a crane or similar. I AM able to model 3D composite structures by designing surfaces which come close to the 3D part and apply a laminate as a workaround. As a first step towards 3D composite optimisation, I would like to have a workaround solution for working with single tows. For example if I have a 2D circular part, let's say a simple ring. If I apply a tensile force (with a bolt or similar), the ideal optimisation result for a minimum displacement of the circle geometry would be a "ring" of carbon fibres. However I am not quite sure how to get this result in Optistruct. This is not possible when the program only "thinks" with plies. is there any way how I could achieve this result with the given Optistruct possibilites? Any way to "cheat" and work with single fibre tows instead of plies? Any help would be greatly apprechiated. Regards, Lenny
  8. When results differ between FEKO and, for example, a measured result, questions arise as to which result should be taken as the right one. This how-to will list some pointers to assist with confirming results. Introduction Results obtained with FEKO can be confirmed in the following ways: Compare with a measured result Compare with an analytical result Compare with another solution method Perform a mesh convergence study 1. Compare with a measured result This is the best method to confirm a result. However, it is often not possible or practical to perform a measurement, therefore the other methods have to be used. If a measurement differs from the FEKO results, then the user should check the following: Is there something in the measurement that was left out of the FEKO model? How was the measurement excited? Maybe a horn was used in the measurement but the horn has a coaxial-to-pin transition, while in FEKO a waveguide port was used? What was the physical connector pin radius? Were losses included in the model? Were spacers used in the measurement (for example, foam spacers) that were not included in the FEKO model? What other objects were nearby that could have interfered with the measurement? Was the measurement done inside an anechoic chamber? 2. Compare with an analytical result Analytical and therefore exact results exist for some problem types. One example is the RCS of a PEC sphere that is exactly known. As another example, a stripline feed network can be compared with analytically computed results using non-radiating transmission line theory due to the low radiation properties of stripline. 3. Compare with another solution method If modelling a dielectric, the solution method can be changed to use either an infinite dielectric or any one of the SEP, FEM/MoM and VEP techniques, provided computational resources are available and practical. 4. Perform a mesh convergence study Guidelines as to how meshing should be done is provided in the FEKO User Manual. In addition, the mesher in CADFEKO when set to the "Standard" option will use mesh sizes appropriate for the frequency. However, there are cases where the meshing can be made coarser than recommended. A good example of this is a reflector antenna excited with a horn at its feed point. The incident fields are mostly planar and uniform in phase onto the reflector. Therefore a mesh size much coarser than the usual lambda/10 can be used. For dielectrics, often the high permittivity could require a finer mesh size. Also, surfaces or objects very close to each other would require finer meshing on the neighbouring surfaces. Also refer to the comments in: In general, once a result is obtained, it can be confirmed by rerunning the model with 50% more mesh elements. If the results agree well, then the mesh can be regarded as converged and thus an accurate representation of the geometry and its behaviour at that specific frequency. If a frequency loop was used, then in most cases the mesh can be regarded as converged for the frequencies below that simulated. If computational resources are limited, or run-times prohibitive, a mesh convergence study can also be done by using 50% less elements. However, if results then disagree, no conclusion can be drawn regarding the original mesh and its convergence.
  9. I have created a model in FEKO and compared the results to measurements, but the results don't agree as much as I would like. How do I confirm that the FEKO results are correct (error in measurements) vs. an error in my model?
  10. If you can not found FIDAP Neutral format within support solver, that means this format is not yet supported by Hypermesh. However, Hypermesh is "open system", you can write yourself the output template to get your output.
  11. Try this:
  12. Having transparent elements with a dot at its center and also having surface meshing instead of a tetra 3D mesh Can anyone solve the issue?
