Engee documentation

Rod

Axially flexible rod or cable.

blockType: Engee1DMechanical.Elements.Translational.Rod

rod

Path in the library:

/Physical Modeling/1D Mechanical/Couplings & Drives/Rod

Description

Block Rod It is an axially flexible rod or cable that stretches or contracts.

rod 1 en

rod 2 en

Model

To represent a rod or cable, the block uses a model with concentrated parameters. The model consists of concentrated masses connected in series by means of sets of parallel connected spring and damper circuits. The spring represents elasticity. A damper represents damping in a material.

rod 3

The model with one flexible element has a natural frequency close to the first natural frequency of the model with distributed parameters. For a more accurate analysis, select 2, 4, 8 or more flexible elements.

An equivalent physical network contains spring and damper circuits and blocks of masses. The total mass of the rod is evenly distributed over the mass blocks. The stiffness of the spring in each spring and damper chain is equal to the stiffness of the rod material multiplied by . rod

The equations

Defining equations for the model:







where

  • — rod damping;

  • — the damping coefficient of the rod material;

  • — stiffness of the rod;

  • — the cross-sectional area of the rod;

  • — the outer diameter of the rod;

  • — the inner diameter of the rod, where

    • for a solid rod,

    • for an annular, i.e. hollow, rod;

  • — Young’s modulus, that is, the modulus of elasticity of the rod material;

  • — the length of the rod;

  • — the mass of the rod;

  • — the density of the rod material.

Assumptions and limitations

  • When stretched, the block does not bend (in the case of a rod) and does not sag (in the case of a cable).

  • The rod has a constant cross-section along its entire length.

  • A model with distributed parameters is approximated by a finite number of flexible elements. .

Ports

Conserving

# B — drive shaft
Translational mechanics

Details

A non-directional port connected to the drive shaft or rod inlet.

Program usage name

base_flange

# F — driven shaft
Translational mechanics

Details

A non-directional port connected to a driven shaft or rod outlet.

Program usage name

follower_flange

Parameters

Rod

# Parameterization — parameterization method
By stiffness and inertia | By material and geometry

Details

The parameterization method.

Values

By stiffness and inertia | By material and geometry
Default value

By stiffness and inertia
Program usage name

parameterization
Evaluatable

Yes

# Stiffness — stiffness of the material
N/m | lbf/ft | lbf/in

Details

The rigidity of the material.

Dependencies

To use this parameter, set for the parameter Parameterization meaning By stiffness and inertia.

Units

N/m | lbf/ft | lbf/in
Default value

5.0e8 N/m
Program usage name

k
Evaluatable

Yes

# Mass — rod weight
g | t | kg | mg | oz | lbm | slug

Details

The mass of the rod.

Dependencies

To use this parameter, set for the parameter Parameterization meaning By stiffness and inertia.

Units

g | t | kg | mg | oz | lbm | slug
Default value

20.0 kg
Program usage name

m
Evaluatable

Yes

# Damping ratio — material damping coefficient

Details

The damping coefficient of the material.

Default value

0.01
Program usage name

material_damping_ratio
Evaluatable

Yes

# Number of flexible elements —

Details

Number of flexible elements for an approximation.

More flexible elements increases the accuracy of the model, but reduces the simulation performance, i.e. the simulation speed. Single-element model ( ) demonstrates a natural frequency close to the first natural frequency of a continuous model with distributed parameters.

If accuracy is more important than performance, choose 2, 4, 8 or more flexible elements. For example, the four lowest natural frequencies are represented with precision 0.1, 1.9, 1.6 and 5.3%, respectively, in the 16-element model.

Default value

1
Program usage name

segment_count
Evaluatable

Yes

# Geometry — cross section of the rod
Solid | Annular

Details

The shape of the cross-section of the rod.

Dependencies

To use this parameter, set for the parameter Parameterization meaning By material and geometry.

Values

Solid | Annular
Default value

Solid
Program usage name

geometry
Evaluatable

Yes

# Length — rod length
m | cm | ft | in | km | mi | mm | um | yd

Details

The length of the rod.

Dependencies

To use this parameter, set for the parameter Parameterization meaning By material and geometry.

Units

m | cm | ft | in | km | mi | mm | um | yd
Default value

1.0 m
Program usage name

rod_length
Evaluatable

Yes

# Outer diameter — the outer diameter of the rod
m | cm | ft | in | km | mi | mm | um | yd

Details

The outer diameter of the rod.

Dependencies

To use this parameter, set for the parameter Parameterization meaning By material and geometry.

Units

m | cm | ft | in | km | mi | mm | um | yd
Default value

0.075 m
Program usage name

outer_diameter
Evaluatable

Yes

# Density — material density
g/cm^3 | kg/m^3 | lbm/gal

Details

The density of the material.

Dependencies

To use this parameter, set for the parameter Parameterization meaning By material and geometry.

Units

g/cm^3 | kg/m^3 | lbm/gal
Default value

7800.0 kg/m^3
Program usage name

rho
Evaluatable

Yes

# Young's modulus — Young’s module
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

Young’s modulus for the rod material.

Dependencies

To use this parameter, set for the parameter Parameterization meaning By material and geometry.

Units

Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Default value

2.0e11 Pa
Program usage name

E
Evaluatable

Yes

# Inner diameter — inner diameter of the rod
m | cm | ft | in | km | mi | mm | um | yd

Details

The inner diameter of the rod. If the rod is solid, specify the value `0'.

Dependencies

To use this parameter, set for the parameter Parameterization meaning By material and geometry, and for the parameter Geometry meaning Annular.

Units

m | cm | ft | in | km | mi | mm | um | yd
Default value

0.05 m
Program usage name

inner_diameter
Evaluatable

Yes

Viscous Losses

# Viscous friction coefficients at base (B) and follower (F) — coefficients of viscous friction
kg/s | N*s/m | N/(m/s) | lbf/(ft/s) | lbf/(in/s)

Details

Coefficients of viscous friction in ports B and F.

Units

kg/s | N*s/m | N/(m/s) | lbf/(ft/s) | lbf/(in/s)
Default value

[0.0, 0.0] N/(m/s)
Program usage name

viscous_coefficient
Evaluatable

Yes

Initial Conditions

# Initial deflection — initial deviation
m | cm | ft | in | km | mi | mm | um | yd

Details

Rod deflection at the beginning of the simulation.

A positive initial deviation leads to a positive displacement of the end of the rod with port B relative to the end of the rod with port F.

Units

m | cm | ft | in | km | mi | mm | um | yd
Default value

0.0 m
Program usage name

delta_p_start
Evaluatable

Yes

# Initial velocity — initial velocity
fpm | fps | kph | mph | m/s | cm/s | ft/s | in/s | km/s | mi/s | mm/s

Details

The longitudinal velocity of the end of the rod with port B relative to the end of the rod with port F at the beginning of the simulation.

Units

fpm | fps | kph | mph | m/s | cm/s | ft/s | in/s | km/s | mi/s | mm/s
Default value

0.0 m/s
Program usage name

v_start
Evaluatable

Yes