## Upgrading Simscape Fluids Models Containing Hydraulics (Isothermal) Blocks

The Isothermal Liquid library, which was introduced in R2020a, models mass-flow-rate-based components. This library introduces updates to existing Hydraulics (Isothermal) library blocks, combines similar Hydraulics (Isothermal) library blocks into single blocks, and better aligns with the Thermal Liquid library, which is mass-flow-rate-based.

All blocks in the Isothermal Liquid library account for density as a function of pressure, and pipe and actuator blocks account for compressibility by default. You should expect some differences between a model that uses Hydraulics (Isothermal) library blocks and a converted model when compressibility effects play a significant role due to the treatment of conservation equations in the volumetric-flow-rate-based and mass-flow-rate-based libraries. An example of this is provided in Conversion When Fluid Dynamic Compressibility is Modeled.

Multiple models can be converted at the same time. For information on the conversion tool, see `hydraulicToIsothermalLiquid`. For information on upgrading models with blocks from the Simscape™ Foundation Library, see Upgrading Hydraulic Models To Use Isothermal Liquid Blocks.

### Special Pre-Conversion Considerations

#### Physical Signal Blocks

During the conversion process, some blocks in the Hydraulics (Isothermal) library are converted into subsystems that contain physical signal blocks. Physical Signal blocks inserted during conversion do not have the option to assign units of `1`, meaning that the block inherits the units of the incoming signal, as is the case for legacy Physical Signal blocks. If there are physical signal blocks providing input to newly-inserted Physical Signal blocks in your model, a compilation error may occur. To avoid an error, you can change the units from `1` to an appropriate unit in existing physical signal blocks. To propagate units through physical signal blocks, you can check and upgrade your model before conversion with the Upgrade Advisor. See Upgrading Models with Legacy Physical Signal Blocks for more information.

#### Derived Parameters

A derived parameter is a new Isothermal liquid block parameter that is constructed from a Hydraulics (Isothermal) block setting, such as area computed from a user-defined diameter. Parameter conversion may depend on the active Hydraulics (Isothermal) block setting during conversion. If the Isothermal Liquid block setting is changed after conversion, a derived parameter may be inaccurate. This is typically true when converting orifice and valve blocks into their Isothermal Liquid equivalents.

If you change a parameter after the block has been converted, you can check that it has been appropriately updated by running the conversion tool on the Hydraulics (Isothermal) block or model with the new setting and comparing the performance of the two blocks.

For example, in the 2-Way, 3-Way, and 4-Way Directional Valve blocks, switching the setting for Model parameterization after conversion may result in different derivations of the spool position at maximum orifice area parameter.

When you change the Model parameterization setting to or from `By maximum area and opening` after converting a block, the expression for spool position is not updated. This is due to the fact that, during conversion, maximum opening is translated into a spool position at maximum opening. In the `By maximum area and opening` parameterization, it is adjusted by the maximum opening value, and in the `Area vs. opening table` parameterization, it is adjusted by the final element of the valve opening vector.

To correct this, manually adjust the expression for spool position at maximum opening if the parameterization changes after conversion, or change the setting in the Isothermal (Hydraulics) library block and run the conversion tool on the block.

#### Element Order When Using Tabulated Area or Volumetric Flow Rate Parameterizations

In Hydraulics (Isothermal) blocks where parameterization by area-opening or pressure-flow rate is an option,vector elements can be in any order. However, the vector elements in Isothermal Liquid blocks must be entered in a specific order.

When an Isothermal Liquid block is parameterized by opening, such as when the Orifice (IL) block Orifice parameterization is set to ```Tabulated data - Area vs. control member position```, the Orifice area vector elements must be increasing. This parameterization corresponds to the Hydraulics (Isothermal) block setting ```By area vs. opening table```.

When an Isothermal Liquid block is parameterized by pressure, such as when the Orifice (IL) block Orifice parameterization is set to ```Tabulated data - Volumetric flow rate vs. control member position and pressure drop```, the Volumetric flow rate table must have increasing rows and increasing or decreasing columns. This parameterization corresponds to the Hydraulics (Isothermal) block setting ```By pressure-flow characteristic```.

If the vector elements are not ordered according to the Isothermal Liquid block requirements, you will receive a warning message like the following:

In the Isothermal Liquid library, Orifice area vector must contain monotonically ascending or descending values. Adjustment of Control member position vector and Orifice area vector may be required.

If a parameter in your Hydraulics (Isothermal) blocks contain comments, the conversion tool may remove % symbols and any comment content. This happens when a parameter is used in a derived parameter. Comments can be manually added again to a converted block parameter.