  13. The details below contain some information regarding coaxial lines and micrstrip lines, but also contains other meshing suggestions. A solved model is only as good as its mesh. Modelling and meshing guidelines are given in the FEKO User Manual. This how-to gives detailed (but not exhaustive) examples of how to create a good mesh, and also shows comparative results for different meshes. Background CEM techniques discretise either the fields (such as FDTD codes) or the currents (such as MoM codes). Discretisation introduces small but controllable errors in the results. To reduce the error, the mesh size can be reduced, however, this increases computational cost. This how-to will show examples of how to create an appropriate mesh given the accuracy vs computational cost consideration. In addition, comparisons are shown between "good" and "bad" meshes. Example 1: A simple strip dipole in free space The first example is an ordinary strip dipole. To show the mesh differences more clearly, the dipole length was made 1.5 free space wavelengths. Figure 1a: Geometry of a strip dipole - dimensions 1.5 x 1/30 wavelegnths We now consider three different meshes and their results. In the first case we set the triangle mesh size under the Create Mesh dialog to a Custom size of 1/10 of the free space wavelength. This results in an average size for a mesh triangle on the dipole of around 1/20 of the free space wavelength. The smaller than requested elements are due to the narrow width of the dipole - the mesher tries to create each triangle so that its edges have similar lengths. The total number of triangles are 57 triangles. Figure 1b: The strip dipole mesh using a triangle edge length of lam0/10 In the second case we use a finer mesh size on the strip dipole. Here we set the triangle edge length to 1/60 of the free space wavelength. The total number of elements are 414 triangles. Figure 1c: The strip dipole mesh with edge length = lam0/60, zoomed view In the third case the edges of the dipole are protruded perpendicular to the dipole surface with a distance of 1.25 mm or lam0/800. The total number of elements were 140. Figure 1d: Strip dipole with edge triangles Zoomed in view Zoomed out view In the latter case the perpendicular protrusion of the edges causes basis functions to be placed all along the edges of the dipole. This provides increased accuracy for modelling the width of the dipole. Fig. 1e compares the input the resistance and input reactance for the three meshes. It can be seen that the mesh with edge triangles and the lam0/60 mesh provide very similar results, but the "standard" lam0/10 mesh shows a deviation. It is clear that a very accurate answer can still be obtained for a small increase in unknowns with the edge triangles method compared to the very fine lam0/60 mesh. Figure 1e: Comparing the input resistance (left) and input reactance (right) for the different meshes Input resistance Input reactance Note that if we were mainly interested in the far fields of the dipole and not interested in modelling the impedance of the dipole accurately, then the mesh size of 1/10 of the free space wavelength would have been sufficient. Example 2: A section of coax A section of coax can be considered to be geometrically complex - the electrically small radius of curvature requires a fine mesh to accurately represent the curvature. If the mesh is inadequate, the TEM wave that is intended to be launched will not be purely TEM and the impedance of the coax could be inaccurate. Consider the section of air-filled coax in Fig. 2a. The inner radius is 3 mm and outer radius is 2.31 times larger, resulting in a 50 Ohm line. Figure 2a: Geometry of a section of air filled 50 Ohm coax We again consider three different meshes, their unknowns and results. The first mesh uses a mesh size of lam0/10 in the Create Mesh dialog and results in 1292 triangles. This is depicted in Fig. 2b. Figure 2b: The coax meshed with a triangle edge length of lam0/10 The second mesh shown in Fig. 2c creates a so-called ruled mesh by imprinting axial lines onto the inner and outer surfaces of the coax every 30 degrees around the surface. These lines force the mesh triangles to be longitudinally shaped. These triangles are more appropriate for the coax as the current flow is mainly along the axis of the coax and not radial. The mesh contains 1710 triangles. Figure 2c: Ruled mesh of the coax Outer conductor view Inner conductor view The third mesh is also a ruled mesh but here the lines were imprinted every 45 degrees instead of 30 degrees. This mesh contains 1854 triangles. The results are shown in Fig. 2d. It can be seen that the ratio between the reflected power vs incident power is smallest for the "30 degree" ruled mesh, despite this mesh having fewer triangles than the "45 degree" mesh. Figure 2d: Input power vs reflected power for different meshes of the coax Note that ruled meshes are automatically created for curved geometry - it is not necessary to imprint lines on the curvature - the imprinting here was just for demonstration purposes. The