Using WAVE: Sub-Models: Simple Load

 

Description:

 

The simple load sub-model represents a compliant system with lumped inertias and a single gear ratio.  It is intended to represent a generic load system and could be adapted to represent a generator, propeller, pump, or even a simple vehicle model.  The sub-model consists of four inertias representing an engine, gears, and load inertias.  These inertias are coupled by flexible drive shafts having universal joints at both ends of each shaft.  The gear inertias are directly coupled.

 

Each compliant shaft has a stiffness and damping rate associated with it.  These compliances allow the simulation to capture some of the important torsional vibrations present.  The universal joints are capable of providing additional torsional excitations when operated through a nonzero angle.  For rigid shafts, the universal joint angles are zero.

 

The model also allows damping between the engine and ground, gearbox and ground, and load and ground.  These represent external load torques on the system caused by bearing and windage losses.

 

The externally supplied torques acting on the drive line are the engine torque and load torque.  The engine torque will be supplied by the WAVE calculation, which depends upon the instantaneous engine speed and fuel rate.  Engine friction losses are also accounted for, using either the Chen-Flynn or IRIS friction sub-model.  The load torque is determined from user inputs.  Three possible specifications of load torque are allowed:

 

  1. Load vs. time

  2. Load table

  3. Actuated load

 

The first method for describing load torque is a table of arbitrary load torques as a function of time.  The second method is to specify the load torque versus angular velocity and another independent load input in a table.  This independent input could represent generator current, propeller pitch or pump pressure ratio, for example.  It is assumed that the user can supply such a correlation.  The independent load input is then specified in the form of a table of arbitrary values as a function of time.  The angular velocity as a function of time is developed from the load model itself.  The third method is to attach a torque actuator on the load side of the model.

 

The net torque on each inertia is used to determine the acceleration of the inertia.  These accelerations are integrated to develop the angular velocity and position of each element.

 

The speeds of each load component are initialized to correspond with the initial engine speed specified by the user with the gearbox ratio taken into consideration.  The initial shaft twists are set to zero.

 

 

Inputs:

 

 

Engine Inertia:

 

The lumped engine rotational inertia.  The engine inertia value needed by the sub-model is the summation of the inertia of all the rotating parts.  Typically this will be dominated by the flywheel and crankshaft values.

 

 

Load Inertia:

 

The lumped rotational inertia of the load.

 

 

Engine Damping:

 

Engine viscous damping coefficient.  Normally this variable is set to zero since it represents friction losses due to engine rotation, which has already been accounted for in the engine friction model.  However, the friction model is only updated on a cyclic basis, while this variable responds to instantaneous speed fluctuations.

 

 

Load Damping:

 

Load viscous damping coefficient.

 

 

Load Type:

 

Switch to specify how loading is to be applied.  It may have one of three values:

 

Load Type Option

Description

Time

The load torque is specified as a function of time.  Two variable arrays, time and load, are required.

Table

An external file is read which contains a two-dimensional array of load torque vs. load speed and an independent control variable.  A schedule of the independent control variable vs. time is also read.  To set the control variable to a constant value, set the value at a time of 0 in the control variable profile.

Actuator

Load is applied via an existing torque or power actuator.

 

 

Torque/Power Actuator:

 

Name or torque or power actuator attached to the engine which is used to represent the load.  Only selectable if the load type is set to "Actuator".

 

 

Characteristics File:

 

File tag or <pathname> of the external load characteristics file containing tabulated values of load rotational speed (rpm), the independent input variable values at which the load torque is specified, and values of the load torque (N*m, N*m, lbf*ft) at those speed and independent variable breakpoints.  If a file tag is used to load the external load characteristics file, it must be defined as type "LOAD" in the active.tags file.

 


 

 

Shaft Type:

 

Switch to specify type of shaft to be modeled.  It may have one of two values:

 

Model Option

Description

Rigid

Shaft is rigid.  The inertia of the gear in the gearbox will be lumped with the engine/load side inertia and the relevant joints are removed from the model.

Compliant

Shaft is compliant.  The inertia of the gear is treated as a separate mass and further shaft and joint definitions are required.

 

 

Stiffness:

 

Shaft stiffness.  Not required if the shaft type is "Rigid".

 

 

Shaft Damping:

 

Shaft viscous damping coefficient.  Not required if the shaft type is "Rigid".

 


 

 

Angle:

 

Angles of the joints where the shafts attach to the engine, gearbox, and load masses.

 

 

Phase:

 

Phasing of the gears in the gearbox and the load mass in respect to the previous joint (from engine to load, directionally).  The first joint (engine-side gear in the gearbox) is measured relative to top dead center of cylinder #1 on the engine.

 


 

 

Number of Teeth:

 

Number of teeth of the engine-side and load-side gears.  This determines the transmission speed ratio of the gearbox.

 

 

Inertia:

 

Inertia of the engine-side and load-side gears.  If the attached shaft is "Rigid", this inertia is lumped with the engine or load inertia, respectively.

 

 

Gearbox Damping:

 

Gearbox viscous damping coefficient.

