Changes
Events/Testrigs
The most significant change to the python modeling templates involves the restructuring of events. Each event is now a class. The portion of the .adm that may change between events has been isolated and is called a testrig. Event class types reference one or more testrigs. The testrig templates can be found in pre_py/testrigs. If you compare .adm files from event to event, you will see differences near the bottom of the .adm file, due to use of different testrigs.The general layout of the .adm file written by ADAMS/Chassis has the following components:
- Header
- Subsystems
- Controls
- Front Suspension
- Steering Column
- Steering Gear
- Rear Suspension
- Body
- Loading
- Powertrain
- Brakes
- Front Wheel and Tires
- Rear Wheel and Tires
- Instrumentation
- Testrig (s)
- Road Graphics
- Footer
- Data file list
- Template file list
To understand more about events, please review the files in ‹topdir›/pre_py/events/full_vehicle/handling.
The process of creating custom events involves deriving an event from a standard ADAMS/Chassis event, or creating an entirely new class. When deriving from a standard ADAMS/Chassis event, you only need to code the methods which you want to behave differently than the base class. If you are creating an entirely event class, you will need to define all the required methods.
The following are required methods for event classes:
| Method name | Purpose |
| register | Method to register attributes. These are the attributes you vary and the attributes that are stored in the fingerprint (.xml) files. |
| __init__ | Standard python constructor. |
| setSIDefaults | Method to set default attribute values for the SI unit system. |
| setEnglishDefaults | Method to set default attribute values for the English unit system. |
| setGlobals | Method to initialize 'G' variables that
depend on event parameters. G variables are used in the preprocessing templates (such as sla.py, rack.py). This method is called at the beginning of the .adm build process. This method is an interface between the object-oriented event code and the procedural preprocessing code. |
| instructSolver | Method to define ADAMS/Solver commands. This method uses functions to build up the .acf file. |
The following are optional methods for event classes:
| Method name | Purpose |
| reportTemplate | Defines prefix for ADAMS/Chassis perl-based report template. |
| plotTemplate | Defines prefix for ADAMS/Chassis aft-based plot template. |
ARRAY/670 moved from svc.py
Front suspension templates: ARRAY/670 was moved from svc.py
into each front suspension template, this ARRAY aids the auto-aligner.
Improved traction control for GristMill
Improved traction control for Gristmill provides better
velocity control and different steady-state behavior.
Improved gravity handling for Steady-State Drift
Improved gravity handling for Steady-State Drift. All
alignment is done on level ground. In previous versions, some alignment
was done on non-level ground.
Improved dynamic loadcase event interface
The new interface provides the ability to set the
simulation final time to be same as the end of active data points in the
RPC-3 file, change the event mask to add RPC-3 file name to the mask name,
graphically view channel information present in the RPC-3 file and to
specify channel numbers to Wheel and Steering input channels.
Additional loadcase support for static loadcase
event
Support for shock and powertrain loads specification,
and analytical loads specification for powertrain, panic braking, wide
open throttle and cornering analysis is available. The loadcase information
are specified in the user interface and stored in XML format. A command
line utility to convert LCD file format to XML file is also available.
Modeling
New bushing features and formulationsThe ADAMS/Chassis 2003 bushing code has been modified and extensively rewritten in order to support the following features:
- Optional 2D or 3D inter-axial coupling.
- Wider choices of stiffness and damping force methods.
- Ability to mix any force formulation with any damping formulation.
- Hysteretic elastic force and k-fraction damping forces.
Bushings are modeled with ADAMS/Solver FIELD elements. Fields apply a translational and rotational action reaction force between two markers. For additional information about the force formulation, please refer to the ADAMS/Chassis component guide.
The following includes brief descriptions of the new features available with ADAMS/Chassis 2003 bushings.
Shape (coupling) methods- Squared
No coupling between coordinate directions (equivalent to the standard BUSHING statement in ADAMS/Solver, but supports nonlinear force-deflection and force-velocity).
- Cylindrical
X and Y force-deflection characteristics are coupled, but Z force-deflection characteristic is independent (equivalent to the nonlinear bushing formulation in ADAMS/Chassis 12.0). TX and Ti torque-angular-deflection characteristics are coupled in the same manner.
- Spherical
X, Y, Z force-deflections are coupled, and TX, Ti, TZ torque-angular-deflections are coupled.
In ADAMS/Chassis 2003, the bushing component supports a variety of stiffness and damping methods. You also may use different stiffness and damping methods for each axis, as specified in the property file.