ruled mesh can be controlled on the Advanced tab of the Create mesh dialog. It can be enabled/disabled by checking/unchecking the box, "Allow elongated triangles". Example 3: A box with a narrow aperture The geometry consists of a box with a wire inside. The wire is fed with a voltage source and the near fields that radiate through the slot are calculated on a sphere about 3m away on the outside of the box. The model is from the article, "EMI from cavity enclosures," IEEE Trans. EMC. Feb. 2000. The geometry of the box is depicted in Fig. 3a. Figure 3a: Geometry of the box with aperture Outer view Inside view (slightly zoomed) We consider two meshes. The first mesh is where we set the triangle edge length to the usual lam0/10 resulting in 1948 triangles. In the second mesh, we set a local mesh size on the edges of the slot of 3x the width of the slot resulting in 2432 triangles. Specifically, we use the following expression for the local mesh size: min(lam0/10, 3*slot_width). This expression ensures that the slot mesh is parametric - the minimum is taken of lam0/10 and 3*slot_width. Should the frequency increase substantially, the first term in the expression will dominate. Should the slot be made narrower, the second term of the expression will dominate. Fig. 3b shows the two meshes. Figure 3b: Mesh of the box with aperture No local meshing applied With local meshing applied on the slot edges (zoomed view) Fig. 3c shows the result comparison. We see a significant shift in some of the peaks in the curves of the near fields for the two meshes. Clearly, the local mesh size is required. Figure 3c: Emitted nearfield from the box for different meshes Example 4: A section of microstrip line When designing feed networks usually the impedance of the microstrip lines need to be modelled accurately. Similar to Example 1, we will see that using edge triangles provide high accuracy without adding to the computational resources. A section of 50 Ohm microstrip line is modelled. We consider a few meshes and their performance. The first mesh uses a mesh size of min(3*h, lambda_d/10) where h is the substrate height and lambda_d is the wavelength in the substrate. The 1st expression is required to ensure that geometry is meshed such that the triangle size is of the order of the spacing between the geometry (here the line itself and the ground plane beneath). The second expression specifies a mesh size of 1/10th of the wavelength in the dielectric. This mesh results in 2 triangles across the width of the line. The second mesh uses a mesh size of min(h, lambda_d/10). This results in about 4 triangles across the width of the line. Figure 4a: Meshed microstrip line Using a mesh size of min(3*0.5, lambda_d/10) Using a mesh size of min(0.5, lambda_d/10) The third mesh uses edge triangles by means of a vertical protrusion of the microstrip edges. The fourth mesh is a slight variation of the third mesh in that the edge triangles are still used but they are in the same plane as all other triangles. Figure 4b: Meshed microstrip line continued Using edge triangles vertically protruded from the line edge Using edge triangles in the same plane Comparing the input resistance and reflection coefficient of the line it is seen that the line with 2 triangles across the width of the line gives the least accurate answer. Using a finer mesh to obtain about 4 triangles across the line provides better accuracy. However, the meshes with edge triangles are the most accurate. Figure 4c: Input resistance and reflection coefficient for the 50 Ohm microstrip line Input resistance Input reflection coefficient The reason that the input resistance is not exactly 50 Ohm is due to the feed. It represents a discontinuity in the microstrip mode. De-embedding the feed should provide more accuracy. (The same feed was used in all cases). Example 5: An F5 generic aircraft model - RCS The monostatic RCS of a generic F5 aircraft model is calculated. We compare the results for different mesh densities. The F5 model is shown in Fig. 5.1 Figure 5.1: Geometry the F5 aircraft The mesh sizes and number of elements evaluated are as follows: lam0/3.5 = 44712 triangles lam0/4.5 = 76111 triangles lam0/6.8 = 170246 triangles The RCS comparison is shown in Fig. 5.2. Figure 5.2: Monostatic RCS from the side and front of the F5, swept from top to bottom RCS from the front RCS from the side It is seen that even for a very coarse mesh, the RCS result is nearly converged. It must be stressed that the above results are very dependent on the geometry. Nearfields computed close to some areas on the surfaces could be inaccurate, or the received power in an antenna attached to the aircraft could also be inaccurate. The model was solved with the MLFMM. It must be noted that in all cases the residuum for the iterative solution for the MLFMM was set to 1e-5 (the default is 3e-3). This is sometimes required when very small values are expected in the results. Here, for example, the RCS goes down to 40 dB below the maximum. Example 6: An F5 generic aircraft model - antenna coupling We use the F5 