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Marko Perkovič, Milan Batista, Dimitrij Najdovski, Peter Vidmar, Blaž Luin

THE EFFECT OF CROSSWINDS ON DYNAMICS OF ROAD VEHICLES…

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MEASURING THE EFFECT OF CROSSWINDS ON

DYNAMICS OF ROAD VEHICLES, FOCUSSING ON THE

BORA ANALYSES

Marko Perkovič1, Milan Batista

1, Dimitrij Najdovski

2, Peter Vidmar

1, Blaž Luin

1

1 University of Ljubljana, Faculty of Maritime Studies and Transport

Pot pomorščakov 4, SI - 6320 Portorož, Slovenia

[email protected], [email protected],

[email protected], [email protected]

2

X3DATA, Ljubljana

ABSTRACT

Vehicles driving along roads exposed to a strong cross wind can not only be forced from their path but be blown

over as well. Other potentially dangerous circumstances include the wind causing a slide or a yawing effect, or

the driver, tiring from continual compensation, reacting too slowly or even over-reacting to strong gusts. The

wind considered here is the bora (Slovene: burja), a katabatic cold montane wind that rushes from high pressure

down to the low pressure primarily over the sea. 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

1 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 - 8]. Measuring real time wind speed and direction around a vehicle and

monitoring a vehicle‟s 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 on road vehicles in a yawed condition started to develop in the 1950s.

The Adriatic region, including especially its northeastern and eastern hinterlands is regularly

subjected to strong wind events from the northeast during winter. These “bora” winds have a

serious effect on road safety. The bora is known to have multiple jets and has been the focus

of many theoretical and numerical modeling studies, yet the detailed spatial structure of these

jets over its dynamic range cannot be observed using in-situ observations.

Further, the bora does not have a constant direction and strength, so it can surprise with

strong, unexpected gusts from various directions. To maintain traffic safety some “general”

measures are implemented considering mainly wind speed:

mailto:[email protected]





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1st level - wind speed 80-100 km/h or 22-28

m/s, ban for camper vans, refrigerator trucks

and sheeted vehicles up to capacity of 8

tonnes, for other vehicles speed limit 40 km/h;

2nd level - wind speed 100-130 km/h or 28-35

m/s, ban for camper vans and all sheeted

vehicles and refrigerator vehicles, for other

vehicles speed limit 40 km/h;

3rd level - wind speed 130-150 km/h or 36-41

m/s, ban for camper vans and all sheeted

vehicles, refrigerator vehicles and buses, for

other vehicles speed limit 40 km/h;

4th level - wind speed above 150 km/h or

above 41 m/s: ban for all vehicles.

2 SENSORS

These four levels are generally accurate as far as we know, but we intend to use our

devices in an attempt to zero in as precisely as possible on the various broad circumstantial

effects of various speeds and effects on the bora‟s domain. But they remain theoretical and the

specific traffic problems are affected in real time and space. For instance, the speeds listed are

gusts, generally of brief duration. When does a bora with gusts of 100 to 130 really pose a

threat? For that matter, when does a gust of 80 to 100 not? The intention is to try to

understand what these measures really are.

2.1 Integration of Inertial Navigation System and Global Positioning - IMU/GPS

Inertial Navigation System can provide position, velocity and attitude of the moving

vehicle but it is overwhelmed with errors due to the fact that any small bias error can grow the

error with time. Errors in the accelerations and angular rates lead to steadily growing errors in

position and velocity components of the vehicle, due to integration. These are called

navigation errors and there are nine of them; three position errors, three velocity errors, two

attitude errors and one heading error [9]. If an unaided INS is used, these errors grow with

time. It is for this reason that the INS is usually aided with either GPS, Doppler heading

sensor or dead reckoning systems. Gravity model can also cause some errors. The

acceleration due to gravity varies from place to place along the earth and also with height.

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 such as 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 [10].



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Figure 1: IMU/GPS architecture overview

2.2 Magnetic Compass

A magnetic compass is used as an additional sensor to

IMU/GPS, 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 value from two orthogonal

sensors of the Earth‟s 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

Figure 2: Fluxgate magnetic compass

2.3 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 range of ±2 g pk.

Figure 3: Tri-axial accelerometer

Table 1: Accelerometers performance table



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2.4 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 and one 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 measurement of vertical wind

component.