Stiffness Methods:
- Linear (same as 12.0)
- Nonlinear spline based (same as 12.0)
- Piecewise linear (same as 12.0)
- Smoothed piecewise linear (
)
- Hysteretic (same as 12.0)
Damping Methods:
- Linear (same as 12.0)
- Spline based (same as 12.0)
- Piecewise linear (same as 12.0)
- K fraction ()
Notes about the new formulations
Hysteretic stiffness implementation:
- Uses two force-deflection splines: one for positive velocity and one for negative velocity.
- Computes the force by switching between the splines based on the sign of velocity, provided the velocity magnitude is greater than a prescribed value.
- Computes the force by blending the two splines when the magnitude of the velocity is less then a prescribed value.
K fraction damping:
- Damping force is proportional to the local stiffness.
- Damping coefficient is user specified.
You can now specify translational and/or rotational offsets for any bushing in the model. To provide maximum flexibility, the following rules will be followed if the you have set a nonzero wheel rise installation parameter:
- If a nonzero Z rotational offset is specified, that value will be used and the wheel installation rise calculation will be ignored for that bushing.
- If a zero rotational offset is specified, the wheel installation rise calculation will be in effect.
These rules allow the wheel installation rise feature to be used within a suspension, with the flexibility to override it for individual bushings.
Bushing data unitsSome unit inconsistencies existed in the ADAMS/Chassis 12.0 XML bushing property files:
- Piecewise Data (rotational) - Break point units modified to deg. Slopes
modified to N-mm/deg.
- Hysteresis type bushings - X spline units on rotational directions
modified
to deg.
Some of the benefits of the new bushing capabilities include:
- Use different descriptions to define stiffness along each axis.
- Apply any stiffness coupling formulation.
- Use different descriptions to define damping along each axis.
- Mix any damping description with any stiffness description and any coupling.
Please see the ADAMS/Chassis online help for additional information about the equations.
Spherical Joint FrictionWhen the Spherical Joint connector type is chosen, an optional property file can be specified for joint friction properties. A friction statement will be included in the ADAMS/Solver model, with parameters specified by a property file. The property file type is SphericalJointFrictionProperties. An example file is in the bushings.tbl directory of the shared_chassis_database.vdb.
Please see the ADAMS/Solver online help for more information on the FRICTION statement.
Complex Strut ModelNew default bushing stiffnesses have been added to aid model robustness. Results will change for models with the complex strut activated. The stiffnesses have been reduced from unrealistically high values (1.0E+9 N/mm).
SLA Auto-alignment
A new construction option is available for front and rear SLA suspensions. With this option, you have three choices for auto-aligner configuration. The default is Option 1 (UCA), which was previously the only option.
- UCA - dummy parts attached to the upper control arms are used to achieve desired camber/caster.
- LCA - dummy parts attached to lower control arms.
- LCA_rear - lca rear inner mount is moved along a line perpendicular to line connecting lca_front and lca_rear hardpoints.
Note: With this option only camber adjustment is performed; caster adjustment is not possible.
This option is automatically added to your front or rear SLA subsystem files when you run ADAMS/Chassis 2003.
Flexible Body/Frame ModelingNew logic has been added to ADAMS/Chassis modeling templates to allow standard (no customization required) connection of flexible bodies/frames to the following elements:
- Simple Cargo Parts (cargo parts that are simply fixed to the attachment part).
- Complex Cargo Parts (cargo parts connected to the attachment part through 1 or more bushings).
- Occupants.
- Instrumentation.
To connect these elements, additional nodes must be associated
from the FEA model. The ADAMS/Chassis node ID's will be the following:
| Attachment Type | Format of hardpoint string in .flx file |
| Simple Cargo Parts | loading.cargo_part_name |
| Complex Cargo Parts | loading.cargo_attach_hardpoint_name_1 loading.cargo_attach_hardpoint_name_2 loading.cargo_attach_hardpoint_name_n |
| Occupants | loading.occupant_name |
| Instrumentation | instrumentation.sensor_name |
To help you find all the required attachments, a new utility event, BodyAttachmentFinder, has also been added. See Simulations section below for more information.
FEA Node Finder
The node finder utility is a command line feature that helps to locate
the relevant interface nodes necessary to connect a flexible body to an
ADAMS/Chassis model. This avoids tedious manual searching using the FEA
input file or a visual preprocessor.