#### Pump and Motor Blocks

Density and kinematic viscosity, which are specified as parameters in the Hydraulics (Isothermal) Fixed-Displacement Motor, Fixed-Displacement Pump, Variable-Displacement Motor, Variable-Displacement Pump, Centrifugal Pump, and Variable-Displacement Pressure-Compensated Pump blocks, are removed as parameters in the associated Isothermal Liquid library blocks. These blocks instead use the network fluid properties. You may need to adjust parameters in the network fluid properties block or adjust the Isothermal Liquid block Volumetric efficiency at nominal conditions in order to match the functionality of your Hydraulics (Isothermal) block.

#### Custom Blocks

The conversion tool will not convert custom blocks with Hydraulics (Isothermal) library ports. These blocks should be connected to converted sections of the model with an Interface (H-IL) block or manually updated.

The examples below show how to run the conversion tool, respond to warning messages, and compare and check converted models with the Simulation Data Inspector.

#### Automatic Conversion

This example uses the Diesel Engine In-Line Injection System model, which you can open by executing `sh_diesel_injection` on the MATLAB command line.

Ensure that logging is enabled by clicking on the signal line connected to a Scope and clicking Log Signals on the Simulation tab.

1. Save the model as `sh_diesel_injection_hydro.slx` to a location where you have write permissions.

2. Set the MATLAB Current Folder to this location. The converted model and the conversion report will also be saved here.

3. Run `sh_diesel_injection_hydro.slx`.

4. On the Simulation tab, click Data Inspector.

5. To see one of the logged flow rates, expand Mux:1 and check Mux:1(1). This shows the outlet flow rate in the Injector 1 subsystem.

6. At the command prompt, enter `hydraulicToIsothermalLiquid('sh_diesel_injection_hydro')`.

7. The conversion report, `sh_diesel_injection_hydro_converted.html`, opens when the model conversion is complete. There are three types of warning messages:

• Predefined fluid has been reparameterized. Behavior change not expected at most temperatures.

This message indicates that the fluid in the Fuel Properties block in `sh_diesel_injection_hydro` has been redefined for the Isothermal Liquid library, but no specific parameter requires user input.

• Critical Reynolds number set to 150. Behavior change not expected.

The parameter that indicates flow regime is updated to the Critical Reynolds number. The parameter has a default value of 150. You will not need to adjust anything in the converted model.

• Original block had Specific heat ratio of 1.4 Set Air polytopic index to this value in an Isothermal Liquid Properties (IL) block or Isothermal Liquid Predefined Properties (IL) block.

In the Fuel Properties block of the converted model, in the Entrained Air tab, set Air polytropic index to `1.4`.

8. Run `sh_diesel_injection_hydro_converted`.

9. Open the Simulation Data Inspector and select Compare at the top of the left-hand pane. Set the Baseline data set to `sh_diesel_injection_hydro`. Set Compare to to `sh_diesel_injection_hydro_converted`.

10. Set Global Abs Tolerance to `1e-5`. Set Global Time Tolerance to `1e-4`.

11. Click Compare. The four green check marks next to the four Mux signals show that the results of the models agree within the specified tolerances.

#### Conversion With Some Manual Adjustments

This example uses a modified dual counterbalance valve model, which you can open by entering `sh_HtoIL_dual_counterbalance_start` at the MATLAB command line.

Data logging for the pump angular velocity and cylinder position is already enabled in the model.

1. Save the model as `sh_cyl_dual_counterbalance_hydro_start` to a location where you have write permissions.

2. Set the MATLAB Current Folder to this location. The converted model and the conversion report will be saved here.

3. Run the model.

4. At the command line, enter `hydraulicToIsothermalLiquid('sh_HtoIL_dual_counterbalance_hydro_start')`.

5. Run the converted model.

6. You will receive the following error: ```Invalid use of -. At least one of the operands must be scalar or the operands must be the same size. The units of the operands must be commensurate```. Click the link to the left of this error to see the block in question.

Go to the Pipe A level of the model to see the PS Subtract inputs.

Notice that the PS Constant blocks attached to the PS Subtract block have different units: the signal from el_B has units of `1`, while the signal from el_A has units of `m`. Change the units of B Elevation to `m` and click OK.

7. Run the converted model.

8. In the Simulation tab, click Data Inspector to compare the pump angular velocity and cylinder position between the two models with the Simulation Data Inspector.

Select Compare at the top of the left-hand pane. Set the Baseline data set to `sh_HtoIL_dual_counterbalance_hydro_start`. Set Compare to to `sh_HtoIL_dual_counterbalance_hydro_start_converted`.

9. Set Global Abs Tolerance to `1e-5`. Set Global Time Tolerance to `1e-4`.

10. Click Compare. Notice that the signals do not agree.

11. Check the conversion report, `sh_HtoIL_dual_counterbalance_hydro_start_converted.html`. The report includes additional warnings from Automatic Conversion:

• B-T Orifice reparameterized.

The directional valves in the Isothermal Liquid library that open in the neutral spool position are reparameterized from two orifices in series to one orifice between ports. This results in a modification to the orifice area when approaching the orifice maximum area, as shown below. No modification is required for this model.

