isep2011_perkovic in drugi

8/7/2019 ISEP2011_Perkovic in drugi

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ISEP 2011

REAL TIME MEASUREMENTS OF INFLUENCE

OF CROSSWIND ON DYNAMICS OF

ROAD VEHICLES

Marko Perkovi1, Milan Batista1, Dimitrij Najdovski2, Franc Dimc1

1 Univerza v Ljubljani, Fakulteta za pomorstvo in promet, Portoro2X3DATA, Ljubljana

Abstract

Different vehicles driving along roads exposed to a strong

cross wind can be forced from their expected path and even be

blown over. Even the drivers natural tendency to compensate

by manipulating the steering wheel may add to the likelihood

of an accident. This paper will primarily present the

equipment used for real time data acquisition and methods

used to determine the relations between wind speed and

direction and the vehicle dynamic.

Keywords

Real time measurements, cross-wind, vehicle dynamic

INTRODUCTION

Vehicle dynamics is a part of engineering for the most

part based on classical mechanics, encompassing the

interaction of a driver, vehicle, load and environment. Cross

wind as a part of environmental influence on vehicle

dynamics will be the main consideration of this paper,

focusing on equipment used for real time data acquisition.The force of the wind can blow a vehicle over or cause it to

slide sideways. Determining whether the vehicle will be

blown over before it slides or whether it will slide before it

is blown over is a complex problem [1 - 7]. Measuring real

time wind speed and direction around a vehicle and

monitoring a vehicles yawed condition (yaw angle

represents the rotation of a vehicle about the gravity vector)

we can obtain more data to calculate whether it is safe to

drive in certain wind conditions. When a vehicle is in a

yawed condition it means that, in addition to the wind

resulting from the relative road velocity, a crosswind

component exists. The interest in aerodynamic loads onroad vehicles in a yawed condition started to develop in the

1950s.

MATERIALS

IMU and GPS

The integration of an inertial sensor (calibrated 3D

accelerometer, 3D rate gyroscope, 3D magnetometer,

barometric altimeter) and L1 GPS (SABAS Satellite

Based Augmentation System to improve accuracy and

reliability) receiver unit provides, in real-time, the vehicle

position, velocity, acceleration, angular velocity, and

orientation, from which vehicle dynamics parameters suchas slip-angle and roll-compensated lateral velocity can be

derived. In our case three MEMS IMU devices were used

on board the Attitude and Heading Reference System

(AHRS). One of them (MTi-G) was combined with GPS

and a static pressure sensor. Within MTi-G, data from

internal sensors and GPS are fused in an onboard Kalman

filter (XKF - see figure 1) to yield real-time output of

vehicle dynamics. For the larger vehicles two additional

GPS receivers are used with positioning frequency of 5 Hz.

Another GPS is used to synchronize PC time every minute[8].

Figure 1: MTi-G (IMU/GPS) Architecture overview

Magnetic Compass

A magnetic compass is used as an additional sensor to

IMU, calculating heading to further evaluate sudden

changes. With a frequency of ten measurements per second

it is possible to detect anomalies in heading when wind

force influences driving direction. The A4020 compass by

Autonnic contains a fluxgate surrounded by high-precision

interface circuits which together with offset nulling

sequence allow a microprocessor to acquire a binary valuefrom two orthogonal sensors of the Earths magnetic field.

The processor calculates the vector from these values, using

a calibration table to correct for local field disturbance

errors, offsetting the result and then presenting direction


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Figure 2: Fluxgate magnetic compass

Accelerometers

To obtain precise transversal offsets of a moving

vehicle, especially for longer or multi-axial or combined

(trailers), additional accelerometers should be placed at

corners or above the wheels. We have used one tri-axial

accelerometer with a sensitivity of 50 mV/G and three very

sensitive tri-axial accelerometers with a measurement rangeof 2 g pk.

