FRM Modelling
1. This is a detailed report of tutorial 9 which involves building a fast running engine model( FRM).
Fast Running Engine Models are dynamic, fully-physical engine models that are designed specifically to run fast. While high-fidelity engine models are commonplace in the engine performance department, they are often too slow running to incorporate into system level models where long transient events may be simulated, or where the simulation model must respond faster than real-time, such as for HiL (Hardware-in-the-Loop) simulations. When simulation speed is of priority, high-fidelity GT-POWER engine models can be simplified into FRMs using a standard conversion process. It is up to the user how far to simplify the model, depending on the accuracy-vs.-runtime requirement.
FRMs are able to achieve such fast run times by two means: (1) increasing the simulation time step size, and (2) decreasing the number of calculations per time step. These two means are often accomplished at the same time by lumping various flow volumes together which will reduce the total number of subvolumes and also allow for a larger time step size by increasing the effective subvolume length (which is responsible for the time step size). In addition to simplifying and combining flow volumes, there are additional solver options that can reduce the number of calculations per time step and, thus, further decrease the run time without changing the time step size.
The model which is converted to a FRM is a 4-cylinder 2.0 liter turbocharged Gasoline Direct Injection (GDI) engine. The turbine wastegate is being dynamically controlled in order to target BMEP. A full-load speed sweep is being simulated, from 5000 RPM down to 1000 RPM. A semi-predictive charge air cooler is included such that the outlet temperature is predicted as a function of inlet gas temperature and mass flow rate, coolant temperature, and charge air cooler effectiveness.
A total of 8 steps were involved in converting this model into a FRM which again involved various sub steps . After converting the model looked like this:
If Real-Time cannot be achieved with an FRM, another method to reduce a detailed model is to build a Mean Value Engine Model. The process to build a Mean Value engine is more complex and time consuming and less physics are included in a mean value engine model, so the FRM is the preferred solution. However, if an FRM cannot meet the run-time requirements (for example, if trying to run a large number of cylinders on a HiL), then a Mean Value engine model may be required.
Various steps involved are:
Step 1: Exhaust Manifold
The FRM Converter should now be at the Model Reduction page, as shown below. It is now time to start simplifying the first subsystem of the model. It is most efficient to start by simplifying the subsystem that is currently restricting the time step. For high-fidelity models, this is almost always the exhaust manifold where the highest gas velocities occur, which in turn restricts the time step.
Step 2 : Exhaust Pipes
For the second step of model simplification, the exhaust pipes downstream of the turbine will be simplified.
Step 3 : Intake Manifold
Name the step \"Intake Manifold\". Select Intake Manifold 1 from the Tagged Subsystems list. Click on \"Simplify for Accuracy\". Click \"Yes\" on the Delete Part dialog; this will be handled later. Collapse the FRM Converter to provide space to work in the model map.
Step 4: Compressor Outlet Pipes
Name the step \"Compressor Outlet Pipes\". Select Boost Pipes 1 from the Tagged Subsystems list. Click on \"Simplify for Accuracy\". Collapse the FRM Converter to provide space to work in the model map.
Step 5: Intake Pipes
Name the step \"Intake Pipes\". Select Intake Pipes 1 from the Tagged Subsystems list. Click on \"Simplify for Accuracy\". Collapse the FRM Converter to provide space to work in the model map. Go into Case Setup and set the value of [DIA_Intake_Pipes_1_Step_5] to 45 mm (this is just an initial guess). Since every subsystem has now been simplified, we will assure that there are no remaining pipes with short discretization lengths. Go to the Data tab in the GT-ISE toolbar and click \"Delete Unused Objects\". Then, in the Model Tree to the left, right-click on the PipeRound template and choose \"Edit Parts in Spreadsheet\". View the Discretization Length column to assure that only [DXI_FRM] and [DXE_FRM] are used. Click \"Return to Map View\". The pipes can be sorted by increasing length clicking on the \"Length\" column.
Step 6: Additional Changes
Name the step \"Additional Changes\". Select Exhaust Manifold 1 from the Tagged Subsystems list. Click on \"Simplify for Speed\".
Step 7: Cylinder Slaving
The final simplification to the model will utilize the Cylinder Slaving capability of the EngCylinder component. Name the new step \"Cylinder Slaving\", then collapse the FRM Converter to provide space to work in the model map. Right-click on any of the EngCylinder parts on the map and choose \"Edit Parent Object\". Go to the \"Advanced\" tab and for \"Cylinder Slaving Option\", select \"slave-RT-full-v2018\", then click OK. Now double-click on Cylinder-01, go to the \"Advanced\" tab, and set the Cylinder-01 override value of \"Cylinder Slaving Option\" to \"master\".
Step 8: Real-Time Solver (optional)
Click \"Next (Begin Next Step)\" in the FRM Converter. Name this new step \"Real-Time Solver\", then collapse the FRM Converter. To run with the real-time solver, the license type of the model must be changed. However, certain templates are not allowed with the real-time solver, and so they must first be removed from the model. In the Main assembly delete the Turbo_Speed-2 monitor part coming off of the turbocharger shaft. Next, right-click on one of the EngCylinder parts and choose \"Edit Parent Object\". Go to the Advanced folder and set \"Evaporation Object\" to \"ign\" and click OK. Next, open the WG_Controller, go to the Convergence folder, and set \"Steady State Error Tolerance\" to \"ign\". Lastly, in the GT-ISE toolbar, go to the Data tab and click the arrow next to \"Delete Unused Objects\" and choose \"Objects and Templates\".
2. Following is the screenshot which i got after following the FRM builder approach:
After i solved , i got the following results :