AUTHOR

Dr. Cornlius Chucholowski General Manager of TESIS DYNAware

GmbH

Understanding Dynamic

Simulation

Dynamic simulation is the numerical

integration of differential equations

that describe system behavior.

Rapid progress in computer tech-

nology now makes it easier to apply

this demanding and time-consuming

computing process in small time

steps to increasingly complex

systems. The tools have also

fundamentally changed. Whereas

the differential equations used to be

created and programmed manually,

we now have special tools for multi-

body systems or generic modeling

programs that can be applied

without the need for mathematical

knowledge. What is more, there are

now ready-made libraries for

increasing numbers of sub-systems

that users can employ.

User-friendly complete solutions for

vehicle-dynamics simulation support

first-time users and quickly lead to

results. However, this simplicity of

use also has a disadvantage.

Users no longer need to deal with

the funda-mental principles and to

critically query the results. Experts

know that there is never one exact

solution, but only an approach to-

wards reality. The result can only be

as exact as the modeling process

and the numerical data permit.

Furthermore, even the best program

is useless if there are no valid data

available for parameterization.

Simulation is an indispensable tool

for the validation of vehicle dy-

namics and active control systems.

However, users must be aware of

the background conditions and must

select the properly adapted tools

and modeling depths. It also goes

without saying that simulation will

not achieve its full benefits unless it

is supported by road tests .

Demands on Vehicle Dynamics

Simulation

The experience of TESIS

DYNAware goes back to a time in

which there were no or only very

few tools for dynamic simulation

and every program had to be

created individually.

Simulation enables trustworthy

predictions to be made, provided

that the user is clear about its

limitations. One danger is to have

blind faith in numerical data.

The integration process and the

computing step size should be

selected in adaptation to the

problem. The computing step size

is oriented towards the dynamics of

the system and must be small

enough to resolve high-frequency

vibrations. A computing step size

that is too small will result in

"numerical noise" and will falsify the

result. TESIS DYNAware is

specialized in real-time-capable

simulation, as is required for testing

ECUs in HiL operation. In real-time

operation, events – for example for

a control mode changeover for the

transition from grip to skid – must

be given special treatment in order

to achieve precise results even with

a fixed step size. This is not covered

by standard libraries. Very large

libraries tempt users to make the

models more detailed than necessa-

ry. Detailed models require high

computing power and are more

complex to parameterize and

validate. An increase in the number

of parameters also increases the

susceptibility to errors.

For proof of concept tests, it is also

advisable to make use of very

simple models, such as a point

mass model for driving performance

and fuel consumption, a single-track

model for lateral dynamics or a

quarter-vehicle model for vertical

dynamics. These models make it

possible to perform an analytical

study that is well suited for

determining control structures and

testing control concepts, but is less

suitable for applying parameters.

Conventional chassis development

uses simulations based on generic

multi-body programs, such as

ADAMS/Car.

The high-fidelity applications can

also consider flexible structures.

The models are derived from

component and design data.

Dynamic truck tipping test: Comparison

of simualtion and test drive in the animation

TESIS DYNAware Suspension Analysis Toolbox enables the determination of axle

kinematic and axle compliance from virtual or real K&C test rig measurements.

Vehicle manufacturers go to great

lengths to parameterize the complex

models and to validate them to such

an extent that they can be used as

virtual reference vehicles. Suppliers

seldom have access to the data

required or cannot afford the effort

involved.

The high-fidelity models are focused

on new designs. For functional

development and the testing of

control systems, active systems, and

ECUs, specialized vehicle dynamics

programs are used that are easy to

parameterize and which can also

run in real time on HiL systems.

The depth of detail is reduced, but is

still fine enough to simulate the most

important vehicle-dynamics effects.

Up to 30 Hz, the results hardly differ

from those of high-fidelity programs.

The TESIS DYNAware programs

use Simulink as the runtime environ-

ment. Simulink is a preferred

platform for developing control

systems from their initial design to

their series production maturity. As an alternative to resolved axle

modeling, users can specify

kinematics maps with compliance,

which they calculate on the real ve-

hicle or by analyses on the complex

full vehicle model. The concept

developed by TESIS DYNAware has

proven itself extremely well and is

used by suppliers who do not have

any design data at their disposal

Full Vehicle Toolkit

3D vehicle dynamics includes

lateral, longitudinal, and vertical

dynamics. The three areas are

strongly interwoven.