Figure 4: 3D and 2D anemometer

2.5 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

2.6 Differential pressure measurements

Cross wind pressure can be distributed quite differently

around the vehicle‟s 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



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2.7 Force Transducers and Load Cells

We have used 1 and 2kNm force transducers and load cells 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

2.8 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

2.9 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

Autonnic‟s low-noise fluxgate magnetometer A3030 is used--

based on technology that has created an industrial component

which can resolve shaft angles to 1 part in 4000 – equivalent to

12bits.

Figure 9: Absolute encoder

2.10 Video Recording

During all experiments we use video cameras to record the driver‟s reactions, the

movement of the vehicle, oncoming traffic, and whatever generally variable conditions. 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].



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Figure 10: Video imaging – object tracking

2.11 Data Acquisition System

LabVIEW, a graphical programming language by National Instruments®, is used using

the PC plug-in Data Acquisition (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 (Transas) 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.

Figure 11: Data Acquisition

4 METHODS AND SOME 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 (figure 12).

Translations (transversal) are derived with accelerations double integrated and corrected 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



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gradient and the steering sensitivity to the crosswind stability [7, 8]. To further understand

load distribution over axis and wheel load cells and force transducers are used.

Figure 11: Sensor alignment

The upper part of figure 12 presents‟ 3D wind speed measurement data acquired with an

anemometer mounted on the roof of the tractor; the figure below shows 2D wind data (a 3

second wind speed average) acquired with an anemometer mounted on a bar three meters

above the roof of the escorting vehicle. It is evident that measurements are similar with

respect to the fact that 3 seconds average cannot reflect short bora gusts. The blue lines are

measurement data processed with a Kalman filter.

Figure 11: 3D wind measurements and 2D three seconds wind speed average processed with Kalman filter



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The first results from the first test drive are presented in Figure 12. The green line

shows the transversal direction of wind speed, derived from three dimensional wind speed

(blue line) and horizontal wind direction (red line), measured from vehicle heading (negative

from heading to the left and positive from heading to the right).

Figure 12: Absolute wind speed (blue), transversal (green) wind speed and wind direction [°] (red)

The graph below (Figure 13) depicts the road segment Ajdovščina to Vipava, with its slow

curve that ultimately significantly shifts the direction of traffic flow. The wind rose shows the wind, in

yellow, as it is measured in Ajdovščina in daily average, while the green depicts the daily average as

measured in Vipava. The arrows are wind direction at the moment of the vehicle‟s passage.

Given the virtually ceaseless change in both driving direction and wind direction, there is no

way to accurately predict the effect of the bora on any given vehicle at any given moment.

Crosswinds, which represent the greatest threat of catastrophic force, cannot be predicted with

precision at any precise moment.

Figure 13: Road segment, wind rose and measured wind



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Figure 14: Wigner-Ville time/frequency distribution

These two graphs visualize the Wigner-Ville time frequency analysis of wind speed

(left) and trailer accelerations (right).

4 CONCLUSION

"...a strong wind from the west hurled itself against the slope of the mountains to the east,

raising dust and a litter of newspaper and cardboard on its way through Santa Teresa, moving in the

clothes that Rosa had hung in the backyard, as if the wind, young and energetic in its brief life, were

trying on Amalfitano's shirts and pants and slipping into his daughter's underpants and reading a few

pages of the 'Testamento Geometrico' to see whether there was anything in it that might be of use,

anything that might explain the strange landscape of streets and houses through which it was

galloping, or that would explain it to itself as wind."

Roberto Bolano, 2666

One might say, in solidarity with the novelist Roberto Bolano, that the essence of the

wind is poetic, its meaning beyond accessibility. Yet, be that as it may, as scientists we must

study what it offers as observable and determine the parameters of its effects.

On exposed roads, cross winds acting laterally on the side of the vehicle during the bora

events are commonly as strong as the vehicle velocity 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 able to use our results, including those from

all sensors described, to determine highway safety parameters.

We have demonstrated that the use of anemometers attached to moving vehicles

expresses a more accurate picture of the bora and its real effects on moving vehicles, which is

essential for understanding the wind – particularly its true directional affects and true

localized phenomena – which is absolutely necessary if parameters are to be safely

established.

ACKNOWLEDGMENTS

We would like to thank Marino Bajec, David Nemec, Franc Dimc, Rick Harsch and

Dmitry Evstigneev (Transas) for their support.



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