Advanced Training Ansoft HFSS Environment Variables and Preferences Ansoft Corporation Pittsburgh, PA
Environment Variables - 1 Environment Variables are used to give HFSS instructions that override default parameters built into the code. Usually they are required to perform features that would be undesirable under normal usage, or are advanced features that should only be used by expert users--if used without discretion they could cause poor results or performance. If others may use your copy of HFSS or need to work with your models, remember to tell them about your settings!
Environment Variables - 2 The implementation of Environment Variable are platformdependent. The common ways of implementing environment variables in unix.ksh and.csh, and PC NT and Win95 will be presented.
Environment Variables - 3 HFSS has many environment variables--they often are created by developers for internal use. When you find that HFSS doesn t seem to be able to do something you want, it is important to contact an Applications Engineer. They may know how to do things that aren t obvious, and if they don t know, they can usually find out because they are in continuous communication with each other and can access developers also.
Environment Variables - 4 Environment variables consist of two parts: a variable and a value. They can be set in such a way that they are the default for your system, or such that they are only applied temporarily. When applied temporarily, they generally exist only as long as the Window they were applied in is used for launching the Maxwell Control Panel. Set them before starting the Maxwell software.
Setting Environment Variables on PC s (Semi)-Permanent method: Windows NT: Control Panel > System > Environment Tab > variable: HFSS_MAX_REFINE value: 3000 Windows 95: in autoexec.bat put the line: set HFSS_MAX_REFINE=3000 One-shot method: Get out of Ansoft s software completely, bring up a DOS window, go to the directory where the maxwell executables reside, and type: set HFSS_MAX_REFINE=3000 maxwell A Maxwell Control Panel will be launched that uses the environment variables.
Setting Environment Variables on unix: CSH: put this line in your.env-ans file, or else type it before starting Maxwell: setenv HFSS_MAX_REFINE 3000 maxwell UNIX KSH: export HFSS_MAX_REFINE=3000 maxwell
Description of environment variables The environment variables that are useful in HFSS are: HFSS_MAX_REFINE LAMBDA_REFINE_TARGET ZERO_ORDER OMIT_FS_ERROR_CALC WAVE_MIN_TRIANGLES USE_COLLOCATION PML_EXISTS AMPLIF_FACTOR ASYMM_AMPLIF
HFSS_MAX_REFINE In the Setup solution Menu, you set a Percentage Tet Refinement (e.g. 20%). The number of tetrahedra actually added per adaptive pass has an upper limit: the value of HFSS_MAX_REFINE. Default 2000-2500. There is also a lower limit: HFSS_MIN_REFINE. Default 6. HFSS_MAX_REFINE is a protection against explosive growth of your RAM and CPU requirements, but you may want to increase its value sometimes.
LAMBDA_REFINE_TARGET The default wavelength seeding is 0.25, which means that the structure will be filled with tetrahedra with edge lengths of at most 0.25-0.25 3 free-space wavelength, depending on object shape. Wavelength seeding ignores ε r and µ r. For resonant cavities, a good value is often 0.10-0.15 or smaller, depending on the size of the cavity and the wavelength of the highest-order mode. For structures filled with dielectric, you may want a smaller value than 0.25. For large antenna models, you may want to start with a larger value than 0.25. Value: any real number
ZERO_ORDER Sometimes a structure is small compared to a wavelength and it is appropriate, or even necessary due to model complexity (# tets!), to set ZERO_ORDER. Setting ZERO_ORDER means that HFSS will use linear rather than quadratic basis functions, which uses much less memory and runs much faster. Never use this unless the structure is small compared to a wavelength. Sometimes, to make sure all the tetrahedra in the problem fit the description of <<lambda, it is useful to set LAMBDA_REFINE_TARGET to.05 or smaller: Value: 1
OMIT_FS_ERROR_CALC In the Fast Frequency Sweep, the error calculation uses a lot of memory. Often, this leads to swapping, which will slow you down. This environment variable forces HFSS to skip the error calculation. You may want to enable it once you have obtained a good feeling for the accuracy of the fast sweep for a typical simulation. Value: 1
WAVE_MIN_TRIANGLES This is a leftover from the past. In older versions of HFSS, sometimes the 2-D port eigenmode solver wave kicks out too early, leaving a port with too few triangles to generate a good field excitation. Setting this environment variable will guarantee that the port solver "wave" will generate enough triangles in the port mesh to accurately calculate the port field pattern. This can improve port solutions and it can prevent crashes in the port solver. This can also prevent crashes in the 3D solver (in particular when it fails in the third or fourth pass, or during the fast sweep). Default value: 100-120
USE_COLLOCATION Although the default mesh refinement scheme works well for the vast majority of models, there are cases where convergence is not optimal. Setting this environment variable forces the mesh generator to refine more agressively in regions of strong field gradients (e.g sharp metal tips and edges). Value: 1
PML_EXISTS When you have a model with a Perfectly-Matched Layer and want to calculate far fields, the Post-Processor will complain about the absence of a radiation boundary unless you set this environment variable. Value: 1
AMPLIF_FACTOR Setting this environment variable to A in the presence of periodic boundaries will enforce E slave = A e iϕ E master, H slave = (1/A) e iϕ H master. ϕ = phase shift you set in the interface. Power = E H* is conserved. Application: ideal transformer. This is just a prototype feature! Value: any real number
ASYMM_AMPLIF Setting this environment variable in conjunction with AMPLIF_FACTOR in the presence of periodic boundaries will enforce E slave = A e iϕ E master,h slave = A e iϕ H master. Power = E H* is multiplied by A 2. Application: ideal amplifier. This is just a prototype feature! Value: 1
Environment Variables in future versions Information on Environment Variables is usually not included in the documentation, so keeping abreast of current and new ones one of many good reasons to stay in touch with your AE s. Remember, one of Ansoft s products is customer support. Working closely with AE s enables you to get better solutions faster, and your needs and suggestions also drive future HFSS enhancements.
