VTKArchive Custom Task

A custom task to archive grid results to a series of "VTK Legacy" files.

Introduction

A VTKArchive custom task allows exporting of data extrapolated to the grid during the calculation. The standard archiving is based on particle data. This task's alternative to get grid data is most useful for visualization of results from 3D calculations. The files can be read by third-party visualization applications. A good option is the free, multi-platform ParaView application. The exported files have been written to work well with ParaView. If you export multiple archives in a single run, ParaView can load them as a block and animate the results. There are books and [web sites] on the use of ParaView and few examples of using with NairnMPM.

Task Scheduling

In scripted files, a VTKArchive custom task is scheduled using

CustomTask VTKArchive
Parameter archiveTime,(timeInterval)
Parameter firstArchiveTime,(firstTime)
Parameter (quantity)
   . . .

In XML files, this tasks is scheduled using a Schedule element, which must be within the single <CustomTasks> block:

<Schedule name='VTKArchive'>
   <Parameter name='archiveTime'>(timeInterval)</Parameter>
   <Parameter name='firstArchiveTime'>(firstTime)</Parameter>
   <Parameter name='(quantity)'/>
        . . .
</Schedule>

where the first two parameters, both of which are optional, are

• (timeInterval) - Enter the time interval (in ms) between saving of VTK archives. If this parameter is omitted, the VTK archive files are written on the same steps as the particle archives. The one difference is that the first particle archive file is written before the calculations start while the first VTK archive file is written after the first time step is completed.
• (firstTime) - Enter the time to save the first results (in ms). After this time is reached, subsequent archives will be spaced by the entered (timeInterval) This parameter is ignored unless the (timeInterval) parameter is set as well.

When first setting up calculations, it is useful to create the grid and particles and check them before running a long calculation. When checking the mesh using particle archives, the process is to run the calculations with the -a flag, which aborts the calculations after setup but before the start. If you want to check the setup using VTK archives, however, this abort will happen before the first VTK archive is written. The solution is run with a very small maximum time (less than the time step). The calculations will then stop after the first time step and the first VTK archive file will be available for visualization.

Archivable Quantities

All remaining parameters define a calculation value (by name in (quantity)) to be archived. You can specify any number of quantities to include as manuy results as you want in the output VTK files. The (quantity) options are:

• mass - Archive nodal mass (in g). This option is useful for creating contours that visualize the boundaries of the object. The surface can then be colored in any other archived result.
• material - The material number to visualize different materials in a composite (it is extrapolated to the grid, which will blur material edges compared to particle plots).
• displacement - Archive displacement vector (in mm).
• velocity - Archive velocity vector (in mm/sec). For problems with cracks, it is the center of mass velocity.
• stress - Archive stress tensor (in MPa).
• pressure - Archive pressure (in MPa).
• equivstress - Archive equivalent stress (also know as von Mises stress) (in MPa).
• strain - Archive strain tensor, which is elastic strain for materials that partition elastic and plastic strain, but total strain for all others (absolute).
• deltav - Archive relative volume change (V-V0)/V0 (absolute).
• equivstrain - Archive equivalent strain from above strain (absolute).
• plasticstrain - Archive plastic strain tensor (absolute). Some materials have plastic strain, but hyperelastic materials have left Cauchy Green strain in the particle's plastic strain.
• totalstrain - Archive total strain tensor (absolute, elastic+plastic strain for materials that separate them).
• temperature - Archive temperature (in K). Mostly useful when conduction calculations are activated.
• concentration - Archive concentration (in wt %). Only useful when diffusion calculations are activated.
• strainenergy - Archive strain energy in J.
• heatenergy - Archive heat energy in J.
• plasticenergy - Archive plastic energy (in J).
• contactforce - Nodal force on the grid for MultiMaterialMode simulations when they include rigid contact materials. It is force of the rigid material on the object in Newtons.
• volumegradient - The volume

Output Style

Archived vectors will include all components of the vector and applications like ParaView can view the magnitude or any single component for constructing graphics. Archived tensors will include all components of the tensor. In ParaView, the magnitude and components 0 through 8 of tensors will be listed. The numbers correspond to the following tensor components:

( xx   xy   xz )   ( 0  1  2 )
| yx   yy   yz | = | 3  4  5 |
( zx   zy   zz ) = ( 6  7  8 )