Introduction

 About ZFEM

This project is part of the DoD Common HPC Software Support Initiative (CHSSI) program sponsored by the DoD High Performance Computing Modernization Program (HPCMP).

ZFEM was developed by Juan Raul Cebral at George Mason University, Fairfax, Virginia as part of a wider project in collaboration with the Naval Research Laboratory in Washington DC, with Dr. W.Sandberg as the effort director.

Code Description

ZFEM is a distributed collaborative system for the visualization of parallel multidisciplinary applications. This code was designed with the following goals and requirements:

• Parallel-Distributed Applications: visualization of the results of parallel-distributed simulations without having to ship the data back to the workstation where the actual rendering is done.
  
• Collaboration: linking of remote sites for collaborative visualization sessions.
  
• On-Line Visualization: interactive visualization of the data being produced by a parallel solver running on remote machines, and solver steering.
  
• Multidisciplinary Applications: simultaneous visualization of the different components of multidisciplinary applications, such as fluid-structure interaction.
  
• Unstructured Grids: visualization of calculations performed on unstructured meshes in 3D. Also create and extract information from the given grid, such as boundary identification, cut-planes, iso-surfaces and computation of derived quantities.
  
• Surface and Volume Data: visualization of data defined on surface meshes (triangular or quad elements) or volume grids (tetrahedral or hexahedral elements).
  
• Movies: for unsteady applications, making of movies automatically from the time-dependent data set by using scripts and navigation cameras.
  
• Interactive and User Friendly: easy to use with a intuitive graphical user interface and on-line documentation.
  
• Portable: currently it runs under LINUX and on Silicon Graphics computers (SGI).

ZFEM was implemented as a set of independent modules which communicate with each other via message passing. The basic modules and their main tasks are:

MASTER:

• control communication between other modules and the user
• launch other modules
• execute scripts

VIEWER:

• display graphical objects
• interact with the user to manipulate the scene (rotate, translate, zoom, clipping planes, translate the origin, etc.)
• dump the scene into image files

WORKER:

• read data files in parallel on remote machines
• perform computations on the data in parallel
• create graphical objects for display

GUI (Graphical User Interface):

• allows the user to interactively read data files, create plots or perform computations

There are three modes of operation: post-processing, on-line and batch. In the first case the user interactively reads a data set and perform computations, plots and actions using the GUI. In the second case the data is received periodically (at a specified frequency) from a running solver. The user interactively perform computations and create plots at any time. These actions are stored and re-executed when the data is updated from the solver. Thus, the same plots are created every time-step from the current solution data. Since the visualization system is independent from the solver, this method of on-line display is completely interactive, allowing the user to manipulate the scene at any time. In the third mode of operation commands read from a script file are executed in order to read data files, perform computations, create plots, set the view, edit the scene components, etc. Every action performed by the user gets recorded as a command into a script file that can later be run in order to reproduce the visualization, or to execute the same set of operations on a different data set or list of data sets (e.g., for composing movies).

The basic architecture and interaction between the modules for post-processing and on-line display are illustrated in the following figure:

In order to be able to port ZFEM to different computers with a minimum of effort, it was programmed in C, the graphical interface in Motif, the graphics in OpenGL and the communications using PVM. Since these libraries are available for most of the computer systems, there should be little portability restrictions.

Since ZFEM is composed of modules which communicate through PVM, in order to run zfem it is necessary to have the PVM deamon already running. For users who do not need all the capabilities provided by ZFEM and to avoid the "trouble" of using PVM, a lite version of ZFEM was implemented (zfemLite). This version is linked into a single executable that combines one worker, one viewer, the master and the GUI. Therefore it is only possible to open a single data file at a time, and use a single viewer (no collaboration or simultaneous visualization). Also it cannot be linked to a running solver for on-line visualization, it only operates on data files.