Note that this is true for converted orifices in the 4-Way 3-Position Directional Valve (IL) that open in the neutral spool position. The P-B Orifice, which opens only in the positive and negative spool positions, is not influenced by this modification.

• Beginning value of Flow rate removed. Adjustment of model initial conditions may be required.

This message indicates that setting the priority and target value of the related block is not an option in the converted model. You can ensure the converted model performs as the original model by setting the priority and target of a variable in an adjacent block.

• In `sh_HtoIL_dual_counterbalance_hydro_start`, check the initial conditions of Fixed Orifice A. In the block dialog, in the Variables tab, the flow rate is set to ```0 m^3/s``` with Priority set to `High`.

• In `sh_HtoIL_dual_counterbalance_hydro_start_converted`, check the initial conditions of Fixed Orifice A. In the Variable Viewer, the mass flow rate is initialized to a nonzero value.

• The initial conditions can be set in the Constant Volume Hydraulic Chamber block, which is located in the Pipe A subsystem, in the block dialog Variables tab. Setting the target and priority of this variable to match the original model should resolve the different starting flow rates in the Fixed Orifice A.

• In `sh_HtoIL_dual_counterbalance_hydro_start`, open the Variable Viewer. The Constant Volume Hydraulic Chamber initialized value is `17010.8 Pa`.

• Set this target in the converted model with high priority. In the Pipe A subsystem of `sh_HtoIL_dual_counterbalance_hydro_start_converted`, in the Constant Volume Hydraulic Chamber dialog on the Variables tab, set Pressure of liquid volume Priority to `High` and Beginning value to ```17010.8 + 101325``` Pa.

• Pressure losses due to kinetic energy change added. Adjustment of Expansion correction factor and Contraction correction factor may be required.

If the area change is large, meaning that the pressure change due to the second term and power adjustment are within your model's tolerance, no adjustment is necessary. If the contraction is small, then you can tune the model by adjusting the smaller or both of the port areas. In the Hydraulics (Isothermal) block, the pressure loss is modeled as:

`$\Delta p\approx \frac{{K}_{PC}{\stackrel{˙}{m}}^{2}}{4\rho {A}_{small}^{2}}{\left(1-\frac{{A}_{small}}{{A}_{large}}\right)}^{0.75};$`

in the Isothermal Liquid block, the pressure loss is modeled as:

`$\Delta p\approx \frac{{K}_{contraction}{\stackrel{˙}{m}}^{2}}{4\overline{\rho }{A}_{small}^{2}}\left(1-\frac{{A}_{small}}{{A}_{large}}\right)+\frac{{\stackrel{˙}{m}}^{2}}{2\overline{\rho }{A}_{small}^{2}}\left(1-\frac{{A}_{small}}{{A}_{large}}\right).$`

In this model, no adjustment is required.

• Contraction loss coefficient reformulated. Adjustment of Contraction correction factor may be required.

The same conditions and corrective actions apply to the Contraction correction factor as they do for the Expansion correction factor. In this model, no adjustment is required.

• Only elements greater than or equal to 0 retained in Reynolds number vector. Expansion loss coefficient values mapped to these Reynolds numbers. Adjustment of Reynolds number vector, Contraction loss coefficient vector, and Expansion loss coefficient vector may be required.

The Reynolds number vector in the original Area Change B block has both negative and positive Reynolds numbers, ```[-6000 -4000 -1000 -200 -50 -30 -20 -10 -1 1 20 40 100 500 2000 5000]```, but the converted Area Change B takes only positive Reynolds numbers. To match the original model behavior, you will need to extend the data set to Re = 6000 in the base workspace. The commands in the following message will resolve model discrepancies due to both warnings.

• Interpolation method changed to Linear. Additional elements in the Reynolds number vector, Contraction loss coefficient vector, and Expansion loss coefficient vector may be required.

You can add additional elements to the Reynolds number and loss coefficient vectors in the command line with the `interp1` function.

