Page added Monday 23rd March 2020

 

Using the Oasys LS-DYNA Environment remotely

Below you can find some general advice for using the Oasys LS-DYNA Environment efficiently when working remotely. For further information or help with any of the points below, please contact us on +44 (0)121 213 3399 or [email protected].

The problem

When we are working remotely, we often need to send large quantities of data back and forth over the network between a high-performance computer (HPC) or cluster (where the LS-DYNA jobs are run) and our remote machine (where models are prepared and results are viewed /processed). Even for smaller LS-DYNA models that we can run locally on our machines, we might still need to share the files and output data with co-workers over the network. Network speed and bandwidth limitations can become the bottleneck and make the process slow and inefficient.

There are multiple ways to make this more efficient, such as:

1. Model set-up strategies to make our input and output files as small as possible
2. Compressing files efficiently using third-party software
3. Rationalising the generation of output files which contain only the data you need
4. Remote post-processing directly on the HPC-side, using relatively low-bandwidth methods such as command-line execution or, where the hardware/software is supported, using efficient remote-desktop solutions such as VNC connections

1. Model set-up strategies

Three important things you can do to reduce the output of your LS-DYNA results files are:

• Set IBINARY to 1 on the *DATABASE_FORMAT card if you are running double-precision LS-DYNA. This reduces the output to 32-bit precision without affecting the precision of the calculation itself. For double-precision analyses, this will halve the size of your binary results files. Note: the IBINARY setting will be ignored if you are running single-precision so there is no harm in setting it for single-precision too.
• If you use the default database output options, consider using the *DATABASE_EXTENT_BINARY card to cut down the output. For example:

– STRFLG controls output of strain tensors – this is off by default but if you have it switched on and no longer need it, consider switching it off

– RLTFLG controls shell force and moment resultant output – this is on by default but if you only want to look at stresses you can switch it off

• Consider using D3Part files to output results for a subset of your model at a higher time resolution. You may be able to output results for the whole model at a fairly coarse time resolution but use D3Part to generate results for the subset at more frequent intervals:

– Switch on *DATABASE_BINARY_D3PART and set the higher time resolution interval you want for the subset

– In PSETID, define the subset of parts for this higher time resolution

2. Compression of files

Some LS-DYNA input and output files can be compressed which reduces their file sizes and makes transferring across a network connection faster.  

Within our Oasys Suite of software, PRIMER can read, write and edit compressed keyword files directly in a number of formats. When writing out LS-DYNA keyword files, just go to Model > Write > LS-DYNA output options > Compress and select the compression type you prefer. The keyword files will need to be un-compressed after you have transferred them across (e.g. to your HPC cluster), before running in LS-DYNA.  

For LS-DYNA binary output files, there are a number of compression tools. We find FEMZIP in particular achieves excellent compressions ratios (typically 50:1) while also enabling quick reading of compressed data, for example when using Oasys D3PLOT with its built-in FEMZIP reader. FEMZIP is optimised for finite element models but may require further configurations to give the best results. We would be happy to provide more information about usage and pricing, just get in touch on +44 (0)121 213 3399 or [email protected]. 

3. (Re)write only the data you need

This is essentially another form of compression or file size reduction method. Using Oasys D3PLOT, you can (re)write out binary output files which contain only the data components, parts, plot states etc., that you are interested in, rather than all data for all parts typically written out by LS-DYNA.

This can be done in Oasys D3PLOT by clicking File > Write Compressed PTF File but this requires loading the whole model in with all the data first. If your model data resides on the HPC cluster, you can run this command remotely and directly on the cluster using the command line without interactive graphics interface. This should make it quicker and more efficient for remote-working. You can find out more about this in sections 6.7.7 (“Cutdown D3PLOT/PTF file”) and 2.4 (“Command Line Options”) of the D3PLOT 16.0 manual or via our support details above.

Something similar can be achieved with LS-DYNA time-history data using Oasys T/HIS. FAST-TCF scripts can be used to extract and post-process data, even automatically or remotely, and these may already be a part of your company’s analysis workflow. These scripts can be generated using the FAST-TCF tab in T/HIS but again, this option requires you to have opened a T/HIS session with all the required data read in first.

It is also possible to run FAST-TCF scripts from T/HIS via a command line without interactive graphics interface. You can find out more about this in sections 7 (“FAST-TCF”) and 1.3 (“Command Line Options”) of the T/HIS 16.0 manual or via our support details above.

Note: the above (and many other) functionalities in the Oasys Suite can also be used via the Oasys JavaScript API which can be executed remotely via command line without needing interactive graphics interface.

4. Remote desktop using VNC connections

Sometimes a Virtual Network Computing (VNC) remote desktop connection to a server/computer located within your organisation’s network can be useful for more efficient remote post-processing while still retaining the use of interactive graphics interface (instead of merely command line options, as described above). 

A VNC “screen scrapes” the graphical output on the machine in your organisation’s network (presumably ‘closer’ or ‘local’ to the LS-DYNA data), compresses the information, then sends it more efficiently across the network to your laptop/computer for remote working. In this way, only efficient and compressed graphical data is sent to your machine (much like video streaming), avoiding the need to copy large LS-DYNA input and output files back and forth. Note: network latency, speed, and bandwidth limits will still likely be the bottleneck in this process but it can still be a more efficient workflow compared to the need for frequent, large file transfers. 

With the pre-requisite of hardware (e.g. graphics card or GPU) and software (e.g. GPU drivers and OpenGL or VirtualGL support) on the server/computer within your organisation’s network, the Oasys Suite of software can be used over a remote desktop or VNC connection with efficient graphical interface performance. 

Want more guidance?

If you want further guidance or have any questions, please get in touch with us on +44 (0)121 213 3399 or [email protected]; we’ll be happy to help.

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