model again but this time compute the coupling between two monopole antennas. This is to further demonstrate the mesh size is dictated also by the type of problem being solved. One monopole is located on the top near the nose of the aircraft. The other monopole is located on the bottom near the tail of the aircraft. Fig. 6.1 depicts the F5 with the monopole antennas (only their ports are visible). Figure 6.1: Geometry of the F5 aircraft showing the ports of the two antennas Again we expect very low values, so we set the residuum for the MLFMM to 1e-5. To save on computation time, the maximum number of samples for the adaptive frequency sampling was set to 31. This causes some discontinuities in the interpolated results displayed. The coupling for different mesh sizes are shown in Fig. 6.2. Figure 6.2: Antenna coupling for different mesh sizes It is seen that there is a 10 to 15 dB difference between the coarsest mesh and the finest mesh. It may even be necessary to use an even smaller than lam0/8 mesh size. Notes on FDTD meshing Surface current techniques in general require that the mesh size is reduced in proportion to the frequency. Doubling the frequency requires the mesh size to be halved. Due to numerical dispersion in the FDTD, this general rule of thumb is not conservative enough. According to Davidson [1], "it is important to appreciate that phase error accumulates across a domain. The absolute phase error over a fixed length L is approximately (k^3)(h^2)L/36" where k is the phase constant and h is the voxel size. This "implies that cell size must scale with frequency as (2*pi*f)^-1.5 to keep the error constant and hence the number of cells in each dimension scales with (2*pi*f)^1.5". For example, if the frequency is doubled, the cell size must be reduced to approximately 0.35 of the cell size at the initial frequency. Final comments This how-to didn't cover all the techniques in FEKO. For example, the ray-launching solver requires that the mesh only represents the geometry accurately. Also the FEM-MoM solver uses higher order basis functions and thus requires mesh sizes of around 1/5 of the wavelength in the dielectric. There are also higher order basis functions for the MoM and physical optics (PO) with large triangles. However, this how-to shows that coarse meshes are useful to obtain fast "ball-park" results, and in some cases very good results. The mesh sizes used in the examples in this how-to should not be taken as final for any model. It is given as a starting guideline. Mesh convergence tests* should always be done before taking results as truly final. [1] David B. Davidson, "Computational Electromagnetics for RF and Microwave Engineering" Second Ed. Cambridge University Press, p 117 * Rerunning the model with 50% more mesh elements and comparing the results with that of the original mesh.
  14. I know there are many tips regarding creating an appropriate mesh in the FEKO manual, but are there any tips for creating a good mesh for coaxial lines and microstrip lines that anyone can share?
  15. FEST3D is a software tool for the synthesis and analysis of passive waveguide components. The performance of a structure designed in FEST3D can be verified by calculating the full-wave Method of Moments (MoM) solution with FEKO. The mode data from FEST3D can also be used for further analysis of more complex, or radiating, structures in FEKO. A two-way interface allows impressed modes and generalised scattering matrices (GSMs) to be exchanged between FEKO and FEST3D. FEKO to FEST3D The DA card is used in FEKO to write out a *.chr file that is then loaded into a 1-Port / N-Port User Defined element in FEST3D. In FEKO The DA card can be used in EDITFEKO to export the generalised scattering matrix to a FEST3D *.chr file. The SP card must be included in the *.pre file for the S-parameters to be calculated. The calculated modes must be set up in order with AW cards in EDITFEKO, or can alternatively be defined using a *.fim file. The order of modes should be according to an increasing order of ports, with the modal expansion sorted according to the increasing value of cut-off frequency, starting with the fundamental mode. If degenerate modes are present, the TE modes should be listed before the TM modes and even modes (with reference to the x coordinate) should be listed before odd modes. Modes are ordered by port and according to cut-off frequency at each physical port, e.g. for a three port structure with two modes at each port the order will be: AW MyWaveguideStructure.Port1 mode1 AW MyWaveguideStructure.Port1 mode2 AW MyWaveguideStructure.Port2 mode1 AW MyWaveguideStructure.Port2 mode2 AW MyWaveguideStructure.Port3 mode1 AW MyWaveguideStructure.Port3 mode2 The same number of linear frequency points used for the computation of the matrix in FEKO must be used by the circuit containing the N-Port User Defined discontinuity in FEST3D. In FEST3D The *.chr file created with FEKO can be loaded into FEST3D using a 1-Port User Defined or N-port User Defined element, depending on the circuit to be analysed. FEST3D to