Part II Solver-related User Preferences Ansoft Corporation Pittsburgh, PA
Optimal memory usage strategy In core Off core Swap Log (Memory) Sufficient Necessary MemLimitHard MemLimitSoft Log (Matrix Size)
Optimal memory usage strategy The previous slide describes the solver s memory and disk usage as a function of matrix size. As long as there is sufficient memory available to do everything in core, the solver follows the line labeled sufficient and solves in core. When it hits MemLimitSoft, it starts doing part of the work off-core to avoid Operating-System-directed swapping. The time penalty for this off-core work is very small! When the matrix size becomes so large that the minimum RAM needed is larger than MemLimitSoft, swapping can no longer be avoided. At MemLimitHard, swapping slows you down so much that it s better to quit.
User Preferences (1) In addition to Environment Variables, there are User Preferences. They are set by editing a preferences file prefs.ini (PC) or.prefs (UNIX). User Preferences allow you to control memory and disk usage.
User Preferences (2) Solver-related User Preferences: DIRECT_SOLVER MemLimitSoft <RAM in kb> DIRECT_SOLVER MemLimitHard <RAM in kb> Maxwell ScratchDir /disk/i/got/by/bribing/sys/admin DIRECT_SOLVER machinename:memlimitsoft <RAM in kb> DIRECT_SOLVER machinename:memlimithard <RAM in kb> Maxwell machinename:scratchdir /disk/i/got/by/bribing/sys/admin
Usage of user preferences DIRECT_SOLVER MemLimitSoft 235000 Default is 128000 kb. Set it to 80% or less of installed RAM. When the solver reaches this limit, it will start to use the disk in a smart way ( spill logic ) and avoid Operating-System-directed swapping. DIRECT_SOLVER MemLimitHard 300000 Less important. Set it to installed RAM + fraction of swap space. When the simulation is so large that the solver needs more than this as a minimum, it will quit rather than wasting your time with too much swapping.
Example of user preferences DIRECT_SOLVER MemLimitSoft 200000 DIRECT_SOLVER orion:memlimitsoft 400000 DIRECT_SOLVER stellar:memlimitsoft 800000 DIRECT_SOLVER MemLimitHard 400000 DIRECT_SOLVER orion:memlimithard 800000 DIRECT_SOLVER stellar:memlimithard 1600000 orion and stellar are names of machines on which you may be running the software. They have 0.5 GB and 1 GB of RAM, respectively.
Maxwell ScratchDir Maxwell orion:scratchdir disk/i/got/by/bribing/sys/admin Maxwell stellar:scratchdir /home/projects Maxwell ScratchDir /my/small/disk orion and stellar are names of machines on which you may be running the software. The directories point to file systems somewhere on the network. This allows you to direct the scratch files to a large disk, and make this action dependent on which machine you re running on.
Preferences file UNIX: Windows: File.maxwellrc in your home directory defines location of a CONFIGDIR. That directory contains a file.prefs. File maxwell.ini may define location of a CONFIGDIR. Default is <directory_where_executables_are>\config That directory contains a file prefs.ini. UNIX and Windows: Prefs files contain lines like the ones just described concerning scratchdir and direct_solver memory settings. Prefs files do not contain environment variables. A prefs file in a project directory has local priority.
More User Preferences DIRECT_SOLVER NofProcessors 2 Tells solver that you have two processors (PC only). Hfss_Solver FSResidualError 1 Creates file fs_resid.dat which contains error function after Fast Frequency Sweep. Can be plotted.
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