Conversion Messages After Converting Hydraulic to Isothermal Liquid Models

The hydraulicToIsothermalLiquid conversion tool tries to preserve the block parameter values, where possible. Sometimes seamless automatic conversion is not possible, and you might have to adjust the parameter values manually or consider using a different modeling option. The table lists examples of warning messages in the HTML report, explanations, and recommended actions. The actual messages you get might be slightly different depending on the parameter values in your model.

Message	Cause	Suggested Actions
Add an Isothermal Liquid Properties (IL) block to specify the liquid properties. Default properties in the Isothermal Liquid domain differ from the Hydraulic domain.	The model does not contain a Custom Hydraulic Fluid block or a Hydraulic Fluid block.	For details and suggested actions, see Fluid Properties.
Beginning value of Flow rate removed. Adjustment of model initial conditions may be required.	The Constant Volume Hydraulic Chamber block in the original model lets you specify initialization priority and target for the Volumetric flow rate into chamber variable. The replacement Constant Volume Chamber (IL) block does not expose this variable for initialization. If the variable in the original Hydraulic block had the initialization priority of None, the behavior of the new block is the same and no action is necessary. The conversion tool issues the warning only if the initialization priority is either High or Low.	To see the initialization priority and beginning value for the variable in question, open the dialog box for the original Hydraulic block and look at the Initial Targets section. Use the Variable Viewer to compare the initialization results.
Beginning values of Diameter increase and Flow rate removed. Adjustment of model initial conditions may be required.	The Constant Volume Hydraulic Chamber block in the original model has the Chamber wall type parameter set to Compliant. In this configuration, the block lets you specify initialization priority and targets for the Diameter increase and Volumetric flow rate into chamber variables. The replacement Constant Volume Chamber (IL) block does not expose these variables for initialization. If the variables in the original Hydraulic block had the initialization priority of None, the behavior of the new block is the same and no action is necessary. The conversion tool issues the warning only for variables with initialization priority of either High or Low. If only one of the two variables had its initialization priority set to High or Low, then the message mentions only that variable.	To see the initialization priority and beginning value for the variable in question, open the dialog box for the original Hydraulic block and look at the Initial Targets section. Use the Variable Viewer to compare the initialization results.
Beginning values of Flow rate and Pressure differential removed. Adjustment of model initial conditions may be required.	Several Hydraulic blocks, such as orifices or hydro-mechanical converters, have the Initial Targets section, where you can specify initialization priority and targets for the Flow rate and Pressure differential variables. The equivalent Isothermal Liquid blocks do not expose these variables for initialization. If the variables in the original Hydraulic block had the initialization priority of None, the behavior of the new block is the same and no action is necessary. The conversion tool issues the warning only for variables with initialization priority of either High or Low. If only one of the two variables had its initialization priority set to High or Low, then the message mentions only that variable.	To see the initialization priority and beginning value for the variable in question, open the dialog box for the original Hydraulic block and look at the Initial Targets section. Use the Variable Viewer to compare the initialization results.
Block uses Dead volume of 1e-4 m^3. Adjustment of Dead volume may be required.	The Rotational Hydro-Mechanical Converter or Translational Hydro-Mechanical Converter block in the original model has the Compressibility parameter set to Off. When compressibility is off, hydro-mechanical converters do not account for liquid volume and do not expose the Dead volume parameter. The equivalent Isothermal Liquid converter blocks log liquid volume even when compressibility is off.	The conversion tool sets the Dead volume parameter in the replacement Isothermal Liquid block to the same value as in the original Hydraulic block. (The original Hydraulic block used this parameter only with compressibility on.) The tool also prints the parameter value, for your convenience. Adjust this value, if desired.