In the hydraulics model, the workspace variable for the Reynolds number vector parameter is defined as `Re_vec` and the Loss coefficient vector parameter as `loss_coeff_vec`. In the MATLAB command window, enter:

```Re_vec_smooth = -6000:100:6000; loss_coeff_vec_smooth = interp1(Re_vec, loss_coeff_vec, Re_vec_new, 'makima', 'extrap');```
In the Area Change B block dialog, replace `Re_vec` with `Re_vec_smooth` and `loss_coeff_vec` with `loss_coeff_vec_smooth`:

• Set the Reynolds number vector parameter to `Re_vec_smooth(Re_vec_smooth>0)`.

• Set the Contraction loss coefficient vector parameter to ```[ interp1( -fliplr(Re_vec_smooth(Re_vec_smooth<0)), fliplr(loss_coeff_vec_smooth(Re_vec_smooth<0)), Re_vec_smooth(Re_vec_smooth>0), 'linear', loss_coeff_vec_smooth(1))]```.

• Set the Expansion loss coefficient vector parameter to``` loss_coeff_vec_smooth(Re_vec_smooth>0)```.

The data set is linearly extrapolated to Re = 6000 and applies a smooth interpolation method the next time the simulation runs.

• Nominal fluid density and kinematic viscosity removed. Pump uses network fluid properties. Adjustment of Volumetric efficiency at nominal conditions may be required.

In the Hydraulics (Isothermal) library, you can define density and viscosity specifically for the pump or motor block. In the Isothermal Liquid blocks, these parameters are removed and the network properties are used. To modify the functionality of the block due to this change, adjust the Volumetric efficiency at nominal conditions parameter in the Fixed-Displacement Pump (IL) block:

• In the Fixed-Displacement Pump (IL) dialog, set the Volumetric efficiency at nominal conditions parameter to `0.957`, which is determined using the following formula:

`${\eta }_{IL,equiv}=1-\frac{{\nu }_{H,nom}{\rho }_{H,nom}}{{\nu }_{IL}{\rho }_{IL}}\left(1-{\eta }_{H}\right),$`

where:

• νH,nom is the Nominal kinematic viscosity in the Fixed-Displacement Pump block.

• ρH,nom is the Nominal fluid density in the Fixed-Displacement Pump block.

• ηH is the Volumetric efficiency at nominal conditions in the Fixed-Displacement Pump block.

• νIL is the Kinematic viscosity at atmospheric pressure in the Isothermal Liquid Properties (IL) block.

• ρIL is the Density at atmospheric pressure (no entrained air) in the Isothermal Liquid Properties (IL) block.

12. Save and run `sh_HtoIL_dual_counterbalance_hydro_converted`.

13. Compare this model with `sh_HtoIL_dual_counterbalance_end`, which includes all post-conversion updates. Run `sh_HtoIL_dual_counterbalance_end` at the command line and inspect the model signals with the Simulation Data Inspector.

#### Conversion When Fluid Dynamic Compressibility is Modeled

This example uses the orifice model `ssc_HtoIL_orifice`, which you can open by executing on the MATLAB command line.

1. Save the model as `ssc_HtoIL_hydro.mdl` to a location where you have write permissions.

2. Set the MATLAB Current Folder to this location. The converted model and the conversion report will be saved here.

3. Run the model.

4. Enter `hydraulicToIsothermalLiquid('ssc_HtoIL_hydro')`.

5. Run the converted model.

6. Open the Simulation Data Inspector and select Compare at the top of the left-hand pane. Set the Baseline data set to `ssc_HtoIL_hydro`. Set Compare to to `ssc_HtoIL_hydro_converted`.

7. Set the Global Abs Tolerance, Global Rel Tolerance, and Global Time Tolerance parameters to `0.01`.

8. Click Compare.

As the applied pressure increases, the mass flow rates in the Hydraulics (Isothermal) and Isothermal Liquid models diverge.

This is due to the fact that density is constant in the Hydraulics (Isothermal) block and varies as a function of pressure in the Isothermal Liquid block.

Depending on your application, your converted model may require tuning to account for density changes due to changes in pressure or temperature.

### Fixing Post-Conversion Warning Messages

While converting blocks between libraries, you may encounter warnings or errors that will require manual adjustments to your model. Warnings are generated when parameters do not map one-to-one, and only when the model behavior may be affected. Below is a selection of messages you may receive during conversion, and suggested actions for fixing the model.

Due to the different structures of the two isothermal domains, some Isothermal Liquid library blocks are parameterized differently from the equivalent Hydraulics (Isothermal) library blocks. When a parameter has been added, removed, or modified, you receive a notification with the new parameter value or the new means of parameterization. Some properties may be recalculated based on a shift from gauge to absolute pressure, or changes to a specified value, such as reservoir pressure at a specified fluid density. If this is the case, you may receive a message indicating that another parameter may require adjustment. Use the Variable Viewer to ensure your model behaves as expected.

In some cases, you can no longer set the priority for some variable initial conditions. If the desired conditions are not met, adjust the initial conditions of other blocks in your model so that they match the initial values in the original model when initial conditions were prioritized for the original block. For example, if you would like to maintain a specific pressure differential over an orifice that is connected to a valve, adjust the valve mass flow rate conditions assigned to the valve during initialization to achieve the desired pressure differential. Use this method when messages indicate that a beginning or initial value has been removed.