Table 1: Accelerometers performance table

Figure 3: Tri-axial accelerometers

Anemometers

For precise real time wind flow measurements around a

vehicle two sonic anemometers are used. One 2D sampling

wind at 4 Hz mounted at the rear part andone other 3D professional anemometer

with a capability of 32 samplings per

second mounted in front of the vehicle.

The Ultrasonic 2D Anemometer consists

of 4 bi-directional ultrasonic transducers,

in pairs of 2 opposite each other. The

transducers act both as acoustic

transmitters and acoustic receivers. The

respective measurement paths and their

measurement direction are selected via

electronic control. When a measurement

starts, a sequence of 4 individual

measurements in all 4 directions of the

measurement paths are carried out at

maximum speed. 3D anemometer

consists of two transducer heads enabling

precise measurment of vertical wind

component.

Figure 4: 3D anemometer

Microphones - Sound imaging

A sufficient number (four) of reference PCB

microphones are distributed around the vehicle in order to

observe sound fields in the frequency range of interest.

Those measurements are complementary to the

anemometers and pressure sensors described in 2.4. This is

a good method of capturing gusts of wind.

Table 2: Microphones performance table

Figure 5: Microphone

Differential pressure measurements

Cross wind pressure can be distributed quite differently

around the vehicles longitudinal sections and this is the

case especially for long vehicles like tractors-trailers or

semi-trailers. Four channel Honeywell Sensing ASDX

sensors can measure absolute,differential, and gauge

pressures. The ASDX-DO

sensors with compensated 14-

bit digital output provide either

an I2C or SPI digital interface

for reading pressure over the

specified full scale pressure

span and temperature range.

Figure 6: ASDX-DO differential pressure sensor

Force Transducers and Load Cells

We have used 1 and 2kNm force transducers and loadcells to measure static and dynamic tensile and compressive

loads (Fx,Fy,Fz and Mx,My,Mz), with virtually no

displacement as the effect of shifting the load from one

cross wind side of the vehicle to the wheels on the other

side.

Figure 7: Force Transducers and Load Cells


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Distance Measurements

When the cross wind hits the trailer the angle between

the truck and trailer can be measured by a Noptel CMP

sensor that uses a wide

laser beam (up to 200 x

200 mm @10 m) that

covers wider measurement

areas at short distances(Used with a retro-

reflector).

Figure 8: Noptel CMP laser

Rotary Encoder

When a cross wind hits the vehicle, steering corrections

are needed to stabilize the driving direction. Wheel

rotations can be measured by applying a high resolution

shaft encoder. For that the

Autonnics low-noise

fluxgate magnetometer

A3030 is used--based ontechnology that has created

an industrial component

which can resolve shaft

angles to 1 part in 4000

equivalent to 12bits.

Figure 9: Absolute encoder

Video Recording

During all experiments we use

video cameras to record the

drivers reactions, the movement

of the vehicle, oncoming traffic,and whatever general conditions

that are variable. In the future we

expect that by utilizing the smart

camera we will be able to apply

object tracking methodology to

more precisely obtain the offset

movement data [9].

Figure 10: Video imaging object tracking

Data Acquisition System

LabVIEW, a graphical programming language by

National Instruments, is used using the PC plug-in DataAcquisition (DAQ) boards for computerized measurement

of real world analog signals. The plug-in DAQ was used for

acquiring data from Accelerometers, Force Transducers,

Load Cells, Microphones, and Smart Cameras. Other data,

from IMU, GPS, Anemometers, Encoders, Compass and

Cameras, were collected by PC through Moxa Uport USB

to a Serial Hub device. IMU data are processed with MT

manager software applying different Kalman filters. Wind,

wheel position, heading, and positioning are visualized and

layered over navigational charts. Using the NaviSailor

application; real time position, course, heading, apparent

and true wind are depicted. This application is capable at

same time of archiving raw data for further post-processing.