Block uses Interface initial displacement of 0 m. Adjustment of Interface initial displacement may be required.	The Translational Hydro-Mechanical Converter block in the original model has the Compressibility parameter set to Off. Hydraulic translational converters expose the Piston initial position parameter only when compressibility is on. The equivalent Isothermal Liquid converter blocks let you specify initial displacement of the interface even when compressibility is off.	The conversion tool sets the Interface initial displacement parameter in the replacement Isothermal Liquid block to the value of the Piston initial position parameter in the original Hydraulic block (even though this parameter was not used with compressibility off.) The tool also prints the parameter value for your convenience. Adjust this value, if desired.
Block uses Interface initial rotation of 0 rad. Adjustment of Interface initial rotation may be required.	The Rotational Hydro-Mechanical Converter block in the original model has the Compressibility parameter set to Off. Hydraulic rotational converters expose the Shaft initial angle parameter only when compressibility is on. The equivalent Isothermal Liquid converter blocks let you specify initial rotation of the interface even when compressibility is off.	The conversion tool sets the Interface initial rotation parameter in the replacement Isothermal Liquid block to the value of the Shaft initial angle parameter in the original Hydraulic block (even though this parameter was not used with compressibility off.) The tool also prints the parameter value for your convenience. Adjust this value, if desired.
Chamber specification set to rigid. To model flexible volume, consider using the Simscape™ Fluids™ Pipe (IL) block.	The Constant Volume Hydraulic Chamber block in the original model has the Chamber wall type parameter set to Compliant. The replacement Constant Volume Chamber (IL) block does not have this option.	If you have a Simscape Fluids license, you can use the Pipe (IL) block from the Fluids > Isothermal Liquid > Pipes & Fittings library as a replacement.
Consider adjusting the initial pressure in a previously connected block.	The Hydraulic Cap block in the original model has been removed.	For details and suggested actions, see Block Substitutions for Foundation Library Hydraulic Blocks.
Consider modeling fluid compressibility with a Translational Mechanical Converter (IL) block.	The Variable Hydraulic Chamber or Hydraulic Piston Chamber block in the original model has been removed.	For details and suggested actions, see Block Substitutions for Foundation Library Hydraulic Blocks.
Consider modeling fluid inertia with a Pipe (IL) block.	The Fluid Inertia block in the original model has been removed.	For details and suggested actions, see Block Substitutions for Foundation Library Hydraulic Blocks.
Critical Reynolds number set to 150.	The block uses the Critical Reynolds number parameter instead of the Laminar pressure ratio parameter to identify the transition between laminar and turbulent flow regimes. The default value of the Critical Reynolds number parameter is 150.	If the flow through the block is in the fully turbulent or fully laminar regime, this change does not influence the model performance. If the block experiences transitional flow during simulation, ensure that the Critical Reynolds number parameter reflects the correct point of flow transition. If the original Hydraulic block used the default Laminar flow pressure ratio parameter value of 0.999, no action is necessary. If the Laminar flow pressure ratio parameter value in the original block was significantly different, you might need to adjust the Critical Reynolds number parameter value in the replacement block.
Maximum restriction area set to 1e10 m^2.	The Variable Area Hydraulic Orifice block does not have a parameter that specifies the maximum area, the block assumes that the maximum area is inf. The replacement Local Restriction (IL) block, with Restriction type set to Variable, requires a Maximum restriction area parameter value less than inf.	The conversion tool sets the Maximum restriction area parameter in the replacement Local Restriction (IL) block to an arbitrary large value, 1e10 m^2. Adjust this value, if desired.
Original block had Specific heat ratio of 1.4. Set Air polytropic index to this value in an Isothermal Liquid Properties (IL) block.	Several Hydraulic blocks, such as chambers or hydro-mechanical converters, have a Specific heat ratio parameter. In the isothermal liquid domain, all of the fluid properties are defined in the Isothermal Liquid Properties (IL) block.	The conversion tool prints the value of the Specific heat ratio parameter in the original block for your convenience. Open the Isothermal Liquid Properties (IL) block connected to the circuit and set its Air polytropic index parameter to this value.

