--- title: "Liquid Simulation" canonical: "https://documentation.chaos.com/space/PHX4MAX/124397120/Liquid%20Simulation" format: markdown --- This page provides information on the Simulation rollout for a LiquidSim object. Overview The Simulation rollout contains the main panel for controlling the simulation process. It also displays statistical information like simulation times, and the content of the cache file for the current frame. The content can be grid channels such as Liquid, Velocity, etc., as well as particle groups. You can select which channels to export to the cache files from the Output rollout , while particle groups are created by the Splash and Foam rollouts. Many simulations require a long time to calculate and it's very convenient to let them run during the night. However, you still have to render the result in the morning, and this also consumes a lot of time. In this case, the Phoenix Scripting system can be helpful, since it enables you to execute any action at the end of the simulation, including rendering. You simply need to enable "Use Script" from the Simulation rollout, and open the script text. For more information, see the Nightly Simulation and Rendering section on the Tips and Tricks page. UI Path: ||Select Liquid Simulator object|| > Modify panel > Simulation rollout Actions Expand  – Opens a floating dialog that contains the selected rollout and automatically folds the command panel rollout. Re-Center – Resets the position of the floating rollout. ?  – Opens up the help documents for the Liquid Simulation options. Start , Pause , Stop , Resume | A_StartSim , A_StopSim – Start, pause, and stop the simulation. Once the simulation has been paused, the option to Resume becomes available. Note that you can stop a running simulation using the  Shift+Escape  key combination, or with the  Escape  key, if the option to do so is enabled in the  Phoenix FD Global Preferences . Load & Start  |  A_StartSim   – Loads the data from a single cache as an initial state for the simulation and starts simulating from the  Start Frame  the same way the  Start  action works. The cache can be of the  .aur ,  .vdb , or  .f3d  formats and so can be imported from a 3rd party software into Phoenix. The loaded grid will be resized to fit the grid's dimensions at the  Start Frame . The loaded cache does not need to be a  Backup  frame or to contain velocity at all - the simulator will load any available channels from the cache file and the rest of the simulated channels will be empty as when starting a brand new simulation. If you wish to smoothly continue a simulated sequence from a given frame, please use the  Restore  command instead. Restore  |  A_StartSim  – Continues a simulation from the currently viewed frame on the timeline, or the latest Backup frame containing the full simulation state up to the current timeline frame, which is controlled by the Backup Interval parameter in the Output rollout . This way, a Phoenix simulation that has been stopped previously can be resumed from the point you left off, even after the software has been closed and reopened. The ability to restore a sim is only possible when the full internal state of a Phoenix simulation has been exported. This is controlled by the  Backup Interval  parameter in the Output rollout , which determines how often the full simulation state is backed up. Frames with the full state are called  Backup  frames. When a  Backup  frame is currently viewed, the text "Can Restore From Here" appears in the Cache File Content list. The Restore command finds the latest  Backup  frame up to the current timeline frame, and continues the simulation from there. Note that restoring does not work for cache sequences imported from 3rd party software. Get Tutorials  – Opens the  Tutorials and Examples  page in the web browser. Phoenix Help  – Opens up the help documents for the  Liquid Simulation . Show Phoenix Main Window  - Opens a floating dialog where floating rollouts of Simulators can be docked. The layout of this window gets saved to the .MAX scene files. Simulation Presets...  |  A_LoadRenderPreset  – Displays a dropdown menu to either load or save  .tpr  or  .slog files, which hold settings for this simulation. Parameters Start Frame  |  startframe  – Explicitly sets the Start frame of the Simulation. This can also be a negative number. Only available when  Timeline  (Start Frame) is disabled. Timeline  |  start_from_timeline - When enabled, the Simulation will run from the Timeline Start Frame. Stop Frame  |  stopframe  – Explicitly sets the End frame of the Simulation. This can also be a negative number. Only available when  Timeline  (Stop Frame) is disabled. Timeline  |  stop_from_timeline  - When enabled, the Simulation will run to the end of the Timeline. Render On Each Sim Frame  |  rend_sim_frame  – During simulation, after each new frame is simulated, this option will start a render with your currently assigned production renderer and with the render settings you have dialed in your Render Setup 3ds Max dialog. You need to have set a Render Output File in the 3ds Max Render Settings in advance. Phoenix will automatically append the frame number to the file name. You can use  Render On Each Sim Frame  when you leave a long simulation overnight, so you will have a ready rendered sequence when you come back to check on it, even if the entire simulation did not have time to finish. When doing test iterations on your simulation setup, you can also speed up the simulation by enabling  Cacheless Simulation  from the  Output rollout . An alternative approach to Render On Each Sim Frame is to automatically start a sequence render after the entire simulation has finished by adding a  'max quick render'  command under the  OnSimulationEnd()  callback of the  Use Script  option below.   Use Script  |  script, use_script  – Enables the use of MAXScript during the simulation. Click  Edit...  to open a window with some skeleton code and a short description of the available commands.  For more information, please see the  Phoenix MaxScript page . Threads Limit  |  maxthreads  – Specifies an upper limit for the number of threads used for the simulation. When the value is set to 0, the maximum number of threads (cores) will be used. NUMA Nodes  – If the simulation is executed over a NUMA machine, you can specify which nodes will be used. Phoenix is very sensitive to memory transfer and if all the nodes are used, performance might decrease due to low bandwidth between the different nodes. NUMA stands for  Non-Uniform Memory Access . It can be used to restrict the threads used for simulation based on the physical CPUs available on the system (in a multiprocessor systems). In this way better memory access can be achieved when multiple simulations are run on the same machine. Cache File Content This area displays information on the current simulation. Any data from channels that have been loaded into the simulator are shown. This includes the minimum and maximum ranges for each channel. Check the  Grid Channel Ranges and  Particle Channel Ranges pages for more information. Note that the  Container Dimensions  show the loaded cache size as seen in the scene, in the currently selected units. This size is not multiplied by the  Scene Scale  parameter from the Grid rollout. If you want to see how big the container is as seen by the Phoenix simulator when the Scene Scale parameter is used, check the  X ,  Y ,  Z info in the Grid rollout.