The distribution of driving and

braking torque to the front and rear

axle changes the self-steering

behaviour. In an electric or hybrid

vehicle with selective drive to each

axle, this has an impact on energy

management. Roll stabilization

systems or active suspensions also

have an influence not only on

vertical dynamics but also on lateral

and longitudinal dynamics. The

same depth of detail is not required

for every aspect in every

development phase. However, it is

advisable to use the same basic full

vehicle toolbox in all areas, which

can then also be used in all phases

of the V model.

For that reason, the DYNA4

simulation framework from TESIS

DYNAware provides the possibility

to adapt and combine the simulation

models without difficulty.

The basic driver-vehicle-

environment architecture is always

the same for full-vehicle simulation.

There are also hardly any

differences in operation and control.

Steering maneuvers, fuel

consumption cycles, or general

driver control are selected from a

maneuver catalogue in a similar

manner. The route or the traffic

conditions can be specified in the

environment module.

The information used is dependent

on the maneuver.

The core of the simulation

environment is the vehicle module,

which can be configured

interactively and flexibly without

knowledge of modeling. One feature

of the model structure is its flexible

data buses. These make it possible

to exchange model components with

very different levels of detail by

check boxes, for example a simple

engine map can be replaced by a

complex engine model with real-

time-capable cyclic process

calculation .

DYNA4 manages Simulink modules.

Separate modules can be integrated

by using wizards that provide the

meta-data. Users with modeling

know-how can also make changes

in the Simulink model themselves

and can have the changes managed

in the model library.

For applications in automotive

technology, a large number of

Modelica-based libraries are

meanwhile available, for example for

powertrain components, electrics, or

hydraulics. If the system limits are

suitably chosen, the physical models

can be used to create functional

modules, which can be integrated

into the DYNA4 user interface as

"functional mockup units" (FMU) and

parameterized. On the other hand, it

is also possible in Simulink to create

very modular libraries and to

manage these in DYNA4 .

Continuous Model Usage of MiL,

SiL to HiL

In the TESIS DYNAware models,

the control system and the route are

strictly separated.

Only in this way is it possible to

ensure continuous usage in the V

process, i.e. to replace the software

ECU in HiL operation by a real ECU

at a later development phase.

Therefore, the simulation framework

is suitable for function-oriented tests.

On the first level same structure of complete vehicle simulation, in detail flexible models for the particular range of applications, e.g.engine models with different level of detail.

"Virtual reality" for vehicle-dynamics

programs for testing driver assistance systems.

Results Representation and

Reporting

Processing and revision-safe

reporting of the results are important

components of vehicle dynamics

simulation. Further support is

provided by animation running

parallel to the simulation, in both

Office and HiL operation. This option

is not included in every generic

simulation program, or the program

may require extensive and complex

configuration before it can offer it.

Driver Assistance Systems and

Vehicle Connectivity

The increasing use of driver

assistance systems and an increase

in vehicle connectivity also present a

challenge for vehicle dynamics

simulation. The focus is no longer on

vehicle dynamics alone, but on the

simulation of the environment, the

sensor systems, and communica-

tion. Apart from the effect of side

wind, the vehicle makes contact with

the environment only through its

tires. The "virtual driver" used in the

simulation program only needs to

get information on the route and will

then perform his task accordingly.

If driver assistance systems are

involved, the driver model must also

behave like an assisted driver. In

this case, the environ-ment must be

simulated much more precisely in

order, for example, to represent

visibility, road junctions, or traffic.

The key element is the quality and

content of the graphical

representation. However, the effort

required in creating the content must

not be under-estimated.

For this purpose, TESIS DYNAware

employs a chain of tools that use

navigation data and other generally

accessible information to generate a

virtual environment which simulates

a virtual reality for the assistance

systems .

Outlook

There are therefore tailor-made

solutions for every application.

Almost as important as correct and

fast vehicle-dynamics simulation is

support for cooperation in the com-

pany across various departments,

areas, and domains. Furthermore,

quality and acceptance specifica-

tions require reproducible simulation

and documentation.

This can be achieved only if the

simulation environment is flexibly

tailored to it. The top priority is that

all use the same basis and can

make use of a managed model

library .

A systematic storage system for

models and results ensures

reproducibility and transparency.

DYNA4 already supports these

requirements and will be further

developed in this direction.

Contact

TESIS DYNAware GmbH

www.tesis-dynaware.com

Phone: +49 89 7473 777 444

E-Mail: tesis.dynaware@tesis.de

Collaborative engineering through cross-company management of simulation objects in a uniform environment

enDYNA library concept for Simulink-based engine simulation