MessageReasonSuggested Actions
Original block had Specific heat ratio of 1.4. Set Air polytropic index to this value in an Isothermal Liquid Properties (IL) block or Isothermal Liquid Predefined Properties (IL) block. The specific heat ratio influences fluid compressibility. For isentropic compression, the polytropic index equals the specific heat ratio.Assign the indicated specific heat ratio in the fluid properties block connected to your network.
Hard-stop model has been reparameterized and uses default parameter values.The Hard stop model used in Hydraulics (Isothermal) library blocks is set to ```Stiffness and damping applied smoothly through transition region, damped rebound``` in the Isothermal Library blocks. Because this does not correspond directly to the former model, the block hard-stop parameters are set to default values.Adjust the Hard stop model, Hard stop stiffness coefficient, Hard stop damping coefficient, and Transition region parameters in the converted block as needed.
20 degC used to evaluate Density, Isothermal bulk modulus, and Kinematic viscosity.The Hydraulic Fluid block is converted to an Isothermal Liquid Properties (IL) block. Parameters in the Isothermal Liquid Properties (IL) block are evaluated at 20°C if the original system temperature cannot be determined.Adjust the Density, Isothermal bulk modulus, and the Kinematic viscosity parameters if your network operates at a different temperature.
The block now models pressure loss due to kinetic energy change. Correction factors have been reformulated to minimize difference in numerical results. Further adjustment of Expansion correction factor and Contraction correction factor may be required.The Gradual Area Change and Sudden Area Change blocks calculate the hydraulic loss coefficient in terms of area change. The Area Change (IL) block calculates the loss coefficient in terms of area change and mass flow rate.Further adjustment of the Expansion correction factor and Contraction correction factor may be required. Refer to the Area Change (IL) and Sudden Area Change block pages to compare changes in the equations.
Power in the contraction loss coefficient has been reformulated from 0.75 to 1. Contraction correction factor has been reformulated to minimize difference in numerical results. Further adjustment of Contraction correction factor may be required.The power of the equation for calculating the loss coefficient for a sudden area contraction is updated from 0.75 to 1. Compare the equations for KSC in Sudden Area Change and KContraction in Area Change (IL).Further adjustment of the Contraction correction factor may be required. Refer to the Area Change (IL) and Sudden Area Change block pages to compare changes in the equations.
Warning for minimum fluid level converted to Warning for liquid level below inlet height.You receive a warning when the fluid level falls below the tank inlet height instead of a minimum fluid level.Adjust the warning setting or the Inlet height to generate a warning at a different fluid level.
Critical Reynolds number set to 150.The block uses the Critical Reynolds number instead of the Laminar pressure ratio to identify the transition between laminar and turbulent flow regimes. The default Critical Reynolds number is 150.If the flow through the block is in the fully turbulent or fully laminar regime, this change will not influence performance. If the block experiences transitional flow during simulation, ensure that the Critical Reynolds number parameter reflects the correct point of flow transition.
Interpolation or Extrapolation method changed to Linear.Interpolation and extrapolation methods are no longer user-defined parameters. Interpolation and extrapolation are linear. If you would like to preserve the 'nearest' method for interpolation or extrapolation, manually enter a vector element next to the 'nearest' element. If you would like to preserve the 'smooth' interpolation method, add additional smoothed elements to the vectors.
Only elements greater than or equal to 0 retained in Reynolds number vector. Expansion loss coefficient values mapped to these Reynolds numbers.The loss coefficient parameterization due to an area change is updated from table look-up to separate vectors for contraction or expansion, which are applied based on the direction of flow.Ensure that the Reynolds number vector elements associated with the loss coefficient vectors are positive, nonzero, and correspond to the desired data limits. Add additional elements to the parameters to capture losses at a specific Reynolds number.
Transition slot angle and Transition slot maximum area removed due to reparameterization of block region smoothing. Significant behavior change not expected.The Transition slot angle and Transition slot maximum area parameters are user-controlled smoothing factors. The Isothermal Liquid library block internally applies a third-order smoothing function.No action required.
If only non-negative values are provided for the Pressure drop vector, then the block internally extends the table to contain negative Pressure differential and Volumetric flow rate values.When the block is parameterized by tabulated data, the vector elements are mirrored for negative pressure differential (pressure gain) if no negative elements are provided. Extend the pressure drop vector and associated volumetric flow rate table manually if you would like to specify the relationship in this region.