Conversion Messages in Simscape Fluids

When you convert a Simulink Fluids model from the Hydraulics to the Isothermal Liquid library, you may encounter warnings or errors that require manual adjustments to your model. The conversion process generates warnings when parameters in the new blocks do not map one-to-one to the original blocks and the change may affect the model behavior.

Due to the different structures of the two isothermal domains, the parameters of some Isothermal Liquid library blocks are different from the parameters in the equivalent Hydraulics (Isothermal) library blocks. When the Isothermal Liquid library block has different parameters, the conversion report lists the new parameter or new parameter value. The converted model may include recalculated properties based on a shift from gauge to absolute pressure, or changes to a specified value, such as reservoir pressure at a specified fluid density. In this case, the conversion report includes a message that indicates 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 model does not meet your desired conditions, 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, to maintain a specific pressure differential over an orifice connected to a valve, you can adjust the valve mass flow rate conditions assigned to the valve during initialization until the model achieves your desired pressure differential. Use this method when the warning message indicates that the conversion tool removed a beginning or initial value.

Message	Cause	Suggested Actions
Hard-stop model has been reparameterized and uses default parameter values.	In the converted Isothermal Liquid model, the Hard stop model parameter is set to Stiffness and damping applied smoothly through transition region, damped rebound, instead of the original Hydraulics (Isothermal) parameter value. Because this parameter value does not correspond directly to the previous setting, the conversion process set the hard-stop parameters to their default values.	Adjust the Hard stop model, Hard stop stiffness coefficient, Hard stop damping coefficient, and Transition region parameters in the converted block.
20 degC used to evaluate Density, Isothermal bulk modulus, and Kinematic viscosity.	The conversion process replaces the Hydraulic Fluid block with an Isothermal Liquid Properties (IL) block. If the conversion process cannot determine the original system temperature, it evaluates the parameters in the Isothermal Liquid Properties (IL) block at 20°C.	Adjust the Density, Isothermal bulk modulus, and the Kinematic viscosity parameters if your network operates at a different temperature.
System temperature limited to below the fluid flash point or critical point of max temp degC	The Hydraulic Fluid block permitted the system temperature to reach 250 °C, but the Isothermal Liquid Predefined Properties (IL) block only supports system temperatures less than the flash point or the critical point of the liquid, max temp, which may be less than 250 °C for some liquids. The conversion process limits the system temperature to less than max temp. If the Hydraulic Fluid block in your model has the System Temperature (deg C) parameter set to a symbolic expression, the conversion tool always issues this warning, because it does not evaluate the expression.	Inspect the simulation results in the converted model to confirm the model behavior at high temperatures.
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.	You may need to adjust the Expansion correction factor and Contraction correction factor parameters. Refer to the Area Change (IL) (Simscape Fluids) and Sudden Area Change (Simscape Fluids) block pages to compare the 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 changed from 0.75 to 1. Compare the equations for KSC in Sudden Area Change (Simscape Fluids) and KContraction in Area Change (IL) (Simscape Fluids).	You may need to adjust the Contraction correction factor parameter. Refer to the Area Change (IL) (Simscape Fluids) and Sudden Area Change (Simscape Fluids) block pages to compare the changes in the equations.
Warning for minimum fluid level converted to Warning for liquid level below inlet height.	The block issues 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 parameter to generate a warning at a different fluid level.
Interpolation or Extrapolation method changed to Linear.	Interpolation and extrapolation methods are no longer user-defined parameters. Interpolation and extrapolation are linear.	If you want to use the nearest method for interpolation or extrapolation, manually enter a vector element next to the nearest element. If you want to use 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 original block used a lookup table to calculate the loss coefficient parameterization due to an area change. The converted block uses separate vectors for contraction or expansion, which apply based on the direction of flow.	Ensure that the elements in the Reynolds number vector parameter 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 original blocks used the user-specified parameters Transition slot angle and Transition slot maximum area. The converted block does not have these parameters, and instead applies a smoothing function automatically.	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 a block uses tabulated data, the Isothermal Liquid block mirrors the vector elements for negative pressure differential (pressure gain) if no negative elements are provided.	If you want to specify the relationship in this region, extend the pressure drop vector and associated volumetric flow rate table manually.
Opening time constant is applied to control pressure instead of valve area.	In the Isothermal Liquid library, valves and orifices that can model dynamics apply dynamic modelling to the valve pressure. In the Hydraulics (Isothermal) library, the blocks apply dynamic modelling to the valve area.	Adjust the Opening time constant parameter to match your desired opening response.
Valve opening adjustment coefficient for smoothing removed.	The Pressure Reducing 3-Way Valve block incorporates smoothing at the extremes of the 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 using a lookup.
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 the Port Y pilot area parameters according to the force balance on Cartridge Valve Actuator (IL) (Simscape Fluids) and Hydraulic 4-Port Cartridge Valve Actuator (Simscape Fluids) if any difference in the poppet force is observed.
Converted subsystem assumes input and output signals have units of 1.	The Proportional and Servo-Valve Actuator block does not have an equivalent Isothermal Liquid library block. The conversion process replaces the block with 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.	The 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 1e-3 MPa, 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 power_threshold W.	The 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.