FEKO A *.fim file is created with FEST3D and loaded into FEKO with the AW card. In FEST3D A one port circuit is needed to create a fim file that contains the impressed modes at the port. If the FEST3D circuit contains more than one port, all other ports should be set to be of SubType “Termination” (“Adapted”) instead of “Input/Output Port”. For a file with one open port, and any other ports adapted, the GSM can be computed (by pressing the “S” button in FEST3D). The GSM is written out to a *.chr file, e.g. MyAdaptedCircuit.chr. A new circuit should be created where a single waveguide is connected to a 1 Port User Defined element which is set up to load the GSM (MyAdaptedCircuit.chr). The impressed modes can now be calculated by pressing the “I” button in FEST3D. This will write out a *.fim file to disk, e.g. MyWaveguideCircuit.fim. Partial FEST3D toolbar showing the "S" and "I" buttons that are used to calculate a GSM (write out a *.chr file) and calculate impressed modes (write out a *.fim file). In FEKO The solution frequency must be defined in FEKO to coincide with the number of frequency points used in the FEST3D calculation. FEKO needs to associate ports of a *.fim file with port face labels in the FEKO model. The CB card can be used in EDITFEKO to change the labels to numbered port names, corresponding to the FEST3D numbering, for example: CB: MyWaveguideStructure.Face1 : Port1 CB: MyWaveguideStructure.Face2 : Port2 The AW card is used in EDITFEKO to excite a waveguide structure with impressed modes calculated in FEST3D by loading the impressed modes from a FEST3D *.fim file. Partial AW card dialog in EDITFEKO. The “Reference point for FEST3D model (named point)” input parameter on the AW card dialog is the origin of the reference coordinate system. This is chosen to be the bottom right corner of a rectangular port, and the centre of a circular port. In both cases the z-axis should be defined to point into the structure. This reference point is used to indicate the translation of the imported model in the FEKO coordinate system. It can be defined with the DP card. Rectangular waveguide port reference coordinate system (reference point O). Circular waveguide port reference coordinate system (reference point O). Notes Geometry import/export Scaling could be required on importing STEP and IGES geometry files into FEKO. Exported 3D geometry files from FEST3D have been found to state dimensions are in ‘mm’ regardless of unit chosen for export (found in version 6.7.3 of FEST3D). The geometry could be incorrectly scaled upon import into FEKO. The user can scale the model in FEKO if necessary, e.g. if exported 3D geometry in FEST3D in ‘inches’, import in CADFEKO will pick up unit is ‘mm’ and incorrectly scale by 0.0393701 if the model unit in FEKO is ‘inches’. Select transform -> scale and scale the model by 25.4 (or 1/0.0393701) to correct. If the geometry was exported in mm no scaling would be required. Symmetry The use of symmetry is not officially supported for the interface. If symmetry is used, it is the user’s responsibility to ensure that symmetry conditions are set up to coincide between FEST3D and FEKO. Possible symmetry conditions in FEKO are geometrical, electrical and magnetic symmetry and symmetry defined in the XY, XZ or YZ planes. Symmetry definitions supported by FEST3D are All-Inductive (H plane, constant height), All-Capacitive (E plane, constant width), All-Cylindrical (All-Centered Circular waveguides), X symmetric (symmetric under horizontal reflection), Y symmetric (symmetric under vertical reflection) and TEM (All-Centered). Symmetry going from FEST3D to FEKO FEKO can handle files for which symmetry was defined in FEST3D and will use the impressed modes that existed with the symmetry in FEST3D as excitation. Files containing modes that cannot exist due to the symmetry conditions in FEKO will cause an error. No checks are performed to ensure that similar symmetry conditions are set up in FEKO as were used in FEST3D. Symmetry going from FEKO to FEST3D FEKO will always write out <symmetries nsymmetries=”0”/> to a *.chr file. If symmetry planes are set up in FEKO, modes that cannot exist due to the symmetry conditions will have zero amplitude in the FEKO formulation. Modes that can exist given the symmetry conditions will be written out to the generalised S matrix in the *.chr file. However, FEST3D will be unable to use this kind of file as a component in a circuit where any global symmetry has been defined. In order for the file to be used successfully with symmetry in FEST3D, it can be manually edited by the user. The user should confirm that the correct modes are taken into account and symmetry is correctly defined. The correct syntax can be obtained from the *.chr file that is written out for the circuit when selecting “Compute Generalized Z matrix” in FEST3D, for example: <symmetries nsymmetries="1"> <symmetry/> </symmetries>
  16. I have heard that FEKO has an interface with FEST3D, but I'm not sure how this interface works. Does anyone have some information regarding using the interface?