Opening time constant is applied to control pressure instead of valve area.In the Isothermal Liquid library, valves and orifices that have the option to model dynamics apply dynamic modelling to the valve pressure. In the Hydraulics (Isothermal) library, dynamic modelling is applied to the valve area.Adjust the Opening time constant parameter to match the desired opening response.
Valve opening adjustment coefficient for smoothing removed.The Pressure Reducing 3-Way Valve incorporates smoothing at the extremes of valve opening and closing for numerical robustness. The Pressure-Reducing 3-Way Valve (IL) does not apply smoothing to opening or closing.You can match the effect of smoothing by adjusting the Opening time constant parameter or adjusting the values in the opening area vectors when parameterizing by look-up table.

Updated actuator response when Initial position is Extended.

Updated actuator response when Initial position is non-neutral.

The Hydraulics (Isothermal) library block maintains its initial position until the position signal turns off, which triggers the piston to return to neutral. In the Isothermal Liquid library block, the initial position begins to return to neutral at the beginning of the simulation and responds dynamically to the position signal.

Adjust the model initial conditions to match the behavior of the Multiposition Valve Actuator block. Use the Variable Viewer to ensure that the model initial conditions are correct.

The area at port B is now calculated as the sum of the area at ports X and Y minus the area at port A. Formerly, it was the difference between the areas at port X and port A.The parameterization of the Hydraulic 4-Port Cartridge Valve Actuator block differs from the Cartridge Valve Actuator (IL) block.Adjust the Port A poppet area, Port A poppet to port X pilot area ratio, and/or the Port Y pilot area parameters according to the force balance on Cartridge Valve Actuator (IL) and Hydraulic 4-Port Cartridge Valve Actuator if any difference in the preload (poppet) force is observed.
Converted subsystem assumes input and output signals have units of 1.There is no equivalent Isothermal Liquid library block to the Proportional and Servo-Valve Actuator block. The block is converted to a subsystem of physical signal blocks that maintain the original block functionality. Convert the subsystem block input and output signal units to `1` if the input and output signals of the Proportional and Servo-Valve Actuator block specify any other units.
New parameters Minimum volumetric efficiency and Minimum mechanical efficiency set to 1e-3. Smaller parameter values may be required to avoid unintended efficiency saturations.New parameters in the Variable-Displacement Motor (IL) block are set to the block defaults.You many need to adjust the block defaults to meet your model requirements.
New parameters Pressure drop threshold for motor-pump transition set to 10 rad/s, Angular velocity threshold for motor-pump transition set to 10 rad/s, and Displacement threshold for motor-pump transition set to 0.1 cm^3/rev. Parameter adjustment may be required to match original Power threshold of <5> W.New parameters in the Variable-Displacement Motor (IL) block are set to the block defaults.You many need to adjust the block defaults to meet your model requirements.

### Block Conversions

Below is a list of Hydraulics (Isothermal) library blocks and their associated Isothermal Liquid library block equivalents. To match the Hydraulics (Isothermal) block configuration, some converted models may include a subsystem with additional Simscape Fluids or Simscape blocks. Some blocks in the Hydraulics (Isothermal) library do not have an equivalent Isothermal Liquid library block. In this case, the functionality is reconstructed from a collection of Simscape and Simscape Fluids blocks.

For more information on conversion between Hydraulics (Isothermal) and Isothermal Liquid blocks in the Simscape Foundation Library, see Upgrading Your Models.

Accumulators: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Gas-Charged Accumulator

Gas-Charged Accumulator (IL)

Hard-stop damping is not modeled in the isothermal liquid block.

Hydraulic Cylinders: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Centrifugal Force in Rotating Cylinder

Rotating Cylinder Force (IL)

The Fluid density parameter is replaced with port X, which senses the network density.

Cylinder Cushion

Cylinder Cushion (IL)

The new block is parameterized in terms of plunger diameter, area, and length. The Hydraulics (Isothermal) block is parameterized in terms of tabulated area and displacement.

The plunger length, or the orifice control member travel, is calculated from the Hydraulics (Isothermal) block as: opening(end) - opening(1).

Cylinder Friction

Cylinder Friction (IL)

The Cylinder Friction (IL) block does not assign beginning values to variables.

Single-Acting Rotary Actuator

Single-Acting Rotary (IL)

The block is converted to a subsystem. If leakage is modeled in the Hydraulics (Isothermal) block, port A connects to port A of a Laminar Leakage (IL) block, which is connected to a Reservoir (IL) block at atmospheric pressure.

Double-Acting Rotary Actuator

Double-Acting Rotary Actuator (IL)

