Hydraulic Pipe LP
Hydraulic pipeline with resistive, fluid compressibility, and elevation properties
The Hydraulic Pipe LP block models hydraulic pipelines with circular and noncircular cross sections. The block accounts for friction loss along the pipe length and for fluid compressibility. The block does not account for fluid inertia and cannot be used for predicting effects like water hammer or changes in pressure caused by fluid acceleration.
The model is a structural model and its schematic diagram is shown below.
The Resistive Pipe LP blocks account for friction losses, while the Constant Volume Hydraulic Chamber block accounts for fluid compressibility. To reduce model complexity, you can use this block to simulate not only a pipe itself, but also a combination of pipes and local resistances such as bends, fittings, inlet and outlet losses, associated with the pipe. You must convert the resistances into their equivalent lengths, and then sum up all the resistances to obtain their aggregate length. Then add this length to the pipe geometrical length. By using the block parameters, you can set the model to simulate pipeline with rigid or flexible walls, including simulation of hydraulic hoses with elastic and viscoelastic properties.
The difference in elevation between ports A and B is distributed evenly between pipe segments.
The block positive direction is from port A to port B. This means that the flow rate is positive if it flows from A to B, and the pressure loss is determined as .
Basic Assumptions and Limitations
Flow is assumed to be fully developed along the pipe length.
Fluid inertia is not taken into account.
Basic Parameters Tab
- Pipe cross section type
The type of pipe cross section:
Noncircular. For a circular pipe, you specify its internal diameter. For a noncircular pipe, you specify its hydraulic diameter and pipe cross-sectional area. The default value of the parameter is
- Pipe internal diameter
Pipe internal diameter. The parameter is used if Pipe cross section type is set to
Circular. The default value is
- Noncircular pipe cross-sectional area
Pipe cross-sectional area. The parameter is used if Pipe cross section type is set to
Noncircular. The default value is
- Noncircular pipe hydraulic diameter
Hydraulic diameter of the pipe cross section. The parameter is used if Pipe cross section type is set to
Noncircular. The default value is
- Geometrical shape factor
Used for computing friction factor at laminar flow. The shape of the pipe cross section determines the value. For a pipe with a noncircular cross section, set the factor to an appropriate value, for example, 56 for a square, 96 for concentric annulus, 62 for rectangle (2:1), and so on. The default value is
64, which corresponds to a pipe with a circular cross section.
- Pipe length
Pipe geometrical length. The default value is
- Aggregate equivalent length of local resistances
This parameter represents total equivalent length of all local resistances associated with the pipe. You can account for the pressure loss caused by local resistances, such as bends, fittings, armature, inlet/outlet losses, and so on, by adding to the pipe geometrical length an aggregate equivalent length of all the local resistances. This length is added to the geometrical pipe length only for hydraulic resistance computation. The fluid volume depends on pipe geometrical length only. The default value is
- Internal surface roughness height
Roughness height on the pipe internal surface. The parameter is typically provided in data sheets or manufacturer’s catalogs. The default value is
15e-6m, which corresponds to drawn tubing.
- Laminar flow upper Reynolds number
Specifies the Reynolds number at which the laminar flow regime is assumed to start converting into turbulent. Mathematically, this is the maximum Reynolds number at fully developed laminar flow. The default value is
- Turbulent flow lower Reynolds number
Specifies the Reynolds number at which the turbulent flow regime is assumed to be fully developed. Mathematically, this is the minimum Reynolds number at turbulent flow. The default value is
- Initial pressure
Gauge pressure in the pipe at time zero. The default value is
Wall Compliance Tab
- Pipe wall type
The parameter is available only for circular pipes and can have one of two values:
Flexible. If the parameter is set to
Rigid, wall compliance is not taken into account, which can improve computational efficiency. The value
Flexibleis recommended for hoses and metal pipes where wall compliance can affect the system behavior. The default value is
- Static pressure-diameter coefficient
Coefficient that establishes relationship between the pressure and the internal diameter at steady-state conditions. This coefficient can be determined analytically for cylindrical metal pipes or experimentally for hoses. The parameter is used if the Pipe wall type parameter is set to
Flexible. The default value is
- Viscoelastic process time constant
Time constant in the transfer function that relates pipe internal diameter to pressure variations. By using this parameter, the simulated elastic or viscoelastic process is approximated with the first-order lag. The value is determined experimentally or provided by the manufacturer. The parameter is used if the Pipe wall type parameter is set to
Flexible. The default value is
- Specific heat ratio
Gas-specific heat ratio for the Constant Volume Hydraulic Chamber block. The default value is
1.4. If Pipe cross section type is set to
Noncircular, then this is the only parameter on the Wall Compliance tab.
Vertical Position Tab
- Port A elevation from reference plane
Vertical position of port A with respect to a reference plane. The reference plane is assumed to be the same as that used in the Port B elevation from reference plane parameter. The default value is
- Port B elevation from reference plane
Vertical position of port B with respect to a reference plane. The reference plane is assumed to be the same as that used in the Port A elevation from reference plane parameter. The default value is
- Gravitational acceleration
Value of the gravitational acceleration constant (g). The block uses this value to compute the pressure differential between the ports due to a change in elevation. The default value is
When your model is in Restricted editing mode, you cannot modify the following parameters:
Pipe cross section type
Pipe wall type
All other block parameters are available for modification. The actual set of modifiable block parameters depends on the values of the Pipe cross section type and Pipe wall type parameters at the time the model entered Restricted mode.
Parameters determined by the type of working fluid:
Fluid kinematic viscosity
The block has the following ports:
Hydraulic conserving port associated with the pipe inlet.
Hydraulic conserving port associated with the pipe outlet.
 White, F.M., Viscous Fluid Flow, McGraw-Hill, 1991
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
Introduced in R2009a
Hydraulic Pipeline | Hydraulic Pipe LP with Variable Elevation | Linear Hydraulic Resistance | Resistive Pipe LP | Resistive Pipe LP with Variable Elevation | Hydraulic Resistive Tube | Segmented Pipeline | Segmented Pipe LP