  17. A dipole antenna made from a cylinder (and thus meshed into triangles) presents two common problems to users: Firstly how to excite the dipole and secondly how to create a mesh that follows the curvature of the dipole but which is not overly discretised. This how-to gives a step-by-step guide to creating this antenna. Step by step Create a cylinder with length equal to the total length of the dipole antenna. Split the cylinder in half on the XY plane (assuming the cylinder was created on the Z-axis). Union the two halves. Create a cutplane in the YZ or XZ plane. Delete the Face inside the cylinder on the XY plane. On the Source/Load tab click on Edge port - for the Positive faces click in the 3D view on the top half of the cylinder (this should populate the Positive faces box. Do the same for Negative faces. Then click Create to complete the port. Create a voltage source. An alternative to the edge port would be to insert a small separation between the dipole halves and create a short wire between the halves. Then a wire port can be used. Meshing: Since the geometry is curved, the mesh will have to represent the curvature. The advanced tab of the Create Mesh dialog can be used to adjust the curved geometry approximation settings. Alternatively, for MoM solutions users can enable Higher Order Basis Functions. CADFEKO will then mesh curved triangles. dipole1.cfx
  18. I have to model a dipole using cylinders (can't use segments since the dipole is very "fat"), but I don't know how to create the excitation for such a dipole. Can someone help?
  19. FEKO has greatly improved the mode tracking capabilities in the last few years and it is recommended that users use the latest version of FEKO. The tips below are still recommended for improved mode tracking. Characteristic mode analysis (CMA) is the numerical calculation of a weighted set of orthogonal current modes that are supported on a conducting surface. This how-to explains how the mode tracking is done in FEKO and why sometimes incomplete traces for modes are obtained in POSTFEKO. Introduction Characteristic modes are obtained by solving a particular weighted eigenvalue equation that is derived from the method of moments (MoM) impedance matrix. FEKO has a built-in solver that calculates these modes, with no need for post-processing by the user. The eigenvalues, modal significance, characteristic angles, currents, near fields and far fields can be visualised in POSTFEKO. However, inadequate setup of the model could result in inaccurate CMA results. Consider a dipole constructed with a cylinder (meshed into triangles). In CADFEKO, a characteristic mode configuration is requested and the standard configuration is deleted. The default number of modes to be calculated is kept at 6 as shown in the image. The frequency range is set from 2.5 to 3.5 GHz. In addition, the output of currents is requested so that we can view them during the post-processing phase. After FEKO is run, a Cartesian graph of the modal significance of the 6 modes are plotted in POSTFEKO. The graph is shown below. We see that only mode indices 1 and 2 are complete for the frequency range. POSTFEKO also shows warnings for traces 3 to 6. The reason for the incomplete traces for the other modes is as follows: When a frequency range is requested, mode numbers (rather indexes) are assigned according to their ranking at the lowest frequency. This initial ranking or sorting is based on the modal significance of the mode, that is, modes with a smaller eigenvalue will have a lower ranking. FEKO tracks the requested number of modes over the complete frequency range. If the user requested, for example, 6 modes, more modes are actually calculated to track every mode index over the whole frequency range. As the frequency changes, mode rankings will change. It could be that a mode that had a very low eigenvalue at the lowest frequency, and that was assigned a very low ranking, changes to a high eigenvalue at a higher frequency. FEKO will order the modes correctly at each frequency, but this ordering will be based on the mode rankings at the lowest frequency. Now since many more modes are to be calculated, these higher order modes often require a much finer mesh than the well known 1/10th of a wavelength for a MoM solution. If the mesh size is not sufficiently small for a particular mode, the mode cannot be represented accurately by the mesh and the mode tracking will fail. The mode tracking could fail at any frequency over the range. Consequently an incomplete curve could be obtained for a mode in POSTFEKO. If we look in the result palette in POSTFEKO in the Mode index dropdown, we see several modes listed, although we only requested 6 modes: This is also because a mode could not be tracked over the entire frequency range. For example a mode could have been assigned an index at the start frequency, but at a higher frequency this mode could not be tracked any more and was assigned a new index. It could even happen that the "new mode" is also untracked at a higher frequency, and again assigned a new index. The remedy is to use a finer mesh. The mesh size is adjusted using a 3 times smaller triangle edge length and the model is rerun. We see in the graph below all the modes are now tracked over the complete frequency range: In addition, if we expand the result palette again we now see only 6 modes listed: Final remarks The requested frequency range for this example was 21 frequencies from 2.5 to 3.5 GHz. In some cases, it could also be required to use finer sampling (more frequency samples) to obtain proper mode tracking. Continuous frequency sampling is not yet supported for CMA. feko_7p0p1_files.zip
  20. For one of my characteristic mode analysis models the modes don't seem to be tracked correctly. Are there any tips for improving mode tracking?