The block is converted to a subsystem. If leakage is modeled in the Hydraulics (Isothermal) block, ports A and B connect in parallel to ports A and B, respectively, of a Laminar Leakage (IL) block.

Single-Acting Hydraulic Cylinder

Single-Acting Actuator (IL)

Single-Acting Hydraulic Cylinder (Simple)

Single-Acting Actuator (IL)

The Hard stop model is set to ```Stiffness and damping applied smoothly through transition region, damped rebound```, with default hard stop parameters.

Double-Acting Hydraulic Cylinder

Double-Acting Actuator (IL)

Double-Acting Hydraulic Cylinder (Simple)

Double-Acting Actuator (IL)

The Hard stop model is set to ```Stiffness and damping applied smoothly through transition region, damped rebound```, with default hard stop parameters.

Utilities: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Hydraulic Fluid

If Hydraulic fluid is set to `Water`, `Water-glycol 60/40`, `Diesel fuel`, or `Jet fuel`, the Hydraulic Fluid block is converted to an Isothermal Liquid Predefined Properties (IL) block.

For all other fluids, the Hydraulic Fluid block is converted to an Isothermal Liquid Properties (IL) block. If the conversion tool cannot assess the fluid temperature definition, the properties are defined for 20°C.

Reservoir

Reservoir (IL), Simscape Foundation Library.

Hydraulic Resistances: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Elbow

Elbow (IL)

Area Change (IL)

The block is converted into a subsystem to maintain the original port orientation.

Local Resistance

Local Resistance (IL)

Pipe Bend

Pipe Bend (IL)

The Initial liquid pressure parameter is converted from gauge to absolute pressure.

The Critical Reynolds number parameter is converted into two internally fixed threshold Reynolds numbers. 2000 indicates a fully laminar flow and 4000 indicates a fully turbulent flow.

Sudden Area Change

Area Change (IL)

T-JunctionThis block is converted to a subsystem with Local Resistance (IL) blocks.

Low Pressure Blocks: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Hydraulic Pipe LP

Resistive Pipe LP

Resistive Pipe LP with Variable Elevation

Segmented Pipe LP

Pipe (IL)

Hydraulic Pipe LP with Variable Elevation

Pipe (IL)

Port EL is exposed for elevation change as a physical signal.

Partially Filled Vertical Pipe LP

Partially Filled Pipe (IL)

The Partially Filled Pipe (IL) block receives a liquid level instead of a liquid volume at its physical signal port. The block divides the original fluid volume by a constant tank cross-section within a subsystem. You will likely need to modify the assumed tank cross-section.

This block is converted to a subsystem of Reservoir (IL), Orifice (IL), PS Integrator, and Flow Rate Sensor blocks.

Tank

Tank (IL)

Orifices: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Annular Orifice

Annular Leakage (IL)

Fixed Orifice

Fixed Orifice With Fluid Inertia

Fixed Orifice Empirical

Variable Orifice

Orifice (IL)

Journal Bearing Pressure-Fed

The block is converted to a subsystem with two Annular Leakage (IL) blocks.

Orifice With Variable Area Round Holes

Orifice With Variable Area Slot

Spool Orifice (IL)

Variable Orifice Between Round Holes

Variable Overlapping Orifice (IL)

Pipes: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Rotating Pipe

Rotating Channel (IL)

Hydraulic Pipeline

Pipe (IL)

Segmented Pipeline

Pipe (IL)

Pumps and Motors: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Angle Sensor

The block is converted to a subsystem containing an Ideal Rotational Motion Sensor.

Centrifugal Pump

Centrifugal Pump (IL)

Fixed-Displacement Motor

Fixed-Displacement Motor (IL)

The Fixed-Displacement Motor (IL) block uses network fluid properties. The Volumetric efficiency at nominal conditions parameter may require adjustment to match the Hydraulics (Isothermal) block functionality.

Fixed-Displacement Pump

Fixed-Displacement Pump (IL)

The Fixed-Displacement Pump (IL) block uses network fluid properties. The Volumetric efficiency at nominal conditions parameter may require adjustment to match the Hydraulics (Isothermal) block functionality.

Jet Pump

Jet Pump (IL)

Porting Plate Variable Orifice

Valve Plate Orifice (IL)

Swash Plate

Swash Plate

Variable-Displacement Motor

Variable Displacement Motor (IL)

The Variable Displacement Motor (IL) block uses network fluid properties. The Volumetric efficiency at nominal conditions may require adjustment to match the Hydraulics (Isothermal) block functionality.

Variable-Displacement Pressure-Compensated Pump

Pressure-Compensated Pump (IL)

The block is converted to a subsystem.

The Pressure-Compensated Pump (IL) block uses network fluid properties. The Volumetric efficiency at nominal conditions may require adjustment to match the Hydraulics (Isothermal) block functionality.

Variable-Displacement Pump

Variable Displacement Pump (IL)

The Variable Displacement Pump (IL) block uses network fluid properties. The Volumetric efficiency at nominal conditions may require adjustment to match the Hydraulics (Isothermal) block functionality.

Directional Valves: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

2-Way Directional Valve

2-Way Directional Valve (IL)

The 2-Way Directional Valve (IL) block is based on the spool position at the maximum orifice area and the maximum spool travel distance, not the initial spool position. Changing the valve parameterization after conversion can lead to inconsistencies. See Derived Parameters.

3-Way Directional Valve

3-Way Directional Valve (IL)

