Scalable Solver

Introduction to the Scalable Solver

In an effort to continuously evolve the solution efficiency of the Autodesk® CFD, the Scalable Solver is available as a solver option. This solver is designed specifically for large simulations containing on the order of 10 to 50 million elements. Unlike the original Classic Solver, the Scalable Solver enables each process to run on multiple threads as a process/thread hybrid and is designed to optimize cache performance. The solver has shown significant solution time speedup for large models when using multiple compute nodes. The performance for smaller models on a single compute node is comparable to that of the default Classic Solver.

The Scalable Solver architecture is ideal for systems with large numbers of processors and clusters consisting of multiple compute nodes. It works well with systems that use standard network connectivity. Higher performance connectivity such as Infiniband further improve solution speed, but is not required to realize the benefits.

Note: The Scalable Solver is not currently available for cloud solves.

Supported Functionality

The Scalable Solver supports the following functionality:

• Incompressible flow
• Transient flow
• Thermal (without radiation)
• Laminar and turbulent flow (k-epsilon and standard K-Omega SST, and K-Omega SST SAS)
• The following advection schemes: ADV1, ADV2, ADV4, and ADV5
• Scalars
• Time-dependent boundary conditions
• The following material types:
  • Constant and variable property (density, viscosity, heat capacity, specific heat) fluids, solids, distributed resistances--including surface parts, internal fans, and centrifugal blowers
  • Non-Newtonian fluids
  • Anisotropic conductivity for solids (Kxx, Kyy, Kzz)

Limitations

The following functional items are not supported by the Scalable Solver:

• Radiation
• Compressible flow
• Two dimensional models
• Turbulence models other than those listed above
• Surface parts (solids)
• Check valve material devices
• TEC material devices
• PCB material devices
• Rotating regions
• Monitor points
• Nodal heat sources
• Period boundary conditions
• Motion
• Extrusion meshing
• Cavitation
• Moist air
• Smoke visibility
• Water age
• Thermal comfort
• Joule Heating
• Heat Exchanger material devices
• Free surface

Additionally, for transient simulations, the value for Inner Iterations (found on the Solve dialog) should not exceed 1 when using the Scalable Solver.

Enable the Scalable Solver

Do one of the following to enable the Scalable Solver:

• On the Solve dialog, choose the Scalable Solver as your Solver Computer
• On the Solver Manager dialog, choose the Scalable Solver as your Solver Computer
• On the Solver Computers dialog, choose the Scalable Solver as your Solver Computer or Configuration

Single Node

Autodesk® CFD automatically defines the following configuration options to enable the Scalable Solver:

Configuration Option	Description
Sockets / Node	Typically set to the number of sockets on a compute node. Note that one MPI process will be launched on each socket.
Cores / Sockets	This is the physical core count per socket, and defines the number of compute threads spawned per MPI process.
Hyper-threading	The Hyper-threading is only used when setting affinity; virtual cores are not loaded to do any work.
Affinity	Affinity locks each computational thread to a particular core. This may improve performance because it avoids having the operating system decide which core to use. If the solution crashes or stops prematurely, particularly if there are two or more sockets, you may need to set the Affinity value to 0. To do this, perform the following steps: 1. Open the CFD2_default.xml file located in the C:\ProgramData\Autodesk\CFD 2017 folder. 2. Change the value of of the NoAffinity argument to 0. The line should appear as: <NoAffinity>0</NoAffinity>
Convergence Criteria	This indicates the criteria cutoff to use for the calculation. A value of 0.01 is fine for most analyses
Time Step Size	This is used to set a fixed pseudo-time step size, and is rarely used.
Display Frequency	As the Scalable Solver runs, it sends results to the CFD user interface at the iteration interval defined by the Display Frequency. This allows you to review results while the simulation is computing in the same manner as with the default solver. Sending results after every iteration is time consuming, so it is a good idea to set a value of 10 for efficient communication between the Scalable Solver and the user interface. If the visual updates occur too quickly, you can reduce the communication by increasing the Display Frequency to 100. This improves the parallel performance as well.

Cluster

To configure the Scalable Solver for use with a cluster, please contact the Sim Squad.

Additional Notes

• Intelligent Solution Control: the Scalable Solver uses a different algorithm than does the Classic Solver, and is always enabled. The Intelligent Solution Control toggle, found in the Solution Controls dialog, does not affect the solution when running the Scalable Solver.
• Automatic Convergence Assessment: the Scalable Solver uses a different algorithm than does the Classic Solver, and is always enabled. The Automatic Convergence Assessment controls, found in Advanced Solution Control dialog, do not affect the solution when running the Scalable Solver. To adjust the convergence, modify the ConvergenceCriteria parameter in the CFD2_default.xml file (located in the C:\ProgramData\Autodesk\CFD 2017 folder).
• Auto Forced Convection is always enabled for steady state heat transfer simulations when the Scalable Solver is in use. The Auto Forced Convection toggle on the Solve dialog does not affect the simulation when running the Scalable Solver.