  21. Users should consider using Compose instead of Octave - it is very quick and easy to convert Octave *.m files to run in Compose. Users working with external programs such as Octave in the past parsed the FEKO *.out file for results data. This parsing is no longer necessary. Any data displayed in POSTFEKO can be exported in a user defined format to a file using Lua scripting in POSTFEKO. The export can automatically be repeated after each successful execution of running FEKO. This how-to, by means of a small example and script, shows how to do this. This is not the only (or maybe even the best) way to export the data, but it shows one possible option for exporting results from FEKO. Background In the past, to obtain the data in an external file users had to first plot the data in POSTFEKO and then use the export data function. This procedure had to be repeated after each successful FEKO run. Alternatively, the OUT file was parsed using an external script or program such as Matlab. Using Lua, it will be shown here that a script can be written in POSTFEKO that automatically writes the data chosen by the user to a file in a format chosen by the user. Some of the images in this how-to were taken from Suite 6.1. The Lua script provided in the attachment is forwards compatible with Suite 6.2. Example overview Consider two dipoles excited with a plane wave. The first dipole has a load attached to its port. The second dipole has a non-radiating network attached to its port and the network is terminated in a load. The plane wave is looped over five angles. The geometry and tree view in CADFEKO is shown below. The schematic view is shown below. Note that a load is attached to the Network Port2 (not shown in the schematic). We will show how to export the currents in the loads to a file. Making and using the script in POSTFEKO After solving the model, run POSTFEKO. Plot the data that must be exported to a file. The currents in the loads are plotted and shown below. In POSTFEKO click on the "New Script" icon and select "Load". After writing the script, the script can be accessed again by clicking on "Modify script". The script text and execution window is shown below. For more details on the scripting syntax, please see the FEKO User Manual. In this example a filename, "loads.dat" was chosen and is written automatically after each execution of RUNFEKO. To stop automatic execution of the script, uncheck the box, "Automatically run the script with bof file reloading". A section of the data file is shown below. suite6p1_files.zip
  22. I am using an external program to process my FEKO results and would like to find a way to export the results to a custom format every time the model is solved. Is this possible? I'm not processing the results in POSTFEKO directly since the scripts to process the results were developed a long time ago and written in Octave.
  23. The memory requirement for the FDTD is roughly 150 MByte per 1 million voxels. Without a model to look at, it is rather difficult to make suggestions, but I have listed a few items that you could consider. Remove unnecessary free space regions from the FDTD bounding box The default behaviour of CADFEKO is to automatically add a free space buffer of size lam0/8 for each of the 6 sides of the FDTD bounding box where lam0 is the free space wavelength at the lowest frequency to be simulated. In some cases this boundary can be set to PEC or to not add this boundary. When S-parameters are requested, limit the number of active ports Each active port for the FDTD requires the restarting of the time steps. When requesting S-parameters, for example, in a two port solution where only S11 and S21 are required, then deactivate the second port in the S-parameter request in CADFEKO. Choose the near field request to be within the existing mesh A voxel is stored for each near field point. If the near field point is such that it is outside the bounding box that would have been used without the request, then the number of the voxels will increase and therefore also the computational resource requirements. Also, if the near field points are closely spaced, then the mesh will need to follow this spacing. This could also lead to an increase in the number of voxels in the mesh.
  24. I have and FDTD model and I'm trying to reduce the required resources. Are there any tips or options that I can consider to try to reduce the resources required to solve the model?
  25. Hi This is usage of bwidget scrollable frame http://wiki.tcl.tk/1091
  26. Hello, How to get FIDAP Neutral file format (in Gambit software) from other mesh generator softwares like Hypermesh, Abaqus and Trelis for exporting of mesh and boundary condition data ? Thanks all.
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