 

 

Outputs:

 

The table below lists all of the available time plots from the simple engine load sub-model.  Click on any plot title to see more details.

 

PLOT #

PLOT TITLE

DATA UNITS

PLOT UNITS

(SI, SIMM, BR)

701

Engine Torque

 

KVAR 701 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:ENGINE_TORQUE:ENGINE

 

N*m

N*m
N*m
lbf*ft

702

Load Torque

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 702 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:LOAD_TORQUE:ENGINE

 

N*m

N*m
N*m
lbf*ft

704

Shaft Torques

 

This plot produces two data curves:  one each of the torque for shafts 1 and 2.

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 704 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:SHAFT_TORQUE:SHAFT:1

WAVE:CASE%c:ENGINE:SHAFT_TORQUE:SHAFT:2

 

N*m

N*m
N*m
lbf*ft

706

Load Angle

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 706 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:LOAD_ANGLE:ENGINE

 

rad

rad
rad
rad

707

Shaft Angles

 

This plot produces four data curves:  one for each universal joint angle.

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 707 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:SHAFT_ANGLE:JOINT:1_1

WAVE:CASE%c:ENGINE:SHAFT_ANGLE:JOINT:1_2

WAVE:CASE%c:ENGINE:SHAFT_ANGLE:JOINT:2_1

WAVE:CASE%c:ENGINE:SHAFT_ANGLE:JOINT:2_2

 

rad

rad
rad
rad

708

Shaft Twists

 

This plot produces two data curves:  one of twist for each shaft.

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 708 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:SHAFT_TWIST:SHAFT:1

WAVE:CASE%c:ENGINE:SHAFT_TWIST:SHAFT:2

 

rad

rad
rad
rad

710

Engine, Gear 1 Speeds

 

This plot produces two data curves:  one of speed for both the engine and gear 1.

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 710 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:ENGINE_SPEED:ENGINE

WAVE:CASE%c:ENGINE:GEAR_1_SPEED:ENGINE

 

rpm, rad/s

rpm
rpm
rpm

711

Load Speed

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 711 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:LOAD_SPEED:ENGINE

 

rpm

rpm
rpm
rpm

712

Load, Gear 2 Speeds

 

This plot produces two data curves:  one of speed for both the engine and gear 2.

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 712 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:LOAD_SPEED:ENGINE

WAVE:CASE%c:ENGINE:GEAR_2_SPEED:ENGINE

 

rpm, rad/s

rpm
rpm
rpm

717

Engine Acceleration

 

KVAR 717 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:ENGINE_ACCELERATION:ENGINE

 

rad/s2

rad/s2
rad/s2
rad/s2

718

Load Acceleration

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 718 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:LOAD_ACCELERATION:ENGINE

 

rad/s2

rad/s2
rad/s2
rad/s2

720

Gear 1 Acceleration

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 720 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:GEAR_1_ACCELERATION:ENGINE

 

rad/s2

rad/s2
rad/s2
rad/s2

721

Gear 2 Acceleration

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 721 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:GEAR_2_ACCELERATION:ENGINE

 

rad/s2

rad/s2
rad/s2
rad/s2

731

Load Independent Control Variable

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 731 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:LOAD_CONTROL_PITCH:ENGINE

 

-

-
-
-

732

U-Joint 1/1 Speed Ratio

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 732 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:U_JOINT_SPEED_RATIO:JOINT:1_1

 

-

-
-
-

733

U-Joint 1/2 Speed Ratio

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 733 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:U_JOINT_SPEED_RATIO:JOINT:1_2

 

-

-
-
-

734

U-Joint 2/1 Speed Ratio

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 734 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:U_JOINT_SPEED_RATIO:JOINT:2_1

 

-

-
-
-

735

U-Joint 2/2 Speed Ratio

 

This plot only produces meaningful output when the Simple Load model is activated.

 

KVAR 735 in the WAVE input file.

 

SDF (.wvd) dataset(s):

 

WAVE:CASE%c:ENGINE:U_JOINT_SPEED_RATIO:JOINT:2_2

 

-

-
-
-

 

 

The simple engine load sub-model creates no specific summary quantities.

 

 

Sensors:

 

There are no sensors which read variables from the simple engine load sub-model.

 

 

Actuators:

 

The table below lists all actuators which can attach to the engine on which the simple engine load sub-model is applied.  Click on any actuator type for more details.

 

ACTUATOR TYPE

VARIABLE UNITS

Power

 

This actuator adds or removes shaft power to an element.

 

A positive value adds shaft power while a negative value removes shaft power.

 

If more than one is attached to an element, the results will be additive.

 

ATYPE=POWER in the CTL:ACTUATOR block.

 

W

Shaft Torque

 

This actuator adds or removes torque to an element.

 

A positive value adds power while a negative value removes power.

 

If more than one is attached to an element, the results will be additive.

 

ATYPE=TORQUE in the CTL:ACTUATOR block.

 

N*m

 

 

Notes:

 

When either the torque or power actuator is attached to the engine and is used as the driver for the simple engine load sub-model, it does not add power to the engine.  Rather, it is the driving load torque or power.