Safety Assessment of Control Design Parameters …...S. Mavromatis, «Safety Assessment of Control...
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Stergios Mavromatis 1 , Alexandra Laiou 2 1 Technological Educational Institute of Athens, Greece School of Civil Eng. and Surveying & Geoinformatics Eng. 2 National Technical University of Athens, Greece Department of Transportation Planning and Engineering email: [email protected] The Hague, October 2017 Safety Assessment of Control Design Parameters through Vehicle Dynamics Model
Transcript of Safety Assessment of Control Design Parameters …...S. Mavromatis, «Safety Assessment of Control...
Stergios Mavromatis1, Alexandra Laiou2
1Technological Educational Institute of Athens, Greece
School of Civil Eng. and Surveying & Geoinformatics Eng.2National Technical University of Athens, Greece
Department of Transportation Planning and Engineering
email: [email protected]
The Hague, October 2017
Safety Assessment
of Control Design Parameters
through Vehicle Dynamics Model
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Background
• Design speed• key parameter for defining critical geometric elements
• Road design practice• simplified approach
• failure to assess interactions between parameters
)e+f(127
V=R
maxperm,R
2
min
whereRmin : minimum curve’s radius (m)
V : vehicle speed – usually design speed (km/h)
emax : maximum superelevation rate (%/100)
m : vehicle’s massfR,perm: permissible side friction factor as a portion of peak friction
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Point Mass Deficiencies
• Steady state cornering is assumed• acceleration effect is ignored
• Key vehicle parameters ignored• type, mass and position of gravity (mass) center,
loading - driving configuration, horse-power supply, etc.
• Vehicle motion is examined independently in tangential - lateral direction of travel• respective friction components interact
• Utilized lateral friction based on empirical vehicle accident considerations• assumed as fixed portion of the relevant peak (40%-50%)
• Longitudinal profile disregarded
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Necessity for More Sophisticated Models
• Current control grade values • based mostly on experience
• limitations from the operational point of view
and not an outcome of a safety assessment
• Simulate vehicle’s cornering process• especially in cases of steep grades
(reduction of safety margin)
• upgrade road sections more critical in terms of horizontal radii requirements
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Objective
• Lift restrictions imposed
by point mass model
• Assess the ability of a typical passenger car
to maintain design speed values
for the corresponding
control design parameters• critical upgrade values
• various tire – road friction values
• Investigate the safety impact of vehicle’s peak attainable constant speed against design parameters imposed by design speed
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Vehicle Dynamics Model
• Moving 3D coordinate system
• Parameters correlated• vehicle technical characteristics
• road geometry
• tire friction
• 4-wheel model• lateral load transfer
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
• Output: Vsafe
vehicle’s peak attainable constant speed
• C class passenger car utilized (KIA Proceed)
• assessment for AASHTO-2011 design guidelines (Vd =50km/h – Vd =90km/h)
• 3 pavement friction values (0.35, 0.50, 0.65)
• definition of critical wheel (impending skid conditions)
Methodology
road
parameters
vehiclefriction
V0
define
critical wheel
dV/dt=0
V=V+Vstep
dV/dt>0
Vsafe , n
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
92.490.4
87.9
84.7
81.0
76.3
70.2
0.11
0.15
0.19
0.22
0.26
0.28
0.310.33
0.32
0.29
0.27
0..24
0.20
0.16
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
60
65
70
75
80
85
90
95
0.0 2.0 4.0 6.0 8.0 10.0 12.0
fric
tio
n v
alu
es
Vsa
fe (
km
/h)
s (%)
Vsafe vs Grade (fmax=0.35, Vd=70km/h, R=184m)
Vsafe
fTfi
fRfi
fR point mass
Grade Impact during Vsafe Determination
• Impending skid
fR demand :critical on mild grades
fT demand :critical on steep grades
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
HP Utilization Rates during Vsafe Determination
• Impending skid
vehicle skids when driven above suggested HP utilization values
92.4
90.4
87.9
84.7
81.0
76.3
70.224
31
37
42
4649
51
0
10
20
30
40
50
60
60
65
70
75
80
85
90
95
0.0 2.0 4.0 6.0 8.0 10.0 12.0
n (
%)
Vsa
fe (
km
/h)
s (%)
HP Utilization vs Grade (fmax=0.35, Vd=70km/h, R=184m)
Vsafe
n (%)
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Friction Safety Margins for V < Vsafe
• Comfortable driving
0.310.29
0.28 0.270.26
0.16
0.13
0.10
0.07
0.050.050.04 0.03 0.03 0.02
0.16
0.12
0.10
0.07
0.05
0.35
0.32
0.300.28
0.26
0.16
0.13
0.10
0.08
0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
70 65 60 55 50
fric
tio
n v
alu
es
V (km/h)
Friction vs Comfortable Speed (fmax=0.35, Vd=70km/h, R=184m)
fTfi (s=12%)
fRfi (s=12%)
fTfi (s=0%)
fRfi (s=0%)
fdemanded (s=12%)
fdemanded (s=0%)
fR point mass
fT : grade dependent
fR ≈ fR point mass model
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Vsafe Variation for Control Design Values (fmax = 0.35)
• Impending skid
critical cases (fmax = 0.35):
• Vd = 50km/h, s>11%
• Vd = 60km/h, s>11%
4446
56
49
59
70
51
62
73
52
64
76
87
97
40
50
60
70
80
90
100
79(Vd=50km/h)
123(Vd=60km/h)
184(Vd=70km/h)
252(Vd=80km/h)
336(Vd=90km/h)
V (
km/h
)
Rmin (m)
Vsafe Calculation, fmax=0.35
VAASHTO
s=14%
s=13%
s=12%
s=11%
s=10%
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Vsafe Variation for Control Design Values (Vd = 50km/h)
• Impending skid
critical cases (Vd = 50km/h):
• fmax < 0.40
• s > 11%
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Conclusions (1/3)
• Investigation of the ability a C-class passenger car
on steep grades to maintain Vd
• AASHTO 2011 design guidelines (Vd =50km/h – Vd =90km/h)
• 3 pavement friction values (0.35, 0.50, 0.65)
• 2 cases examined for assessing safety margins
• comfortable curve negotiation (V<Vsafe)
• Vsafe impending skid conditions
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Conclusions (2/3)
Comfortable curve negotiation (V<Vsafe)
• fR demand independent to grade
• fT demand increases with grade
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Conclusions (3/3)
Vsafe impending skid conditions
• fR demand critical on mild grades
• fT demand critical on steep grades
• Steady state cornering not always feasible• Vd = 50km/h, s>11%, fmax = 0.35
• Vd = 60km/h, s>11%, fmax = 0.35
• Point mass model model somehow underrates
lateral friction requirements
• Vehicles equipped with excessive HP rates
must be driven very conservatively
in road with poor friction pavement
S. Mavromatis, «Safety Assessment of Control Design Parameters through Vehicle Dynamics Model»
Recommendations - Further Research
• Identified critical cases
to be treated cautiously through actions• adoption of acceptable parameter arrangements
(new alignments)
• posted speed management
(existing alignments)
• scheduling friction improvement
programmes more accurately (both cases)
• Assessment on entire vehicle fleet
• Further analysis of interaction between
driver – vehicle
Stergios Mavromatis1, Alexandra Laiou2
1Technological Educational Institute of Athens, Greece
School of Civil Eng. and Surveying & Geoinformatics Eng.2National Technical University of Athens, Greece
Department of Transportation Planning and Engineering
email: [email protected]
The Hague, October 2017
Safety Assessment
of Control Design Parameters
through Vehicle Dynamics Model