Dynamic Loadcase Fingerprint Generator
The Fingerprint generator provides the ability to generate a fingerprint
of loadcase events based on different RPC-3 input files. The Fingerprint
generator automatically sets the final time of the simulation to end of
active data in the RPC-3 file. This functionality is available under the
Test menu in test mode.
Acf Runner
The acf runner utility allows you to run pre-built models in the background.
The utility is available under Utilities menu in test mode.
Adm Trace
The adm trace utility can be used as a debugging tool to determine
which Python file was used to generate specific dataset (adm) statements.
Datasets generated with this option are for debugging purpose only and
should not be used to run simulations. This utility is available under
Test menu in test mode.
Some of the new modeling features in this release require changes in the XML file formats:
- bushings-in-series
- auto-alignment construction options
To facilitate this, a data update process will automatically be applied to your 12.0 XML files when you load them in ADAMS/Chassis 2003.
Note: XML files saved in ADAMS/Chassis 2003 are not compatible with version 12.0. You can use your 12.0 xml files with both 12.0 and 2003, but as soon as you save the files in ADAMS/Chassis 2003 they will no longer function with 12.0.
Wavefront Graphics
Translational and Rotational offset parameters are now available for Wavefront graphics.
Note: The offsets may not work for compound Wavefront graphic files containing multiple sub-objects.
StepSteer Throttle
Three throttle options are now available:
- Throttle Off
- Constant Throttle
- Cruise Control
These options are available during the Steering Wheel Angle and Spline lateral acceleration methods.
SVC-Iterate
The desired inertia units when working in English units have been modified for consistency. The new units are lbm-in-in.
FourPost
The former method Constant Velocity has been re-implemented as SinusoidalVelocity. With this option, you specify the amplitude of jack velocity. An additional method, SinusdoialDisplacement, is also available. With this method, you specify the displacement amplitude.
BodyAttachmentFinder
To aid the complex process of incorporating flexible bodies and frames into a ADAMS/Chassis model, the BodyAttachmentfinder utility has been created. This utility helps you know how many attachment locations exist within the model. The output of the utility is a list with all the hardpoint names (the names needed in the .flx file), and locations (to aid finding the corresponding node in the FEA mesh).
ADAMS/Chassis integration with the Standard Driver Interface (SDI)
PI Traction/Braking Controllers
Most SDI events in ADAMS/Chassis use non-SDI PI controllers for traction and braking. This is due to increased performance of these controllers in some situations. To find out which traction/braking controllers are being used in a particular event, examine the .dcf file. If you see 'VAR(995)' in the traction or braking function expressions the PI controllers are being used. The gains for the PI controllers are stored in the powertrain and braking subsystem parameters tables: 'proportional_gain', and 'integral_gain'.
SDI Traction/Braking Controllers
If the SDI traction/braking controllers are being used, a MACHINE or HUMAN block will be present in the .dcf file. Also, HMAX will be set to .01 in the .acf file. Compared to the PI controllers, the SDI traction controllers are better at maintaining consistent longitudinal speed during high yaw-rate maneuvers. Because of this, ADAMS/Chassis uses these controllers in events such as step-steer. The scale factors for the SDI controllers are stored in the powertrain and braking subsystem parameters tables: 'sdi_throttle_scale' and 'sdi_braking_scale'.
Steering Sign Convention
In ADAMS/Chassis, the sign convention for steer angle is positive steer angle produces a right-hand turn. The sign convention is the opposite in the SDI. In .dcf files, positive steer angle produces a left-hand turn. To accommodate this, ADAMS/Chassis .acf files scale the Driver steer output by -1 to retain the ADAMS/Chassis sign convention.
Integration with ADAMS/Insight
Changes have been made to the ADAMS/Insight conduit for 2003. The first change makes event parameters and auto-alignment parameters available for selection as experiment factors. Only real-value type event parameters will be available (Integer,String, Boolean types will not be available).
The technique when using user factors has also changed. To create a user factor, enter an expression like the following in the Insight factor variable field: event.‹your_factor_name›
Note: The value of this field MUST start with event. By entering an expression like this, a variable will be declared during the .adm build of each trial. You will be able to access this variable in your preprocessing templates by referencing the current event instance (most commonly G.event).
Example:
- Enter event.my_boost in your user factor variable field.
- Use personal version of str_boost.py, construct expression G.event.my_boost.
- As the experiment builds models for each trial, the value of G.event.my_boost will vary according to the experiment worksheet.