Is your RISA-3D software solution running slower than you expected? There are a few things you can do during your model set up in order to make your model more efficient and reduce the solution time. RISA has compiled a list of our most common tips for solving a slow solution in RISA-3D.
1. Is your Analysis Mesh too Small?
RISA software uses a finite element analysis mesh to analyze and solve the structural model. Therefore, RISA-3D creates software generated plates when submeshing elements (such as diaphragms and walls). By default, the FEA mesh size is set to 24 inches. RISA users have the ability to reduce the mesh size. However, reducing the FEA mesh size causes the program to generate a much finer mesh which takes a longer time to solve.
If your model solution is very slow, we suggest reviewing these FEA mesh size settings. You may need to increase this mesh size. This mesh setting is found in your Model Settings, then open the Solution tab.
Please Note: Increasing mesh size can help improve run time, but can also reduce results accuracy, so modify with a balanced approach.
What about Semi-Rigid Diaphragms? In an integrated RISAFloor/RISA-3D model, semi-rigid diaphragms can significantly increase run time due to the need for submeshing and analysis during solution. To manage this, an additional setting for "Semi-Rigid Diaphragm Mesh" can be found under Model Settings on the RISA-3D side. While adjusting mesh size may help, a finer mesh is often required in areas connecting to other elements, like columns, beams, and walls.
Reducing mesh density only goes so far in improving solution time, as the diaphragm still needs to interface with these other elements. Consider using Flexible or Rigid diaphragm types, which offer faster solution times. However, choosing the appropriate diaphragm type should be based on engineering judgment to ensure it meets the project’s design requirements.
Review RISA-3D's mesh results: You can display the mesh from the Reviews View Settings window, see screenshots below for how to do this for wall panels and diaphragms. This will give you a better sense of how the analysis is performed and the pros/cons of a larger/smaller submesh.
2. Do you have a Large Number of Plate Elements?
RISA-3D has the capability of modeling plate elements. Having a large number of user and software generated plates can slow down the solution speed of your model. When drawing your plates in RISA-3D, you may have used the Submesh Plates tool to submesh larger plates into much smaller plates. This is an easy and quick tool to create potentially hundreds of plates. However, this large number of plates makes the model large for rendering and large for FEA meshing during solving. If your model is solving very slowly, you may want to consider using a larger plate size for your user drawn plates.
3. Do you have a Large Number of Unused Nodes?
How does this happen? Unused nodes can be lingering from previously deleted elements or perhaps maybe even accidentally drawn from the Node Spreadsheet. They may be tightly packed or close to other used nodes. In that case, you may not be able to graphically see them with just your eye.
When your RISA-3D model has a large number of unused nodes, this can cause a long solution time while the program is trying to generate the analysis mesh. In order for the mesher not to get overloaded with these unused nodes, it is important to remove these unused nodes in the model. In RISA-3D, you can use the tool Delete Unattached Node under Modify.
4. Do you need to adjust wall panels' Max Number of Iterations for solution?
In RISA-3D, adjusting the "Max Number of Iterations" for Wall Panels can significantly impact solution speed and load distribution, especially when dealing with multiple wood shear walls. Wood Wall Panels require multiple iterations for each load combination to achieve accurate stiffness and load distribution results. Reducing the iteration count can reduce run-time but requires additional engineering discretion. However, engineers should carefully review the design and make manual adjustments as needed to maintain reliability and accuracy.
5. Is your P-Delta Analysis slow to converge?
If P-Delta iterations are taking a long time, it may indicate that the model is slow to converge. Temporarily disabling P-Delta and observing a faster run time can suggest the model is nearing instability. In such cases, focusing on stiffening the lateral system can help improve solution speed.
Another useful test is to temporarily increase load factors by 10-50% to check for P-Delta divergence. If a small load increase causes divergence, this further indicates that stiffening the lateral system may reduce run-time and improve model stability.
6. Do you need more Processing Power?
Sometimes you have a very large model file size that cannot be reduced. You cannot reduce the number of plates. There are no unused nodes to delete, etc. In RISA-3D you can increase the utilization of your computer’s processing cores. In your Model Settings, choose the Solution tab. Then you can choose Max under Processor Core Utilization.
Please Note: The Max option will use all of the available cores on your computer minus one. This will take processing power and speed away from other programs running on your computer. For instance, if you have 8 available cores and select the Maximum option the program will use 7 cores in the processing of the solution. This option will provide the fastest solution time but will only apportion a single core to be used for other programs and computer processes.
Need More: Consider your computer's hardware, a higher-performance processor with more cores can improve solution speed by handling multiple load combinations simultaneously.