The 3-Way Directional Valve (IL) block is based on the spool position at the maximum orifice area and the maximum spool travel distance, not the initial spool position. Changing the valve parameterization after conversion can lead to inconsistencies. See Derived Parameters.

4-Way Ideal Valve

4-Way 3-Position Directional Valve (IL)

The 4-Way 3-Position Directional Valve (IL) block is based on the spool position at the maximum orifice area and the maximum spool travel distance, not the initial spool position. Changing the valve parameterization after conversion can lead to inconsistencies. See Derived Parameters.

4-Way Directional Valve

4-Way 3-Position Directional Valve (IL)

The 4-Way 3-Position Directional Valve (IL) block is based on the spool position at the maximum orifice area and the maximum spool travel distance, not the initial spool position. Changing the valve parameterization after conversion can lead to inconsistencies. See Derived Parameters.

4-Way Directional Valves A-K

4-Way 3-Position Directional Valve (IL)

The 4-Way 3-Position Directional Valve (IL) block is based on the spool position at the maximum orifice area and the maximum spool travel distance, not the initial spool position. Changing the valve parameterization after conversion can lead to inconsistencies. See Derived Parameters.

Cartridge Valve Insert

Cartridge Valve Insert With Conical Seat

Cartridge Valve Insert (IL)

Check Valve

Check Valve (IL)

When dynamics are enabled, the valve area is impacted in the Hydraulics (Isothermal) library block and the valve pressure in the Isothermal Liquid library block.

Hydraulically Operated Remote control Valve

Pressure Compensator Valve (IL)

Pilot-Operated Check Valve

Pilot-Operated Check Valve (IL)

Shuttle Valve

Shuttle Valve (IL)

Flow Control Valves: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Ball Valve

Poppet Valve (IL)

Counterbalance Valve

Counterbalance Valve (IL)

Flow Divider

The block is converted to a subsystem.

Flow Divider-Combiner

The block is converted to a subsystem.

Gate Valve

Variable Overlapping Orifice (IL)

Needle Valve

Needle Valve (IL)

Poppet Valve

Poppet Valve (IL)

Pressure-Compensated 3-Way Flow Control Valve

Pressure-Compensated 3-Way Flow Control Valve (IL)

Pressure-Compensated Flow Control Valve

Pressure-Compensated Flow Control Valve (IL)

Pressure Control Valves: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Pressure Compensator

Pressure Compensator Valve (IL)

When dynamics are enabled, the valve area is impacted in the Hydraulics (Isothermal) library block and the valve pressure in the Isothermal Liquid library block.

Pressure Reducing Valve

Pressure-Reducing Valve (IL)

When dynamics are enabled, the valve area is impacted in the Hydraulics (Isothermal) library block and the valve pressure in the Isothermal Liquid library block.

Pressure Relief Valve

Pressure Relief Valve (IL)

When dynamics are enabled, the valve area is impacted in the Hydraulics (Isothermal) library block and the valve pressure in the Isothermal Liquid library block.

Pressure Reducing 3-way Valve

Pressure-Reducing 3-Way Valve (IL)

When dynamics are enabled, the valve area is impacted in the Hydraulics (Isothermal) library block and the valve pressure in the Isothermal Liquid library block.

Valve Actuators: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

2-Position Valve Actuator

3-Position Valve Actuator

Multiposition Valve Actuator

Double-Acting Servo Cylinder

Double-Acting Servo Valve Actuator (IL)

The Hard stop model is set to ```Stiffness and damping applied smoothly through transition region, damped rebound```, with default hard stop parameters.

Hydraulic 4-Port Cartridge Valve Actuator

Cartridge Valve Actuator (IL)

The block is converted to a subsystem.

The area at port B is now calculated as the sum of the area at ports X and Y minus the area at port A. Formerly, it was the difference between the areas at port X and port A.

Hydraulic Cartridge Valve Actuator

Cartridge Valve Actuator (IL)

Hydraulic Single-Acting Valve Actuator

Hydraulic Double-Acting Valve Actuator

Pilot Valve Actuator (IL)

Proportional and Servo-Valve Actuator

The block is converted into a susbsytem of physical signal blocks.

Valve Actuator

Proportional Valve Actuator

Valve Forces: Block Substitution

Hydraulics (Isothermal) BlockIsothermal Liquid Block

Spool Orifice Hydraulic Force

Spool Orifice Flow Force (IL)

Valve Hydraulic Force

The block is converted to a subsystem.

Fluid Network Interfaces Library: Block Substitution

Interface (TL-IL)

Interface (TL-IL)

The additional setting ```Thermal Liquid (TL) - Isothermal Liquid (IL)``` is added and selected for the Fluids domain interface parameter.

Note that in R2020a and R2020b, this block is named Interface.

Double-Acting Actuator (H-G)

Double-Acting Actuator (G-IL)

This block is converted to a subsystem.

SimHydraulics Legacy Library: Block Substitution

Variable-Displacement Hydraulic Machine

Variable-Displacement Motor (IL)

This block is converted to a subsystem. The Variable-Displacement Motor (IL) Leakage and friction paramerization is set to ```Input signal - volumetric and mechanical losses```.

Variable-Displacement Hydraulic Machine (External Efficiencies)

Variable-Displacement Motor (IL)

This block is converted to a subsystem. The Variable-Displacement Motor (IL) Leakage and friction paramerization is set to ```Input signal - volumetric and mechanical efficiencies```.