Advanced Training Ansoft HFSS Environment …dl.edatop.com/mte/ansoft/edatop.com_Advanced Training Ansoft HFSS...Advanced Training Ansoft HFSS Environment Variables and Preferences

Advanced Training Ansoft HFSS

Environment Variablesand Preferences

Ansoft CorporationPittsburgh, 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 platform-dependent. 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 yoursystem, 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 directorywhere the maxwell executables reside, and type:

set HFSS_MAX_REFINE=3000maxwell

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 beforestarting Maxwell:

setenv HFSS_MAX_REFINE 3000maxwell

UNIX KSH:

export HFSS_MAX_REFINE=3000maxwell

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_TRIANGLESUSE_COLLOCATIONPML_EXISTSAMPLIF_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 yourRAM and CPU requirements, but you may want to increase its valuesometimes.

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 εr and µr.

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 forthe 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

Eslave = A eiϕ Emaster , Hslave = (1/A) eiϕ Hmaster .

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

Eslave = A eiϕ Emaster , Hslave = A eiϕ Hmaster .

Power = E•H* is multiplied by A2.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-relatedUser Preferences

Ansoft CorporationPittsburgh, PA

Optimal memory usage strategy

Necessary

Sufficient

In core Off core Swap

Log

(Mem

ory) 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” toavoid Operating-System-directed swapping. The time penalty for this off-corework 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 200000DIRECT_SOLVER orion:MemLimitSoft 400000DIRECT_SOLVER stellar:MemLimitSoft 800000DIRECT_SOLVER MemLimitHard 400000DIRECT_SOLVER orion:MemLimitHard 800000DIRECT_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/adminMaxwell stellar:ScratchDir /home/projectsMaxwell 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: File .maxwellrc in your home directory defines location of aCONFIGDIR. That directory contains a file .prefs .

Windows: File maxwell.ini may define location of a CONFIGDIR.Default is <directory_where_executables_are>\configThat 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 2Tells solver that you have two processors (PC only).

Hfss_Solver FSResidualError 1Creates file fs_resid.dat which contains error function after Fast Frequency Sweep. Can be plotted.

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