METHODS AND RESULTS

A variety of tools have been adopted and different data

sources were utilized where Inertial Measurement was a key

sensor of the Inertial Navigation System. Precise Inertial 3D

data (slip angle, longitudinal, lateral accelerations and rate

of turn) were obtained by setting sensor alignment with

respect to the vehicle frame and integrating GPP data.Translations (transversal) are derived with accelerations

double integrated to correct for the angle of roll. To

determine wind force, which affects vehicle driving

stability, in addition to the anemometers pressure sensors

around the vehicle were mounted. Such a system enables

the study of effects of the longitudinal location of the centre

of pressure, the under-steer gradient and the steering

sensitivity on the crosswind stability [6, 7]. To further

understand load distribution over axis and wheel load cells

and force transducers are used.

The first results from first test drive are presented within

next Figure 12. The green line shows car speed where GPS

signals are lost when the vehicle enters a tunnel. At the

same time it can be observed that wind conditions in the

tunnel are more stable than outside. Apparent wind speed

and wind direction correspond to the sped and course of the

vehicle, so true wind is close to zero. The blue line indicates

some wind gusts which, with a direction close to the

opposite of the vehicle heading results in a sudden drop in

speed.

This Figure 13 is a magnification of the highest wind

gust (15 seconds). The blue lines show longitudinal

accelerations; red corresponds to the transversal; the purple

diagonal line describes the yaw of the vehicle; the top line

shows the roll angle. A comparison between the red and rolllines illustrates the correspondence between roll and

transversal acceleration.

Figure 11: Test vehicle with visible anemometers and GPS

sensors


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Figure 12: Vehicle speed, wind speed and wind direction

Figure 13: Track, accelerations, yawing and roll angle

CONCLUSIONS

On exposed roads, cross winds acting laterally on the

side of the vehicle are commonly as strong as the vehiclevelocity induced air-speed; the air pressure acting sideways

can thus be as high as the drag force in the driving

direction, potentially resulting in a catastrophic loss of

stability. The application of one testing moment is seen

here, but as the experiment is ongoing we are unable to

present the results of the rest of our measurements. The

expectation is that we will be use our results, including

those from all sensors described, to determine highway

safety parameters.

ACKNOWLEDGMENTS

We would like to thank Marino Bajec, Peter Vidmar and

David Nemec, for their support.

REFERENCES

1. Georg Rill (2009), Vehicle Dynamics, HochschuleRegensburg University of Applied Sciences

2. Graham R Greatrix, Wind Forces, www.greatrix.co.uk/3. Soon-Duck Kwon, Dong Hyawn Kim, Ho Sung Song,

Il-Keun Lee and Jun-Sang Cho, Korean Program for

Enhancing Driving Stability of Vehicles in High Winds,

The Seventh Asia-Pacific Conference on Wind

Engineering, November 8-12, 2009, Taipei, Taiwan

4. Skuli Thordarson, Bjorn Olafsson, Weather inducedroad accidents, winter maintenance and user

information, Transport Research Arena Europe 2008,

Ljubljana5. Thordarson, S. & Snbjrnsson, J. (2006). Traffic

accidents and wind conditions, parts I & II. Reports for

ICERA and The Icelandic Board for Road Traffic Safety

Research.


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6. Thordarson, S. (2006). Traffic safety on wind-exposedroads in Iceland. Nordic Road and, Transport Research,

No. 2, pp. 14-15.

7. Nair Sidharth, A Multiple Antenna Global PositioningSystem Configuration for Enhanced Performance,

Master of Science (MS), Ohio University, Electrical

Engineering (Engineering), 2004

http://etd.ohiolink.edu/send-pdf.cgi/Nair%20Sidharth.pdf?ohiou1090937438

8. Xsens Technologies, Orientation Performance Test ofXsens MTi-G AHRS for Automotive Applications,

http://www.xsens.com/images/stories/PDF/dl_54_dl_54

_mtig_prewhite_paper_automotive_a.pdf

9. Yannick Morvan, Richard P. Kleihorst, Anteneh Abbo,Harry Broers, Peter Raedts, Real time object tracking

with a low-cost smart camera, Philips Research

Laboratories, Philips Centre for Industrial Technology,

http://docs.google.com

isep2011_perkovic in drugi

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